LIBABIGAIL(7)

NAME
libabigail - Library to analyze and compare ELF ABIs

OVERVIEW OF THE ABIGAIL FRAMEWORK

ABIGAIL stands for the Application Binary Interface Generic Analysis and Instrumentation Library.

It's a framework which aims at helping developers and software distributors to spot some ABI-related issues like interface incompatibility in ELF shared libraries by performing a static analysis of the ELF binaries at hand.

The type of interface incompatibilities that Abigail focuses on is related to changes on the exported ELF functions and variables symbols, as well as layout and size changes of data types of the functions and variables exported by shared libraries.

In other words, if the return type of a function exported by a shared library changes in an incompatible way from one version of a given shared library to another, we want Abigail to help people catch that.

In more concrete terms, the Abigail framwork provides a shared library named libabigail which exposes an API to parse a shared library in ELF format (accompanied with its associated debug information in DWARF format) build an internal representation of all the functions and variables it exports, along with their types. Libabigail also builds an internal representation of the ELF symbols of these functions and variables. That information about these exported functions and variables is roughly what we consider as being the ABI of the shared library, at least, in the scope of Libabigail.

Aside of this internal representation, libabigail provides facilities to perform deep comparisons of two ABIs. That is, it can compare the types of two sets of functions or variables and represents the result in a way that allows it to emit textual reports about the differences.

This allows us to write tools like abidiff that can compare the ABI of two shared libraries and represent the result in a meaningful enough way to help us spot ABI incompatibilities. There are several other tools that are built using the Abigail framwork.

TOOLS

  Overview

The upstream code repository of Libabigail contains several tools written using the library. They are maintained and released as part of the project. All tools come with a bash-completion script.

  Tools manuals

  abidiff

abidiff compares the Application Binary Interfaces (ABI) of two shared libraries in ELF format. It emits a meaningful report describing the differences between the two ABIs.

This tool can also compare the textual representations of the ABI of two ELF binaries (as emitted by abidw) or an ELF binary against a textual representation of another ELF binary.

For a comprehensive ABI change report between two input shared libraries that includes changes about function and variable sub-types, abidiff uses by default, debug information in DWARF format, if present, otherwise it compares interfaces using debug information in CTF format, if present, finally, if neither is found, it uses only ELF symbols to report which of them were added or removed.

This tool uses the libabigail library to analyze the binary as well as its associated debug information. Here is its general mode of operation.

When instructed to do so, a binary and its associated debug information is read and analyzed. To that effect, libabigail analyzes by default the descriptions of the types reachable by the interfaces (functions and variables) that are visible outside of their translation unit. Once that analysis is done, an Application Binary Interface Corpus is constructed by only considering the subset of types reachable from interfaces associated to ELF symbols that are defined and exported by the binary. It’s that final ABI corpus which libabigail considers as representing the ABI of the analyzed binary.

Libabigail then has capabilities to generate textual representations of ABI Corpora, compare them, analyze their changes and report about them.

  Invocation

abidiff [options] <first-shared-library> <second-shared-library>

  Environment

abidiff loads two default suppression specifications files, merges their content and use it to filter out ABI change reports that might be considered as false positives to users.

•   Default system-wide suppression specification file

    It’s located by the optional environment variable LIBABIGAIL_DEFAULT_SYSTEM_SUPPRESSION_FILE. If that environment variable is not set, then abidiff tries to load the suppression file $libdir/libabigail/libabigail-default.abignore. If that file is not present, then no default system-wide suppression specification file is loaded.

•   Default user suppression specification file.

    It’s located by the optional environment LIBABIGAIL_DEFAULT_USER_SUPPRESSION_FILE. If that environment variable is not set, then abidiff tries to load the suppression file $HOME/.abignore. If that file is not present, then no default user suppression specification is loaded.

  Options

•   --help | -h

    Display a short help about the command and exit.

•   --debug-self-comparison

    In this mode, error messages are emitted for types which fail type canonicalization, in some circumstances, when comparing a binary against itself.

    When comparing a binary against itself, canonical types of the second binary should be equal (as much as possible) to canonical types of the first binary. When some discrepancies are detected in this mode, an abort signal is emitted and execution is halted. This option should be used while executing the tool in a debugger, for troubleshooting purposes.

    This is an optional debugging and sanity check option. To enable it the libabigail package needs to be configured with the –enable-debug-self-comparison configure option.

•   --debug-tc

    In this mode, the process of type canonicalization is put under heavy scrutiny. Basically, during type canonicalization, each type comparison is performed twice: once in a structural mode (comparing every sub-type member-wise), and once using canonical comparison. The two comparisons should yield the same result. Otherwise, an abort signal is emitted and the process can be debugged to understand why the two kinds of comparison yield different results.

    This is an optional debugging and sanity check option. To enable it the libabigail package needs to be configured with the –enable-debug-type-canonicalization configure option.

•   --version | -v

    Display the version of the program and exit.

•   --debug-info-dir1 | --d1 <di-path1>

    For cases where the debug information for first-shared-library is split out into a separate file, tells abidiff where to find that separate debug information file.

    Note that di-path must point to the root directory under which the debug information is arranged in a tree-like manner. Under Red Hat based systems, that directory is usually <root>/usr/lib/debug.

    This option can be provided several times with different root directories. In that case, abidiff will potentially look into all those root directories to find the split debug info for first-shared-library.

    Note also that this option is not mandatory for split debug information installed by your system’s package manager because then abidiff knows where to find it.

•   --debug-info-dir2 | --d2 <di-path2>

    Like --debug-info-dir1, this options tells abidiff where to find the split debug information for the second-shared-library file.

    This option can be provided several times with different root directories. In that case, abidiff will potentially look into all those root directories to find the split debug info for second-shared-library.

•   --headers-dir1 | --hd1 <headers-directory-path-1>

    Specifies where to find the public headers of the first shared library (or binary in general) that the tool has to consider. The tool will thus filter out ABI changes on types that are not defined in public headers.

    Note that several public header directories can be specified for the first shared library. In that case the --headers-dir1 option should be present several times on the command line, like in the following example:

    $ abidiff --headers-dir1 /some/path       \
              --headers-dir1 /some/other/path \
              binary-version-1 binary-version-2

•   --header-file1 | --hf1 <header-file-path-1>

    Specifies where to find one public header of the first shared library that the tool has to consider. The tool will thus filter out ABI changes on types that are not defined in public headers.

•   --headers-dir2 | --hd2 <headers-directory-path-2>

    Specifies where to find the public headers of the second shared library that the tool has to consider. The tool will thus filter out ABI changes on types that are not defined in public headers.

    Note that several public header directories can be specified for the second shared library. In that case the --headers-dir2 option should be present several times like in the following example:

    $ abidiff --headers-dir2 /some/path       \
              --headers-dir2 /some/other/path \
              binary-version-1 binary-version-2

•   --header-file2 | --hf2 <header-file-path-2>

    Specifies where to find one public header of the second shared library that the tool has to consider. The tool will thus filter out ABI changes on types that are not defined in public headers.

•   --no-linux-kernel-mode

    Without this option, if abidiff detects that the binaries it is looking at are Linux Kernel binaries (either vmlinux or modules) then it only considers functions and variables which ELF symbols are listed in the __ksymtab and __ksymtab_gpl sections.

    With this option, abidiff considers the binary as a non-special ELF binary. It thus considers functions and variables which are defined and exported in the ELF sense.

•   --kmi-whitelist | -kaw <path-to-whitelist>

    When analyzing a Linux kernel binary, this option points to the white list of names of ELF symbols of functions and variables which ABI must be considered. That white list is called a “Kernel Module Interface white list”. This is because for the Kernel, we don’t talk about ABI; we rather talk about the interface between the Kernel and its module. Hence the term KMI rather than ABI.

    Any other function or variable which ELF symbol are not present in that white list will not be considered by this tool.

    If this option is not provided – thus if no white list is provided – then the entire KMI, that is, the set of all publicly defined and exported functions and global variables by the Linux Kernel binaries, is considered.

•   --drop-private-types

    This option is to be used with the --headers-dir1, header-file1, header-file2 and --headers-dir2 options. With this option, types that are NOT defined in the headers are entirely dropped from the internal representation build by Libabigail to represent the ABI. They thus don’t have to be filtered out from the final ABI change report because they are not even present in Libabigail’s representation.

    Without this option however, those private types are kept in the internal representation and later filtered out from the report.

    This options thus potentially makes Libabigail consume less memory. It’s meant to be mainly used to optimize the memory consumption of the tool on binaries with a lot of publicly defined and exported types.

•   --exported-interfaces-only

    By default, when looking at the debug information accompanying a binary, this tool analyzes the descriptions of the types reachable by the interfaces (functions and variables) that are visible outside of their translation unit. Once that analysis is done, an ABI corpus is constructed by only considering the subset of types reachable from interfaces associated to ELF symbols that are defined and exported by the binary. It’s those final ABI Corpora that are compared by this tool.

    The problem with that approach however is that analyzing all the interfaces that are visible from outside their translation unit can amount to a lot of data, especially when those binaries are applications, as opposed to shared libraries. One example of such applications is the
    `Linux Kernel`_
    . Analyzing massive ABI corpora like these can be extremely slow.

    To mitigate that performance issue, this option allows libabigail to only analyze types that are reachable from interfaces associated with defined and exported ELF symbols.

    Note that this option is turned on by default when analyzing the
    `Linux Kernel`_
    . Otherwise, it’s turned off by default.

•   --allow-non-exported-interfaces

    When looking at the debug information accompanying a binary, this tool analyzes the descriptions of the types reachable by the interfaces (functions and variables) that are visible outside of their translation unit. Once that analysis is done, an ABI corpus is constructed by only considering the subset of types reachable from interfaces associated to ELF symbols that are defined and exported by the binary. It’s those final ABI Corpora that are compared by this tool.

    The problem with that approach however is that analyzing all the interfaces that are visible from outside their translation unit can amount to a lot of data, especially when those binaries are applications, as opposed to shared libraries. One example of such applications is the
    `Linux Kernel`_
    . Analyzing massive ABI Corpora like these can be extremely slow.

    In the presence of an “average sized” binary however one can afford having libabigail analyze all interfaces that are visible outside of their translation unit, using this option.

    Note that this option is turned on by default, unless we are in the presence of the
    `Linux Kernel`_
    .

•   --stat

    Rather than displaying the detailed ABI differences between first-shared-library and second-shared-library, just display some summary statistics about these differences.

•   --symtabs

    Only display the symbol tables of the first-shared-library and second-shared-library.

•   --deleted-fns

    In the resulting report about the differences between first-shared-library and second-shared-library, only display the globally defined functions that got deleted from first-shared-library.

•   --changed-fns

    In the resulting report about the differences between first-shared-library and second-shared-library, only display the changes in sub-types of the global functions defined in first-shared-library.

•   --added-fns

    In the resulting report about the differences between first-shared-library and second-shared-library, only display the globally defined functions that were added to second-shared-library.

•   --deleted-vars

    In the resulting report about the differences between first-shared-library and second-shared-library, only display the globally defined variables that were deleted from first-shared-library.

•   --changed-vars

    In the resulting report about the differences between first-shared-library and second-shared-library, only display the changes in the sub-types of the global variables defined in first-shared-library

•   --added-vars

    In the resulting report about the differences between first-shared-library and second-shared-library, only display the global variables that were added (defined) to second-shared-library.

•   --non-reachable-types|-t

    Analyze and emit change reports for all the types of the binary, including those that are not reachable from global functions and variables.

    This option might incur some serious performance degradation as the number of types analyzed can be huge. However, if paired with the --headers-dir{1,2} and/or header-file{1,2} options, the additional non-reachable types analyzed are restricted to those defined in public headers files, thus hopefully making the performance hit acceptable.

    Also, using this option alongside suppression specifications (by also using the --suppressions option) might help keep the number of analyzed types (and the potential performance degradation) in control.

    Note that without this option, only types that are reachable from global functions and variables are analyzed, so the tool detects and reports changes on these reachable types only.

•   --no-added-syms

    In the resulting report about the differences between first-shared-library and second-shared-library, do not display added functions or variables. Do not display added functions or variables ELF symbols either. All other kinds of changes are displayed unless they are explicitely forbidden by other options on the command line.

•   --no-linkage-name

    In the resulting report, do not display the linkage names of the added, removed, or changed functions or variables.

•   --no-show-locs Do not show information about where in the second shared library the respective type was changed.

•   --show-bytes

    Show sizes and offsets in bytes, not bits. By default, sizes and offsets are shown in bits.

•   --show-bits

    Show sizes and offsets in bits, not bytes. This option is activated by default.

•   --show-hex

    Show sizes and offsets in hexadecimal base.

•   --show-dec

    Show sizes and offsets in decimal base. This option is activated by default.

•   --ignore-soname

    Ignore differences in the SONAME when doing a comparison

•   --no-show-relative-offset-changes

    Without this option, when the offset of a data member changes, the change report not only mentions the older and newer offset, but it also mentions by how many bits the data member changes. With this option, the latter is not shown.

•   --no-unreferenced-symbols

    In the resulting report, do not display change information about function and variable symbols that are not referenced by any debug information. Note that for these symbols not referenced by any debug information, the change information displayed is either added or removed symbols.

•   --no-default-suppression

    Do not load the default suppression specification files.

•   --suppressions | --suppr <path-to-suppressions>

    Use a suppression specification file located at path-to-suppressions. Note that this option can appear multiple times on the command line. In that case, all of the provided suppression specification files are taken into account.

    Please note that, by default, if this option is not provided, then the default suppression specification files are loaded .

•   --drop <regex>

    When reading the first-shared-library and second-shared-library ELF input files, drop the globally defined functions and variables which name match the regular expression regex. As a result, no change involving these functions or variables will be emitted in the diff report.

•   --drop-fn <regex>

    When reading the first-shared-library and second-shared-library ELF input files, drop the globally defined functions which name match the regular expression regex. As a result, no change involving these functions will be emitted in the diff report.

