[lwip-users] Re:use of struct timeval in sys_jiffies, UNIX port

[R. D. Flowers, Chattanooga TN USA]

> Date: Thu, 19 Jun 2008 16:37:30 +0200
> From: address@hidden
> Subject: [lwip-users] use of struct timeval in sys_jiffies, UNIX port
> To: address@hidden
> Message-ID: <address@hidden>
> Content-Type: text/plain;       charset=ISO-8859-1;     DelSp="Yes";
>         format="flowed"
>
> My compiler complained about tv.tv_sec being used before it was
> initialized, and upon inspection I must say I don't really understand
> what is happening.
>
> Depending on the compiler, isn't the value of tv_sec at best
> initialized to zero, otherwise unpredictable? And the result from  
> gettimeofday is not used for anything?
>
>   From sys_arch.c, UNIX port, latest version in CVS.
>
> unsigned long
> sys_jiffies(void)
> {
>       struct timeval tv;
>       unsigned long sec = tv.tv_sec;
>       long usec = tv.tv_usec;
>
>       gettimeofday(&tv,NULL);

Unless it has changed from the documentation and from what's obvious, it 
IS exactly the call to gettimeofday that stuffs tv and all its members.

You are trying to use one of those members to initialize usec before tv 
is defined.

What am I missing ?

>       if (sec >= (MAX_JIFFY_OFFSET / HZ))
>         return MAX_JIFFY_OFFSET;
>       usec += 1000000L / HZ - 1;
>       usec /= 1000000L / HZ;
>       return HZ * sec + usec;
> }
>
> Index: sys_arch.c
> ===================================================================
> RCS file: /sources/lwip/contrib/ports/unix/sys_arch.c,v
> retrieving revision 1.21
> diff -u -5 -p -r1.21 sys_arch.c
> --- sys_arch.c  30 May 2008 11:41:51 -0000      1.21
> +++ sys_arch.c  19 Jun 2008 15:29:50 -0000
> @@ -585,14 +585,16 @@ sys_arch_unprotect(sys_prot_t pval)
>
>  unsigned long
>  sys_jiffies(void)
>  {
>      struct timeval tv;
> -    unsigned long sec = tv.tv_sec;
> -    long usec = tv.tv_usec;
> +    unsigned long sec;
> +    long usec;

Yes. Declared here. Defined later.

>      gettimeofday(&tv,NULL);
> +    sec = tv.tv_sec - starttime.tv_sec;
> +    usec = tv.tv_usec;
>
>      if (sec >= (MAX_JIFFY_OFFSET / HZ))
>         return MAX_JIFFY_OFFSET;
>      usec += 1000000L / HZ - 1;
>      usec /= 1000000L / HZ;