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powerpc/64: Use -mprofile-kernel for big endian ELFv2 kernels 

-mprofile-kernel is an optimised calling convention for mcount that
Linux  has only implemented with the ELFv2 ABI, so it was disabled for
big endian kernels. However it does work with ELFv2 big endian, so let's
allow that if the compiler supports it.

Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230606093832.199712-4-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2023-06-06 19:38:31 +10:00 committed by Michael Ellerman
parent 8c5fa3b5c4
commit aec0ba7472
2 changed files with 9 additions and 7 deletions
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5
arch/powerpc/Kconfig
View File

@ -547,8 +547,9 @@ config LD_HEAD_STUB_CATCH
If unsure, say "N".
config MPROFILE_KERNEL
depends on PPC64 && CPU_LITTLE_ENDIAN && FUNCTION_TRACER
def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-mprofile-kernel.sh $(CC) -I$(srctree)/include -D__KERNEL__)
depends on PPC64_ELF_ABI_V2 && FUNCTION_TRACER
def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-mprofile-kernel.sh $(CC) -mlittle-endian) if CPU_LITTLE_ENDIAN
def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-mprofile-kernel.sh $(CC) -mbig-endian) if CPU_BIG_ENDIAN
config HOTPLUG_CPU
bool "Support for enabling/disabling CPUs"

11
arch/powerpc/tools/gcc-check-mprofile-kernel.sh
View File

@ -7,20 +7,21 @@ set -o pipefail
# To debug, uncomment the following line
# set -x
# -mprofile-kernel is only supported on 64le, so this should not be invoked
# for other targets. Therefore we can pass in -m64 and -mlittle-endian
# explicitly, to take care of toolchains defaulting to other targets.
# -mprofile-kernel is only supported on 64-bit, so this should not be invoked
# for 32-bit. We pass in -m64 explicitly, and -mbig-endian and -mlittle-endian
# are passed in from Kconfig, which takes care of toolchains defaulting to
# other targets.
# Test whether the compile option -mprofile-kernel exists and generates
# profiling code (ie. a call to _mcount()).
echo "int func() { return 0; }" | \
$* -m64 -mlittle-endian -S -x c -O2 -p -mprofile-kernel - -o - \
$* -m64 -S -x c -O2 -p -mprofile-kernel - -o - \
2> /dev/null | grep -q "_mcount"
# Test whether the notrace attribute correctly suppresses calls to _mcount().
echo -e "#include <linux/compiler.h>\nnotrace int func() { return 0; }" | \
$* -m64 -mlittle-endian -S -x c -O2 -p -mprofile-kernel - -o - \
$* -m64 -S -x c -O2 -p -mprofile-kernel - -o - \
2> /dev/null | grep -q "_mcount" && \
exit 1