[PATCH bpf-next v1] bpf: guard BTF_ID_FLAGS(bpf_cgroup_read_xattr) with CONFIG_BPF_LSM

[Eduard Zingerman <eddyz87@xxxxxxxxx>]

Function bpf_cgroup_read_xattr is defined in fs/bpf_fs_kfuncs.c,
which is compiled only when CONFIG_BPF_LSM is set. Add CONFIG_BPF_LSM
check to bpf_cgroup_read_xattr spec in common_btf_ids in
kernel/bpf/helpers.c to avoid build failures for configs w/o
CONFIG_BPF_LSM.

Build failure example:

    BTF     .tmp_vmlinux1.btf.o
  btf_encoder__tag_kfunc: failed to find kfunc 'bpf_cgroup_read_xattr' in BTF
  ...
  WARN: resolve_btfids: unresolved symbol bpf_cgroup_read_xattr
  make[2]: *** [scripts/Makefile.vmlinux:91: vmlinux.unstripped] Error 255

Fixes: 535b070f4a80 ("bpf: Introduce bpf_cgroup_read_xattr to read xattr of cgroup's node")
Reported-by: Jake Hillion <jakehillion@xxxxxxxx>
Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
 kernel/bpf/helpers.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index b4117681137e..f48fa3fe8dec 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3779,7 +3779,7 @@ BTF_ID_FLAGS(func, bpf_strspn);
 BTF_ID_FLAGS(func, bpf_strcspn);
 BTF_ID_FLAGS(func, bpf_strstr);
 BTF_ID_FLAGS(func, bpf_strnstr);
-#ifdef CONFIG_CGROUPS
+#if defined(CONFIG_BPF_LSM) && defined(CONFIG_CGROUPS)
 BTF_ID_FLAGS(func, bpf_cgroup_read_xattr, KF_RCU)
 #endif
 BTF_KFUNCS_END(common_btf_ids)
-- 
2.47.1