[PATCH][next] leds: Avoid -Wflex-array-member-not-at-end warning

[PATCH][next] leds: Avoid -Wflex-array-member-not-at-end warning

[Gustavo A. R. Silva]

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition of
a flexible structure where the size of the flexible-array member
is known at compile-time, and refactor the rest of the code,
accordingly.

So, with these changes, fix the following warning:

drivers/leds/leds-cros_ec.c:70:40: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/leds/leds-cros_ec.c | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/drivers/leds/leds-cros_ec.c b/drivers/leds/leds-cros_ec.c
index 275522b81ea5..6eab0474f52d 100644
--- a/drivers/leds/leds-cros_ec.c
+++ b/drivers/leds/leds-cros_ec.c
@@ -66,24 +66,20 @@ static int cros_ec_led_send_cmd(struct cros_ec_device *cros_ec,
 				union cros_ec_led_cmd_data *arg)
 {
 	int ret;
-	struct {
-		struct cros_ec_command msg;
-		union cros_ec_led_cmd_data data;
-	} __packed buf = {
-		.msg = {
-			.version = 1,
-			.command = EC_CMD_LED_CONTROL,
-			.insize  = sizeof(arg->resp),
-			.outsize = sizeof(arg->req),
-		},
-		.data.req = arg->req
-	};
-
-	ret = cros_ec_cmd_xfer_status(cros_ec, &buf.msg);
+	DEFINE_RAW_FLEX(struct cros_ec_command, msg, data,
+			sizeof(union cros_ec_led_cmd_data));
+
+	msg->version = 1;
+	msg->command = EC_CMD_LED_CONTROL;
+	msg->insize  = sizeof(arg->resp);
+	msg->outsize = sizeof(arg->req);
+	*(struct ec_params_led_control *)msg->data = arg->req;
+
+	ret = cros_ec_cmd_xfer_status(cros_ec, msg);
 	if (ret < 0)
 		return ret;
 
-	arg->resp = buf.data.resp;
+	arg->resp = *(struct ec_response_led_control *)msg->data;
 
 	return 0;
 }
-- 
2.43.0

Re: [PATCH][next] leds: Avoid -Wflex-array-member-not-at-end warning

[Thomas Weißschuh]

Hi Gustavo,

On 2025-03-28 08:33:22-0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition of
> a flexible structure where the size of the flexible-array member
> is known at compile-time, and refactor the rest of the code,
> accordingly.
> 
> So, with these changes, fix the following warning:
> 
> drivers/leds/leds-cros_ec.c:70:40: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
>  drivers/leds/leds-cros_ec.c | 26 +++++++++++---------------
>  1 file changed, 11 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/leds/leds-cros_ec.c b/drivers/leds/leds-cros_ec.c
> index 275522b81ea5..6eab0474f52d 100644
> --- a/drivers/leds/leds-cros_ec.c
> +++ b/drivers/leds/leds-cros_ec.c
> @@ -66,24 +66,20 @@ static int cros_ec_led_send_cmd(struct cros_ec_device *cros_ec,
>  				union cros_ec_led_cmd_data *arg)
>  {
>  	int ret;
> -	struct {
> -		struct cros_ec_command msg;
> -		union cros_ec_led_cmd_data data;
> -	} __packed buf = {
> -		.msg = {
> -			.version = 1,
> -			.command = EC_CMD_LED_CONTROL,
> -			.insize  = sizeof(arg->resp),
> -			.outsize = sizeof(arg->req),
> -		},
> -		.data.req = arg->req
> -	};
> -
> -	ret = cros_ec_cmd_xfer_status(cros_ec, &buf.msg);
> +	DEFINE_RAW_FLEX(struct cros_ec_command, msg, data,
> +			sizeof(union cros_ec_led_cmd_data));
> +
> +	msg->version = 1;
> +	msg->command = EC_CMD_LED_CONTROL;
> +	msg->insize  = sizeof(arg->resp);
> +	msg->outsize = sizeof(arg->req);
> +	*(struct ec_params_led_control *)msg->data = arg->req;

To be honest this looks really ugly and it's not at all obvious what is
going on. We have the utility function cros_ec_cmd() which would be the
nicer alternative. (Without having verified that it avoids the warning).
While it is slightly more expensive, I don't think it matters.
And if it does, the helper can be optimized.

