[PATCH 0/2][next] scsi: qla2xxx: Replace one-element array with flexible-array member

[PATCH 0/2][next] scsi: qla2xxx: Replace one-element array with flexible-array member

[Gustavo A. R. Silva]

Hi!

This series aims to replace a one-element array with flexible-array
member in drivers/scsi/qla2xxx/qla_def.h through the use of the
DECLARE_FLEX_ARRAY() helper.

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].

Link: https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
Link: https://github.com/KSPP/linux/issues/79
Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]

Gustavo A. R. Silva (2):
  scsi: qla2xxx: Replace one-element array with DECLARE_FLEX_ARRAY()
    helper
  scsi: qla2xxx: Use struct_size() in code related to struct
    ct_sns_gpnft_rsp

 drivers/scsi/qla2xxx/qla_def.h | 4 ++--
 drivers/scsi/qla2xxx/qla_gs.c  | 5 ++---
 2 files changed, 4 insertions(+), 5 deletions(-)

-- 
2.34.1

[PATCH 1/2][next] scsi: qla2xxx: Replace one-element array with DECLARE_FLEX_ARRAY() helper

[Gustavo A. R. Silva]

One-element arrays as fake flex arrays are deprecated and we are moving
towards adopting C99 flexible-array members, instead. So, replace
one-element array declaration in struct ct_sns_gpnft_rsp, which is
ultimately being used inside a union:

drivers/scsi/qla2xxx/qla_def.h:
3240 struct ct_sns_gpnft_pkt {
3241         union {
3242                 struct ct_sns_req req;
3243                 struct ct_sns_gpnft_rsp rsp;
3244         } p;
3245 };

Important to mention is that doing a build before/after this patch results
in no binary differences.

This help us make progress towards globally enabling
-fstrict-flex-arrays=3 [1].

Link: https://github.com/KSPP/linux/issues/245
Link: https://github.com/KSPP/linux/issues/193
Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/scsi/qla2xxx/qla_def.h | 4 ++--
 drivers/scsi/qla2xxx/qla_gs.c  | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/qla2xxx/qla_def.h b/drivers/scsi/qla2xxx/qla_def.h
index a26a373be9da..1eea977ef426 100644
--- a/drivers/scsi/qla2xxx/qla_def.h
+++ b/drivers/scsi/qla2xxx/qla_def.h
@@ -3151,12 +3151,12 @@ struct ct_sns_gpnft_rsp {
 		uint8_t vendor_unique;
 	};
 	/* Assume the largest number of targets for the union */
-	struct ct_sns_gpn_ft_data {
+	DECLARE_FLEX_ARRAY(struct ct_sns_gpn_ft_data {
 		u8 control_byte;
 		u8 port_id[3];
 		u32 reserved;
 		u8 port_name[8];
-	} entries[1];
+	}, entries);
 };
 
 /* CT command response */
diff --git a/drivers/scsi/qla2xxx/qla_gs.c b/drivers/scsi/qla2xxx/qla_gs.c
index 64ab070b8716..69d3bc795f90 100644
--- a/drivers/scsi/qla2xxx/qla_gs.c
+++ b/drivers/scsi/qla2xxx/qla_gs.c
@@ -4073,7 +4073,7 @@ int qla24xx_async_gpnft(scsi_qla_host_t *vha, u8 fc4_type, srb_t *sp)
 		sp->u.iocb_cmd.u.ctarg.req_size = GPN_FT_REQ_SIZE;
 
 		rspsz = sizeof(struct ct_sns_gpnft_rsp) +
-			((vha->hw->max_fibre_devices - 1) *
+			(vha->hw->max_fibre_devices *
 			    sizeof(struct ct_sns_gpn_ft_data));
 
 		sp->u.iocb_cmd.u.ctarg.rsp = dma_alloc_coherent(&vha->hw->pdev->dev,
-- 
2.34.1

[PATCH 2/2][next] scsi: qla2xxx: Use struct_size() in code related to struct ct_sns_gpnft_rsp

[Gustavo A. R. Silva]

Prefer struct_size() over open-coded versions of idiom:

sizeof(struct-with-flex-array) + sizeof(typeof-flex-array-elements) * count

where count is the max number of items the flexible array is supposed to
contain.

