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Replace all setjmp()/longjmp() with sigsetjmp()/siglongjmp()

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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>
This commit is contained in:
Peter Maydell 2013-02-20 15:21:09 +00:00 • committed by Blue Swirl
parent d1c36ba707
commit 6ab7e5465a
9 changed files with 52 additions and 42 deletions
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6
cpu-exec.c
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@ -35,7 +35,7 @@ void cpu_loop_exit(CPUArchState *env)
CPUState *cpu = ENV_GET_CPU(env);
cpu->current_tb = NULL;
longjmp(env->jmp_env, 1);
siglongjmp(env->jmp_env, 1);
}
/* exit the current TB from a signal handler. The host registers are
@ -47,7 +47,7 @@ void cpu_resume_from_signal(CPUArchState *env, void *puc)
/* XXX: restore cpu registers saved in host registers */
env->exception_index = -1;
longjmp(env->jmp_env, 1);
siglongjmp(env->jmp_env, 1);
}
#endif
@ -234,7 +234,7 @@ int cpu_exec(CPUArchState *env)
/* prepare setjmp context for exception handling */
for(;;) {
if (setjmp(env->jmp_env) == 0) {
if (sigsetjmp(env->jmp_env, 0) == 0) {
/* if an exception is pending, we execute it here */
if (env->exception_index >= 0) {
if (env->exception_index >= EXCP_INTERRUPT) {