linux-kernel - Re: [PATCH v2] ARM: warn if pre-UAL assembler syntax is used

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Message-ID: <CAKwvOdkJLROtbMSf1pOV2XMV7LB0TTnLx-43WMt34wiT2VEMew@mail.gmail.com>
Date:   Mon, 30 Mar 2020 09:48:07 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Stefan Agner <stefan@...er.ch>
Cc:     Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Robin Murphy <robin.murphy@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Manoj Gupta <manojgupta@...gle.com>,
        Jian Cai <jiancai@...gle.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v2] ARM: warn if pre-UAL assembler syntax is used

On Sun, Mar 29, 2020 at 11:43 AM Stefan Agner <stefan@...er.ch> wrote:
>
> Remove the -mno-warn-deprecated assembler flag to make sure the GNU
> assembler warns in case non-unified syntax is used.
>
> This also prevents a warning when building with Clang and enabling its
> integrated assembler:
> clang-10: error: unsupported argument '-mno-warn-deprecated' to option 'Wa,'
>
> GCC before 5.1 emits pre-UAL assembler. This can lead to warnings if
> inline assembler explicitly switches to unified syntax by using the
> ".syntax unified" directive (e.g. arch/arm/include/asm/unified.h).
> Hence keep the flag for GCC versions before 5.1.
>
> This is a second attempt of commit e8c24bbda7d5 ("ARM: 8846/1: warn if
> divided syntax assembler is used") which has subsequently been reverted
> with commit b752bb405a13 ("Revert "ARM: 8846/1: warn if divided syntax
> assembler is used"").
>
> Signed-off-by: Stefan Agner <stefan@...er.ch>

Thanks for the added context.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
> Changes in v2:
> - Reference revert commit b752bb405a13 ("Revert "ARM: 8846/1: warn if
>   divided syntax assembler is used"")
> - Reword commit message
>
>  arch/arm/Makefile | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> index 1fc32b611f8a..b37bb985a3c2 100644
> --- a/arch/arm/Makefile
> +++ b/arch/arm/Makefile
> @@ -119,21 +119,25 @@ ifeq ($(CONFIG_CC_IS_CLANG),y)
>  CFLAGS_ABI     += -meabi gnu
>  endif
>
> -# Accept old syntax despite ".syntax unified"
> -AFLAGS_NOWARN  :=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)
> -
>  ifeq ($(CONFIG_THUMB2_KERNEL),y)
> -CFLAGS_ISA     :=-mthumb -Wa,-mimplicit-it=always $(AFLAGS_NOWARN)
> +CFLAGS_ISA     :=-mthumb -Wa,-mimplicit-it=always
>  AFLAGS_ISA     :=$(CFLAGS_ISA) -Wa$(comma)-mthumb
>  # Work around buggy relocation from gas if requested:
>  ifeq ($(CONFIG_THUMB2_AVOID_R_ARM_THM_JUMP11),y)
>  KBUILD_CFLAGS_MODULE   +=-fno-optimize-sibling-calls
>  endif
>  else
> -CFLAGS_ISA     :=$(call cc-option,-marm,) $(AFLAGS_NOWARN)
> +CFLAGS_ISA     :=$(call cc-option,-marm,)
>  AFLAGS_ISA     :=$(CFLAGS_ISA)
>  endif
>
> +ifeq ($(CONFIG_CC_IS_GCC),y)
> +ifeq ($(call cc-ifversion, -lt, 0501, y), y)
> +# GCC <5.1 emits pre-UAL code and causes assembler warnings, suppress them
> +CFLAGS_ISA     +=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)
> +endif
> +endif
> +
>  # Need -Uarm for gcc < 3.x
>  KBUILD_CFLAGS  +=$(CFLAGS_ABI) $(CFLAGS_ISA) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm
>  KBUILD_AFLAGS  +=$(CFLAGS_ABI) $(AFLAGS_ISA) $(arch-y) $(tune-y) -include asm/unified.h -msoft-float
> --
> 2.25.1
>


-- 
Thanks,
~Nick Desaulniers