Re: [PATCH 3/7] x86, LLVM: suppress clang warnings about unaligned accesses

From	Matthias Kaehlcke <mka@chromium.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 3/7] x86, LLVM: suppress clang warnings about unaligned accesses
Date	2017-04-14 02:30 +0200
Message-ID	<tvXhE-2eF-5@gated-at.bofh.it> (permalink)
References	(1 earlier) <tlNWh-6eK-7@gated-at.bofh.it> <tm9WN-5YC-7@gated-at.bofh.it> <tsjgJ-4ZI-13@gated-at.bofh.it> <tvWbU-1xv-7@gated-at.bofh.it> <tvWOB-1Nu-3@gated-at.bofh.it>
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El Thu, Apr 13, 2017 at 04:55:00PM -0700 H. Peter Anvin ha dit:

> On 04/13/17 16:14, Matthias Kaehlcke wrote:
> > El Mon, Apr 03, 2017 at 04:01:58PM -0700 Matthias Kaehlcke ha dit:
> > 
> >> El Fri, Mar 17, 2017 at 04:50:19PM -0700 hpa@zytor.com ha dit:
> >>
> >>> On March 16, 2017 5:15:16 PM PDT, Michael Davidson <md@google.com> wrote:
> >>>> Suppress clang warnings about potential unaliged accesses
> >>>> to members in packed structs. This gets rid of almost 10,000
> >>>> warnings about accesses to the ring 0 stack pointer in the TSS.
> >>>>
> >>>> Signed-off-by: Michael Davidson <md@google.com>
> >>>> ---
> >>>> arch/x86/Makefile | 5 +++++
> >>>> 1 file changed, 5 insertions(+)
> >>>>
> >>>> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> >>>> index 894a8d18bf97..7f21703c475d 100644
> >>>> --- a/arch/x86/Makefile
> >>>> +++ b/arch/x86/Makefile
> >>>> @@ -128,6 +128,11 @@ endif
> >>>>         KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args)
> >>>> endif
> >>>>
> >>>> +ifeq ($(cc-name),clang)
> >>>> +# Suppress clang warnings about potential unaligned accesses.
> >>>> +KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
> >>>> +endif
> >>>> +
> >>>> ifdef CONFIG_X86_X32
> >>>> 	x32_ld_ok := $(call try-run,\
> >>>> 			/bin/echo -e '1: .quad 1b' | \
> >>>
> >>> Why conditional on clang?
> >>
> >> My understanding is that this warning is clang specific, it is not
> >> listed on https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
> > 
> > Actually this warning affects other platforms besides x86
> > (e.g. arm64), I'll submit a patch that disables the warning on all
> > platforms.
> > 
> 
> Drop the ifeq ($(cc-name),clang).
> 
> You should assume that if you have to add one of those ifeq's then you
> are doing something fundamentally wrong.

Thanks, however in the case of the global Makefile it seems we should
put it inside the already existing clang section:

http://lxr.free-electrons.com/source/Makefile#L692

Cheers

Matthias

Thread

Re: [PATCH 3/7] x86, LLVM: suppress clang warnings about unaligned  accesses Matthias Kaehlcke <mka@chromium.org> - 2017-04-14 01:20 +0200
  Re: [PATCH 3/7] x86, LLVM: suppress clang warnings about unaligned  accesses "H. Peter Anvin" <hpa@zytor.com> - 2017-04-14 02:00 +0200
    Re: [PATCH 3/7] x86, LLVM: suppress clang warnings about unaligned  accesses Matthias Kaehlcke <mka@chromium.org> - 2017-04-14 02:30 +0200
      Re: [PATCH 3/7] x86, LLVM: suppress clang warnings about unaligned accesses hpa@zytor.com - 2017-04-14 07:40 +0200

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