On Thu, 29 May 2025 20:01:31 +0200 Christian Franke wrote: > Takashi Yano via Cygwin wrote: > > On Thu, 29 May 2025 17:32:19 +0200 > > Christian Franke wrote: > > ... > >> I still don't fully understand why a SIGSEGV triggered by an instruction > >> could interrupt a SIGALRM handler. > >> https://sourceware.org/pipermail/cygwin/2025-May/258145.html > >> > >> I guess such behavior is valid from the POSIX point of view, but it is > >> at least unexpected. If the SIGALRM handler is already running, it > >> should have interrupted the thread such that the instruction triggering > >> the segfault is not executed until the SIGALRM handler returns. > > I try to explain what is happing using the figure below. > > > > <<<<<< Main thread >>>>>> < Signal Thread > > > SIGNAL > > main() handler1() handler2() QUEUE wait_sig() > > | . . | | > > | . . ALRM | | > > +----------------------------------------->| ALRM | > > | . . SEGV +--------->| > > X----------------------------------------->| | > > | . arm ALRM | | > > +----------+ <----------------------------------------+ > > | . | SEGV | > > | . +--------->| > > | . | | > > | . arm SEGV | | > > +----------+ <-----------------------------+ > > . | | | > > longjmp() | | | > > +---------------------+ | | > > | . . | | > > | . . | | > > > > The point is the exception handler does not arm SIGSEGV handler > > directly. It just pushes the SIGSEGV into the signal queue. > > The signal thread reads the queue and process it asynchronously, > > and arms the handler(). > > > > I see. Thanks for nice explanation! > > I created an issue at stress-ng upstream because at least the --mprotect > test is affected: > https://github.com/ColinIanKing/stress-ng/issues/529
Thanks! BTW, do you think this is the right thing? https://github.com/RISCV-Tools/stress-ng/commit/bf24393357cde137bb8e7b38f917f565946199fd I think the patch should set SIGSEGV mask on SIGALRM. -- Takashi Yano <takashi.y...@nifty.ne.jp> -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