•   --drop-var <regex>

    When reading the first-shared-library and second-shared-library ELF input files, drop the globally defined variables matching a the regular expression regex.

•   --keep <regex>

    When reading the first-shared-library and second-shared-library ELF input files, keep the globally defined functions and variables which names match the regular expression regex. All other functions and variables are dropped on the floor and will thus not appear in the resulting diff report.

•   --keep-fn <regex>

    When reading the first-shared-library and second-shared-library ELF input files, keep the globally defined functions which name match the regular expression regex. All other functions are dropped on the floor and will thus not appear in the resulting diff report.

•   --keep-var <regex>

    When reading the first-shared-library and second-shared-library ELF input files, keep the globally defined which names match the regular expression regex. All other variables are dropped on the floor and will thus not appear in the resulting diff report.

•   --harmless

    In the diff report, display only the harmless changes. By default, the harmless changes are filtered out of the diff report keep the clutter to a minimum and have a greater chance to spot real ABI issues.

•   --no-harmful

    In the diff report, do not display the harmful changes. By default, only the harmful changes are displayed in diff report.

•   --redundant

    In the diff report, do display redundant changes. A redundant change is a change that has been displayed elsewhere in the report.

•   --no-redundant

    In the diff report, do NOT display redundant changes. A redundant change is a change that has been displayed elsewhere in the report. This option is switched on by default.

•   --no-architecture

    Do not take architecture in account when comparing ABIs.

•   --no-corpus-path

    Do not emit the path attribute for the ABI corpus.

•   --fail-no-debug-info

    If no debug info was found, then this option makes the program to fail. Otherwise, without this option, the program will attempt to compare properties of the binaries that are not related to debug info, like pure ELF properties.

•   --leaf-changes-only|-l only show leaf changes, so don’t show impact analysis report. This option implies --redundant.

    The typical output of abidiff when comparing two binaries looks like this

    $ abidiff libtest-v0.so libtest-v1.so
    Functions changes summary: 0 Removed, 1 Changed, 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    1 function with some indirect sub-type change:
      [C]'function void fn(C&)' at test-v1.cc:13:1 has some indirect sub-type changes:
        parameter 1 of type 'C&' has sub-type changes:
          in referenced type 'struct C' at test-v1.cc:7:1:
            type size hasn't changed
            1 data member change:
             type of 'leaf* C::m0' changed:
               in pointed to type 'struct leaf' at test-v1.cc:1:1:
                 type size changed from 32 to 64 bits
                 1 data member insertion:
                   'char leaf::m1', at offset 32 (in bits) at test-v1.cc:4:1
    $

    So in that example the report emits information about how the data member insertion change of “struct leaf” is reachable from function “void fn(C&)”. In other words, the report not only shows the data member change on “struct leaf”, but it also shows the impact of that change on the function “void fn(C&)”.

    In abidiff parlance, the change on “struct leaf” is called a leaf change. So the --leaf-changes-only --impacted-interfaces options show, well, only the leaf change. And it goes like this:

    $ abidiff -l libtest-v0.so libtest-v1.so
    'struct leaf' changed:
      type size changed from 32 to 64 bits
      1 data member insertion:
        'char leaf::m1', at offset 32 (in bits) at test-v1.cc:4:1
      one impacted interface:
        function void fn(C&)
    $

    Note how the report ends by showing the list of interfaces impacted by the leaf change.

    Now if you don’t want to see that list of impacted interfaces, then you can just avoid using the --impacted-interface option. You can learn about that option below, in any case.

•   --impacted-interfaces

    When showing leaf changes, this option instructs abidiff to show the list of impacted interfaces. This option is thus to be used in addition the --leaf-changes-only option, otherwise, it’s ignored.

•   --dump-diff-tree After the diff report, emit a textual representation of the diff nodes tree used by the comparison engine to represent the changed functions and variables. That representation is emitted to the error output for debugging purposes. Note that this diff tree is relevant only to functions and variables that have some sub-type changes. Added or removed functions and variables do not have any diff nodes tree associated to them.

•   --no-assume-odr-for-cplusplus

    When analysing a binary originating from C++ code using DWARF debug information, libabigail assumes the One Definition Rule to speed-up the analysis. In that case, when several types have the same name in the binary, they are assumed to all be equal.

    This option disables that assumption and instructs libabigail to actually actually compare the types to determine if they are equal.

•   --no-leverage-dwarf-factorization

    When analysing a binary which DWARF debug information was processed with the DWZ tool, the type information is supposed to be already factorized. That context is used by libabigail to perform some speed optimizations.

    This option disables those optimizations.

•   --ctf

    When comparing binaries, extract ABI information from CTF debug information, if present.

•   --stats

    Emit statistics about various internal things.

•   --verbose

    Emit verbose logs about the progress of miscellaneous internal things.

  Return values

The exit code of the abidiff command is either 0 if the ABI of the binaries being compared are equal, or non-zero if they differ or if the tool encountered an error.

In the later case, the exit code is a 8-bits-wide bit field in which each bit has a specific meaning.

The first bit, of value 1, named ABIDIFF_ERROR means there was an error.

The second bit, of value 2, named ABIDIFF_USAGE_ERROR means there was an error in the way the user invoked the tool. It might be set, for instance, if the user invoked the tool with an unknown command line switch, with a wrong number or argument, etc. If this bit is set, then the ABIDIFF_ERROR bit must be set as well.

The third bit, of value 4, named ABIDIFF_ABI_CHANGE means the ABI of the binaries being compared are different.

The fourth bit, of value 8, named ABIDIFF_ABI_INCOMPATIBLE_CHANGE means the ABI of the binaries compared are different in an incompatible way. If this bit is set, then the ABIDIFF_ABI_CHANGE bit must be set as well. If the ABIDIFF_ABI_CHANGE is set and the ABIDIFF_INCOMPATIBLE_CHANGE is NOT set, then it means that the ABIs being compared might or might not be compatible. In that case, a human being needs to review the ABI changes to decide if they are compatible or not.

Note that, at the moment, there are only a few kinds of ABI changes that would result in setting the flag ABIDIFF_ABI_INCOMPATIBLE_CHANGE. Those ABI changes are either:

•   the removal of the symbol of a function or variable that has been defined and exported.

•   the modification of the index of a member of a virtual function table (for C++ programs and libraries).

    With time, when more ABI change patterns are found to always constitute incompatible ABI changes, we will adapt the code to recognize those cases and set the ABIDIFF_ABI_INCOMPATIBLE_CHANGE accordingly. So, if you find such patterns, please let us know.

    The remaining bits are not used for the moment.

  Usage examples

1.  Detecting a change in a sub-type of a function:

    $ cat -n test-v0.cc
             1      // Compile this with:
             2      //   g++ -g -Wall -shared -o libtest-v0.so test-v0.cc
             3
             4      struct S0
             5      {
             6        int m0;
             7      };
             8
             9      void
            10      foo(S0* /*parameter_name*/)
            11      {
            12        // do something with parameter_name.
            13      }
    $
    $ cat -n test-v1.cc
             1      // Compile this with:
             2      //   g++ -g -Wall -shared -o libtest-v1.so test-v1.cc
             3
             4      struct type_base
             5      {
             6        int inserted;
             7      };
             8
             9      struct S0 : public type_base
            10      {
            11        int m0;
            12      };
            13
            14      void
            15      foo(S0* /*parameter_name*/)
            16      {
            17        // do something with parameter_name.
            18      }
    $
    $ g++ -g -Wall -shared -o libtest-v0.so test-v0.cc
    $ g++ -g -Wall -shared -o libtest-v1.so test-v1.cc
    $
    $ ../build/tools/abidiff libtest-v0.so libtest-v1.so
    Functions changes summary: 0 Removed, 1 Changed, 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    1 function with some indirect sub-type change:
      [C]'function void foo(S0*)' has some indirect sub-type changes:
            parameter 0 of type 'S0*' has sub-type changes:
              in pointed to type 'struct S0':
                size changed from 32 to 64 bits
                1 base class insertion:
                  struct type_base
                1 data member change:
                 'int S0::m0' offset changed from 0 to 32
    $

2.  Detecting another change in a sub-type of a function:

    $ cat -n test-v0.cc
             1      // Compile this with:
             2      //   g++ -g -Wall -shared -o libtest-v0.so test-v0.cc
             3
             4      struct S0
             5      {
             6        int m0;
             7      };
             8
             9      void
            10      foo(S0& /*parameter_name*/)
            11      {
            12        // do something with parameter_name.
            13      }
    $
    $ cat -n test-v1.cc
             1      // Compile this with:
             2      //   g++ -g -Wall -shared -o libtest-v1.so test-v1.cc
             3
             4      struct S0
             5      {
             6        char inserted_member;
             7        int m0;
             8      };
             9
            10      void
            11      foo(S0& /*parameter_name*/)
            12      {
            13        // do something with parameter_name.
            14      }
    $
    $ g++ -g -Wall -shared -o libtest-v0.so test-v0.cc
    $ g++ -g -Wall -shared -o libtest-v1.so test-v1.cc
    $
    $ ../build/tools/abidiff libtest-v0.so libtest-v1.so
    Functions changes summary: 0 Removed, 1 Changed, 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    1 function with some indirect sub-type change:
      [C]'function void foo(S0&)' has some indirect sub-type changes:
            parameter 0 of type 'S0&' has sub-type changes:
              in referenced type 'struct S0':
                size changed from 32 to 64 bits
                1 data member insertion:
                  'char S0::inserted_member', at offset 0 (in bits)
                1 data member change:
                 'int S0::m0' offset changed from 0 to 32
    $

3.  Detecting that functions got removed or added to a library:

    $ cat -n test-v0.cc
             1      // Compile this with:
             2      //   g++ -g -Wall -shared -o libtest-v0.so test-v0.cc
             3
             4      struct S0
             5      {
             6        int m0;
             7      };
             8
             9      void
            10      foo(S0& /*parameter_name*/)
            11      {
            12        // do something with parameter_name.
            13      }
    $
    $ cat -n test-v1.cc
             1      // Compile this with:
             2      //   g++ -g -Wall -shared -o libtest-v1.so test-v1.cc
             3
             4      struct S0
             5      {
             6        char inserted_member;
             7        int m0;
             8      };
             9
            10      void
            11      bar(S0& /*parameter_name*/)
            12      {
            13        // do something with parameter_name.
            14      }
    $
    $ g++ -g -Wall -shared -o libtest-v0.so test-v0.cc
    $ g++ -g -Wall -shared -o libtest-v1.so test-v1.cc
    $
    $ ../build/tools/abidiff libtest-v0.so libtest-v1.so
    Functions changes summary: 1 Removed, 0 Changed, 1 Added functions
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    1 Removed function:
      'function void foo(S0&)'    {_Z3fooR2S0}
    1 Added function:
      'function void bar(S0&)'    {_Z3barR2S0}
    $

  abipkgdiff

abipkgdiff compares the Application Binary Interfaces (ABI) of the ELF binaries contained in two software packages. The software package formats currently supported are Deb, RPM, tar archives (either compressed or not) and plain directories that contain binaries.

For a comprehensive ABI change report that includes changes about function and variable sub-types, the two input packages must be accompanied with their debug information packages that contain debug information either in DWARF or in CTF formats. Please note however that some packages contain binaries that embed the debug information directly in a section of said binaries. In those cases, obviously, no separate debug information package is needed as the tool will find the debug information inside the binaries.

By default, abipkgdiff uses debug information in DWARF format, if present, otherwise it compares binaries interfaces using debug information in CTF format, if present, finally, if neither is found, it uses only ELF symbols to report which of them were added or removed.

This tool uses the libabigail library to analyze the binary as well as its associated debug information. Here is its general mode of operation.

When instructed to do so, a binary and its associated debug information is read and analyzed. To that effect, libabigail analyzes by default the descriptions of the types reachable by the interfaces (functions and variables) that are visible outside of their translation unit. Once that analysis is done, an Application Binary Interface Corpus is constructed by only considering the subset of types reachable from interfaces associated to ELF symbols that are defined and exported by the binary. It’s that final ABI corpus which libabigail considers as representing the ABI of the analyzed binary.

Libabigail then has capabilities to generate textual representations of ABI Corpora, compare them, analyze their changes and report about them.

  Invocation

abipkgdiff [option] <package1> <package2>

package1 and package2 are the packages that contain the binaries to be compared.

  Environment

abipkgdiff loads two default suppression specifications files, merges their content and use it to filter out ABI change reports that might be considered as false positives to users.

•   Default system-wide suppression specification file

    It’s located by the optional environment variable LIBABIGAIL_DEFAULT_SYSTEM_SUPPRESSION_FILE. If that environment variable is not set, then abipkgdiff tries to load the suppression file $libdir/libabigail/libabigail-default.abignore. If that file is not present, then no default system-wide suppression specification file is loaded.

•   Default user suppression specification file.

    It’s located by the optional environment LIBABIGAIL_DEFAULT_USER_SUPPRESSION_FILE. If that environment variable is not set, then abipkgdiff tries to load the suppression file $HOME/.abignore. If that file is not present, then no default user suppression specification is loaded.

    In addition to those default suppression specification files, abipkgdiff will also look inside the packages being compared and if it sees a file that ends with the extension .abignore, then it will consider it as a suppression specification and it will combine it to the default suppression specification that might be already loaded.

    The user might as well use the --suppressions option (that is documented further below) to provide a suppression specification.

  Options

•   --help | -h

    Display a short help about the command and exit.

•   –version | -v

    Display the version of the program and exit.

•   --debug-info-pkg1 | --d1 <path>

    For cases where the debug information for package1 is split out into a separate file, tells abipkgdiff where to find that separate debug information package.

    Note that the debug info for package1 can have been split into several different debug info packages. In that case, several instances of this options can be provided, along with those several different debug info packages.

•   --debug-info-pkg2 | --d2 <path>

    For cases where the debug information for package2 is split out into a separate file, tells abipkgdiff where to find that separate debug information package.

