linux-kernel - [PATCH 2/4] arm64: vdso32: Detect binutils support for dmb ishld

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Message-Id: <20190926060353.54894-3-vincenzo.frascino@arm.com>
Date:   Thu, 26 Sep 2019 07:03:51 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     vincenzo.frascino@....com, ard.biesheuvel@...aro.org,
        ndesaulniers@...gle.com, catalin.marinas@....com, will@...nel.org,
        tglx@...utronix.de
Subject: [PATCH 2/4] arm64: vdso32: Detect binutils support for dmb ishld

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@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
---
 arch/arm64/include/asm/vdso/compat_barrier.h | 2 +-
 arch/arm64/kernel/vdso32/Makefile            | 5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

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..1a3299d901b1 100644
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -55,6 +55,9 @@ endif
 VDSO_CAFLAGS += -fPIC -fno-builtin -fno-stack-protector
 VDSO_CAFLAGS += -DDISABLE_BRANCH_PROFILING
 
+# Check for binutils support for dmb ishld
+dmbinstr := $(call as-instr,dmb ishld,-DCONFIG_AS_DMB_ISHLD=1)
+
 # 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).
@@ -62,7 +65,7 @@ VDSO_CAFLAGS += $(call cc32-option,-march=armv8-a -D__LINUX_ARM_ARCH__=8,\
                                    -march=armv7-a -D__LINUX_ARM_ARCH__=7)
 
 VDSO_CFLAGS := $(VDSO_CAFLAGS)
-VDSO_CFLAGS += -DENABLE_COMPAT_VDSO=1
+VDSO_CFLAGS += -DENABLE_COMPAT_VDSO=1 $(dmbinstr)
 # KBUILD_CFLAGS from top-level Makefile
 VDSO_CFLAGS += -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
                -fno-strict-aliasing -fno-common \
-- 
2.23.0