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

[Vineet Gupta <vineet.gupta@linux.dev>]

On 6/18/26 7:38 AM, Alan Maguire wrote:
> 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 <alan.maguire@oracle.com>
>>>
>>> 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 <alan.maguire@oracle.com>
>>> Signed-off-by: Vineet Gupta <vineet.gupta@linux.dev>
>> With one nit:
>>
>> Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
>>
>> (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.

Cool, works for me and and indeed it will be nice to avoid a v6 :-)

Thx,
-Vineet

>
> 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!