On 16/01/17 14:11, Marc Zyngier wrote:
On 16/01/17 13:30, Marc Zyngier wrote:
On 13/01/17 14:56, Suzuki K Poulose wrote:
On 13/01/17 13:30, Marc Zyngier wrote:
[+ Suzuki, who wrote the whole cpus_have_const_cap thing]
[...]
But maybe we should have have some stronger guarantees that we'll
always get things inlined, and that the "const" side is enforced:
Agreed.
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)
I think we should have the above change and make it inline always.
{
- if (num >= ARM64_NCAPS)
- return false;
+ BUILD_BUG_ON(!__builtin_constant_p(num));
This is not needed, as the compilation would fail if num is not a constant with
static key code.
I also just checked this, and it doesn't fail if the compiler doesn't
directly supports jump labels (we then fallback to the static key being
a standard memory access).
Ah, I missed that part of the story. Sorry about that. Please go ahead with the
changes. I had a similar check in my first version and was dropped later with a
similar review comment. We hadn't considered older tool chain.
Suzuki
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