@@ -29,11 +29,13 @@ __times (struct tms *buf)
&& __builtin_expect (INTERNAL_SYSCALL_ERRNO (ret, err) == EFAULT, 0)
&& buf)
{
- /* This might be an error or not. For architectures which have
- no separate return value and error indicators we cannot
- distinguish a return value of -1 from an error. Do it the
- hard way. We crash applications which pass in an invalid
- non-NULL BUF pointer. Linux allows BUF to be NULL. */
+ /* This might be an error or not. For architectures which have no
+ separate return value and error indicators we cannot
+ distinguish a return value of e.g. (clock_t) -14 from -EFAULT.
+ Therefore the only course of action is to dereference the user
+ -supplied structure on a return of (clock_t) -14. This will crash
+ applications which pass in an invalid non-NULL BUF pointer.
+ Note that Linux allows BUF to be NULL in which case we skip this. */
#define touch(v) \
do { \
clock_t temp = v; \
@@ -45,13 +47,18 @@ __times (struct tms *buf)
touch (buf->tms_cutime);
touch (buf->tms_cstime);
- /* If we come here the memory is valid (or BUF is NULL, which is
- a valid condition for the kernel syscall) and the kernel did not
- return an EFAULT error. Return the value given by the kernel. */
+ /* If we come here the memory is valid and the kernel did not
+ return an EFAULT error, but rather e.g. (clock_t) -14.
+ Return the value given by the kernel. */
}
- /* Return value (clock_t) -1 signals an error, but if there wasn't any,
- return the following value. */
+ /* On Linux this function never fails except with EFAULT.
+ POSIX says that returning a value (clock_t) -1 indicates an error,
+ but on Linux this is simply one of the valid clock values after
+ clock_t wraps. Therefore when we would return (clock_t) -1, we
+ instead return (clock_t) 0, and loose a tick of accuracy (having
+ returned 0 for two consecutive calls even though the clock
+ advanced). */
if (ret == (clock_t) -1)
return (clock_t) 0;
---