* [PATCH][next] r8152: Replace zero-length array with flexible-array member
@ 2020-03-02 12:23 Gustavo A. R. Silva
2020-03-02 19:28 ` David Miller
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-03-02 12:23 UTC (permalink / raw)
To: David S. Miller; +Cc: linux-usb, 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/usb/r8152.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
index feedc0f964d8..9adfa2bbf593 100644
--- a/drivers/net/usb/r8152.c
+++ b/drivers/net/usb/r8152.c
@@ -891,7 +891,7 @@ struct fw_block {
struct fw_header {
u8 checksum[32];
char version[RTL_VER_SIZE];
- struct fw_block blocks[0];
+ struct fw_block blocks[];
} __packed;
/**
@@ -930,7 +930,7 @@ struct fw_mac {
__le32 reserved;
__le16 fw_ver_reg;
u8 fw_ver_data;
- char info[0];
+ char info[];
} __packed;
/**
@@ -982,7 +982,7 @@ struct fw_phy_nc {
__le16 bp_start;
__le16 bp_num;
__le16 bp[4];
- char info[0];
+ char info[];
} __packed;
enum rtl_fw_type {
--
2.25.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH][next] r8152: Replace zero-length array with flexible-array member
2020-03-02 12:23 [PATCH][next] r8152: Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-03-02 19:28 ` David Miller
0 siblings, 0 replies; 2+ messages in thread
From: David Miller @ 2020-03-02 19:28 UTC (permalink / raw)
To: gustavo; +Cc: linux-usb, netdev, linux-kernel
From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Date: Mon, 2 Mar 2020 06:23:05 -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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