musl/arch/x86_64/pthread_arch.h

static inline struct pthread *__pthread_self()
{
	struct pthread *self;
	__asm__ __volatile__ ("movq %%fs:0,%0" : "=r" (self) );
	return self;
}

#define CANCEL_REG_SP 15
#define CANCEL_REG_IP 16
Port musl to x86-64. One giant commit! 2011-02-15 12:32:09 +00:00			`static inline struct pthread *__pthread_self()`
			`{`
			`struct pthread *self;`
ensure the compiler does not move around thread-register-based reads if gcc decided to move this across a conditional that checks validity of the thread register, an invalid thread-register-based read could be performed and raise sigsegv. 2011-08-07 00:45:30 +00:00			`__asm__ __volatile__ ("movq %%fs:0,%0" : "=r" (self) );`
Port musl to x86-64. One giant commit! 2011-02-15 12:32:09 +00:00			`return self;`
			`}`
overhaul cancellation to fix resource leaks and dangerous behavior with signals this commit addresses two issues: 1. a race condition, whereby a cancellation request occurring after a syscall returned from kernelspace but before the subsequent CANCELPT_END would cause cancellable resource-allocating syscalls (like open) to leak resources. 2. signal handlers invoked while the thread was blocked at a cancellation point behaved as if asynchronous cancellation mode wer in effect, resulting in potentially dangerous state corruption if a cancellation request occurs. the glibc/nptl implementation of threads shares both of these issues. with this commit, both are fixed. however, cancellation points encountered in a signal handler will not be acted upon if the signal was received while the thread was already at a cancellation point. they will of course be acted upon after the signal handler returns, so in real-world usage where signal handlers quickly return, it should not be a problem. it's possible to solve this problem too by having sigaction() wrap all signal handlers with a function that uses a pthread_cleanup handler to catch cancellation, patch up the saved context, and return into the cancellable function that will catch and act upon the cancellation. however that would be a lot of complexity for minimal if any benefit... 2011-03-24 18:18:00 +00:00
overhaul pthread cancellation 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. 2011-04-17 15:43:03 +00:00			`#define CANCEL_REG_SP 15`
			`#define CANCEL_REG_IP 16`