diff options
Diffstat (limited to 'sysdeps/unix/sysv/linux/times.c')
| -rw-r--r-- | sysdeps/unix/sysv/linux/times.c | 29 |
1 files changed, 18 insertions, 11 deletions
diff --git a/sysdeps/unix/sysv/linux/times.c b/sysdeps/unix/sysv/linux/times.c index 8f3033bdea..e9c93428c4 100644 --- a/sysdeps/unix/sysv/linux/times.c +++ b/sysdeps/unix/sysv/linux/times.c @@ -1,4 +1,4 @@ -/* Copyright (C) 2008-2016 Free Software Foundation, Inc. +/* Copyright (C) 2008-2018 Free Software Foundation, Inc. This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or @@ -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; |