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Date: Thu, 6 Mar 2014 17:46:53 -0300 From: Arnaldo Carvalho de Melo <acme@...stprotocols.net> To: Peter Zijlstra <peterz@...radead.org> Cc: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>, Corey Ashford <cjashfor@...ux.vnet.ibm.com>, David Ahern <dsahern@...il.com>, Frederic Weisbecker <fweisbec@...il.com>, Ingo Molnar <mingo@...e.hu>, Namhyung Kim <namhyung@...nel.org>, Paul Mackerras <paulus@...ba.org> Subject: Re: [PATCH 2/2] perf tools: Fix strict alias issue for find_first_bit Em Fri, Feb 28, 2014 at 10:29:23PM +0100, Peter Zijlstra escreveu: > On Fri, Feb 28, 2014 at 06:25:51PM -0300, Arnaldo Carvalho de Melo wrote: > > From: Jiri Olsa <jolsa@...hat.com> > > The gcc documentation offers workaround for valid aliasing by using > > __may_alias__ attribute: > > http://gcc.gnu.org/onlinedocs/gcc-4.4.0/gcc/Type-Attributes.html > > Using this workaround for the find_first_bit function. > Hurm; didn't I suggest using -fno-strict-aliasing just like the kernel > does? Because the C aliasing rules are bonghits heavy? Either way would solve the problem at hand, I just used the smaller hammer offered. I thought that Ingo had something against this, but only reference I could find now about it was this: -------------------------------------------- commit 65014ab36196f6d86edc9ee23759d6930b9d89a8 Author: Ingo Molnar <mingo@...e.hu> Date: Wed Sep 2 14:55:55 2009 +0200 perf tools: Work around strict aliasing related warnings Older versions of GCC are rather stupid about strict aliasing: <SNIP> Make it clear to GCC that we intend with those pointers, by passing them through via an explicit (void *) cast. We might want to add -fno-strict-aliasing as well, like the kernel itself does. Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl> Cc: Mike Galbraith <efault@....de> Cc: Paul Mackerras <paulus@...ba.org> Cc: Arnaldo Carvalho de Melo <acme@...hat.com> Cc: Frederic Weisbecker <fweisbec@...il.com> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@...e.hu> -------------------------------------------- Jiri's bandaid is for _newer_ compilers, so... - Arnaldo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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