Re: [RFC PATCH] linux-user: trap internal SIGABRT's

[Richard Henderson <richard.henderson@linaro.org>]

On 2/9/22 22:22, Alex Bennée wrote:
> linux-user wants to trap all signals in case they are related to the
> guest. This however results in less than helpful core dumps when the
> error is internal to QEMU. We can detect when an assert failure is in
> progress by examining __glib_assert_msg and fall through to
> cpu_abort() which will pretty print something before restoring the
> default SIGABRT behaviour and dumping core.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>   linux-user/signal.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/linux-user/signal.c b/linux-user/signal.c
> index 32854bb375..8ecc1215f7 100644
> --- a/linux-user/signal.c
> +++ b/linux-user/signal.c
> @@ -809,6 +809,8 @@ static inline void rewind_if_in_safe_syscall(void *puc)
>       }
>   }
>   
> +GLIB_VAR char *__glib_assert_msg;
> +
>   static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
>   {
>       CPUArchState *env = thread_cpu->env_ptr;
> @@ -821,6 +823,10 @@ static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
>       uintptr_t pc = 0;
>       bool sync_sig = false;
>   
> +    if (__glib_assert_msg) {
> +        cpu_abort(cpu, "internal QEMU error, aborting...");
> +    }

I think we should not be trapping SIGABRT.  I think we can preserve all guest behaviour 
wrt SIGABRT by stealing another SIGRTMIN value, and remapping the guest signal number.  We 
can produce the correct result for the system by mapping it back to host SIGABRT in 
core_dump_and_abort().


r~