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>

1 files changed, 3 insertions, 3 deletions

diff --git a/monitor.c b/monitor.c
index 6a0f2573f5..32a6e74fd9 100644
--- a/monitor.c
+++ b/monitor.c
@@ -2740,7 +2740,7 @@ static const mon_cmd_t qmp_cmds[] = {
 /*******************************************************************/
 
 static const char *pch;
-static jmp_buf expr_env;
+static sigjmp_buf expr_env;
 
 #define MD_TLONG 0
 #define MD_I32   1
@@ -3135,7 +3135,7 @@ static const MonitorDef monitor_defs[] = {
 static void expr_error(Monitor *mon, const char *msg)
 {
     monitor_printf(mon, "%s\n", msg);
-    longjmp(expr_env, 1);
+    siglongjmp(expr_env, 1);
 }
 
 /* return 0 if OK, -1 if not found */
@@ -3345,7 +3345,7 @@ static int64_t expr_sum(Monitor *mon)
 static int get_expr(Monitor *mon, int64_t *pval, const char **pp)
 {
     pch = *pp;
-    if (setjmp(expr_env)) {
+    if (sigsetjmp(expr_env, 0)) {
         *pp = pch;
         return -1;
     }