Wireshark · Ethereal-dev: Re: [Ethereal-dev] H.225 problem, and running under gdb

["Martin Mathieson" <martin.mathieson@xxxxxxxxxxxx>]

I couldn't find a convenient configure option or makefile target to get rid
of the -O2.  Is there one?

----- Original Message -----
From: "Guy Harris" <gharris@xxxxxxxxx>
To: "Ethereal development" <ethereal-dev@xxxxxxxxxxxx>
Sent: 19 June 2004 10:43
Subject: Re: [Ethereal-dev] H.225 problem, and running under gdb


> On Fri, Jun 18, 2004 at 04:59:39PM +0100, Martin Mathieson wrote:
> > - stepping through the code would work a little then it would jump back
to
> > the breakpoint
>
> Welcome to the wonderful world of instruction scheduling.
>
> Modern compilers don't necessarily turn, for example
>
> a = b + c;
> d = e + f;
>
> into code such as
>
> load r1, b
> add r1, c
> store r1, a
> load r1, e
> add r1, f
> store r1, d
>
> It might, instead, generate
>
> load r1, b
> load r2, e
> add r1, c
> add r2, f
> store r1, a
> store r2, d
>
> as a superscalar processor might be able to execute two instructions
> with no interdependencies in parallel, e.g.
>
> add r1, c
> add r2, f
>
> but wouldn't necessarily be able to execute
>
> add r1, c
> store r1, a
>
> in parallel, so the first code sequence might take 6 clock cycles
> (assuming cache hits on the loads) but the second code sequence might
> take only 3.
>
> This means that single-stepping through code might appear to jump among
> statements.
>
> Compiling without optimization might get rid of the
> instruction-scheduling pass, and make single-stepping behave a bit more
> as one would expect.
>
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