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[OpenMP] Fix transient divide by zero bug in 32-bit code 

The value returned by __kmp_now_nsec() can overflow 32-bit values causing
incorrect values to be returned. The overflow can end up causing a divide
by zero error because in __kmp_initialize_system_tick(), the value
(__kmp_now_nsec() - nsec) can end up being much larger than the numerator:
1e6 * (delay + (now - goal))
during a pathological timing where the current time calculated is much larger
than nsec. When this happens, the value of __kmp_ticks_per_msec is set to zero
which is then used as the denominator in the KMP_NOW_MSEC() macro leading to
the divide by zero error.

Differential Revision: https://reviews.llvm.org/D55300

llvm-svn: 349090
This commit is contained in:
Jonathan Peyton 2018-12-13 23:18:55 +00:00
parent 6d88e049dc
commit bdb0a2ffaa
1 changed files with 11 additions and 4 deletions
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15
openmp/runtime/src/z_Linux_util.cpp
View File

@ -1935,20 +1935,27 @@ void __kmp_elapsed_tick(double *t) { *t = 1 / (double)CLOCKS_PER_SEC; }
kmp_uint64 __kmp_now_nsec() {
struct timeval t;
gettimeofday(&t, NULL);
return KMP_NSEC_PER_SEC * t.tv_sec + 1000 * t.tv_usec;
kmp_uint64 nsec = (kmp_uint64)KMP_NSEC_PER_SEC * (kmp_uint64)t.tv_sec +
(kmp_uint64)1000 * (kmp_uint64)t.tv_usec;
return nsec;
}
#if KMP_ARCH_X86 || KMP_ARCH_X86_64
/* Measure clock ticks per millisecond */
void __kmp_initialize_system_tick() {
kmp_uint64 now, nsec2, diff;
kmp_uint64 delay = 100000; // 50~100 usec on most machines.
kmp_uint64 nsec = __kmp_now_nsec();
kmp_uint64 goal = __kmp_hardware_timestamp() + delay;
kmp_uint64 now;
while ((now = __kmp_hardware_timestamp()) < goal)
;
__kmp_ticks_per_msec =
(kmp_uint64)(1e6 * (delay + (now - goal)) / (__kmp_now_nsec() - nsec));
nsec2 = __kmp_now_nsec();
diff = nsec2 - nsec;
if (diff > 0) {
kmp_uint64 tpms = (kmp_uint64)(1e6 * (delay + (now - goal)) / diff);
if (tpms > 0)
__kmp_ticks_per_msec = tpms;
}
}
#endif