libbpf: use negative fd to specify missing BTF

0 is a valid FD, so it's better to initialize it to -1, as is done in
other places. Also, technically, BTF type ID 0 is valid (it's a VOID
type), so it's more reliable to check btf_fd, instead of
btf_key_type_id, to determine if there is any BTF associated with a map.

Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 7 insertions, 6 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 9f421206d3e7..b43913fc8b1b 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1751,7 +1751,7 @@ bpf_object__create_maps(struct bpf_object *obj)
                 create_attr.key_size = def->key_size;
                 create_attr.value_size = def->value_size;
                 create_attr.max_entries = def->max_entries;
-                create_attr.btf_fd = 0;
+                create_attr.btf_fd = -1;
                 create_attr.btf_key_type_id = 0;
                 create_attr.btf_value_type_id = 0;
                 if (bpf_map_type__is_map_in_map(def->type) &&
@@ -1765,11 +1765,11 @@ bpf_object__create_maps(struct bpf_object *obj)
                 }
 
                 *pfd = bpf_create_map_xattr(&create_attr);
-                if (*pfd < 0 && create_attr.btf_key_type_id) {
+                if (*pfd < 0 && create_attr.btf_fd >= 0) {
                         cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
                         pr_warning("Error in bpf_create_map_xattr(%s):%s(%d). Retrying without BTF.\n",
                                    map->name, cp, errno);
-                        create_attr.btf_fd = 0;
+                        create_attr.btf_fd = -1;
                         create_attr.btf_key_type_id = 0;
                         create_attr.btf_value_type_id = 0;
                         map->btf_key_type_id = 0;
@@ -2053,6 +2053,9 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
         char *log_buf;
         int ret;
 
+        if (!insns || !insns_cnt)
+                return -EINVAL;
+
         memset(&load_attr, 0, sizeof(struct bpf_load_program_attr));
         load_attr.prog_type = prog->type;
         load_attr.expected_attach_type = prog->expected_attach_type;
@@ -2063,7 +2066,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
         load_attr.license = license;
         load_attr.kern_version = kern_version;
         load_attr.prog_ifindex = prog->prog_ifindex;
-        load_attr.prog_btf_fd = prog->btf_fd >= 0 ? prog->btf_fd : 0;
+        load_attr.prog_btf_fd = prog->btf_fd;
         load_attr.func_info = prog->func_info;
         load_attr.func_info_rec_size = prog->func_info_rec_size;
         load_attr.func_info_cnt = prog->func_info_cnt;
@@ -2072,8 +2075,6 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
         load_attr.line_info_cnt = prog->line_info_cnt;
         load_attr.log_level = prog->log_level;
         load_attr.prog_flags = prog->prog_flags;
-        if (!load_attr.insns || !load_attr.insns_cnt)
-                return -EINVAL;
 
 retry_load:
         log_buf = malloc(log_buf_size);