[PATCH v4 23/39] arm64: Enable armv8.5-a asm-arch option

[Andrey Konovalov]

From: Vincenzo Frascino <vincenzo.frascino at arm.com>

Hardware tag-based KASAN relies on Memory Tagging Extension (MTE) which
is an armv8.5-a architecture extension.

Enable the correct asm option when the compiler supports it in order to
allow the usage of ALTERNATIVE()s with MTE instructions.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino at arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>
---
Change-Id: I172e15e4c189f073e4c14a10276b276092e76536
---
 arch/arm64/Kconfig  | 4 ++++
 arch/arm64/Makefile | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index e875db8e1c86..192544fcd1a5 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1600,6 +1600,9 @@ endmenu
 
 menu "ARMv8.5 architectural features"
 
+config AS_HAS_ARMV8_5
+	def_bool $(cc-option,-Wa$(comma)-march=armv8.5-a)
+
 config ARM64_BTI
 	bool "Branch Target Identification support"
 	default y
@@ -1676,6 +1679,7 @@ config ARM64_MTE
 	bool "Memory Tagging Extension support"
 	default y
 	depends on ARM64_AS_HAS_MTE && ARM64_TAGGED_ADDR_ABI
+	depends on AS_HAS_ARMV8_5
 	select ARCH_USES_HIGH_VMA_FLAGS
 	help
 	  Memory Tagging (part of the ARMv8.5 Extensions) provides
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 130569f90c54..afcd61f7d2b0 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -94,6 +94,11 @@ ifeq ($(CONFIG_AS_HAS_ARMV8_4), y)
 asm-arch := armv8.4-a
 endif
 
+ifeq ($(CONFIG_AS_HAS_ARMV8_5), y)
+# make sure to pass the newest target architecture to -march.
+asm-arch := armv8.5-a
+endif
+
 ifdef asm-arch
 KBUILD_CFLAGS	+= -Wa,-march=$(asm-arch) \
 		   -DARM64_ASM_ARCH='"$(asm-arch)"'
-- 
2.28.0.709.gb0816b6eb0-goog