Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper

Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper

[Greg Kroah-Hartman]

On Thu, Nov 17, 2022 at 03:48:45PM +0530, Deepak R Varma wrote:
> The code currently uses C90 standard extension based zero length arrays.
> The zero length array member also happens to be the only member of the
> structs. Such zero length array declarations are deprecated and the
> new C99 standard extension of flexible array declarations are to be
> used instead.
> 
> The DECLARE_FLEX_ARRAY() helper allows for a flexible array member as
> the only member in a structure. Refer to these links [1], [2] for
> details.
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://lkml.kernel.org/r/YxKY6O2hmdwNh8r8@work
> 
> Issue identified using Coccinelle.
> 
> Signed-off-by: Deepak R Varma <drv@mailo.com>
> ---
> 
> Notes:
>    1. Proposed change is compile tested only.
>    2. Solution feedback from gustavoars@kernel.org
> 
> 
>  drivers/staging/wlan-ng/hfa384x.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/wlan-ng/hfa384x.h b/drivers/staging/wlan-ng/hfa384x.h
> index 0611e37df6ac..3a1edcb43e07 100644
> --- a/drivers/staging/wlan-ng/hfa384x.h
> +++ b/drivers/staging/wlan-ng/hfa384x.h
> @@ -960,15 +960,15 @@ struct hfa384x_pdr_nicid {
>  } __packed;
> 
>  struct hfa384x_pdr_refdac_measurements {
> -	u16 value[0];
> +	DECLARE_FLEX_ARRAY(u16, value);
>  } __packed;

Why?  This structure is never used anywhere, right?  So why is this
needed to be changed and not just removed entirely?  Same for the other
structures in this patch.

thanks,

greg k-h

Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper

[Deepak R Varma]

On Thu, Nov 17, 2022 at 01:54:49PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Nov 17, 2022 at 03:48:45PM +0530, Deepak R Varma wrote:
> > The code currently uses C90 standard extension based zero length arrays.
> > The zero length array member also happens to be the only member of the
> > structs. Such zero length array declarations are deprecated and the
> > new C99 standard extension of flexible array declarations are to be
> > used instead.
> >
> > The DECLARE_FLEX_ARRAY() helper allows for a flexible array member as
> > the only member in a structure. Refer to these links [1], [2] for
> > details.
> >
> > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> > [2] https://lkml.kernel.org/r/YxKY6O2hmdwNh8r8@work
> >
> > Issue identified using Coccinelle.
> >
> > Signed-off-by: Deepak R Varma <drv@mailo.com>
> > ---
> >
> > Notes:
> >    1. Proposed change is compile tested only.
> >    2. Solution feedback from gustavoars@kernel.org
> >
> >
> >  drivers/staging/wlan-ng/hfa384x.h | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/staging/wlan-ng/hfa384x.h b/drivers/staging/wlan-ng/hfa384x.h
> > index 0611e37df6ac..3a1edcb43e07 100644
> > --- a/drivers/staging/wlan-ng/hfa384x.h
> > +++ b/drivers/staging/wlan-ng/hfa384x.h
> > @@ -960,15 +960,15 @@ struct hfa384x_pdr_nicid {
> >  } __packed;
> >
> >  struct hfa384x_pdr_refdac_measurements {
> > -	u16 value[0];
> > +	DECLARE_FLEX_ARRAY(u16, value);
> >  } __packed;
>
> Why?  This structure is never used anywhere, right?  So why is this
> needed to be changed and not just removed entirely?  Same for the other
> structures in this patch.

Hello Greg,
I am unable to confirm that these structures are truly not needed in the absence
if a real device based testing. I could only validate that using the compile
build and driver loading.

This change that I am proposing in the interim would enable the compiler to
protect the structure from addition of a new member below the zero length array.

If there is a way to confirm that the structures are indeed not needed, I can
revise the patch and send the cleanup accordingly. Please suggest.

