arm64: vdso32: drop the test for dmb ishld

Binutils added support for this instruction in commit
e797f7e0b2bedc9328d4a9a0ebc63ca7a2dbbebc which shipped in 2.24 (just
missing the 2.23 release) but was cherry-picked into 2.23 in commit
27a50d6755bae906bc73b4ec1a8b448467f0bea1. Thanks to Christian and Simon
for helping me with the patch archaeology.

According to Documentation/process/changes.rst, the minimum supported
version of binutils is 2.23. Since all supported versions of GAS support
this instruction, drop the assembler invocation, preprocessor
flags/guards, and the cross assembler macro that's now unused.

This also avoids a recursive self reference in a follow up cleanup
patch.

Cc: Christian Biesinger <[email protected]>
Cc: Simon Marchi <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
Reviewed-by: Vincenzo Frascino <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

Author: nickdesaulniers

arch/arm64/include/asm/vdso/compat_barrier.h

@@ -20,7 +20,7 @@
 
 #define dmb(option) __asm__ __volatile__ ("dmb " #option : : : "memory")
 
-#if __LINUX_ARM_ARCH__ >= 8 && defined(CONFIG_AS_DMB_ISHLD)
+#if __LINUX_ARM_ARCH__ >= 8
 #define aarch32_smp_mb()	dmb(ish)
 #define aarch32_smp_rmb()	dmb(ishld)
 #define aarch32_smp_wmb()	dmb(ishst)

arch/arm64/kernel/vdso32/Makefile

@@ -29,8 +29,6 @@ cc32-option = $(call try-run,\
         $(CC_COMPAT) $(1) -c -x c /dev/null -o "$$TMP",$(1),$(2))
 cc32-disable-warning = $(call try-run,\
 	$(CC_COMPAT) -W$(strip $(1)) -c -x c /dev/null -o "$$TMP",-Wno-$(strip $(1)))
-cc32-as-instr = $(call try-run,\
-	printf "%b\n" "$(1)" | $(CC_COMPAT) $(VDSO_AFLAGS) -c -x assembler -o "$$TMP" -,$(2),$(3))
 
 # We cannot use the global flags to compile the vDSO files, the main reason
 # being that the 32-bit compiler may be older than the main (64-bit) compiler
@@ -113,12 +111,6 @@ endif
 VDSO_AFLAGS := $(VDSO_CAFLAGS)
 VDSO_AFLAGS += -D__ASSEMBLY__
 
-# Check for binutils support for dmb ishld
-dmbinstr := $(call cc32-as-instr,dmb ishld,-DCONFIG_AS_DMB_ISHLD=1)
-
-VDSO_CFLAGS += $(dmbinstr)
-VDSO_AFLAGS += $(dmbinstr)
-
 # From arm vDSO Makefile
 VDSO_LDFLAGS += -Bsymbolic --no-undefined -soname=linux-vdso.so.1
 VDSO_LDFLAGS += -z max-page-size=4096 -z common-page-size=4096