    Note that the debug info for package2 can have been split into several different debug info packages. In that case, several instances of this options can be provided, along with those several different debug info packages.

•   --devel-pkg1 | --devel1 <path>

    Specifies where to find the Development Package associated with the first package to be compared. That Development Package at path should at least contain header files in which public types exposed by the libraries (of the first package to be compared) are defined. When this option is provided, the tool filters out reports about ABI changes to types that are NOT defined in these header files.

•   --devel-pkg2 | --devel2 <path>

    Specifies where to find the Development Package associated with the second package to be compared. That Development Package at path should at least contains header files in which public types exposed by the libraries (of the second package to be compared) are defined. When this option is provided, the tool filters out reports about ABI changes to types that are NOT defined in these header files.

•   --drop-private-types

    This option is to be used with the --devel-pkg1 and --devel-pkg2 options. With this option, types that are NOT defined in the headers are entirely dropped from the internal representation build by Libabigail to represent the ABI. They thus don’t have to be filtered out from the final ABI change report because they are not even present in Libabigail’s representation.

    Without this option however, those private types are kept in the internal representation and later filtered out from the report.

    This options thus potentially makes Libabigail consume less memory. It’s meant to be mainly used to optimize the memory consumption of the tool on binaries with a lot of publicly defined and exported types.

•   --dso-only

    Compare ELF files that are shared libraries, only. Do not compare executable files, for instance.

•   --private-dso

    By default, abipkgdiff does not compare DSOs that are private to the RPM package. A private DSO is a DSO which SONAME is NOT advertised in the “provides” property of the RPM.

    This option instructs abipkgdiff to also compare DSOs that are NOT advertised in the “provides” property of the RPM.

    Please note that the fact that (by default) abipkgdiff skips private DSO is a feature that is available only for RPMs, at the moment. We would happily accept patches adding that feature for other package formats.

•   --leaf-changes-only|-l only show leaf changes, so don’t show impact analysis report. This option implies --redundant

    The typical output of abipkgdiff and abidiff when comparing two binaries, that we shall call full impact report, looks like this

    $ abidiff libtest-v0.so libtest-v1.so
    Functions changes summary: 0 Removed, 1 Changed, 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    1 function with some indirect sub-type change:
      [C]'function void fn(C&)' at test-v1.cc:13:1 has some indirect sub-type changes:
        parameter 1 of type 'C&' has sub-type changes:
          in referenced type 'struct C' at test-v1.cc:7:1:
            type size hasn't changed
            1 data member change:
             type of 'leaf* C::m0' changed:
               in pointed to type 'struct leaf' at test-v1.cc:1:1:
                 type size changed from 32 to 64 bits
                 1 data member insertion:
                   'char leaf::m1', at offset 32 (in bits) at test-v1.cc:4:1
    $

    So in that example the report emits information about how the data member insertion change of “struct leaf” is reachable from function “void fn(C&)”. In other words, the report not only shows the data member change on “struct leaf”, but it also shows the impact of that change on the function “void fn(C&)”.

    In abidiff (and abipkgdiff) parlance, the change on “struct leaf” is called a leaf change. So the --leaf-changes-only --impacted-interfaces options show, well, only the leaf change. And it goes like this:

    $ abidiff -l libtest-v0.so libtest-v1.so
    'struct leaf' changed:
      type size changed from 32 to 64 bits
      1 data member insertion:
        'char leaf::m1', at offset 32 (in bits) at test-v1.cc:4:1
      one impacted interface:
        function void fn(C&)
    $

    Note how the report ends up by showing the list of interfaces impacted by the leaf change. That’s the effect of the additional --impacted-interfaces option.

    Now if you don’t want to see that list of impacted interfaces, then you can just avoid using the --impacted-interface option. You can learn about that option below, in any case.

    Please note that when comparing two Linux Kernel packages, it’s this leaf changes report that is emitted, by default. The normal so-called full impact report can be emitted with the option --full-impact which is documented later below.

•   --impacted-interfaces

    When showing leaf changes, this option instructs abipkgdiff to show the list of impacted interfaces. This option is thus to be used in addition to the --leaf-changes-only option, or, when comparing two Linux Kernel packages. Otherwise, it’s simply ignored.

•   --full-impact|-f

    When comparing two Linux Kernel packages, this function instructs abipkgdiff to emit the so-called full impact report, which is the default report kind emitted by the abidiff tool:

    $ abidiff libtest-v0.so libtest-v1.so
    Functions changes summary: 0 Removed, 1 Changed, 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    1 function with some indirect sub-type change:
      [C]'function void fn(C&)' at test-v1.cc:13:1 has some indirect sub-type changes:
        parameter 1 of type 'C&' has sub-type changes:
          in referenced type 'struct C' at test-v1.cc:7:1:
            type size hasn't changed
            1 data member change:
             type of 'leaf* C::m0' changed:
               in pointed to type 'struct leaf' at test-v1.cc:1:1:
                 type size changed from 32 to 64 bits
                 1 data member insertion:
                   'char leaf::m1', at offset 32 (in bits) at test-v1.cc:4:1
    $

•   --non-reachable-types|-t

    Analyze and emit change reports for all the types of the binary, including those that are not reachable from global functions and variables.

    This option might incur some serious performance degradation as the number of types analyzed can be huge. However, if paired with the --devel-pkg{1,2} options, the additional non-reachable types analyzed are restricted to those defined in the public headers files carried by the referenced development packages, thus hopefully making the performance hit acceptable.

    Also, using this option alongside suppression specifications (by also using the --suppressions option) might help keep the number of analyzed types (and the potential performance degradation) in control.

    Note that without this option, only types that are reachable from global functions and variables are analyzed, so the tool detects and reports changes on these reachable types only.

•   --exported-interfaces-only

    By default, when looking at the debug information accompanying a binary, this tool analyzes the descriptions of the types reachable by the interfaces (functions and variables) that are visible outside of their translation unit. Once that analysis is done, an ABI corpus is constructed by only considering the subset of types reachable from interfaces associated to ELF symbols that are defined and exported by the binary. It’s those final ABI Corpora that are compared by this tool.

    The problem with that approach however is that analyzing all the interfaces that are visible from outside their translation unit can amount to a lot of data, especially when those binaries are applications, as opposed to shared libraries. One example of such applications is the
    `Linux Kernel`_
    . Analyzing massive ABI corpora like these can be extremely slow.

    To mitigate that performance issue, this option allows libabigail to only analyze types that are reachable from interfaces associated with defined and exported ELF symbols.

    Note that this option is turned on by default when analyzing the
    `Linux Kernel`_
    . Otherwise, it’s turned off by default.

•   --allow-non-exported-interfaces

    When looking at the debug information accompanying a binary, this tool analyzes the descriptions of the types reachable by the interfaces (functions and variables) that are visible outside of their translation unit. Once that analysis is done, an ABI corpus is constructed by only considering the subset of types reachable from interfaces associated to ELF symbols that are defined and exported by the binary. It’s those final ABI Corpora that are compared by this tool.

    The problem with that approach however is that analyzing all the interfaces that are visible from outside their translation unit can amount to a lot of data, especially when those binaries are applications, as opposed to shared libraries. One example of such applications is the
    `Linux Kernel`_
    . Analyzing massive ABI Corpora like these can be extremely slow.

    In the presence of an “average sized” binary however one can afford having libabigail analyze all interfaces that are visible outside of their translation unit, using this option.

    Note that this option is turned on by default, unless we are in the presence of the
    `Linux Kernel`_
    .

•   --redundant In the diff reports, do display redundant changes. A redundant change is a change that has been displayed elsewhere in a given report.

•   --harmless

    In the diff report, display only the harmless changes. By default, the harmless changes are filtered out of the diff report keep the clutter to a minimum and have a greater chance to spot real ABI issues.

•   --no-linkage-name

    In the resulting report, do not display the linkage names of the added, removed, or changed functions or variables.

•   --no-added-syms

    Do not show the list of functions, variables, or any symbol that was added.

•   --no-added-binaries

    Do not show the list of binaries that got added to the second package.

    Please note that the presence of such added binaries is not considered like an ABI change by this tool; as such, it doesn’t have any impact on the exit code of the tool. It does only have an informational value. Removed binaries are, however, considered as an ABI change.

•   --no-abignore

    Do not search the package for the presence of suppression files.

•   --no-parallel

    By default, abipkgdiff will use all the processors it has available to execute concurrently. This option tells it not to extract packages or run comparisons in parallel.

•   --no-default-suppression

    Do not load the default suppression specification files.

•   --suppressions | --suppr <path-to-suppressions>

    Use a suppression specification file located at path-to-suppressions. Note that this option can appear multiple times on the command line. In that case, all of the suppression specification files are taken into account.

    Please note that, by default, if this option is not provided, then the default suppression specification files are loaded .

•   --linux-kernel-abi-whitelist | -w <path-to-whitelist>

    When comparing two Linux kernel RPM packages, this option points to the white list of names of ELF symbols of functions and variables that must be compared for ABI changes. That white list is called a “Linux kernel ABI white list”.

    Any other function or variable which ELF symbol are not present in that white list will not be considered by the ABI comparison process.

    If this option is not provided – thus if no white list is provided – then the ABI of all publicly defined and exported functions and global variables by the Linux Kernel binaries are compared.

    Please note that if a white list package is given in parameter, this option handles it just fine, like if the –wp option was used.

•   --wp <path-to-whitelist-package>

    When comparing two Linux kernel RPM packages, this option points an RPM package containining several white lists of names of ELF symbols of functions and variables that must be compared for ABI changes. Those white lists are called “Linux kernel ABI white lists”.

    From the content of that white list package, this program then chooses the appropriate Linux kernel ABI white list to consider when comparing the ABI of Linux kernel binaries contained in the Linux kernel packages provided on the command line.

    That choosen Linux kernel ABI white list contains the list of names of ELF symbols of functions and variables that must be compared for ABI changes.

    Any other function or variable which ELF symbol are not present in that white list will not be considered by the ABI comparison process.

    Note that this option can be provided twice (not mor than twice), specifying one white list package for each Linux Kernel package that is provided on the command line.

    If this option is not provided – thus if no white list is provided – then the ABI of all publicly defined and exported functions and global variables by the Linux Kernel binaries are compared.

•   --no-unreferenced-symbols

    In the resulting report, do not display change information about function and variable symbols that are not referenced by any debug information. Note that for these symbols not referenced by any debug information, the change information displayed is either added or removed symbols.

•   --no-show-locs Do not show information about where in the second shared library the respective type was changed.

•   --show-bytes

    Show sizes and offsets in bytes, not bits. By default, sizes and offsets are shown in bits.

•   --show-bits

    Show sizes and offsets in bits, not bytes. This option is activated by default.

•   --show-hex

    Show sizes and offsets in hexadecimal base.

•   --show-dec

    Show sizes and offsets in decimal base. This option is activated by default.

•   --no-show-relative-offset-changes

    Without this option, when the offset of a data member changes, the change report not only mentions the older and newer offset, but it also mentions by how many bits the data member changes. With this option, the latter is not shown.

•   --show-identical-binaries Show the names of the all binaries compared, including the binaries whose ABI compare equal. By default, when this option is not provided, only binaries with ABI changes are mentionned in the output.

•   --fail-no-dbg

    Make the program fail and return a non-zero exit code if couldn’t read any of the debug information that comes from the debug info packages that were given on the command line. If no debug info package were provided on the command line then this option is not active.

    Note that the non-zero exit code returned by the program as a result of this option is the constant ABIDIFF_ERROR. To know the numerical value of that constant, please refer to the exit code documentation.

•   --keep-tmp-files

    Do not erase the temporary directory files that are created during the execution of the tool.

•   --verbose

    Emit verbose progress messages.

•   --self-check

    This is used to test the underlying Libabigail library. When in used, the command expects only on input package, along with its associated debug info packages. The command then compares each binary inside the package against its own ABIXML representation. The result of the comparison should yield the empty set if Libabigail behaves correctly. Otherwise, it means there is an issue that ought to be fixed. This option is used by people interested in Libabigail development for regression testing purposes. Here is an example of the use of this option:

    $ abipkgdiff --self-check --d1 mesa-libGLU-debuginfo-9.0.1-3.fc33.x86_64.rpm  mesa-libGLU-9.0.1-3.fc33.x86_64.rpm
     ==== SELF CHECK SUCCEEDED for 'libGLU.so.1.3.1' ====
    $

•   --no-assume-odr-for-cplusplus

    When analysing a binary originating from C++ code using DWARF debug information, libabigail assumes the One Definition Rule to speed-up the analysis. In that case, when several types have the same name in the binary, they are assumed to all be equal.

    This option disables that assumption and instructs libabigail to actually actually compare the types to determine if they are equal.

•   --no-leverage-dwarf-factorization

    When analysing a binary which DWARF debug information was processed with the DWZ tool, the type information is supposed to be already factorized. That context is used by libabigail to perform some speed optimizations.

    This option disables those optimizations.

•   --ctf This is used to compare packages with CTF debug information, if present.

  Return value

The exit code of the abipkgdiff command is either 0 if the ABI of the binaries compared are equal, or non-zero if they differ or if the tool encountered an error.

In the later case, the value of the exit code is the same as for the abidiff tool.

  kmidiff

kmidiff compares the binary Kernel Module Interfaces of two Linux Kernel trees. The binary KMI is the interface that the Linux Kernel exposes to its modules. The trees we are interested in here are the result of the build of the Linux Kernel source tree.

  General approach

And example of how to build your kernel if you want to compare it to another one using kmidiff is:

git clone -b v4.5 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git linux/v4.5
cd linux/v4.5
make allyesconfig all

Then install the modules into a directory, for instance, the build/modules sub-directory of the your kernel source tree:

mkdir build/modules
make modules_install INSTALL_MOD_DIR=build/modules

Then construct a list of interfaces exported by the kernel, that you want to compare:

cat > kmi-whitelist << EOF
[kernel_4.5_kmi_whitelist]
 init_task
 schedule
 dev_queue_xmit
 __kmalloc
 printk
EOF

Suppose you’ve done something similar for the v4.6 branch of the Linux kernel, you now have these two directories: linux/v4.5 and linux/v4.6. Their modules are present under the directories linux/v4.5/build/modules and linux/v4.6/build/modules.

