arm64: errata: Pass --fix-cortex-a53-843419 to ld if workaround enabled

Cortex-A53 erratum 843419 is worked around by the linker, although it is
a configure-time option to GCC as to whether ld is actually asked to
apply the workaround or not.

This patch ensures that we pass --fix-cortex-a53-843419 to the linker
when both CONFIG_ARM64_ERRATUM_843419=y and the linker supports the
option.

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 5b54f8c..0b53c75 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -18,6 +18,14 @@
 LDFLAGS_vmlinux		+= -pie -Bsymbolic
 endif
 
+ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
+  ifeq ($(call ld-option, --fix-cortex-a53-843419),)
+$(warning ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum)
+  else
+LDFLAGS_vmlinux	+= --fix-cortex-a53-843419
+  endif
+endif
+
 KBUILD_DEFCONFIG := defconfig
 
 # Check for binutils support for specific extensions