Message ID | 20241029-sparc-cflags-v3-1-b28745a6bd71@protonmail.com |
---|---|
State | New |
Headers | show |
Series | sparc/build: Rework CFLAGS for clang compatibility | expand |
On Tue, Oct 29, 2024 at 09:49:07PM +0700, Koakuma via B4 Relay wrote: > From: Koakuma <koachan@protonmail.com> > > Place -fcall-used* flags behind cc-option so that clang (which doesn't > support them) can still compile the kernel. > > This is a safe change, the reasoning is as follows: > > In the (normal) 32-bit ABI, %g5 and %g7 is normally reserved, and in > the 64-bit ABI, %g7 is the reserved one. > Linux turns them into volatile registers by the way of -fcall-used-*, > but on the other hand, omitting the flags shouldn't be harmful; > compilers will now simply refuse to touch them, and any assembly > code that happens to touch them would still work like usual (because > Linux' conventions already treats them as volatile anyway). > > Signed-off-by: Koakuma <koachan@protonmail.com> Clang builds now succeed with this series and builds with GCC 14.2.0 continue to pass and boot successfully. Reviewed-by: Nathan Chancellor <nathan@kernel.org> Tested-by: Nathan Chancellor <nathan@kernel.org> One comment below, please carry these tags forward if there are future revisions without substantial technical changes. > --- > arch/sparc/Makefile | 4 ++-- > arch/sparc/vdso/Makefile | 2 +- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/sparc/Makefile b/arch/sparc/Makefile > index 757451c3ea1df63b948e68a45988c78f5974f9ea..0400078076e588be93a702d1c64eb9fd34466075 100644 > --- a/arch/sparc/Makefile > +++ b/arch/sparc/Makefile > @@ -29,7 +29,7 @@ UTS_MACHINE := sparc > # versions of gcc. Some gcc versions won't pass -Av8 to binutils when you > # give -mcpu=v8. This silently worked with older bintutils versions but > # does not any more. > -KBUILD_CFLAGS += -m32 -mcpu=v8 -pipe -mno-fpu -fcall-used-g5 -fcall-used-g7 > +KBUILD_CFLAGS += -m32 -mcpu=v8 -pipe -mno-fpu $(call cc-option,-fcall-used-g5) $(call cc-option,-fcall-used-g7) Small nit, this (and the one in the vdso) could probably be one cc-option call? Is it likely that one flag would be implemented in the compiler without the other? $(call cc-option,-fcall-used-g5 -fcall-used-g7) > KBUILD_CFLAGS += -Wa,-Av8 > > KBUILD_AFLAGS += -m32 -Wa,-Av8 > @@ -45,7 +45,7 @@ export BITS := 64 > UTS_MACHINE := sparc64 > > KBUILD_CFLAGS += -m64 -pipe -mno-fpu -mcpu=ultrasparc -mcmodel=medlow > -KBUILD_CFLAGS += -ffixed-g4 -ffixed-g5 -fcall-used-g7 -Wno-sign-compare > +KBUILD_CFLAGS += -ffixed-g4 -ffixed-g5 $(call cc-option,-fcall-used-g7) -Wno-sign-compare > KBUILD_CFLAGS += -Wa,--undeclared-regs > KBUILD_CFLAGS += $(call cc-option,-mtune=ultrasparc3) > KBUILD_AFLAGS += -m64 -mcpu=ultrasparc -Wa,--undeclared-regs > diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile > index 243dbfc4609d804fc221c3591eebe891107ffdab..50ec2978cda5397841daad6ffdc9682811b9b38e 100644 > --- a/arch/sparc/vdso/Makefile > +++ b/arch/sparc/vdso/Makefile > @@ -46,7 +46,7 @@ CFL := $(PROFILING) -mcmodel=medlow -fPIC -O2 -fasynchronous-unwind-tables -m64 > -fno-omit-frame-pointer -foptimize-sibling-calls \ > -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO > > -SPARC_REG_CFLAGS = -ffixed-g4 -ffixed-g5 -fcall-used-g5 -fcall-used-g7 > +SPARC_REG_CFLAGS = -ffixed-g4 -ffixed-g5 $(call cc-option,-fcall-used-g5) $(call cc-option,-fcall-used-g7) > > $(vobjs): KBUILD_CFLAGS := $(filter-out $(RANDSTRUCT_CFLAGS) $(GCC_PLUGINS_CFLAGS) $(SPARC_REG_CFLAGS),$(KBUILD_CFLAGS)) $(CFL) > > > -- > 2.47.0 > > >
Nathan Chancellor <nathan@kernel.org> wrote: > > Clang builds now succeed with this series and builds with GCC 14.2.0 > continue to pass and boot successfully. > > Reviewed-by: Nathan Chancellor nathan@kernel.org > > Tested-by: Nathan Chancellor nathan@kernel.org > > One comment below, please carry these tags forward if there are future > revisions without substantial technical changes. Forgive me for still being unfamiliar with the term, but does this mean that when I send a v4 I should paste the Reviewed-by and Tested-by lines into the commit message of the patch? > > -KBUILD_CFLAGS += -m32 -mcpu=v8 -pipe -mno-fpu -fcall-used-g5 -fcall-used-g7 > > +KBUILD_CFLAGS += -m32 -mcpu=v8 -pipe -mno-fpu $(call cc-option,-fcall-used-g5) $(call cc-option,-fcall-used-g7) > > > Small nit, this (and the one in the vdso) could probably be one > cc-option call? Is it likely that one flag would be implemented in the > compiler without the other? > > $(call cc-option,-fcall-used-g5 -fcall-used-g7) Ah, didn't know it's possible to do that, the other uses of it I see seem to use one flag per call. I'll test and send a new revision, thanks.
