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

From: Ulf Hansson
Date: Wed Mar 11 2020 - 11:35:04 EST

On Wed, 26 Feb 2020 at 23:28, Gustavo A. R. Silva
<gustavo@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>

Applied for next, thanks!

Kind regards
Uffe


> ---
> 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
>