linux-kernel - Re: [PATCH v2 2/2] arm64/vdso: fix flip/flop vdso build bug

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Message-ID: <b3d06dc3-f8be-9744-f45b-608e17a4f76f@arm.com>
Date:   Fri, 12 Jul 2019 13:10:23 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Naohiro Aota <naohiro.aota@....com>, linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>
Subject: Re: [PATCH v2 2/2] arm64/vdso: fix flip/flop vdso build bug

On 12/07/2019 11:15, Naohiro Aota wrote:
> Running "make" on an already compiled kernel tree will rebuild the kernel
> even without any modifications:
> 
> $ make ARCH=arm64 CROSS_COMPILE=/usr/bin/aarch64-unknown-linux-gnu-
> arch/arm64/Makefile:58: CROSS_COMPILE_COMPAT not defined or empty, the compat vDSO will not be built
>   CALL    scripts/checksyscalls.sh
>   CALL    scripts/atomic/check-atomics.sh
>   VDSOCHK arch/arm64/kernel/vdso/vdso.so.dbg
>   VDSOSYM include/generated/vdso-offsets.h
>   CHK     include/generated/compile.h
>   CC      arch/arm64/kernel/signal.o
>   CC      arch/arm64/kernel/vdso.o
>   CC      arch/arm64/kernel/signal32.o
>   LD      arch/arm64/kernel/vdso/vdso.so.dbg
>   OBJCOPY arch/arm64/kernel/vdso/vdso.so
>   AS      arch/arm64/kernel/vdso/vdso.o
>   AR      arch/arm64/kernel/vdso/built-in.a
>   AR      arch/arm64/kernel/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
> 
> 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@...ionext.com>
> Fixes: 28b1a824a4f4 ("arm64: vdso: Substitute gettimeofday() with C implementation")
> Signed-off-by: Naohiro Aota <naohiro.aota@....com>

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@....com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@....com>

> ---
>  arch/arm64/kernel/vdso/Makefile | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> index 4ab863045188..068c614b1231 100644
> --- a/arch/arm64/kernel/vdso/Makefile
> +++ b/arch/arm64/kernel/vdso/Makefile
> @@ -57,8 +57,7 @@ $(obj)/vdso.o : $(obj)/vdso.so
>  
>  # Link rule for the .so file, .lds has to be first
>  $(obj)/vdso.so.dbg: $(obj)/vdso.lds $(obj-vdso) FORCE
> -	$(call if_changed,ld)
> -	$(call if_changed,vdso_check)
> +	$(call if_changed,ld_and_vdso_check)
>  
>  # Strip rule for the .so file
>  $(obj)/%.so: OBJCOPYFLAGS := -S
> @@ -77,6 +76,9 @@ include/generated/vdso-offsets.h: $(obj)/vdso.so.dbg FORCE
>  quiet_cmd_vdsocc = VDSOCC   $@
>        cmd_vdsocc = $(CC) $(a_flags) $(c_flags) -c -o $@ $<
>  
> +quiet_cmd_ld_and_vdso_check = LD      $@
> +      cmd_ld_and_vdso_check = $(cmd_ld); $(cmd_vdso_check)
> +
>  # Install commands for the unstripped file
>  quiet_cmd_vdso_install = INSTALL $@
>        cmd_vdso_install = cp $(obj)/$@...g $(MODLIB)/vdso/$@
> 

-- 
Regards,
Vincenzo