Re: Who's insane: gdb or I? (Answer: I am)

[Bernd Jendrissek <berndj@prism.co.za>]

Okay, I think I'm convinced that this is simply normal -O2 behaviour.

On Wed, Jul 03, 2002 at 03:15:47PM +0200, Bernd Jendrissek wrote:
> 1083            OVERtime+=(etv.tv_sec - stv.tv_sec) * 1000;
> (gdb) s
> 1084            OVERtime+=(etv.tv_usec - stv.tv_usec) / 1000;
> (gdb) s
> 1083            OVERtime+=(etv.tv_sec - stv.tv_sec) * 1000;
> (gdb) s
> 1084            OVERtime+=(etv.tv_usec - stv.tv_usec) / 1000;
> (gdb) s
> 1083            OVERtime+=(etv.tv_sec - stv.tv_sec) * 1000;
> (gdb) s
> 1084            OVERtime+=(etv.tv_usec - stv.tv_usec) / 1000;
> (gdb) list
> 1079            return;
> 1080        }
> 1081        if (PERMaccessconf->nnrpdoverstats) {
> 1082            gettimeofday(&etv, NULL);
> 1083            OVERtime+=(etv.tv_sec - stv.tv_sec) * 1000;
> 1084            OVERtime+=(etv.tv_usec - stv.tv_usec) / 1000;
> 1085        }

For those still interested, here's the assembly generated by gcc -save-temps
at -O2.  (Complete gcc options: -g -O2 -save-temps)

        movl PERMaccessconf,%eax
        cmpl $0,116(%eax)
        je .L799
.stabn 68,0,1082,.LM674-CMDxover
.LM674:
        addl $-8,%esp
        pushl $0
        leal -48(%ebp),%ebx
        pushl %ebx
        call gettimeofday
.stabn 68,0,1083,.LM675-CMDxover
.LM675:
        movl -40(%ebp),%eax
        movl -48(%ebp),%ecx
        subl %eax,%ecx
.stabn 68,0,1084,.LM676-CMDxover
.LM676:
        movl -36(%ebp),%eax
        movl 4(%ebx),%esi
.stabn 68,0,1083,.LM677-CMDxover
.LM677:
        imull $1000,%ecx,%ecx
.stabn 68,0,1084,.LM678-CMDxover
.LM678:
        subl %eax,%esi
        movl $274877907,%ebx
        movl %esi,%eax
        imull %ebx
.stabn 68,0,1083,.LM679-CMDxover
.LM679:
        addl OVERtime,%ecx
.stabn 68,0,1084,.LM680-CMDxover
.LM680:
        sarl $6,%edx
        movl %esi,%eax
        sarl $31,%eax
        subl %eax,%edx
        addl %edx,%ecx
        movl %ecx,OVERtime
.stabn 68,0,1085,.LM681-CMDxover
.LM681:
        addl $16,%esp
.L799:

So it appears the bouncing between lines 1083 and 1084 really is due to
interleaving of instructions.  Thanks for everyone's help; I consider this
resolved.

-- 
berndj@users.sourceforge.net is probably better to bookmark than any