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?
Looks like it's a weakness in LLVM with inlining: #include <assert.h> #if 1 static inline void foo(unsigned long x) { assert(__builtin_constant_p(x)); } #else #define foo(X) assert(__builtin_constant_p(X)) #endif int main(void) { foo(1); return 0; } And there is an old bug on it: https://llvm.org/bugs/show_bug.cgi?id=4898 Anton