[PATCH] bpftool: Try to read btf as raw data if elf read fails

[Jiri Olsa]

The bpftool interface stays the same, but now it's possible
to run it over BTF raw data, like:

  $ bpftool btf dump file /sys/kernel/btf/vmlinux
  libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux
  [1] INT '(anon)' size=4 bits_offset=0 nr_bits=32 encoding=(none)
  [2] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
  [3] CONST '(anon)' type_id=2

I'm also adding err init to 0 because I was getting uninitialized
warnings from gcc.

Signed-off-by: Jiri Olsa <jo...@kernel.org>
---
 tools/bpf/bpftool/btf.c | 47 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 42 insertions(+), 5 deletions(-)

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 9a9376d1d3df..100fb7e02329 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -12,6 +12,9 @@
 #include <libbpf.h>
 #include <linux/btf.h>
 #include <linux/hashtable.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
 
 #include "btf.h"
 #include "json_writer.h"
@@ -388,6 +391,35 @@ static int dump_btf_c(const struct btf *btf,
        return err;
 }
 
+static struct btf *btf__parse_raw(const char *file)
+{
+       struct btf *btf = ERR_PTR(-EINVAL);
+       __u8 *buf = NULL;
+       struct stat st;
+       FILE *f;
+
+       if (stat(file, &st))
+               return btf;
+
+       f = fopen(file, "rb");
+       if (!f)
+               return btf;
+
+       buf = malloc(st.st_size);
+       if (!buf)
+               goto err;
+
+       if ((size_t) st.st_size != fread(buf, 1, st.st_size, f))
+               goto err;
+
+       btf = btf__new(buf, st.st_size);
+
+err:
+       free(buf);
+       fclose(f);
+       return btf;
+}
+
 static int do_dump(int argc, char **argv)
 {
        struct btf *btf = NULL;
@@ -397,7 +429,7 @@ static int do_dump(int argc, char **argv)
        __u32 btf_id = -1;
        const char *src;
        int fd = -1;
-       int err;
+       int err = 0;
 
        if (!REQ_ARGS(2)) {
                usage();
@@ -468,10 +500,15 @@ static int do_dump(int argc, char **argv)
                btf = btf__parse_elf(*argv, NULL);
                if (IS_ERR(btf)) {
                        err = PTR_ERR(btf);
-                       btf = NULL;
-                       p_err("failed to load BTF from %s: %s", 
-                             *argv, strerror(err));
-                       goto done;
+                       if (err == -LIBBPF_ERRNO__FORMAT)
+                               btf = btf__parse_raw(*argv);
+                       if (IS_ERR(btf)) {
+                               btf = NULL;
+                               /* Display the original error value. */
+                               p_err("failed to load BTF from %s: %s",
+                                     *argv, strerror(err));
+                               goto done;
+                       }
                }
                NEXT_ARG();
        } else {
-- 
2.21.0