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

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Date:   Tue, 25 Jun 2019 13:31:28 -0400
From:   Qian Cai <cai@....pw>
To:     Vincenzo Frascino <vincenzo.frascino@....com>,
        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

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.