To Comparing their KMI kmidiff needs to know where to find the vmlinux binaries and their associated modules. Here would be what the command line looks like:

kmidiff                                     \
  --kmi-whitelist  linux/v4.6/kmi-whitelist \
  --vmlinux1       linux/v4.5/vmlinux       \
  --vmlinux2       linux/v4.6/vmlinux       \
                   linux/v4.5/build/modules \
                   linux/v4.6/build/modules

This tool uses the libabigail library to analyze the binary as well as its associated debug information. Here is its general mode of operation.

When instructed to do so, a binary and its associated debug information is read and analyzed. To that effect, libabigail analyzes by default the descriptions of the types reachable by the interfaces (functions and variables) that are visible outside of their translation unit. Once that analysis is done, an Application Binary Interface Corpus is constructed by only considering the subset of types reachable from interfaces associated to ELF symbols that are defined and exported by the binary. It’s that final ABI corpus which libabigail considers as representing the ABI of the analyzed binary.

Libabigail then has capabilities to generate textual representations of ABI Corpora, compare them, analyze their changes and report about them.

  Invocation

More generally, kmidiff is invoked under the form:

kmidiff [options] <first-modules-dir> <second-modules-dir>

  Environment

By default, kmidiff compares all the interfaces (exported functions and variables) between the Kernel and its modules. In practice, though, some users might want to compare a subset of the those interfaces.

By default, kmidiff uses debug information in DWARF format, if present, otherwise it compares interfaces using debug information in CTF format, if present, finally, if neither is found, it uses only ELF symbols to report which were added or removed.

Users can then define a “white list” of the interfaces to compare. Such a white list is a just a file in the “INI” format that looks like:

[kernel_version_x86_64_whitelist]
  function1_name
  function2_name
  global_variable1_name
  ....

Note that the name of the section (the name that is between the two brackets) of that INI file just has to end with the string “whitelist”. So you can define the name you want, for instance [kernel_46_x86_64_whitelist].

Then each line of that whitelist file is the name of an exported function or variable. Only those interfaces along with the types reachable from their signatures are going to be compared by kmidiff recursively.

Note that by default kmidiff analyzes the types reachable from the interfaces associated with ELF symbols that are defined and exported by the Linux Kernel as being the union of the vmlinux binary and all its compiled modules. It then compares those interfaces (along with their types).

  Options

•   --help | -h

    Display a short help about the command and exit.

•   --version | -v

    Display the version of the program and exit.

•   --verbose

    Display some verbose messages while executing.

•   --debug-info-dir1 | --d1 <di-path1>

    For cases where the debug information for the binaries of the first Linux kernel is split out into separate files, tells kmidiff where to find those separate debug information files.

    Note that di-path must point to the root directory under which the debug information is arranged in a tree-like manner. Under Red Hat based systems, that directory is usually <root>/usr/lib/debug.

•   --debug-info-dir2 | --d2 <di-path2>

    Like --debug-info-dir1, this options tells kmidiff where to find the split debug information for the binaries of the second Linux kernel.

•   --vmlinux1 | --l1 <path-to-first-vmlinux>

    Sets the path to the first vmlinux binary to consider. This has to be the uncompressed vmlinux binary compiled with debug info.

•   --vmlinux2 | --l2 <path-to-first-vmlinux>

    Sets the path to the second vmlinux binary to consider. This has to be the uncompressed vmlinux binary compiled with debug info.

•   --kmi-whitelist | -w <path-to-interface-whitelist>

    Set the path to the white list of interfaces to compare while comparing the Kernel Module Interface of the first kernel against the one of the second kernel.

    If this option is not provided, all the exported interfaces of the two kernels are compared. That takes a lot of times and is not necessarily meaningful because many interface are probably meant to see their reachable types change.

    So please, make sure you always use this option unless you really know what you are doing.

•   --suppressions | --suppr <path-to-suppressions>

    Use a suppression specification file located at path-to-suppressions. Note that this option can appear multiple times on the command line. In that case, all of the provided suppression specification files are taken into account.

    Please note that, by default, if this option is not provided, then the default suppression specification files are loaded .

•   --ctf

    Extract ABI information from CTF debug information, if present in the Kernel and Modules.

•   --impacted-interfaces | -i

    Tell what interfaces got impacted by each individual ABI change.

•   --full-impact | -f

    Emit a change report that shows the full impact of each change on exported interfaces. This is the default kind of report emitted by tools like abidiff or abipkgdiff.

•   --exported-interfaces-only

    When using this option, this tool analyzes the descriptions of the types reachable by the interfaces (functions and variables) associated with ELF symbols that are defined and exported by the Linux Kernel.

    Otherwise, the tool also has the ability to analyze the descriptions of the types reachable by the interfaces associated with ELF symbols that are visible outside their translation unit. This later possibility is however much more resource intensive and results in much slower operations.

    That is why this option is enabled by default.

•   --allow-non-exported-interfaces

    When using this option, this tool analyzes the descriptions of the types reachable by the interfaces (functions and variables) that are visible outside of their translation unit. Once that analysis is done, an ABI Corpus is constructed by only considering the subset of types reachable from interfaces associated to ELF symbols that are defined and exported by the binary. It’s that final ABI corpus which is compared against another one.

    The problem with that approach however is that analyzing all the interfaces that are visible from outside their translation unit can amount to a lot of data, leading to very slow operations.

    Note that this option is turned off by default.

•   --show-bytes

    Show sizes and offsets in bytes, not bits. This option is activated by default.

•   --show-bits

    Show sizes and offsets in bits, not bytes. By default, sizes and offsets are shown in bytes.

•   --show-hex

    Show sizes and offsets in hexadecimal base. This option is activated by default.

•   --show-dec

    Show sizes and offsets in decimal base.

  abidw

abidw reads a shared library in ELF format and emits an XML representation of its ABI to standard output. The emitted representation format, named ABIXML, includes all the globally defined functions and variables, along with a complete representation of their types. It also includes a representation of the globally defined ELF symbols of the file.

When given the --linux-tree option, this program can also handle a Linux kernel tree. That is, a directory tree that contains both the vmlinux binary and Linux Kernel modules. It analyses those Linux Kernel binaries and emits an XML representation of the interface between the kernel and its module, to standard output. In this case, we don’t call it an ABI, but a KMI (Kernel Module Interface). The emitted KMI includes all the globally defined functions and variables, along with a complete representation of their types.

To generate either ABI or KMI representation, by default abidw uses debug information in DWARF format, if present, otherwise it looks for debug information in CTF format, if present, finally, if neither is found, it uses only ELF symbols to report which of them were added or removed.

This tool uses the libabigail library to analyze the binary as well as its associated debug information. Here is its general mode of operation.

When instructed to do so, a binary and its associated debug information is read and analyzed. To that effect, libabigail analyzes by default the descriptions of the types reachable by the interfaces (functions and variables) that are visible outside of their translation unit. Once that analysis is done, an Application Binary Interface Corpus is constructed by only considering the subset of types reachable from interfaces associated to ELF symbols that are defined and exported by the binary. It’s that final ABI corpus which libabigail considers as representing the ABI of the analyzed binary.

Libabigail then has capabilities to generate textual representations of ABI Corpora, compare them, analyze their changes and report about them.

  Invocation

abidw [options] [<path-to-elf-file>]

  Options

•   --help | -h

    Display a short help about the command and exit.

•   –version | -v

    Display the version of the program and exit.

•   –abixml-version

    Display the version of the ABIXML format emitted by this program and exit.

•   --debug-info-dir | -d <dir-path>

    In cases where the debug info for path-to-elf-file is in a separate file that is located in a non-standard place, this tells abidw where to look for that debug info file.

    Note that dir-path must point to the root directory under which the debug information is arranged in a tree-like manner. Under Red Hat based systems, that directory is usually <root>/usr/lib/debug.

    This option can be provided several times with different root directories. In that case, abidw will potentially look into all those root directories to find the split debug info for the elf file.

    Note that this option is not mandatory for split debug information installed by your system’s package manager because then abidw knows where to find it.

•   --out-file <file-path>

    This option instructs abidw to emit the XML representation of path-to-elf-file into the file file-path, rather than emitting it to its standard output.

•   --noout

    This option instructs abidw to not emit the XML representation of the ABI. So it only reads the ELF and debug information, builds the internal representation of the ABI and exits. This option is usually useful for debugging purposes.

•   --no-corpus-path

    Do not emit the path attribute for the ABI corpus.

•   --suppressions | suppr <path-to-suppression-specifications-file>

    Use a suppression specification file located at path-to-suppression-specifications-file. Note that this option can appear multiple times on the command line. In that case, all of the provided suppression specification files are taken into account. ABI artifacts matched by the suppression specifications are suppressed from the output of this tool.

•   --kmi-whitelist | -kaw <path-to-whitelist>

    When analyzing a Linux Kernel binary, this option points to the white list of names of ELF symbols of functions and variables which ABI must be written out. That white list is called a ” Kernel Module Interface white list”. This is because for the Kernel, we don’t talk about the ABI; we rather talk about the interface between the Kernel and its module. Hence the term KMI rather than ABI

    Any other function or variable which ELF symbol are not present in that white list will not be considered by the KMI writing process.

    If this option is not provided – thus if no white list is provided – then the entire KMI, that is, all publicly defined and exported functions and global variables by the Linux Kernel binaries is emitted.

•   --linux-tree | --lt

    Make abidw to consider the input path as a path to a directory containing the vmlinux binary as several kernel modules binaries. In that case, this program emits the representation of the Kernel Module Interface (KMI) on the standard output.

    Below is an example of usage of abidw on a Linux Kernel tree.

    First, checkout a Linux Kernel source tree and build it. Then install the kernel modules in a directory somewhere. Copy the vmlinux binary into that directory too. And then serialize the KMI of that kernel to disk, using abidw:

    $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
    $ cd linux && git checkout v4.5
    $ make allyesconfig all
    $ mkdir build-output
    $ make INSTALL_MOD_PATH=./build-output modules_install
    $ cp vmlinux build-output/modules/4.5.0
    $ abidw --linux-tree build-output/modules/4.5.0 > build-output/linux-4.5.0.kmi

•   --headers-dir | --hd <headers-directory-path-1>

    Specifies where to find the public headers of the binary that the tool has to consider. The tool will thus filter out types that are not defined in public headers.

    Note that several public header directories can be specified for the binary to consider. In that case the --header-dir option should be present several times on the command line, like in the following example:

    $ abidw --header-dir /some/path       \
            --header-dir /some/other/path \
            binary > binary.abi

•   --header-file | --hf <header-file-path>

    Specifies where to find one of the public headers of the abi file that the tool has to consider. The tool will thus filter out types that are not defined in public headers.

•   --drop-private-types

    This option is to be used with the --headers-dir and/or header-file options. With this option, types that are NOT defined in the headers are entirely dropped from the internal representation build by Libabigail to represent the ABI and will not end up in the abi XML file.

•   --no-elf-needed

    Do not include the list of DT_NEEDED dependency names in the corpus.

•   --drop-undefined-syms

    With this option functions or variables for which the (exported) ELF symbol is undefined are dropped from the internal representation build by Libabigail to represent the ABI and will not end up in the abi XML file.

•   --exported-interfaces-only

    By default, when looking at the debug information accompanying a binary, this tool analyzes the descriptions of the types reachable by the interfaces (functions and variables) that are visible outside of their translation unit. Once that analysis is done, an ABI corpus is constructed by only considering the subset of types reachable from interfaces associated to ELF symbols that are defined and exported by the binary. It’s that final ABI corpus which textual representation is saved as ABIXML.

    The problem with that approach however is that analyzing all the interfaces that are visible from outside their translation unit can amount to a lot of data, especially when those binaries are applications, as opposed to shared libraries. One example of such applications is the Linux Kernel. Analyzing massive ABI corpora like these can be extremely slow.

    To mitigate that performance issue, this option allows libabigail to only analyze types that are reachable from interfaces associated with defined and exported ELF symbols.

    Note that this option is turned on by default when analyzing the Linux Kernel. Otherwise, it’s turned off by default.

•   --allow-non-exported-interfaces

    When looking at the debug information accompanying a binary, this tool analyzes the descriptions of the types reachable by the interfaces (functions and variables) that are visible outside of their translation unit. Once that analysis is done, an ABI corpus is constructed by only considering the subset of types reachable from interfaces associated to ELF symbols that are defined and exported by the binary. It’s that final ABI corpus which textual representation is saved as ABIXML.

    The problem with that approach however is that analyzing all the interfaces that are visible from outside their translation unit can amount to a lot of data, especially when those binaries are applications, as opposed to shared libraries. One example of such applications is the Linux Kernel. Analyzing massive ABI corpora like these can be extremely slow.

    In the presence of an “average sized” binary however one can afford having libabigail analyze all interfaces that are visible outside of their translation unit, using this option.

    Note that this option is turned on by default, unless we are in the presence of the Linux Kernel.

•   --no-linux-kernel-mode

    Without this option, if abipkgiff detects that the binaries it is looking at are Linux Kernel binaries (either vmlinux or modules) then it only considers functions and variables which ELF symbols are listed in the __ksymtab and __ksymtab_gpl sections.

    With this option, abipkgdiff considers the binary as a non-special ELF binary. It thus considers functions and variables which are defined and exported in the ELF sense.

•   --check-alternate-debug-info <elf-path>

    If the debug info for the file elf-path contains a reference to an alternate debug info file, abidw checks that it can find that alternate debug info file. In that case, it emits a meaningful success message mentioning the full path to the alternate debug info file found. Otherwise, it emits an error code.

