[PATCH v3] powerpc/64: Option to use ELFv2 ABI for big-endian kernels

Michal Suchánek msuchanek at suse.de
Thu May 6 01:55:56 AEST 2021


On Wed, May 05, 2021 at 05:23:37PM +0200, Michal Suchánek wrote:
> Hello,
> 
> looks like the ABI flags are not correctly applied when cross-compiling.
> 
> While building natively success of BTFIDS depends on the kernel ABI but
> when cross-compiling success of BTFIDS depends on the default toolchain
> ABI.
> 
> It's problem independent of this patch - the problem exists both before
> and after.

Actually this is not the case. Now retested with LE toolchain and BTFIDS
fails on BE v2 kernel with either one but earlier the default LE
toolchain produced BTFIDS on BE v1 kernel.

No idea what is going on except the general issue that success/failure
of BTFIDS when cross-compiling ppc64 is not representative of
success/failure when building natively. Don't even want to know what
would happen if I tried to link a BPF program with the kernel code using
that info.

Thanks

Michal

> 
> Thanks
> 
> Michal
> 
> On Mon, May 03, 2021 at 09:07:13PM +1000, Nicholas Piggin wrote:
> > Provide an option to build big-endian kernels using the ELFv2 ABI. This
> > works on GCC only so far, although it is rumored to work with clang
> > that's not been tested yet.
> > 
> > This can give big-endian kernels some useful advantages of the ELFv2 ABI
> > (e.g., less stack usage, -mprofile-kernel, better compatibility with bpf
> > tools).
> > 
> > BE+ELFv2 is not officially supported by the GNU toolchain, but it works
> > fine in testing and has been used by some userspace for some time (e.g.,
> > Void Linux).
> > 
> > Tested-by: Michal Suchánek <msuchanek at suse.de>
> > Reviewed-by: Segher Boessenkool <segher at kernel.crashing.org>
> > Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> > ---
> > 
> > I didn't add the -mprofile-kernel change but I think it would be a good
> > one that can be merged independently if it works.
> > 
> > Since v2:
> > - Rebased, tweaked changelog.
> > - Changed ELF_V2 to ELF_V2_ABI in config options, to be clearer.
> > 
> > Since v1:
> > - Improved the override flavour name suggested by Segher.
> > - Improved changelog wording.
> > 
> >  arch/powerpc/Kconfig                | 22 ++++++++++++++++++++++
> >  arch/powerpc/Makefile               | 18 ++++++++++++------
> >  arch/powerpc/boot/Makefile          |  4 +++-
> >  arch/powerpc/kernel/vdso64/Makefile | 13 +++++++++++++
> >  drivers/crypto/vmx/Makefile         |  8 ++++++--
> >  drivers/crypto/vmx/ppc-xlate.pl     | 10 ++++++----
> >  6 files changed, 62 insertions(+), 13 deletions(-)
> > 
> > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > index 1e6230bea09d..d3f78d3d574d 100644
> > --- a/arch/powerpc/Kconfig
> > +++ b/arch/powerpc/Kconfig
> > @@ -160,6 +160,7 @@ config PPC
> >  	select ARCH_WEAK_RELEASE_ACQUIRE
> >  	select BINFMT_ELF
> >  	select BUILDTIME_TABLE_SORT
> > +	select PPC64_BUILD_ELF_V2_ABI		if PPC64 && CPU_LITTLE_ENDIAN
> >  	select CLONE_BACKWARDS
> >  	select DCACHE_WORD_ACCESS		if PPC64 && CPU_LITTLE_ENDIAN
> >  	select DMA_OPS				if PPC64
> > @@ -568,6 +569,27 @@ config KEXEC_FILE
> >  config ARCH_HAS_KEXEC_PURGATORY
> >  	def_bool KEXEC_FILE
> >  
> > +config PPC64_BUILD_ELF_V2_ABI
> > +	bool
> > +
> > +config PPC64_BUILD_BIG_ENDIAN_ELF_V2_ABI
> > +	bool "Build big-endian kernel using ELF ABI V2 (EXPERIMENTAL)"
> > +	depends on PPC64 && CPU_BIG_ENDIAN && EXPERT
> > +	depends on CC_IS_GCC && LD_VERSION >= 22400
> > +	default n
> > +	select PPC64_BUILD_ELF_V2_ABI
> > +	help
