lkml.org 
[lkml]   [2022]   [Jun]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 5.18 295/879] libbpf: Dont error out on CO-RE relos for overriden weak subprogs
    Date
    From: Andrii Nakryiko <andrii@kernel.org>

    [ Upstream commit e89d57d938c8fa80c457982154ed6110804814fe ]

    During BPF static linking, all the ELF relocations and .BTF.ext
    information (including CO-RE relocations) are preserved for __weak
    subprograms that were logically overriden by either previous weak
    subprogram instance or by corresponding "strong" (non-weak) subprogram.
    This is just how native user-space linkers work, nothing new.

    But libbpf is over-zealous when processing CO-RE relocation to error out
    when CO-RE relocation belonging to such eliminated weak subprogram is
    encountered. Instead of erroring out on this expected situation, log
    debug-level message and skip the relocation.

    Fixes: db2b8b06423c ("libbpf: Support CO-RE relocations for multi-prog sections")
    Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Link: https://lore.kernel.org/bpf/20220408181425.2287230-2-andrii@kernel.org
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    tools/lib/bpf/libbpf.c | 15 +++++++++++----
    1 file changed, 11 insertions(+), 4 deletions(-)

    diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
    index dabf9a1451c3..7af6805a863d 100644
    --- a/tools/lib/bpf/libbpf.c
    +++ b/tools/lib/bpf/libbpf.c
    @@ -5665,10 +5665,17 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
    insn_idx = rec->insn_off / BPF_INSN_SZ;
    prog = find_prog_by_sec_insn(obj, sec_idx, insn_idx);
    if (!prog) {
    - pr_warn("sec '%s': failed to find program at insn #%d for CO-RE offset relocation #%d\n",
    - sec_name, insn_idx, i);
    - err = -EINVAL;
    - goto out;
    + /* When __weak subprog is "overridden" by another instance
    + * of the subprog from a different object file, linker still
    + * appends all the .BTF.ext info that used to belong to that
    + * eliminated subprogram.
    + * This is similar to what x86-64 linker does for relocations.
    + * So just ignore such relocations just like we ignore
    + * subprog instructions when discovering subprograms.
    + */
    + pr_debug("sec '%s': skipping CO-RE relocation #%d for insn #%d belonging to eliminated weak subprogram\n",
    + sec_name, i, insn_idx);
    + continue;
    }
    /* no need to apply CO-RE relocation if the program is
    * not going to be loaded
    --
    2.35.1


    \
     
     \ /
      Last update: 2022-06-08 00:27    [W:2.480 / U:1.036 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site