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>

cpu-exec.c

diff --git a/cpu-exec.c b/cpu-exec.c
index 9fcfe9e..afbe497 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -35,7 +35,7 @@
     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 @@
     /* 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 @@
 
     /* 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) {