linux-kernel - Re: "arm64: vdso: Substitute gettimeofday() with C implementation" breaks clang build

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Message-ID: <b25d3952-abe5-def5-fe42-0300f0b4c73c@arm.com>
Date:   Tue, 25 Jun 2019 18:33:15 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Qian Cai <cai@....pw>, Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: Re: "arm64: vdso: Substitute gettimeofday() with C implementation"
 breaks clang build

Hi Qian,

On 25/06/2019 18:31, Qian Cai wrote:
> On Tue, 2019-06-25 at 18:00 +0100, Vincenzo Frascino wrote:
>> Hi Nick,
>>
>> On 25/06/2019 17:26, Nick Desaulniers wrote:
>>> On Tue, Jun 25, 2019 at 7:54 AM Vincenzo Frascino
>>> <vincenzo.frascino@....com> wrote:
>>>>
>>>> Hi Qian,
>>>>
>>>> ...
>>>>
>>>>>
>>>>> but clang 7.0 is still use in many distros by default, so maybe this
>>>>> commit can
>>>>> be fixed by adding a conditional check to use "small" if clang version <
>>>>> 8.0.
>>>>>
>>>>
>>>> Could you please verify that the patch below works for you?
>>>
>>> Should it be checking against CONFIG_CLANG_VERSION, or better yet be
>>> using cc-option macro?
>>>
>>
>> This is what I did in my proposed patch, but I was surprised that clang-7
>> generates relocations that clang-8 does not.
>>
>>   LD      arch/arm64/kernel/vdso/vdso.so.dbg
>>   VDSOCHK arch/arm64/kernel/vdso/vdso.so.dbg
>> 00000000000009d0 R_AARCH64_JUMP_SLOT  _mcount
>>
>> arch/arm64/kernel/vdso/vdso.so.dbg: dynamic relocations are not supported
>> make[1]: *** [arch/arm64/kernel/vdso/Makefile:59:
>> arch/arm64/kernel/vdso/vdso.so.dbg] Error 1
>> make: *** [arch/arm64/Makefile:180: vdso_prepare] Error 2
>>
>> This is the the result of the macro I introduced in lib/vdso/Makefile.
>>
>> And I just found out why. I forgot to add a "+" in the patch provided :)
>>
>> @Qian: Could you please retry with the one provided below?
>>
> 
> It works fine.
> 

Thanks for the confirmation, I will push the patch in a short while.

-- 
Regards,
Vincenzo