[PATCH] mtd: rawnand: Replace zero-length array with flexible-array member

[PATCH] mtd: rawnand: Replace zero-length array with flexible-array member

[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/mtd/nand/raw/denali.h       | 2 +-
 drivers/mtd/nand/raw/marvell_nand.c | 2 +-
 drivers/mtd/nand/raw/meson_nand.c   | 2 +-
 drivers/mtd/nand/raw/mtk_nand.c     | 2 +-
 drivers/mtd/nand/raw/nand_hynix.c   | 2 +-
 drivers/mtd/nand/raw/sunxi_nand.c   | 2 +-
 6 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/mtd/nand/raw/denali.h b/drivers/mtd/nand/raw/denali.h
index e5cdcda56d14..ac46eb7956ce 100644
--- a/drivers/mtd/nand/raw/denali.h
+++ b/drivers/mtd/nand/raw/denali.h
@@ -328,7 +328,7 @@ struct denali_chip {
 	struct nand_chip chip;
 	struct list_head node;
 	unsigned int nsels;
-	struct denali_chip_sel sels[0];
+	struct denali_chip_sel sels[];
 };
 
 /**
diff --git a/drivers/mtd/nand/raw/marvell_nand.c b/drivers/mtd/nand/raw/marvell_nand.c
index fb5abdcfb007..7082bef1c8a7 100644
--- a/drivers/mtd/nand/raw/marvell_nand.c
+++ b/drivers/mtd/nand/raw/marvell_nand.c
@@ -334,7 +334,7 @@ struct marvell_nand_chip {
 	int addr_cyc;
 	int selected_die;
 	unsigned int nsels;
-	struct marvell_nand_chip_sel sels[0];
+	struct marvell_nand_chip_sel sels[];
 };
 
 static inline struct marvell_nand_chip *to_marvell_nand(struct nand_chip *chip)
diff --git a/drivers/mtd/nand/raw/meson_nand.c b/drivers/mtd/nand/raw/meson_nand.c
index 9f17b5b8efbf..f6fb5c0e6255 100644
--- a/drivers/mtd/nand/raw/meson_nand.c
+++ b/drivers/mtd/nand/raw/meson_nand.c
@@ -118,7 +118,7 @@ struct meson_nfc_nand_chip {
 	u8 *data_buf;
 	__le64 *info_buf;
 	u32 nsels;
-	u8 sels[0];
+	u8 sels[];
 };
 
 struct meson_nand_ecc {
diff --git a/drivers/mtd/nand/raw/mtk_nand.c b/drivers/mtd/nand/raw/mtk_nand.c
index b8305e39ab51..ef149e8b26d0 100644
--- a/drivers/mtd/nand/raw/mtk_nand.c
+++ b/drivers/mtd/nand/raw/mtk_nand.c
@@ -131,7 +131,7 @@ struct mtk_nfc_nand_chip {
 	u32 spare_per_sector;
 
 	int nsels;
-	u8 sels[0];
+	u8 sels[];
 	/* nothing after this field */
 };
 
diff --git a/drivers/mtd/nand/raw/nand_hynix.c b/drivers/mtd/nand/raw/nand_hynix.c
index 194e4227aefe..7caedaa5b9e5 100644
--- a/drivers/mtd/nand/raw/nand_hynix.c
+++ b/drivers/mtd/nand/raw/nand_hynix.c
@@ -26,7 +26,7 @@
 struct hynix_read_retry {
 	int nregs;
 	const u8 *regs;
-	u8 values[0];
+	u8 values[];
 };
 
 /**
diff --git a/drivers/mtd/nand/raw/sunxi_nand.c b/drivers/mtd/nand/raw/sunxi_nand.c
index 37a4ac0dd85b..6ede3934a5f4 100644
--- a/drivers/mtd/nand/raw/sunxi_nand.c
+++ b/drivers/mtd/nand/raw/sunxi_nand.c
@@ -195,7 +195,7 @@ struct sunxi_nand_chip {
 	u32 timing_cfg;
 	u32 timing_ctl;
 	int nsels;
-	struct sunxi_nand_chip_sel sels[0];
+	struct sunxi_nand_chip_sel sels[];
 };
 
 static inline struct sunxi_nand_chip *to_sunxi_nand(struct nand_chip *nand)
-- 
2.25.0


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Re: [PATCH] mtd: rawnand: Replace zero-length array with flexible-array member

[Masahiro Yamada]

On Thu, Feb 27, 2020 at 7:25 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>
> ---
>  drivers/mtd/nand/raw/denali.h       | 2 +-


Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>


>  drivers/mtd/nand/raw/marvell_nand.c | 2 +-
>  drivers/mtd/nand/raw/meson_nand.c   | 2 +-
>  drivers/mtd/nand/raw/mtk_nand.c     | 2 +-
>  drivers/mtd/nand/raw/nand_hynix.c   | 2 +-
>  drivers/mtd/nand/raw/sunxi_nand.c   | 2 +-
>  6 files changed, 6 insertions(+), 6 deletions(-)
>

-- 
Best Regards
Masahiro Yamada

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Re: [PATCH] mtd: rawnand: Replace zero-length array with flexible-array member

[Miquel Raynal]

On Wed, 2020-02-26 at 22:27:22 UTC, "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")
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git nand/next, thanks.

Miquel

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Re: [PATCH] mtd: rawnand: Replace zero-length array with flexible-array member

[Gustavo A. R. Silva]

On 3/10/20 1:31 PM, Miquel Raynal wrote:

>>
>> [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>
> 
> Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git nand/next, thanks.
> 

Thanks, Miquel.
--
Gustavo

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