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arm64: Work around broken GCC 4.9 handling of "S" constraint

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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>
This commit is contained in:
Marc Zyngier 2020-12-17 11:11:35 +00:00 committed by Catalin Marinas
parent 31f80a4e96
commit 9fd339a45b
1 changed files with 7 additions and 1 deletions
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8
arch/arm64/include/asm/kvm_asm.h
View File

@ -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; \
})