[Qemu-devel] User emulation & gdb & sigsegv

[Qemu-devel] User emulation & gdb & sigsegv

[Lionel Landwerlin]

Hello,

Currently, when using gdb connected to qemu, if a sigsegv is raised,
Qemu just exits.

How should I modify Qemu to redirect this last signal to the connected
gdb and print a stack trace at least ?

I tried to call gdb_handlesig(gdbstub.c) from
force_sig(linux-user/signal.c) but Qemu just crashes.

Any idea is welcome :)

Regards,

-- 
Lione Landwerlin                                         

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

Re: [Qemu-devel] User emulation & gdb & sigsegv

[Edgar E. Iglesias]

On Thu, Dec 11, 2008 at 12:06:53AM +0100, Lionel Landwerlin wrote:
> Hello,
> 
> Currently, when using gdb connected to qemu, if a sigsegv is raised,
> Qemu just exits.
> 
> How should I modify Qemu to redirect this last signal to the connected
> gdb and print a stack trace at least ?
> 
> I tried to call gdb_handlesig(gdbstub.c) from
> force_sig(linux-user/signal.c) but Qemu just crashes.
> 
> Any idea is welcome :)

Hello,

I've got this in my git, IIRC it helped me out in those situations.

Cheers

commit 1efa40a743e16dbe2803a8d16902bf89850e80a3
Author: Edgar E. Iglesias <edgar.iglesias@axis.com>
Date:   Mon Sep 29 14:14:24 2008 +0200

    Pass default handler signals to gdb aswell.

diff --git a/linux-user/signal.c b/linux-user/signal.c
index 9640923..b7d22a1 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -365,6 +365,7 @@ int queue_signal(CPUState *env, int sig, target_siginfo_t *info)
         if (sig != TARGET_SIGCHLD &&
             sig != TARGET_SIGURG &&
             sig != TARGET_SIGWINCH) {
+	    sig = gdb_handlesig(env, sig);
             force_sig(sig);
         } else {
             return 0; /* indicate ignored */

Re: [Qemu-devel] User emulation & gdb & sigsegv

[Lionel Landwerlin]

Le jeudi 11 décembre 2008 à 00:18 +0100, Edgar E. Iglesias a écrit :
> On Thu, Dec 11, 2008 at 12:06:53AM +0100, Lionel Landwerlin wrote:
> > Hello,
> > 
> > Currently, when using gdb connected to qemu, if a sigsegv is raised,
> > Qemu just exits.
> > 
> > How should I modify Qemu to redirect this last signal to the connected
> > gdb and print a stack trace at least ?
> > 
> > I tried to call gdb_handlesig(gdbstub.c) from
> > force_sig(linux-user/signal.c) but Qemu just crashes.
> > 
> > Any idea is welcome :)
> 
> Hello,
> 
> I've got this in my git, IIRC it helped me out in those situations.
> 
> Cheers
> 
> commit 1efa40a743e16dbe2803a8d16902bf89850e80a3
> Author: Edgar E. Iglesias <edgar.iglesias@axis.com>
> Date:   Mon Sep 29 14:14:24 2008 +0200
> 
>     Pass default handler signals to gdb aswell.
> 
> diff --git a/linux-user/signal.c b/linux-user/signal.c
> index 9640923..b7d22a1 100644
> --- a/linux-user/signal.c
> +++ b/linux-user/signal.c
> @@ -365,6 +365,7 @@ int queue_signal(CPUState *env, int sig, target_siginfo_t *info)
>          if (sig != TARGET_SIGCHLD &&
>              sig != TARGET_SIGURG &&
>              sig != TARGET_SIGWINCH) {
> +	    sig = gdb_handlesig(env, sig);
>              force_sig(sig);
>          } else {
>              return 0; /* indicate ignored */
> 
> 

In fact this patch just make qemu crash too.
Have you tested this patch on the current svn  ?
What cpu did you use to test it ?

Regards,



-- 
Lione Landwerlin                                         

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

Re: [Qemu-devel] User emulation & gdb & sigsegv

[Edgar E. Iglesias]

On Thu, Dec 11, 2008 at 10:42:10PM +0100, Lionel Landwerlin wrote:
> Le jeudi 11 décembre 2008 à 00:18 +0100, Edgar E. Iglesias a écrit :
> > On Thu, Dec 11, 2008 at 12:06:53AM +0100, Lionel Landwerlin wrote:
> > > Hello,
> > > 
> > > Currently, when using gdb connected to qemu, if a sigsegv is raised,
> > > Qemu just exits.
> > > 
> > > How should I modify Qemu to redirect this last signal to the connected
> > > gdb and print a stack trace at least ?
> > > 
> > > I tried to call gdb_handlesig(gdbstub.c) from
> > > force_sig(linux-user/signal.c) but Qemu just crashes.
> > > 
> > > Any idea is welcome :)
> > 
> > Hello,
> > 
> > I've got this in my git, IIRC it helped me out in those situations.
> > 
> > Cheers
> > 
> > commit 1efa40a743e16dbe2803a8d16902bf89850e80a3
> > Author: Edgar E. Iglesias <edgar.iglesias@axis.com>
> > Date:   Mon Sep 29 14:14:24 2008 +0200
> > 
> >     Pass default handler signals to gdb aswell.
> > 
> > diff --git a/linux-user/signal.c b/linux-user/signal.c
> > index 9640923..b7d22a1 100644
> > --- a/linux-user/signal.c
> > +++ b/linux-user/signal.c
> > @@ -365,6 +365,7 @@ int queue_signal(CPUState *env, int sig, target_siginfo_t *info)
> >          if (sig != TARGET_SIGCHLD &&
> >              sig != TARGET_SIGURG &&
> >              sig != TARGET_SIGWINCH) {
> > +	    sig = gdb_handlesig(env, sig);
> >              force_sig(sig);
> >          } else {
> >              return 0; /* indicate ignored */
> > 
> > 
> 
> In fact this patch just make qemu crash too.
> Have you tested this patch on the current svn  ?

Nope, it's on my git with other patches, don't know if there are
dependencies. Feel free to have a look at
git://repo.or.cz/qemu/cris-port.git if you're interested. No
guarantees that it will help though :)

> What cpu did you use to test it ?

I run it on CRIS all the time.

Regards

Re: [Qemu-devel] User emulation & gdb & sigsegv

[Daniel Jacobowitz]

On Thu, Dec 11, 2008 at 12:06:53AM +0100, Lionel Landwerlin wrote:
> Hello,
> 
> Currently, when using gdb connected to qemu, if a sigsegv is raised,
> Qemu just exits.
> 
> How should I modify Qemu to redirect this last signal to the connected
> gdb and print a stack trace at least ?
> 
> I tried to call gdb_handlesig(gdbstub.c) from
> force_sig(linux-user/signal.c) but Qemu just crashes.

Hi Lionel - I didn't see this message until today (I read the list
only infrequently), but I posted a patch for this exact issue the next
day.  Let me know if it doesn't work for you, please.

-- 
Daniel Jacobowitz
CodeSourcery