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From: Richard Henderson <rth@twiddle.net>
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Date: Wed, 27 Feb 2019 16:17:47 -0800
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Subject: Re: [Qemu-devel] [PATCH RFC 2/2] tests/tcg: target/s390: Add test
 for VECTOR LOAD GR FROM VR ELEMENT
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To: David Hildenbrand <david@redhat.com>, qemu-devel@nongnu.org
Cc: qemu-s390x@nongnu.org, Thomas Huth <thuth@redhat.com>, Cornelia Huck <cohuck@redhat.com>, =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>, =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= <f4bug@amsat.org>

On 2/27/19 11:37 AM, David Hildenbrand wrote:
> #define CHECK_SIGILL(STATEMENT)                  \
> do {                                             \
>     if (signal(SIGILL, sig_sigill) == SIG_ERR) { \
>         check("SIGILL not registered", false);   \
>     }                                            \
>     if (setjmp(jmp_env) == 0) {                  \
>         STATEMENT;                               \
>         check("SIGILL not triggered", false);    \
>     }                                            \
>     if (signal(SIGILL, SIG_DFL) == SIG_ERR) {    \
>         check("SIGILL not registered", false);   \
>     }                                            \
> } while (0)
> 
> 
> However it only works once. During the second signal, QEMU decides to
> set the default handler.
> 
> 1. In a signal handler that signal is blocked. We leave that handler via
> a longjump. So after the first signal, the signal is blocked.

And this is why we use sigaction not signal.

You can set action.sa_flags |= SA_RESETHAND to avoid needing the explicit reset
(or leave it clear to avoid the reset action that you are seeing).

You can set action.sa_flags |= SA_NODEFER to avoid having the signal added to
the signal mask of the thread, to avoid neeing to use sigsetjmp/siglongjmp.  Or
you can just use sigsetjmp/siglongjmp.  ;-)


r~