Thank you,
./drv


>
> thanks,
>
> greg k-h

Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper

[Greg Kroah-Hartman]

On Thu, Nov 17, 2022 at 06:50:55PM +0530, Deepak R Varma wrote:
> On Thu, Nov 17, 2022 at 01:54:49PM +0100, Greg Kroah-Hartman wrote:
> > On Thu, Nov 17, 2022 at 03:48:45PM +0530, Deepak R Varma wrote:
> > > The code currently uses C90 standard extension based zero length arrays.
> > > The zero length array member also happens to be the only member of the
> > > structs. Such zero length array declarations are deprecated and the
> > > new C99 standard extension of flexible array declarations are to be
> > > used instead.
> > >
> > > The DECLARE_FLEX_ARRAY() helper allows for a flexible array member as
> > > the only member in a structure. Refer to these links [1], [2] for
> > > details.
> > >
> > > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> > > [2] https://lkml.kernel.org/r/YxKY6O2hmdwNh8r8@work
> > >
> > > Issue identified using Coccinelle.
> > >
> > > Signed-off-by: Deepak R Varma <drv@mailo.com>
> > > ---
> > >
> > > Notes:
> > >    1. Proposed change is compile tested only.
> > >    2. Solution feedback from gustavoars@kernel.org
> > >
> > >
> > >  drivers/staging/wlan-ng/hfa384x.h | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/staging/wlan-ng/hfa384x.h b/drivers/staging/wlan-ng/hfa384x.h
> > > index 0611e37df6ac..3a1edcb43e07 100644
> > > --- a/drivers/staging/wlan-ng/hfa384x.h
> > > +++ b/drivers/staging/wlan-ng/hfa384x.h
> > > @@ -960,15 +960,15 @@ struct hfa384x_pdr_nicid {
> > >  } __packed;
> > >
> > >  struct hfa384x_pdr_refdac_measurements {
> > > -	u16 value[0];
> > > +	DECLARE_FLEX_ARRAY(u16, value);
> > >  } __packed;
> >
> > Why?  This structure is never used anywhere, right?  So why is this
> > needed to be changed and not just removed entirely?  Same for the other
> > structures in this patch.
> 
> Hello Greg,
> I am unable to confirm that these structures are truly not needed in the absence
> if a real device based testing. I could only validate that using the compile
> build and driver loading.

Think this through, if no one is actually using this structure, and it
is of 0 size, then do you think it is being used?

> This change that I am proposing in the interim would enable the compiler to
> protect the structure from addition of a new member below the zero length array.

Why would you want to add a new member below this?  That's not what is
happening here at all.

Please think this through a bit more.

good luck!

greg k-h

Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper

[Deepak R Varma]

On Sat, Nov 19, 2022 at 08:08:15PM +0530, Deepak R Varma wrote:
> On Thu, Nov 17, 2022 at 07:03:21PM +0100, Greg Kroah-Hartman wrote:
> > On Thu, Nov 17, 2022 at 06:50:55PM +0530, Deepak R Varma wrote:
> > > On Thu, Nov 17, 2022 at 01:54:49PM +0100, Greg Kroah-Hartman wrote:
> > > > On Thu, Nov 17, 2022 at 03:48:45PM +0530, Deepak R Varma wrote:
> > > > >
> > > > >  struct hfa384x_pdr_refdac_measurements {
> > > > > -	u16 value[0];
> > > > > +	DECLARE_FLEX_ARRAY(u16, value);
> > > > >  } __packed;
> > > >
> > > > Why?  This structure is never used anywhere, right?  So why is this
> > > > needed to be changed and not just removed entirely?  Same for the other
> > > > structures in this patch.
> > >
> > > Hello Greg,
> > > I am unable to confirm that these structures are truly not needed in the absence
> > > if a real device based testing. I could only validate that using the compile
> > > build and driver loading.
> >
> > Think this through, if no one is actually using this structure, and it
> > is of 0 size, then do you think it is being used?
>
> Hello Greg,
> I did not find any memory allocation for these zero length array structures.
> Also, the union or its enclosing structure do not appear to access the members.
> Hence I am leaning towards concluding that these zero length array structures do
> not appear to be necessary.
>
> There are a few other structures that are part of the same union, however, they
> too do not appear to be used for accessing the memory assigned to the union [or
> its enclosing structure]. I think most of the members of these unions can be
> replaced by one max size structure of this union [e.g. struct
> hfa384x_pdr_mkk_measurements].
>
> Could you please comment if I am reading the code right?
>
> For your quick reference, the zero length structure declaration are online 963
> whereas the union is on line number 1080 of the file drivers/staging/wlan-ng/hfa384x.h

