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 <[email protected]>
Suggested-by: Christophe Leroy <[email protected]>
Signed-off-by: Nicholas Piggin <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://msgid.link/[email protected]

Author: npiggin

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"

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