linux-kernel - [PATCH] net_sched: force endianness annotation

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Date:   Sun, 28 Apr 2019 07:54:59 +0200
From:   Nicholas Mc Guire <hofrat@...dl.org>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Nicholas Mc Guire <hofrat@...dl.org>
Subject: [PATCH] net_sched: force endianness annotation

While the endiannes is being handled correctly sparse was unhappy with
the missing annotation as be16_to_cpu()/be32_to_cpu() expects a __be16
respectively __be32. To mitigate this annotation issue forced annotation
is introduced. Note that this patch has no impact on the generated binary.

Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
---

Problem located by an experimental cocci script to locate sparse annontation isues.
net/sched/em_cmp.c:44:31: warning: cast to restricted __be16
net/sched/em_cmp.c:44:31: warning: cast to restricted __be16
net/sched/em_cmp.c:44:31: warning: cast to restricted __be16
net/sched/em_cmp.c:44:31: warning: cast to restricted __be16
net/sched/em_cmp.c:54:31: warning: cast to restricted __be32
net/sched/em_cmp.c:54:31: warning: cast to restricted __be32
net/sched/em_cmp.c:54:31: warning: cast to restricted __be32
net/sched/em_cmp.c:54:31: warning: cast to restricted __be32
net/sched/em_cmp.c:54:31: warning: cast to restricted __be32
net/sched/em_cmp.c:54:31: warning: cast to restricted __be32

This is due to the variable being converted and thus the type is the
teget system type and it must be caset to __be16/__be32 here for sparse
to understand that endianness is adequately handled.

Patch was compile-tested with: x86_64_defconfig

Verification that the patch has no impact on the binary being generated
was done by diff on the binary before and after applying the patch.

Patch is against 5.1-rc6 (localversion-next is next-20190426)

 net/sched/em_cmp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sched/em_cmp.c b/net/sched/em_cmp.c
index 1c8360a..3045ee1 100644
--- a/net/sched/em_cmp.c
+++ b/net/sched/em_cmp.c
@@ -41,7 +41,7 @@ static int em_cmp_match(struct sk_buff *skb, struct tcf_ematch *em,
 		val = get_unaligned_be16(ptr);

 		if (cmp_needs_transformation(cmp))
-			val = be16_to_cpu(val);
+			val = be16_to_cpu((__force __be16)val);
 		break;

 	case TCF_EM_ALIGN_U32:
@@ -51,7 +51,7 @@ static int em_cmp_match(struct sk_buff *skb, struct tcf_ematch *em,
 		val = get_unaligned_be32(ptr);

 		if (cmp_needs_transformation(cmp))
-			val = be32_to_cpu(val);
+			val = be32_to_cpu((__force __be32)val);
 		break;

 	default:
-- 
2.1.4