[Qemu-devel] [PATCH] linux-user: Proper exit code for uncaught signals

[Riku Voipio <riku.voipio@iki.fi>]

The proper exit code for dieing from an uncaught signal is -<signal>.
The kernel doesn't allow exit() or _exit() to pass a negative value.
To get the proper exit code we need to actually die from an uncaught
signal.

A default signal handler is installed, we send ourself a signal
and we wait for it to arrive.

Patch originates from Scratchbox

Signed-off-by: Riku Voipio <riku.voipio@iki.fi>
---
 linux-user/signal.c |   37 +++++++++++++++++++++++++------------
 1 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/linux-user/signal.c b/linux-user/signal.c
index e0f6aaf..dac9933 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -24,6 +24,7 @@
 #include <unistd.h>
 #include <signal.h>
 #include <errno.h>
+#include <assert.h>
 #include <sys/ucontext.h>
 
 #include "qemu.h"
@@ -328,21 +329,33 @@ static inline void free_sigqueue(CPUState *env, struct sigqueue *q)
 static void __attribute((noreturn)) force_sig(int sig)
 {
     int host_sig;
+    struct sigaction act;
     host_sig = target_to_host_signal(sig);
     fprintf(stderr, "qemu: uncaught target signal %d (%s) - exiting\n",
             sig, strsignal(host_sig));
-#if 1
-    _exit(-host_sig);
-#else
-    {
-        struct sigaction act;
-        sigemptyset(&act.sa_mask);
-        act.sa_flags = SA_SIGINFO;
-        act.sa_sigaction = SIG_DFL;
-        sigaction(SIGABRT, &act, NULL);
-        abort();
-    }
-#endif
+
+    /* The proper exit code for dieing from an uncaught signal is
+     * -<signal>.  The kernel doesn't allow exit() or _exit() to pass
+     * a negative value.  To get the proper exit code we need to
+     * actually die from an uncaught signal.  Here the default signal
+     * handler is installed, we send ourself a signal and we wait for
+     * it to arrive. */
+    sigfillset(&act.sa_mask);
+    act.sa_handler = SIG_DFL;
+    sigaction(host_sig, &act, NULL);
+
+    /* For some reason raise(host_sig) doesn't send the signal when
+     * statically linked on x86-64. */
+    kill(getpid(), host_sig);
+
+    /* Make sure the signal isn't masked (just reuse the mask inside
+    of act) */
+    sigdelset(&act.sa_mask, host_sig);
+    sigsuspend(&act.sa_mask);
+
+    /* unreachable */
+    assert(0);
+
 }
 
 /* queue a signal so that it will be send to the virtual CPU as soon
-- 
1.5.6.5


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