xref: /third_party/libabigail/doc/manuals/abidw.rst (revision e01aa904)

======
abidw
======

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

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

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

.. include:: tools-use-libabigail.txt

.. _abidiff_invocation_label:

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


  * ``--kmi-whitelist | -kaw`` <*path-to-whitelist*>

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

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

    If this option is not provided -- thus if no white list is
    provided -- then the entire KMI, that is, all publicly defined and
    exported functions and global variables by the `Linux Kernel`_
    binaries is emitted.
    
  * ``--linux-tree | --lt``

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

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

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

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

  * ``--headers-dir | --hd`` <headers-directory-path-1>

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

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

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

  * ``--header-file | --hf`` <header-file-path>

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

  * ``--drop-private-types``

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

  * ``--no-elf-needed``

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

  * ``--drop-undefined-syms``

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

  * ``--exported-interfaces-only``

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

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

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

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

  * ``--allow-non-exported-interfaces``

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

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

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

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

  * ``--no-linux-kernel-mode``

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

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

  * ``--check-alternate-debug-info`` <*elf-path*>

    If the debug info for the file *elf-path* contains a reference to
    an `alternate debug info <alt-di-label>`_ 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
=====

.. _alt-di-label:

Alternate debug info files
--------------------------

As of the version 4 of the DWARF specification, `Alternate debug
information <http://www.dwarfstd.org/ShowIssue.php?issue=120604.1>`_
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
<https://fedorahosted.org/elfutils/wiki/DwarfExtensions>`_.

.. _ELF: http://en.wikipedia.org/wiki/Executable_and_Linkable_Format
.. _DWARF: http://www.dwarfstd.org
.. _GNU: http://www.gnu.org
.. _Linux Kernel: https://kernel.org/
.. _CTF: https://raw.githubusercontent.com/wiki/oracle/binutils-gdb/files/ctf-spec.pdf
.. _ODR: https://en.wikipedia.org/wiki/One_Definition_Rule
.. _One Definition Rule: https://en.wikipedia.org/wiki/One_Definition_Rule
.. _DWZ: https://sourceware.org/dwz