Hello Greg,
can you please suggest how should I approach this clean-up/correction?

Thank you,
./drv

>
>
> Thank you,
> ./drv
>
>
> >
> > > This change that I am proposing in the interim would enable the compiler to
> > > protect the structure from addition of a new member below the zero length array.
> >
> > Why would you want to add a new member below this?  That's not what is
> > happening here at all.
>
> I came across this one old commit where such an accident happened. This is from
> a recent LWN article:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e48f129c2f20
>
> I understand the C99 now protects from such an attempt at the compile time
> itself.
>
> Thank you,
> ./drv
>
>
> >
> > Please think this through a bit more.
> >
> > good luck!
> >
> > greg k-h
> >

Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper

[Dan Carpenter]

On Mon, Nov 28, 2022 at 01:15:43PM +0530, Deepak R Varma wrote:
> On Sat, Nov 19, 2022 at 08:08:15PM +0530, Deepak R Varma wrote:
> > On Thu, Nov 17, 2022 at 07:03:21PM +0100, Greg Kroah-Hartman wrote:
> > > On Thu, Nov 17, 2022 at 06:50:55PM +0530, Deepak R Varma wrote:
> > > > On Thu, Nov 17, 2022 at 01:54:49PM +0100, Greg Kroah-Hartman wrote:
> > > > > On Thu, Nov 17, 2022 at 03:48:45PM +0530, Deepak R Varma wrote:
> > > > > >
> > > > > >  struct hfa384x_pdr_refdac_measurements {
> > > > > > -	u16 value[0];
> > > > > > +	DECLARE_FLEX_ARRAY(u16, value);
> > > > > >  } __packed;
> > > > >
> > > > > Why?  This structure is never used anywhere, right?  So why is this
> > > > > needed to be changed and not just removed entirely?  Same for the other
> > > > > structures in this patch.
> > > >
> > > > Hello Greg,
> > > > I am unable to confirm that these structures are truly not needed in the absence
> > > > if a real device based testing. I could only validate that using the compile
> > > > build and driver loading.
> > >
> > > Think this through, if no one is actually using this structure, and it
> > > is of 0 size, then do you think it is being used?
> >
> > Hello Greg,
> > I did not find any memory allocation for these zero length array structures.
> > Also, the union or its enclosing structure do not appear to access the members.
> > Hence I am leaning towards concluding that these zero length array structures do
> > not appear to be necessary.
> >
> > There are a few other structures that are part of the same union, however, they
> > too do not appear to be used for accessing the memory assigned to the union [or
> > its enclosing structure]. I think most of the members of these unions can be
> > replaced by one max size structure of this union [e.g. struct
> > hfa384x_pdr_mkk_measurements].
> >
> > Could you please comment if I am reading the code right?
> >
> > For your quick reference, the zero length structure declaration are online 963
> > whereas the union is on line number 1080 of the file drivers/staging/wlan-ng/hfa384x.h
> 
> Hello Greg,
> can you please suggest how should I approach this clean-up/correction?
> 

