On Mon, 26 Jun 2006, Richard Guenther wrote:
> On Mon, 26 Jun 2006, Andrew Pinski wrote:
>
> >
> > On Jun 26, 2006, at 2:07 AM, Richard Guenther wrote:
> >
> > >So even
> > >(len + sizeof (struct tree_string)) & ~__alignof__(struct tree_string)
> > >might magically work in every case.
> >
> > Of course using __alignof__ is wrong in GCC sources since that would mean
> > you have to use GCC to bootstrap with which is not documented.
> >
> > But this does not explain PPC-Darwin's problem as PPC is not a
> > STRICT_ALIGNMENT target.
> > So either we are allocating too little or someone is going past an array
> > bounds somewhere.
>
> I'll currently investigate "fixing" build_string, which interestingly
> fails and may hint at a problem elsewhere. Of course alignof is wrong,
> but one can use
>
> /* Make sure to request aligned storage and do not waste bytes
> provided by padding of struct tree_string. */
> length = ((len + sizeof (struct tree_string))
> & ~(sizeof (struct tree_string)
> - offsetof (struct tree_string, str) - 1));
>
> instead (not pretty, but works).
Though it will not fix the alignment problem, only not waste the
bytes from the padding (which is why using __alignof__ didn't work,
it was wrong). A fix that also fixes the alignment problem would
look like
/* Make sure to request aligned storage and do not waste bytes
provided by padding of struct tree_string. */
length = ((len + sizeof (struct tree_string))
& ~(sizeof (struct tree_string)
- offsetof (struct tree_string, str) - 1));
length = ((length + __alignof__ (struct tree_string) - 1)
& ~(__alignof__ (struct tree_string) - 1));
that is, align length - I don't know how to avoid using __alignof__
here, though, other than using a fake struct like
struct foo_align_for_tree_string {
char c;
struct tree_string s;
}
and offsetof (struct foo_align_for_tree_string, s). Which would make it
as ugly as
struct dummy_to_get_alignof_tree_string {
char c;
struct tree_string s;
};
/* Make sure to request aligned storage and do not waste bytes
provided by padding of struct tree_string. */
length = ((len + sizeof (struct tree_string))
& ~(sizeof (struct tree_string)
- offsetof (struct tree_string, str) - 1));
length = ((length + offsetof (struct dummy_to_get_alignof_tree_string,
s) - 1)
& ~(offsetof (struct dummy_to_get_alignof_tree_string, s) -
1));
:/
I'll go ahead and revert the ggc-page.c patch now.
Richard.
--
Richard Guenther <[EMAIL PROTECTED]>
Novell / SUSE Labs
