| Message ID | 20200507190706.GA15730@embeddedor (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | media: pwc: Replace zero-length array with flexible-array | expand |
diff --git a/drivers/media/usb/pwc/pwc.h b/drivers/media/usb/pwc/pwc.h index 3362962d0d00..b02a3c7b7742 100644 --- a/drivers/media/usb/pwc/pwc.h +++ b/drivers/media/usb/pwc/pwc.h @@ -193,7 +193,7 @@ struct pwc_raw_frame { decompressor) */ __u8 cmd[4]; /* the four byte of the command (in case of nala, only the first 3 bytes is filled) */ - __u8 rawframe[0]; /* frame_size = H / 4 * vbandlength */ + __u8 rawframe[]; /* frame_size = H / 4 * vbandlength */ } __packed; /* intermediate buffers with raw data from the USB cam */
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] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. 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 <gustavoars@kernel.org> --- drivers/media/usb/pwc/pwc.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)