| Message ID | cd74f11eaee5d8fe3599280eb1e3812ce577c835.1582849064.git.stefan@agner.ch (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | ARM: warn if pre-UAL assembler syntax is used | expand |
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? > > 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"")? > > 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. > - > 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) $(tune-y) -include asm/unified.h -msoft-float > --
On 2020-03-17 01:00, Nick Desaulniers wrote: > Revert "ARM: 8846/1: warn if divided syntax assembler is used"On Thu, > Feb 27, 2020 at 4:19 PM Stefan Agner <stefan@agner.ch> wrote: >> >> Remove the -mno-warn-deprecated assembler flag for GCC versions newer >> than 5.1 to make sure the GNU assembler warns in case non-unified >> syntax is used. > > Hi Stefan, sorry for the late reply from me; digging out my backlog. > Do you happen to have a godbolt link perhaps that demonstrates this? > It sounds like GCC itself is emitting pre-UAL? Yes, that is what Russell observed and caused the revert: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b752bb405a13 I do not have a godbolt link at hand, I just built the complete kernel using some GCC toolchains I had locally available and noticed that the problem persists up to and including GCC 5.0. I did not track down what exactly is causing GCC to emit pre-UAL. > >> >> This also prevents a warning when building with Clang and enabling >> its integrated assembler: >> clang-10: error: unsupported argument '-mno-warn-deprecated' to option 'Wa,' >> >> This is a second attempt of commit e8c24bbda7d5 ("ARM: 8846/1: warn if >> divided syntax assembler is used"). > > Would it be helpful to also make note of > commit b752bb405a13 ("Revert "ARM: 8846/1: warn if divided syntax > assembler is used"")? Sure, I can do that. > > >> >> Signed-off-by: Stefan Agner <stefan@agner.ch> >> --- >> arch/arm/Makefile | 14 +++++++++----- >> 1 file changed, 9 insertions(+), 5 deletions(-) >> >> diff --git a/arch/arm/Makefile b/arch/arm/Makefile >> index db857d07114f..a6c8c9f39185 100644 >> --- a/arch/arm/Makefile >> +++ b/arch/arm/Makefile >> @@ -119,21 +119,25 @@ ifeq ($(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 >> --
On 2020-03-17 08:55, Stefan Agner wrote: > 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. Godbolt link: https://godbolt.org/z/fxYq_s However, the warning does not appear on godbolt.org, presumably because the compiler is started such that it does not invoke the assembler (at least that is what I understand when using -v). However, on my end this leads to: $ arm-linux-gnueabihf-gcc -marm -march=armv7-a -O2 -c test.c -o test --save-temps test.s: Assembler messages: test.s:33: Warning: conditional infixes are deprecated in unified syntax $ arm-linux-gnueabihf-gcc --version arm-linux-gnueabihf-gcc (Linaro GCC 4.9-2016.02) 4.9.4 20151028 (prerelease) And line 33 contains a non-unified assembler mnemonic: strneb r2, [r3] Note: I do have to explicitly use .syntax unified. It seems that gcc is not explicitly doing this, but if any inline assembly is changing the assembler mode (e.g. what including arch/arm/include/asm/unified.h is doing) then the assembler warnings start to appear. -- Stefan > >> >>> >>> 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) $(tune-y) -include asm/unified.h -msoft-float >>> --
diff --git a/arch/arm/Makefile b/arch/arm/Makefile index db857d07114f..a6c8c9f39185 100644 --- a/arch/arm/Makefile +++ b/arch/arm/Makefile @@ -119,21 +119,25 @@ ifeq ($(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$(comma)-W) - ifeq ($(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
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. 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"). Signed-off-by: Stefan Agner <stefan@agner.ch> --- arch/arm/Makefile | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)