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authorMarc Zyngier <maz@kernel.org>2020-12-17 11:11:35 +0000
committerCatalin Marinas <catalin.marinas@arm.com>2020-12-17 11:46:20 +0000
commit9fd339a45be5c06e239d45a042eab9d25de87882 (patch)
treea5c3d1eb0e47cc2f099fe072688fb93e83fb818f /arch
parent31f80a4e9603c3d1668bc3a1401d49321d547d54 (diff)
arm64: Work around broken GCC 4.9 handling of "S" constraint
GCC 4.9 seems to have a problem with the "S" asm constraint when the symbol lives in the same compilation unit, and pretends the constraint is impossible: $ cat x.c void *foo(void) { static int x; int *addr; asm("adrp %0, %1" : "=r" (addr) : "S" (&x)); return addr; } $ ~/Work/gcc-linaro-aarch64-linux-gnu-4.9-2014.09_linux/bin/aarch64-linux-gnu-gcc -S -x c -O2 x.c x.c: In function ‘foo’: x.c:5:2: error: impossible constraint in ‘asm’ asm("adrp %0, %1" : "=r" (addr) : "S" (&x)); ^ Boo. Following revisions of the compiler work just fine, though. We can fallback to the "i" constraint for GCC version prior to 5.0, which *seems* to do the right thing. Hopefully we will be able to remove this at some point, but in the meantime this gets us going. Signed-off-by: Marc Zyngier <maz@kernel.org> Acked-by: Ard Biesheuvel <ardb@kernel.org> Link: https://lore.kernel.org/r/20201217111135.1536658-1-maz@kernel.org Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/arm64/include/asm/kvm_asm.h8
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 54387ccd1ab2..8e5fa28b78c2 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -200,6 +200,12 @@ extern u32 __kvm_get_mdcr_el2(void);
extern char __smccc_workaround_1_smc[__SMCCC_WORKAROUND_1_SMC_SZ];
+#if defined(GCC_VERSION) && GCC_VERSION < 50000
+#define SYM_CONSTRAINT "i"
+#else
+#define SYM_CONSTRAINT "S"
+#endif
+
/*
* Obtain the PC-relative address of a kernel symbol
* s: symbol
@@ -216,7 +222,7 @@ extern char __smccc_workaround_1_smc[__SMCCC_WORKAROUND_1_SMC_SZ];
typeof(s) *addr; \
asm("adrp %0, %1\n" \
"add %0, %0, :lo12:%1\n" \
- : "=r" (addr) : "S" (&s)); \
+ : "=r" (addr) : SYM_CONSTRAINT (&s)); \
addr; \
})