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mtd: spi-nor: controllers: aspeed-smc: Replace zero-length array with flexible-array member

PATCH Applied Gustavo A. R. Silva 2 participants 2 messages Mar 19, 2020 – Mar 23, 2020

Subsystems (3)
Memory technology devices (MTD) Arm/Aspeed machine support SPI NOR
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Gustavo A. R. Silva

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PATCH 1/1 mtd: spi-nor: controllers: aspeed-smc: 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 <[email protected]>
---
 drivers/mtd/spi-nor/controllers/aspeed-smc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
drivers/mtd/spi-nor/controllers/aspeed-smc.c +1 -1
index 395127349aa8..e26a1897db0e 100644
@@ -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 */
 };
 
 /*
Signature · 1 line
2.23.0
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Quoted 27 lines · EET Gustavo A. R. Silva

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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.

Quoted 8 lines

[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 <[email protected]>
---
 drivers/mtd/spi-nor/controllers/aspeed-smc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Applied, thanks.
ta