Merge branch 'bpf: CO-RE support in the kernel'

Alexei Starovoitov says:

====================

From: Alexei Starovoitov <ast@kernel.org>

v4->v5:
. Reduce number of memory allocations in candidate cache logic
. Fix couple UAF issues
. Add Andrii's patch to cleanup struct bpf_core_cand
. More thorough tests
. Planned followups:
  - support -v in lskel
  - move struct bpf_core_spec out of bpf_core_apply_relo_insn to
    reduce stack usage
  - implement bpf_core_types_are_compat

v3->v4:
. complete refactor of find candidates logic.
  Now it has small permanent cache.
. Fix a bug in gen_loader related to attach_kind.
. Fix BTF log size limit.
. More tests.

v2->v3:
. addressed Andrii's feedback in every patch.
  New field in union bpf_attr changed from "core_relo" to "core_relos".
. added one more test and checkpatch.pl-ed the set.

v1->v2:
. Refactor uapi to pass 'struct bpf_core_relo' from LLVM into libbpf and further
into the kernel instead of bpf_core_apply_relo() bpf helper. Because of this
change the CO-RE algorithm has an ability to log error and debug events through
the standard bpf verifer log mechanism which was not possible with helper
approach.
. #define RELO_CORE macro was removed and replaced with btf_member_bit_offset() patch.

This set introduces CO-RE support in the kernel.
There are several reasons to add such support:
1. It's a step toward signed BPF programs.
2. It allows golang like languages that struggle to adopt libbpf
   to take advantage of CO-RE powers.
3. Currently the field accessed by 'ldx [R1 + 10]' insn is recognized
   by the verifier purely based on +10 offset. If R1 points to a union
   the verifier picks one of the fields at this offset.
   With CO-RE the kernel can disambiguate the field access.

Alexei Starovoitov (16):
  libbpf: Replace btf__type_by_id() with btf_type_by_id().
  bpf: Rename btf_member accessors.
  bpf: Prepare relo_core.c for kernel duty.
  bpf: Define enum bpf_core_relo_kind as uapi.
  bpf: Pass a set of bpf_core_relo-s to prog_load command.
  bpf: Adjust BTF log size limit.
  bpf: Add bpf_core_add_cands() and wire it into
    bpf_core_apply_relo_insn().
  libbpf: Use CO-RE in the kernel in light skeleton.
  libbpf: Support init of inner maps in light skeleton.
  libbpf: Clean gen_loader's attach kind.
  selftests/bpf: Add lskel version of kfunc test.
  selftests/bpf: Improve inner_map test coverage.
  selftests/bpf: Convert map_ptr_kern test to use light skeleton.
  selftests/bpf: Additional test for CO-RE in the kernel.
  selftests/bpf: Revert CO-RE removal in test_ksyms_weak.
  selftests/bpf: Add CO-RE relocations to verifier scale test.
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>