Like this:

diff --git a/drivers/staging/wlan-ng/hfa384x.h b/drivers/staging/wlan-ng/hfa384x.h
index 0611e37df6ac..6a3df58c9e9c 100644
--- a/drivers/staging/wlan-ng/hfa384x.h
+++ b/drivers/staging/wlan-ng/hfa384x.h
@@ -959,10 +959,6 @@ struct hfa384x_pdr_nicid {
 	u16 minor;
 } __packed;
 
-struct hfa384x_pdr_refdac_measurements {
-	u16 value[0];
-} __packed;
-
 struct hfa384x_pdr_vgdac_measurements {
 	u16 value[0];
 } __packed;
@@ -1077,7 +1073,6 @@ struct hfa384x_pdrec {
 		struct hfa384x_pdr_mfisuprange mfisuprange;
 		struct hfa384x_pdr_cfisuprange cfisuprange;
 		struct hfa384x_pdr_nicid nicid;
-		struct hfa384x_pdr_refdac_measurements refdac_measurements;
 		struct hfa384x_pdr_vgdac_measurements vgdac_measurements;
 		struct hfa384x_pdr_level_comp_measurements level_compc_measurements;
 		struct hfa384x_pdr_mac_address mac_address;

Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper

[Greg Kroah-Hartman]

On Mon, Nov 28, 2022 at 01:15:43PM +0530, Deepak R Varma wrote:
> On Sat, Nov 19, 2022 at 08:08:15PM +0530, Deepak R Varma wrote:
> > On Thu, Nov 17, 2022 at 07:03:21PM +0100, Greg Kroah-Hartman wrote:
> > > On Thu, Nov 17, 2022 at 06:50:55PM +0530, Deepak R Varma wrote:
> > > > On Thu, Nov 17, 2022 at 01:54:49PM +0100, Greg Kroah-Hartman wrote:
> > > > > On Thu, Nov 17, 2022 at 03:48:45PM +0530, Deepak R Varma wrote:
> > > > > >
> > > > > >  struct hfa384x_pdr_refdac_measurements {
> > > > > > -	u16 value[0];
> > > > > > +	DECLARE_FLEX_ARRAY(u16, value);
> > > > > >  } __packed;
> > > > >
> > > > > Why?  This structure is never used anywhere, right?  So why is this
> > > > > needed to be changed and not just removed entirely?  Same for the other
> > > > > structures in this patch.
> > > >
> > > > Hello Greg,
> > > > I am unable to confirm that these structures are truly not needed in the absence
> > > > if a real device based testing. I could only validate that using the compile
> > > > build and driver loading.
> > >
> > > Think this through, if no one is actually using this structure, and it
> > > is of 0 size, then do you think it is being used?
> >
> > Hello Greg,
> > I did not find any memory allocation for these zero length array structures.
> > Also, the union or its enclosing structure do not appear to access the members.
> > Hence I am leaning towards concluding that these zero length array structures do
> > not appear to be necessary.
> >
> > There are a few other structures that are part of the same union, however, they
> > too do not appear to be used for accessing the memory assigned to the union [or
> > its enclosing structure]. I think most of the members of these unions can be
> > replaced by one max size structure of this union [e.g. struct
> > hfa384x_pdr_mkk_measurements].
> >
> > Could you please comment if I am reading the code right?
> >
> > For your quick reference, the zero length structure declaration are online 963
> > whereas the union is on line number 1080 of the file drivers/staging/wlan-ng/hfa384x.h
> 
> Hello Greg,
> can you please suggest how should I approach this clean-up/correction?

