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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>
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@ -21,14 +21,19 @@ extern int _gettimeofday(struct timeval *, void *);
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clock_t
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_times(struct tms *buf)
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{
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// when called for the first time, initialize t0
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static char initialized;
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static struct timeval t0;
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if (t0.tv_sec == 0 && t0.tv_usec == 0)
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_gettimeofday (&t0, 0);
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struct timeval t;
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_gettimeofday (&t, 0);
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// when called for the first time, initialize t0
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if (!initialized) {
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t0.tv_sec = t.tv_sec;
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t0.tv_usec = t.tv_usec;
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initialized = 1;
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}
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long long utime = (t.tv_sec - t0.tv_sec) * 1000000 + (t.tv_usec - t0.tv_usec);
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buf->tms_utime = utime * CLOCKS_PER_SEC / 1000000;
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buf->tms_stime = buf->tms_cstime = buf->tms_cutime = 0;
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