[PATCH][next] qlogic: Replace zero-length array with flexible-array member

[PATCH][next] qlogic: Replace zero-length array with flexible-array member

[Gustavo A. R. Silva]

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 detected 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@embeddedor.com>
---
 drivers/net/ethernet/qlogic/netxen/netxen_nic.h | 2 +-
 drivers/net/ethernet/qlogic/qlcnic/qlcnic.h     | 8 ++++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/qlogic/netxen/netxen_nic.h b/drivers/net/ethernet/qlogic/netxen/netxen_nic.h
index 3dce769d83a1..86153660d245 100644
--- a/drivers/net/ethernet/qlogic/netxen/netxen_nic.h
+++ b/drivers/net/ethernet/qlogic/netxen/netxen_nic.h
@@ -1316,7 +1316,7 @@ struct netxen_minidump_template_hdr {
 	u32 driver_info_word4;
 	u32 saved_state_array[NX_DUMP_STATE_ARRAY_LEN];
 	u32 capture_size_array[NX_DUMP_CAP_SIZE_ARRAY_LEN];
-	u32 rsvd[0];
+	u32 rsvd[];
 };
 
 /* Common Entry Header:  Common to All Entry Types */
diff --git a/drivers/net/ethernet/qlogic/qlcnic/qlcnic.h b/drivers/net/ethernet/qlogic/qlcnic/qlcnic.h
index 374a4d4371f9..134611aa2c9a 100644
--- a/drivers/net/ethernet/qlogic/qlcnic/qlcnic.h
+++ b/drivers/net/ethernet/qlogic/qlcnic/qlcnic.h
@@ -418,7 +418,7 @@ struct qlcnic_83xx_dump_template_hdr {
 	u32	saved_state[16];
 	u32	cap_sizes[8];
 	u32	ocm_wnd_reg[16];
-	u32	rsvd[0];
+	u32	rsvd[];
 };
 
 struct qlcnic_82xx_dump_template_hdr {
@@ -436,7 +436,7 @@ struct qlcnic_82xx_dump_template_hdr {
 	u32	cap_sizes[8];
 	u32	rsvd[7];
 	u32	capabilities;
-	u32	rsvd1[0];
+	u32	rsvd1[];
 };
 
 #define QLC_PEX_DMA_READ_SIZE	(PAGE_SIZE * 16)
@@ -740,7 +740,7 @@ struct qlcnic_hostrq_rx_ctx {
 	   The following is packed:
 	   - N hostrq_rds_rings
 	   - N hostrq_sds_rings */
-	char data[0];
+	char data[];
 } __packed;
 
 struct qlcnic_cardrsp_rds_ring{
@@ -769,7 +769,7 @@ struct qlcnic_cardrsp_rx_ctx {
 	   The following is packed:
 	   - N cardrsp_rds_rings
 	   - N cardrs_sds_rings */
-	char data[0];
+	char data[];
 } __packed;
 
 #define SIZEOF_HOSTRQ_RX(HOSTRQ_RX, rds_rings, sds_rings)	\
-- 
2.25.0

Re: [PATCH][next] qlogic: Replace zero-length array with flexible-array member

[David Miller]

From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Date: Mon, 24 Feb 2020 18:03:55 -0600

> 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 detected 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@embeddedor.com>

Applied.