Re: [PATCH 4/8] user: Introduce host_interrupt_signal

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

On 10/24/24 20:59, Ilya Leoshkevich wrote:
> Attaching to the gdbstub of a running process requires stopping its
> threads. For threads that run on a CPU, cpu_exit() is enough, but the
> only way to grab attention of a thread that is stuck in a long-running
> syscall is to interrupt it with a signal.
> 
> Reserve a host realtime signal for this, just like it's already done
> for TARGET_SIGABRT on Linux. This may reduce the number of available
> guest realtime signals by one, but this is acceptable, since there are
> quite a lot of them, and it's unlikely that there are apps that need
> them all.
> 
> Set signal_pending for the safe_sycall machinery to prevent invoking
> the syscall. This is a lie, since we don't queue a guest signal, but
> process_pending_signals() can handle the absence of pending signals.
> The syscall returns with QEMU_ERESTARTSYS errno, which arranges for
> the automatic restart. This is important, because it helps avoiding
> disturbing poorly written guests.
> 
> Signed-off-by: Ilya Leoshkevich<iii@linux.ibm.com>
> ---
>   bsd-user/signal.c     | 12 ++++++++++++
>   include/user/signal.h |  2 ++
>   linux-user/signal.c   | 11 +++++++++++
>   3 files changed, 25 insertions(+)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~