Link: https://github.com/KSPP/linux/issues/160
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/scsi/qla2xxx/qla_gs.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/qla2xxx/qla_gs.c b/drivers/scsi/qla2xxx/qla_gs.c
index 69d3bc795f90..27e1df56b0fb 100644
--- a/drivers/scsi/qla2xxx/qla_gs.c
+++ b/drivers/scsi/qla2xxx/qla_gs.c
@@ -4072,9 +4072,8 @@ int qla24xx_async_gpnft(scsi_qla_host_t *vha, u8 fc4_type, srb_t *sp)
 		}
 		sp->u.iocb_cmd.u.ctarg.req_size = GPN_FT_REQ_SIZE;
 
-		rspsz = sizeof(struct ct_sns_gpnft_rsp) +
-			(vha->hw->max_fibre_devices *
-			    sizeof(struct ct_sns_gpn_ft_data));
+		rspsz = struct_size((struct ct_sns_gpnft_rsp *)0, entries,
+				vha->hw->max_fibre_devices);
 
 		sp->u.iocb_cmd.u.ctarg.rsp = dma_alloc_coherent(&vha->hw->pdev->dev,
 								rspsz,
-- 
2.34.1

Re: [PATCH 1/2][next] scsi: qla2xxx: Replace one-element array with DECLARE_FLEX_ARRAY() helper

[Kees Cook]

On Fri, Nov 18, 2022 at 05:47:13PM -0600, Gustavo A. R. Silva wrote:
> One-element arrays as fake flex arrays are deprecated and we are moving
> towards adopting C99 flexible-array members, instead. So, replace
> one-element array declaration in struct ct_sns_gpnft_rsp, which is
> ultimately being used inside a union:
> 
> drivers/scsi/qla2xxx/qla_def.h:
> 3240 struct ct_sns_gpnft_pkt {
> 3241         union {
> 3242                 struct ct_sns_req req;
> 3243                 struct ct_sns_gpnft_rsp rsp;
> 3244         } p;
> 3245 };
> 
> Important to mention is that doing a build before/after this patch results
> in no binary differences.
> 
> This help us make progress towards globally enabling
> -fstrict-flex-arrays=3 [1].
> 
> Link: https://github.com/KSPP/linux/issues/245
> Link: https://github.com/KSPP/linux/issues/193
> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

Re: [PATCH 2/2][next] scsi: qla2xxx: Use struct_size() in code related to struct ct_sns_gpnft_rsp

[Kees Cook]

On Fri, Nov 18, 2022 at 05:47:56PM -0600, Gustavo A. R. Silva wrote:
> Prefer struct_size() over open-coded versions of idiom:
> 
> sizeof(struct-with-flex-array) + sizeof(typeof-flex-array-elements) * count
> 
> where count is the max number of items the flexible array is supposed to
> contain.
> 
> Link: https://github.com/KSPP/linux/issues/160
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
>  drivers/scsi/qla2xxx/qla_gs.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/qla2xxx/qla_gs.c b/drivers/scsi/qla2xxx/qla_gs.c
> index 69d3bc795f90..27e1df56b0fb 100644
> --- a/drivers/scsi/qla2xxx/qla_gs.c
> +++ b/drivers/scsi/qla2xxx/qla_gs.c
> @@ -4072,9 +4072,8 @@ int qla24xx_async_gpnft(scsi_qla_host_t *vha, u8 fc4_type, srb_t *sp)
>  		}
>  		sp->u.iocb_cmd.u.ctarg.req_size = GPN_FT_REQ_SIZE;
>  
> -		rspsz = sizeof(struct ct_sns_gpnft_rsp) +
> -			(vha->hw->max_fibre_devices *
> -			    sizeof(struct ct_sns_gpn_ft_data));
> +		rspsz = struct_size((struct ct_sns_gpnft_rsp *)0, entries,
> +				vha->hw->max_fibre_devices);

This should be able to use sp->u.iocb_cmd.u.ctarg.rsp instead of the
explicit struct with a NULL. (It's just using typeof() internally, so
it's okay that it isn't allocated yet.)

