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

[Jonathan Larmour]

Kieran Mansley wrote:
> On Thu, 2008-06-19 at 16:37 +0200, address@hidden wrote:
>> 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);
> 
> I agree that this looks wrong.  Should be a straightforward thing to fix
> though.  Could you file a bug?

I think that's not the only issue in that function; it goes on to return this:

    return HZ * sec + usec;
with HZ probably 100 (and if anything else, higher).

But on a unix system, sec is around 1.2 billion, and so multiplying by 100
will overflow. It's probably not a big deal as in practice it will wrap,
and so still increase monotonically, but it's also easy to fix by
subtracting starttime.tv_sec so that's what I'm checking in as well. I
think the fix is obvious, so no need to file a bug

Jifl

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;

     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;

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