| Message ID | 20200214171536.GA24077@embeddedor (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | dmaengine: sprd: Replace zero-length array with flexible-array member | expand |
Hi, On Sat, Feb 15, 2020 at 2:04 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") Looks good to me. Thanks. Reviewed-by: Baolin Wang <baolin.wang7@gmail.com> > Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> > --- > drivers/dma/sprd-dma.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/dma/sprd-dma.c b/drivers/dma/sprd-dma.c > index 9a31a315dbef..954eff32cc05 100644 > --- a/drivers/dma/sprd-dma.c > +++ b/drivers/dma/sprd-dma.c > @@ -212,7 +212,7 @@ struct sprd_dma_dev { > struct clk *ashb_clk; > int irq; > u32 total_chns; > - struct sprd_dma_chn channels[0]; > + struct sprd_dma_chn channels[]; > }; > > static void sprd_dma_free_desc(struct virt_dma_desc *vd); > -- > 2.25.0 >
On 14-02-20, 11:15, 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] Applied, thanks
diff --git a/drivers/dma/sprd-dma.c b/drivers/dma/sprd-dma.c index 9a31a315dbef..954eff32cc05 100644 --- a/drivers/dma/sprd-dma.c +++ b/drivers/dma/sprd-dma.c @@ -212,7 +212,7 @@ struct sprd_dma_dev { struct clk *ashb_clk; int irq; u32 total_chns; - struct sprd_dma_chn channels[0]; + struct sprd_dma_chn channels[]; }; static void sprd_dma_free_desc(struct virt_dma_desc *vd);
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/sprd-dma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)