Re: Many instances of "no BTF func for kfunc ..." and "unresolved symbol ..." from resolve_btfids after pahole 1.32 upgrade

[Yonghong Song <yonghong.song@linux.dev>]

On 10/3/26 1:33 AM, Alan Maguire wrote:
> On 02/10/2026 17:25, Nathan Chancellor wrote:
>> Hi Yonghong,
>>
>> On Fri, Oct 02, 2026 at 10:40:12AM +0100, Yonghong Song wrote:
>>> Could you try the following patch to see whether it solved the issue.
>>> I didn't have environment to test arm, powerpc, riscv, etc.
>> Yes, I had to manually apply it but it does appear to resolve this
>> issue. I'll put it through my full build matrix soon but should you send
>> it formally, feel free to add
>>
>>    Tested-by: Nathan Chancellor <nathan@kernel.org> # build
>>
> thanks for doing that. If all looks good on your end with the build matrix
> let me know and we can land it asap. Thanks also for the quick turnaround
> Yonghong!

I just send the fix to the upstream. See
    https://lore.kernel.org/bpf/20261003084357.4185491-1-yonghong.song@linux.dev/

>   
>>> diff --git a/btf_encoder.c b/btf_encoder.c
>>> index d6b9be6..2f137ee 100644
>>> --- a/btf_encoder.c
>>> +++ b/btf_encoder.c
>>> @@ -2913,7 +2913,7 @@ struct btf_encoder *btf_encoder__new(struct cu *cu, const char *detached_filenam
>>>                  encoder->tag_kfuncs      = conf_load->btf_decl_tag_kfuncs;
>>>                  encoder->gen_distilled_base = conf_load->btf_gen_distilled_base;
>>>                  encoder->encode_attributes = conf_load->btf_attributes;
>>> -               encoder->true_signature = conf_load->true_signature;
>>> +               encoder->true_signature = conf_load->true_signature && cu->param_loc_supported;
>>>                  encoder->verbose         = verbose;
>>>                  encoder->has_index_type  = false;
>>>                  encoder->need_index_type = false;
>>> diff --git a/dwarf_loader.c b/dwarf_loader.c
>>> index 1e5363a..9f9b9c9 100644
>>> --- a/dwarf_loader.c
>>> +++ b/dwarf_loader.c
>>> @@ -1518,6 +1518,22 @@ static bool arch__arg_align_two_regs(const GElf_Ehdr *ehdr)
>>>          }
>>>   }
>>> +/*
>>> + * Architectures whose argument register mapping has been validated for
>>> + * matching clang parameter locations and reconstructing true signatures.
>>> + * Other architectures keep only the basic optimized-out detection.
>>> + */
>>> +static bool arch__param_loc_supported(const GElf_Ehdr *ehdr)
>>> +{
>>> +       switch (ehdr->e_machine) {
>>> +       case EM_X86_64:
>>> +       case EM_AARCH64:
>>> +               return true;
>>> +       default:
>>> +               return false;
>>> +       }
>>> +}
>>> +
>>>   static struct template_type_param *template_type_param__new(Dwarf_Die *die, struct cu *cu, struct conf_load *conf)
>>>   {
>>>          struct template_type_param *ttparm = tag__alloc(cu, sizeof(*ttparm));
>>> @@ -3777,7 +3793,8 @@ static void function__analyze_parameter_locations(struct function *fn, struct cu
>>>   {
>>>          struct ftype *ftype = &fn->proto;
>>>          struct parameter *pos;
>>> -       bool true_sig_enabled = conf->true_signature && ftype->signature_changed;
>>> +       bool true_sig_enabled = cu->param_loc_supported && conf->true_signature &&
>>> +                               ftype->signature_changed;
>>>          bool check_locations = !cu->producer_clang || ftype->signature_changed;
>>>          int reg_idx = 0;
>>> @@ -3785,7 +3802,8 @@ static void function__analyze_parameter_locations(struct function *fn, struct cu
>>>                  /* Producer is clang and the signature was not changed: match
>>>                   * each parameter against its expected ABI argument register.
>>>                   */
>>> -               function__match_clang_parameter_locations(ftype, cu);
>>> +               if (cu->param_loc_supported)
>>> +                       function__match_clang_parameter_locations(ftype, cu);
>>>                  return;
>>>          }
>>> @@ -4533,6 +4551,7 @@ static int cu__set_common(struct cu *cu, struct conf_load *conf,
>>>          cu->nr_register_params = arch__nr_register_params(&ehdr);
>>>          cu->agg_use_two_regs = arch__agg_use_two_regs(&ehdr);
>>>          cu->arg_align_two_regs = arch__arg_align_two_regs(&ehdr);
>>> +       cu->param_loc_supported = arch__param_loc_supported(&ehdr);
>>>          arch__set_register_params(&ehdr, cu);
>>>          return 0;
>>>   }
>>> diff --git a/dwarves.h b/dwarves.h
>>> index f3453ed..6b75ece 100644
>>> --- a/dwarves.h
>>> +++ b/dwarves.h
>>> @@ -305,6 +305,7 @@ struct cu {
>>>          uint8_t          producer_clang:1;
>>>          uint8_t          agg_use_two_regs:1;    /* An aggregate like {long a; long b;} */
>>>          uint8_t          arg_align_two_regs:1;  /* An over-aligned arg starts on an even register */
>>> +       uint8_t          param_loc_supported:1; /* Parameter location analysis is validated for this arch */
>>>          uint8_t          nr_register_params;
>>>          int              register_params[ARCH_MAX_REGISTER_PARAMS];
>>>          int              functions_saved;
>>>