-Kees

>  
>  		sp->u.iocb_cmd.u.ctarg.rsp = dma_alloc_coherent(&vha->hw->pdev->dev,
>  								rspsz,
> -- 
> 2.34.1
> 

-- 
Kees Cook

Re: [PATCH 2/2][next] scsi: qla2xxx: Use struct_size() in code related to struct ct_sns_gpnft_rsp

[Gustavo A. R. Silva]

On Fri, Nov 18, 2022 at 11:10:44PM -0800, Kees Cook wrote:
> On Fri, Nov 18, 2022 at 05:47:56PM -0600, Gustavo A. R. Silva wrote:
> > Prefer struct_size() over open-coded versions of idiom:
> > 
> > sizeof(struct-with-flex-array) + sizeof(typeof-flex-array-elements) * count
> > 
> > where count is the max number of items the flexible array is supposed to
> > contain.
> > 
> > Link: https://github.com/KSPP/linux/issues/160
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> > ---
> >  drivers/scsi/qla2xxx/qla_gs.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/scsi/qla2xxx/qla_gs.c b/drivers/scsi/qla2xxx/qla_gs.c
> > index 69d3bc795f90..27e1df56b0fb 100644
> > --- a/drivers/scsi/qla2xxx/qla_gs.c
> > +++ b/drivers/scsi/qla2xxx/qla_gs.c
> > @@ -4072,9 +4072,8 @@ int qla24xx_async_gpnft(scsi_qla_host_t *vha, u8 fc4_type, srb_t *sp)
> >  		}
> >  		sp->u.iocb_cmd.u.ctarg.req_size = GPN_FT_REQ_SIZE;
> >  
> > -		rspsz = sizeof(struct ct_sns_gpnft_rsp) +
> > -			(vha->hw->max_fibre_devices *
> > -			    sizeof(struct ct_sns_gpn_ft_data));
> > +		rspsz = struct_size((struct ct_sns_gpnft_rsp *)0, entries,
> > +				vha->hw->max_fibre_devices);
> 
> This should be able to use sp->u.iocb_cmd.u.ctarg.rsp instead of the
> explicit struct with a NULL. (It's just using typeof() internally, so
> it's okay that it isn't allocated yet.)

mmh... yeah; and considering they're already going all the way down to
sp->u.iocb_cmd.u.ctarg.req_size, I think accessing sp->u.iocb_cmd.u.ctarg.rsp
is perfectly fine. :)

I'll respin. Thanks for the feedback!
--
Gustavo

> 
> -Kees
> 
> >  
> >  		sp->u.iocb_cmd.u.ctarg.rsp = dma_alloc_coherent(&vha->hw->pdev->dev,
> >  								rspsz,
> > -- 
> > 2.34.1
> > 
> 
> -- 
> Kees Cook

Re: [PATCH 2/2][next] scsi: qla2xxx: Use struct_size() in code related to struct ct_sns_gpnft_rsp

[Gustavo A. R. Silva]

