[PATCH bpf-next 03/13] bpf, libbpf: load prog BTF in the skel_internal loader

[KP Singh <kpsingh@kernel.org>]

bpf_load_and_run loads only the loader insns and the metadata map.
To match the kernel's extended signature scope (insns || btf), the
loader needs to BPF_BTF_LOAD the prog BTF before BPF_PROG_LOAD so
attr->prog_btf_fd can be filled in.

Add btf and btf_sz to bpf_load_and_run_opts; when set, do the
BPF_BTF_LOAD before BPF_PROG_LOAD and pass the resulting fd as
attr->prog_btf_fd.

Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 tools/lib/bpf/skel_internal.h | 44 ++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/skel_internal.h b/tools/lib/bpf/skel_internal.h
index 6a8f5c7a02eb..0b6b1ecedd45 100644
--- a/tools/lib/bpf/skel_internal.h
+++ b/tools/lib/bpf/skel_internal.h
@@ -11,6 +11,8 @@
 #include <linux/bpf.h>
 #else
 #include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
 #include <sys/syscall.h>
 #include <sys/mman.h>
 #include <linux/keyctl.h>
@@ -66,8 +68,10 @@ struct bpf_load_and_run_opts {
 	struct bpf_loader_ctx *ctx;
 	const void *data;
 	const void *insns;
+	const void *btf;
 	__u32 data_sz;
 	__u32 insns_sz;
+	__u32 btf_sz;
 	const char *errstr;
 	void *signature;
 	__u32 signature_sz;
@@ -88,6 +92,22 @@ static inline int skel_sys_bpf(enum bpf_cmd cmd, union bpf_attr *attr,
 #endif
 }
 
+#ifndef __KERNEL__
+static inline int skel_sys_btf_load(union bpf_attr *attr, unsigned int size)
+{
+	int fd;
+
+	fd = skel_sys_bpf(BPF_BTF_LOAD, attr, size);
+	if (fd >= 0 && fd < 3) {
+		int new_fd = fcntl(fd, F_DUPFD_CLOEXEC, 3);
+
+		close(fd);
+		fd = new_fd;
+	}
+	return fd;
+}
+#endif
+
 #ifdef __KERNEL__
 static inline int close(int fd)
 {
@@ -353,8 +373,9 @@ static inline int skel_map_freeze(int fd)
 static inline int bpf_load_and_run(struct bpf_load_and_run_opts *opts)
 {
 	const size_t prog_load_attr_sz = offsetofend(union bpf_attr, keyring_id);
+	const size_t btf_load_attr_sz = offsetofend(union bpf_attr, btf_token_fd);
 	const size_t test_run_attr_sz = offsetofend(union bpf_attr, test);
-	int map_fd = -1, prog_fd = -1, key = 0, err;
+	int map_fd = -1, prog_fd = -1, btf_fd = -1, key = 0, err;
 	union bpf_attr attr;
 
 	err = map_fd = skel_map_create(BPF_MAP_TYPE_ARRAY, "__loader.map", 4, opts->data_sz, 1,
@@ -387,11 +408,30 @@ static inline int bpf_load_and_run(struct bpf_load_and_run_opts *opts)
 	}
 #endif
 
+#ifndef __KERNEL__
+	if (opts->btf && opts->btf_sz) {
+		memset(&attr, 0, btf_load_attr_sz);
+		attr.btf = (long) opts->btf;
+		attr.btf_size = opts->btf_sz;
+		attr.btf_log_level = opts->ctx->log_level;
+		attr.btf_log_size = opts->ctx->log_size;
+		attr.btf_log_buf = opts->ctx->log_buf;
+		err = btf_fd = skel_sys_btf_load(&attr, btf_load_attr_sz);
+		if (btf_fd < 0) {
+			opts->errstr = "failed to load loader BTF";
+			set_err;
+			goto out;
+		}
+	}
+#endif
+
 	memset(&attr, 0, prog_load_attr_sz);
 	attr.prog_type = BPF_PROG_TYPE_SYSCALL;
 	attr.insns = (long) opts->insns;
 	attr.insn_cnt = opts->insns_sz / sizeof(struct bpf_insn);
 	attr.license = (long) "Dual BSD/GPL";
+	if (btf_fd >= 0)
+		attr.prog_btf_fd = btf_fd;
 #ifndef __KERNEL__
 	attr.signature = (long) opts->signature;
 	attr.signature_size = opts->signature_sz;
@@ -437,6 +477,8 @@ static inline int bpf_load_and_run(struct bpf_load_and_run_opts *opts)
 		close(map_fd);
 	if (prog_fd >= 0)
 		close(prog_fd);
+	if (btf_fd >= 0)
+		close(btf_fd);
 	return err;
 }
 
-- 
2.53.0