Found because 'stress-ng --priv-instr ...' hangs and then requires
'/bin/kill --force ...':
Testcase with
[PATCH v2] Cygwin: signal: Copy context to alternate stack in the
SA_ONSTACK case
already applied:
$ uname -r
3.7.0-dev-16-g2ef1a37e7823-dirty.x86_64
$ cat loopsigill.c
#include <setjmp.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
static volatile sig_atomic_t sigcnt;
static sigjmp_buf sjb;
static void sighandler(int sig)
{
(void)sig;
++sigcnt;
siglongjmp(sjb, 1);
write(1, "[FAIL]\n", 7);
}
int main()
{
signal(SIGILL, sighandler);
printf("pid=%d\n", (int)getpid());
while (sigsetjmp(sjb, 1))
;
// loop:
if (sigcnt < 10 || !(sigcnt % 1000))
printf("%06d\n", sigcnt);
if (sigcnt >= 100000)
return 42;
asm volatile ("invd"); // goto loop;
return 13; // NOT REACHED
}
$ gcc -o loopsigill loopsigill.c
$ ./loopsigill # may succeed ...
pid=122
000000
000001
...
099000
100000
$ echo $?
42
$ ./loopsigill # ... or crash silently ...
pid=130
000000
000001
...
026000
027000
$ echo $?
0
$ ./loopsigill # ... or hang
pid=135
000000
000001
...
037000
038000
[requires '/bin/kill --force ...']
$ strace -o trace.log ./loopsigill # run '/bin/kill --force ...' ASAP!
pid=142
000000
[always hangs after first signal and fills trace.log quickly]
$ less trace.log
...
25 25501 [main] loopsigill 142 write: 7 = write(1, 0xA00017710, 7)
--- Process 6856 (pid: 142), exception c0000096 at 00000001004011b9
142 25643 [main] loopsigill 142 exception::handle: In
cygwin_except_handler exception 0xC0000096 at 0x1004011B9 sp 0x7FFFFCBE0
26 25669 [main] loopsigill 142 exception::handle: In
cygwin_except_handler signal 4 at 0x1004011B9
38 25707 [main] loopsigill 142 break_here: break here
--- Process 6856 (pid: 142), exception c0000096 at 00000001004011b9
--- Process 6856 (pid: 142), exception c0000096 at 00000001004011b9
... likely repeated until disk is full or time_t wraps around...
--- Process 6856 (pid: 142), exception c0000096 at 00000001004011b9
Problem also occurs
- without the mentioned patch,
- with get/setcontext() instead of sig*jmp(),
- with nullptr access and SIGSEGV handler,
- with Cygwin 3.5.7-1.
I agree that this is not a common use case :-)
--
Regards,
Christian
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