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, 13 insertions, 13 deletions

diff --git a/coroutine-sigaltstack.c b/coroutine-sigaltstack.c
index e37ebac9c4..1fb41c9f14 100644
--- a/coroutine-sigaltstack.c
+++ b/coroutine-sigaltstack.c
@@ -45,7 +45,7 @@ static unsigned int pool_size;
 typedef struct {
     Coroutine base;
     void *stack;
-    jmp_buf env;
+    sigjmp_buf env;
 } CoroutineUContext;
 
 /**
@@ -59,7 +59,7 @@ typedef struct {
     CoroutineUContext leader;
 
     /** Information for the signal handler (trampoline) */
-    jmp_buf tr_reenter;
+    sigjmp_buf tr_reenter;
     volatile sig_atomic_t tr_called;
     void *tr_handler;
 } CoroutineThreadState;
@@ -115,8 +115,8 @@ static void __attribute__((constructor)) coroutine_init(void)
 static void coroutine_bootstrap(CoroutineUContext *self, Coroutine *co)
 {
     /* 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 +145,14 @@ static void coroutine_trampoline(int signal)
     /*
      * Here we have to do a bit of a ping pong between the caller, given that
      * this is a signal handler and we have to do a return "soon". Then the
-     * caller can reestablish everything and do a longjmp here again.
+     * caller can reestablish everything and do a siglongjmp here again.
      */
-    if (!setjmp(coTS->tr_reenter)) {
+    if (!sigsetjmp(coTS->tr_reenter, 0)) {
         return;
     }
 
     /*
-     * Ok, the caller has longjmp'ed back to us, so now prepare
+     * Ok, the caller has siglongjmp'ed back to us, so now prepare
      * us for the real machine state switching. We have to jump
      * into another function here to get a new stack context for
      * the auto variables (which have to be auto-variables
@@ -179,7 +179,7 @@ static Coroutine *coroutine_new(void)
 
     /* The way to manipulate stack is with the sigaltstack function. We
      * prepare a stack, with it delivering a signal to ourselves and then
-     * put setjmp/longjmp where needed.
+     * put sigsetjmp/siglongjmp where needed.
      * This has been done keeping coroutine-ucontext as a model and with the
      * pth ideas (GNU Portable Threads). See coroutine-ucontext for the basics
      * of the coroutines and see pth_mctx.c (from the pth project) for the
@@ -220,7 +220,7 @@ static Coroutine *coroutine_new(void)
 
     /*
      * Now transfer control onto the signal stack and set it up.
-     * It will return immediately via "return" after the setjmp()
+     * It will return immediately via "return" after the sigsetjmp()
      * was performed. Be careful here with race conditions.  The
      * signal can be delivered the first time sigsuspend() is
      * called.
@@ -261,8 +261,8 @@ static Coroutine *coroutine_new(void)
      * type-conversion warnings related to the `volatile' qualifier and
      * the fact that `jmp_buf' usually is an array type.
      */
-    if (!setjmp(old_env)) {
-        longjmp(coTS->tr_reenter, 1);
+    if (!sigsetjmp(old_env, 0)) {
+        siglongjmp(coTS->tr_reenter, 1);
     }
 
     /*
@@ -311,9 +311,9 @@ 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;
 }