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Subject: strace: infinite exception c0000005 loop on segmentation fault
To: cygwin AT cygwin DOT com
Message-ID: <320ee4eb-a06d-150d-ef12-3dc501bbd60b@t-online.de>
Date: Fri, 16 May 2025 13:46:21 +0200
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From: Christian Franke via Cygwin <cygwin AT cygwin DOT com>
Reply-To: cygwin AT cygwin DOT com
Cc: Christian Franke <Christian DOT Franke AT t-online DOT de>
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Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>
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Found during check why SIGSEGV handler could interrupt SIGALRM handler 
(which does not happen on Linux):
https://sourceware.org/pipermail/cygwin-patches/2025q2/013703.html

Testcase:

$ uname -r # Also occurs with 3.6.1-1.x86_64
3.7.0-0.95.g854150fda310.x86_64

$ cat sigsegv.c
int main()
{
   *(volatile char *)0 = 0;
   return 42; // NOTREACHED
}

$ gcc -o sigsegv sigsegv.c

$ ./sigsegv # OK
Segmentation fault

$ echo $?
139

$ (sleep 5; taskkill /f /im strace.exe) & strace ./sigsegv # Infinite loop
...
--- Process 11224 (pid: 2162), exception c0000005 at 0000000100401092
--- Process 11224 (pid: 2162), exception c0000005 at 0000000100401092
--- Process 11224 (pid: 2162), exception c0000005 at 0000000100401092
--- Process 11224 (pid: 2162), exception c0000005 at 0000000100401092
--- Process 11224 (pid: 2162), exception c0000005 at 0000000100401092
--- Process 11224 (pid: 2162), exception c0000005 at 0000000100401092
--- Process 11224 (pid: 2162), exception c0000005 at 0000000100401092
--- Process 11224 (pid: 2162), exception c0000005 at 0000000
SUCCESS: ... (localized message from taskkill)


The problem also occurs if a SIGSEGV handler is present. The handler 
code is not executed if strace is used but works as expected without strace.

-- 
Regards,
Christian


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