netdev - [PATCH bpf-next v2] bpf: fix a compilation error when CONFIG_BPF

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Date:   Tue, 20 Nov 2018 14:08:20 -0800
From:   Yonghong Song <yhs@...com>
To:     <ast@...com>, <daniel@...earbox.net>, <netdev@...r.kernel.org>,
        <kbuild-all@...org>
CC:     <kernel-team@...com>, Martin KaFai Lau <kafai@...com>
Subject: [PATCH bpf-next v2] bpf: fix a compilation error when CONFIG_BPF_SYSCALL is not defined

Kernel test robot (lkp@...el.com) reports a compilation error at
  https://www.spinics.net/lists/netdev/msg534913.html
introduced by commit 838e96904ff3 ("bpf: Introduce bpf_func_info").

If CONFIG_BPF is defined and CONFIG_BPF_SYSCALL is not defined,
the following error will appear:
  kernel/bpf/core.c:414: undefined reference to `btf_type_by_id'
  kernel/bpf/core.c:415: undefined reference to `btf_name_by_offset'

When CONFIG_BPF_SYSCALL is not defined,
let us define stub inline functions for btf_type_by_id()
and btf_name_by_offset() in include/linux/btf.h.
This way, the compilation failure can be avoided.

Fixes: 838e96904ff3 ("bpf: Introduce bpf_func_info")
Reported-by: kbuild test robot <lkp@...el.com>
Cc: Martin KaFai Lau <kafai@...com>
Signed-off-by: Yonghong Song <yhs@...com>
---
 include/linux/btf.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

Changelog:
  v1 -> v2:
    . Two functions should be static inline functions
      if CONFIG_BPF_SYSCALL is not defined.

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 7f2c0a4a45ea..8c2199b5d250 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -46,7 +46,21 @@ void btf_type_seq_show(const struct btf *btf, u32 type_id, void *obj,
 		       struct seq_file *m);
 int btf_get_fd_by_id(u32 id);
 u32 btf_id(const struct btf *btf);
+
+#ifdef CONFIG_BPF_SYSCALL
 const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id);
 const char *btf_name_by_offset(const struct btf *btf, u32 offset);
+#else
+static inline const struct btf_type *btf_type_by_id(const struct btf *btf,
+						    u32 type_id)
+{
+	return NULL;
+}
+static inline const char *btf_name_by_offset(const struct btf *btf,
+					     u32 offset)
+{
+	return NULL;
+}
+#endif
 
 #endif
-- 
2.17.1