•   --no-show-locs In the emitted ABI representation, do not show file, line or column where ABI artifacts are defined.

•   --no-parameter-names

    In the emitted ABI representation, do not show names of function parameters, just the types.

•   --no-write-default-sizes

    In the XML ABI representation, do not write the size-in-bits for pointer type definitions, reference type definitions, function declarations and function types when they are equal to the default address size of the translation unit. Note that libabigail before 1.8 will not set the default size and will interpret types without a size-in-bits attribute as zero sized.

•   --type-id-style <sequence``|``hash>

    This option controls how types are idenfied in the generated XML files. The default sequence style just numbers (with type-id- as prefix) the types in the order they are encountered. The hash style uses a (stable, portable) hash of libabigail’s internal type names and is intended to make the XML files easier to diff.

•   --check-alternate-debug-info-base-name <elf-path>

    Like --check-alternate-debug-info, but in the success message, only mention the base name of the debug info file; not its full path.

•   --load-all-types

    By default, libabigail (and thus abidw) only loads types that are reachable from functions and variables declarations that are publicly defined and exported by the binary. So only those types are present in the output of abidw. This option however makes abidw load all the types defined in the binaries, even those that are not reachable from public declarations.

•   --abidiff Load the ABI of the ELF binary given in argument, save it in libabigail’s XML format in a temporary file; read the ABI from the temporary XML file and compare the ABI that has been read back against the ABI of the ELF binary given in argument. The ABIs should compare equal. If they don’t, the program emits a diagnostic and exits with a non-zero code.

    This is a debugging and sanity check option.

•   --debug-abidiff

    Same as --abidiff but in debug mode. In this mode, error messages are emitted for types which fail type canonicalization.

    This is an optional debugging and sanity check option. To enable it the libabigail package needs to be configured with the –enable-debug-self-comparison option.

•   --debug-type-canonicalization | --debug-tc

    Debug the type canonicalization process. This is done by using structural and canonical equality when canonicalizing every single type. Structural and canonical equality should yield the same result. If they don’t yield the same result for a given type, then it means that the canonicalization of that type went wrong. In that case, an error message is emitted and the execution of the program is aborted.

    This option is available only if the package was configured with the –enable-debug-type-canonicalization option.

•   --no-assume-odr-for-cplusplus

    When analysing a binary originating from C++ code using DWARF debug information, libabigail assumes the One Definition Rule to speed-up the analysis. In that case, when several types have the same name in the binary, they are assumed to all be equal.

    This option disables that assumption and instructs libabigail to actually actually compare the types to determine if they are equal.

•   --no-leverage-dwarf-factorization

    When analysing a binary which DWARF debug information was processed with the DWZ tool, the type information is supposed to be already factorized. That context is used by libabigail to perform some speed optimizations.

    This option disables those optimizations.

•   --ctf

    Extract ABI information from CTF debug information, if present in the given object.

•   --annotate Annotate the ABIXML output with comments above most elements. The comments are made of the pretty-printed form types, declaration or even ELF symbols. The purpose is to make the ABIXML output more human-readable for debugging or documenting purposes.

•   --stats

    Emit statistics about various internal things.

•   --verbose

    Emit verbose logs about the progress of miscellaneous internal things.

  Notes

  Alternate debug info files

As of the version 4 of the DWARF specification, Alternate debug information is a GNU extension to the DWARF specification. It has however been proposed for inclusion into the upcoming version 5 of the DWARF standard. You can read more about the GNU extensions to the DWARF standard here.

  abicompat

abicompat checks that an application that links against a given shared library is still ABI compatible with a subsequent version of that library. If the new version of the library introduces an ABI incompatibility, then abicompat hints the user at what exactly that incompatibility is.

  Invocation

abicompat [options] [<application> <shared-library-first-version> <shared-library-second-version>]

  Options

•   --help

    Display a short help about the command and exit.

•   –version | -v

    Display the version of the program and exit.

•   --list-undefined-symbols | -u

    Display the list of undefined symbols of the application and exit.

•   --show-base-names | -b

    In the resulting report emitted by the tool, this option makes the application and libraries be referred to by their base names only; not by a full absolute name. This can be useful for use in scripts that wants to compare names of the application and libraries independently of what their directory names are.

•   --app-debug-info-dir | --appd <path-to-app-debug-info-directory>

    Set the path to the directory under which the debug information of the application is supposed to be laid out. This is useful for application binaries for which the debug info is in a separate set of files.

•   --lib-debug-info-dir1 | --libd1 <path-to-lib1-debug-info>

    Set the path to the directory under which the debug information of the first version of the shared library is supposed to be laid out. This is useful for shared library binaries for which the debug info is in a separate set of files.

•   --lib-debug-info-dir2 | --libd2 <path-to-lib1-debug-info>

    Set the path to the directory under which the debug information of the second version of the shared library is supposed to be laid out. This is useful for shared library binaries for which the debug info is in a separate set of files.

•   --suppressions | --suppr <path-to-suppressions>

    Use a suppression specification file located at path-to-suppressions. Note that this option can appear multiple times on the command line; all the suppression specification files are then taken into account.

•   --no-show-locs Do not show information about where in the second shared library the respective type was changed.

•   --ctf

    When comparing binaries, extract ABI information from CTF debug information, if present.

•   --fail-no-debug-info

    If no debug info was found, then this option makes the program to fail. Otherwise, without this option, the program will attempt to compare properties of the binaries that are not related to debug info, like pure ELF properties.

•   --ignore-soname

    Ignore differences in the SONAME when doing a comparison

•   --weak-mode

    This triggers the weak mode of abicompat. In this mode, only one version of the library is required. That is, abicompat is invoked like this:

    abicompat --weak-mode <the-application> <the-library>

    Note that the --weak-mode option can even be omitted if only one version of the library is given, along with the application; in that case, abicompat automatically switches to operate in weak mode:

    abicompat <the-application> <the-library>

    In this weak mode, the types of functions and variables exported by the library and consumed by the application (as in, the symbols of the these functions and variables are undefined in the application and are defined and exported by the library) are compared to the version of these types as expected by the application. And if these two versions of types are different, abicompat tells the user what the differences are.

    In other words, in this mode, abicompat checks that the types of the functions and variables exported by the library mean the same thing as what the application expects, as far as the ABI is concerned.

    Note that in this mode, abicompat doesn’t detect exported functions or variables (symbols) that are expected by the application but that are removed from the library. That is why it is called weak mode.

  Return values

The exit code of the abicompat command is either 0 if the ABI of the binaries being compared are equal, or non-zero if they differ or if the tool encountered an error.

In the later case, the exit code is a 8-bits-wide bit field in which each bit has a specific meaning.

The first bit, of value 1, named ABIDIFF_ERROR means there was an error.

The second bit, of value 2, named ABIDIFF_USAGE_ERROR means there was an error in the way the user invoked the tool. It might be set, for instance, if the user invoked the tool with an unknown command line switch, with a wrong number or argument, etc. If this bit is set, then the ABIDIFF_ERROR bit must be set as well.

The third bit, of value 4, named ABIDIFF_ABI_CHANGE means the ABI of the binaries being compared are different.

The fourth bit, of value 8, named ABIDIFF_ABI_INCOMPATIBLE_CHANGE means the ABI of the binaries compared are different in an incompatible way. If this bit is set, then the ABIDIFF_ABI_CHANGE bit must be set as well. If the ABIDIFF_ABI_CHANGE is set and the ABIDIFF_INCOMPATIBLE_CHANGE is NOT set, then it means that the ABIs being compared might or might not be compatible. In that case, a human being needs to review the ABI changes to decide if they are compatible or not.

The remaining bits are not used for the moment.

  Usage examples

•   Detecting a possible ABI incompatibility in a new shared library version:

    $ cat -n test0.h
         1  struct foo
         2  {
         3    int m0;
         4
         5    foo()
         6      : m0()
         7    {}
         8  };
         9
        10  foo*
        11  first_func();
        12
        13  void
        14  second_func(foo&);
        15
        16  void
        17  third_func();
    $
    $ cat -n test-app.cc
         1  // Compile with:
         2  //  g++ -g -Wall -o test-app -L. -ltest-0 test-app.cc
         3
         4  #include "test0.h"
         5
         6  int
         7  main()
         8  {
         9    foo* f = first_func();
        10    second_func(*f);
        11    return 0;
        12  }
    $
    $ cat -n test0.cc
         1  // Compile this with:
         2  //  g++ -g -Wall -shared -o libtest-0.so test0.cc
         3
         4  #include "test0.h"
         5
         6  foo*
         7  first_func()
         8  {
         9    foo* f = new foo();
        10    return f;
        11  }
        12
        13  void
        14  second_func(foo&)
        15  {
        16  }
        17
        18  void
        19  third_func()
        20  {
        21  }
    $
    $ cat -n test1.h
         1  struct foo
         2  {
         3    int  m0;
         4    char m1; /* <-- a new member got added here! */
         5
         6    foo()
         7    : m0(),
         8      m1()
         9    {}
        10  };
        11
        12  foo*
        13  first_func();
        14
        15  void
        16  second_func(foo&);
        17
        18  void
        19  third_func();
    $
    $ cat -n test1.cc
         1  // Compile this with:
         2  //  g++ -g -Wall -shared -o libtest-1.so test1.cc
         3
         4  #include "test1.h"
         5
         6  foo*
         7  first_func()
         8  {
         9    foo* f = new foo();
        10    return f;
        11  }
        12
        13  void
        14  second_func(foo&)
        15  {
        16  }
        17
        18  /* Let's comment out the definition of third_func()
        19     void
        20     third_func()
        21     {
        22     }
        23  */
    $

•   Compile the first and second versions of the libraries: libtest-0.so and libtest-1.so:

    $ g++ -g -Wall -shared -o libtest-0.so test0.cc
    $ g++ -g -Wall -shared -o libtest-1.so test1.cc

•   Compile the application and link it against the first version of the library, creating the test-app binary:

    $ g++ -g -Wall -o test-app -L. -ltest-0.so test-app.cc

•   Now, use abicompat to see if libtest-1.so is ABI compatible with app, with respect to the ABI of libtest-0.so:

    $ abicompat test-app libtest-0.so libtest-1.so
    ELF file 'test-app' might not be ABI compatible with 'libtest-1.so' due to differences with 'libtest-0.so' below:
    Functions changes summary: 0 Removed, 2 Changed, 0 Added functions
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    2 functions with some indirect sub-type change:
      [C]'function foo* first_func()' has some indirect sub-type changes:
        return type changed:
          in pointed to type 'struct foo':
            size changed from 32 to 64 bits
            1 data member insertion:
              'char foo::m1', at offset 32 (in bits)
      [C]'function void second_func(foo&)' has some indirect sub-type changes:
        parameter 0 of type 'foo&' has sub-type changes:
          referenced type 'struct foo' changed, as reported earlier
    $

•   Now use the weak mode of abicompat, that is, providing just the application and the new version of the library:

    $ abicompat --weak-mode test-app libtest-1.so
    functions defined in library
        'libtest-1.so'
    have sub-types that are different from what application
        'test-app'
    expects:
      function foo* first_func():
        return type changed:
          in pointed to type 'struct foo':
            size changed from 32 to 64 bits
            1 data member insertion:
              'char foo::m1', at offset 32 (in bits)
    $

  abilint

abilint parses the native XML representation of an ABI as emitted by abidw. Once it has parsed the XML representation of the ABI, abilint builds and in-memory model from it. It then tries to save it back to an XML form, to standard output. If that read-write operation succeeds chances are the input XML ABI representation is meaningful.

Note that the main intent of this tool to help debugging issues in the underlying Libabigail library.

Note also that abilint can also read an ELF input file, build the in-memory model for its ABI, and serialize that model back into XML to standard output. In that case, the ELF input file must be accompanied with its debug information in the DWARF format.

  Invocation

abilint [options] [<abi-file1>]

  Options

•   --help

    Display a short help message and exits.

•   –version | -v

    Display the version of the program and exit.

•   --debug-info-dir <path>

    When reading an ELF input file which debug information is split out into a separate file, this options tells abilint where to find that separate debug information file.

    Note that path must point to the root directory under which the debug information is arranged in a tree-like manner. Under Red Hat based systems, that directory is usually <root>/usr/lib/debug.

    Note also that this option is not mandatory for split debug information installed by your system’s package manager because then abidiff knows where to find it.

•   --diff

    For XML inputs, perform a text diff between the input and the memory model saved back to disk. This can help to spot issues in the handling of the XML format by the underlying Libabigail library.

•   --noout

    Do not display anything on standard output. The return code of the command is the only way to know if the command succeeded.

•   --suppressions | suppr <path-to-suppression-specifications-file>

    Use a suppression specification file located at path-to-suppression-specifications-file. Note that this option can appear multiple times on the command line. In that case, all of the provided suppression specification files are taken into account. ABI artifacts matched by the suppression specifications are suppressed from the output of this tool.

•   --headers-dir | --hd <headers-directory-path-1>

    Specifies where to find the public headers of the first shared library that the tool has to consider. The tool will thus filter out types that are not defined in public headers.

•   --header-file | --hf <header-file-path>

    Specifies where to find one of the public headers of the abi file that the tool has to consider. The tool will thus filter out types that are not defined in public headers.

•   --stdin | --

    Read the input content from standard input.

•   --tu

    Expect the input XML to represent a single translation unit.

•   --ctf

    Extract ABI information from CTF debug information, if present in the given object.

  fedabipkgdiff

fedabipkgdiff compares the ABI of shared libraries in Fedora packages. It’s a convenient way to do so without having to manually download packages from the Fedora Build System.

fedabipkgdiff knows how to talk with the Fedora Build System to find the right packages versions, their associated debug information and development packages, download them, compare their ABI locally, and report about the possible ABI changes.

Note that by default, this tool reports ABI changes about types that are defined in public header files found in the development packages associated with the packages being compared. It also reports ABI changes about functions and global variables whose symbols are defined and exported in the ELF binaries found in the packages being compared.

