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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Fri, 12 Jul 2019 23:54:37 +0900
Message-ID: <CAK7LNARBunev7O3k06hv22aPh9DuW53CKbuvM1TwscuM_5uOUg@mail.gmail.com>
Subject: Re: [PATCH v2 1/2] x86/vdso: fix flip/flop vdso build bug
To:     Naohiro Aota <naohiro.aota@wdc.com>
Cc:     Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>, Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Peter Collingbourne <pcc@google.com>
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On Fri, Jul 12, 2019 at 7:16 PM Naohiro Aota <naohiro.aota@wdc.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
> 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.
>
> Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> Fixes: 7ac870747988 ("x86/vdso: Switch to generic vDSO implementation")
> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
> ---

Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>


-- 
Best Regards
Masahiro Yamada