From 9fd339a45be5c06e239d45a042eab9d25de87882 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Thu, 17 Dec 2020 11:11:35 +0000 Subject: [PATCH] arm64: Work around broken GCC 4.9 handling of "S" constraint MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Acked-by: Ard Biesheuvel Link: https://lore.kernel.org/r/20201217111135.1536658-1-maz@kernel.org Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/kvm_asm.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) 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; \ }) -- 2.34.1