[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
git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@349090 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/runtime/src/z_Linux_util.cpp b/runtime/src/z_Linux_util.cpp
index c2f37eb..aa0302c 100644
--- a/runtime/src/z_Linux_util.cpp
+++ b/runtime/src/z_Linux_util.cpp
@@ -1935,20 +1935,27 @@
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
