linux-kernel - [PATCH bpf-next] bpf: Fix bpf-next builds without CONFIG_BPF

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Date:   Wed, 25 Aug 2021 18:48:31 -0700
From:   Daniel Xu <dxu@...uu.xyz>
To:     bpf@...r.kernel.org, ast@...nel.org
Cc:     Daniel Xu <dxu@...uu.xyz>, kernel-team@...com,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: [PATCH bpf-next] bpf: Fix bpf-next builds without CONFIG_BPF_EVENTS

This commit fixes linker errors along the lines of:

    s390-linux-ld: task_iter.c:(.init.text+0xa4): undefined reference to `btf_task_struct_ids'`

Fix by defining btf_task_struct_ids unconditionally in kernel/bpf/btf.c
since there exists code that unconditionally uses btf_task_struct_ids.

Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Daniel Xu <dxu@...uu.xyz>
---
 include/linux/btf_ids.h  | 1 +
 kernel/bpf/btf.c         | 2 ++
 kernel/trace/bpf_trace.c | 2 --
 3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
index 93d881ab0d48..47d9abfbdb55 100644
--- a/include/linux/btf_ids.h
+++ b/include/linux/btf_ids.h
@@ -151,6 +151,7 @@ extern struct btf_id_set name;
 #define BTF_ID_UNUSED
 #define BTF_ID_LIST_GLOBAL(name) u32 name[1];
 #define BTF_ID_LIST_SINGLE(name, prefix, typename) static u32 name[1];
+#define BTF_ID_LIST_GLOBAL_SINGLE(name, prefix, typename) u32 name[1];
 #define BTF_SET_START(name) static struct btf_id_set name = { 0 };
 #define BTF_SET_START_GLOBAL(name) static struct btf_id_set name = { 0 };
 #define BTF_SET_END(name)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index c395024610ed..dfe61df4f974 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6213,3 +6213,5 @@ const struct bpf_func_proto bpf_btf_find_by_name_kind_proto = {
 	.arg3_type	= ARG_ANYTHING,
 	.arg4_type	= ARG_ANYTHING,
 };
+
+BTF_ID_LIST_GLOBAL_SINGLE(btf_task_struct_ids, struct, task_struct)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 580e14ee7ff9..8e2eb950aa82 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -714,8 +714,6 @@ BPF_CALL_0(bpf_get_current_task_btf)
 	return (unsigned long) current;
 }
 
-BTF_ID_LIST_GLOBAL_SINGLE(btf_task_struct_ids, struct, task_struct)
-
 const struct bpf_func_proto bpf_get_current_task_btf_proto = {
 	.func		= bpf_get_current_task_btf,
 	.gpl_only	= true,
-- 
2.33.0