  Invocation

fedabipkgdiff [option] <NVR> ...

  Environment

fedabipkgdiff loads two default suppression specifications files, merges their content and use it to filter out ABI change reports that might be considered as false positives to users.

•   Default system-wide suppression specification file

    It’s located by the optional environment variable LIBABIGAIL_DEFAULT_SYSTEM_SUPPRESSION_FILE. If that environment variable is not set, then fedabipkgdiff tries to load the suppression file $libdir/libabigail/libabigail-default.abignore. If that file is not present, then no default system-wide suppression specification file is loaded.

•   Default user suppression specification file.

    It’s located by the optional environment LIBABIGAIL_DEFAULT_USER_SUPPRESSION_FILE. If that environment variable is not set, then fedabipkgdiff tries to load the suppression file $HOME/.abignore. If that file is not present, then no default user suppression specification is loaded.

  Options

•   --help | -h

    Display a short help about the command and exit.

•   --dry-run

    Don’t actually perform the ABI comparison. Details about what is going to be done are emitted on standard output.

•   --debug

    Emit debugging messages about the execution of the program. Details about each method invocation, including input parameters and returned values, are emitted.

•   --traceback

    Show traceback when an exception raised. This is useful for developers of the tool itself to know more exceptional errors.

•   --server <URL>

    Specifies the URL of the Koji XMLRPC service the tool talks to. The default value of this option is http://koji.fedoraproject.org/kojihub.

•   --topurl <URL>

    Specifies the URL of the package store the tool downloads RPMs from. The default value of this option is https://kojipkgs.fedoraproject.org.

•   --from <distro>

    Specifies the name of the baseline Fedora distribution in which to find the first build that is used for comparison. The distro value can be any valid value of the RPM macro %{?dist} for Fedora, for example, fc4, fc23, fc25.

•   --to <distro>

    Specifies the name of the Fedora distribution in which to find the build that is compared against the baseline specified by option --from. The distro value could be any valid value of the RPM macro %{?dist} for Fedora, for example, fc4, fc23.

•   --all-subpackages

    Instructs the tool to also compare the ABI of the binaries in the sub-packages of the packages specified.

•   --dso-only

    Compares the ABI of shared libraries only. If this option is not provided, the tool compares the ABI of all ELF binaries found in the packages.

•   --suppressions <path-to-suppresions>

    Use a suppression specification file located at path-to-suppressions.

•   --no-default-suppression

    Do not load the default suppression specification files.

•   --no-devel-pkg

    Do not take associated development packages into account when performing the ABI comparison. This makes the tool report ABI changes about all types that are reachable from functions and global variables which symbols are defined and publicly exported in the binaries being compared, even if those types are not defined in public header files available from the packages being compared.

•   --show-identical-binaries Show the names of the all binaries compared, including the binaries whose ABI compare equal. By default, when this option is not provided, only binaries with ABI changes are mentionned in the output.

•   --abipkgdiff <path/to/abipkgdiff>

    Specify an alternative abipkgdiff instead of the one installed in system.

•   --clean-cache-before

    Clean cache before ABI comparison.

•   --clean-cache-after

    Clean cache after ABI comparison.

•   --clean-cache

    If you want to clean cache both before and after ABI comparison, --clean-cache is the convenient way for you to save typing of two options at same time.

    Note that a build is a specific version and release of an RPM package. It’s specified by its the package name, version and release. These are specified by the Fedora Naming Guidelines

  Return value

The exit code of the abipkgdiff command is either 0 if the ABI of the binaries compared are equivalent, or non-zero if they differ or if the tool encountered an error.

In the later case, the value of the exit code is the same as for the abidiff tool.

  Use cases

Below are some usage examples currently supported by fedabipkgdiff.

1.  Compare the ABI of binaries in a local package against the ABI of the latest stable package in Fedora 23.

    Suppose you have built just built the httpd package and you want to compare the ABI of the binaries in this locally built package against the ABI of the binaries in the latest http build from Fedora 23. The command line invocation would be:

    $ fedabipkgdiff --from fc23 ./httpd-2.4.18-2.fc24.x86_64.rpm

2.  Compare the ABI of binaries in two local packages.

    Suppose you have built two versions of package httpd, and you want to see what ABI differences between these two versions of RPM files. The command line invocation would be:

    $ fedabipkgdiff path/to/httpd-2.4.23-3.fc23.x86_64.rpm another/path/to/httpd-2.4.23-4.fc24.x86_64.rpm

    All what fedabipkgdiff does happens on local machine without the need of querying or downloading RPMs from Koji.

3.  Compare the ABI of binaries in the latest build of the httpd package in Fedora 23 against the ABI of the binaries in the latest build of the same package in 24.

    In this case, note that neither of the two packages are available locally. The tool is going to talk with the Fedora Build System, determine what the versions and releases of the latest packages are, download them and perform the comparison locally. The command line invocation would be:

    $ fedabipkgdiff --from fc23 --to fc24 httpd

4.  Compare the ABI of binaries of two builds of the httpd package, designated their versions and releases.

    If we want to do perform the ABI comparison for all the processor architectures supported by Fedora the command line invocation would be:

    $ fedabipkgdiff httpd-2.8.14.fc23 httpd-2.8.14.fc24

    But if we want to perform the ABI comparison for a specific architecture, say, x86_64, then the command line invocation would be:

    $ fedabipkgdiff httpd-2.8.14.fc23.x86_64 httpd-2.8.14.fc24.x86_64

5.  If the use wants to also compare the sub-packages of a given package, she can use the –all-subpackages option. The first command of the previous example would thus look like:

    $ fedabipkgdiff --all-subpackages httpd-2.8.14.fc23 httpd-2.8.14.fc24

CONCEPTS

  ABI artifacts

An ABI artifact is a relevant part of the ABI of a shared library or program. Examples of ABI artifacts are exported types, variables, functions, or ELF symbols exported by a shared library.

The set of ABI artifact for a binary is called an ABI Corpus.

  Harmful changes

A change in the diff report is considered harmful if it might cause ABI compatibility issues. That is, it might prevent an application dynamically linked against a given version of a library to keep working with the changed subsequent versions of the same library.

  Harmless changes

A change in the diff report is considered harmless if it will not cause any ABI compatibility issue. That is, it will not prevent an application dynamically linked against given version of a library to keep working with the changed subsequent versions of the same library.

By default, abidiff filters harmless changes from the diff report.

  Suppression specifications

  Definition

A suppression specification file is a way for a user to instruct abidiff, abipkgdiff or any other relevant libabigail tool to avoid emitting reports for changes involving certain ABI artifacts.

It contains directives (or specifications) that describe the set of ABI artifacts to avoid emitting change reports about.

  Introductory examples

Its syntax is based on a simplified and customized form of Ini File Syntax. For instance, to specify that change reports on a type named FooPrivateType should be suppressed, one could write this suppression specification:

[suppress_type]
  name = FooPrivateType

If we want to ensure that only change reports about structures named FooPrivateType should be suppressed, we could write:

[suppress_type]
  type_kind = struct
  name = FooPrivateType

But we could also want to suppress change reports avoid typedefs named FooPrivateType. In that case we would write:

[suppress_type]
  type_kind = typedef
  name = FooPrivateType

Or, we could want to suppress change reports about all struct which names end with the string "PrivateType":

[suppress_type]
  type_kind = struct
  name_regexp = ^.*PrivateType

Let's now look at the generic syntax of suppression specification files.

  Syntax

  Properties

More generally, the format of suppression lists is organized around the concept of property. Every property has a name and a value, delimited by the = sign. E.g:

name = value

Leading and trailing white spaces are ignored around property names and values.

  Regular expressions

The value of some properties might be a regular expression. In that case, they must comply with the syntax of extended POSIX regular expressions. Note that Libabigail uses the regular expression engine of the GNU C Library.

  Escaping a character in a regular expression

When trying to match a string that contains a * character, like in the pointer type int*, one must be careful to notice that the character * is a special character in the extended POSIX regular expression syntax. And that character must be escaped for the regular expression engine. Thus the regular expression that would match the string int* in a suppression file should be

int\\*

Wait; but then why the two \ characters? Well, because the \ character is a special character in the Ini File Syntax used for specifying suppressions. So it must be escaped as well, so that the Ini File parser leaves a \ character intact in the data stream that is handed to the regular expression engine. Hence the \\ targeted at the Ini File parser.

So, in short, to escape a character in a regular expression, always prefix the character with the \\ sequence.

  Modus operandi

Suppression specifications can be applied at two different points of the processing pipeline of libabigail.

In the default operating mode called "late suppression mode", suppression specifications are applied to the result of comparing the in-memory internal representations of two ABIs. In this mode, if an ABI artifact matches a suppression specification, its changes are not mentioned in the ABI change report. The internal representation of the "suppressed" changed ABI artifact is still present in memory; it is just not mentioned in the ABI change report. The change report can still mention statistics about the number of changed ABI artifacts that were suppressed.

There is another operating mode called the "early suppression mode" where suppression specifications are applied during the construction of the in-memory internal representation of a given ABI. In that mode, if an ABI artifact matches a suppression specification, no in-memory internal representation is built for it. As a result, no change about the matched ABI artifact is going to be mentioned in the ABI change report and no statistic about the number of suppressed ABI changes is available. Also, please note that because suppressed ABI artifacts are removed from the in-memory internal representation in this mode, the amount memory used by the internal representation is potentially smaller than the memory consumption in the late suppression mode.

  Sections

Properties are then grouped into arbitrarily named sections that shall not be nested. The name of the section is on a line by itself and is surrounded by square brackets, i.e:

[section_name]
property1_name = property1_value
property2_name = property2_value

A section might or might not have properties. Sections that expect to have properties and which are found nonetheless empty are just ignored. Properties that are not recognized by the reader are ignored as well.

  Section names

Each different section can be thought of as being a directive to suppress ABI change reports for a particular kind of ABI artifact.

  [suppress_file]

This directive prevents a given tool from loading a file (binary or abixml file) if its file name or other properties match certain properties. Thus, if the tool is meant to compare the ABIs of two files, and if the directive prevents it from loading either one of the files, then no comparison is performed.

Note that for the [suppress_file] directive to work, at least one of the following properties must be provided: file_name_regexp, file_name_not_regexp, soname_regexp, soname_not_regexp.

If none of the above properties are provided, then the [suppress_file] directive is simply ignored.

The potential properties of this sections are listed below:

•   file_name_regexp

    Usage: file_name_regexp = <regular-expression>

    Prevents the system from loading the file which name matches the regular expression specified as value of this property.

•   file_name_not_regexp

    Usage: file_name_not_regexp = <regular-expression>

    Prevents the system from loading the file which name does not match the regular expression specified as value of this property.

•   soname_regexp

    Usage: soname_regexp = <regular-expression>

    Prevents the system from loading the file which contains a SONAME property that matches the regular expression of this property. Note that this property also works on an abixml file if it contains a SONAME property.

•   soname_not_regexp

    Usage: soname_not_regexp = <regular-expression>

    Prevents the system from loading the file which contains a SONAME property that does NOT match the regular expression of this property. Note that this property also works on an abixml file if it contains a SONAME property.

•   label Usage: label = <some-value>

    Define a label for the section. A label is just an informative string that might be used by the tool to refer to a type suppression in error messages.

  [suppress_type]

This directive suppresses report messages about a type change.

Note that for the [suppress_type] directive to work, at least one of the following properties must be provided: file_name_regexp, file_name_not_regexp, soname_regexp, soname_not_regexp, name, name_regexp, name_not_regexp, type_kind, source_location_not_in, source_location_not_regexp.

If none of the above properties are provided, then the [suppress_type] directive is simply ignored.

The potential properties of this sections are listed below:

•   file_name_regexp

    Usage: file_name_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a binary file which name matches the regular expression specified as value of this property.

•   file_name_not_regexp

    Usage: file_name_not_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a binary file which name does not match the regular expression specified as value of this property.

•   soname_regexp

    Usage: soname_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a shared library which SONAME property matches the regular expression specified as value of this property.

•   soname_not_regexp

    Usage: soname_not_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a shared library which SONAME property does not match the regular expression specified as value of this property.

•   name_regexp Usage: name_regexp = <regular-expression>

    Suppresses change reports involving types whose name matches the regular expression specified as value of this property.

•   name_not_regexp Usage: name_not_regexp = <regular-expression>

    Suppresses change reports involving types whose name does NOT match the regular expression specified as value of this property. Said otherwise, this property specifies which types to keep, rather than types to suppress from reports.

•   name Usage: name = <a-value>

    Suppresses change reports involving types whose name equals the value of this property.

•   type_kind Usage:

type_kind = class | struct | union | enum |
    array | typedef | builtin

    Suppresses change reports involving a certain kind of type. The kind of type to suppress change reports for is specified by the possible values listed above:

•

class: suppress change reports for class types. Note that
    even if class types don't exist for C, this value still triggers the suppression of change reports for struct types, in C. In C++ however, it should do what it suggests.

•

struct: suppress change reports for struct types in C or C++.
    Note that the value class above is a super-set of this one.

•   union: suppress change reports for union types.

•   enum: suppress change reports for enum types.

•   array: suppress change reports for array types.

•   typedef: suppress change reports for typedef types.

•   builtin: suppress change reports for built-in (or native) types. Example of built-in types are char, int, unsigned int, etc.

•   source_location_not_in Usage: source_location_not_in = <list-of-file-paths>

    Suppresses change reports involving a type which is defined in a file which path is NOT listed in the value list-of-file-paths. Note that the value is a comma-separated list of file paths e.g, this property

    source_location_not_in = libabigail/abg-ir.h, libabigail/abg-dwarf-reader.h

    suppresses change reports about all the types that are NOT defined in header files whose path end up with the strings libabigail/abg-ir.h or libabigail/abg-dwarf-reader.h.