Sorry, but I do not have the bandwidth to help out with this.  I will
gladly review changes submitted only.

greg k-h

Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper

[Deepak R Varma]

On Mon, Nov 28, 2022 at 10:50:19AM +0300, Dan Carpenter wrote:
> On Mon, Nov 28, 2022 at 01:15:43PM +0530, Deepak R Varma wrote:
> > On Sat, Nov 19, 2022 at 08:08:15PM +0530, Deepak R Varma wrote:
> > > On Thu, Nov 17, 2022 at 07:03:21PM +0100, Greg Kroah-Hartman wrote:
> > > > On Thu, Nov 17, 2022 at 06:50:55PM +0530, Deepak R Varma wrote:
> > > > > On Thu, Nov 17, 2022 at 01:54:49PM +0100, Greg Kroah-Hartman wrote:
> > > > > > On Thu, Nov 17, 2022 at 03:48:45PM +0530, Deepak R Varma wrote:
> > > > > > >
> > > > > > >  struct hfa384x_pdr_refdac_measurements {
> > > > > > > -	u16 value[0];
> > > > > > > +	DECLARE_FLEX_ARRAY(u16, value);
> > > > > > >  } __packed;
> > > > > >
> > > > > > Why?  This structure is never used anywhere, right?  So why is this
> > > > > > needed to be changed and not just removed entirely?  Same for the other
> > > > > > structures in this patch.
> > > > >
> > > > > Hello Greg,
> > > > > I am unable to confirm that these structures are truly not needed in the absence
> > > > > if a real device based testing. I could only validate that using the compile
> > > > > build and driver loading.
> > > >
> > > > Think this through, if no one is actually using this structure, and it
> > > > is of 0 size, then do you think it is being used?
> > >
> > > Hello Greg,
> > > I did not find any memory allocation for these zero length array structures.
> > > Also, the union or its enclosing structure do not appear to access the members.
> > > Hence I am leaning towards concluding that these zero length array structures do
> > > not appear to be necessary.
> > >
> > > There are a few other structures that are part of the same union, however, they
> > > too do not appear to be used for accessing the memory assigned to the union [or
> > > its enclosing structure]. I think most of the members of these unions can be
> > > replaced by one max size structure of this union [e.g. struct
> > > hfa384x_pdr_mkk_measurements].
> > >
> > > Could you please comment if I am reading the code right?
> > >
> > > For your quick reference, the zero length structure declaration are online 963
> > > whereas the union is on line number 1080 of the file drivers/staging/wlan-ng/hfa384x.h
> >
> > Hello Greg,
> > can you please suggest how should I approach this clean-up/correction?
> >
>
> Like this:

Thank you Dan. This takes me back to the very first version of this patch. I
will send in the clean up.

./drv

>
> diff --git a/drivers/staging/wlan-ng/hfa384x.h b/drivers/staging/wlan-ng/hfa384x.h
> index 0611e37df6ac..6a3df58c9e9c 100644
> --- a/drivers/staging/wlan-ng/hfa384x.h
> +++ b/drivers/staging/wlan-ng/hfa384x.h
> @@ -959,10 +959,6 @@ struct hfa384x_pdr_nicid {
>  	u16 minor;
>  } __packed;
>
> -struct hfa384x_pdr_refdac_measurements {
> -	u16 value[0];
> -} __packed;
> -
>  struct hfa384x_pdr_vgdac_measurements {
>  	u16 value[0];
>  } __packed;
> @@ -1077,7 +1073,6 @@ struct hfa384x_pdrec {
>  		struct hfa384x_pdr_mfisuprange mfisuprange;
>  		struct hfa384x_pdr_cfisuprange cfisuprange;
>  		struct hfa384x_pdr_nicid nicid;
> -		struct hfa384x_pdr_refdac_measurements refdac_measurements;
>  		struct hfa384x_pdr_vgdac_measurements vgdac_measurements;
>  		struct hfa384x_pdr_level_comp_measurements level_compc_measurements;
>  		struct hfa384x_pdr_mac_address mac_address;
>

Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper

[Deepak R Varma]

On Mon, Nov 28, 2022 at 08:53:28AM +0100, Greg Kroah-Hartman wrote:
> On Mon, Nov 28, 2022 at 01:15:43PM +0530, Deepak R Varma wrote:
> > >
> > > For your quick reference, the zero length structure declaration are online 963
> > > whereas the union is on line number 1080 of the file drivers/staging/wlan-ng/hfa384x.h
> >
> > Hello Greg,
> > can you please suggest how should I approach this clean-up/correction?
>
> Sorry, but I do not have the bandwidth to help out with this.  I will
> gladly review changes submitted only.

