[PATCH bpf-next 02/20] bpf: Add the bpf_unwind_resume() kfunc

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

A compiler-emitted cleanup landing pad ends with a call to
_Unwind_Resume(), which carries the unwind on once that frame's cleanups
have run. The kernel provides the same terminator as a kfunc, named
bpf_unwind_resume() to keep the 'bpf_' prefix kfunc convention; a later
libbpf patch resolves the compiler's name to it.

The body never runs. A JIT emits the way back out of a landing pad in its
place.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 kernel/bpf/helpers.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 051b6654e57c..31d84de4d318 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3407,6 +3407,17 @@ __bpf_kfunc void bpf_throw(u64 cookie)
 	WARN(1, "A call to BPF exception callback should never return\n");
 }
 
+/*
+ * Terminator of a compiler-emitted cleanup landing pad. The compiler names
+ * this _Unwind_Resume, the base unwind ABI's entry point for carrying an
+ * unwind on once a frame's cleanups have run. To match kernel kfunc
+ * convention, the kernel calls it bpf_unwind_resume and libbpf maps the
+ * compiler's name onto it.
+ */
+__bpf_kfunc void bpf_unwind_resume(void)
+{
+}
+
 __bpf_kfunc int bpf_wq_init(struct bpf_wq *wq, void *p__const_map, unsigned int flags)
 {
 	struct bpf_async_kern *async = (struct bpf_async_kern *)wq;
@@ -4853,6 +4864,7 @@ BTF_ID_FLAGS(func, bpf_task_get_cgroup1, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_task_from_vpid, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_throw)
+BTF_ID_FLAGS(func, bpf_unwind_resume)
 #ifdef CONFIG_BPF_EVENTS
 BTF_ID_FLAGS(func, bpf_send_signal_task)
 #endif
-- 
2.53.0-Meta