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

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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: Michal Suchánek <msuchanek@suse.de>
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221128041539.1742489-5-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2022-11-28 14:15:39 +10:00 committed by Michael Ellerman
parent 505ea33089
commit 5017b45946
2 changed files with 23 additions and 2 deletions
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21
arch/powerpc/Kconfig
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@ -1,6 +1,9 @@
# SPDX-License-Identifier: GPL-2.0
source "arch/powerpc/platforms/Kconfig.cputype"
config CC_HAS_ELFV2
def_bool PPC64 && $(cc-option, -mabi=elfv2)
config 32BIT
bool
default y if PPC32
@ -586,6 +589,24 @@ config KEXEC_FILE
config ARCH_HAS_KEXEC_PURGATORY
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
bool "Build a relocatable kernel"
depends on PPC64 || (FLATMEM && (44x || PPC_85xx))

4
arch/powerpc/platforms/Kconfig.cputype
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@ -580,10 +580,10 @@ config CPU_LITTLE_ENDIAN
endchoice
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
def_bool PPC64 && CPU_LITTLE_ENDIAN
def_bool PPC64 && !PPC64_ELF_ABI_V1
config PPC64_BOOT_WRAPPER
def_bool n