linux-kernel - Re: [PATCH 2/7] Makefile, x86, LLVM: disable unsupported optimization flags

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Date:   Wed, 5 Apr 2017 12:01:30 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Michael Davidson <md@...gle.com>, Michal Marek <mmarek@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Shaohua Li <shli@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, X86 ML <x86@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-crypto@...r.kernel.org, linux-raid@...r.kernel.org
Subject: Re: [PATCH 2/7] Makefile, x86, LLVM: disable unsupported
 optimization flags

Hi Masahiro,

El Thu, Apr 06, 2017 at 03:08:26AM +0900 Masahiro Yamada ha dit:

> 2017-03-17 9:15 GMT+09:00 Michael Davidson <md@...gle.com>:
> > Unfortunately, while clang generates a warning about these flags
> > being unsupported it still exits with a status of 0 so we have
> > to explicitly disable them instead of just using a cc-option check.
> >
> > Signed-off-by: Michael Davidson <md@...gle.com>
> 
> 
> Instead, does the following work for you?
> https://patchwork.kernel.org/patch/9657285/

Thanks for the pointer, I was about to give this change (or rather its
ancestor) a rework myself :)

> You need to use
> $(call cc-option, ...)
> for -falign-jumps=1 and -falign-loops=1

I can confirm that this works.

Thanks

Matthias