On Sat, Nov 19, 2022 at 01:20:09AM -0600, Gustavo A. R. Silva wrote:
> On Fri, Nov 18, 2022 at 11:10:44PM -0800, Kees Cook wrote:
> > On Fri, Nov 18, 2022 at 05:47:56PM -0600, Gustavo A. R. Silva wrote:
> > > Prefer struct_size() over open-coded versions of idiom:
> > > 
> > > sizeof(struct-with-flex-array) + sizeof(typeof-flex-array-elements) * count
> > > 
> > > where count is the max number of items the flexible array is supposed to
> > > contain.
> > > 
> > > Link: https://github.com/KSPP/linux/issues/160
> > > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> > > ---
> > >  drivers/scsi/qla2xxx/qla_gs.c | 5 ++---
> > >  1 file changed, 2 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/scsi/qla2xxx/qla_gs.c b/drivers/scsi/qla2xxx/qla_gs.c
> > > index 69d3bc795f90..27e1df56b0fb 100644
> > > --- a/drivers/scsi/qla2xxx/qla_gs.c
> > > +++ b/drivers/scsi/qla2xxx/qla_gs.c
> > > @@ -4072,9 +4072,8 @@ int qla24xx_async_gpnft(scsi_qla_host_t *vha, u8 fc4_type, srb_t *sp)
> > >  		}
> > >  		sp->u.iocb_cmd.u.ctarg.req_size = GPN_FT_REQ_SIZE;
> > >  
> > > -		rspsz = sizeof(struct ct_sns_gpnft_rsp) +
> > > -			(vha->hw->max_fibre_devices *
> > > -			    sizeof(struct ct_sns_gpn_ft_data));
> > > +		rspsz = struct_size((struct ct_sns_gpnft_rsp *)0, entries,
> > > +				vha->hw->max_fibre_devices);
> > 
> > This should be able to use sp->u.iocb_cmd.u.ctarg.rsp instead of the
> > explicit struct with a NULL. (It's just using typeof() internally, so
> > it's okay that it isn't allocated yet.)
> 
> mmh... yeah; and considering they're already going all the way down to
> sp->u.iocb_cmd.u.ctarg.req_size, I think accessing sp->u.iocb_cmd.u.ctarg.rsp
> is perfectly fine. :)

except that... it seems sp->u.iocb_cmd.u.ctarg.rsp is a pointer to void
and not a struct of type struct ct_sns_gpnft_rsp. :O

drivers/scsi/qla2xxx/qla_def.h:474:
struct ct_arg {
        void            *iocb;
        u16             nport_handle;
        dma_addr_t      req_dma;
        dma_addr_t      rsp_dma;
        u32             req_size;
        u32             rsp_size;
        u32             req_allocated_size;
        u32             rsp_allocated_size;
        void            *req;
        void            *rsp;
        port_id_t       id;
};

I wonder if you wanted to point out something entirely different...?

--
Gustavo

Re: [PATCH 1/2][next] scsi: qla2xxx: Replace one-element array with DECLARE_FLEX_ARRAY() helper

[Christophe JAILLET]

Le 19/11/2022 à 00:47, Gustavo A. R. Silva a écrit :
> One-element arrays as fake flex arrays are deprecated and we are moving
> towards adopting C99 flexible-array members, instead. So, replace
> one-element array declaration in struct ct_sns_gpnft_rsp, which is
> ultimately being used inside a union:
> 
> drivers/scsi/qla2xxx/qla_def.h:
> 3240 struct ct_sns_gpnft_pkt {
> 3241         union {
> 3242                 struct ct_sns_req req;
> 3243                 struct ct_sns_gpnft_rsp rsp;
> 3244         } p;
> 3245 };
> 
> Important to mention is that doing a build before/after this patch results
> in no binary differences.

Hi,

even with the:

 >   		rspsz = sizeof(struct ct_sns_gpnft_rsp) +
 > -			((vha->hw->max_fibre_devices - 1) *
 > +			(vha->hw->max_fibre_devices *
 >   			    sizeof(struct ct_sns_gpn_ft_data));

change ?

