libucontext

libucontext is a library which provides the ucontext.h C API. Unlike other implementations, it faithfully follows the kernel process ABI when doing context swaps.

Notably, when combined with gcompat, it provides a fully compatible implementation of the ucontext functions that are ABI compatible with glibc.

Since version 0.13, for some architectures, you can deploy to bare metal using newlib via the FREESTANDING=yes make option. Systems which use a syscall cannot work this way. The table below shows which architecture ports have been adapted to build with FREESTANDING=yes.

supported architectures

Adding support for new architectures is easy, but you need to know assembly language to do it.

Architecture	Works on musl	Syscall	Supports FREESTANDING
aarch64	✓		✓
arm	✓		✓
m68k	✓		✓
mips	✓		✓
mips64	✓		✓
ppc	✓	✓
ppc64	✓	✓
riscv64	✓		✓
s390x	✓		✓
x86	✓		✓
x86_64	✓		✓

building

libucontext uses a simple makefile build system. You should define ARCH= at build time, otherwise the build system will attempt to guess using uname -m.

$ make ARCH=x86_64
$ make ARCH=x86_64 check
$ make ARCH=x86_64 DESTDIR=out install