NAME

abidiff - compare ABIs of ELF files
 
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}


$





AUTHOR

Dodji Seketeli 2014-2023, Red Hat, Inc.