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 <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Tested-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/coroutine-ucontext.c b/coroutine-ucontext.c
index a9c30e9..bd20e38 100644
--- a/coroutine-ucontext.c
+++ b/coroutine-ucontext.c
@@ -46,7 +46,7 @@
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 @@
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 @@
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 @@
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 @@
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;
}
