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netronome: Replace zero-length array with flexible-array member

PATCH Applied Gustavo A. R. Silva 2 participants 2 messages Feb 24, 2020

Subsystems (5)
Networking Network drivers BPF Netronome Ethernet drivers +1 more subsystems
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Gustavo A. R. Silva

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PATCH 1/1 netronome: 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]

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 <[email protected]>
---
 drivers/net/ethernet/netronome/nfp/bpf/fw.h            | 6 +++---
 drivers/net/ethernet/netronome/nfp/flower/cmsg.h       | 4 ++--
 drivers/net/ethernet/netronome/nfp/nfp_main.h          | 2 +-
 drivers/net/ethernet/netronome/nfp/nfp_net_debugdump.c | 8 ++++----
 drivers/net/ethernet/netronome/nfp/nfp_net_repr.h      | 2 +-
 drivers/net/ethernet/netronome/nfp/nfpcore/nfp_nsp.h   | 2 +-
 6 files changed, 12 insertions(+), 12 deletions(-)
drivers/net/ethernet/netronome/nfp/bpf/fw.h +3 -3
index a83a0ad5e27d..4268a7e0f344 100644
@@ -104,14 +104,14 @@ struct cmsg_req_map_op {
 	__be32 tid;
 	__be32 count;
 	__be32 flags;
-	u8 data[0];
+	u8 data[];
 };
 
 struct cmsg_reply_map_op {
 	struct cmsg_reply_map_simple reply_hdr;
 	__be32 count;
 	__be32 resv;
-	u8 data[0];
+	u8 data[];
 };
 
 struct cmsg_bpf_event {

@@ -120,6 +120,6 @@ struct cmsg_bpf_event {
 	__be64 map_ptr;
 	__be32 data_size;
 	__be32 pkt_size;
-	u8 data[0];
+	u8 data[];
 };
 #endif
drivers/net/ethernet/netronome/nfp/flower/cmsg.h +2 -2
index 9b50d76bbc09..bf516285510f 100644
@@ -587,7 +587,7 @@ struct nfp_flower_cmsg_mac_repr {
 		u8 info;
 		u8 nbi_port;
 		u8 phys_port;
-	} ports[0];
+	} ports[];
 };
 
 #define NFP_FLOWER_CMSG_MAC_REPR_NBI		GENMASK(1, 0)

@@ -619,7 +619,7 @@ struct nfp_flower_cmsg_merge_hint {
 	struct {
 		__be32 host_ctx;
 		__be64 host_cookie;
-	} __packed flow[0];
+	} __packed flow[];
 };
 
 enum nfp_flower_cmsg_port_type {
drivers/net/ethernet/netronome/nfp/nfp_main.h +1 -1
index 5d5812fd9317..fa6b13a05941 100644
@@ -42,7 +42,7 @@ struct nfp_shared_buf;
  */
 struct nfp_dumpspec {
 	u32 size;
-	u8 data[0];
+	u8 data[];
 };
 
 /**
drivers/net/ethernet/netronome/nfp/nfp_net_debugdump.c +4 -4
index 769ceef09756..a614df095b08 100644
@@ -36,7 +36,7 @@ enum nfp_dumpspec_type {
 struct nfp_dump_tl {
 	__be32 type;
 	__be32 length;	/* chunk length to follow, aligned to 8 bytes */
-	char data[0];
+	char data[];
 };
 
 /* NFP CPP parameters */

@@ -62,7 +62,7 @@ struct nfp_dumpspec_csr {
 
 struct nfp_dumpspec_rtsym {
 	struct nfp_dump_tl tl;
-	char rtsym[0];
+	char rtsym[];
 };
 
 /* header for register dumpable */

@@ -79,7 +79,7 @@ struct nfp_dump_rtsym {
 	struct nfp_dump_common_cpp cpp;
 	__be32 error;		/* error code encountered while reading */
 	u8 padded_name_length;	/* pad so data starts at 8 byte boundary */
-	char rtsym[0];
+	char rtsym[];
 	/* after padded_name_length, there is dump_length data */
 };
 

@@ -92,7 +92,7 @@ struct nfp_dump_error {
 	struct nfp_dump_tl tl;
 	__be32 error;
 	char padding[4];
-	char spec[0];
+	char spec[];
 };
 
 /* to track state through debug size calculation TLV traversal */
drivers/net/ethernet/netronome/nfp/nfp_net_repr.h +1 -1
index e0f13dfe1f39..48a74accbbd3 100644
@@ -18,7 +18,7 @@ struct nfp_port;
  */
 struct nfp_reprs {
 	unsigned int num_reprs;
-	struct net_device __rcu *reprs[0];
+	struct net_device __rcu *reprs[];
 };
 
 /**
drivers/net/ethernet/netronome/nfp/nfpcore/nfp_nsp.h +1 -1
index 1531c1870020..f5360bae6f75 100644
@@ -183,7 +183,7 @@ struct nfp_eth_table {
 		bool is_split;
 
 		unsigned int fec_modes_supported;
-	} ports[0];
+	} ports[];
 };
 
 struct nfp_eth_table *nfp_eth_read_ports(struct nfp_cpp *cpp);
Signature · 1 line
2.25.0
maintainer Applied
#1 lore raw

From: "Gustavo A. R. Silva" <[email protected]>
Date: Mon, 24 Feb 2020 10:36:52 -0600

Quoted 22 lines

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]

Quoted 7 lines

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 <[email protected]>

Applied.