moslab-code/src/l4/pkg/l4re-core/libgcc

Libgcc

This package contains the libgcc library from GCC together with make files for building them inside the L4Re tree.

We maintain one libgcc version per GCC major version, assuming that there are no breaking changes in libgcc within GCC minor versions, neither in terms of forward nor backward compatibility.

Package structure

The contrib directory contains unmodified libgcc, gcc and include directories from each supported major GCC version, but not in there entirety, only the subset of files required to compile libgcc.

The build directory contains the build infrastructure to build libgcc with L4Re's BID build system.

The generated directory contains files required for building libgcc that would be generated by Autoconf during a regular GCC build. Fortunately, their content is mostly stable across GCC versions.

The libgcc package is split into five packages:

libgcc

Main package, contains contrib code and build infrastructure. Provides static (libgcc.a) and shared (libgcc_s.so) variants of the libgcc.

libgcc-pure

Provides static variant of libgcc without L4 specific functionality (libgcc-pure.a).

Required when building l4sys, to break a circular dependency, because libgcc depends on l4sys for L4 specific implementations of certain functionality (currently limited to atomic operations on arm), but at the same time l4sys relies on functionality from the libgcc.

In addition, libgcc-pure is used by components such as bootstrap that do not run in an L4 environment.

libgcc-crt

Provides C runtime library object files (crt<...>.o), used by ldscripts package.

libgcc_eh

Provides exception handling and unwinding parts of libgcc as a static library (libgcc_eh.a). Not used when linking against shared libgcc as in that case the functionality in libgcc_eh is already included in the shared libgcc.

Depends on libpthread, but only for building, not for linking, because the libpthread symbols are weakly referenced. If the executable using this library does not link against libpthread, libgcc_eh detects that the program is not threaded, and works fine without functionality from libpthread.

libgcc_eh-pure

Provides exception handling and unwinding parts of libgcc as a static library without L4 specific functionality, in particular no libpthread, i.e. single-threaded, (libgcc_eh-pure.a).

Use libgcc from toolchain

Optionally, by enabling the Kconfig option COMPILER_RT_USE_TOOLCHAIN_LIBGCC, instead of building the libgcc for L4Re from source, the libgcc shipped with the compiler toolchain can be used. On PowerPC and SPARC this option is forcibly enabled, since it seemed unreasonable to invest the effort to maintain the libgcc source package for them.

Libgcc as shared library

Optionally, by enabling the Kconfig option COMPILER_RT_LIBGCC_SHARED it is possible to link against a shared variant of libgcc (libgcc_s.so). This feature is only available when libgcc is built from source, i.e. not when using the libgcc shipped with the toolchain.