| Message ID | 20200320232556.GA24989@embeddedor.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 2d4ccc2ac61b1a407a1c75633a3bf2f878ff44b5 |
| Headers | show |
| Series | [next] spi: spi-s3c24xx: Replace zero-length array with flexible-array member | expand |
Hi Gustavo, On Fri, Mar 20, 2020 at 06:25:56PM -0500, Gustavo A. R. Silva wrote: > 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> yes, thank you! Reviewed-by: Andi Shyti <andi@etezian.org> Andi
diff --git a/drivers/spi/spi-s3c24xx.c b/drivers/spi/spi-s3c24xx.c index 2d6e37f25e2d..2cb3b611c294 100644 --- a/drivers/spi/spi-s3c24xx.c +++ b/drivers/spi/spi-s3c24xx.c @@ -227,7 +227,7 @@ static inline unsigned int hw_txbyte(struct s3c24xx_spi *hw, int count) struct spi_fiq_code { u32 length; u32 ack_offset; - u8 data[0]; + u8 data[]; }; extern struct spi_fiq_code s3c24xx_spi_fiq_txrx;
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/spi/spi-s3c24xx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)