On 3/23/25 4:11 AM, Alan Maguire wrote: > [...] > > hi Ihor, I took a look at the series and merged it with latest next > branch; results are in > > https://web.git.kernel.org/pub/scm/devel/pahole/pahole.git/log/?h=next.attributes-v4 > > ...if you want to take a look. > > There are a few small things I think that it would be good to resolve > before landing this. > > First, when testing this with -DLIBBPF_EMBEDDED=OFF and a packaged > libbpf 1.5 - which means we wouldn't have the latest attributes-related > libbpf function; I saw: > > BTF .tmp_vmlinux1.btf.o > btf__add_type_attr is not available, is libbpf < 1.6? > error: failed to encode function 'bbr_cwnd_event': invalid proto > Failed to encode BTF > NM .tmp_vmlinux1.syms Hi Alan. Thanks for testing. This is my mistake, I should've checked for attributes feature here: @@ -731,6 +812,10 @@ static int32_t btf_encoder__add_func_proto(struct btf_encoder *encoder, struct f assert(ftype != NULL || state != NULL); + if (is_kfunc_state(state) && encoder->tag_kfuncs) + if (btf__add_bpf_arena_type_tags(encoder->btf, state) < 0) + return -1; > > ...and we got no BTF as a result. Ideally we'd like pahole to encode but > without the attributes feature if not available. Related, we also report > features that are not present, i.e. attributes with > "--supported_btf_features". So I propose that we make use of the weak > declarations being NULL in an optional feature check function. It is > optionally declared for a feature, and if declared must return true if > the feature is available. > > Something like the below works (it's in the next.attributes-v4 branch > too for reference) and it resolves the issue of BTF generation failure > and accurate supported_btf_features reporting. What do you think? Thanks! I think failing fast is a good approach here: check that all requested/default features are available on startup. > > Alan > > From: Alan Maguire <alan.maguire@xxxxxxxxxx> > Date: Sun, 23 Mar 2025 11:06:18 +0000 > Subject: [PATCH] pahole: add a BTF feature check function > > It is used to see if functions that BTF features rely on are > really there; weak declarations mean they will be NULL if not > in non-embedded linked libbpf. > > This gives us more accurate --supported_btf_features reporting also. > > Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx> > --- > pahole.c | 39 +++++++++++++++++++++++++++++++++------ > 1 file changed, 33 insertions(+), 6 deletions(-) > Acked-by: Ihor Solodrai <ihor.solodrai@xxxxxxxxx> > diff --git a/pahole.c b/pahole.c > index 4a2b1ce..8304ba4 100644 > --- a/pahole.c > +++ b/pahole.c > @@ -1183,10 +1183,31 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = > dwarves_print_version; > * floats, etc. This ensures backwards compatibility. > */ > #define BTF_DEFAULT_FEATURE(name, alias, initial_value) \ > - { #name, #alias, &conf_load.alias, initial_value, true } > + { #name, #alias, &conf_load.alias, initial_value, true, NULL } > + > +#define BTF_DEFAULT_FEATURE_CHECK(name, alias, initial_value, > feature_check) \ > + { #name, #alias, &conf_load.alias, initial_value, true, feature_check } > > #define BTF_NON_DEFAULT_FEATURE(name, alias, initial_value) \ > - { #name, #alias, &conf_load.alias, initial_value, false } > + { #name, #alias, &conf_load.alias, initial_value, false, NULL } > + > +#define BTF_NON_DEFAULT_FEATURE_CHECK(name, alias, initial_value, > feature_check) \ > + { #name, #alias, &conf_load.alias, initial_value, false, feature_check } > + > +static bool enum64_check(void) > +{ > + return btf__add_enum64 != NULL; > +} > + > +static bool distilled_base_check(void) > +{ > + return btf__distill_base != NULL; > +} > + > +static bool attributes_check(void) > +{ > + return btf__add_type_attr != NULL; > +} > > struct btf_feature { > const char *name; > @@ -1196,20 +1217,23 @@ struct btf_feature { > bool default_enabled; /* some nonstandard features may not > * be enabled for --btf_features=default > */ > + bool (*feature_check)(void); > } btf_features[] = { > BTF_DEFAULT_FEATURE(encode_force, btf_encode_force, false), > BTF_DEFAULT_FEATURE(var, skip_encoding_btf_vars, true), > BTF_DEFAULT_FEATURE(float, btf_gen_floats, false), > BTF_DEFAULT_FEATURE(decl_tag, skip_encoding_btf_decl_tag, true), > BTF_DEFAULT_FEATURE(type_tag, skip_encoding_btf_type_tag, true), > - BTF_DEFAULT_FEATURE(enum64, skip_encoding_btf_enum64, true), > + BTF_DEFAULT_FEATURE_CHECK(enum64, skip_encoding_btf_enum64, true, > enum64_check), > BTF_DEFAULT_FEATURE(optimized_func, btf_gen_optimized, false), > BTF_DEFAULT_FEATURE(consistent_func, > skip_encoding_btf_inconsistent_proto, false), > BTF_DEFAULT_FEATURE(decl_tag_kfuncs, btf_decl_tag_kfuncs, false), > BTF_NON_DEFAULT_FEATURE(reproducible_build, reproducible_build, false), > - BTF_NON_DEFAULT_FEATURE(distilled_base, btf_gen_distilled_base, false), > + BTF_NON_DEFAULT_FEATURE_CHECK(distilled_base, btf_gen_distilled_base, > false, > + distilled_base_check), > BTF_NON_DEFAULT_FEATURE(global_var, encode_btf_global_vars, false), > - BTF_NON_DEFAULT_FEATURE(attributes, btf_attributes, false), > + BTF_NON_DEFAULT_FEATURE_CHECK(attributes, btf_attributes, false, > + attributes_check), > }; > > #define BTF_MAX_FEATURE_STR 1024 > @@ -1248,7 +1272,8 @@ static void enable_btf_feature(struct btf_feature > *feature) > /* switch "initial-off" features on, and "initial-on" features > * off; i.e. negate the initial value. > */ > - *feature->conf_value = !feature->initial_value; > + if (!feature->feature_check || feature->feature_check()) > + *feature->conf_value = !feature->initial_value; > } > > static void show_supported_btf_features(FILE *output) > @@ -1256,6 +1281,8 @@ static void show_supported_btf_features(FILE *output) > int i; > > for (i = 0; i < ARRAY_SIZE(btf_features); i++) { > + if (btf_features[i].feature_check && !btf_features[i].feature_check()) > + continue; > if (i > 0) > fprintf(output, ","); > fprintf(output, "%s", btf_features[i].name);
