[PATCH v2] powerpc/64: BE option to use ELFv2 ABI for big endian kernels
Nicholas Piggin
npiggin at gmail.com
Tue Apr 28 21:25:17 AEST 2020
Provide an option to use ELFv2 ABI for big endian builds. This works on
GCC and clang (since 2014). It is less well tested and supported by the
GNU toolchain, but it can give some useful advantages of the ELFv2 ABI
for BE (e.g., less stack usage). Some distros even build BE ELFv2
userspace.
Reviewed-by: Segher Boessenkool <segher at kernel.crashing.org>
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
Since v1:
- Improved the override flavour name suggested by Segher.
- Improved changelog wording.
arch/powerpc/Kconfig | 19 +++++++++++++++++++
arch/powerpc/Makefile | 15 ++++++++++-----
arch/powerpc/boot/Makefile | 4 ++++
drivers/crypto/vmx/Makefile | 8 ++++++--
drivers/crypto/vmx/ppc-xlate.pl | 10 ++++++----
5 files changed, 45 insertions(+), 11 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 924c541a9260..d9d2abc06c2c 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -147,6 +147,7 @@ config PPC
select ARCH_WEAK_RELEASE_ACQUIRE
select BINFMT_ELF
select BUILDTIME_TABLE_SORT
+ select BUILD_ELF_V2 if PPC64 && CPU_LITTLE_ENDIAN
select CLONE_BACKWARDS
select DCACHE_WORD_ACCESS if PPC64 && CPU_LITTLE_ENDIAN
select DYNAMIC_FTRACE if FUNCTION_TRACER
@@ -541,6 +542,24 @@ config KEXEC_FILE
config ARCH_HAS_KEXEC_PURGATORY
def_bool KEXEC_FILE
+config BUILD_ELF_V2
+ bool
+
+config BUILD_BIG_ENDIAN_ELF_V2
+ bool "Build big-endian kernel using ELFv2 ABI (EXPERIMENTAL)"
+ depends on PPC64 && CPU_BIG_ENDIAN && EXPERT
+ default n
+ select BUILD_ELF_V2
+ help
+ This builds the kernel image using the ELFv2 ABI, which has a
+ reduced stack overhead and faster function calls. This does not
+ affect the userspace ABIs.
+
+ ELFv2 is the standard ABI for little-endian, but for big-endian
+ this is an experimental option that is less tested (kernel and
+ toolchain). This requires gcc 4.9 or newer 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 f310c32e88a4..e306b39d847e 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -92,10 +92,14 @@ 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_BUILD_ELF_V2
+cflags-y += $(call cc-option,-mabi=elfv2,$(call cc-option,-mcall-aixdesc))
+aflags-y += $(call cc-option,-mabi=elfv2)
+else
+cflags-y += $(call cc-option,-mabi=elfv1)
+cflags-y += $(call cc-option,-mcall-aixdesc)
+aflags-y += $(call cc-option,-mabi=elfv1)
+endif
endif
endif
@@ -144,7 +148,7 @@ endif
CFLAGS-$(CONFIG_PPC64) := $(call cc-option,-mtraceback=no)
ifndef CONFIG_CC_IS_CLANG
-ifdef CONFIG_CPU_LITTLE_ENDIAN
+ifdef CONFIG_BUILD_ELF_V2
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv2,$(call cc-option,-mcall-aixdesc))
AFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv2)
else
@@ -153,6 +157,7 @@ CFLAGS-$(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 c53a1b8bba8b..03942d08695d 100644
--- a/arch/powerpc/boot/Makefile
+++ b/arch/powerpc/boot/Makefile
@@ -41,6 +41,10 @@ endif
BOOTCFLAGS += -isystem $(shell $(BOOTCC) -print-file-name=include)
+ifdef CONFIG_BUILD_ELF_V2
+BOOTCFLAGS += $(call cc-option,-mabi=elfv2)
+endif
+
ifdef CONFIG_CPU_BIG_ENDIAN
BOOTCFLAGS += -mbig-endian
else
diff --git a/drivers/crypto/vmx/Makefile b/drivers/crypto/vmx/Makefile
index 709670d2b553..9aea34602beb 100644
--- a/drivers/crypto/vmx/Makefile
+++ b/drivers/crypto/vmx/Makefile
@@ -5,18 +5,22 @@ vmx-crypto-objs := vmx.o aesp8-ppc.o ghashp8-ppc.o aes.o aes_cbc.o aes_ctr.o aes
ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),y)
override flavour := linux-ppc64le
else
+ifdef CONFIG_BUILD_ELF_V2
+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
$(call if_changed,perl)
clean-files := aesp8-ppc.S ghashp8-ppc.S
diff --git a/drivers/crypto/vmx/ppc-xlate.pl b/drivers/crypto/vmx/ppc-xlate.pl
index 36db2ef09e5b..9db0937d318b 100644
--- a/drivers/crypto/vmx/ppc-xlate.pl
+++ b/drivers/crypto/vmx/ppc-xlate.pl
@@ -9,6 +9,8 @@ open STDOUT,">$output" || die "can't open $output: $!";
my %GLOBALS;
my $dotinlocallabels=($flavour=~/linux/)?1:0;
+my $abielfv2=(($flavour =~ /linux-ppc64le/) or ($flavour =~ /linux-ppc64-elfv2/))?1:0;
+my $dotfunctions=($abielfv2=~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 ($abielfv2);
$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 $no_vrsave = ($abielfv2);
my $mtspr = sub {
my ($f,$idx,$ra) = @_;
if ($idx == 256 && $no_vrsave) {
--
2.23.0
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