[PATCH] arm64: extract a field correctly in cpuid_feature_extract_field()
AKASHI Takahiro
takahiro.akashi at linaro.org
Mon Nov 16 21:05:39 PST 2015
Basically, cpuid_feature_extract_field() does shift-left and then
shift-right to extract a specific field in an operand. But
a shift-left'ed value is casted to 's64' and so a succeeding shift-right
operation results in creating a sign-extended (and bogus) value.
For example, commit 3085bb01b406 ("arm64/debug: Make use of the system
wide safe value") changed get_num_brps() using this function, and so
we cannot identify the correct number of hw breakpoints available:
> hw-breakpoint: found 0 breakpoint and 0 watchpoint registers.
ID_AARCH64DFR0_EL1 is 0xf0f0f106 (on fast model), but get_num_brps()
returns zero.
This patch fixes the issue by removing the casting.
I think that cpuid_featuer_extract_field(), arm64_ftr_value() and others
should return an unsigned value as an extracted field.
Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
---
arch/arm64/include/asm/cpufeature.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 11d5bb0f..ab01508 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -114,7 +114,7 @@ static inline void cpus_set_cap(unsigned int num)
static inline int __attribute_const__
cpuid_feature_extract_field_width(u64 features, int field, int width)
{
- return (s64)(features << (64 - width - field)) >> (64 - width);
+ return (features << (64 - width - field)) >> (64 - width);
}
static inline int __attribute_const__
--
1.7.9.5
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