abidw

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

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

To generate either ABI or KMI representation, by default abidw uses debug information in the DWARF format, if present, otherwise it looks for debug information in CTF or BTF formats, if present. Finally, if no debug info in these formats is found, it only considers ELF symbols and report about their addition or removal.

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.

  • --add-binaries <bin1,bin2,…>

    For each of the comma-separated binaries given in argument to this option, if the binary is found in the directory specified by the –added-binaries-dir option, then load the ABI corpus of the binary and add it to a set of ABI corpora (called a ABI Corpus Group) made of the binary denoted by the Argument of abidw. That corpus group is then serialized out.

  • --follow-dependencies

    For each dependency of the input binary of abidw, if it is found in the directory specified by the --added-binaries-dir option, then construct an ABI corpus out of the dependency and add it to a set of ABI corpora (called an ABI Corpus Group) along with the ABI corpus of the input binary of the program. The ABI Corpus Group is then serialized out.

  • --list-dependencies

    For each dependency of the input binary of``abidw``, if it’s found in the directory specified by the --added-binaries-dir option, then the name of the dependency is printed out.

  • --added-binaries-dir | --abd <dir-path>

    This option is to be used in conjunction with the --add-binaries, the --follow-dependencies or the --list-dependencies option. Binaries listed as arguments of the --add-binaries option or being dependencies of the input binary in the case of the --follow-dependencies option and found in the directory <dir-path> are going to be loaded as ABI corpus and added to the set of ABI corpora (called an ABI corpus group) built and serialized.

  • --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 | -o <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 | --kmi-stablelist |-w <path-to-stablelist>

    When analyzing a Linux Kernel binary, this option points to the list of names of ELF symbols of functions and variables which ABI must be written out. Any function or variable with a name that is not included in that list will not ignored. That list is called a “ Kernel Module Interface stable 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 KABI.

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

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

  • --linux-tree | --lt

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

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

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

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

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

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

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

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

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

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

  • --drop-private-types

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

  • --no-elf-needed

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

  • --drop-undefined-syms

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

  • --exported-interfaces-only

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

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

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

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

  • --allow-non-exported-interfaces

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

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

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

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

  • --no-linux-kernel-mode

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

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

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

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

  • --no-show-locs

In the emitted ABI representation, do not show file, line or column where ABI artifacts are defined.

  • --no-parameter-names

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

  • --no-write-default-sizes

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

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

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

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

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

  • --load-all-types

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

    • --no-load-undefined-interfaces

    By default, libabigail (and thus abidw) loads information about undefined function and variable symbols as well as functions and variables that are associated with those undefined symbols. Those are called undefined interfaces. This option however makes makes abidw avoid loading information about undefined interfaces. The resulting XML file thus doesn’t contain information about those undefined interfaces.

  • --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.

Usage examples

  1. Emitting an ABIXML representation of a binary:

    $ abidw binary > binary.abi

  2. Emitting an ABIXML representation of a set of binaries specified on the command line:

    $ abidw --added-binaries=bin1,bin2,bin3  \
        --added-binaries-dir /some/where \
        binary > binaries.abi

    Note that the binaries bin1, bin2 and bin3 are to be found in the directory /some/where. A representation of the ABI of the set of binaries binary, bin1, bin2 and bin3 called an ABI corpus group is serialized in the file binaries.abi.

  3. Emitting an ABIXML representation of a binary and its dependencies:

    $ abidw --follow-dependencies              \
        --added-binaries-dir /some/where   \
        binary > binary.abi

    Note that only the dependencies that are found in the directory /some/where are analysed. Their ABIs, along with the ABI the binary named binary are represented as an ABI corpus group and serialized in the file binary.abi, in the ABIXML format.

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.