Re: [PAHOLE v5 1/5] btf_loader: Handle decl tag component_idx for parameters

On 18/06/2026 05:46, Emil Tsalapatis wrote:
> On Wed Jun 17, 2026 at 8:57 PM EDT, Vineet Gupta wrote:
>> From: Alan Maguire <[email protected]>
>>
>> A BTF_KIND_DECL_TAG with a non-negative component_idx applies to a
>> specific function parameter (or struct/union member), not to the
>> function itself. btf_loader.c however attached every decl tag to the
>> type named by btf_type->type, so parameter decl tags were recorded on
>> the function rather than on the parameter, and pfunct never printed
>> them with the parameter.
>>
>> Resolve a non-negative component_idx to the corresponding parameter via
>> new helpers ftype__parameter()/function__parameter(), and attach the
>> tag there. Teach the pretty printer to emit a parameter's attributes by
>> factoring the function-level attribute loop into tag__attributes_fprintf()
>> and calling it from ftype__fprintf_parms() for each parameter.
>>
>> Signed-off-by: Alan Maguire <[email protected]>
>> Signed-off-by: Vineet Gupta <[email protected]>
> 
> With one nit:
> 
> Reviewed-by: Emil Tsalapatis <[email protected]>
> 
> (Also feel free to keep the tags for the other 3 patches since the 
> changes are minimal).
> 
> </SNIP>
> 
>> +	if (component_idx >= 0) {
>> +		struct tag *func_tag = cu__function(cu, tp->type);
>> +
>> +		if (func_tag != NULL) {
>> +			tag = function__parameter(tag__function(func_tag), cu,
>> +						  component_idx);
>> +			if (tag == NULL) {
>> +				fprintf(stderr, "WARNING: BTF_KIND_DECL_TAG for unknown parameter %d in BTF id %d\n",
>> +					component_idx, tp->type);
>> +				return 0;
>> +			}
>> +		}
>> +	}
>> +
>> +	if (tag == NULL && component_idx < 0)
>>  		tag = cu__function(cu, tp->type);
> 
> Nit, I think this can be simplified as follows:
> 
> tag = cu__function(cu, tp->type);
> if (component_idx >= 0 && tag != NULL) {
> 	tag = function__parameter(tag__function(tag), cu, component_idx);
> 	if (tag == NULL) {
> 		fprintf(stderr, "WARNING: BTF_KIND_DECL_TAG for unknown parameter %d in BTF id %d\n",
> 			component_idx, tp->type);
> 		return 0;
> 	}
> }
> 
> <SNIP>

yep, that looks good to me. if there are no other issues arising from this
round and Vineet is happy with that change I can roll it in when landing this
to save having to roll a v6.

One other issue; we need to install bpftool for CI. I'm working on a change to
support this (installing the version from the kernel tree), I'll try and get
this in place ASAP. Thanks!