On Fri, Mar 19, 2021 at 9:23 AM Jiri Olsa <[email protected]> wrote:
>
> On Thu, Mar 18, 2021 at 12:40:31PM -0700, Andrii Nakryiko wrote:
>
> SNIP
>
> > +
> > + return NULL;
> > +}
> > +
> > +static int linker_fixup_btf(struct src_obj *obj)
> > +{
> > + const char *sec_name;
> > + struct src_sec *sec;
> > + int i, j, n, m;
> > +
> > + n = btf__get_nr_types(obj->btf);
>
> hi,
> I'm getting bpftool crash when building tests,
>
> looks like above obj->btf can be NULL:
I lost if (!obj->btf) return 0; somewhere along the rebases. I'll send
a fix shortly. But how did you end up with selftests BPF objects built
without BTF?
>
> (gdb) r gen object
> /home/jolsa/linux/tools/testing/selftests/bpf/btf_data2.linked1.o
> /home/jolsa/linux/tools/testing/selftests/bpf/btf_data2.o
> Starting program:
> /home/jolsa/linux/tools/testing/selftests/bpf/tools/sbin/bpftool gen object
> /home/jolsa/linux/tools/testing/selftests/bpf/btf_data2.linked1.o
> /home/jolsa/linux/tools/testing/selftests/bpf/btf_data2.o
>
> Program received signal SIGSEGV, Segmentation fault.
> btf__get_nr_types (btf=0x0) at btf.c:425
>
> 425 return btf->start_id + btf->nr_types - 1;
> Missing separate debuginfos, use: dnf debuginfo-install
> elfutils-libelf-0.182-1.fc33.x86_64 libcap-2.48-2.fc33.x86_64
> zlib-1.2.11-23.fc33.x86_64
> (gdb)
> (gdb) bt
> #0 btf__get_nr_types (btf=0x0) at btf.c:425
> #1 0x000000000043c4ba in linker_fixup_btf
> (obj=obj@entry=0x7fffffffda50) at linker.c:1316
> #2 0x000000000043caf7 in linker_load_obj_file
> (linker=linker@entry=0x8612a0, filename=filename@entry=0x7fffffffe0db
> "/home/jolsa/linux/tools/testing/selftests/bpf/btf_data2.o",
> obj=obj@entry=0x7fffffffda50) at linker.c:653
> #3 0x000000000043df43 in bpf_linker__add_file
> (linker=linker@entry=0x8612a0, filename=filename@entry=0x7fffffffe0db
> "/home/jolsa/linux/tools/testing/selftests/bpf/btf_data2.o") at linker.c:412
> #4 0x000000000040d710 in do_object (argc=0, argv=0x7fffffffdce0) at
> gen.c:639
> #5 0x000000000040efd7 in cmd_select (cmds=cmds@entry=0x50a600
> <cmds>, argc=3, argv=0x7fffffffdcc8, help=help@entry=0x40c6f7 <do_help>) at
> main.c:134
> #6 0x000000000040d7c4 in do_gen (argc=<optimized out>,
> argv=<optimized out>) at gen.c:686
> #7 0x000000000040efd7 in cmd_select (cmds=cmds@entry=0x50b400
> <cmds>, argc=4, argv=0x7fffffffdcc0, help=help@entry=0x40ee93 <do_help>) at
> main.c:134
> #8 0x000000000040f88e in main (argc=<optimized out>, argv=<optimized
> out>) at main.c:469
>
> I'm on current bpf-next/master
>
>
> jirka
>
>
> > + for (i = 1; i <= n; i++) {
> > + struct btf_var_secinfo *vi;
> > + struct btf_type *t;
> > +
> > + t = btf_type_by_id(obj->btf, i);
> > + if (btf_kind(t) != BTF_KIND_DATASEC)
> > + continue;
> > +
> > + sec_name = btf__str_by_offset(obj->btf, t->name_off);
> > + sec = find_src_sec_by_name(obj, sec_name);
> > + if (sec) {
> > + /* record actual section size, unless ephemeral */
> > + if (sec->shdr)
> > + t->size = sec->shdr->sh_size;
> > + } else {
> > + /* BTF can have some sections that are not represented
> > + * in ELF, e.g., .kconfig and .ksyms, which are used
> > + * for special extern variables. Here we'll
> > + * pre-create "section shells" for them to be able to
> > + * keep track of extra per-section metadata later
> > + * (e.g., BTF variables).
> > + */
> > + sec = add_src_sec(obj, sec_name);
> > + if (!sec)
> > + return -ENOMEM;
> > +
> > + sec->ephemeral = true;
> > + sec->sec_idx = 0; /* will match UNDEF shndx in ELF */
> > + }
> > +
> > + /* remember ELF section and its BTF type ID match */
> > + sec->sec_type_id = i;
> > +
> > + /* fix up variable offsets */
> > + vi = btf_var_secinfos(t);
> > + for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
> > + const struct btf_type *vt = btf__type_by_id(obj->btf,
> > vi->type);
> > + const char *var_name = btf__str_by_offset(obj->btf,
> > vt->name_off);
> > + int var_linkage = btf_var(vt)->linkage;
> > + Elf64_Sym *sym;
> > +
> > + /* no need to patch up static or extern vars */
> > + if (var_linkage != BTF_VAR_GLOBAL_ALLOCATED)
> > + continue;
> > +
> > + sym = find_sym_by_name(obj, sec->sec_idx, STT_OBJECT,
> > var_name);
> > + if (!sym) {
> > + pr_warn("failed to find symbol for variable
> > '%s' in section '%s'\n", var_name, sec_name);
> > + return -ENOENT;
> > + }
> > +
> > + vi->offset = sym->st_value;
> > + }
> > + }
> > +
> > + return 0;
> > +}
>
> SNIP
>