> > +	  This builds the kernel image using the "Power Architecture 64-Bit ELF
> > +	  V2 ABI Specification", which has a reduced stack overhead and faster
> > +	  function calls. This internal kernel ABI option does not affect
> > +          userspace compatibility.
> > +
> > +	  The V2 ABI is standard for 64-bit little-endian, but for big-endian
> > +	  it is less well tested by kernel and toolchain. However some distros
> > +	  build userspace this way, and it can produce a functioning kernel.
> > +
> > +	  This requires GCC and binutils 2.24 or newer.
> > +
> >  config RELOCATABLE
> >  	bool "Build a relocatable kernel"
> >  	depends on PPC64 || (FLATMEM && (44x || FSL_BOOKE))
> > diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> > index 3212d076ac6a..b90b5cb799aa 100644
> > --- a/arch/powerpc/Makefile
> > +++ b/arch/powerpc/Makefile
> > @@ -91,10 +91,14 @@ endif
> >  
> >  ifdef CONFIG_PPC64
> >  ifndef CONFIG_CC_IS_CLANG
> > -cflags-$(CONFIG_CPU_BIG_ENDIAN)		+= $(call cc-option,-mabi=elfv1)
> > -cflags-$(CONFIG_CPU_BIG_ENDIAN)		+= $(call cc-option,-mcall-aixdesc)
> > -aflags-$(CONFIG_CPU_BIG_ENDIAN)		+= $(call cc-option,-mabi=elfv1)
> > -aflags-$(CONFIG_CPU_LITTLE_ENDIAN)	+= -mabi=elfv2
> > +ifdef CONFIG_PPC64_BUILD_ELF_V2_ABI
> > +cflags-y				+= $(call cc-option,-mabi=elfv2)
> > +aflags-y				+= $(call cc-option,-mabi=elfv2)
> > +else
> > +cflags-y				+= $(call cc-option,-mabi=elfv1)
> > +cflags-y				+= $(call cc-option,-mcall-aixdesc)
> > +aflags-y				+= $(call cc-option,-mabi=elfv1)
> > +endif
> >  endif
> >  endif
> >  
> > @@ -142,15 +146,17 @@ endif
> >  
> >  CFLAGS-$(CONFIG_PPC64)	:= $(call cc-option,-mtraceback=no)
> >  ifndef CONFIG_CC_IS_CLANG
> > -ifdef CONFIG_CPU_LITTLE_ENDIAN
> > -CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mabi=elfv2,$(call cc-option,-mcall-aixdesc))
> > +ifdef CONFIG_PPC64_BUILD_ELF_V2_ABI
> > +CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mabi=elfv2)
> >  AFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mabi=elfv2)
> >  else
> > +# Keep these in synch with arch/powerpc/kernel/vdso64/Makefile
> >  CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mabi=elfv1)
> >  CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mcall-aixdesc)
> >  AFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mabi=elfv1)
> >  endif
> >  endif
> > +
> >  CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mcmodel=medium,$(call cc-option,-mminimal-toc))
> >  CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mno-pointers-to-nested-functions)
> >  
> > diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
> > index 2b8da923ceca..be84a72f8258 100644
> > --- a/arch/powerpc/boot/Makefile
> > +++ b/arch/powerpc/boot/Makefile
> > @@ -40,6 +40,9 @@ BOOTCFLAGS    := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
> >  
> >  ifdef CONFIG_PPC64_BOOT_WRAPPER
> >  BOOTCFLAGS	+= -m64
> > +ifdef CONFIG_PPC64_BUILD_ELF_V2_ABI
> > +BOOTCFLAGS	+= $(call cc-option,-mabi=elfv2)
> > +endif
> >  else
> >  BOOTCFLAGS	+= -m32
> >  endif
> > @@ -50,7 +53,6 @@ ifdef CONFIG_CPU_BIG_ENDIAN
> >  BOOTCFLAGS	+= -mbig-endian
> >  else
> >  BOOTCFLAGS	+= -mlittle-endian
> > -BOOTCFLAGS	+= $(call cc-option,-mabi=elfv2)
> >  endif
> >  
> >  BOOTAFLAGS	:= -D__ASSEMBLY__ $(BOOTCFLAGS) -nostdinc
> > diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
> > index 2813e3f98db6..d783c07e558f 100644
> > --- a/arch/powerpc/kernel/vdso64/Makefile
> > +++ b/arch/powerpc/kernel/vdso64/Makefile
> > @@ -25,6 +25,19 @@ KCOV_INSTRUMENT := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> >  