•   source_location_not_regexp Usage: source_location_not_regexp = <regular-expression>

    Suppresses change reports involving a type which is defined in a file which path does NOT match the regular expression provided as value of the property. E.g, this property

    source_location_not_regexp = libabigail/abg-.*\\.h

    suppresses change reports involving all the types that are NOT defined in header files whose path match the regular expression provided a value of the property.

•   has_data_member_inserted_at Usage: has_data_member_inserted_at = <offset-in-bit>

    Suppresses change reports involving a type which has at least one data member inserted at an offset specified by the property value offset-in-bit. Please note that if a type has a change in which at least one of its data members is removed or its size is reduced, the type will NOT be suppressed by the evaluation of this property.

    The value offset-in-bit is either:

•   an integer value, expressed in bits, which denotes the offset of the insertion point of the data member, starting from the beginning of the relevant structure or class.

•   the keyword end which is a named constant which value equals the offset of the end of the of the structure or class.

•   the function call expression offset_of(data-member-name) where data-member-name is the name of a given data member of the relevant structure or class. The value of this function call expression is an integer that represents the offset of the data member denoted by data-member-name.

•   the function call expression offset_after(data-member-name) where data-member-name is the name of a given data member of the relevant structure or class. The value of this function call expression is an integer that represents the offset of the point that comes right after the region occupied by the data member denoted by data-member-name.

•   has_data_member_inserted_between Usage: has_data_member_inserted_between = {<range-begin>, <range-end>}

    Suppresses change reports involving a type which has at least one data member inserted at an offset that is comprised in the range between range-begin and range-end. Please note that each of the values range-begin and range-end can be of the same form as the has_data_member_inserted_at property above. Please also note that if a type has a change in which at least one of its data members is removed or its size is reduced, the type will NOT be suppressed by the evaluation of this property.

    Usage examples of this properties are:

    has_data_member_inserted_between = {8, 64}

    or:

    has_data_member_inserted_between = {16, end}

    or:

    has_data_member_inserted_between = {offset_after(member1), end}

•   has_data_members_inserted_between Usage: has_data_members_inserted_between = {<sequence-of-ranges>}

    Suppresses change reports involving a type which has multiple data member inserted in various offset ranges. A usage example of this property is, for instance:

    has_data_members_inserted_between = {{8, 31}, {72, 95}}

    This usage example suppresses change reports involving a type which has data members inserted in bit offset ranges [8 31] and [72 95]. The length of the sequence of ranges or this has_data_members_inserted_between is not bounded; it can be as long as the system can cope with. The values of the boundaries of the ranges are of the same kind as for the has_data_member_inserted_at property above. Please note that if a type has a change in which at least one of its data members is removed or its size is reduced, the type will NOT be suppressed by the evaluation of this property.

    Another usage example of this property is thus:

    has_data_members_inserted_between =
      {
           {offset_after(member0), offset_of(member1)},
           {72, end}
      }

•   accessed_through Usage: accessed_through = <some-predefined-values>

    Suppress change reports involving a type which is referred to either directly or through a pointer or a reference. The potential values of this property are the predefined keywords below:

•   direct

    So if the [suppress_type] contains the property description:

    accessed_through = direct

    then changes about a type that is referred-to directly (i.e, not through a pointer or a reference) are going to be suppressed.

•   pointer

    If the accessed_through property is set to the value pointer then changes about a type that is referred-to through a pointer are going to be suppressed.

•   reference

    If the accessed_through property is set to the value reference then changes about a type that is referred-to through a reference are going to be suppressed.

•   reference-or-pointer

    If the accessed_through property is set to the value reference-or-pointer then changes about a type that is referred-to through either a reference or a pointer are going to be suppressed.

    For an extensive example of how to use this property, please check out the example below about suppressing change reports about types accessed either directly or through pointers.

•   drop Usage: drop = yes | no

    If a type is matched by a suppression specification which contains the "drop" property set to "yes" (or to "true") then the type is not even going to be represented in the internal representation of the ABI being analyzed. This property makes its enclosing suppression specification to be applied in the early suppression specification mode. The net effect is that it potentially reduces the memory used to represent the ABI being analyzed.

    Please note that for this property to be effective, the enclosing suppression specification must have at least one of the following properties specified: name_regexp, name, name_regexp, source_location_not_in or source_location_not_regexp.

•   label Usage: label = <some-value>

    Define a label for the section. A label is just an informative string that might be used by a tool to refer to a type suppression in error messages.

•   changed_enumerators

    Usage: changed_enumerators = <list-of-enumerators>

    Suppresses change reports involving changes in the value of enumerators of a given enum type. This property is applied if the type_kind property is set to the value enum, at least. The value of the changed_enumerators is a comma-separated list of the enumerators that the user expects to change. For instance:

    changed_enumerators = LAST_ENUMERATORS0, LAST_ENUMERATOR1

  [suppress_function]

This directive suppresses report messages about changes on a set of functions.

Note that for the [suppress_function] directive to work, at least one of the following properties must be provided: label, file_name_regexp, file_name_not_regexp, soname_regexp, soname_not_regexp, name, name_regexp, name_not_regexp, parameter, return_type_name, return_type_regexp, symbol_name, symbol_name_regexp, symbol_name_not_regexp, symbol_version, symbol_version_regexp.

If none of the above properties are provided, then the [suppress_function] directive is simply ignored.

The potential properties of this sections are:

•   label Usage: label = <some-value>

    This property is the same as the label property defined above.

•   file_name_regexp

    Usage:

    file_name_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a binary file which name matches the regular expression specified as value of this property.

•   file_name_not_regexp

    Usage: file_name_not_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a binary file which name does not match the regular expression specified as value of this property.

•   soname_regexp

    Usage: soname_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a shared library which SONAME property matches the regular expression specified as value of this property.

•   soname_not_regexp

    Usage: soname_not_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a shared library which SONAME property does not match the regular expression specified as value of this property.

•   name Usage: name = <some-value>

    Suppresses change reports involving functions whose name equals the value of this property.

•   name_regexp Usage: name_regexp = <regular-expression>

    Suppresses change reports involving functions whose name matches the regular expression specified as value of this property.

    Let's consider the case of functions that have several symbol names. This happens when the underlying symbol for the function has aliases. Each symbol name is actually one alias name.

    In this case, if the regular expression matches the name of at least one of the aliases names, then it must match the names of all of the aliases of the function for the directive to actually suppress the diff reports for said function.

•   name_not_regexp Usage: name_not_regexp = <regular-expression>

    Suppresses change reports involving functions whose names don't match the regular expression specified as value of this property.

    The rules for functions that have several symbol names are the same rules as for the name_regexp property above.

•   change_kind Usage: change_kind = <predefined-possible-values>

    Specifies the kind of changes this suppression specification should apply to. The possible values of this property as well as their meaning are listed below:

•   function-subtype-change

    This suppression specification applies to functions that which have at least one sub-type that has changed.

•   added-function

    This suppression specification applies to functions that have been added to the binary.

•   deleted-function

    This suppression specification applies to functions that have been removed from the binary.

•   all

    This suppression specification applies to functions that have all of the changes above. Note that not providing the change_kind property at all is equivalent to setting it to the value all.

•   parameter Usage: parameter = <function-parameter-specification>

    Suppresses change reports involving functions whose parameters match the parameter specification indicated as value of this property.

    The format of the function parameter specification is:

    ' <parameter-index> <space> <type-name-or-regular-expression>

    That is, an apostrophe followed by a number that is the index of the parameter, followed by one of several spaces, followed by either the name of the type of the parameter, or a regular expression describing a family of parameter type names.

    If the parameter type name is designated by a regular expression, then said regular expression must be enclosed between two slashes; like /some-regular-expression/.

    The index of the first parameter of the function is zero. Note that for member functions (methods of classes), the this is the first parameter that comes after the implicit "this" pointer parameter.

    Examples of function parameter specifications are:

    '0 int

    Which means, the parameter at index 0, whose type name is int.

    '4 unsigned char*

    Which means, the parameter at index 4, whose type name is unsigned char*.

    '2 /^foo.*&/

    Which means, the parameter at index 2, whose type name starts with the string "foo" and ends with an '&'. In other words, this is the third parameter and it's a reference on a type that starts with the string "foo".

•   return_type_name Usage: return_type_name = <some-value>

    Suppresses change reports involving functions whose return type name equals the value of this property.

•   return_type_regexp Usage: return_type_regexp = <regular-expression>

    Suppresses change reports involving functions whose return type name matches the regular expression specified as value of this property.

•   symbol_name Usage: symbol_name = <some-value>

    Suppresses change reports involving functions whose symbol name equals the value of this property.

•   symbol_name_regexp Usage: symbol_name_regexp = <regular-expression>

    Suppresses change reports involving functions whose symbol name matches the regular expression specified as value of this property.

    Let's consider the case of functions that have several symbol names. This happens when the underlying symbol for the function has aliases. Each symbol name is actually one alias name.

    In this case, the regular expression must match the names of all of the aliases of the function for the directive to actually suppress the diff reports for said function.

•   symbol_name_not_regexp Usage: symbol_name_not_regexp = <regular-expression>

    Suppresses change reports involving functions whose symbol name does not match the regular expression specified as value of this property.

•   symbol_version Usage: symbol_version = <some-value>

    Suppresses change reports involving functions whose symbol version equals the value of this property.

•   symbol_version_regexp Usage: symbol_version_regexp = <regular-expression>

    Suppresses change reports involving functions whose symbol version matches the regular expression specified as value of this property.

•   drop Usage: drop = yes | no

    If a function is matched by a suppression specification which contains the "drop" property set to "yes" (or to "true") then the function is not even going to be represented in the internal representation of the ABI being analyzed. This property makes its enclosing suppression specification to be applied in the early suppression specification mode. The net effect is that it potentially reduces the memory used to represent the ABI being analyzed.

    Please note that for this property to be effective, the enclosing suppression specification must have at least one of the following properties specified: name_regexp, name, name_regexp, source_location_not_in or source_location_not_regexp.

  [suppress_variable]

This directive suppresses report messages about changes on a set of variables.

Note that for the [suppress_variable] directive to work, at least one of the following properties must be provided: label, file_name_regexp, file_name_not_regexp, soname_regexp, soname_not_regexp, name, name_regexp, name_not_regexp, symbol_name, symbol_name_regexp, symbol_name_not_regexp, symbol_version, symbol_version_regexp, type_name, type_name_regexp.

If none of the above properties are provided, then the [suppress_variable] directive is simply ignored.

The potential properties of this sections are:

•   label Usage: label = <some-value>

    This property is the same as the label property defined above.

•   file_name_regexp

    Usage:

    file_name_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a binary file which name matches the regular expression specified as value of this property.

•   file_name_not_regexp

    Usage: file_name_not_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a binary file which name does not match the regular expression specified as value of this property.

•   soname_regexp

    Usage: soname_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a shared library which SONAME property matches the regular expression specified as value of this property.

•   soname_not_regexp

    Usage: soname_not_regexp = <regular-expression>

    Suppresses change reports about ABI artifacts that are defined in a shared library which SONAME property does not match the regular expression specified as value of this property.

•   name Usage: name = <some-value>

    Suppresses change reports involving variables whose name equals the value of this property.

•   name_regexp Usage: name_regexp = <regular-expression>

    Suppresses change reports involving variables whose name matches the regular expression specified as value of this property.

•   change_kind Usage: change_kind = <predefined-possible-values>

    Specifies the kind of changes this suppression specification should apply to. The possible values of this property as well as their meaning are the same as when it's used in the [suppress_function] section.

•   symbol_name Usage: symbol_name = <some-value>

    Suppresses change reports involving variables whose symbol name equals the value of this property.

•   symbol_name_regexp Usage: symbol_name_regexp = <regular-expression>

    Suppresses change reports involving variables whose symbol name matches the regular expression specified as value of this property.

•   symbol_name_not_regexp Usage: symbol_name_not_regexp = <regular-expression>

    Suppresses change reports involving variables whose symbol name does not match the regular expression specified as value of this property.

•   symbol_version Usage: symbol_version = <some-value>

    Suppresses change reports involving variables whose symbol version equals the value of this property.

•   symbol_version_regexp Usage: symbol_version_regexp = <regular-expression>

    Suppresses change reports involving variables whose symbol version matches the regular expression specified as value of this property.

•   type_name Usage: type_name = <some-value>

    Suppresses change reports involving variables whose type name equals the value of this property.

•   type_name_regexp Usage: type_name_regexp = <regular-expression>

    Suppresses change reports involving variables whose type name matches the regular expression specified as value of this property.

  Comments

; or # ASCII character at the beginning of a line indicates a comment. Comment lines are ignored.

  Code examples

1.  Suppressing change reports about types.

    Suppose we have a library named libtest1-v0.so which contains this very useful code:

    $ cat -n test1-v0.cc
         1  // A forward declaration for a type considered to be opaque to
         2  // function foo() below.
         3  struct opaque_type;
         4
         5  // This function cannot touch any member of opaque_type.  Hence,
         6  // changes to members of opaque_type should not impact foo, as far as
         7  // ABI is concerned.
         8  void
         9  foo(opaque_type*)
        10  {
        11  }
        12
        13  struct opaque_type
        14  {
        15    int member0;
        16    char member1;
        17  };
    $

    Let's change the layout of struct opaque_type by inserting a data member around line 15, leading to a new version of the library, that we shall name libtest1-v1.so:

    $ cat -n test1-v1.cc
         1  // A forward declaration for a type considered to be opaque to
         2  // function foo() below.
         3  struct opaque_type;
         4
         5  // This function cannot touch any member of opaque_type;  Hence,
         6  // changes to members of opaque_type should not impact foo, as far as
         7  // ABI is concerned.
         8  void
         9  foo(opaque_type*)
        10  {
        11  }
        12
        13  struct opaque_type
        14  {
        15    char added_member; // <-- a new member got added here now.
        16    int member0;
        17    char member1;
        18  };
    $

    Let's compile both examples. We shall not forget to compile them with debug information generation turned on:

    $ g++ -shared -g -Wall -o libtest1-v0.so test1-v0.cc
    $ g++ -shared -g -Wall -o libtest1-v1.so test1-v1.cc

    Let's ask abidiff which ABI differences it sees between libtest1-v0.so and libtest1-v1.so:

    $ abidiff libtest1-v0.so libtest1-v1.so
    Functions changes summary: 0 Removed, 1 Changed, 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    1 function with some indirect sub-type change:
      [C]'function void foo(opaque_type*)' has some indirect sub-type changes:
        parameter 0 of type 'opaque_type*' has sub-type changes:
          in pointed to type 'struct opaque_type':
            size changed from 64 to 96 bits
            1 data member insertion:
              'char opaque_type::added_member', at offset 0 (in bits)
            2 data member changes:
             'int opaque_type::member0' offset changed from 0 to 32
             'char opaque_type::member1' offset changed from 32 to 64

    So abidiff reports that the opaque_type's layout has changed in a significant way, as far as ABI implications are concerned, in theory. After all, a sub-type (struct opaque_type) of an exported function (foo()) has seen its layout change. This might have non negligible ABI implications. But in practice here, the programmer of the litest1-v1.so library knows that the "soft" contract between the function foo() and the type struct opaque_type is to stay away from the data members of the type. So layout changes of struct opaque_type should not impact foo().

