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:
(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
