path: root/src/time/clock.c
diff options
authorRich Felker <>2013-05-23 14:31:02 -0400
committerRich Felker <>2013-05-23 14:31:02 -0400
commit05453b37fc0343e53bc7f332047e901b3e1abb84 (patch)
tree46aec81077cc8062cb3a63e7a6504d9498bb1d25 /src/time/clock.c
parent1e5eb73545ca6cfe8b918798835aaf6e07af5beb (diff)
fix overflow behavior of clock() function
per Austin Group interpretation for issue #686, which cites the requirements of ISO C, clock() cannot wrap. if the result is not representable, it must return (clock_t)-1. in addition, the old code was performing wrapping via signed overflow and thus invoking undefined behavior. since it seems impossible to accurately check for overflow with the old times()-based fallback code, I have simply dropped the fallback code for now, thus always returning -1 on ancient systems. if there's a demand for making it work and somebody comes up with a way, it could be reinstated, but the clock() function is essentially useless on 32-bit system anyway (it overflows in less than an hour). it should be noted that I used LONG_MAX rather than ULONG_MAX, despite 32-bit archs using an unsigned type for clock_t. this discrepency with the glibc/LSB type definitions will be fixed now; since wrapping of clock_t is no longer supported, there's no use in it being unsigned.
Diffstat (limited to 'src/time/clock.c')
1 files changed, 10 insertions, 7 deletions
diff --git a/src/time/clock.c b/src/time/clock.c
index 78403af3..c348e398 100644
--- a/src/time/clock.c
+++ b/src/time/clock.c
@@ -1,15 +1,18 @@
#include <time.h>
-#include <sys/times.h>
-#include "syscall.h"
+#include <limits.h>
int __clock_gettime(clockid_t, struct timespec *);
clock_t clock()
struct timespec ts;
- struct tms tms;
- if (!__clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts))
- return ts.tv_sec*1000000 + ts.tv_nsec/1000;
- __syscall(SYS_times, &tms);
- return (tms.tms_utime + tms.tms_stime)*10000;
+ if (__clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts))
+ return -1;
+ if (ts.tv_sec > LONG_MAX/1000000
+ || ts.tv_nsec/1000 > LONG_MAX-1000000*ts.tv_sec)
+ return -1;
+ return ts.tv_sec*1000000 + ts.tv_nsec/1000;