netdev - [PATCH bpf-next v2] bpf: fix a (false) compiler warning

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Message-Id: <20190116184301.218106-1-posk@google.com>
Date:   Wed, 16 Jan 2019 10:43:01 -0800
From:   Peter Oskolkov <posk@...gle.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org
Cc:     Peter Oskolkov <posk.devel@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Peter Oskolkov <posk@...gle.com>
Subject: [PATCH bpf-next v2] bpf: fix a (false) compiler warning

An older GCC compiler complains:

kernel/bpf/verifier.c: In function 'bpf_check':
kernel/bpf/verifier.c:4***:13: error: 'prev_offset' may be used uninitialized
      in this function [-Werror=maybe-uninitialized]
   } else if (krecord[i].insn_offset <= prev_offset) {
             ^
kernel/bpf/verifier.c:4***:38: note: 'prev_offset' was declared here
  u32 i, nfuncs, urec_size, min_size, prev_offset;

Although the compiler is wrong here, the patch makes sure
that prev_offset is always initialized, just to silence the warning.

v2: fix a spelling error in the commit message.

Signed-off-by: Peter Oskolkov <posk@...gle.com>
---
 kernel/bpf/verifier.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 56674a7c3778..ce87198ecd01 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4997,13 +4997,14 @@ static int check_btf_func(struct bpf_verifier_env *env,
 			  const union bpf_attr *attr,
 			  union bpf_attr __user *uattr)
 {
-	u32 i, nfuncs, urec_size, min_size, prev_offset;
+	u32 i, nfuncs, urec_size, min_size;
 	u32 krec_size = sizeof(struct bpf_func_info);
 	struct bpf_func_info *krecord;
 	const struct btf_type *type;
 	struct bpf_prog *prog;
 	const struct btf *btf;
 	void __user *urecord;
+	u32 prev_offset = 0;
 	int ret = 0;
 
 	nfuncs = attr->func_info_cnt;
--