On 4/10/18 2:07 PM, Peter Zijlstra wrote:
On Tue, Apr 10, 2018 at 01:42:59PM -0700, Yonghong Song wrote:Commit d0266046ad54 ("x86: Remove FAST_FEATURE_TESTS") removed X86_FAST_FEATURE_TESTS and make macro static_cpu_has() always use __always_inline function _static_cpu_has() funciton. The static_cpu_has() uses gcc feature asm_volatile_goto construct, which is not supported by clang.There will be more unconditional asm-goto usage, clang is in the process of growing asm-goto.
Eventually yes, but we need a solution today. Right now all of bpf based tracing is broken because we have to compile on the fly with clang. Instead of #ifdef CC_HAVE_ASM_GOTO we can replace it with #ifndef __BPF__ or some other name, but it's more hacky, since we'd need add -D__BPF__ to samples/bpf and to all other places that use native clang to compile. Whereas with 'ifdef CC_HAVE_ASM_GOTO' everything works as-is. Top kernel makefile defines it and kernel is still compiled with asm-goto, whereas native clang path for the purpose of compiling bpf progs doesn't have this define and also fine. imo this patch is the best solution _today_. bpf compilation needs kernel headers only. If later you add unconditional asm-goto to .c, it's all fine.
