netdev - Re: [PATCHv2] bpftool: Try to read btf as raw data if elf read fails

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Date:   Thu, 24 Oct 2019 15:31:00 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Andrii Nakryiko <andriin@...com>,
        Yonghong Song <yhs@...com>, Martin KaFai Lau <kafai@...com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: Re: [PATCHv2] bpftool: Try to read btf as raw data if elf read fails

On Thu, Oct 24, 2019 at 03:23:41PM +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
>   [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
> 
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---

ugh, wrong title.. I sent v3 :-\ sry

jirka

> v2 changes:
>  - added is_btf_raw to find out which btf__parse_* function to call
>  - changed labels and error propagation in btf__parse_raw 
>  - drop the err initialization, which is not needed under this change
> 
>  tools/bpf/bpftool/btf.c | 57 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 56 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index 9a9376d1d3df..a7b8bf233cf5 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 +391,54 @@ static int dump_btf_c(const struct btf *btf,
>  	return err;
>  }
>  
> +static struct btf *btf__parse_raw(const char *file)
> +{
> +	struct btf *btf;
> +	struct stat st;
> +	__u8 *buf;
> +	FILE *f;
> +
> +	if (stat(file, &st))
> +		return NULL;
> +
> +	f = fopen(file, "rb");
> +	if (!f)
> +		return NULL;
> +
> +	buf = malloc(st.st_size);
> +	if (!buf) {
> +		btf = ERR_PTR(-ENOMEM);
> +		goto exit_close;
> +	}
> +
> +	if ((size_t) st.st_size != fread(buf, 1, st.st_size, f)) {
> +		btf = ERR_PTR(-EINVAL);
> +		goto exit_free;
> +	}
> +
> +	btf = btf__new(buf, st.st_size);
> +
> +exit_free:
> +	free(buf);
> +exit_close:
> +	fclose(f);
> +	return btf;
> +}
> +
> +static bool is_btf_raw(const char *file)
> +{
> +	__u16 magic = 0;
> +	int fd;
> +
> +	fd = open(file, O_RDONLY);
> +	if (fd < 0)
> +		return false;
> +
> +	read(fd, &magic, sizeof(magic));
> +	close(fd);
> +	return magic == BTF_MAGIC;
> +}
> +
>  static int do_dump(int argc, char **argv)
>  {
>  	struct btf *btf = NULL;
> @@ -465,7 +516,11 @@ static int do_dump(int argc, char **argv)
>  		}
>  		NEXT_ARG();
>  	} else if (is_prefix(src, "file")) {
> -		btf = btf__parse_elf(*argv, NULL);
> +		if (is_btf_raw(*argv))
> +			btf = btf__parse_raw(*argv);
> +		else
> +			btf = btf__parse_elf(*argv, NULL);
> +
>  		if (IS_ERR(btf)) {
>  			err = PTR_ERR(btf);
>  			btf = NULL;
> -- 
> 2.21.0
>