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author | Christoph Muellner <cmuellner@linux.com> | 2021-08-02 18:46:16 +0200 |
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committer | Corinna Vinschen <corinna@vinschen.de> | 2021-08-04 11:44:33 +0200 |
commit | 0cb40f415b7d4f11f819b03320770737fa072be8 (patch) | |
tree | 841c7815e0a392bfb60aba1fdb581702e3dbf103 /libgloss/riscv | |
parent | 94ead7b76d18fbb11e446d35f1afb5c9485d9dca (diff) | |
download | newlib-0cb40f415b7d4f11f819b03320770737fa072be8.zip newlib-0cb40f415b7d4f11f819b03320770737fa072be8.tar.gz newlib-0cb40f415b7d4f11f819b03320770737fa072be8.tar.bz2 |
RISC-V: Reliably initialize t0 in _times()
The current implementation does not reliably initialize t0 once.
Additionally the initialization requires two calls to _gettimeofday().
Let's sacrifice a byte to keep the initialization status
and reduce the maximum number of calls to _gettimeofday().
This has caused issues in an application that invokes clock().
The problematic situation is as follows:
1) The program calls clock() which calls _times().
2) _gettimeofday(&t0, 0) puts 0 in t0.tv_usec (because less than 1 us has
elapsed since the beginning of time).
3) _gettimeofday(&t, 0) puts 1 in t.tv_usec (since now more than 1 us has
elapsed since the beginning of time).
4) That call to clock() returns 1 (the value from step 3 minus the value in
step 2).
5) The program does a second call to clock().
6) The code above still sees 0 in t0 so it tries to update t0 again and
_gettimeofday(&t0, 0) puts 1 in t0.tv_usec.
7) The _gettimeofday(&t, 0) puts 1 in t.tv_usec (since less than 1us has
elapsed since step 3).
8) clock() returns 0 (step 7 minus step 6) and indicates that time is
moving backwards.
Signed-off-by: Christoph Muellner <cmuellner@gcc.gnu.org>
Diffstat (limited to 'libgloss/riscv')
-rw-r--r-- | libgloss/riscv/sys_times.c | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/libgloss/riscv/sys_times.c b/libgloss/riscv/sys_times.c index fc8133a..a029bcf 100644 --- a/libgloss/riscv/sys_times.c +++ b/libgloss/riscv/sys_times.c @@ -21,14 +21,19 @@ extern int _gettimeofday(struct timeval *, void *); clock_t _times(struct tms *buf) { - // when called for the first time, initialize t0 + static char initialized; static struct timeval t0; - if (t0.tv_sec == 0 && t0.tv_usec == 0) - _gettimeofday (&t0, 0); - struct timeval t; + _gettimeofday (&t, 0); + // when called for the first time, initialize t0 + if (!initialized) { + t0.tv_sec = t.tv_sec; + t0.tv_usec = t.tv_usec; + initialized = 1; + } + long long utime = (t.tv_sec - t0.tv_sec) * 1000000 + (t.tv_usec - t0.tv_usec); buf->tms_utime = utime * CLOCKS_PER_SEC / 1000000; buf->tms_stime = buf->tms_cstime = buf->tms_cutime = 0; |