* [PATCH][next] mtd: spi-nor: controllers: aspeed-smc: Replace zero-length array with flexible-array member
@ 2020-03-19 22:43 Gustavo A. R. Silva
2020-03-23 18:05 ` Tudor.Ambarus
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-03-19 22:43 UTC (permalink / raw)
To: Tudor Ambarus, Miquel Raynal, Richard Weinberger,
Vignesh Raghavendra, Joel Stanley, Andrew Jeffery
Cc: Gustavo A. R. Silva, linux-mtd, linux-aspeed, linux-arm-kernel,
linux-kernel
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/mtd/spi-nor/controllers/aspeed-smc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/mtd/spi-nor/controllers/aspeed-smc.c b/drivers/mtd/spi-nor/controllers/aspeed-smc.c
index 395127349aa8..e26a1897db0e 100644
--- a/drivers/mtd/spi-nor/controllers/aspeed-smc.c
+++ b/drivers/mtd/spi-nor/controllers/aspeed-smc.c
@@ -109,7 +109,7 @@ struct aspeed_smc_controller {
void __iomem *ahb_base; /* per-chip windows resource */
u32 ahb_window_size; /* full mapping window size */
- struct aspeed_smc_chip *chips[0]; /* pointers to attached chips */
+ struct aspeed_smc_chip *chips[]; /* pointers to attached chips */
};
/*
--
2.23.0
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^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH][next] mtd: spi-nor: controllers: aspeed-smc: Replace zero-length array with flexible-array member
2020-03-19 22:43 [PATCH][next] mtd: spi-nor: controllers: aspeed-smc: Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-03-23 18:05 ` Tudor.Ambarus
0 siblings, 0 replies; 2+ messages in thread
From: Tudor.Ambarus @ 2020-03-23 18:05 UTC (permalink / raw)
To: gustavo
Cc: vigneshr, linux-aspeed, andrew, richard, linux-kernel, linux-mtd,
joel, miquel.raynal, linux-arm-kernel
On Friday, March 20, 2020 12:43:26 AM EET Gustavo A. R. Silva wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the
> content is safe
>
> 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/mtd/spi-nor/controllers/aspeed-smc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Applied, thanks.
ta
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