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

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Date:   Fri, 11 Jun 2021 08:07:54 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Nick Desaulniers' <ndesaulniers@...gle.com>,
        Tor Vic <torvic9@...lbox.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "nathan@...nel.org" <nathan@...nel.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

From: Nick Desaulniers
> Sent: 10 June 2021 20:21
> 
> 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!

Actually, give that LTO is still 'experimental' is it worth just
removing the flags and requiring clang-13 for LTO builds?

	David

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