(The same goes for my other cros_ec drivers)

> +
> +	ret = cros_ec_cmd_xfer_status(cros_ec, msg);
>  	if (ret < 0)
>  		return ret;
>  
> -	arg->resp = buf.data.resp;
> +	arg->resp = *(struct ec_response_led_control *)msg->data;
>  
>  	return 0;
>  }


Thomas

Re: [PATCH][next] leds: Avoid -Wflex-array-member-not-at-end warning

[Gustavo A. R. Silva]

Hi!

On 28/03/25 12:31, Thomas Weißschuh wrote:
> Hi Gustavo,
> 
> On 2025-03-28 08:33:22-0600, Gustavo A. R. Silva wrote:
>> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
>> getting ready to enable it, globally.
>>
>> Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition of
>> a flexible structure where the size of the flexible-array member
>> is known at compile-time, and refactor the rest of the code,
>> accordingly.
>>
>> So, with these changes, fix the following warning:
>>
>> drivers/leds/leds-cros_ec.c:70:40: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>> ---
>>   drivers/leds/leds-cros_ec.c | 26 +++++++++++---------------
>>   1 file changed, 11 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/leds/leds-cros_ec.c b/drivers/leds/leds-cros_ec.c
>> index 275522b81ea5..6eab0474f52d 100644
>> --- a/drivers/leds/leds-cros_ec.c
>> +++ b/drivers/leds/leds-cros_ec.c
>> @@ -66,24 +66,20 @@ static int cros_ec_led_send_cmd(struct cros_ec_device *cros_ec,
>>   				union cros_ec_led_cmd_data *arg)
>>   {
>>   	int ret;
>> -	struct {
>> -		struct cros_ec_command msg;
>> -		union cros_ec_led_cmd_data data;
>> -	} __packed buf = {
>> -		.msg = {
>> -			.version = 1,
>> -			.command = EC_CMD_LED_CONTROL,
>> -			.insize  = sizeof(arg->resp),
>> -			.outsize = sizeof(arg->req),
>> -		},
>> -		.data.req = arg->req
>> -	};
>> -
>> -	ret = cros_ec_cmd_xfer_status(cros_ec, &buf.msg);
>> +	DEFINE_RAW_FLEX(struct cros_ec_command, msg, data,
>> +			sizeof(union cros_ec_led_cmd_data));
>> +
>> +	msg->version = 1;
>> +	msg->command = EC_CMD_LED_CONTROL;
>> +	msg->insize  = sizeof(arg->resp);
>> +	msg->outsize = sizeof(arg->req);
>> +	*(struct ec_params_led_control *)msg->data = arg->req;
> 
> To be honest this looks really ugly and it's not at all obvious what is

We can do something like this, instead:

diff --git a/drivers/leds/leds-cros_ec.c b/drivers/leds/leds-cros_ec.c
index 275522b81ea5..c7235f4e577b 100644
--- a/drivers/leds/leds-cros_ec.c
+++ b/drivers/leds/leds-cros_ec.c
@@ -66,24 +66,24 @@ static int cros_ec_led_send_cmd(struct cros_ec_device *cros_ec,
                                 union cros_ec_led_cmd_data *arg)
  {
         int ret;
-       struct {
-               struct cros_ec_command msg;
-               union cros_ec_led_cmd_data data;
-       } __packed buf = {
-               .msg = {
-                       .version = 1,
-                       .command = EC_CMD_LED_CONTROL,
-                       .insize  = sizeof(arg->resp),
-                       .outsize = sizeof(arg->req),
-               },
-               .data.req = arg->req
-       };
-
-       ret = cros_ec_cmd_xfer_status(cros_ec, &buf.msg);
+       DEFINE_RAW_FLEX(struct cros_ec_command, msg, data,
+                       sizeof(union cros_ec_led_cmd_data));
+       struct ec_params_led_control *req =
+                               (struct ec_params_led_control *)msg->data;
+       struct ec_response_led_control *resp =
+                               (struct ec_response_led_control *)msg->data;
+
+       msg->version = 1;
+       msg->command = EC_CMD_LED_CONTROL;
+       msg->insize  = sizeof(arg->resp);
+       msg->outsize = sizeof(arg->req);
+       *req = arg->req;
+
+       ret = cros_ec_cmd_xfer_status(cros_ec, msg);
         if (ret < 0)
                 return ret;

