linux-kernel - Re: [PATCH] x86/vdso, arm64/vdso: fix flip/flop vdso build bug

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Date:   Fri, 12 Jul 2019 18:35:22 +0900
From:   Naohiro Aota <naohiro.aota@....com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>
Subject: Re: [PATCH] x86/vdso, arm64/vdso: fix flip/flop vdso build bug

On Fri, Jul 12, 2019 at 03:24:01PM +0900, Masahiro Yamada wrote:
>On Fri, Jul 12, 2019 at 2:46 PM Naohiro Aota <naohiro.aota@....com> wrote:
>>
>> Two consecutive "make" on an already compiled kernel tree will show
>> different behavior:
>>
>> $ make
>>   CALL    scripts/checksyscalls.sh
>>   CALL    scripts/atomic/check-atomics.sh
>>   DESCEND  objtool
>>   CHK     include/generated/compile.h
>>   VDSOCHK arch/x86/entry/vdso/vdso64.so.dbg
>>   VDSOCHK arch/x86/entry/vdso/vdso32.so.dbg
>> Kernel: arch/x86/boot/bzImage is ready  (#3)
>>   Building modules, stage 2.
>>   MODPOST 12 modules
>>
>> $ make
>>   CALL    scripts/checksyscalls.sh
>>   CALL    scripts/atomic/check-atomics.sh
>>   DESCEND  objtool
>>   CHK     include/generated/compile.h
>>   VDSO    arch/x86/entry/vdso/vdso64.so.dbg
>>   OBJCOPY arch/x86/entry/vdso/vdso64.so
>>   VDSO2C  arch/x86/entry/vdso/vdso-image-64.c
>>   CC      arch/x86/entry/vdso/vdso-image-64.o
>>   VDSO    arch/x86/entry/vdso/vdso32.so.dbg
>>   OBJCOPY arch/x86/entry/vdso/vdso32.so
>>   VDSO2C  arch/x86/entry/vdso/vdso-image-32.c
>>   CC      arch/x86/entry/vdso/vdso-image-32.o
>>   AR      arch/x86/entry/vdso/built-in.a
>>   AR      arch/x86/entry/built-in.a
>>   AR      arch/x86/built-in.a
>>   GEN     .version
>>   CHK     include/generated/compile.h
>>   UPD     include/generated/compile.h
>>   CC      init/version.o
>>   AR      init/built-in.a
>>   LD      vmlinux.o
>> <snip>
>>
>> This is causing "LD vmlinux" once every two times even without any
>> modifications. This is the same bug fixed in commit 92a4728608a8
>> ("x86/boot: Fix if_changed build flip/flop bug").  We cannot use two
>> "if_changed" in one target. Fix this build bug by merging two commands
>> into one function.
>>
>> Signed-off-by: Naohiro Aota <naohiro.aota@....com>
>
>
>The code looks OK, but you should split this
>into two patches, for arm64 and x86,
>and then add Fixes: for each of them.

Thanks, I'll split and add the tags.

>
>
>-- 
>Best Regards
>Masahiro Yamada