CJ

> 
> This help us make progress towards globally enabling
> -fstrict-flex-arrays=3 [1].
> 
> Link: https://github.com/KSPP/linux/issues/245
> Link: https://github.com/KSPP/linux/issues/193
> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
>   drivers/scsi/qla2xxx/qla_def.h | 4 ++--
>   drivers/scsi/qla2xxx/qla_gs.c  | 2 +-
>   2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/qla2xxx/qla_def.h b/drivers/scsi/qla2xxx/qla_def.h
> index a26a373be9da..1eea977ef426 100644
> --- a/drivers/scsi/qla2xxx/qla_def.h
> +++ b/drivers/scsi/qla2xxx/qla_def.h
> @@ -3151,12 +3151,12 @@ struct ct_sns_gpnft_rsp {
>   		uint8_t vendor_unique;
>   	};
>   	/* Assume the largest number of targets for the union */
> -	struct ct_sns_gpn_ft_data {
> +	DECLARE_FLEX_ARRAY(struct ct_sns_gpn_ft_data {
>   		u8 control_byte;
>   		u8 port_id[3];
>   		u32 reserved;
>   		u8 port_name[8];
> -	} entries[1];
> +	}, entries);
>   };
>   
>   /* CT command response */
> diff --git a/drivers/scsi/qla2xxx/qla_gs.c b/drivers/scsi/qla2xxx/qla_gs.c
> index 64ab070b8716..69d3bc795f90 100644
> --- a/drivers/scsi/qla2xxx/qla_gs.c
> +++ b/drivers/scsi/qla2xxx/qla_gs.c
> @@ -4073,7 +4073,7 @@ int qla24xx_async_gpnft(scsi_qla_host_t *vha, u8 fc4_type, srb_t *sp)
>   		sp->u.iocb_cmd.u.ctarg.req_size = GPN_FT_REQ_SIZE;
>   
>   		rspsz = sizeof(struct ct_sns_gpnft_rsp) +
> -			((vha->hw->max_fibre_devices - 1) *
> +			(vha->hw->max_fibre_devices *
>   			    sizeof(struct ct_sns_gpn_ft_data));
>   
>   		sp->u.iocb_cmd.u.ctarg.rsp = dma_alloc_coherent(&vha->hw->pdev->dev,

Re: [PATCH 1/2][next] scsi: qla2xxx: Replace one-element array with DECLARE_FLEX_ARRAY() helper

[Gustavo A. R. Silva]

On Sat, Nov 19, 2022 at 09:44:02AM +0100, Christophe JAILLET wrote:
> Le 19/11/2022 à 00:47, Gustavo A. R. Silva a écrit :
> > One-element arrays as fake flex arrays are deprecated and we are moving
> > towards adopting C99 flexible-array members, instead. So, replace
> > one-element array declaration in struct ct_sns_gpnft_rsp, which is
> > ultimately being used inside a union:
> > 
> > drivers/scsi/qla2xxx/qla_def.h:
> > 3240 struct ct_sns_gpnft_pkt {
> > 3241         union {
> > 3242                 struct ct_sns_req req;
> > 3243                 struct ct_sns_gpnft_rsp rsp;
> > 3244         } p;
> > 3245 };
> > 
> > Important to mention is that doing a build before/after this patch results
> > in no binary differences.
> 
> Hi,
> 
> even with the:
> 
> >   		rspsz = sizeof(struct ct_sns_gpnft_rsp) +
> > -			((vha->hw->max_fibre_devices - 1) *
> > +			(vha->hw->max_fibre_devices *
> >   			    sizeof(struct ct_sns_gpn_ft_data));
> 
> change ?

Yep; that change compensates for the removal of the 1 in the declaration
of entries[].

The above piece of code is a common idiom to calculate the size for an
allocation when a one-element array is involved. In the original code
(vha->hw->max_fibre_devices - 1) compensates for the _extra_ size of one
element of type struct ct_sns_gpn_ft_data in sizeof(struct ct_sns_gpnft_rsp).

