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

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Message-ID: <bf7a6fa8-5cc3-0a7a-08ab-7607ca79d279@arm.com>
Date:   Tue, 25 Jun 2019 15:30:36 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Qian Cai <cai@....pw>
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

Hi Qian,

On 25/06/2019 15:28, Qian Cai wrote:
> 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.
> 

It is what I thought that's why I asked to cross-check. I did not want to remove
tiny.

Thanks for your support, I will post a patch adding your tag as reported-by if
you are ok with that.

>>
>> 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
>>>>>>
>>>>
>>>>
>>
>>

-- 
Regards,
Vincenzo