linux-kernel - Re: [PATCH] x86/Makefile: make -stack-alignment conditional on LLD

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Date:   Thu, 10 Jun 2021 13:40:07 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Tor Vic <torvic9@...lbox.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH] x86/Makefile: make -stack-alignment conditional on LLD <
 13.0.0

On 6/10/2021 1:16 PM, Tor Vic wrote:
> 
> 
> On 10.06.21 19:20, Nick Desaulniers wrote:
>> On Thu, Jun 10, 2021 at 2:28 AM <torvic9@...lbox.org> wrote:
>>>
>>> Since LLVM commit 3787ee4, the '-stack-alignment' flag has been dropped [1],
>>> leading to the following error message when building a LTO kernel with
>>> Clang-13 and LLD-13:
>>>
>>>      ld.lld: error: -plugin-opt=-: ld.lld: Unknown command line argument
>>>      '-stack-alignment=8'.  Try 'ld.lld --help'
>>>      ld.lld: Did you mean '--stackrealign=8'?
>>>
>>> It also appears that the '-code-model' flag is not necessary anymore starting
>>> with LLVM-9 [2].
>>>
>>> Drop '-code-model' and make '-stack-alignment' conditional on LLD < 13.0.0.
>>
>> Please include this additional context in v2:
>> ```
>> These flags were necessary because these flags were not encoded in the
>> IR properly, so the link would restart optimizations without them. Now
>> there are properly encoded in the IR, and these flags exposing
>> implementation details are no longer necessary.
>> ```
>> That way it doesn't sound like we're not using an 8B stack alignment
>> on x86; we very much are so; AMDGPU GPFs without it!
>>
> 
> Will do so.
> Does this have to be a v2 (with a "changes from v1" info) or just a
> resend? It is based on mainline now and the line numbers have changed.

Yes, this should be a v2 because the commit message changed. It would be 
considered a resend if nothing changed and the patch just needed to be 
picked up rather than re-reviewed.

Cheers,
Nathan