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Date: Sat, 21 Jan 2017 12:03:39 +1100
From: Anton Blanchard <anton@samba.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>, Benjamin
 Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras
 <paulus@samba.org>, Nicholas Piggin  <npiggin@gmail.com>, Michael Ellerman
 <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Subject: BUILD_BUG_ON(!__builtin_constant_p(feature)) breaks bcc trace tool
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Hi,

We added:

BUILD_BUG_ON(!__builtin_constant_p(feature)) 

to cpu_has_feature() and mmu_has_feature() in order to catch usage
issues (such as cpu_has_feature(cpu_has_feature(X)). Unfortunately LLVM
isn't smart enough to resolve this, and it errors out.

I work around it in my clang/LLVM builds of the kernel, but I have just
discovered that it causes a lot of issues for the bcc (eBPF) trace tool
(which uses LLVM).

How should we work around this? Wrap the checks in !clang perhaps?

Anton