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Subject[PATCH v4 2/6] arm64: vdso32: Detect binutils support for dmb ishld
Date
Older versions of binutils that do not support certain types of memory
barriers can cause build failure of the vdso32 library.

Add a compilation time mechanism that detects if binutils supports those
instructions and configure the kernel accordingly.

Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Will Deacon <will@kernel.org>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Catalin Marinas <catalin.marinas@arm.com>
---
arch/arm64/include/asm/vdso/compat_barrier.h | 2 +-
arch/arm64/kernel/vdso32/Makefile | 9 +++++++++
2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/vdso/compat_barrier.h b/arch/arm64/include/asm/vdso/compat_barrier.h
index fb60a88b5ed4..3fd8fd6d8fc2 100644
--- a/arch/arm64/include/asm/vdso/compat_barrier.h
+++ b/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
+#if __LINUX_ARM_ARCH__ >= 8 && defined(CONFIG_AS_DMB_ISHLD)
#define aarch32_smp_mb() dmb(ish)
#define aarch32_smp_rmb() dmb(ishld)
#define aarch32_smp_wmb() dmb(ishst)
diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
index 19e0d3115ffe..77aa61340374 100644
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -15,6 +15,8 @@ cc32-disable-warning = $(call try-run,\
$(COMPATCC) -W$(strip $(1)) -c -x c /dev/null -o "$$TMP",-Wno-$(strip $(1)))
cc32-ldoption = $(call try-run,\
$(COMPATCC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
+cc32-as-instr = $(call try-run,\
+ printf "%b\n" "$(1)" | $(COMPATCC) $(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
@@ -53,6 +55,7 @@ endif
VDSO_CAFLAGS += -fPIC -fno-builtin -fno-stack-protector
VDSO_CAFLAGS += -DDISABLE_BRANCH_PROFILING

+
# Try to compile for ARMv8. If the compiler is too old and doesn't support it,
# fall back to v7. There is no easy way to check for what architecture the code
# is being compiled, so define a macro specifying that (see arch/arm/Makefile).
@@ -89,6 +92,12 @@ VDSO_CFLAGS += -Wno-int-to-pointer-cast
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)
+
VDSO_LDFLAGS := $(VDSO_CPPFLAGS)
# From arm vDSO Makefile
VDSO_LDFLAGS += -Wl,-Bsymbolic -Wl,--no-undefined -Wl,-soname=linux-vdso.so.1
--
2.23.0
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