Re: [PATCH v2 dwarves 4/5] man-pages: document true_signature btf_feature
Yonghong Song <[email protected]>
| Newsgroups | org.kernel.vger.dwarves,org.kernel.vger.bpf |
|---|---|
| Message-ID | <[email protected]> |
On 1/26/26 9:10 AM, Alan Maguire wrote: > On 26/01/2026 11:21, Matt Bobrowski wrote: >> On Mon, Jan 26, 2026 at 10:51:31AM +0000, Alan Maguire wrote: >>> On 26/01/2026 10:02, Matt Bobrowski wrote: >>>> On Fri, Jan 23, 2026 at 05:26:49PM +0000, Alan Maguire wrote: >>>>> Ensure non-default "true_signature" feature is documented in >>>>> the manual page. >>>>> >>>>> Signed-off-by: Alan Maguire <[email protected]> >>>> Acked-by: Matt Bobrowski <[email protected]> >>>> >>>>> --- >>>>> man-pages/pahole.1 | 5 +++++ >>>>> 1 file changed, 5 insertions(+) >>>>> >>>>> diff --git a/man-pages/pahole.1 b/man-pages/pahole.1 >>>>> index 3125de3..90a8f45 100644 >>>>> --- a/man-pages/pahole.1 >>>>> +++ b/man-pages/pahole.1 >>>>> @@ -337,6 +337,11 @@ Supported non-standard features (not enabled for 'default') >>>>> of split BTF with a possibly changed base, storing >>>>> it in a .BTF.base ELF section. >>>>> global_var Encode all global variables using BTF_KIND_VAR in BTF. >>>>> + true_signature Encode functions ensuring that binary-level >>>>> + (rather than source-level) signatures are used; >>>> ^ >>>> within the generated BTF. >>>> >>>>> + for gcc these are ".isra.0" and ".costprop.0" >>>>> + optimized functions >>>> For BTF generation, would there ever be a situation whereby we >>>> wouldn't want true signature support? I'm just trying to understand >>>> why this isn't defaulted to true. >>> The key reason is the "." in the name for gcc-optimized functions >>> "function.isra.0" ; older kernels will reject BTF function names with >>> a "." in them, so we have to guard against new pahole with the feature >>> enabled by default being run on older kernels. So by having the newer >>> kernels request the feature only we avoid this. >> Oh, yes, that makes sense. Once a new pahole version is released with >> true_signature support available, will you also be looking to update >> scripts/Makefile.btf and conditionally enable it based on >> availability? > Yep, we're hoping to get some support on the LLVM side for true signatures, but > absolutely, that's the plan. Because the --btf_features option will simply > ignore features that it does not know about, this approach works with older > pahole too without erroring out. I actually have started to work on this from llvm side. Once Alan's patch lands (which has true_signature infrastructure implemented), I should be able to send some patch to address true_signature for llvm-built kernel.