linux-kernel - [PATCH][next] net: cisco: Replace zero-length array with flexible-array member

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Date:   Mon, 24 Feb 2020 18:18:26 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Christian Benvenuti <benve@...co.com>,
        Govindarajulu Varadarajan <_govind@....com>,
        Parvi Kaustubhi <pkaustub@...co.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH][next] net: cisco: Replace zero-length array with
 flexible-array member

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

Lastly, fix the following checkpatch warning:
CHECK: Prefer kernel type 'u32' over 'u_int32_t'
#61: FILE: drivers/net/ethernet/cisco/enic/vnic_devcmd.h:653:
+	u_int32_t val[];

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 drivers/net/ethernet/cisco/enic/vnic_devcmd.h | 8 ++++----
 drivers/net/ethernet/cisco/enic/vnic_vic.h    | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/cisco/enic/vnic_devcmd.h b/drivers/net/ethernet/cisco/enic/vnic_devcmd.h
index fef5a0a0663d..fcc4a3ccdd94 100644
--- a/drivers/net/ethernet/cisco/enic/vnic_devcmd.h
+++ b/drivers/net/ethernet/cisco/enic/vnic_devcmd.h
@@ -541,7 +541,7 @@ struct vnic_devcmd_notify {
 struct vnic_devcmd_provinfo {
 	u8 oui[3];
 	u8 type;
-	u8 data[0];
+	u8 data[];
 };
 
 /* These are used in flags field of different filters to denote
@@ -648,9 +648,9 @@ enum {
 #define FILTER_MAX_BUF_SIZE 100
 
 struct filter_tlv {
-	u_int32_t type;
-	u_int32_t length;
-	u_int32_t val[0];
+	u32 type;
+	u32 length;
+	u32 val[];
 };
 
 enum {
diff --git a/drivers/net/ethernet/cisco/enic/vnic_vic.h b/drivers/net/ethernet/cisco/enic/vnic_vic.h
index 9ef81f148351..057776908828 100644
--- a/drivers/net/ethernet/cisco/enic/vnic_vic.h
+++ b/drivers/net/ethernet/cisco/enic/vnic_vic.h
@@ -59,7 +59,7 @@ struct vic_provinfo {
 		u16 type;
 		u16 length;
 		u8 value[0];
-	} tlv[0];
+	} tlv[];
 } __packed;
 
 #define VIC_PROVINFO_ADD_TLV(vp, tlvtype, tlvlen, data) \
-- 
2.25.0