On 17/07/2025 16:25, Jiri Olsa wrote: > Menglong reported issue where we can have function in BTF which has > multiple addresses in kallsysm [1]. > > Rather than filtering this in runtime, let's teach pahole to remove > such functions. > > Removing duplicate records from functions entries that have more > at least one different address. This way btf_encoder__find_function > won't find such functions and they won't be added in BTF. > > In my setup it removed 428 functions out of 77141. > Is such removal necessary? If the presence of an mcount annotation is the requirement, couldn't we just utilize /sys/kernel/tracing/available_filter_functions_addrs to map name to address safely? It identifies mcount-containing functions and some of these appear to be duplicates, for example there I see ffffffff8376e8b4 acpi_attr_is_visible ffffffff8379b7d4 acpi_attr_is_visible ? > [1] https://lore.kernel.org/bpf/20250710070835.260831-1-dongml2@xxxxxxxxxxxxxxx/ > Reported-by: Menglong Dong <menglong8.dong@xxxxxxxxx> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx> > --- > > Alan, > I'd like to test this in the pahole CI, is there a way to manualy trigger it? > Easiest way is to base from pahole's next branch and push to a github repo; the tests will run as actions there. I've just merged the function comparison work so that will be available if you base/sync a branch on next from git.kernel.org/pub/scm/devel/pahole/pahole.git/ . Thanks! Alan > thanks, > jirka > > > --- > btf_encoder.c | 37 +++++++++++++++++++++++++++++++++++++ > 1 file changed, 37 insertions(+) > > diff --git a/btf_encoder.c b/btf_encoder.c > index 16739066caae..a25fe2f8bfb1 100644 > --- a/btf_encoder.c > +++ b/btf_encoder.c > @@ -99,6 +99,7 @@ struct elf_function { > size_t prefixlen; > bool kfunc; > uint32_t kfunc_flags; > + unsigned long addr; > }; > > struct elf_secinfo { > @@ -1469,6 +1470,7 @@ static void elf_functions__collect_function(struct elf_functions *functions, GEl > > func = &functions->entries[functions->cnt]; > func->name = name; > + func->addr = sym->st_value; > if (strchr(name, '.')) { > const char *suffix = strchr(name, '.'); > > @@ -2143,6 +2145,40 @@ int btf_encoder__encode(struct btf_encoder *encoder, struct conf_load *conf) > return err; > } > > +/* > + * Remove name duplicates from functions->entries that have > + * at least 2 different addresses. > + */ > +static void functions_remove_dups(struct elf_functions *functions) > +{ > + struct elf_function *n = &functions->entries[0]; > + bool matched = false, diff = false; > + int i, j; > + > + for (i = 0, j = 1; i < functions->cnt && j < functions->cnt; i++, j++) { > + struct elf_function *a = &functions->entries[i]; > + struct elf_function *b = &functions->entries[j]; > + > + if (!strcmp(a->name, b->name)) { > + matched = true; > + diff |= a->addr != b->addr; > + continue; > + } > + > + /* > + * Keep only not-matched entries and last one of the matched/duplicates > + * ones if all of the matched entries had the same address. > + **/ > + if (!matched || !diff) > + *n++ = *a; > + matched = diff = false; > + } > + > + if (!matched || !diff) > + *n++ = functions->entries[functions->cnt - 1]; > + functions->cnt = n - &functions->entries[0]; > +} > + > static int elf_functions__collect(struct elf_functions *functions) > { > uint32_t nr_symbols = elf_symtab__nr_symbols(functions->symtab); > @@ -2168,6 +2204,7 @@ static int elf_functions__collect(struct elf_functions *functions) > > if (functions->cnt) { > qsort(functions->entries, functions->cnt, sizeof(*functions->entries), functions_cmp); > + functions_remove_dups(functions); > } else { > err = 0; > goto out_free;
