bpf: Add bpf_stream_print_stack stack dumping kfunc

Add a new kfunc called bpf_stream_print_stack to be used by programs
that need to print out their current BPF stack. The kfunc is essentially
a wrapper around the existing bpf_stream_dump_stack functionality used
to generate stack traces for error events like may_goto violations and
BPF-side arena page faults.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260203180424.14057-2-emil@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: etsal

kernel/bpf/helpers.c

@@ -4562,6 +4562,7 @@ BTF_ID_FLAGS(func, bpf_strncasestr);
 BTF_ID_FLAGS(func, bpf_cgroup_read_xattr, KF_RCU)
 #endif
 BTF_ID_FLAGS(func, bpf_stream_vprintk, KF_IMPLICIT_ARGS)
+BTF_ID_FLAGS(func, bpf_stream_print_stack, KF_IMPLICIT_ARGS)
 BTF_ID_FLAGS(func, bpf_task_work_schedule_signal, KF_IMPLICIT_ARGS)
 BTF_ID_FLAGS(func, bpf_task_work_schedule_resume, KF_IMPLICIT_ARGS)
 BTF_ID_FLAGS(func, bpf_dynptr_from_file)

kernel/bpf/stream.c

@@ -245,6 +245,25 @@ __bpf_kfunc int bpf_stream_vprintk(int stream_id, const char *fmt__str, const vo
 	return ret;
 }
 
+/* Directly trigger a stack dump from the program. */
+__bpf_kfunc int bpf_stream_print_stack(int stream_id, struct bpf_prog_aux *aux)
+{
+	struct bpf_stream_stage ss;
+	struct bpf_prog *prog;
+
+	/* Make sure the stream ID is valid. */
+	if (!bpf_stream_get(stream_id, aux))
+		return -ENOENT;
+
+	prog = aux->main_prog_aux->prog;
+
+	bpf_stream_stage(ss, prog, stream_id, ({
+		bpf_stream_dump_stack(ss);
+	}));
+
+	return 0;
+}
+
 __bpf_kfunc_end_defs();
 
 /* Added kfunc to common_btf_ids */