On Tue, Jan 31, 2023 at 9:43 AM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> On Tue, Jan 31, 2023 at 4:14 AM 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)
>
> replied in the other thread. This attr is broken and discouraged by gcc.
>
> For kfuncs where aregs are unused, please try __used and __may_unused
> applied to arguments.
> If that won't work, please add barrier_var(arg) to the body of kfunc
> the way we do in selftests.
There is also
# define __visible __attribute__((__externally_visible__))
that probably fits the best here.
