Messages in this thread | | | Subject | Re: [PATCH] x86/cpufeature: guard asm_volatile_goto usage with CC_HAVE_ASM_GOTO | From | Alexei Starovoitov <> | Date | Tue, 10 Apr 2018 14:28:04 -0700 |
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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.
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