-       arg->resp = buf.data.resp;
+       arg->resp = *resp;

         return 0;
  }

as in other cases:

https://lore.kernel.org/linux-hardening/Z-a4meHAy-t58bcE@kspp/

-Gustavo

> going on. We have the utility function cros_ec_cmd() which would be the
> nicer alternative. (Without having verified that it avoids the warning).
> While it is slightly more expensive, I don't think it matters.
> And if it does, the helper can be optimized.
> 
> (The same goes for my other cros_ec drivers)
> 
>> +
>> +	ret = cros_ec_cmd_xfer_status(cros_ec, msg);
>>   	if (ret < 0)
>>   		return ret;
>>   
>> -	arg->resp = buf.data.resp;
>> +	arg->resp = *(struct ec_response_led_control *)msg->data;
>>   
>>   	return 0;
>>   }
> 
> 
> Thomas

Re: [PATCH][next] leds: Avoid -Wflex-array-member-not-at-end warning

[Thomas Weißschuh]

Hi!

On 2025-03-28 12:51:02-0600, Gustavo A. R. Silva wrote:
> On 28/03/25 12:31, Thomas Weißschuh wrote:
> > On 2025-03-28 08:33:22-0600, Gustavo A. R. Silva wrote:
> > > -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> > > getting ready to enable it, globally.
> > > 
> > > Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition of
> > > a flexible structure where the size of the flexible-array member
> > > is known at compile-time, and refactor the rest of the code,
> > > accordingly.
> > > 
> > > So, with these changes, fix the following warning:
> > > 
> > > drivers/leds/leds-cros_ec.c:70:40: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> > > 
> > > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> > > ---
> > >   drivers/leds/leds-cros_ec.c | 26 +++++++++++---------------
> > >   1 file changed, 11 insertions(+), 15 deletions(-)
> > > 
> > > diff --git a/drivers/leds/leds-cros_ec.c b/drivers/leds/leds-cros_ec.c
> > > index 275522b81ea5..6eab0474f52d 100644
> > > --- a/drivers/leds/leds-cros_ec.c
> > > +++ b/drivers/leds/leds-cros_ec.c
> > > @@ -66,24 +66,20 @@ static int cros_ec_led_send_cmd(struct cros_ec_device *cros_ec,
> > >   				union cros_ec_led_cmd_data *arg)
> > >   {
> > >   	int ret;
> > > -	struct {
> > > -		struct cros_ec_command msg;
> > > -		union cros_ec_led_cmd_data data;
> > > -	} __packed buf = {
> > > -		.msg = {
> > > -			.version = 1,
> > > -			.command = EC_CMD_LED_CONTROL,
> > > -			.insize  = sizeof(arg->resp),
> > > -			.outsize = sizeof(arg->req),
> > > -		},
> > > -		.data.req = arg->req
> > > -	};
> > > -
> > > -	ret = cros_ec_cmd_xfer_status(cros_ec, &buf.msg);
> > > +	DEFINE_RAW_FLEX(struct cros_ec_command, msg, data,
> > > +			sizeof(union cros_ec_led_cmd_data));
> > > +
> > > +	msg->version = 1;
> > > +	msg->command = EC_CMD_LED_CONTROL;
> > > +	msg->insize  = sizeof(arg->resp);
> > > +	msg->outsize = sizeof(arg->req);
> > > +	*(struct ec_params_led_control *)msg->data = arg->req;
> > 
> > To be honest this looks really ugly and it's not at all obvious what is
> 
> We can do something like this, instead:
> 
> diff --git a/drivers/leds/leds-cros_ec.c b/drivers/leds/leds-cros_ec.c
> index 275522b81ea5..c7235f4e577b 100644
> --- a/drivers/leds/leds-cros_ec.c
> +++ b/drivers/leds/leds-cros_ec.c
> @@ -66,24 +66,24 @@ static int cros_ec_led_send_cmd(struct cros_ec_device *cros_ec,
>                                 union cros_ec_led_cmd_data *arg)
>  {
>         int ret;
> -       struct {
> -               struct cros_ec_command msg;
> -               union cros_ec_led_cmd_data data;
> -       } __packed buf = {
> -               .msg = {
> -                       .version = 1,
> -                       .command = EC_CMD_LED_CONTROL,
> -                       .insize  = sizeof(arg->resp),
> -                       .outsize = sizeof(arg->req),
> -               },
> -               .data.req = arg->req
> -       };
> -
> -       ret = cros_ec_cmd_xfer_status(cros_ec, &buf.msg);
> +       DEFINE_RAW_FLEX(struct cros_ec_command, msg, data,
> +                       sizeof(union cros_ec_led_cmd_data));
> +       struct ec_params_led_control *req =
> +                               (struct ec_params_led_control *)msg->data;
> +       struct ec_response_led_control *resp =
> +                               (struct ec_response_led_control *)msg->data;
> +
> +       msg->version = 1;
> +       msg->command = EC_CMD_LED_CONTROL;
> +       msg->insize  = sizeof(arg->resp);
> +       msg->outsize = sizeof(arg->req);
> +       *req = arg->req;
> +
> +       ret = cros_ec_cmd_xfer_status(cros_ec, msg);
>         if (ret < 0)
>                 return ret;
> 
> -       arg->resp = buf.data.resp;
> +       arg->resp = *resp;
> 
>         return 0;
>  }