--
Gustavo

> 
> CJ
> 
> > 
> > This help us make progress towards globally enabling
> > -fstrict-flex-arrays=3 [1].
> > 
> > Link: https://github.com/KSPP/linux/issues/245
> > Link: https://github.com/KSPP/linux/issues/193
> > Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> > ---
> >   drivers/scsi/qla2xxx/qla_def.h | 4 ++--
> >   drivers/scsi/qla2xxx/qla_gs.c  | 2 +-
> >   2 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/scsi/qla2xxx/qla_def.h b/drivers/scsi/qla2xxx/qla_def.h
> > index a26a373be9da..1eea977ef426 100644
> > --- a/drivers/scsi/qla2xxx/qla_def.h
> > +++ b/drivers/scsi/qla2xxx/qla_def.h
> > @@ -3151,12 +3151,12 @@ struct ct_sns_gpnft_rsp {
> >   		uint8_t vendor_unique;
> >   	};
> >   	/* Assume the largest number of targets for the union */
> > -	struct ct_sns_gpn_ft_data {
> > +	DECLARE_FLEX_ARRAY(struct ct_sns_gpn_ft_data {
> >   		u8 control_byte;
> >   		u8 port_id[3];
> >   		u32 reserved;
> >   		u8 port_name[8];
> > -	} entries[1];
> > +	}, entries);
> >   };
> >   /* CT command response */
> > diff --git a/drivers/scsi/qla2xxx/qla_gs.c b/drivers/scsi/qla2xxx/qla_gs.c
> > index 64ab070b8716..69d3bc795f90 100644
> > --- a/drivers/scsi/qla2xxx/qla_gs.c
> > +++ b/drivers/scsi/qla2xxx/qla_gs.c
> > @@ -4073,7 +4073,7 @@ int qla24xx_async_gpnft(scsi_qla_host_t *vha, u8 fc4_type, srb_t *sp)
> >   		sp->u.iocb_cmd.u.ctarg.req_size = GPN_FT_REQ_SIZE;
> >   		rspsz = sizeof(struct ct_sns_gpnft_rsp) +
> > -			((vha->hw->max_fibre_devices - 1) *
> > +			(vha->hw->max_fibre_devices *
> >   			    sizeof(struct ct_sns_gpn_ft_data));
> >   		sp->u.iocb_cmd.u.ctarg.rsp = dma_alloc_coherent(&vha->hw->pdev->dev,
> 

Re: [PATCH 1/2][next] scsi: qla2xxx: Replace one-element array with DECLARE_FLEX_ARRAY() helper

[Christophe JAILLET]

Le 19/11/2022 à 09:56, Gustavo A. R. Silva a écrit :
> On Sat, Nov 19, 2022 at 09:44:02AM +0100, Christophe JAILLET wrote:
>> Le 19/11/2022 à 00:47, Gustavo A. R. Silva a écrit :
>>> One-element arrays as fake flex arrays are deprecated and we are moving
>>> towards adopting C99 flexible-array members, instead. So, replace
>>> one-element array declaration in struct ct_sns_gpnft_rsp, which is
>>> ultimately being used inside a union:
>>>
>>> drivers/scsi/qla2xxx/qla_def.h:
>>> 3240 struct ct_sns_gpnft_pkt {
>>> 3241         union {
>>> 3242                 struct ct_sns_req req;
>>> 3243                 struct ct_sns_gpnft_rsp rsp;
>>> 3244         } p;
>>> 3245 };
>>>
>>> Important to mention is that doing a build before/after this patch results
>>> in no binary differences.
>>
>> Hi,
>>
>> even with the:
>>
>>>    		rspsz = sizeof(struct ct_sns_gpnft_rsp) +
>>> -			((vha->hw->max_fibre_devices - 1) *
>>> +			(vha->hw->max_fibre_devices *
>>>    			    sizeof(struct ct_sns_gpn_ft_data));
>>
>> change ?
> 
> Yep; that change compensates for the removal of the 1 in the declaration
> of entries[].
> 
> The above piece of code is a common idiom to calculate the size for an
> allocation when a one-element array is involved. In the original code
> (vha->hw->max_fibre_devices - 1) compensates for the _extra_ size of one
> element of type struct ct_sns_gpn_ft_data in sizeof(struct ct_sns_gpnft_rsp).
> 

Yes, I do agree, that the code is equivalent. I was surprised that a 
compiler was smart enough to generate the same binary code.

