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

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Date:	Tue, 27 Oct 2009 14:50:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	David Miller <davem@...emloft.net>
Cc:	lethal@...ux-sh.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf tools: Kill off -Wcast-align


* David Miller <davem@...emloft.net> wrote:

> From: Paul Mundt <lethal@...ux-sh.org>
> Date: Mon, 26 Oct 2009 18:47:30 +0900
> 
> > On Mon, Oct 26, 2009 at 07:25:20AM +0100, Ingo Molnar wrote:
> >> 
> >> * 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>
> >> 
> >> 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.
> >> 
> > 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.
> 
> sparc64 hits this too when building 32-bit perf binary, the first 
> thing I do after a pull is remove this warning option from the 
> Makefile :-)

Generally if you run into such issues in Sparc let us know so we can fix 
it :-)

Paul's fix is queued up for Linus.

	Ingo
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