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

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Message-ID: <ba06e4f5-709a-08cc-0f62-e50c64fc301f@mailbox.org>
Date:   Thu, 10 Jun 2021 18:39:45 +0000
From:   Tor Vic <torvic9@...lbox.org>
To:     Nathan Chancellor <nathan@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>
Cc:     "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

Hi Nathan,

On 10.06.21 16:42, Nathan Chancellor wrote:
> Hi Tor,
> 
> On 6/10/2021 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.
>>
>> This is for linux-stable 5.12.
>> Another patch will be submitted for 5.13 shortly (unless there are
>> objections).
> 
> This patch needs to be accepted into mainline first before it can go to
> stable so this line needs to be removed. The rest of the description
> looks good to me, good job on being descriptive!
> 

Thank you for explaining this.
I wasn't exactly sure how the procedure for stable was.
Does this mean that the patch should be based on 5.13?
I usually use Linus' tree mirrored at GitHub.

>> Discussion: https://github.com/ClangBuiltLinux/linux/issues/1377
>> [1]: https://reviews.llvm.org/D103048
>> [2]: https://reviews.llvm.org/D52322
> 
> As Greg's auto-response points out, there needs to be an actual
> 
> Cc: stable@...r.kernel.org
> 
> here in the patch, rather than just cc'ing stable@...r.kernel.org
> through email.
> 

Yes I misinterpreted this in the sense of "put stable mail in CC".
So if I get this right, I should NOT put stable email in CC, but only
add the "Cc: stable@...r.kernel.org" tag above the "Signed-off-by"?

>> Signed-off-by: Tor Vic <torvic9@...lbox.org>
> 
> The actual patch itself looks good and I have verified that it fixes the
> build error. On the resend with the above fixed, please feel free to add:
> 
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> Tested-by: Nathan Chancellor <nathan@...nel.org>
> 
>> ---
>>   arch/x86/Makefile | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
>> index 1f2e5bf..2855a1a 100644
>> --- a/arch/x86/Makefile
>> +++ b/arch/x86/Makefile
>> @@ -192,8 +192,9 @@ endif
>>   KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE)
>>     ifdef CONFIG_LTO_CLANG
>> -KBUILD_LDFLAGS    += -plugin-opt=-code-model=kernel \
>> -           -plugin-opt=-stack-alignment=$(if $(CONFIG_X86_32),4,8)
>> +ifeq ($(shell test $(CONFIG_LLD_VERSION) -lt 130000; echo $$?),0)
>> +KBUILD_LDFLAGS    += -plugin-opt=-stack-alignment=$(if
>> $(CONFIG_X86_32),4,8)
>> +endif
>>   endif
>>     ifdef CONFIG_X86_NEED_RELOCS
>>
> 
> Cheers,
> Nathan

Thanks for your help!
Tor