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

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Date:   Tue, 25 Jun 2019 08:56:09 -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 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

> 
> 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
>