* [PATCH] dmaengine: sprd: Replace zero-length array with flexible-array member
@ 2020-02-14 17:15 Gustavo A. R. Silva
2020-02-17 1:55 ` Baolin Wang
2020-02-19 12:20 ` Vinod Koul
0 siblings, 2 replies; 3+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-14 17:15 UTC (permalink / raw)
To: Vinod Koul, Dan Williams, Orson Zhai, Baolin Wang, Chunyan Zhang
Cc: dmaengine, linux-kernel, Gustavo A. R. Silva
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(-)
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] dmaengine: sprd: Replace zero-length array with flexible-array member
2020-02-14 17:15 [PATCH] dmaengine: sprd: Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-02-17 1:55 ` Baolin Wang
2020-02-19 12:20 ` Vinod Koul
1 sibling, 0 replies; 3+ messages in thread
From: Baolin Wang @ 2020-02-17 1:55 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Vinod Koul, Dan Williams, Orson Zhai, Chunyan Zhang, dmaengine, LKML
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
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] dmaengine: sprd: Replace zero-length array with flexible-array member
2020-02-14 17:15 [PATCH] dmaengine: sprd: Replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-02-17 1:55 ` Baolin Wang
@ 2020-02-19 12:20 ` Vinod Koul
1 sibling, 0 replies; 3+ messages in thread
From: Vinod Koul @ 2020-02-19 12:20 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Dan Williams, Orson Zhai, Baolin Wang, Chunyan Zhang, dmaengine,
linux-kernel
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
--
~Vinod
^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-02-17 1:55 ` Baolin Wang
2020-02-19 12:20 ` Vinod Koul
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