Provided by: abigail-doc_1.2-1_all 
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 that includes changes about function and variable sub-types, the
two input shared libraries must be accompanied with their debug information in DWARF format. Otherwise,
only ELF symbols that were added or removed are reported.
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.
• --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.
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.
• --headers-dir1 | --hd1 <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 ABI changes on types that are not defined in public
headers.
• --headers-dir2 | --hd2 <headers-directory-path-1>
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.
• --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 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.
• --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.
• --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.
• --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.
• --leaf-changes-only|-l only show leaf changes, so don’t show impact analysis report.
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.
• --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 in DWARF format.
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.
• --leaf-changes-only|-l only show leaf changes, so don’t show impact analysis report.
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
$
• --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.
• --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.
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
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, users want to compare a subset of the those interfaces.
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 kmidiff compares the interfaces exported by the vmlinux binary and by the all of the compiled
modules.
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 .
• --full-impact | -f
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.
abidw
abidw reads a shared library in ELF format and emits an XML representation of its ABI to standard output.
The emitted representation 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. The input shared library must contain associated debug information in DWARF format.
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. The input binaries must contain associated debug information in DWARF
format.
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.
• --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.
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 first shared library that the tool has to
consider. The tool will thus filter out types that are not defined in public headers.
• --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.
• --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.
• --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.
• --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.
• --stdin | --
Read the input content from standard input.
• --tu
Expect the input XML to represent a single translation unit.
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 not) if its file name matches 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.
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.
• 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,
type_kind, source_location_not_in, source_location_not_regexp.
If none of the following 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
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. 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 mber inserted at an offset that
is comprised in the range between range-begin`` and range-end. Please note that each of the lues
range-begin and range-end can be of the same form as the has_data_member_inserted_at property above.
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.
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.
[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,
symbol_name, symbol_name_regexp, symbol_version,
symbol_version_regexp.
If none of the following 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_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,
symbol_name, symbol_name_regexp, symbol_version, symbol_version_regexp.
If none of the following properties are provided, then the [suppres_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_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
2014-2018, Red Hat, Inc.
Apr 24, 2018 LIBABIGAIL(7)