As part of the mono CLR virtual machine, we rely on the operation system
to deliver a signal when a NULL pointer is dereferenced, this avoids
adding checks in the generated native code for NULL pointers.
The program below will show a problem I found: it takes a long time to
get to the signal handler for the faulting instruction (note that
issuing the same signal with kill is fast).
Now, this should not happen normally, but still, waiting one second for
a signal handler is a lot, even if it's an error condition.
Anybody can reproduce it or suggest workarounds?
System version is 10.2.2.
Thanks!
#include <signal.h>
#include <stdio.h>
void segv (int signalid) {
printf ("SEGV %d\n", signalid);
fflush (stdout);
if (signalid == SIGSEGV)
return;
_exit (0);
}
int main () {
volatile int *p = NULL;
struct sigaction sa;
sa.sa_handler = segv;
sigemptyset (&sa.sa_mask);
sa.sa_flags = 0;
if (sigaction (SIGBUS, &sa, NULL) == -1)
perror ("sigaction");
if (sigaction (SIGSEGV, &sa, NULL) == -1)
perror ("sigaction");
// this is fast
kill (getpid(), SIGSEGV);
// this is sloow
*p = 10; //segv
return 0;
}
/*
kdump -R output below:
[...]
19567 a.out 0.001180 CALL sigaction(0xa,0xbffffb10,0)
19567 a.out 0.000104 RET sigaction 0
19567 a.out 0.000043 CALL sigaction(0xb,0xbffffb10,0)
19567 a.out 0.000031 RET sigaction 0
19567 a.out 0.000030 CALL getpid
19567 a.out 0.000029 RET getpid 19567/0x4c6f
19567 a.out 0.000029 CALL kill(0x4c6f,0xb)
19567 a.out 0.000042 RET kill 0
19567 a.out 0.000037 PSIG SIGSEGV caught handler=0x1b7c mask=0x0 code=0x0
^^^^^^^^
19567 a.out 0.000095 CALL fstat(0x1,0xbfffefe0)
19567 a.out 0.000048 RET fstat 0
19567 a.out 0.000069 CALL ioctl(0x1,TIOCGETA,0xbffff010)
19567 a.out 0.000051 RET ioctl 0
19567 a.out 0.000097 CALL write(0x1,0x84000,0x8)
19567 a.out 0.000075 GIO fd 1 wrote 8 bytes
"SEGV 11
"
19567 a.out 0.000059 RET write 8
19567 a.out 0.000033 CALL sigreturn(0xbffffa30)
19567 a.out 0.000037 RET sigreturn JUSTRETURN
19567 a.out 1.005463 PSIG SIGBUS caught handler=0x1b7c mask=0x0 code=0x0
^^^^^^^^
19567 a.out 0.000316 CALL write(0x1,0x84000,0x8)
19567 a.out 0.000138 GIO fd 1 wrote 8 bytes
"SEGV 10
"
19567 a.out 0.000069 RET write 8
19567 a.out 0.000034 CALL exit(0)
*/
lupus
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