The attached testcase was originally intended to investigate why a
SIGSEGV from non-signal code could interrupt an already running signal
handler.
https://sourceware.org/pipermail/cygwin-patches/2025q2/013703.html
If run without strace, the testcase may crash silently (with exit status 0):
$ uname -r
3.7.0-0.98.gb39b510c1ce6.x86_64
$ gcc -o sigsegvalrm sigsegvalrm.c
$ while { ./sigsegvalrm; s=$?; echo exit $s; test $s = 42; }; do :; done
...
[SEGV during ALRM]
[SEGV]
[ALRM during SEGV]
[ALRM]
101 total, 24 ALRM during SEGV, 13 SEGV during ALRM
exit 42
...
[SEGV during ALRM]
[ALRM]
[SEGV]
[ALRM]
[SEGV]
[ALRM during SEGV]
[SEGV]
[ALRM]
[SEGV]
exit 0
If the above was run with 'strace ./sigsegvalrm', the result was an
infinte loop:
https://cygwin.com/pipermail/cygwin/2025-May/258144.html
Fortunately this is fixed since b39b510c. A new result:
...
[SEGV during ALRM]
205 556472 [main] sigsegvalrm 1342 fhandler_console::write: 19 =
fhandler_console::write(...)
91 556563 [main] sigsegvalrm 1342 write: 19 = write(1, 0x100403020, 19)
81 556644 [main] sigsegvalrm 1342 clock_nanosleep: clock_nanosleep
(0.001000000)
8396 565040 [itimer] sigsegvalrm 1342 timer_tracker::thread_func:
0x7FFE4CC69640 timer expired
230 565270 [main] sigsegvalrm 1342 clock_nanosleep: 0 =
clock_nanosleep(1, 0, 0.001000000, 0.d)
123 565393 [itimer] sigsegvalrm 1342 timer_tracker::thread_func:
0x7FFE4CC69640 sending signal 14
230 565623 [main] sigsegvalrm 1342 set_signal_mask: setmask 2400,
newmask 0, mask_bits 2400
147 565770 [main] sigsegvalrm 1342 pthread_sigmask: 0 =
pthread_sigmask(0, 0x100407128, 0x0)
220 565990 [itimer] sigsegvalrm 1342 sig_send: sendsig 0x158, pid
1342, signal 14, its_me 1
278 566268 [main] sigsegvalrm 1342 pthread_sigmask: 0 =
pthread_sigmask(0, 0x0, 0x100407128)
--- Process 148 (pid: 1342), exception c0000005 at 0000000100401287
1579 567847 [sig] sigsegvalrm 1342 sigpacket::process: signal 14
processing
189 568036 [sig] sigsegvalrm 1342 init_cygheap::find_tls: sig 14
235 568271 [sig] sigsegvalrm 1342 sigpacket::process: using tls
0x7FFFFCE00
195 568466 [main] sigsegvalrm 1342 exception::handle: In
cygwin_except_handler exception 0xC0000005 at 0x100401287 sp 0x7FFFFCBE0
131 568597 [sig] sigsegvalrm 1342 sigpacket::process: signal 14,
signal handler 0x100401080
82 568679 [main] sigsegvalrm 1342 exception::handle: In
cygwin_except_handler signal 11 at 0x100401287
79 568758 [sig] sigsegvalrm 1342 sigpacket::setup_handler:
suspending thread, tls 0x7FFFFCE00, _main_tls 0x7FFFFCE00
[~30s delay]
--- Process 148 (pid: 1342) thread 14964 created
--- Process 148 (pid: 1342) thread 14048 created
[~30s delay]
--- Process 148 (pid: 1342) thread 5184 exited with status 0x0
--- Process 148 (pid: 1342) thread 5056 exited with status 0x0
[several minutes delay]
--- Process 148 (pid: 1342) thread 9388 created
The process then ignores SIGKILL.
BTW, this testcase without a second signal now works as expected:
https://sourceware.org/pipermail/cygwin/2025-March/257726.html
--
Regards,
Christian
#include <setjmp.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
static volatile sig_atomic_t total, nest1, nest2;
static volatile sig_atomic_t insig1, insig2;
static sigjmp_buf sjb;
static const int delay = 1000;
static void sighandler1(int sig)
{
(void)sig;
insig1 = 1;
total++;
if (insig2) {
write(1, "[ALRM during SEGV]\n", 19);
nest1++;
}
else
write(1, "[ALRM]\n", 7);
insig1 = 0;
}
static void sighandler2(int sig)
{
(void)sig;
insig2 = 1;
total++;
if (insig1) {
insig1 = 0;
write(1, "[SEGV during ALRM]\n", 19);
nest2++;
}
else
write(1, "[SEGV]\n", 7);
usleep(delay);
insig2 = 0;
siglongjmp(sjb, 1);
write(1, "[FAIL]\n", 7);
}
int main()
{
signal(SIGALRM, sighandler1);
signal(SIGSEGV, sighandler2);
ualarm(delay, delay);
while (sigsetjmp(sjb, 1))
;
// loop:
if (total < 100)
*(volatile char *)0 = 0; // goto loop;
ualarm(0, 0);
printf("%d total, %d ALRM during SEGV, %d SEGV during ALRM\n",
total, nest1, nest2);
return 42;
}
--
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