6.1-stable review patch. If anyone has any objections, please let me know.
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From: Nicholas Piggin npiggin@gmail.com
[ Upstream commit 5017b45946722bdd20ac255c9ae7273b78d1f12e ]
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 Stable-dep-of: 39190ac7cff1 ("powerpc/atomic: Use YZ constraints for DS-form instructions") Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/Kconfig | 21 +++++++++++++++++++++ arch/powerpc/platforms/Kconfig.cputype | 4 ++-- 2 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index 6050e6e10d321..345b8b4c60e1e 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -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 @@ -583,6 +586,24 @@ 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)) diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype index 54d655a647cec..ce88910d54cf0 100644 --- a/arch/powerpc/platforms/Kconfig.cputype +++ b/arch/powerpc/platforms/Kconfig.cputype @@ -585,10 +585,10 @@ 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