powerpc/64: Linker on-demand sfpr functions for modules

For final link, the powerpc64 linker generates fpr save/restore
functions on-demand, placing them in the .sfpr section. Starting with
binutils 2.25, these can be provided for non-final links with
--save-restore-funcs. Use that where possible for module links.

This saves about 200 bytes per module (~60kB) on powernv defconfig
build.

Signed-off-by: Nicholas Piggin <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>

arch/powerpc/Makefile

···
 CHECKFLAGS	+= -D__LITTLE_ENDIAN__
 endif
 
+ifdef CONFIG_PPC32
 KBUILD_LDFLAGS_MODULE += arch/powerpc/lib/crtsavres.o
+else
+ifeq ($(call ld-ifversion, -ge, 225000000, y),y)
+# Have the linker provide sfpr if possible.
+# There is a corresponding test in arch/powerpc/lib/Makefile
+KBUILD_LDFLAGS_MODULE += --save-restore-funcs
+else
+KBUILD_LDFLAGS_MODULE += arch/powerpc/lib/crtsavres.o
+endif
+endif
 
 ifeq ($(CONFIG_476FPE_ERR46),y)
 	KBUILD_LDFLAGS_MODULE += --ppc476-workaround \

arch/powerpc/lib/Makefile

···
 
 obj-y += string.o alloc.o code-patching.o feature-fixups.o
 
-# 64-bit linker creates .sfpr on demand for final link (vmlinux),
-# so it is only needed for modules.
-obj-$(CONFIG_PPC32) += crtsavres.o
-extra-$(CONFIG_PPC64) += crtsavres.o
+obj-$(CONFIG_PPC32)	+= div64.o copy_32.o crtsavres.o
 
-obj-$(CONFIG_PPC32)	+= div64.o copy_32.o
+# See corresponding test in arch/powerpc/Makefile
+# 64-bit linker creates .sfpr on demand for final link (vmlinux),
+# so it is only needed for modules, and only for older linkers which
+# do not support --save-restore-funcs
+ifeq ($(call ld-ifversion, -lt, 225000000, y),y)
+extra-$(CONFIG_PPC64)	+= crtsavres.o
+endif
 
 obj64-y	+= copypage_64.o copyuser_64.o mem_64.o hweight_64.o \
 	   copyuser_power7.o string_64.o copypage_power7.o memcpy_power7.o \