:Authors:

• A. Wilcox, initial concept, maintainer, lead developer
• Adélie Linux and its contributors, development :Status: Production :Copyright: © 2022 Adélie Linux and its contributors. NCSA open source license.

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This distribution contains the implementation of gcompat, a library which provides glibc-compatible APIs for use on musl libc systems.

This library is designed to be used for binaries that are already compiled against glibc. It does not contain any headers, and cannot be used to build software that requires glibc. It is instead recommended that any software that requires glibc APIs be modified to become more portable.

This library can optionally be compiled with other libraries to make a single, unfied solution. This can include fts_, libucontext_, obstack_, and others.

gcompat additionally provides a loader stub. This is a small library that has the same name as the glibc dynamic linker on glibc platforms; when a binary is run that uses glibc as its dynamic linker, the stub will run, redirecting it to use musl and automatically preloading the gcompat library.

.. _fts: https://github.com/pullmoll/musl-fts/ .. _libucontext: https://github.com/kaniini/libucontext/ .. _obstack: https://github.com/pullmoll/musl-obstack/

License

This library is provided under the NCSA open source license.


Changes

Any changes to this repository must be reviewed before being pushed to the current branch. There are no exceptions to this rule. For security-sensitive updates, contact the Security Team at sec-bugs@adelielinux.org.

Many applications distributed for Linux are built against glibc. Unfortunately, many of glibc's internals are leaked out in to the resultant binary which makes it difficult or impossible to run these binaries on systems using the musl libc_.

While the goal of Adélie Linux is to support only true Libre Software that can be built from source code, we recognise that some users may require the ability to run pre-compiled binaries on their computers. This may include older software that does not compile with modern compilers, or non-libre software such as firmware or device management software.

.. _musl libc: http://www.musl-libc.org/

The following architectures are supported:

• x86 (32-bit)

  This is a Tier 1 architecture in the Adélie Linux system, as pmmx.

• x86_64

  This is a Tier 1 architecture in the Adélie Linux system.

• armv6+ (as arm)

  This is a Tier 2 architecture in the Adélie Linux system, as armv6 and armv7. As such, it may not receive thorough testing.

• aarch64

  This is a Tier 1 architecture in the Adélie Linux system.

• ppc (32-bit)

  This is a Tier 1 architecture in the Adélie Linux system.

• ppc64

  This is a Tier 1 architecture in the Adélie Linux system. Only the ELFv2 ABI is supported, and only Big Endian modes of operation are tested by the release team. Most glibc installations use ELFv1; only Void Linux currently utilises ELFv2 and glibc. For that reason, it is difficult to test gcompat on ppc64.

In order to build correctly, the gcompat build system requires a few details about the host environment, regarding both the musl host and glibc target. To provide this information to the build system, you will need to set the following variables or pass them to make.

• LINKER_PATH

  The location of the musl ELF interpreter. On PowerPC, this is /lib/ld-musl-powerpc64.so.1.

• LOADER_NAME

  The location of the glibc ELF interpreter. On PowerPC, this is ld.so.2.

You may additionally specify any of the following optional variables for further customisation:

• DESTDIR

  The directory in which to install files. The default value is /.

• LIBGCOMPAT_PATH

  The location in which to install libgcompat.so, relative to DESTDIR. The default value is /lib/libgcompat.so.0.

• LOADER_PATH

  The location in which to install the glibc interpreter stub. The default value is /lib/$LOADER_NAME.

• WITH_LIBUCONTEXT

  Determines whether to build with libucontext_.

For example, on an x86_64 musl host and x86_64 glibc target, you may run:

$ make LINKER_PATH=/lib/ld-musl-x86_64.so.1 LOADER_NAME=ld-linux-x86-64.so.2

$ make LINKER_PATH=/lib/ld-musl-x86_64.so.1 LOADER_NAME=ld-linux-x86-64.so.2 install

Please note that the gcompat build system does not attempt to guess the correct values for you; specifying at least LINKER_PATH and LOADER_NAME are required.

Running binaries linked against glibc

If the values specified during build were correct, programs built for glibc
should run normally on your musl host.  If they are not working, check the
program's ELF interpreter entry, using scanelf(8) like so:

::

  $ scanelf -i ~/glibcfile
   TYPE   INTERP FILE
  ET_EXEC /lib64/ld-linux-x86-64.so.2 /home/kaniini/glibcfile

If the interpreter path is different than expected, use PatchELF or install a
symlink from ``LOADER_PATH`` to the specified interpreter.


Using glibc binaries via dlopen(3) from a musl program

There are two ways to accomplish this:

• You can add libgcompat.so to the DT_NEEDED entries in the ELF that you want to have the gcompat symbols available in. Use a tool such as PatchELF for this.

• Alternatively, you can link the musl binary against libgcompat.

Environment variables

* ``GLIBC_FAKE_VERSION``

  The value of ``GLIBC_FAKE_VERSION`` will be returned as the result of
  ``gnu_get_libc_version``.  The current default is "2.8".

* ``GLIBC_FAKE_DEBUG``

  Setting this variable will cause dlmopen and dlvsym to display the overrides
  they are performing, and may cause additional output to stderr with other
  functions in the future.




Reporting Issues
================

gcompat is released by the Adélie Linux project in the hopes that it is useful
to the community.  Current issues may be found at our BTS_; you may also
`submit an issue`_ there.

For general discussion, questions, or to submit a patch, please use the gcompat
mailing list, hosted on `WTI Lists`_.

.. _BTS: https://git.adelielinux.org/adelie/gcompat/-/issues
.. _`submit an issue`: https://git.adelielinux.org/adelie/gcompat/-/issues/new
.. _`WTI Lists`: https://lists.wilcox-tech.com/