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

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>