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musl - an implementation of the standard library for Linux-based systems
fa4a8abd06
the clone() function has been effectively unusable since it was added, due to producing a child process with inconsistent state. in particular, the child process's thread structure still contains the tid, thread list pointers, thread count, and robust list for the parent. this will cause malfunction in interfaces that attempt to use the tid or thread list, some of which are specified to be async-signal-safe. this patch attempts to make clone() consistent in a _Fork-like sense. as in _Fork, when the parent process is multi-threaded, the child process inherits an async-signal context where it cannot call AS-unsafe functions, but its context is now intended to be safe for calling AS-safe functions. making clone fork-like would also be a future option, if it turns out that this is what makes sense to applications, but it's not done at this time because the changes would be more invasive. in the case where the CLONE_VM flag is used, clone is only vfork-like, not _Fork-like. in particular, the child will see itself as having the parent's tid, and cannot safely call any libc functions but one of the exec family or _exit. handling of flags and variadic arguments is also changed so that arguments are only consumed with flags that indicate their presence, and so that flags which produce an inconsistent state are disallowed (reported as EINVAL). in particular, all libc functions carry a contract that they are only callable with ABI requirements met, which includes having a valid thread pointer to a thread structure that's unique within the process, and whose contents are opaque and only able to be setup internally by the implementation. the only way for an application to use flags that violate these requirements without executing any libc code is to perform the syscall from application-provided asm. |
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| .gitignore | ||
| .mailmap | ||
| configure | ||
| COPYRIGHT | ||
| dynamic.list | ||
| INSTALL | ||
| Makefile | ||
| README | ||
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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/