linux-kernel - Re: [PATCH 5/7] x86, boot, LLVM: Use regparm=0 for memcpy and memset

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Message-ID: <c6f5b08c-1de8-15a7-81c2-b41aad7d1c8b@zytor.com>
Date:   Thu, 22 Jun 2017 15:38:19 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Michael Davidson <md@...gle.com>
Cc:     Michal Marek <mmarek@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.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>,
        Matthias Kaehlcke <mka@...omium.org>, x86@...nel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-raid@...r.kernel.org
Subject: Re: [PATCH 5/7] x86, boot, LLVM: Use regparm=0 for memcpy and memset

On 03/17/17 05:08, Peter Zijlstra wrote:
> On Thu, Mar 16, 2017 at 05:15:18PM -0700, Michael Davidson wrote:
>> Use the standard regparm=0 calling convention for memcpy and
>> memset when building with clang.
>>
>> This is a work around for a long standing clang bug
>> (see https://llvm.org/bugs/show_bug.cgi?id=3997) where
>> clang always uses the standard regparm=0 calling convention
>> for any implcit calls to memcpy and memset that it generates
>> (eg for structure assignments and initialization) even if an
>> alternate calling convention such as regparm=3 has been specified.
> 
> Seriously, fix LLVM already.
> 

Yes, this is a real stinker, in no small part because once clang is
fixed to DTRT then this is actually broken...

	-hpa