atmel: at76c50x-usb.h: Replace zero-length array with flexible-array member
Subsystems (4)
PATCH 1/1 atmel: at76c50x-usb.h: 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")
--- drivers/net/wireless/atmel/at76c50x-usb.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
drivers/net/wireless/atmel/at76c50x-usb.h +1 -1
@@ -151,7 +151,7 @@ struct at76_command {u8 cmd;u8 reserved;__le16 size; -u8 data[0 ]; +u8 data[]; } __packed;/* Length of Atmel-specific Rx header before 802.11 frame */
Signature · 1 line
2.23.0
Re: [PATCH][next] atmel: at76c50x: Replace zero-length array with flexible-array member
Quoted 22 lines · 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]
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] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")Signed-off-by Gustavo A. R. Silva <[email protected]>
Patch applied to wireless-drivers-next.git, thanks.
b0c40588161d atmel: at76c50x: Replace zero-length array with flexible-array member
Signature · 3 lines
https://patchwork.kernel.org/patch/11448171/ https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches