Ubuntu Manpage: abidw - serialize the ABI of an ELF file

NAME

abidw - serialize the ABI of an ELF file

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

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

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

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

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

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

INVOCATION

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

OPTIONS

• --help | -h

Display a short help about the command and exit.

• –version | -v

Display the version of the program and exit.

• –abixml-version

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

• --debug-info-dir | -d <dir-path>

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

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

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

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

• --out-file <file-path>

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

• --noout

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

• --no-corpus-path

Do not emit the path attribute for the ABI corpus.

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

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

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

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

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

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

• --linux-tree | --lt

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

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

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

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

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

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

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

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

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

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

• --drop-private-types

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

• --no-elf-needed

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

• --drop-undefined-syms

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

• --exported-interfaces-only

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

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

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

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

• --allow-non-exported-interfaces

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

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

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

• --no-linux-kernel-mode

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

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

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

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

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

• --no-parameter-names

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

• --no-write-default-sizes

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

• --type-id-style <sequence``|``hash>

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

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

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

• --load-all-types

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

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

This is a debugging and sanity check option.

• --debug-abidiff

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

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

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

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

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

• --no-assume-odr-for-cplusplus

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

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

• --no-leverage-dwarf-factorization

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

This option disables those optimizations.

• --ctf

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

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

• --stats

Emit statistics about various internal things.

• --verbose

Emit verbose logs about the progress of miscellaneous internal things.

NOTES

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

AUTHOR

       Dodji Seketeli

COPYRIGHT

       2014-2023, Red Hat, Inc.

                                           Feb 05, 2023                                  ABIDW(1)