Re: [PATCH v2 dwarves 4/5] man-pages: document true_signature btf_feature

[Alan Maguire <alan.maguire@oracle.com>]

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 <alan.maguire@oracle.com>
> 
> Acked-by: Matt Bobrowski <mattbobrowski@google.com>
> 
>> ---
>>  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.