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

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Date:	Mon, 26 Oct 2009 12:08:34 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf tools: Kill off -Wcast-align

* Paul Mundt <lethal@...ux-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@...ux-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@...ux-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?
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