linux-kernel - Re: [PATCH v2 1/2] x86/vdso: fix flip/flop vdso build bug

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Date:   Fri, 12 Jul 2019 13:09:46 +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 1/2] x86/vdso: fix flip/flop vdso build bug

Hi Naohiro,

I was working on a similar patch set, but I just noticed you posted this one.
Thanks for that.

In reply to your series I am adding similar fix for arm64 compat.

On 12/07/2019 11:15, Naohiro Aota 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@...ionext.com>
> Fixes: 7ac870747988 ("x86/vdso: Switch to generic vDSO implementation")
> Signed-off-by: Naohiro Aota <naohiro.aota@....com>

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

> ---
>  arch/x86/entry/vdso/Makefile | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index 39106111be86..34773395139a 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -56,8 +56,7 @@ VDSO_LDFLAGS_vdso.lds = -m elf_x86_64 -soname linux-vdso.so.1 --no-undefined \
>  			-z max-page-size=4096
>  
>  $(obj)/vdso64.so.dbg: $(obj)/vdso.lds $(vobjs) FORCE
> -	$(call if_changed,vdso)
> -	$(call if_changed,vdso_check)
> +	$(call if_changed,vdso_and_check)
>  
>  HOST_EXTRACFLAGS += -I$(srctree)/tools/include -I$(srctree)/include/uapi -I$(srctree)/arch/$(SUBARCH)/include/uapi
>  hostprogs-y			+= vdso2c
> @@ -127,8 +126,7 @@ $(obj)/%.so: $(obj)/%.so.dbg FORCE
>  	$(call if_changed,objcopy)
>  
>  $(obj)/vdsox32.so.dbg: $(obj)/vdsox32.lds $(vobjx32s) FORCE
> -	$(call if_changed,vdso)
> -	$(call if_changed,vdso_check)
> +	$(call if_changed,vdso_and_check)
>  
>  CPPFLAGS_vdso32.lds = $(CPPFLAGS_vdso.lds)
>  VDSO_LDFLAGS_vdso32.lds = -m elf_i386 -soname linux-gate.so.1
> @@ -167,8 +165,7 @@ $(obj)/vdso32.so.dbg: FORCE \
>  		      $(obj)/vdso32/note.o \
>  		      $(obj)/vdso32/system_call.o \
>  		      $(obj)/vdso32/sigreturn.o
> -	$(call if_changed,vdso)
> -	$(call if_changed,vdso_check)
> +	$(call if_changed,vdso_and_check)
>  
>  #
>  # The DSO images are built using a special linker script.
> @@ -184,6 +181,9 @@ VDSO_LDFLAGS = -shared $(call ld-option, --hash-style=both) \
>  	-Bsymbolic
>  GCOV_PROFILE := n
>  
> +quiet_cmd_vdso_and_check = VDSO    $@
> +      cmd_vdso_and_check = $(cmd_vdso); $(cmd_vdso_check)
> +
>  #
>  # Install the unstripped copies of vdso*.so.  If our toolchain supports
>  # build-id, install .build-id links as well.
> 

-- 
Regards,
Vincenzo