Acked-by: Hao Luo <haoluo@xxxxxxxxxx>, with a couple of nits.
On Fri, Jan 8, 2021 at 2:09 PM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>
> Add support for searching for ksym externs not just in vmlinux BTF, but across
> all module BTFs, similarly to how it's done for CO-RE relocations. Kernels
> that expose module BTFs through sysfs are assumed to support new ldimm64
> instruction extension with BTF FD provided in insn[1].imm field, so no extra
> feature detection is performed.
>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 47 +++++++++++++++++++++++++++---------------
> 1 file changed, 30 insertions(+), 17 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6ae748f6ea11..57559a71e4de 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
[...]
> @@ -7319,7 +7321,8 @@ static int bpf_object__read_kallsyms_file(struct bpf_object *obj)
> static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
> {
> struct extern_desc *ext;
> - int i, id;
> + struct btf *btf;
> + int i, j, id, btf_fd, err;
>
> for (i = 0; i < obj->nr_extern; i++) {
> const struct btf_type *targ_var, *targ_type;
> @@ -7331,8 +7334,22 @@ static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
> if (ext->type != EXT_KSYM || !ext->ksym.type_id)
> continue;
>
> - id = btf__find_by_name_kind(obj->btf_vmlinux, ext->name,
> - BTF_KIND_VAR);
> + btf = obj->btf_vmlinux;
> + btf_fd = 0;
> + id = btf__find_by_name_kind(btf, ext->name, BTF_KIND_VAR);
Is "if (id <= 0)" better? Just in case, more error code is introduced in future.
> + if (id == -ENOENT) {
> + err = load_module_btfs(obj);
> + if (err)
> + return err;
> +
> + for (j = 0; j < obj->btf_module_cnt; j++) {
> + btf = obj->btf_modules[j].btf;
> + btf_fd = obj->btf_modules[j].fd;
> + id = btf__find_by_name_kind(btf, ext->name, BTF_KIND_VAR);
> + if (id != -ENOENT)
> + break;
> + }
> + }
> if (id <= 0) {
Nit: the warning message isn't accurate any more, right? We also
searched kernel modules' BTF.
> pr_warn("extern (ksym) '%s': failed to find BTF ID in vmlinux BTF.\n",
> ext->name);
> @@ -7343,24 +7360,19 @@ static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
[...]
> --
> 2.24.1
>
