| Message ID | 20200213003535.GA3269@embeddedor.com (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | 6a8785082c83f0a223bc970d99edcd742435dab2 |
| Headers | show |
| Series | dmaengine: uniphier-mdmac: replace zero-length array with flexible-array member | expand |
On 12-02-20, 18:35, 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") Applied, thanks
On Thu, Feb 13, 2020 at 9:35 AM Gustavo A. R. Silva <gustavo@embeddedor.com> 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> Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com> > --- > drivers/dma/uniphier-mdmac.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/dma/uniphier-mdmac.c b/drivers/dma/uniphier-mdmac.c > index 21b8f1131d55..618839df0748 100644 > --- a/drivers/dma/uniphier-mdmac.c > +++ b/drivers/dma/uniphier-mdmac.c > @@ -68,7 +68,7 @@ struct uniphier_mdmac_device { > struct dma_device ddev; > struct clk *clk; > void __iomem *reg_base; > - struct uniphier_mdmac_chan channels[0]; > + struct uniphier_mdmac_chan channels[]; > }; > > static struct uniphier_mdmac_chan * > -- > 2.23.0 >
diff --git a/drivers/dma/uniphier-mdmac.c b/drivers/dma/uniphier-mdmac.c index 21b8f1131d55..618839df0748 100644 --- a/drivers/dma/uniphier-mdmac.c +++ b/drivers/dma/uniphier-mdmac.c @@ -68,7 +68,7 @@ struct uniphier_mdmac_device { struct dma_device ddev; struct clk *clk; void __iomem *reg_base; - struct uniphier_mdmac_chan channels[0]; + struct uniphier_mdmac_chan channels[]; }; static struct uniphier_mdmac_chan *
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/dma/uniphier-mdmac.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)