On 23/10/2014 16:37, Corinna Vinschen wrote:
On Oct 23 08:04, Ken Brown wrote:
On 10/23/2014 7:31 AM, Jon TURNEY wrote:
On 20/10/2014 14:03, Ken Brown wrote:
Or is there some other plausible explanation for "impossible" crashes?
This can't just be a result of a gdb bug, because in at least one case
the assertion can be shown to be valid by using printf instead of gdb.
[*] By "impossible" I mean that examination of the relevant variables in
gdb shows that the assertions are in fact true. Two ongoing examples are
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=18438
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=18769
As a suggestion, you might want to also take a careful look at how signal
delivery is implemented in cygwin on x86_64
I had a vague idea that there was, at some time in the past, a fix made for
register corruption on x86_64 after a signal was handled, but I can't find it
now, so maybe I imagined it.
Is this what you're thinking of?
https://cygwin.com/ml/cygwin-cvs/2014-q1/msg00020.html
But if for e.g. the flags register was getting
corrupted when a signal interrupts the main thread, that could perhaps also
explain what is being seen.
Yes, flags register corruption is exactly what Eli suggested in the other
bug report I cited.
The aforementioned patch was supposed to fix this problem and it is
definitely in the current 1.7.32 release...
I didn't mean to suggest otherwise, just that perhaps a similar problem
exists now.
So I made the attached test case to explore that. Maybe I've made an
obvious mistake with it, but on the face of it, it seems to demonstrate
something...
jon@tambora /
$ gcc signal-stress.c -Wall -O0 -g
jon@tambora /
$ ./a
failed: 2144210386 isn't equal to 2144210386, apparently
Note there is some odd load dependency. For me, it works fine when it's
the only thing running, but when I start up something CPU intensive, it
often fails...
#include <assert.h>
#include <sys/time.h>
#include <signal.h>
#include <stdio.h>
long SmartScheduleInterval = 1; /* ms */
long SmartScheduleTime = 0;
static void
SmartScheduleTimer(int sig)
{
if (sig != 0)
SmartScheduleTime += SmartScheduleInterval;
}
void
SmartScheduleStartTimer(void)
{
struct itimerval timer;
timer.it_interval.tv_sec = 0;
timer.it_interval.tv_usec = SmartScheduleInterval * 1000;
timer.it_value.tv_sec = 0;
timer.it_value.tv_usec = SmartScheduleInterval * 1000;
setitimer(ITIMER_REAL, &timer, 0);
}
int main()
{
/* Set up the timer signal function */
struct sigaction act;
act.sa_handler = SmartScheduleTimer;
sigemptyset(&act.sa_mask);
sigaddset(&act.sa_mask, SIGALRM);
if (sigaction(SIGALRM, &act, 0) < 0) {
perror("sigaction failed");
return -1;
}
/* start timer */
SmartScheduleStartTimer();
/* Loop forever, doing tests which should always succeed, with lots of
signals */
int x = 0;
int i = 0;
while (1) {
x = i;
int j = x;
if (j != i)
{
printf("failed: %d isn't equal to %d, apparently\n", i, j);
break;
}
i++;
}
return 0;
}
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