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libbpf: Add typeless ksym support to gen_loader

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This uses the bpf_kallsyms_lookup_name helper added in previous patches
to relocate typeless ksyms. The return value ENOENT can be ignored, and
the value written to 'res' can be directly stored to the insn, as it is
overwritten to 0 on lookup failure. For repeating symbols, we can simply
copy the previously populated bpf_insn.

Also, we need to take care to not close fds for typeless ksym_desc, so
reuse the 'off' member's space to add a marker for typeless ksym and use
that to skip them in cleanup_relos.

We add a emit_ksym_relo_log helper that avoids duplicating common
logging instructions between typeless and weak ksym (for future commit).

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211028063501.2239335-3-memxor@gmail.com
This commit is contained in:
Kumar Kartikeya Dwivedi
2021-10-28 12:04:55 +05:30
committed by Andrii Nakryiko
parent 1dd20d7144
commit 8e697cf9fd
3 changed files with 99 additions and 23 deletions
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13
src/libbpf.c
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@@ -6575,17 +6575,14 @@ static int bpf_program__record_externs(struct bpf_program *prog)
case RELO_EXTERN_VAR:
if (ext->type != EXT_KSYM)
continue;
if (!ext->ksym.type_id) {
pr_warn("typeless ksym %s is not supported yet\n",
ext->name);
return -ENOTSUP;
}
bpf_gen__record_extern(obj->gen_loader, ext->name, ext->is_weak,
bpf_gen__record_extern(obj->gen_loader, ext->name,
ext->is_weak, !ext->ksym.type_id,
BTF_KIND_VAR, relo->insn_idx);
break;
case RELO_EXTERN_FUNC:
bpf_gen__record_extern(obj->gen_loader, ext->name, ext->is_weak,
BTF_KIND_FUNC, relo->insn_idx);
bpf_gen__record_extern(obj->gen_loader, ext->name,
ext->is_weak, false, BTF_KIND_FUNC,
relo->insn_idx);
break;
default:
continue;