linux-kernel - Re: [PATCH 3/3] perf tools: Fix a misuse of for_each_set

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Date:	Mon, 27 Aug 2012 16:18:15 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	<acme@...hat.com>, <mingo@...e.hu>, <a.p.zijlstra@...llo.nl>,
	<dsahern@...il.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] perf tools: Fix a misuse of for_each_set_bit() in
 session.c

Hi,

On Mon, 27 Aug 2012 16:59:07 +0900
Namhyung Kim <namhyung@...nel.org> wrote:

> Hi,
> 
> On Mon, 27 Aug 2012 15:38:27 +0800, Feng Tang wrote:
> > In regs_dump__printf() it use for_each_set_bit() for bit ops by
> > casting a (u64 *) to a (unsigned long *), this works for 64 bits
> > machine, but will fail on 32 bits ones.
> >
> > Fix it by using the raw bit comparing method.
> 
> Did it really cause a build failure or a program error?  If not, it
> looks better to keep using for_each_set_bit() interface.  How about
> casting the @mask to (void *) ?

It's a compile error:

cc1: warnings being treated as errors
util/session.c: In function ‘perf_session_deliver_event’:
util/include/linux/bitops.h:104: error: dereferencing pointer ‘p’ does break strict-aliasing rules
util/include/linux/bitops.h:96: error: dereferencing pointer ‘p’ does break strict-aliasing rules
util/session.c:907: note: initialized from here
util/include/linux/bitops.h:96: note: initialized from here
make: *** [util/session.o] Error 1
make: *** Waiting for unfinished jobs....

Casting the @mask to (void *) still sees the same error

Thanks,
Feng
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