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

[Ulf Hansson <ulf.hansson@linaro.org>]

On Wed, 26 Feb 2020 at 23:28, 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>

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
>