[tip:perf/core] bpf tools: Check endianness and make libbpf fail early

From: tip-bot for Wang Nan
Date: Sat Aug 08 2015 - 04:11:48 EST

Commit-ID: cc4228d57c4c35ae0a29efa1e7687a817dc038d9
Gitweb: http://git.kernel.org/tip/cc4228d57c4c35ae0a29efa1e7687a817dc038d9
Author: Wang Nan <wangnan0@xxxxxxxxxx>
AuthorDate: Wed, 1 Jul 2015 02:13:55 +0000
Committer: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Fri, 7 Aug 2015 10:16:56 -0300

bpf tools: Check endianness and make libbpf fail early

Check endianness according to EHDR. Code is taken from

Libbpf doesn't magically convert missmatched endianness. Even if we swap
eBPF instructions to correct byte order, we are unable to deal with
endianness in code logical generated by LLVM.

Therefore, libbpf should simply reject missmatched ELF object, and let
LLVM to create good code.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Acked-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
Cc: Brendan Gregg <brendan.d.gregg@xxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: He Kuang <hekuang@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kaixu Xia <xiakaixu@xxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
Link: http://lkml.kernel.org/r/1435716878-189507-8-git-send-email-wangnan0@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
tools/lib/bpf/libbpf.c | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 36dfbc1..15b3e82 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -192,6 +192,34 @@ errout:
return err;

+static int
+bpf_object__check_endianness(struct bpf_object *obj)
+ static unsigned int const endian = 1;
+ switch (obj->efile.ehdr.e_ident[EI_DATA]) {
+ /* We are big endian, BPF obj is little endian. */
+ if (*(unsigned char const *)&endian != 1)
+ goto mismatch;
+ break;
+ /* We are little endian, BPF obj is big endian. */
+ if (*(unsigned char const *)&endian != 0)
+ goto mismatch;
+ break;
+ default:
+ return -EINVAL;
+ }
+ return 0;
+ pr_warning("Error: endianness mismatch.\n");
+ return -EINVAL;
static struct bpf_object *
__bpf_object__open(const char *path, void *obj_buf, size_t obj_buf_sz)
@@ -208,6 +236,8 @@ __bpf_object__open(const char *path, void *obj_buf, size_t obj_buf_sz)

if (bpf_object__elf_init(obj))
goto out;
+ if (bpf_object__check_endianness(obj))
+ goto out;

return obj;
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