Re: [Qemu-devel] [PATCH] vl.c: Implement SIGILL signal handler for triggering SIGSEGV

[Anthony Liguori]

On Thu, Sep 5, 2013 at 7:20 AM, Michal Novotny <address@hidden> wrote:
> This is the patch to introduce SIGILL handler to be able to trigger
> SIGSEGV signal in qemu. This has been written to help debugging
> state when qemu crashes by SIGSEGV as a simple reproducer to
> emulate such situation in case of need.
>
> Signed-off-by: Michal Novotny <address@hidden>
> ---
>  vl.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/vl.c b/vl.c
> index 7e04641..3966271 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2897,6 +2897,26 @@ static int object_create(QemuOpts *opts, void *opaque)
>      return 0;
>  }
>
> +#ifdef CONFIG_POSIX
> +static void signal_handler(int signal)
> +{
> +    int *p = NULL;
> +
> +    *p = 0xDEADBEEF;

I won't repeat the questions from Paolo and Lazlo (I share their
confusion) but will simply add that you cannot rely on NULL address
accessing causing a SEGV.  Even with all the use of volatile in the
world, there's no guarantee this is going to crash.

Regards,

Anthony Liguori

> +}
> +
> +static void setup_signal_handlers(void)
> +{
> +    struct sigaction action;
> +
> +    memset(&action, 0, sizeof(action));
> +    sigfillset(&action.sa_mask);
> +    action.sa_handler = signal_handler;
> +    action.sa_flags = 0;
> +    sigaction(SIGILL, &action, NULL);
> +}
> +#endif
> +
>  int main(int argc, char **argv, char **envp)
>  {
>      int i;
> @@ -2945,6 +2965,10 @@ int main(int argc, char **argv, char **envp)
>  #endif
>      }
>
> +#ifdef CONFIG_POSIX
> +    setup_signal_handlers();
> +#endif
> +
>      module_call_init(MODULE_INIT_QOM);
>
>      qemu_add_opts(&qemu_drive_opts);
> --
> 1.7.11.7
>