Skip to contentSkip to conversation

mtd: rawnand: Replace zero-length array with flexible-array member

PATCH Applied Gustavo A. R. Silva 4 participants 5 messages Feb 26, 2020 – Apr 16, 2020

Subsystems (9)
Memory technology devices (MTD) Arm/Amlogic Meson SoC support Arm MediaTek Arm/Allwinner sunXi SoC support +5 more subsystems
lore
Share & tools
lore

Gustavo A. R. Silva

author
#0 lore raw

PATCH 1/1 mtd: rawnand: 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/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(-)
drivers/mtd/nand/raw/denali.h +1 -1
index e5cdcda56d14..ac46eb7956ce 100644
@@ -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[];
 };
 
 /**
drivers/mtd/nand/raw/marvell_nand.c +1 -1
index fb5abdcfb007..7082bef1c8a7 100644
@@ -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)
drivers/mtd/nand/raw/meson_nand.c +1 -1
index 9f17b5b8efbf..f6fb5c0e6255 100644
@@ -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 {
drivers/mtd/nand/raw/mtk_nand.c +1 -1
index b8305e39ab51..ef149e8b26d0 100644
@@ -131,7 +131,7 @@ struct mtk_nfc_nand_chip {
 	u32 spare_per_sector;
 
 	int nsels;
-	u8 sels[0];
+	u8 sels[];
 	/* nothing after this field */
 };
drivers/mtd/nand/raw/nand_hynix.c +1 -1
index 194e4227aefe..7caedaa5b9e5 100644
@@ -26,7 +26,7 @@
 struct hynix_read_retry {
 	int nregs;
 	const u8 *regs;
-	u8 values[0];
+	u8 values[];
 };
 
 /**
drivers/mtd/nand/raw/sunxi_nand.c +1 -1
index 37a4ac0dd85b..6ede3934a5f4 100644
@@ -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)
Signature · 1 line
2.25.0
Acked-by on v1 1/1
#1 lore raw
Quoted 25 lines · 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.

Quoted 7 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/nand/raw/denali.h       | 2 +-
Acked-by Masahiro Yamada <[email protected]>
Quoted 7 lines
 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(-)
Signature · 2 lines
Best Regards
Masahiro Yamada
maintainer Applied
#2 lore raw
In reply to Gustavo A. R. Silva
Quoted 22 lines · 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]

Quoted 8 lines

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]>
Acked-by Masahiro Yamada <[email protected]>

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

Miquel

CI Applied
#4 lore raw
In reply to Gustavo A. R. Silva
This patch was applied to khilman/linux-amlogic.git (refs/heads/for-next).

Hello:

This patch was applied to khilman/linux-amlogic.git (refs/heads/for-next).

Quoted 11 lines · On Wed, 26 Feb 2020 16:27:22 -0600 you 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[];
};

[...]

Here is a summary with links:
- mtd: rawnand: Replace zero-length array with flexible-array member

    https://git.kernel.org/khilman/linux-amlogic/c/49f1c33076ca56871ffddc4800b04524204ea889

You are awesome, thank you!

Signature · 7 lines
Deet-doot-dot, I am a bot.
https://korg.wiki.kernel.org/userdoc/pwbot

_______________________________________________
linux-amlogic mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/linux-amlogic