> > +# Always build vdso64 with ELFv1 ABI for BE kernels
> > +ifdef CONFIG_PPC64_BUILD_ELF_V2_ABI
> > +ifdef CONFIG_CPU_BIG_ENDIAN
> > +KBUILD_CFLAGS := $(filter-out -mabi=elfv2,$(KBUILD_CFLAGS))
> > +KBUILD_AFLAGS := $(filter-out -mabi=elfv2,$(KBUILD_AFLAGS))
> > +
> > +# These are derived from arch/powerpc/Makefile
> > +KBUILD_CFLAGS += $(call cc-option,-mabi=elfv1)
> > +KBUILD_CFLAGS += $(call cc-option,-mcall-aixdesc)
> > +KBUILD_AFLAGS += $(call cc-option,-mabi=elfv1)
> > +endif
> > +endif
> > +
> >  ccflags-y := -shared -fno-common -fno-builtin -nostdlib \
> >  	-Wl,-soname=linux-vdso64.so.1 -Wl,--hash-style=both
> >  asflags-y := -D__VDSO64__ -s
> > diff --git a/drivers/crypto/vmx/Makefile b/drivers/crypto/vmx/Makefile
> > index 709670d2b553..d9ccf9fc3483 100644
> > --- a/drivers/crypto/vmx/Makefile
> > +++ b/drivers/crypto/vmx/Makefile
> > @@ -5,18 +5,22 @@ vmx-crypto-objs := vmx.o aesp8-ppc.o ghashp8-ppc.o aes.o aes_cbc.o aes_ctr.o aes
> >  ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),y)
> >  override flavour := linux-ppc64le
> >  else
> > +ifdef CONFIG_PPC64_BUILD_ELF_V2_ABI
> > +override flavour := linux-ppc64-elfv2
> > +else
> >  override flavour := linux-ppc64
> >  endif
> > +endif
> >  
> >  quiet_cmd_perl = PERL $@
> >        cmd_perl = $(PERL) $(<) $(flavour) > $(@)
> >  
> >  targets += aesp8-ppc.S ghashp8-ppc.S
> >  
> > -$(obj)/aesp8-ppc.S: $(src)/aesp8-ppc.pl FORCE
> > +$(obj)/aesp8-ppc.S: $(src)/aesp8-ppc.pl $(src)/ppc-xlate.pl FORCE
> >  	$(call if_changed,perl)
> >    
> > -$(obj)/ghashp8-ppc.S: $(src)/ghashp8-ppc.pl FORCE
> > +$(obj)/ghashp8-ppc.S: $(src)/ghashp8-ppc.pl $(src)/ppc-xlate.pl FORCE
> >  	$(call if_changed,perl)
> >  
> >  clean-files := aesp8-ppc.S ghashp8-ppc.S
> > diff --git a/drivers/crypto/vmx/ppc-xlate.pl b/drivers/crypto/vmx/ppc-xlate.pl
> > index 36db2ef09e5b..b583898c11ae 100644
> > --- a/drivers/crypto/vmx/ppc-xlate.pl
> > +++ b/drivers/crypto/vmx/ppc-xlate.pl
> > @@ -9,6 +9,8 @@ open STDOUT,">$output" || die "can't open $output: $!";
> >  
> >  my %GLOBALS;
> >  my $dotinlocallabels=($flavour=~/linux/)?1:0;
> > +my $elfv2abi=(($flavour =~ /linux-ppc64le/) or ($flavour =~ /linux-ppc64-elfv2/))?1:0;
> > +my $dotfunctions=($elfv2abi=~1)?0:1;
> >  
> >  ################################################################
> >  # directives which need special treatment on different platforms
> > @@ -40,7 +42,7 @@ my $globl = sub {
> >  };
> >  my $text = sub {
> >      my $ret = ($flavour =~ /aix/) ? ".csect\t.text[PR],7" : ".text";
> > -    $ret = ".abiversion	2\n".$ret	if ($flavour =~ /linux.*64le/);
> > +    $ret = ".abiversion	2\n".$ret	if ($elfv2abi);
> >      $ret;
> >  };
> >  my $machine = sub {
> > @@ -56,8 +58,8 @@ my $size = sub {
> >      if ($flavour =~ /linux/)
> >      {	shift;
> >  	my $name = shift; $name =~ s|^[\.\_]||;
> > -	my $ret  = ".size	$name,.-".($flavour=~/64$/?".":"").$name;
> > -	$ret .= "\n.size	.$name,.-.$name" if ($flavour=~/64$/);
> > +	my $ret  = ".size	$name,.-".($dotfunctions?".":"").$name;
> > +	$ret .= "\n.size	.$name,.-.$name" if ($dotfunctions);
> >  	$ret;
> >      }
> >      else
> > @@ -142,7 +144,7 @@ my $vmr = sub {
> >  
> >  # Some ABIs specify vrsave, special-purpose register #256, as reserved
> >  # for system use.
> > -my $no_vrsave = ($flavour =~ /linux-ppc64le/);
> > +my $no_vrsave = ($elfv2abi);
> >  my $mtspr = sub {
> >      my ($f,$idx,$ra) = @_;
> >      if ($idx == 256 && $no_vrsave) {
> > -- 
> > 2.23.0
> > 


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