* [PATCH] dmaengine: uniphier-mdmac: replace zero-length array with flexible-array member
@ 2020-02-13 0:35 Gustavo A. R. Silva
2020-02-13 14:46 ` Vinod Koul
2020-02-18 1:25 ` Masahiro Yamada
0 siblings, 2 replies; 3+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-13 0:35 UTC (permalink / raw)
To: Dan Williams, Vinod Koul, Masahiro Yamada
Cc: dmaengine, linux-arm-kernel, 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/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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] dmaengine: uniphier-mdmac: replace zero-length array with flexible-array member
2020-02-13 0:35 [PATCH] dmaengine: uniphier-mdmac: replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-02-13 14:46 ` Vinod Koul
2020-02-18 1:25 ` Masahiro Yamada
1 sibling, 0 replies; 3+ messages in thread
From: Vinod Koul @ 2020-02-13 14:46 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Dan Williams, Masahiro Yamada, dmaengine, linux-arm-kernel, linux-kernel
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
--
~Vinod
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] dmaengine: uniphier-mdmac: replace zero-length array with flexible-array member
2020-02-13 0:35 [PATCH] dmaengine: uniphier-mdmac: replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-02-13 14:46 ` Vinod Koul
@ 2020-02-18 1:25 ` Masahiro Yamada
1 sibling, 0 replies; 3+ messages in thread
From: Masahiro Yamada @ 2020-02-18 1:25 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Dan Williams, Vinod Koul,
open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM, linux-arm-kernel,
Linux Kernel Mailing List
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
>
--
Best Regards
Masahiro Yamada
^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-02-13 0:35 [PATCH] dmaengine: uniphier-mdmac: replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-02-13 14:46 ` Vinod Koul
2020-02-18 1:25 ` Masahiro Yamada
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