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Subject[PATCH v2 2/4] arm64: vdso32: Detect binutils support for dmb ishld
Date
As reported by Will Deacon, 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>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
---
arch/arm64/Kbuild | 6 ++++++
arch/arm64/include/asm/vdso/compat_barrier.h | 2 +-
arch/arm64/kernel/vdso32/Makefile | 9 +++++++++
3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kbuild b/arch/arm64/Kbuild
index d6465823b281..75cf8c796d0e 100644
--- a/arch/arm64/Kbuild
+++ b/arch/arm64/Kbuild
@@ -4,3 +4,9 @@ obj-$(CONFIG_NET) += net/
obj-$(CONFIG_KVM) += kvm/
obj-$(CONFIG_XEN) += xen/
obj-$(CONFIG_CRYPTO) += crypto/
+
+# as-instr-compat
+# Usage: cflags-y += $(call as-instr-compat,instr,option1,option2)
+
+as-instr-compat = $(call try-run,\
+ printf "%b\n" "$(1)" | $(COMPATCC) $(KBUILD_AFLAGS) -c -x assembler -o "$$TMP" -,$(2),$(3))
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 1fba0776ed40..22f0d31ea528 100644
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -17,6 +17,8 @@ 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
@@ -55,6 +57,7 @@ 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).
@@ -91,6 +94,12 @@ 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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