bpf: Don't reference arena kfuncs when arena isn't built

kernel/bpf/Makefile builds arena.o only for CONFIG_MMU && CONFIG_64BIT,
but special_kfunc_list references bpf_arena_alloc_pages() and
bpf_arena_free_pages() unconditionally, so on 32-bit and !MMU kernels
resolve_btfids can't resolve them:

  WARN: resolve_btfids: unresolved symbol bpf_arena_free_pages
  WARN: resolve_btfids: unresolved symbol bpf_arena_alloc_pages

Since commit 201a454df948 ("resolve_btfids: Fix the --fatal_warnings
exit status") these warnings fail the build with CONFIG_WERROR=y, which
breaks i386 builds with CONFIG_DEBUG_INFO_BTF=y:

  Failed to generate BTF for vmlinux
  Try to disable CONFIG_DEBUG_INFO_BTF

Only reference them under the condition arena.o is built with, and use
BTF_ID_UNUSED otherwise to keep the list in sync with enum
special_kfunc_type. An unresolved ID is zero, like BTF_ID_UNUSED, so the
contents of the list don't change.

Fixes: b8467290edab ("bpf: arena: make arena kfuncs any context safe")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20261019211006.2574350-3-sashal@kernel.org

0 files changed, 0 insertions, 0 deletions