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Date:   Thu, 18 May 2023 07:12:54 +0200
Message-ID: <87y1lmz0h5.wl-tiwai@suse.de>
From:   Takashi Iwai <tiwai@suse.de>
To:     "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc:     Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
        alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org,
        linux-hardening@vger.kernel.org
Subject: Re: [PATCH][next] ALSA: mixart: Replace one-element arrays with simple object declarations
In-Reply-To: <ZGVlcpuvx1rSOMP8@work>
References: <ZGVlcpuvx1rSOMP8@work>
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On Thu, 18 May 2023 01:38:26 +0200,
Gustavo A. R. Silva wrote:
> 
> One-element arrays are deprecated, and we are replacing them with flexible
> array members, instead. However, in this case it seems those one-element
> arrays have never actually been used as fake flexible arrays.
> 
> See this code that dates from Linux-2.6.12-rc2 initial git repository build
> (commit 1da177e4c3f4 ("Linux-2.6.12-rc2")):
> 
> sound/pci/mixart/mixart_core.h:
>  215 struct mixart_stream_state_req
>  216 {
>  217         u32                 delayed;
>  218         u64                 scheduler;
>  219         u32                 reserved4np[3];
>  220         u32                 stream_count;  /* set to 1 for instance */
>  221         struct mixart_flow_info  stream_info;   /* could be an array[stream_cou    nt] */
>  222 } __attribute__((packed));
> 
> sound/pci/mixart/mixart.c:
>  388
>  389         memset(&stream_state_req, 0, sizeof(stream_state_req));
>  390         stream_state_req.stream_count = 1;
>  391         stream_state_req.stream_info.stream_desc.uid_pipe = stream->pipe->group_uid;
>  392         stream_state_req.stream_info.stream_desc.stream_idx = stream->substream->number;
>  393
> 
> So, taking the code above as example, replace multiple one-element
> arrays with simple object declarations, and refactor the rest of the
> code, accordingly.
> 
> This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
> routines on memcpy() and help us make progress towards globally
> enabling -fstrict-flex-arrays=3 [1].
> 
> This results in no differences in binary output.
> 
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/296
> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Replacing with a simple object itself is OK, but please keep the
comment; the statement there is still valid, as it could be rather a multi-member array in theory.


thanks,

Takashi

> ---
>  sound/pci/mixart/mixart.c      | 8 ++++----
>  sound/pci/mixart/mixart_core.h | 7 +++----
>  2 files changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/sound/pci/mixart/mixart.c b/sound/pci/mixart/mixart.c
> index 1b078b789604..7ceaf6a7a77e 100644
> --- a/sound/pci/mixart/mixart.c
> +++ b/sound/pci/mixart/mixart.c
> @@ -98,7 +98,7 @@ static int mixart_set_pipe_state(struct mixart_mgr *mgr,
>  
>  	memset(&group_state, 0, sizeof(group_state));
>  	group_state.pipe_count = 1;
> -	group_state.pipe_uid[0] = pipe->group_uid;
> +	group_state.pipe_uid = pipe->group_uid;
>  
>  	if(start)
>  		request.message_id = MSG_STREAM_START_STREAM_GRP_PACKET;
> @@ -185,7 +185,7 @@ static int mixart_set_clock(struct mixart_mgr *mgr,
>  	clock_properties.clock_mode = CM_STANDALONE;
>  	clock_properties.frequency = rate;
>  	clock_properties.nb_callers = 1; /* only one entry in uid_caller ! */
> -	clock_properties.uid_caller[0] = pipe->group_uid;
> +	clock_properties.uid_caller = pipe->group_uid;
>  
>  	dev_dbg(&mgr->pci->dev, "mixart_set_clock to %d kHz\n", rate);
>  
> @@ -565,8 +565,8 @@ static int mixart_set_format(struct mixart_stream *stream, snd_pcm_format_t form
>  
>  	stream_param.pipe_count = 1;      /* set to 1 */
>  	stream_param.stream_count = 1;    /* set to 1 */
> -	stream_param.stream_desc[0].uid_pipe = stream->pipe->group_uid;
> -	stream_param.stream_desc[0].stream_idx = stream->substream->number;
> +	stream_param.stream_desc.uid_pipe = stream->pipe->group_uid;
> +	stream_param.stream_desc.stream_idx = stream->substream->number;
>  
>  	request.message_id = MSG_STREAM_SET_INPUT_STAGE_PARAM;
>  	request.uid = (struct mixart_uid){0,0};
> diff --git a/sound/pci/mixart/mixart_core.h b/sound/pci/mixart/mixart_core.h
> index 2f0e29ed5d63..ac74b2133c97 100644
> --- a/sound/pci/mixart/mixart_core.h
> +++ b/sound/pci/mixart/mixart_core.h
> @@ -231,7 +231,7 @@ struct mixart_group_state_req
>  	u64           scheduler;
>  	u32           reserved4np[2];
>  	u32           pipe_count;    /* set to 1 for instance */
> -	struct mixart_uid  pipe_uid[1];   /* could be an array[pipe_count] */
> +	struct mixart_uid  pipe_uid;
>  } __attribute__((packed));
>  
>  struct mixart_group_state_resp
> @@ -314,7 +314,7 @@ struct mixart_clock_properties
>  	u32 format;
>  	u32 board_mask;
>  	u32 nb_callers; /* set to 1 (see below) */
> -	struct mixart_uid uid_caller[1];
> +	struct mixart_uid uid_caller;
>  } __attribute__((packed));
>  
>  struct mixart_clock_properties_resp
> @@ -401,8 +401,7 @@ struct mixart_stream_param_desc
>  	u32 reserved4np[3];
>  	u32 pipe_count;                           /* set to 1 (array size !) */
>  	u32 stream_count;                         /* set to 1 (array size !) */
> -	struct mixart_txx_stream_desc stream_desc[1];  /* only one stream per command, but this could be an array */
> -
> +	struct mixart_txx_stream_desc stream_desc;
>  } __attribute__((packed));
>  
>  
> -- 
> 2.34.1
>