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From: Corinna Vinschen <corinna@sourceware.org> To: newlib-cvs@sourceware.org Subject: [newlib-cygwin] RISC-V: Reliably initialize t0 in _times() Date: Wed, 4 Aug 2021 09:44:46 +0000 (GMT) [thread overview] Message-ID: <20210804094446.267AE3853817@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=0cb40f415b7d4f11f819b03320770737fa072be8 commit 0cb40f415b7d4f11f819b03320770737fa072be8 Author: Christoph Muellner <cmuellner@linux.com> Date: Mon Aug 2 18:46:16 2021 +0200 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> Diff: --- libgloss/riscv/sys_times.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/libgloss/riscv/sys_times.c b/libgloss/riscv/sys_times.c index fc8133ade..a029bcfb5 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;
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