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From:   David Vernet <void@manifault.com>
To:     bpf@vger.kernel.org
Cc:     ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
        martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev,
        john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com,
        haoluo@google.com, jolsa@kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@meta.com, kernel test robot <lkp@intel.com>
Subject: [PATCH bpf-next] bpf: Disable -Wmissing-declarations for globally-linked kfuncs
Date:   Wed, 16 Aug 2023 10:06:34 -0500
Message-ID: <20230816150634.1162838-1-void@manifault.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

We recently got an lkp warning about missing declarations, as in e.g.
[0]. This warning is largely redundant with -Wmissing-prototypes, which
we already disable for kfuncs that have global linkage and are meant to
be exported in BTF, and called from BPF programs. Let's also disable
-Wmissing-declarations for kfuncs. For what it's worth, I wasn't able to
reproduce the warning even on W <= 3, so I can't actually be 100% sure
this fixes the issue.

[0]: https://lore.kernel.org/all/202308162115.Hn23vv3n-lkp@intel.com/

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202308162115.Hn23vv3n-lkp@intel.com/
Signed-off-by: David Vernet <void@manifault.com>
---
 Documentation/bpf/kfuncs.rst                          | 4 +++-
 kernel/bpf/bpf_iter.c                                 | 2 ++
 kernel/bpf/cpumask.c                                  | 2 ++
 kernel/bpf/helpers.c                                  | 2 ++
 kernel/bpf/map_iter.c                                 | 2 ++
 kernel/cgroup/rstat.c                                 | 2 ++
 kernel/trace/bpf_trace.c                              | 2 ++
 net/bpf/test_run.c                                    | 2 ++
 net/core/filter.c                                     | 4 ++++
 net/core/xdp.c                                        | 2 ++
 net/ipv4/fou_bpf.c                                    | 2 ++
 net/netfilter/nf_conntrack_bpf.c                      | 2 ++
 net/netfilter/nf_nat_bpf.c                            | 2 ++
 net/xfrm/xfrm_interface_bpf.c                         | 2 ++
 tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c | 2 ++
 15 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst
index 0d2647fb358d..62ce5a7b92b4 100644
--- a/Documentation/bpf/kfuncs.rst
+++ b/Documentation/bpf/kfuncs.rst
@@ -36,10 +36,12 @@ prototype in a header for the wrapper kfunc.
 
 An example is given below::
 
-        /* Disables missing prototype warnings */
+        /* Disables missing prototypes and declarations warnings */
         __diag_push();
         __diag_ignore_all("-Wmissing-prototypes",
                           "Global kfuncs as their definitions will be in BTF");
+        __diag_ignore_all("-Wmissing-declarations",
+                          "Global kfuncs as their definitions will be in BTF");
 
         __bpf_kfunc struct task_struct *bpf_find_get_task_by_vpid(pid_t nr)
         {
diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 96856f130cbf..b8def6e4e5e8 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -785,6 +785,8 @@ struct bpf_iter_num_kern {
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in vmlinux BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in vmlinux BTF");
 
 __bpf_kfunc int bpf_iter_num_new(struct bpf_iter_num *it, int start, int end)
 {
diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
index 6983af8e093c..111b0e062e7f 100644
--- a/kernel/bpf/cpumask.c
+++ b/kernel/bpf/cpumask.c
@@ -37,6 +37,8 @@ static bool cpu_valid(u32 cpu)
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global kfuncs as their definitions will be in BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global kfuncs as their definitions will be in BTF");
 
 /**
  * bpf_cpumask_create() - Create a mutable BPF cpumask.
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index eb91cae0612a..6d2f84371892 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1885,6 +1885,8 @@ void bpf_rb_root_free(const struct btf_field *field, void *rb_root,
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in vmlinux BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in vmlinux BTF");
 
 __bpf_kfunc void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign)
 {
diff --git a/kernel/bpf/map_iter.c b/kernel/bpf/map_iter.c
index 6fc9dae9edc8..f7c7c5044630 100644
--- a/kernel/bpf/map_iter.c
+++ b/kernel/bpf/map_iter.c
@@ -196,6 +196,8 @@ late_initcall(bpf_map_iter_init);
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in vmlinux BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in vmlinux BTF");
 
 __bpf_kfunc s64 bpf_map_sum_elem_count(const struct bpf_map *map)
 {
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index 2542c21b6b6d..f5231a58ad3c 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -162,6 +162,8 @@ static struct cgroup *cgroup_rstat_cpu_pop_updated(struct cgroup *pos,
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "kfuncs which will be used in BPF programs");
+__diag_ignore_all("-Wmissing-declarations",
+		  "kfuncs which will be used in BPF programs");
 
