linux-kernel - Re: [PATCH] ARM: pass -msoft-float to gcc earlier

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Message-ID: <CAKwvOdmH6bMJHzxSs2mVN=P5BBYjYrDs13-oq-Qq+S4ykHSYvA@mail.gmail.com>
Date:   Tue, 19 May 2020 17:37:37 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Russell King <linux@...linux.org.uk>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: pass -msoft-float to gcc earlier

On Tue, May 19, 2020 at 3:09 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> Szabolcs Nagy ran into a kernel build failure with a custom gcc
> toochain that sets -mfpu=auto -mfloat-abi=hard:
>
>  /tmp/ccmNdcdf.s:1898: Error: selected processor does not support `cpsid i' in ARM mode
>
> The problem is that $(call cc-option, -march=armv7-a) fails before the
> kernel overrides the gcc options to also pass -msoft-float.

The call to `$(call cc-option, -march=armv7-a)

>
> Move the option to the beginning the Makefile, before we call

beginning of the

> cc-option for the first time.
>
> Reported-by: Szabolcs Nagy <szabolcs.nagy@....com>
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87302
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Moving this looks harmless enough, though it's not clear to me how the
failure you're describing would occur.  I don't see calls to as-instr
in arch/arm/Makefile.  Which object is being built before -msoft-float
is being set?

> ---
>  arch/arm/Makefile | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> index 7d5cd0f85461..e428ea6eb0fa 100644
> --- a/arch/arm/Makefile
> +++ b/arch/arm/Makefile
> @@ -16,6 +16,8 @@ LDFLAGS_vmlinux       += --be8
>  KBUILD_LDFLAGS_MODULE  += --be8
>  endif
>
> +KBUILD_CFLAGS  += -msoft-float
> +
>  ifeq ($(CONFIG_ARM_MODULE_PLTS),y)
>  KBUILD_LDS_MODULE      += $(srctree)/arch/arm/kernel/module.lds
>  endif
> @@ -135,7 +137,7 @@ AFLAGS_ISA  :=$(CFLAGS_ISA)
>  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_CFLAGS  +=$(CFLAGS_ABI) $(CFLAGS_ISA) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -Uarm
>  KBUILD_AFLAGS  +=$(CFLAGS_ABI) $(AFLAGS_ISA) $(arch-y) $(tune-y) -include asm/unified.h -msoft-float
>
>  CHECKFLAGS     += -D__arm__
> --
> 2.26.2
>


-- 
Thanks,
~Nick Desaulniers