With gcc 11.3.0 (x86_64), I do get some differences when I do:
    make drivers/scsi/qla2xxx/qla_gs.o
    objdump -D  drivers/scsi/qla2xxx/qla_gs.o > before.asm

    patch -p1 < patch.diff

    make drivers/scsi/qla2xxx/qla_gs.o
    objdump -D  drivers/scsi/qla2xxx/qla_gs.o > after.asm

    diff -u before.asm after.asm

Mostly some slight ordering of instruction changes, but the binary are 
not the same.

CJ

> --
> Gustavo
> 
>>
>> CJ
>>
>>>
>>> This help us make progress towards globally enabling
>>> -fstrict-flex-arrays=3 [1].
>>>
>>> Link: https://github.com/KSPP/linux/issues/245
>>> Link: https://github.com/KSPP/linux/issues/193
>>> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
>>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>>> ---
>>>    drivers/scsi/qla2xxx/qla_def.h | 4 ++--
>>>    drivers/scsi/qla2xxx/qla_gs.c  | 2 +-
>>>    2 files changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/scsi/qla2xxx/qla_def.h b/drivers/scsi/qla2xxx/qla_def.h
>>> index a26a373be9da..1eea977ef426 100644
>>> --- a/drivers/scsi/qla2xxx/qla_def.h
>>> +++ b/drivers/scsi/qla2xxx/qla_def.h
>>> @@ -3151,12 +3151,12 @@ struct ct_sns_gpnft_rsp {
>>>    		uint8_t vendor_unique;
>>>    	};
>>>    	/* Assume the largest number of targets for the union */
>>> -	struct ct_sns_gpn_ft_data {
>>> +	DECLARE_FLEX_ARRAY(struct ct_sns_gpn_ft_data {
>>>    		u8 control_byte;
>>>    		u8 port_id[3];
>>>    		u32 reserved;
>>>    		u8 port_name[8];
>>> -	} entries[1];
>>> +	}, entries);
>>>    };
>>>    /* CT command response */
>>> diff --git a/drivers/scsi/qla2xxx/qla_gs.c b/drivers/scsi/qla2xxx/qla_gs.c
>>> index 64ab070b8716..69d3bc795f90 100644
>>> --- a/drivers/scsi/qla2xxx/qla_gs.c
>>> +++ b/drivers/scsi/qla2xxx/qla_gs.c
>>> @@ -4073,7 +4073,7 @@ int qla24xx_async_gpnft(scsi_qla_host_t *vha, u8 fc4_type, srb_t *sp)
>>>    		sp->u.iocb_cmd.u.ctarg.req_size = GPN_FT_REQ_SIZE;
>>>    		rspsz = sizeof(struct ct_sns_gpnft_rsp) +
>>> -			((vha->hw->max_fibre_devices - 1) *
>>> +			(vha->hw->max_fibre_devices *
>>>    			    sizeof(struct ct_sns_gpn_ft_data));
>>>    		sp->u.iocb_cmd.u.ctarg.rsp = dma_alloc_coherent(&vha->hw->pdev->dev,
>>
> 

Re: [PATCH 1/2][next] scsi: qla2xxx: Replace one-element array with DECLARE_FLEX_ARRAY() helper

[Gustavo A. R. Silva]

> Yes, I do agree, that the code is equivalent. I was surprised that a
> compiler was smart enough to generate the same binary code.

We discard the tiny changes that don't affect the logic or the control
flow of the program.

--
Gustavo