[PATCH] arm64/cpufeatures: Enforce inline/const properties of cpus_have_const_cap

[Marc Zyngier]

Despite being flagged "inline", cpus_have_const_cap may end-up being
placed out of line if the compiler decides so. This would be unfortunate,
as we want to be able to use this function in HYP, where we need to
be 100% sure of what is mapped there. __always_inline seems to be a
better choice given the constraint.

Also, be a lot tougher on non-const or out-of-range capability values
(a non-const cap value shouldn't be used here, and the semantic of an
OOR value is at best ill defined). In those two case, BUILD_BUG_ON is
what you get.

Reviewed-by: Suzuki K Poulose <suzuki.poulose at arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
---
 arch/arm64/include/asm/cpufeature.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index b4989df..4710469 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -105,10 +105,11 @@ static inline bool cpu_have_feature(unsigned int num)
 }
 
 /* System capability check for constant caps */
-static inline bool cpus_have_const_cap(int num)
+static __always_inline bool cpus_have_const_cap(int num)
 {
-	if (num >= ARM64_NCAPS)
-		return false;
+	BUILD_BUG_ON(!__builtin_constant_p(num));
+	BUILD_BUG_ON(num >= ARM64_NCAPS);
+
 	return static_branch_unlikely(&cpu_hwcap_keys[num]);
 }
 
-- 
2.1.4