No problem. I completely understand and appreciate. Thank you Greg.

./drv

>
> greg k-h
>

Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper

[Dan Carpenter]

On Mon, Nov 28, 2022 at 01:51:58PM +0530, Deepak R Varma wrote:
> On Mon, Nov 28, 2022 at 10:50:19AM +0300, Dan Carpenter wrote:
> > On Mon, Nov 28, 2022 at 01:15:43PM +0530, Deepak R Varma wrote:
> > > On Sat, Nov 19, 2022 at 08:08:15PM +0530, Deepak R Varma wrote:
> > > > On Thu, Nov 17, 2022 at 07:03:21PM +0100, Greg Kroah-Hartman wrote:
> > > > > On Thu, Nov 17, 2022 at 06:50:55PM +0530, Deepak R Varma wrote:
> > > > > > On Thu, Nov 17, 2022 at 01:54:49PM +0100, Greg Kroah-Hartman wrote:
> > > > > > > On Thu, Nov 17, 2022 at 03:48:45PM +0530, Deepak R Varma wrote:
> > > > > > > >
> > > > > > > >  struct hfa384x_pdr_refdac_measurements {
> > > > > > > > -	u16 value[0];
> > > > > > > > +	DECLARE_FLEX_ARRAY(u16, value);
> > > > > > > >  } __packed;
> > > > > > >
> > > > > > > Why?  This structure is never used anywhere, right?  So why is this
> > > > > > > needed to be changed and not just removed entirely?  Same for the other
> > > > > > > structures in this patch.
> > > > > >
> > > > > > Hello Greg,
> > > > > > I am unable to confirm that these structures are truly not needed in the absence
> > > > > > if a real device based testing. I could only validate that using the compile
> > > > > > build and driver loading.
> > > > >
> > > > > Think this through, if no one is actually using this structure, and it
> > > > > is of 0 size, then do you think it is being used?
> > > >
> > > > Hello Greg,
> > > > I did not find any memory allocation for these zero length array structures.
> > > > Also, the union or its enclosing structure do not appear to access the members.
> > > > Hence I am leaning towards concluding that these zero length array structures do
> > > > not appear to be necessary.
> > > >
> > > > There are a few other structures that are part of the same union, however, they
> > > > too do not appear to be used for accessing the memory assigned to the union [or
> > > > its enclosing structure]. I think most of the members of these unions can be
> > > > replaced by one max size structure of this union [e.g. struct
> > > > hfa384x_pdr_mkk_measurements].
> > > >
> > > > Could you please comment if I am reading the code right?
> > > >
> > > > For your quick reference, the zero length structure declaration are online 963
> > > > whereas the union is on line number 1080 of the file drivers/staging/wlan-ng/hfa384x.h
> > >
> > > Hello Greg,
> > > can you please suggest how should I approach this clean-up/correction?
> > >
> >
> > Like this:
> 
> Thank you Dan. This takes me back to the very first version of this patch. I
> will send in the clean up.

Don't just send what I sent you, look around and try to see if there are
other issues with the code.

regards,
dan carpenter

Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX_ARRAY() helper

[Deepak R Varma]

On Mon, Nov 28, 2022 at 11:25:01AM +0300, Dan Carpenter wrote:
> On Mon, Nov 28, 2022 at 01:51:58PM +0530, Deepak R Varma wrote:
> > On Mon, Nov 28, 2022 at 10:50:19AM +0300, Dan Carpenter wrote:
> > > Like this:
> >
> > Thank you Dan. This takes me back to the very first version of this patch. I
> > will send in the clean up.
>
> Don't just send what I sent you, look around and try to see if there are
> other issues with the code.

Yes, I will follow your advise.

Thanks,
./drv

>
> regards,
> dan carpenter
>
>