Messages in this thread | | | Date | Tue, 17 Mar 2020 08:55:45 +0100 | From | Stefan Agner <> | Subject | Re: [PATCH] ARM: warn if pre-UAL assembler syntax is used |
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On 2020-03-17 01:00, Nick Desaulniers wrote: > Revert "ARM: 8846/1: warn if divided syntax assembler is used"On Thu, > Feb 27, 2020 at 4:19 PM Stefan Agner <stefan@agner.ch> wrote: >> >> Remove the -mno-warn-deprecated assembler flag for GCC versions newer >> than 5.1 to make sure the GNU assembler warns in case non-unified >> syntax is used. > > Hi Stefan, sorry for the late reply from me; digging out my backlog. > Do you happen to have a godbolt link perhaps that demonstrates this? > It sounds like GCC itself is emitting pre-UAL?
Yes, that is what Russell observed and caused the revert: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b752bb405a13
I do not have a godbolt link at hand, I just built the complete kernel using some GCC toolchains I had locally available and noticed that the problem persists up to and including GCC 5.0. I did not track down what exactly is causing GCC to emit pre-UAL.
> >> >> 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,' >> >> This is a second attempt of commit e8c24bbda7d5 ("ARM: 8846/1: warn if >> divided syntax assembler is used"). > > Would it be helpful to also make note of > commit b752bb405a13 ("Revert "ARM: 8846/1: warn if divided syntax > assembler is used"")?
Sure, I can do that.
> > >> >> Signed-off-by: Stefan Agner <stefan@agner.ch> >> --- >> arch/arm/Makefile | 14 +++++++++----- >> 1 file changed, 9 insertions(+), 5 deletions(-) >> >> diff --git a/arch/arm/Makefile b/arch/arm/Makefile >> index db857d07114f..a6c8c9f39185 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) > > This existing code is quite bad for Clang, which doesn't support > `-Wa,-mno-warn-deprecated`, so this falls back to `-Wa,-W`, which > disables all warnings from the assembler, which we definitely do not > want. That alone is worth putting in the GCC guard. But I would like > more info about GCC above before signing off.
FWIW, I submitted this to the patch tracker already, but I don't think it got merged already.
-- Stefan
> >> - >> 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 >> --
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