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

* [PATCH] mmc: Replace zero-length array with flexible-array member
@ 2020-02-26 22:31 Gustavo A. R. Silva
  2020-02-27 13:11 ` Adrian Hunter
  2020-03-11 15:34 ` Ulf Hansson
  0 siblings, 2 replies; 4+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-26 22:31 UTC (permalink / raw)
  To: Adrian Hunter, Ulf Hansson; +Cc: linux-mmc, 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/mmc/host/sdhci-acpi.c    | 2 +-
 drivers/mmc/host/sdhci-cadence.c | 2 +-
 drivers/mmc/host/sdhci-pci.h     | 2 +-
 drivers/mmc/host/sdhci-pltfm.h   | 2 +-
 drivers/mmc/host/sdhci.h         | 2 +-
 drivers/mmc/host/vub300.c        | 2 +-
 include/linux/mmc/host.h         | 2 +-
 include/linux/mmc/sdio_func.h    | 2 +-
 include/uapi/linux/mmc/ioctl.h   | 2 +-
 9 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/mmc/host/sdhci-acpi.c b/drivers/mmc/host/sdhci-acpi.c
index 9651dca6863e..ea0e4fda3a9e 100644
--- a/drivers/mmc/host/sdhci-acpi.c
+++ b/drivers/mmc/host/sdhci-acpi.c
@@ -72,7 +72,7 @@ struct sdhci_acpi_host {
 	const struct sdhci_acpi_slot	*slot;
 	struct platform_device		*pdev;
 	bool				use_runtime_pm;
-	unsigned long			private[0] ____cacheline_aligned;
+	unsigned long			private[] ____cacheline_aligned;
 };
 
 static inline void *sdhci_acpi_priv(struct sdhci_acpi_host *c)
diff --git a/drivers/mmc/host/sdhci-cadence.c b/drivers/mmc/host/sdhci-cadence.c
index 5827d3751b81..9af3fe48d62f 100644
--- a/drivers/mmc/host/sdhci-cadence.c
+++ b/drivers/mmc/host/sdhci-cadence.c
@@ -67,7 +67,7 @@ struct sdhci_cdns_priv {
 	void __iomem *hrs_addr;
 	bool enhanced_strobe;
 	unsigned int nr_phy_params;
-	struct sdhci_cdns_phy_param phy_params[0];
+	struct sdhci_cdns_phy_param phy_params[];
 };
 
 struct sdhci_cdns_phy_cfg {
diff --git a/drivers/mmc/host/sdhci-pci.h b/drivers/mmc/host/sdhci-pci.h
index 981bbbe63aff..42ccd123b046 100644
--- a/drivers/mmc/host/sdhci-pci.h
+++ b/drivers/mmc/host/sdhci-pci.h
@@ -163,7 +163,7 @@ struct sdhci_pci_slot {
 	bool			cd_override_level;
 
 	void (*hw_reset)(struct sdhci_host *host);
-	unsigned long		private[0] ____cacheline_aligned;
+	unsigned long		private[] ____cacheline_aligned;
 };
 
 struct sdhci_pci_chip {
diff --git a/drivers/mmc/host/sdhci-pltfm.h b/drivers/mmc/host/sdhci-pltfm.h
index 2af445b8c325..6301b81cf573 100644
--- a/drivers/mmc/host/sdhci-pltfm.h
+++ b/drivers/mmc/host/sdhci-pltfm.h
@@ -25,7 +25,7 @@ struct sdhci_pltfm_host {
 	unsigned int clock;
 	u16 xfer_mode_shadow;
 
-	unsigned long private[0] ____cacheline_aligned;
+	unsigned long private[] ____cacheline_aligned;
 };
 
 #ifdef CONFIG_MMC_SDHCI_BIG_ENDIAN_32BIT_BYTE_SWAPPER
diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
index cac2d97782e6..249635692112 100644
--- a/drivers/mmc/host/sdhci.h
+++ b/drivers/mmc/host/sdhci.h
@@ -614,7 +614,7 @@ struct sdhci_host {
 
 	u64			data_timeout;
 
-	unsigned long private[0] ____cacheline_aligned;
+	unsigned long private[] ____cacheline_aligned;
 };
 
 struct sdhci_ops {
diff --git a/drivers/mmc/host/vub300.c b/drivers/mmc/host/vub300.c
index 6ced1b7f642f..a5a90d133f1f 100644
--- a/drivers/mmc/host/vub300.c
+++ b/drivers/mmc/host/vub300.c
@@ -95,7 +95,7 @@ struct sd_response_header {
 	u8 port_number;
 	u8 command_type;
 	u8 command_index;
-	u8 command_response[0];
+	u8 command_response[];
 } __packed;
 
 struct sd_status_header {
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 562ed06881b0..2629329ab9f2 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -465,7 +465,7 @@ struct mmc_host {
 	/* Host Software Queue support */
 	bool			hsq_enabled;
 
-	unsigned long		private[0] ____cacheline_aligned;
+	unsigned long		private[] ____cacheline_aligned;
 };
 
 struct device_node;
diff --git a/include/linux/mmc/sdio_func.h b/include/linux/mmc/sdio_func.h
index 5a177f7a83c3..fa2aaab5e57a 100644
--- a/include/linux/mmc/sdio_func.h
+++ b/include/linux/mmc/sdio_func.h
@@ -25,7 +25,7 @@ struct sdio_func_tuple {
 	struct sdio_func_tuple *next;
 	unsigned char code;
 	unsigned char size;
-	unsigned char data[0];
+	unsigned char data[];
 };
 
 /*
diff --git a/include/uapi/linux/mmc/ioctl.h b/include/uapi/linux/mmc/ioctl.h
index 00c08120f3ba..98e29e7f54ac 100644
--- a/include/uapi/linux/mmc/ioctl.h
+++ b/include/uapi/linux/mmc/ioctl.h
@@ -57,7 +57,7 @@ struct mmc_ioc_cmd {
  */
 struct mmc_ioc_multi_cmd {
 	__u64 num_of_cmds;
-	struct mmc_ioc_cmd cmds[0];
+	struct mmc_ioc_cmd cmds[];
 };
 
 #define MMC_IOC_CMD _IOWR(MMC_BLOCK_MAJOR, 0, struct mmc_ioc_cmd)
-- 
2.25.0


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