    Now to teach abidiff about this soft contract and have it avoid emitting what amounts to false positives in this case, we write the suppression specification file below:

    $ cat test1.suppr
    [suppress_type]
      type_kind = struct
      name = opaque_type

    Translated in plain English, this suppression specification would read: "Do not emit change reports about a struct which name is opaque_type".

    Let's now invoke abidiff on the two versions of the library again, but this time with the suppression specification:

    $ abidiff --suppressions test1.suppr libtest1-v0.so libtest1-v1.so
    Functions changes summary: 0 Removed, 0 Changed (1 filtered out), 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable

    As you can see, abidiff does not report the change anymore; it tells us that it was filtered out instead.

    Suppressing change reports about types with data member insertions

    Suppose the first version of a library named libtest3-v0.so has this source code:

    /* Compile this with:
         gcc -g -Wall -shared -o libtest3-v0.so test3-v0.c
     */
    struct S
    {
      char member0;
      int member1; /*
                      between member1 and member2, there is some padding,
                      at least on some popular platforms.  On
                      these platforms, adding a small enough data
                      member into that padding shouldn't change
                      the offset of member1.  Right?
                    */
    };
    int
    foo(struct S* s)
    {
      return s->member0 + s->member1;
    }

    Now, suppose the second version of the library named libtest3-v1.so has this source code in which a data member has been added in the padding space of struct S and another data member has been added at its end:

    /* Compile this with:
         gcc -g -Wall -shared -o libtest3-v1.so test3-v1.c
     */
    struct S
    {
      char member0;
      char inserted1; /* <---- A data member has been added here...  */
      int member1;
      char inserted2; /* <---- ... and another one has been added here.  */
    };
    int
    foo(struct S* s)
    {
      return s->member0 + s->member1;
    }

    In libtest3-v1.so, adding char data members S::inserted1 and S::inserted2 can be considered harmless (from an ABI compatibility perspective), at least on the x86 platform, because that doesn't change the offsets of the data members S::member0 and S::member1. But then running abidiff on these two versions of library yields:

    $ abidiff libtest3-v0.so libtest3-v1.so
    Functions changes summary: 0 Removed, 1 Changed, 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    1 function with some indirect sub-type change:
      [C]'function int foo(S*)' has some indirect sub-type changes:
        parameter 0 of type 'S*' has sub-type changes:
          in pointed to type 'struct S':
            type size changed from 64 to 96 bits
            2 data member insertions:
              'char S::inserted1', at offset 8 (in bits)
              'char S::inserted2', at offset 64 (in bits)
    $

    That is, abidiff shows us the two changes, even though we (the developers of that very involved library) know that these changes are harmless in this particular context.

    Luckily, we can devise a suppression specification that essentially tells abidiff to filter out change reports about adding a data member between S::member0 and S::member1, and adding a data member at the end of struct S. We have written such a suppression specification in a file called test3-1.suppr and it unsurprisingly looks like:

    [suppress_type]
      name = S
      has_data_member_inserted_between = {offset_after(member0), offset_of(member1)}
      has_data_member_inserted_at = end

    Now running abidiff with this suppression specification yields:

    $ ../build/tools/abidiff --suppressions test3-1.suppr libtest3-v0.so libtest3-v1.so
    Functions changes summary: 0 Removed, 0 Changed (1 filtered out), 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    $

    Hooora! \o/ (I guess)

    Suppressing change reports about types accessed either directly or through pointers

    Suppose we have a first version of an object file which source code is the file widget-v0.cc below:

    // Compile with: g++ -g -c widget-v0.cc
    struct widget
    {
      int x;
      int y;
      widget()
        :x(), y()
      {}
    };
    void
    fun0(widget*)
    {
      // .. do stuff here.
    }
    void
    fun1(widget&)
    {
      // .. do stuff here ..
    }
    void
    fun2(widget w)
    {
      // ... do other stuff here ...
    }

    Now suppose in the second version of that file, named widget-v1.cc, we have added some data members at the end of the type struct widget; here is what the content of that file would look like:

    // Compile with: g++ -g -c widget-v1.cc
    struct widget
    {
      int x;
      int y;
      int w; // We have added these two new data members here ..
      int h; // ... and here.
      widget()
        : x(), y(), w(), h()
      {}
    };
    void
    fun0(widget*)
    {
      // .. do stuff here.
    }
    void
    fun1(widget&)
    {
      // .. do stuff here ..
    }
    void
    fun2(widget w)
    {
      // ... do other stuff here ...
    }

    When we invoke abidiff on the object files resulting from the compilation of the two file above, here is what we get:

     $ abidiff widget-v0.o widget-v1.o
     Functions changes summary: 0 Removed, 2 Changed (1 filtered out), 0 Added functions
     Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
     2 functions with some indirect sub-type change:
       [C]'function void fun0(widget*)' has some indirect sub-type changes:
         parameter 1 of type 'widget*' has sub-type changes:
           in pointed to type 'struct widget':
             type size changed from 64 to 128 bits
             2 data member insertions:
               'int widget::w', at offset 64 (in bits)
               'int widget::h', at offset 96 (in bits)
       [C]'function void fun2(widget)' has some indirect sub-type changes:
         parameter 1 of type 'struct widget' has sub-type changes:
           details were reported earlier
    $

    I guess a little bit of explaining is due here. abidiff detects that two data member got added at the end of struct widget. it also tells us that the type change impacts the exported function fun0() which uses the type struct widget through a pointer, in its signature.

    Careful readers will notice that the change to struct widget also impacts the exported function fun1(), that uses type struct widget through a reference. But then abidiff doesn't tell us about the impact on that function fun1() because it has evaluated that change as being redundant with the change it reported on fun0(). It has thus filtered it out, to avoid cluttering the output with noise.

    Redundancy detection and filtering is fine and helpful to avoid burying the important information in a sea of noise. However, it must be treated with care, by fear of mistakenly filtering out relevant and important information.

    That is why abidiff tells us about the impact that the change to struct widget has on function fun2(). In this case, that function uses the type struct widget directly (in its signature). It does not use it via a pointer or a reference. In this case, the direct use of this type causes fun2() to be exposed to a potentially harmful ABI change. Hence, the report about fun2() is not filtered out, even though it's about that same change on struct widget.

    To go further in suppressing reports about changes that are harmless and keeping only those that we know are harmful, we would like to go tell abidiff to suppress reports about this particular struct widget change when it impacts uses of struct widget through a pointer or reference. In other words, suppress the change reports about fun0() and fun1(). We would then write this suppression specification, in file widget.suppr:

    [suppress_type]
      name = widget
      type_kind = struct
      has_data_member_inserted_at = end
      accessed_through = reference-or-pointer
      # So this suppression specification says to suppress reports about
      # the type 'struct widget', if this type was added some data member
      # at its end, and if the change impacts uses of the type through a
      # reference or a pointer.

    Invoking abidiff on widget-v0.o and widget-v1.o with this suppression specification yields:

    $ abidiff --suppressions widget.suppr widget-v0.o widget-v1.o
    Functions changes summary: 0 Removed, 1 Changed (2 filtered out), 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    1 function with some indirect sub-type change:
      [C]'function void fun2(widget)' has some indirect sub-type changes:
        parameter 1 of type 'struct widget' has sub-type changes:
          type size changed from 64 to 128 bits
          2 data member insertions:
            'int widget::w', at offset 64 (in bits)
            'int widget::h', at offset 96 (in bits)
    $

    As expected, I guess.

    Suppressing change reports about functions.

    Suppose we have a first version a library named libtest2-v0.so whose source code is:

     $ cat -n test2-v0.cc
      1     struct S1
      2     {
      3       int m0;
      4
      5       S1()
      6         : m0()
      7       {}
      8     };
      9
     10     struct S2
     11     {
     12       int m0;
     13
     14       S2()
     15         : m0()
     16       {}
     17     };
     18
     19     struct S3
     20     {
     21       int m0;
     22
     23       S3()
     24         : m0()
     25       {}
     26     };
     27
     28     int
     29     func(S1&)
     30     {
     31       // suppose the code does something with the argument.
     32       return 0;
     33
     34     }
     35
     36     char
     37     func(S2*)
     38     {
     39       // suppose the code does something with the argument.
     40       return 0;
     41     }
     42
     43     unsigned
     44     func(S3)
     45     {
     46       // suppose the code does something with the argument.
     47       return 0;
     48     }
    $

    And then we come up with a second version libtest2-v1.so of that library; the source code is modified by making the structures S1, S2, S3 inherit another struct:

    $ cat -n test2-v1.cc
          1 struct base_type
          2 {
          3   int m_inserted;
          4 };
          5
          6 struct S1 : public base_type // <--- S1 now has base_type as its base
          7                              // type.
          8 {
          9   int m0;
         10
         11   S1()
         12     : m0()
         13   {}
         14 };
         15
         16 struct S2 : public base_type // <--- S2 now has base_type as its base
         17                              // type.
         18 {
         19   int m0;
         20
         21   S2()
         22     : m0()
         23   {}
         24 };
         25
         26 struct S3 : public base_type // <--- S3 now has base_type as its base
         27                              // type.
         28 {
         29   int m0;
         30
         31   S3()
         32     : m0()
         33   {}
         34 };
         35
         36 int
         37 func(S1&)
         38 {
         39   // suppose the code does something with the argument.
         40   return 0;
         41
         42 }
         43
         44 char
         45 func(S2*)
         46 {
         47   // suppose the code does something with the argument.
         48   return 0;
         49 }
         50
         51 unsigned
         52 func(S3)
         53 {
         54   // suppose the code does something with the argument.
         55   return 0;
         56 }
     $

    Now let's build the two libraries:

    g++ -Wall -g -shared -o libtest2-v0.so test2-v0.cc
    g++ -Wall -g -shared -o libtest2-v0.so test2-v0.cc

    Let's look at the output of abidiff:

    $ abidiff libtest2-v0.so libtest2-v1.so
    Functions changes summary: 0 Removed, 3 Changed, 0 Added functions
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    3 functions with some indirect sub-type change:
      [C]'function unsigned int func(S3)' has some indirect sub-type changes:
        parameter 0 of type 'struct S3' has sub-type changes:
          size changed from 32 to 64 bits
          1 base class insertion:
            struct base_type
          1 data member change:
           'int S3::m0' offset changed from 0 to 32
      [C]'function char func(S2*)' has some indirect sub-type changes:
        parameter 0 of type 'S2*' has sub-type changes:
          in pointed to type 'struct S2':
            size changed from 32 to 64 bits
            1 base class insertion:
              struct base_type
            1 data member change:
             'int S2::m0' offset changed from 0 to 32
      [C]'function int func(S1&)' has some indirect sub-type changes:
        parameter 0 of type 'S1&' has sub-type changes:
          in referenced type 'struct S1':
            size changed from 32 to 64 bits
            1 base class insertion:
              struct base_type
            1 data member change:
             'int S1::m0' offset changed from 0 to 32
    $

    Let's tell abidiff to avoid showing us the differences on the overloads of func that takes either a pointer or a reference. For that, we author this simple suppression specification:

    $ cat -n libtest2.suppr
         1 [suppress_function]
         2   name = func
         3   parameter = '0 S1&
         4
         5 [suppress_function]
         6   name = func
         7   parameter = '0 S2*
    $

    And then let's invoke abidiff with the suppression specification:

    $ ../build/tools/abidiff --suppressions libtest2.suppr libtest2-v0.so libtest2-v1.so
    Functions changes summary: 0 Removed, 1 Changed (2 filtered out), 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    1 function with some indirect sub-type change:
           [C]'function unsigned int func(S3)' has some indirect sub-type changes:
             parameter 0 of type 'struct S3' has sub-type changes:
               size changed from 32 to 64 bits
               1 base class insertion:
                 struct base_type
               1 data member change:
                'int S3::m0' offset changed from 0 to 32

    The suppression specification could be reduced using regular expressions:

    $ cat -n libtest2-1.suppr
              1   [suppress_function]
              2     name = func
              3     parameter = '0 /^S.(&|\\*)/
    $
    $ ../build/tools/abidiff --suppressions libtest2-1.suppr libtest2-v0.so libtest2-v1.so
    Functions changes summary: 0 Removed, 1 Changed (2 filtered out), 0 Added function
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    1 function with some indirect sub-type change:
           [C]'function unsigned int func(S3)' has some indirect sub-type changes:
             parameter 0 of type 'struct S3' has sub-type changes:
               size changed from 32 to 64 bits
               1 base class insertion:
                 struct base_type
               1 data member change:
                'int S3::m0' offset changed from 0 to 32
    $

AUTHOR
Dodji Seketeli

COPYRIGHT
2014-2022, Red Hat, Inc.