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* block all signals (even internal ones) in cancellation signal handlerRich Felker2015-03-161-1/+2
| | | | | | | | | | | previously the implementation-internal signal used for multithreaded set*id operations was left unblocked during handling of the cancellation signal. however, on some archs, signal contexts are huge (up to 5k) and the possibility of nested signal handlers drastically increases the minimum stack requirement. since the cancellation signal handler will do its job and return in bounded time before possibly passing execution to application code, there is no need to allow other signals to interrupt it.
* add new masked cancellation modeRich Felker2015-02-211-9/+15
| | | | | | | | | | | | this is a new extension which is presently intended only for experimental and internal libc use. interface and behavior details may change subject to feedback and experience from using it internally. the basic concept for the new PTHREAD_CANCEL_MASKED state is that the first cancellation point to observe the cancellation request fails with an errno value of ECANCELED rather than acting on cancellation, allowing the caller to process the status and choose whether/how to act upon it.
* prepare cancellation syscall asm for possibility of __cancel returningRich Felker2015-02-201-0/+7
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* make pthread_exit responsible for disabling cancellationRich Felker2015-02-161-3/+0
| | | | | this requirement is tucked away in XSH 2.9.5 Thread Cancellation under the heading Thread Cancellation Cleanup Handlers.
* fix missing memory barrier in cancellation signal handlerRich Felker2015-02-031-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | in practice this was probably a non-issue, because the necessary barrier almost certainly exists in kernel space -- implementing signal delivery without such a barrier seems impossible -- but for the sake of correctness, it should be done here too. in principle, without a barrier, it is possible that the thread to be cancelled does not see the store of its cancellation flag performed by another thread. this affects both the case where the signal arrives before entering the critical program counter range from __cp_begin to __cp_end (in which case both the signal handler and the inline check fail to see the value which was already stored) and the case where the signal arrives during the critical range (in which case the signal handler should be responsible for cancellation, but when it does not see the cancellation flag, it assumes the signal is spurious and refuses to act on it). in the fix, the barrier is placed only in the signal handler, not in the inline check at the beginning of the critical program counter range. if the signal handler runs before the critical range is entered, it will of course take no action, but its barrier will ensure that the inline check subsequently sees the store. if on the other hand the inline check runs first, it may miss seeing the store, but the subsequent signal handler in the critical range will act upon the cancellation request. this strategy avoids adding a memory barrier in the common, non-cancellation code path.
* rework cancellation weak alias logic not to depend on archive orderRich Felker2014-07-061-0/+85
| | | | | | | | | | | if the order of object files in the static archive libc.a was not respected by the linker, the old logic could wrongly cause POSIX symbols outside of the ISO C namespace to be pulled into pure C programs. this should not happen with well-behaved linkers, but relying on the link order was a bad idea anyway. files are renamed to better reflect their contents now that they don't need names to control their order as members in the archive file.
* overhaul pthread cancellationRich Felker2011-04-171-7/+0
| | | | | | | | | | | | | | | | | | | | | | this patch improves the correctness, simplicity, and size of cancellation-related code. modulo any small errors, it should now be completely conformant, safe, and resource-leak free. the notion of entering and exiting cancellation-point context has been completely eliminated and replaced with alternative syscall assembly code for cancellable syscalls. the assembly is responsible for setting up execution context information (stack pointer and address of the syscall instruction) which the cancellation signal handler can use to determine whether the interrupted code was in a cancellable state. these changes eliminate race conditions in the previous generation of cancellation handling code (whereby a cancellation request received just prior to the syscall would not be processed, leaving the syscall to block, potentially indefinitely), and remedy an issue where non-cancellable syscalls made from signal handlers became cancellable if the signal handler interrupted a cancellation point. x86_64 asm is untested and may need a second try to get it right.
* use a_store to set cancel flag in pthread_cancel, to ensure a barrierRich Felker2011-04-011-1/+1
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* major improvements to cancellation handlingRich Felker2011-03-291-0/+1
| | | | | | | | | | | | | - there is no longer any risk of spoofing cancellation requests, since the cancel flag is set in pthread_cancel rather than in the signal handler. - cancellation signal is no longer unblocked when running the cancellation handlers. instead, pthread_create will cause any new threads created from a cancellation handler to unblock their own cancellation signal. - various tweaks in preparation for POSIX timer support.
* syscall overhaul part two - unify public and internal syscall interfaceRich Felker2011-03-191-2/+1
| | | | | | | | | | | | | | | | with this patch, the syscallN() functions are no longer needed; a variadic syscall() macro allows syscalls with anywhere from 0 to 6 arguments to be made with a single macro name. also, manually casting each non-integer argument with (long) is no longer necessary; the casts are hidden in the macros. some source files which depended on being able to define the old macro SYSCALL_RETURNS_ERRNO have been modified to directly use __syscall() instead of syscall(). references to SYSCALL_SIGSET_SIZE and SYSCALL_LL have also been changed. x86_64 has not been tested, and may need a follow-up commit to fix any minor bugs/oversights.
* initial check-in, version 0.5.0 v0.5.0Rich Felker2011-02-121-0/+7