Re: [PATCH dwarves 3/3] btf_encoder: learn BTF_KIND_MAX value from base BTF when generating split BTF

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2023-09-13 at 15:26 +0100, Alan Maguire wrote:
> > When creating module BTF, the module likely will not have a DWARF
> > specificiation of BTF_KIND_MAX, so look for it in the base BTF.  For
> > vmlinux base BTF, the enumeration value is present, so the base BTF
> > can be checked to limit BTF kind representation.
> > 
> > Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> > ---
> >  btf_encoder.c | 24 ++++++++++++++++++++++++
> >  btf_encoder.h |  2 ++
> >  pahole.c      |  2 ++
> >  3 files changed, 28 insertions(+)
> > 
> > diff --git a/btf_encoder.c b/btf_encoder.c
> > index ad0158f..6cb3df6 100644
> > --- a/btf_encoder.c
> > +++ b/btf_encoder.c
> > @@ -1902,3 +1902,27 @@ void dwarves__set_btf_kind_max(struct conf_load *conf_load, int btf_kind_max)
> >  	if (btf_kind_max < BTF_KIND_ENUM64)
> >  		conf_load->skip_encoding_btf_enum64 = true;
> >  }
> > +
> > +void btf__set_btf_kind_max(struct conf_load *conf_load, struct btf *btf)
> > +{

Nitpick: same function for DWARF has name dwarf__find_btf_kind_max,
 which seems to be a bit inconsistent.

> > +	__u32 id, type_cnt = btf__type_cnt(btf);
> > +
> > +	for (id = 1; id < type_cnt; id++) {
> > +		const struct btf_type *t = btf__type_by_id(btf, id);
> > +		const struct btf_enum *e;
> > +		__u16 vlen, i;
> > +
> > +		if (!t || !btf_is_enum(t))
> > +			continue;
> > +		vlen = btf_vlen(t);
> > +		e = btf_enum(t);
> > +		for (i = 0; i < vlen; e++, i++) {
> > +			const char *name = btf__name_by_offset(btf, e->name_off);
> > +
> > +			if (!name || strcmp(name, "BTF_KIND_MAX"))
> > +				continue;
> > +			dwarves__set_btf_kind_max(conf_load, e->val);
> > +			return;
> > +		}
> > +	}
> > +}
> > diff --git a/btf_encoder.h b/btf_encoder.h
> > index 34516bb..e5e12ef 100644
> > --- a/btf_encoder.h
> > +++ b/btf_encoder.h
> > @@ -27,4 +27,6 @@ struct btf *btf_encoder__btf(struct btf_encoder *encoder);
> >  
> >  int btf_encoder__add_encoder(struct btf_encoder *encoder, struct btf_encoder *other);
> >  
> > +void btf__set_btf_kind_max(struct conf_load *conf_load, struct btf *btf);
> > +
> >  #endif /* _BTF_ENCODER_H_ */
> > diff --git a/pahole.c b/pahole.c
> > index aca2704..4d6d059 100644
> > --- a/pahole.c
> > +++ b/pahole.c
> > @@ -3470,6 +3470,7 @@ int main(int argc, char *argv[])
> >  				base_btf_file, libbpf_get_error(conf_load.base_btf));
> >  			goto out;
> >  		}
> > +		btf__set_btf_kind_max(&conf_load, conf_load.base_btf);
> >  		if (!btf_encode && !ctf_encode) {
> >  			// Force "btf" since a btf_base is being informed
> >  			conf_load.format_path = "btf";
> > @@ -3513,6 +3514,7 @@ try_sole_arg_as_class_names:
> >  					base_btf_file, libbpf_get_error(conf_load.base_btf));
> >  				goto out;
> >  			}
> > +			btf__set_btf_kind_max(&conf_load, conf_load.base_btf);
> >  		}
> >  	}
> >