Re: [PATCH kernel v2] powerpc/makefile: Do not redefine $(CPP) for preprocessor

[Alexey Kardashevskiy]

On 5/12/21 05:18, Nathan Chancellor wrote:
> On 5/10/2021 9:48 PM, Alexey Kardashevskiy wrote:
> > The $(CPP) (do only preprocessing) macro is already defined in Makefile.
> > However POWERPC redefines it and adds $(KBUILD_CFLAGS) which results
> > in flags duplication. Which is not a big deal by itself except for
> > the flags which depend on other flags and the compiler checks them
> > as it parses the command line.
> >
> > Specifically, scripts/Makefile.build:304 generates ksyms for .S files.
> > If clang+llvm+sanitizer are enabled, this results in
> >
> > -emit-llvm-bc -fno-lto -flto -fvisibility=hidden \
> >   -fsanitize=cfi-mfcall -fno-lto  ...
> >
> > in the clang command line and triggers error:
> >
> > clang-13: error: invalid argument '-fsanitize=cfi-mfcall' only allowed 
> > with '-flto'
> >
> > This removes unnecessary CPP redefinition. Which works fine as in most
> > place KBUILD_CFLAGS is passed to $CPP except
> > arch/powerpc/kernel/vdso64/vdso(32|64).lds (and probably some others,
> > not yet detected). To fix vdso, we do:
> > 1. explicitly add -m(big|little)-endian to $CPP
> > 2. (for clang) add $CLANG_FLAGS to $KBUILD_CPPFLAGS as otherwise clang
> > silently ignores -m(big|little)-endian if the building platform does not
> > support big endian (such as x86) so --prefix= is required.
> >
> > While at this, remove some duplication from CPPFLAGS_vdso(32|64)
> > as cmd_cpp_lds_S has them anyway. It still puzzles me why we need -C
> > (preserve comments in the preprocessor output) flag here.
> >
> > Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
> > ---
> > Changes:
> > v2:
> > * fix KBUILD_CPPFLAGS
> > * add CLANG_FLAGS to CPPFLAGS
> > ---
> >   Makefile                            | 1 +
> >   arch/powerpc/Makefile               | 3 ++-
> >   arch/powerpc/kernel/vdso32/Makefile | 2 +-
> >   arch/powerpc/kernel/vdso64/Makefile | 2 +-
> >   4 files changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 72af8e423f11..13acd2183d55 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -591,6 +591,7 @@ CLANG_FLAGS    += 
> > --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
> >   endif
> >   CLANG_FLAGS    += -Werror=unknown-warning-option
> >   KBUILD_CFLAGS    += $(CLANG_FLAGS)
> > +KBUILD_CPPFLAGS    += $(CLANG_FLAGS)
>
> This is going to cause flag duplication, which would be nice to avoid. I 
> do not know if we can get away with just adding $(CLANG_FLAGS) to 
> KBUILD_CPPFLAGS instead of KBUILD_CFLAGS though. It seems like this 
> assignment might be better in arch/powerpc/Makefile with the 
> KBUILD_CPPFLAGS additions there.


It is a fair point about the duplication (which is woooow, I often see 
-mbig-endian 3 - three - times) and I think I only need --prefix= there 
but this is still exactly the place to do such thing as it potentially 
affects all archs supporting both endianness (not many though, yeah). 
Thanks,




> Cheers,
> Nathan
>
> >   KBUILD_AFLAGS    += $(CLANG_FLAGS)
> >   export CLANG_FLAGS
> >   endif
> > diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> > index 3212d076ac6a..306bfd2797ad 100644
> > --- a/arch/powerpc/Makefile
> > +++ b/arch/powerpc/Makefile
> > @@ -76,6 +76,7 @@ endif
> >   ifdef CONFIG_CPU_LITTLE_ENDIAN
> >   KBUILD_CFLAGS    += -mlittle-endian
> > +KBUILD_CPPFLAGS    += -mlittle-endian
> >   KBUILD_LDFLAGS    += -EL
> >   LDEMULATION    := lppc
> >   GNUTARGET    := powerpcle
> > @@ -83,6 +84,7 @@ MULTIPLEWORD    := -mno-multiple
> >   KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-save-toc-indirect)
> >   else
> >   KBUILD_CFLAGS += $(call cc-option,-mbig-endian)
> > +KBUILD_CPPFLAGS += $(call cc-option,-mbig-endian)
> >   KBUILD_LDFLAGS    += -EB
> >   LDEMULATION    := ppc
> >   GNUTARGET    := powerpc
> > @@ -208,7 +210,6 @@ KBUILD_CPPFLAGS    += -I $(srctree)/arch/$(ARCH) 
> > $(asinstr)
> >   KBUILD_AFLAGS    += $(AFLAGS-y)
> >   KBUILD_CFLAGS    += $(call cc-option,-msoft-float)
> >   KBUILD_CFLAGS    += -pipe $(CFLAGS-y)
> > -CPP        = $(CC) -E $(KBUILD_CFLAGS)
> >   CHECKFLAGS    += -m$(BITS) -D__powerpc__ -D__powerpc$(BITS)__
> >   ifdef CONFIG_CPU_BIG_ENDIAN
> > diff --git a/arch/powerpc/kernel/vdso32/Makefile 
> > b/arch/powerpc/kernel/vdso32/Makefile
> > index 7d9a6fee0e3d..ea001c6df1fa 100644
> > --- a/arch/powerpc/kernel/vdso32/Makefile
> > +++ b/arch/powerpc/kernel/vdso32/Makefile
> > @@ -44,7 +44,7 @@ asflags-y := -D__VDSO32__ -s
> >   obj-y += vdso32_wrapper.o
> >   targets += vdso32.lds
> > -CPPFLAGS_vdso32.lds += -P -C -Upowerpc
> > +CPPFLAGS_vdso32.lds += -C
> >   # link rule for the .so file, .lds has to be first
> >   $(obj)/vdso32.so.dbg: $(src)/vdso32.lds $(obj-vdso32) 
> > $(obj)/vgettimeofday.o FORCE
> > diff --git a/arch/powerpc/kernel/vdso64/Makefile 
> > b/arch/powerpc/kernel/vdso64/Makefile
> > index 2813e3f98db6..07eadba48c7a 100644
> > --- a/arch/powerpc/kernel/vdso64/Makefile
> > +++ b/arch/powerpc/kernel/vdso64/Makefile
> > @@ -30,7 +30,7 @@ ccflags-y := -shared -fno-common -fno-builtin 
> > -nostdlib \
> >   asflags-y := -D__VDSO64__ -s
> >   targets += vdso64.lds
> > -CPPFLAGS_vdso64.lds += -P -C -U$(ARCH)
> > +CPPFLAGS_vdso64.lds += -C
> >   # link rule for the .so file, .lds has to be first
> >   $(obj)/vdso64.so.dbg: $(src)/vdso64.lds $(obj-vdso64) 
> > $(obj)/vgettimeofday.o FORCE

--
Alexey