Thibaud GUERIN writes:
> On 4/20/06, Andrew Haley <aph@xxxxxxxxxxx> wrote:
> > Thibaud GUERIN writes:
> > > hi,
> > > I'm actually writing a program in C and i'm fighting with an address
> > > dereferencing since some days now.
> > >
> > > int the_bug(const char *fmt, ...)
> > > {
> > > char **ap;
> > > char **s = (char **)(&fmt);
> > >
> > > /* __asm__ volatile ( */
> > > /* "\tleal %1, %%eax\n" */
> > > /* "\tmovl %%eax,%0\n" */
> > > /* "\tmovl %1, %%eax\n" */
> > > /* "\tmovl %2, %%ebx \n" */
> > > /* "\tmovl %%eax, (%%ebx)\n" */
> > > /* : "=m"(ap) : "m" (fmt), "m"(ap)); */
> >
> > This is wrong in so many ways I don't know where to start.
> >
> > It may be better if you try to tell us what you are trying to do.
> >
> > Redirecting gcc-help@xxxxxxxxxxxx
>
>
> Not clear in the first message, (and maybe not in this one too..), sorry
>
>
> This asm inline was something like a "test/patch code".
>
> I try to have a simple :
>
> char **ap = (char **)(&fmt);
I don't think that's legal. (Actually, I'm not perfectly sure it's
not legal, but I think not.) Also, I have no idea why you're trying
to do such a thing.
> working, It didn't :
> ap was equal to &fmt BUT *ap wasn't equal to fmt (don't kown why...)
I'm sure that's impossible. :-)
> so i try by my self... to do :
>
> ap = &fmt;
> *ap = fmt;
>
> in asm inline.... (dirty i know...)
>
> problem is :
> With this asm code in the binary *s is equal to fmt
> Without this asm code in the binary *s isn't equal to fmt
>
>
> All the 's' variable stuffs are from my debug...
> Again :
> My only aim is to have an 'ap = &fmt' valid (->ap = &fmt AND *ap = fmt)
So why not do the obvious
const char **ap = &fmt ;
?
> The resulting asm was here to help you to understand wath's wrong ....
> I'm looking for some days now without answer...
You're still not explaining yourself. You have a const char* arg that
you are trying to alter, but instead of doing it the obvious way with
an assignment, you're taking the address of the arg, casting the
resulting pointer to a different pointer type, and then overwriting
the arg through the resulting pointer.
What's the point of all this?
Andrew.
