From 6ab7e5465a4d6188e29398fb43a30dbab1015b75 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Wed, 20 Feb 2013 15:21:09 +0000 Subject: Replace all setjmp()/longjmp() with sigsetjmp()/siglongjmp() The setjmp() function doesn't specify whether signal masks are saved and restored; on Linux they are not, but on BSD (including MacOSX) they are. We want to have consistent behaviour across platforms, so we should always use "don't save/restore signal mask" (this is also generally going to be faster). This also works around a bug in MacOSX where the signal-restoration on longjmp() affects the signal mask for a completely different thread, not just the mask for the thread which did the longjmp. The most visible effect of this was that ctrl-C was ignored on MacOSX because the CPU thread did a longjmp which resulted in its signal mask being applied to every thread, so that all threads had SIGINT and SIGTERM blocked. The POSIX-sanctioned portable way to do a jump without affecting signal masks is to siglongjmp() to a sigjmp_buf which was created by calling sigsetjmp() with a zero savemask parameter, so change all uses of setjmp()/longjmp() accordingly. [Technically POSIX allows sigsetjmp(buf, 0) to save the signal mask; however the following siglongjmp() must not restore the signal mask, so the pair can be effectively considered as "sigjmp/longjmp which don't touch the mask".] For Windows we provide a trivial sigsetjmp/siglongjmp in terms of setjmp/longjmp -- this is OK because no user will ever pass a non-zero savemask. The setjmp() uses in tests/tcg/test-i386.c and tests/tcg/linux-test.c are left untouched because these are self-contained singlethreaded test programs intended to be run under QEMU's Linux emulation, so they have neither the portability nor the multithreading issues to deal with. Signed-off-by: Peter Maydell Reviewed-by: Richard Henderson Tested-by: Stefan Weil Reviewed-by: Laszlo Ersek Signed-off-by: Blue Swirl --- coroutine-ucontext.c | 27 ++++++++++++++------------- 1 file changed, 14 insertions(+), 13 deletions(-) (limited to 'coroutine-ucontext.c') diff --git a/coroutine-ucontext.c b/coroutine-ucontext.c index a9c30e9df4..bd20e384b7 100644 --- a/coroutine-ucontext.c +++ b/coroutine-ucontext.c @@ -46,7 +46,7 @@ static unsigned int pool_size; typedef struct { Coroutine base; void *stack; - jmp_buf env; + sigjmp_buf env; #ifdef CONFIG_VALGRIND_H unsigned int valgrind_stack_id; @@ -130,8 +130,8 @@ static void coroutine_trampoline(int i0, int i1) co = &self->base; /* Initialize longjmp environment and switch back the caller */ - if (!setjmp(self->env)) { - longjmp(*(jmp_buf *)co->entry_arg, 1); + if (!sigsetjmp(self->env, 0)) { + siglongjmp(*(sigjmp_buf *)co->entry_arg, 1); } while (true) { @@ -145,14 +145,15 @@ static Coroutine *coroutine_new(void) const size_t stack_size = 1 << 20; CoroutineUContext *co; ucontext_t old_uc, uc; - jmp_buf old_env; + sigjmp_buf old_env; union cc_arg arg = {0}; - /* The ucontext functions preserve signal masks which incurs a system call - * overhead. setjmp()/longjmp() does not preserve signal masks but only - * works on the current stack. Since we need a way to create and switch to - * a new stack, use the ucontext functions for that but setjmp()/longjmp() - * for everything else. + /* The ucontext functions preserve signal masks which incurs a + * system call overhead. sigsetjmp(buf, 0)/siglongjmp() does not + * preserve signal masks but only works on the current stack. + * Since we need a way to create and switch to a new stack, use + * the ucontext functions for that but sigsetjmp()/siglongjmp() for + * everything else. */ if (getcontext(&uc) == -1) { @@ -178,8 +179,8 @@ static Coroutine *coroutine_new(void) makecontext(&uc, (void (*)(void))coroutine_trampoline, 2, arg.i[0], arg.i[1]); - /* swapcontext() in, longjmp() back out */ - if (!setjmp(old_env)) { + /* swapcontext() in, siglongjmp() back out */ + if (!sigsetjmp(old_env, 0)) { swapcontext(&old_uc, &uc); } return &co->base; @@ -242,9 +243,9 @@ CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_, s->current = to_; - ret = setjmp(from->env); + ret = sigsetjmp(from->env, 0); if (ret == 0) { - longjmp(to->env, action); + siglongjmp(to->env, action); } return ret; } -- cgit v1.2.1