[PATCH bpf-next 13/20] libbpf: Resolve the compiler's _Unwind_Resume to the kernel's kfunc

[Yonghong Song <yonghong.song@linux.dev>]

LLVM terminates a cleanup landing pad with a call to _Unwind_Resume: the
base unwind ABI's entry point for carrying an unwind on once a frame's
cleanups have run. The kernel provides that terminator as a kfunc, but
not under that name: claiming _Unwind_Resume in the kernel's own symbol
table, for a function whose body never runs, would be needlessly confusing,
so it is called bpf_unwind_resume.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 tools/lib/bpf/libbpf.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 613afae26519..ea1c09fa3793 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8346,6 +8346,15 @@ static void fixup_verifier_log(struct bpf_program *prog, char *buf, size_t buf_s
 	}
 }
 
+/* LLVM terminates a cleanup landing pad with a call to _Unwind_Resume, the
+ * base unwind ABI's entry point for carrying an unwind on once a frame's
+ * cleanups have run. The kernel knows it as bpf_unwind_resume.
+ */
+static const char *kern_extern_name(const char *name)
+{
+	return strcmp(name, "_Unwind_Resume") ? name : "bpf_unwind_resume";
+}
+
 static int bpf_program_record_relos(struct bpf_program *prog)
 {
 	struct bpf_object *obj = prog->obj;
@@ -8807,17 +8816,19 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,
 	struct module_btf *mod_btf = NULL;
 	const struct btf_type *kern_func;
 	struct btf *kern_btf = NULL;
+	const char *kern_name;
 	int ret;
 
 	local_func_proto_id = ext->ksym.type_id;
 
-	kfunc_id = find_ksym_btf_id(obj, ext->essent_name ?: ext->name, BTF_KIND_FUNC, &kern_btf,
-				    &mod_btf);
+	kern_name = kern_extern_name(ext->essent_name ?: ext->name);
+
+	kfunc_id = find_ksym_btf_id(obj, kern_name, BTF_KIND_FUNC, &kern_btf, &mod_btf);
 	if (kfunc_id < 0) {
 		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);
+			strcmp(kern_name, "bpf_unwind_resume") ? ext->name : kern_name);
 		return kfunc_id;
 	}
 
-- 
2.53.0-Meta