dmaengine: sprd: Replace zero-length array with flexible-array member

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>
Reviewed-by: Baolin Wang <baolin.wang7@gmail.com>
Link: https://lore.kernel.org/r/20200214171536.GA24077@embeddedor
Signed-off-by: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/dma/sprd-dma.c b/drivers/dma/sprd-dma.c
index 9a31a31..954eff3 100644 (file)
--- 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);