 __weak noinline void bpf_rstat_flush(struct cgroup *cgrp,
 				     struct cgroup *parent, int cpu)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 792445e1f3f0..1fa197aa428c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1224,6 +1224,8 @@ static const struct bpf_func_proto bpf_get_func_arg_cnt_proto = {
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "kfuncs which will be used in BPF programs");
+__diag_ignore_all("-Wmissing-declarations",
+		  "kfuncs which will be used in BPF programs");
 
 /**
  * bpf_lookup_user_key - lookup a key by its serial
diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 57a7a64b84ed..38aedb720a52 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -506,6 +506,8 @@ static int bpf_test_finish(const union bpf_attr *kattr,
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in vmlinux BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in vmlinux BTF");
 __bpf_kfunc int bpf_fentry_test1(int a)
 {
 	return a + 1;
diff --git a/net/core/filter.c b/net/core/filter.c
index a094694899c9..c2b32b94c6bd 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -11727,6 +11727,8 @@ bpf_sk_base_func_proto(enum bpf_func_id func_id)
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in vmlinux BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in vmlinux BTF");
 __bpf_kfunc int bpf_dynptr_from_skb(struct sk_buff *skb, u64 flags,
 				    struct bpf_dynptr_kern *ptr__uninit)
 {
@@ -11808,6 +11810,8 @@ late_initcall(bpf_kfunc_init);
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in vmlinux BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in vmlinux BTF");
 
 /* bpf_sock_destroy: Destroy the given socket with ECONNABORTED error code.
  *
diff --git a/net/core/xdp.c b/net/core/xdp.c
index a70670fe9a2d..3d14e7be411d 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -699,6 +699,8 @@ struct xdp_frame *xdpf_clone(struct xdp_frame *xdpf)
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in vmlinux BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in vmlinux BTF");
 
 /**
  * bpf_xdp_metadata_rx_timestamp - Read XDP frame RX timestamp.
diff --git a/net/ipv4/fou_bpf.c b/net/ipv4/fou_bpf.c
index 3760a14b6b57..2b394703770a 100644
--- a/net/ipv4/fou_bpf.c
+++ b/net/ipv4/fou_bpf.c
@@ -25,6 +25,8 @@ enum bpf_fou_encap_type {
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in BTF");
 
 /* bpf_skb_set_fou_encap - Set FOU encap parameters
  *
diff --git a/net/netfilter/nf_conntrack_bpf.c b/net/netfilter/nf_conntrack_bpf.c
index c7a6114091ae..e24e2e4b2d49 100644
--- a/net/netfilter/nf_conntrack_bpf.c
+++ b/net/netfilter/nf_conntrack_bpf.c
@@ -233,6 +233,8 @@ static int _nf_conntrack_btf_struct_access(struct bpf_verifier_log *log,
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in nf_conntrack BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in nf_conntrack BTF");
 
 /* bpf_xdp_ct_alloc - Allocate a new CT entry
  *
diff --git a/net/netfilter/nf_nat_bpf.c b/net/netfilter/nf_nat_bpf.c
index 141ee7783223..e903a6eb732e 100644
--- a/net/netfilter/nf_nat_bpf.c
+++ b/net/netfilter/nf_nat_bpf.c
@@ -15,6 +15,8 @@
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in nf_nat BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in nf_nat BTF");
 
 /* bpf_ct_set_nat_info - Set source or destination nat address
  *
diff --git a/net/xfrm/xfrm_interface_bpf.c b/net/xfrm/xfrm_interface_bpf.c
index d74f3fd20f2b..d40060bcc398 100644
--- a/net/xfrm/xfrm_interface_bpf.c
+++ b/net/xfrm/xfrm_interface_bpf.c
@@ -30,6 +30,8 @@ struct bpf_xfrm_info {
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in xfrm_interface BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in xfrm_interface BTF");
 
 /* bpf_skb_get_xfrm_info - Get XFRM metadata
  *
diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index cefc5dd72573..201a41cd47e5 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
@@ -42,6 +42,8 @@ struct bpf_testmod_struct_arg_4 {
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "Global functions as their definitions will be in bpf_testmod.ko BTF");
+__diag_ignore_all("-Wmissing-declarations",
+		  "Global functions as their definitions will be in bpf_testmod.ko BTF");
 
 noinline int
 bpf_testmod_test_struct_arg_1(struct bpf_testmod_struct_arg_2 a, int b, int c) {
-- 
2.41.0