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Re: [PATCH 10/12] Warn when gettimeofday is called with non-null tzp argument.
On 20/08/2019 10:21, Zack Weinberg wrote:
> At this stage I don’t think we can issue warnings for settimeofday
> with a non-null tzp argument, nor for arbitrary use of struct
> timezone. But we can warn about gettimeofday with non-null tzp.
>
> This uses a macro instead of an inline (fortify-style) function
> because I got false positives with an inline, even with GCC 9.
Would be troublesome to add a check for the new warning? Also is the
false positive a GCC defect or something limited with the inline
usage?
>
> * time/sys/time.h (__timezone_ptr_t): Delete.
> (gettimeofday): Always declare second argument with type ‘void *’.
> When possible, wrap with a macro that detects non-null and
> non-constant second argument and issues a warning.
> Improve commentary.
> (settimeofday): Improve commentary.
>
> * time/gettimeofday.c (gettimeofday):
> Declare second argument as type ‘void *’.
> ---
> time/gettimeofday.c | 4 ++--
> time/sys/time.h | 36 +++++++++++++++++++++++++-----------
> 2 files changed, 27 insertions(+), 13 deletions(-)
>
> diff --git a/time/gettimeofday.c b/time/gettimeofday.c
> index 22a996a220..bd1fc3cb5e 100644
> --- a/time/gettimeofday.c
> +++ b/time/gettimeofday.c
> @@ -23,10 +23,10 @@
> If *TZ is not NULL, clear it.
> Returns 0 on success, -1 on errors. */
> int
> -__gettimeofday (struct timeval *tv, struct timezone *tz)
> +__gettimeofday (struct timeval *restrict tv, void *restrict tz)
> {
> if (__glibc_unlikely (tz != 0))
> - memset (tz, 0, sizeof *tz);
> + memset (tz, 0, sizeof (struct timezone));
>
> struct timespec ts;
> if (__clock_gettime (CLOCK_REALTIME, &ts))
> diff --git a/time/sys/time.h b/time/sys/time.h
> index 5dbc7fc627..1b6c112274 100644
> --- a/time/sys/time.h
> +++ b/time/sys/time.h
> @@ -54,23 +54,37 @@ struct timezone
> int tz_minuteswest; /* Minutes west of GMT. */
> int tz_dsttime; /* Nonzero if DST is ever in effect. */
> };
> -
> -typedef struct timezone *__restrict __timezone_ptr_t;
> -#else
> -typedef void *__restrict __timezone_ptr_t;
> #endif
>
> -/* Get the current time of day and timezone information,
> - putting it into *TV and *TZ. If TZ is NULL, *TZ is not filled.
> - Returns 0 on success, -1 on errors.
> - NOTE: This form of timezone information is obsolete.
> - Use the functions and variables declared in <time.h> instead. */
> +/* Get the current time of day, putting it into *TV.
> + If TZ is not null, *TZ must be a struct timezone, and both fields
> + will be set to zero.
> + Calling this function with a non-null TZ is obsolete;
> + use localtime etc. instead.
> + This function itself is semi-obsolete;
> + most callers should use time or clock_gettime instead. */
> extern int gettimeofday (struct timeval *__restrict __tv,
> - __timezone_ptr_t __tz) __THROW __nonnull ((1));
> + void *__restrict __tz) __THROW __nonnull ((1));
> +
> +#if __GNUC_PREREQ (4,3)
> +/* Issue a warning for use of gettimeofday with a non-null __tz argument. */
> +__warndecl (__warn_gettimeofday_timezone,
> + "gettimeofday with non-null or non-constant timezone parameter;"
> + " this is obsolete and inaccurate, use localtime instead");
> +
> +#define gettimeofday(__tv, __tz) \
> + (((!__builtin_constant_p (__tz) || (__tz) != 0) \
> + ? __warn_gettimeofday_timezone () \
> + : (void) 0), \
> + (gettimeofday) (__tv, __tz))
> +#endif
>
> #ifdef __USE_MISC
> /* Set the current time of day and timezone information.
> - This call is restricted to the super-user. */
> + This call is restricted to the super-user.
> + Setting the timezone in this way is obsolete, but we don't yet
> + warn about it because it still has some uses for which there is
> + no alternative. */
> extern int settimeofday (const struct timeval *__tv,
> const struct timezone *__tz)
> __THROW;
>