Commit 5017b459 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/64: Option to build big-endian with ELFv2 ABI 



Provide an option to build big-endian kernels using the ELFv2 ABI. This
works on GCC only for now. Clang is rumored to support this, but core
build files need updating first, at least.

This gives big-endian kernels useful advantages of the ELFv2 ABI, e.g.,
less stack usage, -mprofile-kernel support, better compatibility with
eBPF 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: default avatarMichal Suchánek <msuchanek@suse.de>
Reviewed-by: default avatarSegher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Reviewed-by: default avatarJoel Stanley <joel@jms.id.au>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221128041539.1742489-5-npiggin@gmail.com
parent 505ea330

arch/powerpc/Kconfig

+21 −0
Original line number Original line Diff line number Diff line 
# SPDX-License-Identifier: GPL-2.0

# SPDX-License-Identifier: GPL-2.0

source "arch/powerpc/platforms/Kconfig.cputype"

source "arch/powerpc/platforms/Kconfig.cputype"





config CC_HAS_ELFV2

	def_bool PPC64 && $(cc-option, -mabi=elfv2)



config 32BIT

config 32BIT

	bool

	bool

	default y if PPC32

	default y if PPC32
@@ -586,6 +589,24 @@ config KEXEC_FILE 
config ARCH_HAS_KEXEC_PURGATORY

config ARCH_HAS_KEXEC_PURGATORY

	def_bool KEXEC_FILE

	def_bool KEXEC_FILE





config PPC64_BIG_ENDIAN_ELF_ABI_V2

	bool "Build big-endian kernel using ELF ABI V2 (EXPERIMENTAL)"

	depends on PPC64 && CPU_BIG_ENDIAN

	depends on CC_HAS_ELFV2

	depends on LD_IS_BFD && LD_VERSION >= 22400

	default n

	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

config RELOCATABLE

	bool "Build a relocatable kernel"

	bool "Build a relocatable kernel"

	depends on PPC64 || (FLATMEM && (44x || PPC_85xx))

	depends on PPC64 || (FLATMEM && (44x || PPC_85xx))

arch/powerpc/platforms/Kconfig.cputype

+2 −2
Original line number Original line Diff line number Diff line
@@ -580,10 +580,10 @@ config CPU_LITTLE_ENDIAN 
endchoice

endchoice





config PPC64_ELF_ABI_V1

config PPC64_ELF_ABI_V1

	def_bool PPC64 && CPU_BIG_ENDIAN

	def_bool PPC64 && (CPU_BIG_ENDIAN && !PPC64_BIG_ENDIAN_ELF_ABI_V2)





config PPC64_ELF_ABI_V2

config PPC64_ELF_ABI_V2

	def_bool PPC64 && CPU_LITTLE_ENDIAN

	def_bool PPC64 && !PPC64_ELF_ABI_V1





config PPC64_BOOT_WRAPPER

config PPC64_BOOT_WRAPPER

	def_bool n

	def_bool n