On Thu, Nov 07, 2024 at 04:59:14AM +0000, Koakuma wrote: > Nathan Chancellor <nathan@kernel.org> wrote: > > > > Clang builds now succeed with this series and builds with GCC 14.2.0 > > continue to pass and boot successfully. > > > > Reviewed-by: Nathan Chancellor nathan@kernel.org > > > > Tested-by: Nathan Chancellor nathan@kernel.org > > > > One comment below, please carry these tags forward if there are future > > revisions without substantial technical changes. > > Forgive me for still being unfamiliar with the term, but does this mean that No worries, it is definitely a customary thing. > when I send a v4 I should paste the Reviewed-by and Tested-by lines into the > commit message of the patch? Yes, you should add them either right above or right below your signoff. It is up to the submitter to add tags that have been sent on prior revisions when sending an updated version, assuming that there has not been a reason to drop them, such as substantial changes from a prior version that might require a new review or testing. In that case, I typically add a note in the changelog as to why I did not carry them forward. The tip documentation 4.2.3 through 4.2.6 has some good information about some other Linux kernel commit message expectations if you find yourself submitting more patches in the future: https://docs.kernel.org/process/maintainer-tip.html#changelog > > > -KBUILD_CFLAGS += -m32 -mcpu=v8 -pipe -mno-fpu -fcall-used-g5 -fcall-used-g7 > > > +KBUILD_CFLAGS += -m32 -mcpu=v8 -pipe -mno-fpu $(call cc-option,-fcall-used-g5) $(call cc-option,-fcall-used-g7) > > > > > > Small nit, this (and the one in the vdso) could probably be one > > cc-option call? Is it likely that one flag would be implemented in the > > compiler without the other? > > > > $(call cc-option,-fcall-used-g5 -fcall-used-g7) > > Ah, didn't know it's possible to do that, the other uses of it I see seem > to use one flag per call. I'll test and send a new revision, thanks. Yeah, I would agree that it is typical to use cc-option for one flag at a time but the entire string just gets passed to $(CC), so there is technically no limitation for how many flags can be tested. This happens to be a rare instance where the flags share a common internal compiler implementation so we know that one cannot be implemented without the other. Cheers, Nathan
diff --git a/arch/sparc/Makefile b/arch/sparc/Makefile index 757451c3ea1df63b948e68a45988c78f5974f9ea..0400078076e588be93a702d1c64eb9fd34466075 100644 --- a/arch/sparc/Makefile +++ b/arch/sparc/Makefile @@ -29,7 +29,7 @@ UTS_MACHINE := sparc # versions of gcc. Some gcc versions won't pass -Av8 to binutils when you # give -mcpu=v8. This silently worked with older bintutils versions but # does not any more. -KBUILD_CFLAGS += -m32 -mcpu=v8 -pipe -mno-fpu -fcall-used-g5 -fcall-used-g7 +KBUILD_CFLAGS += -m32 -mcpu=v8 -pipe -mno-fpu $(call cc-option,-fcall-used-g5) $(call cc-option,-fcall-used-g7) KBUILD_CFLAGS += -Wa,-Av8 KBUILD_AFLAGS += -m32 -Wa,-Av8 @@ -45,7 +45,7 @@ export BITS := 64 UTS_MACHINE := sparc64 KBUILD_CFLAGS += -m64 -pipe -mno-fpu -mcpu=ultrasparc -mcmodel=medlow -KBUILD_CFLAGS += -ffixed-g4 -ffixed-g5 -fcall-used-g7 -Wno-sign-compare +KBUILD_CFLAGS += -ffixed-g4 -ffixed-g5 $(call cc-option,-fcall-used-g7) -Wno-sign-compare KBUILD_CFLAGS += -Wa,--undeclared-regs KBUILD_CFLAGS += $(call cc-option,-mtune=ultrasparc3) KBUILD_AFLAGS += -m64 -mcpu=ultrasparc -Wa,--undeclared-regs diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile index 243dbfc4609d804fc221c3591eebe891107ffdab..50ec2978cda5397841daad6ffdc9682811b9b38e 100644 --- a/arch/sparc/vdso/Makefile +++ b/arch/sparc/vdso/Makefile @@ -46,7 +46,7 @@ CFL := $(PROFILING) -mcmodel=medlow -fPIC -O2 -fasynchronous-unwind-tables -m64 -fno-omit-frame-pointer -foptimize-sibling-calls \ -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO -SPARC_REG_CFLAGS = -ffixed-g4 -ffixed-g5 -fcall-used-g5 -fcall-used-g7 +SPARC_REG_CFLAGS = -ffixed-g4 -ffixed-g5 $(call cc-option,-fcall-used-g5) $(call cc-option,-fcall-used-g7) $(vobjs): KBUILD_CFLAGS := $(filter-out $(RANDSTRUCT_CFLAGS) $(GCC_PLUGINS_CFLAGS) $(SPARC_REG_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)