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SubjectBUG (non-kernel), can hurt developers.

Note to hackers. Even though this is a lib-c bug, be
aware that many versions of the 'C' runtime library
have a rand() function that can (read will) segfault
in threads or signals.

glibc-2.1.3
libc.so.6

Are two culprits. This "little" problem just took me
a week to find. Rand() was used as a source of test
data in a system diagnostic. The diagnostic kept blowing
up. The following code tests for the problem.

//-----------------
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/time.h>
static int spare;
static int inside;
void handler(int unused)
{
struct itimerval it;
inside++;
spare = rand();
it.it_interval.tv_sec = 0L;
it.it_interval.tv_usec = 0L;
it.it_value.tv_sec = 0L;
it.it_value.tv_usec = 1L;
(void)signal(SIGALRM, handler);
setitimer(ITIMER_REAL, &it, &it);
inside--;
}
void bad(int sig)
{
char *where;
if(inside)
where = "inside";
else
where = "outside";
fprintf(stderr, "Failed %s handler on %d\n", where, spare);
exit(EXIT_FAILURE);
}
int main(void);
int main()
{
(void)signal(SIGSEGV, bad);
handler(0);
for(;;)
(void)rand();
return 0;
}
//---------------------

Run this for a few minutes.

Script started on Wed Nov 26 11:50:23 2003
$ gcc -Wall -o xxx -O2 xxx.c
$ ./xxx
Failed inside handler on 1735818301
$ ./xxx
Failed inside handler on 129960814
$ ./xxx
Failed inside handler on 1999426653
$ exit
exit
Script done on Wed Nov 26 11:50:52 2003


Cheers,
Dick Johnson
Penguin : Linux version 2.4.22 on an i686 machine (797.90 BogoMips).
Note 96.31% of all statistics are fiction.


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