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    Subject[PATCH v11 07/39] bpf tools: Check endianness and make libbpf fail early
    Date
    Check endianness according to EHDR. Code is taken from
    tools/perf/util/symbol-elf.c.

    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@huawei.com>
    Acked-by: Alexei Starovoitov <ast@plumgrid.com>
    Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
    Cc: Daniel Borkmann <daniel@iogearbox.net>
    Cc: David Ahern <dsahern@gmail.com>
    Cc: He Kuang <hekuang@huawei.com>
    Cc: Jiri Olsa <jolsa@kernel.org>
    Cc: Kaixu Xia <xiakaixu@huawei.com>
    Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Zefan Li <lizefan@huawei.com>
    Cc: pi3orama@163.com
    Link: http://lkml.kernel.org/r/1435716878-189507-8-git-send-email-wangnan0@huawei.com
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    ---
    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]) {
    + case ELFDATA2LSB:
    + /* We are big endian, BPF obj is little endian. */
    + if (*(unsigned char const *)&endian != 1)
    + goto mismatch;
    + break;
    +
    + case ELFDATA2MSB:
    + /* We are little endian, BPF obj is big endian. */
    + if (*(unsigned char const *)&endian != 0)
    + goto mismatch;
    + break;
    + default:
    + return -EINVAL;
    + }
    +
    + return 0;
    +
    +mismatch:
    + 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;

    bpf_object__elf_finish(obj);
    return obj;
    --
    1.8.3.4


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