arm64: atomics: patch in lse instructions when supported by the CPU
On CPUs which support the LSE atomic instructions introduced in ARMv8.1,
it makes sense to use them in preference to ll/sc sequences.
This patch introduces runtime patching of atomic_t and atomic64_t
routines so that the call-site for the out-of-line ll/sc sequences is
patched with an LSE atomic instruction when we detect that
the CPU supports it.
If binutils is not recent enough to assemble the LSE instructions, then
the ll/sc sequences are inlined as though CONFIG_ARM64_LSE_ATOMICS=n.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 0953a97..15ff5b4 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -17,7 +17,18 @@
KBUILD_DEFCONFIG := defconfig
-KBUILD_CFLAGS += -mgeneral-regs-only
+# Check for binutils support for specific extensions
+lseinstr := $(call as-instr,.arch_extension lse,-DCONFIG_AS_LSE=1)
+
+ifeq ($(CONFIG_ARM64_LSE_ATOMICS), y)
+ ifeq ($(lseinstr),)
+$(warning LSE atomics not supported by binutils)
+ endif
+endif
+
+KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr)
+KBUILD_AFLAGS += $(lseinstr)
+
ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
KBUILD_CPPFLAGS += -mbig-endian
AS += -EB