Re: [PATCH] perf tools: Kill off -Wcast-align

[Ingo Molnar <mingo@elte.hu>]

* Pekka Enberg <penberg@cs.helsinki.fi> wrote:

> * Paul Mundt <lethal@linux-sh.org> wrote:
> >> > The present use of -Wcast-align causes the build to blow up on SH due to
> >> > generating a "cast increases required alignment of target type" error on
> >> > each invocation of list_for_each_entry().
> >> >
> >> > It seems that this was previously reported and killed off in the ia64
> >> > support patch, but nothing seems to have happened with that. Presumably
> >> > the same problem still remains there, too.
> >> >
> >> > Signed-off-by: Paul Mundt <lethal@linux-sh.org>
> 
> On Mon, Oct 26, 2009 at 07:25:20AM +0100, Ingo Molnar wrote:
> >> Is this a GCC bug producing false positive warnings? The GCC manpage
> >> says:
> >>
> >>        -Wcast-align
> >>            Warn whenever a pointer is cast such that the required alignment of the
> >>            target is increased.  For example, warn if a "char *" is cast to an
> >>            "int *" on machines where integers can only be accessed at two- or
> >>            four-byte boundaries.
> >>
> >> Which looks moderately useful - if it works.
> 
> On Mon, Oct 26, 2009 at 11:47 AM, Paul Mundt <lethal@linux-sh.org> wrote:
>
> > Well, both ia64 and sh have hit this in the current compilers, and 
> > it doesn't seem to pose any code generation issues. In the areas 
> > where it is generated it seems to relate to 64-bit data types in the 
> > data structures, which in itself doesn't seem inherently 
> > problematic.
> >
> > I'll submit a bug report to the GCC folks, but for the time being 
> > given that multiple architectures are hitting this and it doesn't 
> > seem to be causing any issues, it would be better to have this flag 
> > dropped.
> 
> Can we disable the flag for affected architectures but keep it enabled 
> for x86?

For now i've applied Paul's fix - x86 doesnt have such type restrictions 
and i dont remember this warning having flagged some real data structure 
alignment bug anywhere.

	Ingo