libbpf: Resolve invalid weak kfunc calls with imm = 0, off = 0
Preserve these calls as it allows verifier to succeed in loading the
program if they are determined to be unreachable after dead code
elimination during program load. If not, the verifier will fail at
runtime. This is done for ext->is_weak symbols similar to the case for
variable ksyms.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-8-memxor@gmail.com
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index ea1c51d..092cf4b 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3439,11 +3439,6 @@
return -ENOTSUP;
}
} else if (strcmp(sec_name, KSYMS_SEC) == 0) {
- if (btf_is_func(t) && ext->is_weak) {
- pr_warn("extern weak function %s is unsupported\n",
- ext->name);
- return -ENOTSUP;
- }
ksym_sec = sec;
ext->type = EXT_KSYM;
skip_mods_and_typedefs(obj->btf, t->type,
@@ -5416,8 +5411,13 @@
case RELO_EXTERN_FUNC:
ext = &obj->externs[relo->sym_off];
insn[0].src_reg = BPF_PSEUDO_KFUNC_CALL;
- insn[0].imm = ext->ksym.kernel_btf_id;
- insn[0].off = ext->ksym.btf_fd_idx;
+ if (ext->is_set) {
+ insn[0].imm = ext->ksym.kernel_btf_id;
+ insn[0].off = ext->ksym.btf_fd_idx;
+ } else { /* unresolved weak kfunc */
+ insn[0].imm = 0;
+ insn[0].off = 0;
+ }
break;
case RELO_SUBPROG_ADDR:
if (insn[0].src_reg != BPF_PSEUDO_FUNC) {
@@ -6807,9 +6807,9 @@
int id, err;
id = find_ksym_btf_id(obj, ext->name, BTF_KIND_VAR, &btf, &mod_btf);
- if (id == -ESRCH && ext->is_weak) {
- return 0;
- } else if (id < 0) {
+ if (id < 0) {
+ if (id == -ESRCH && ext->is_weak)
+ return 0;
pr_warn("extern (var ksym) '%s': not found in kernel BTF\n",
ext->name);
return id;
@@ -6862,7 +6862,9 @@
kfunc_id = find_ksym_btf_id(obj, ext->name, BTF_KIND_FUNC, &kern_btf, &mod_btf);
if (kfunc_id < 0) {
- pr_warn("extern (func ksym) '%s': not found in kernel BTF\n",
+ if (kfunc_id == -ESRCH && ext->is_weak)
+ return 0;
+ pr_warn("extern (func ksym) '%s': not found in kernel or module BTFs\n",
ext->name);
return kfunc_id;
}
