tools/bpftool: Auto-detect split BTFs in common cases

In case of working with module's split BTF from /sys/kernel/btf/*,
auto-substitute /sys/kernel/btf/vmlinux as the base BTF. This makes using
bpftool with module BTFs faster and simpler.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201202065244.530571-4-andrii@kernel.org

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index bd46af6..94cd3ba 100644 (file)
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -357,11 +357,13 @@ static int dump_btf_raw(const struct btf *btf,
                        dump_btf_type(btf, root_type_ids[i], t);
                }
        } else {
+               const struct btf *base;
                int cnt = btf__get_nr_types(btf);
                int start_id = 1;
 
-               if (base_btf)
-                       start_id = btf__get_nr_types(base_btf) + 1;
+               base = btf__base_btf(btf);
+               if (base)
+                       start_id = btf__get_nr_types(base) + 1;
 
                for (i = start_id; i <= cnt; i++) {
                        t = btf__type_by_id(btf, i);
@@ -428,7 +430,7 @@ done:
 
 static int do_dump(int argc, char **argv)
 {
-       struct btf *btf = NULL;
+       struct btf *btf = NULL, *base = NULL;
        __u32 root_type_ids[2];
        int root_type_cnt = 0;
        bool dump_c = false;
@@ -502,7 +504,21 @@ static int do_dump(int argc, char **argv)
                }
                NEXT_ARG();
        } else if (is_prefix(src, "file")) {
-               btf = btf__parse_split(*argv, base_btf);
+               const char sysfs_prefix[] = "/sys/kernel/btf/";
+               const char sysfs_vmlinux[] = "/sys/kernel/btf/vmlinux";
+
+               if (!base_btf &&
+                   strncmp(*argv, sysfs_prefix, sizeof(sysfs_prefix) - 1) == 0 &&
+                   strcmp(*argv, sysfs_vmlinux) != 0) {
+                       base = btf__parse(sysfs_vmlinux, NULL);
+                       if (libbpf_get_error(base)) {
+                               p_err("failed to parse vmlinux BTF at '%s': %ld\n",
+                                     sysfs_vmlinux, libbpf_get_error(base));
+                               base = NULL;
+                       }
+               }
+
+               btf = btf__parse_split(*argv, base ?: base_btf);
                if (IS_ERR(btf)) {
                        err = -PTR_ERR(btf);
                        btf = NULL;
@@ -567,6 +583,7 @@ static int do_dump(int argc, char **argv)
 done:
        close(fd);
        btf__free(btf);
+       btf__free(base);
        return err;
 }