My issue was with the general usage of DEFINE_RAW_FLEX(), the reply was
placed badly. For somebody not knowing this construct it's not clear
what is happening under the hood.
It's probably fine in a regular header file with some explanation,
but in a random driver it looks off.

The following is what I had in mind. Now actually tested.

--- a/drivers/leds/leds-cros_ec.c
+++ b/drivers/leds/leds-cros_ec.c
@@ -60,31 +60,18 @@ static inline struct cros_ec_led_priv *cros_ec_led_cdev_to_priv(struct led_class
 union cros_ec_led_cmd_data {
        struct ec_params_led_control req;
        struct ec_response_led_control resp;
-} __packed;
+};

 static int cros_ec_led_send_cmd(struct cros_ec_device *cros_ec,
                                union cros_ec_led_cmd_data *arg)
 {
        int ret;
-       struct {
-               struct cros_ec_command msg;
-               union cros_ec_led_cmd_data data;
-       } __packed buf = {
-               .msg = {
-                       .version = 1,
-                       .command = EC_CMD_LED_CONTROL,
-                       .insize  = sizeof(arg->resp),
-                       .outsize = sizeof(arg->req),
-               },
-               .data.req = arg->req
-       };
-
-       ret = cros_ec_cmd_xfer_status(cros_ec, &buf.msg);
+
+       ret = cros_ec_cmd(cros_ec, 1, EC_CMD_LED_CONTROL,
+                         &arg->req, sizeof(arg->req), &arg->resp, sizeof(arg->resp));
        if (ret < 0)
                return ret;

-       arg->resp = buf.data.resp;
-
        return 0;
 }


> 
> as in other cases:
> 
> https://lore.kernel.org/linux-hardening/Z-a4meHAy-t58bcE@kspp/
> 
> -Gustavo
> 
> > going on. We have the utility function cros_ec_cmd() which would be the
> > nicer alternative. (Without having verified that it avoids the warning).
> > While it is slightly more expensive, I don't think it matters.
> > And if it does, the helper can be optimized.
> > 
> > (The same goes for my other cros_ec drivers)
> > 
> > > +
> > > +	ret = cros_ec_cmd_xfer_status(cros_ec, msg);
> > >   	if (ret < 0)
> > >   		return ret;
> > > -	arg->resp = buf.data.resp;
> > > +	arg->resp = *(struct ec_response_led_control *)msg->data;
> > >   	return 0;
> > >   }


Thomas

Re: [PATCH][next] leds: Avoid -Wflex-array-member-not-at-end warning

[Gustavo A. R. Silva]

> My issue was with the general usage of DEFINE_RAW_FLEX(), the reply was
> placed badly. For somebody not knowing this construct it's not clear
> what is happening under the hood.
> It's probably fine in a regular header file with some explanation,
> but in a random driver it looks off.
> 
> The following is what I had in mind. Now actually tested.

OK, let's go with that :)

https://lore.kernel.org/linux-hardening/Z-rKcgFjsyKvd58q@kspp/

Thanks!
--
Gustavo