[PATCH bpf-next 02/11] bpf: always emit struct bpf_perf_link BTF

[Alexander Lobakin <alobakin@pm.me>]

When building bpftool with !CONFIG_PERF_EVENTS:

skeleton/pid_iter.bpf.c:47:14: error: incomplete definition of type 'struct bpf_perf_link'
        perf_link = container_of(link, struct bpf_perf_link, link);
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:74:22: note: expanded from macro 'container_of'
                ((type *)(__mptr - offsetof(type, member)));    \
                                   ^~~~~~~~~~~~~~~~~~~~~~
tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:68:60: note: expanded from macro 'offsetof'
 #define offsetof(TYPE, MEMBER)  ((unsigned long)&((TYPE *)0)->MEMBER)
                                                  ~~~~~~~~~~~^
skeleton/pid_iter.bpf.c:44:9: note: forward declaration of 'struct bpf_perf_link'
        struct bpf_perf_link *perf_link;
               ^

&bpf_perf_link is being defined and used only under the ifdef.
Move it out of the block and explicitly emit a BTF to fix
compilation.

Fixes: cbdaf71f7e65 ("bpftool: Add bpf_cookie to link output")
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
---
 kernel/bpf/syscall.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e9621cfa09f2..34fdf27d14cf 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2952,12 +2952,12 @@ static const struct bpf_link_ops bpf_raw_tp_link_lops = {
 	.fill_link_info = bpf_raw_tp_link_fill_link_info,
 };

-#ifdef CONFIG_PERF_EVENTS
 struct bpf_perf_link {
 	struct bpf_link link;
 	struct file *perf_file;
 };

+#ifdef CONFIG_PERF_EVENTS
 static void bpf_perf_link_release(struct bpf_link *link)
 {
 	struct bpf_perf_link *perf_link = container_of(link, struct bpf_perf_link, link);
@@ -4333,6 +4333,7 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
 #endif
 	case BPF_PROG_TYPE_PERF_EVENT:
 	case BPF_PROG_TYPE_TRACEPOINT:
+		BTF_TYPE_EMIT(struct bpf_perf_link);
 		ret = bpf_perf_link_attach(attr, prog);
 		break;
 	case BPF_PROG_TYPE_KPROBE:
--
2.35.2