| Message ID | 20200214171657.GA25663@embeddedor (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | dmaengine: tegra210-adma: Replace zero-length array with flexible-array member | expand |
On 14-02-20, 11:16, 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/tegra210-adma.c b/drivers/dma/tegra210-adma.c index 6e1268552f74..c4ce5dfb149b 100644 --- a/drivers/dma/tegra210-adma.c +++ b/drivers/dma/tegra210-adma.c @@ -164,7 +164,7 @@ struct tegra_adma { const struct tegra_adma_chip_data *cdata; /* Last member of the structure */ - struct tegra_adma_chan channels[0]; + struct tegra_adma_chan channels[]; }; static inline void tdma_write(struct tegra_adma *tdma, u32 reg, u32 val)
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/tegra210-adma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)