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musl - an implementation of the standard library for Linux-based systems
a5aff1972c
taking the deprecated/dropped vfork spec strictly, doing pretty much anything but execve in the child is wrong and undefined. however, these are commonly needed operations to setup the child state before exec, and historical implementations tolerated them. for single-threaded parents, these operations already worked as expected in the vforked child. however, due to the need for __synccall to synchronize id/resource limit changes among all threads, calling these functions in the vforked child of a multithreaded parent caused a misdirected broadcast signaling of all threads in the parent. these signals could kill the parent entirely if the synccall signal handler had never been installed in the parent, or could be ignored if it had, or could signal/kill one or more utterly wrong processes if the parent already terminated (due to vfork semantics, only possible via fatal signal) and the parent tids were recycled. in any case, the expected number of semaphore posts would never happen, so the child would permanently hang (with all signals blocked) waiting for them. to mitigate this, and also make the normal usage case work as intended, treat the condition where the caller's actual tid does not match the tid in its thread structure as single-threaded, and bypass the entire synccall broadcast operation. |
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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/