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

Jakub Kicinski
2019-10-18T22:39:16Z

On Fri, 18 Oct 2019 12:34:04 +0200, Jiri Olsa wrote:
> 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 <jolsa@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;

Please drop the inits

> + struct stat st;
> + FILE *f;
> +
> + if (stat(file, &st))
> + return btf;

And return constants here

> + f = fopen(file, "rb");
> + if (!f)
> + return btf;

and here

> + buf = malloc(st.st_size);
> + if (!buf)
> + goto err;

and jump to the right place here.

> + if ((size_t) st.st_size != fread(buf, 1, st.st_size, f))
> + goto err;
> +
> + btf = btf__new(buf, st.st_size);
> +
> +err:

The prefix for error labels which is shared with non-error path is exit_

> + 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;

This change looks unnecessary.

> 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 {