* [PATCH][next] freescale: Replace zero-length array with flexible-array member
@ 2020-02-24 16:43 Gustavo A. R. Silva
2020-02-24 23:27 ` David Miller
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-24 16:43 UTC (permalink / raw)
To: Claudiu Manoil, David S. Miller, Fugang Duan
Cc: netdev, linux-kernel, 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 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@embeddedor.com>
---
drivers/net/ethernet/freescale/enetc/enetc.h | 2 +-
drivers/net/ethernet/freescale/enetc/enetc_hw.h | 2 +-
drivers/net/ethernet/freescale/fec.h | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/net/ethernet/freescale/enetc/enetc.h b/drivers/net/ethernet/freescale/enetc/enetc.h
index dd4a227ffc7a..9938f7a5fc0a 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.h
+++ b/drivers/net/ethernet/freescale/enetc/enetc.h
@@ -163,7 +163,7 @@ struct enetc_int_vector {
char name[ENETC_INT_NAME_MAX];
struct enetc_bdr rx_ring ____cacheline_aligned_in_smp;
- struct enetc_bdr tx_ring[0];
+ struct enetc_bdr tx_ring[];
};
struct enetc_cls_rule {
diff --git a/drivers/net/ethernet/freescale/enetc/enetc_hw.h b/drivers/net/ethernet/freescale/enetc/enetc_hw.h
index 62554f28ce07..da134e211c1a 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc_hw.h
+++ b/drivers/net/ethernet/freescale/enetc/enetc_hw.h
@@ -588,7 +588,7 @@ struct tgs_gcl_data {
__le32 bth;
__le32 ct;
__le32 cte;
- struct gce entry[0];
+ struct gce entry[];
};
struct enetc_cbd {
diff --git a/drivers/net/ethernet/freescale/fec.h b/drivers/net/ethernet/freescale/fec.h
index f79e57f735b3..bd898f5b4da5 100644
--- a/drivers/net/ethernet/freescale/fec.h
+++ b/drivers/net/ethernet/freescale/fec.h
@@ -584,7 +584,7 @@ struct fec_enet_private {
int pps_enable;
unsigned int next_counter;
- u64 ethtool_stats[0];
+ u64 ethtool_stats[];
};
void fec_ptp_init(struct platform_device *pdev, int irq_idx);
--
2.25.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH][next] freescale: Replace zero-length array with flexible-array member
2020-02-24 16:43 [PATCH][next] freescale: Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-02-24 23:27 ` David Miller
0 siblings, 0 replies; 2+ messages in thread
From: David Miller @ 2020-02-24 23:27 UTC (permalink / raw)
To: gustavo; +Cc: claudiu.manoil, fugang.duan, netdev, linux-kernel
From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Date: Mon, 24 Feb 2020 10:43:46 -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 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@embeddedor.com>
Applied.
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