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

["Gustavo A. R. Silva" <gustavoars@kernel.org>]

Hi all,

Friendly ping: who can take this?

Thanks
--
Gustavo

On Thu, May 07, 2020 at 01:55:38PM -0500, 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]
> 
> sizeof(flexible-array-member) triggers a warning because flexible array
> members have incomplete type[1]. There are some instances of code in
> which the sizeof operator is being incorrectly/erroneously applied to
> zero-length arrays and the result is zero. Such instances may be hiding
> some bugs. So, this work (flexible-array member conversions) will also
> help to get completely rid of those sorts of issues.
> 
> 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 <gustavoars@kernel.org>
> ---
>  drivers/net/wireless/intel/iwlwifi/dvm/commands.h   |   12 ++++++------
>  drivers/net/wireless/intel/iwlwifi/fw/api/nvm-reg.h |    4 ++--
>  drivers/net/wireless/intel/iwlwifi/fw/debugfs.c     |    2 +-
>  drivers/net/wireless/intel/iwlwifi/iwl-op-mode.h    |    2 +-
>  drivers/net/wireless/intel/iwlwifi/iwl-trans.h      |    2 +-
>  5 files changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/dvm/commands.h b/drivers/net/wireless/intel/iwlwifi/dvm/commands.h
> index 0f4be4be181c..fdcc1292a92b 100644
> --- a/drivers/net/wireless/intel/iwlwifi/dvm/commands.h
> +++ b/drivers/net/wireless/intel/iwlwifi/dvm/commands.h
> @@ -1023,7 +1023,7 @@ struct iwl_wep_cmd {
>  	u8 global_key_type;
>  	u8 flags;
>  	u8 reserved;
> -	struct iwl_wep_key key[0];
> +	struct iwl_wep_key key[];
>  } __packed;
>  
>  #define WEP_KEY_WEP_TYPE 1
> @@ -1305,7 +1305,7 @@ struct iwl_tx_cmd {
>  	 * length is 26 or 30 bytes, followed by payload data
>  	 */
>  	u8 payload[0];
> -	struct ieee80211_hdr hdr[0];
> +	struct ieee80211_hdr hdr[];
>  } __packed;
>  
>  /*
> @@ -2380,7 +2380,7 @@ struct iwl_scan_cmd {
>  	 * for one scan to complete (i.e. receive SCAN_COMPLETE_NOTIFICATION)
>  	 * before requesting another scan.
>  	 */
> -	u8 data[0];
> +	u8 data[];
>  } __packed;
>  
>  /* Can abort will notify by complete notification with abort status. */
> @@ -2475,7 +2475,7 @@ struct iwl_tx_beacon_cmd {
>  	__le16 tim_idx;
>  	u8 tim_size;
>  	u8 reserved1;
> -	struct ieee80211_hdr frame[0];	/* beacon frame */
> +	struct ieee80211_hdr frame[];	/* beacon frame */
>  } __packed;
>  
>  /******************************************************************************
> @@ -3188,7 +3188,7 @@ struct iwl_calib_hdr {
>  
>  struct iwl_calib_cmd {
>  	struct iwl_calib_hdr hdr;
> -	u8 data[0];
> +	u8 data[];
>  } __packed;
>  
>  struct iwl_calib_xtal_freq_cmd {
> @@ -3216,7 +3216,7 @@ struct iwl_calib_temperature_offset_v2_cmd {
>  /* IWL_PHY_CALIBRATE_CHAIN_NOISE_RESET_CMD */
>  struct iwl_calib_chain_noise_reset_cmd {
>  	struct iwl_calib_hdr hdr;
> -	u8 data[0];
> +	u8 data[];
>  };
>  
>  /* IWL_PHY_CALIBRATE_CHAIN_NOISE_GAIN_CMD */
> diff --git a/drivers/net/wireless/intel/iwlwifi/fw/api/nvm-reg.h b/drivers/net/wireless/intel/iwlwifi/fw/api/nvm-reg.h
> index 97b49843e318..397ac89a04c2 100644
> --- a/drivers/net/wireless/intel/iwlwifi/fw/api/nvm-reg.h
> +++ b/drivers/net/wireless/intel/iwlwifi/fw/api/nvm-reg.h
> @@ -351,7 +351,7 @@ struct iwl_mcc_update_resp_v3 {
>  	__le16 time;
>  	__le16 geo_info;
>  	__le32 n_channels;
> -	__le32 channels[0];
> +	__le32 channels[];
>  } __packed; /* LAR_UPDATE_MCC_CMD_RESP_S_VER_3 */
>  
>  /**
> @@ -380,7 +380,7 @@ struct iwl_mcc_update_resp {
>  	u8 source_id;
>  	u8 reserved[3];
>  	__le32 n_channels;
> -	__le32 channels[0];
> +	__le32 channels[];
>  } __packed; /* LAR_UPDATE_MCC_CMD_RESP_S_VER_4 */
>  
>  /**
> diff --git a/drivers/net/wireless/intel/iwlwifi/fw/debugfs.c b/drivers/net/wireless/intel/iwlwifi/fw/debugfs.c
> index 89f74116569d..cc1d93606d9b 100644
> --- a/drivers/net/wireless/intel/iwlwifi/fw/debugfs.c
> +++ b/drivers/net/wireless/intel/iwlwifi/fw/debugfs.c
> @@ -261,7 +261,7 @@ struct hcmd_write_data {
>  	__be32 cmd_id;
>  	__be32 flags;
>  	__be16 length;
> -	u8 data[0];
> +	u8 data[];
>  } __packed;
>  
>  static ssize_t iwl_dbgfs_send_hcmd_write(struct iwl_fw_runtime *fwrt, char *buf,
> diff --git a/drivers/net/wireless/intel/iwlwifi/iwl-op-mode.h b/drivers/net/wireless/intel/iwlwifi/iwl-op-mode.h
> index 3008a5246be8..b35b8920941b 100644
> --- a/drivers/net/wireless/intel/iwlwifi/iwl-op-mode.h
> +++ b/drivers/net/wireless/intel/iwlwifi/iwl-op-mode.h
> @@ -175,7 +175,7 @@ void iwl_opmode_deregister(const char *name);
>  struct iwl_op_mode {
>  	const struct iwl_op_mode_ops *ops;
>  
> -	char op_mode_specific[0] __aligned(sizeof(void *));
> +	char op_mode_specific[] __aligned(sizeof(void *));
>  };
>  
>  static inline void iwl_op_mode_stop(struct iwl_op_mode *op_mode)
> diff --git a/drivers/net/wireless/intel/iwlwifi/iwl-trans.h b/drivers/net/wireless/intel/iwlwifi/iwl-trans.h
> index bba527b339b5..3fbbbac0953d 100644
> --- a/drivers/net/wireless/intel/iwlwifi/iwl-trans.h
> +++ b/drivers/net/wireless/intel/iwlwifi/iwl-trans.h
> @@ -878,7 +878,7 @@ struct iwl_trans {
>  
>  	/* pointer to trans specific struct */
>  	/*Ensure that this pointer will always be aligned to sizeof pointer */
> -	char trans_specific[0] __aligned(sizeof(void *));
> +	char trans_specific[] __aligned(sizeof(void *));
>  };
>  
>  const char *iwl_get_cmd_string(struct iwl_trans *trans, u32 id);
>