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

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Date:   Tue, 25 Jun 2019 10:28:07 -0400
From:   Qian Cai <cai@....pw>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        natechancellor@...il.com, ndesaulniers@...gle.com
Subject: Re: "arm64: vdso: Substitute gettimeofday() with C implementation"
 breaks clang build

On Tue, 2019-06-25 at 15:11 +0100, Vincenzo Frascino wrote:
> Hi Qian,
> 
> On 25/06/2019 14:51, Qian Cai wrote:
> > On Tue, 2019-06-25 at 14:40 +0100, Vincenzo Frascino wrote:
> > > On 25/06/2019 13:56, Qian Cai wrote:
> > > > On Tue, 2019-06-25 at 13:47 +0100, Vincenzo Frascino wrote:
> > > > > Hi Qian,
> > > > > 
> > > > > On 25/06/2019 13:16, Qian Cai wrote:
> > > > > > The linux-next commit "arm64: vdso: Substitute gettimeofday() with C
> > > > > > implementation" [1] breaks clang build.
> > > > > > 
> > > > > > error: invalid value 'tiny' in '-mcode-model tiny'
> > > > > > make[1]: *** [scripts/Makefile.build:279:
> > > > > > arch/arm64/kernel/vdso/vgettimeofday.o] Error 1
> > > > > > make[1]: *** Waiting for unfinished jobs....
> > > > > > make: *** [arch/arm64/Makefile:180: vdso_prepare] Error 2
> > > > > > 
> > > > > > [1] https://patchwork.kernel.org/patch/11009663/
> > > > > > 
> > > > > 
> > > > > I am not sure what does exactly break from your report. Could you
> > > > > please
> > > > > provide
> > > > > more details?
> > > > 
> > > > Here is the config to reproduce.
> > > > 
> > > > https://raw.githubusercontent.com/cailca/linux-mm/master/arm64.config
> > > > 
> > > > # make CC=clang -j $(nr_cpus)
> > > > 
> > > > I can get it working again by removing "-mcmodel=tiny" in
> > > > arch/arm64/kernel/vdso/Makefile
> > > > 
> > > 
> > > With your defconfig I can't still reproduce the problem. Which version of
> > > clang
> > > are you using?
> > 
> > Compiler: clang version 7.0.1 (tags/RELEASE_701/final)
> > 
> 
> I am using clang 8.0.0. Could you please try with it and see if the issue goes
> away?

Looks like the "tiny" was added since clang 8.0.

https://reviews.llvm.org/D49674

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.

> 
> Thanks,
> Vincenzo
> 
> > > 
> > > > > 
> > > > > On my env:
> > > > > 
> > > > > $ make mrproper && make defconfig && make CC=clang HOSTCC=clang
> > > > > -j$(nproc)
> > > > > 
> > > > > ...
> > > > > 
> > > > > arch/arm64/Makefile:56: CROSS_COMPILE_COMPAT is clang, the compat vDSO
> > > > > will
> > > > > not
> > > > > be built
> > > > > 
> > > > > ...
> > > > > 
> > > > >   LDS     arch/arm64/kernel/vdso/vdso.lds
> > > > >   AS      arch/arm64/kernel/vdso/note.o
> > > > >   AS      arch/arm64/kernel/vdso/sigreturn.o
> > > > >   CC      arch/arm64/kernel/vdso/vgettimeofday.o
> > > > >   LD      arch/arm64/kernel/vdso/vdso.so.dbg
> > > > >   VDSOCHK arch/arm64/kernel/vdso/vdso.so.dbg
> > > > >   VDSOSYM include/generated/vdso-offsets.h
> > > > > 
> > > > > ...
> > > > > 
> > > > >   LD      vmlinux.o
> > > > >   MODPOST vmlinux.o
> > > > >   MODINFO modules.builtin.modinfo
> > > > >   KSYM    .tmp_kallsyms1.o
> > > > >   KSYM    .tmp_kallsyms2.o
> > > > >   LD      vmlinux
> > > > >   SORTEX  vmlinux
> > > > >   SYSMAP  System.map
> > > > >   Building modules, stage 2.
> > > > >   OBJCOPY arch/arm64/boot/Image
> > > > >   MODPOST 483 modules
> > > > > 
> > > 
> > > 
> 
>