Rich Felker
a01ff71f7c
this is a workaround to avoid a crashing regression on qemu-user when dynamic TLS is installed at dlopen time. the sigaction syscall should not be able to fail, but it does fail for implementation-internal signals under qemu user-level emulation if the host libc qemu is running under reserves the same signals for implementation-internal use, since qemu makes no provision to redirect/emulate them. after sigaction fails, the subsequent tkill would terminate the process abnormally as the default action. no provision to account for membarrier failing is made in the dynamic linker code that installs new TLS. at the formal level, the missing barrier in this case is incorrect, and perhaps we should fail the dlopen operation, but in practice all the archs we support (and probably all real-world archs except alpha, which isn't yet supported) should give the right behavior with no barrier at all as a consequence of consume-order properties. in the long term, this workaround should be supplemented or replaced by something better -- a different fallback approach to ensuring memory consistency, or dynamic allocation of implementation-internal signals. the latter is appealing in that it would allow cancellation to work under qemu-user too, and would even allow many levels of nested emulation.
musl libc
musl, pronounced like the word "mussel", is an MIT-licensed
implementation of the standard C library targetting the Linux syscall
API, suitable for use in a wide range of deployment environments. musl
offers efficient static and dynamic linking support, lightweight code
and low runtime overhead, strong fail-safe guarantees under correct
usage, and correctness in the sense of standards conformance and
safety. musl is built on the principle that these goals are best
achieved through simple code that is easy to understand and maintain.
The 1.1 release series for musl features coverage for all interfaces
defined in ISO C99 and POSIX 2008 base, along with a number of
non-standardized interfaces for compatibility with Linux, BSD, and
glibc functionality.
For basic installation instructions, see the included INSTALL file.
Information on full musl-targeted compiler toolchains, system
bootstrapping, and Linux distributions built on musl can be found on
the project website:
http://www.musl-libc.org/