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

[Thiemo Seufer <ths@networkno.de>]

Riku Voipio wrote:
> 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

So, who holds the copyright (and deserves the credit)?


Thiemo

> 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
> 
> 
> -- 
> "rm -rf" only sounds scary if you don't have backups
>