On January 31, 2023 9:14:05 AM GMT-03:00, Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
>On 31/01/2023 01:04, Arnaldo Carvalho de Melo wrote:
>> Em Mon, Jan 30, 2023 at 09:25:17PM -0300, Arnaldo Carvalho de Melo escreveu:
>>> Em Mon, Jan 30, 2023 at 10:37:56PM +0000, Alan Maguire escreveu:
>>>> On 30/01/2023 20:23, Arnaldo Carvalho de Melo wrote:
>>>>> Em Mon, Jan 30, 2023 at 05:10:51PM -0300, Arnaldo Carvalho de Melo escreveu:
>>>>>> +++ b/dwarves.h
>>>>>> @@ -262,6 +262,7 @@ struct cu {
>>>>>> uint8_t has_addr_info:1;
>>>>>> uint8_t uses_global_strings:1;
>>>>>> uint8_t little_endian:1;
>>>>>> + uint8_t nr_register_params;
>>>>>> uint16_t language;
>>>>>> unsigned long nr_inline_expansions;
>>>>>> size_t size_inline_expansions;
>>>>>
>>>
>>>> Thanks for this, never thought of cross-builds to be honest!
>>>
>>>> Tested just now on x86_64 and aarch64 at my end, just ran
>>>> into one small thing on one system; turns out EM_RISCV isn't
>>>> defined if using a very old elf.h; below works around this
>>>> (dwarves otherwise builds fine on this system).
>>>
>>> Ok, will add it and will test with containers for older distros too.
>>
>> Its on the 'next' branch, so that it gets tested in the libbpf github
>> repo at:
>>
>> https://github.com/libbpf/libbpf/actions/workflows/pahole.yml
>>
>> It failed yesterday and today due to problems with the installation of
>> llvm, probably tomorrow it'll be back working as I saw some
>> notifications floating by.
>>
>> I added the conditional EM_RISCV definition as well as removed the dup
>> iterator that Jiri noticed.
>>
>
>Thanks again Arnaldo! I've hit an issue with this series in
>BTF encoding of kfuncs; specifically we see some kfuncs missing
>from the BTF representation, and as a result:
>
>WARN: resolve_btfids: unresolved symbol bpf_xdp_metadata_rx_hash
>WARN: resolve_btfids: unresolved symbol bpf_task_kptr_get
>WARN: resolve_btfids: unresolved symbol bpf_ct_change_status
>
>Not sure why I didn't notice this previously.
>
>The problem is the DWARF - and therefore BTF - generated for a function like
>
>int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash)
>{
> return -EOPNOTSUPP;
>}
>
>looks like this:
>
> <8af83a2> DW_AT_external : 1
> <8af83a2> DW_AT_name : (indirect string, offset: 0x358bdc): bpf_xdp_metadata_rx_hash
> <8af83a6> DW_AT_decl_file : 5
> <8af83a7> DW_AT_decl_line : 737
> <8af83a9> DW_AT_decl_column : 5
> <8af83aa> DW_AT_prototyped : 1
> <8af83aa> DW_AT_type : <0x8ad8547>
> <8af83ae> DW_AT_sibling : <0x8af83cd>
> <2><8af83b2>: Abbrev Number: 38 (DW_TAG_formal_parameter)
> <8af83b3> DW_AT_name : ctx
> <8af83b7> DW_AT_decl_file : 5
> <8af83b8> DW_AT_decl_line : 737
> <8af83ba> DW_AT_decl_column : 51
> <8af83bb> DW_AT_type : <0x8af421d>
> <2><8af83bf>: Abbrev Number: 35 (DW_TAG_formal_parameter)
> <8af83c0> DW_AT_name : (indirect string, offset: 0x27f6a2): hash
> <8af83c4> DW_AT_decl_file : 5
> <8af83c5> DW_AT_decl_line : 737
> <8af83c7> DW_AT_decl_column : 61
> <8af83c8> DW_AT_type : <0x8adc424>
>
>...and because there are no further abstract origin references
>with location information either, we classify it as lacking
>locations for (some of) the parameters, and as a result
>we skip BTF encoding. We can work around that by doing this:
>
>__attribute__ ((optimize("O0"))) int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash)
>{
> return -EOPNOTSUPP;
>}
>
>Should we #define some kind of "kfunc" prefix equivalent to the
>above to handle these cases in include/linux/bpf.h perhaps?
>If that makes sense, I'll send bpf-next patches to cover the
>set of kfuncs.
Jiri?
>The other thing we might want to do is bump the libbpf version
>for dwarves 1.25, what do you think? I've tested with libbpf 1.1
>and aside from the above issue all looks good (there's a few dedup
>improvements that this version will give us). I can send a patch for
>the libbpf update if that makes sense.
Please send it, then we give it some more days of wider testing,
Yonghong, Andrii, comments on updating libbpf in the pahole submodule?
- Arnaldo
