[Qemu-devel] [PATCH] Fix qemu endless loop when raising a SIGSEGV/SIGBUS signal with gdbstub in user emulation

[Qemu-devel] [PATCH] Fix qemu endless loop when raising a SIGSEGV/SIGBUS signal with gdbstub in user emulation

[Lionel Landwerlin]

Let's compile a very simple program :

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

int
main (int argc, char *argv[])
{
        int *i = NULL;

        sleep (1);

        *i = 42;

        return EXIT_SUCCESS;
}

Now run this program under qemu with gdbstub :

qemu -g 1234 ./test-segfault

Run gdb on the same program, connect it to qemu and start execution.
This program will raise a SIGSEGV signal and qemu will be locked in an
endless loop. Gdb will never be notify by qemu of SIGSEGV signal.

The following post provides a fix for that.

Regards,


-- 
Lione Landwerlin                                         

O p e n W i d e                    14, rue Gaillon 75002 Paris

Re: [Qemu-devel] [PATCH] Fix qemu endless loop when raising a SIGSEGV/SIGBUS signal with gdbstub in user emulation

[Lionel Landwerlin]

When a SIGSEGV signal is raised in user mode emulation the current
test to know whether the signal is sent by the kernel is wrong :

info->si_code == SI_KERNEL

according to /usr/include/bits/siginfo.h it should be

info->si_code > 0

/* Values for `si_code'.  Positive values are reserved for kernel-generated
   signals.  */

there is a lot of enums for that, all starting at positives values :

/* `si_code' values for SIGILL signal.  */
enum
{
  ILL_ILLOPC = 1,               /* Illegal opcode.  */
...

/* `si_code' values for SIGFPE signal.  */
enum
{
  FPE_INTDIV = 1,               /* Integer divide by zero.  */
...

/* `si_code' values for SIGSEGV signal.  */
enum
{
  SEGV_MAPERR = 1,              /* Address not mapped to object.  */
....

Signed-off-by: Lionel Landwerlin <lionel.landwerlin@openwide.fr>
---
 linux-user/signal.c |   4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/linux-user/signal.c b/linux-user/signal.c
index 5e30522..0d81106 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -441,9 +441,9 @@ static void host_signal_handler(int host_signum, siginfo_t *info,
     target_siginfo_t tinfo;
 
     /* the CPU emulator uses some host signals to detect exceptions,
-       we we forward to it some signals */
+       we forward to it some signals */
     if ((host_signum == SIGSEGV || host_signum == SIGBUS)
-        && info->si_code == SI_KERNEL) {
+        && info->si_code > 0) {
         if (cpu_signal_handler(host_signum, info, puc))
             return;
     }
 
-- 
1.5.6.5


-- 
Lione Landwerlin                                         

O p e n W i d e                    14, rue Gaillon 75002 Paris

Re: [Qemu-devel] [PATCH] Fix qemu endless loop when raising a SIGSEGV/SIGBUS signal with gdbstub in user emulation

[Aurelien Jarno]

On Sat, Jan 03, 2009 at 01:50:39PM +0100, Lionel Landwerlin wrote:
> When a SIGSEGV signal is raised in user mode emulation the current
> test to know whether the signal is sent by the kernel is wrong :
> 
> info->si_code == SI_KERNEL
> 
> according to /usr/include/bits/siginfo.h it should be
> 
> info->si_code > 0
> 

We were working on the same thing at the same time, but you has been
faster :) Patch applied, thanks.

-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   aurel32@debian.org         | aurelien@aurel32.net
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