diff mbox series

[bpf-next,v5,07/12] libbpf: Resolve invalid weak kfunc calls with imm = 0, off = 0

Message ID 20210927145941.1383001-8-memxor@gmail.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series Support kernel module function calls from eBPF | expand

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netdev/build_allmodconfig_warn success Errors and warnings before: 0 this patch: 0
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bpf/vmtest-bpf-next-PR success PR summary

Commit Message

Kumar Kartikeya Dwivedi Sept. 27, 2021, 2:59 p.m. UTC 
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.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 tools/lib/bpf/libbpf.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)
diff mbox series

Patch

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0f4d203f926e..4b2d0511c1e7 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3416,11 +3416,6 @@  static int bpf_object__collect_externs(struct bpf_object *obj)
 				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,
@@ -5369,8 +5364,13 @@  bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
 		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.offset;
+			if (ext->is_set) {
+				insn[0].imm = ext->ksym.kernel_btf_id;
+				insn[0].off = ext->ksym.offset;
+			} 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) {
@@ -6719,9 +6719,9 @@  static int bpf_object__resolve_ksym_var_btf_id(struct bpf_object *obj,
 	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;
@@ -6774,7 +6774,9 @@  static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,
 
 	kfunc_id = find_ksym_btf_id(obj, ext->name, BTF_KIND_FUNC, &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;
 	}