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

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Message-ID: <193c179e-16ca-4b4e-2584-75e8f6c1819f@arm.com>
Date:   Tue, 25 Jun 2019 18:00:27 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Qian Cai <cai@....pw>, 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 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?

-- 
Regards,
Vincenzo

--->8----




View attachment "0001-arm64-vdso-Fix-compilation-with-clang-8.patch" of type "text/x-patch" (1133 bytes)