Subject: [PATCH v2 3/4] powerpc/64: Use -mprofile-kernel for big endian ELFv2 kernels

From: Nicholas Piggin <[email-masked]>
Date: Tue, 6 Jun 2023 19:38:31 +1000

-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 <[email-masked]>
Suggested-by: Christophe Leroy <[email-masked]>
Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/Kconfig                            |  5 +++--
 arch/powerpc/tools/gcc-check-mprofile-kernel.sh | 11 ++++++-----
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 296e0448b5fc..9db707829638 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -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"
diff --git a/arch/powerpc/tools/gcc-check-mprofile-kernel.sh b/arch/powerpc/tools/gcc-check-mprofile-kernel.sh
index 137f3376ac2b..a31a56016c09 100755
--- a/arch/powerpc/tools/gcc-check-mprofile-kernel.sh
+++ b/arch/powerpc/tools/gcc-check-mprofile-kernel.sh
@@ -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
 
-- 
2.40.1