Re: [PATCH] RISC-V: Reliably initialize t0 in _times()

[Corinna Vinschen <vinschen@redhat.com>]

On Aug  2 18:46, Christoph Muellner wrote:
> From: Christoph Muellner <cmuellner@linux.com>
> 
> 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>
> ---
>  libgloss/riscv/sys_times.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)

Pushed.


Thanks,
Corinna