[PATCH iwl-net v2] idpf: avoid compiler padding in virtchnl2_ptype struct

[PATCH iwl-net v2] idpf: avoid compiler padding in virtchnl2_ptype struct

[Pavan Kumar Linga]

In the arm random config file, kconfig option 'CONFIG_AEABI' is
disabled which results in adding the compiler flag '-mabi=apcs-gnu'.
This causes the compiler to add padding in virtchnl2_ptype
structure to align it to 8 bytes, resulting in the following
size check failure:

include/linux/build_bug.h:78:41: error: static assertion failed: "(6) == sizeof(struct virtchnl2_ptype)"
      78 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
         |                                         ^~~~~~~~~~~~~~
include/linux/build_bug.h:77:34: note: in expansion of macro '__static_assert'
      77 | #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
         |                                  ^~~~~~~~~~~~~~~
drivers/net/ethernet/intel/idpf/virtchnl2.h:26:9: note: in expansion of macro 'static_assert'
      26 |         static_assert((n) == sizeof(struct X))
         |         ^~~~~~~~~~~~~
drivers/net/ethernet/intel/idpf/virtchnl2.h:982:1: note: in expansion of macro 'VIRTCHNL2_CHECK_STRUCT_LEN'
     982 | VIRTCHNL2_CHECK_STRUCT_LEN(6, virtchnl2_ptype);
         | ^~~~~~~~~~~~~~~~~~~~~~~~~~

Avoid the compiler padding by using "__packed" structure
attribute for the virtchnl2_ptype struct.

Fixes: 0d7502a9b4a7 ("virtchnl: add virtchnl version 2 ops")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202312220250.ufEm8doQ-lkp@intel.com
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Pavan Kumar Linga <pavan.kumar.linga@intel.com>

---
v2:
 - add the kconfig option causing the compile failure to the commit message
---
 drivers/net/ethernet/intel/idpf/virtchnl2.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/idpf/virtchnl2.h b/drivers/net/ethernet/intel/idpf/virtchnl2.h
index 8dc83788972..dd750e6dcd0 100644
--- a/drivers/net/ethernet/intel/idpf/virtchnl2.h
+++ b/drivers/net/ethernet/intel/idpf/virtchnl2.h
@@ -978,7 +978,7 @@ struct virtchnl2_ptype {
 	u8 proto_id_count;
 	__le16 pad;
 	__le16 proto_id[];
-};
+} __packed;
 VIRTCHNL2_CHECK_STRUCT_LEN(6, virtchnl2_ptype);
 
 /**
-- 
2.43.0

Re: [PATCH iwl-net v2] idpf: avoid compiler padding in virtchnl2_ptype struct

[Simon Horman]

On Thu, Jan 04, 2024 at 05:32:32PM -0800, Pavan Kumar Linga wrote:
> In the arm random config file, kconfig option 'CONFIG_AEABI' is
> disabled which results in adding the compiler flag '-mabi=apcs-gnu'.
> This causes the compiler to add padding in virtchnl2_ptype
> structure to align it to 8 bytes, resulting in the following
> size check failure:
> 
> include/linux/build_bug.h:78:41: error: static assertion failed: "(6) == sizeof(struct virtchnl2_ptype)"
>       78 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
>          |                                         ^~~~~~~~~~~~~~
> include/linux/build_bug.h:77:34: note: in expansion of macro '__static_assert'
>       77 | #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
>          |                                  ^~~~~~~~~~~~~~~
> drivers/net/ethernet/intel/idpf/virtchnl2.h:26:9: note: in expansion of macro 'static_assert'
>       26 |         static_assert((n) == sizeof(struct X))
>          |         ^~~~~~~~~~~~~
> drivers/net/ethernet/intel/idpf/virtchnl2.h:982:1: note: in expansion of macro 'VIRTCHNL2_CHECK_STRUCT_LEN'
>      982 | VIRTCHNL2_CHECK_STRUCT_LEN(6, virtchnl2_ptype);
>          | ^~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Avoid the compiler padding by using "__packed" structure
> attribute for the virtchnl2_ptype struct.
> 
> Fixes: 0d7502a9b4a7 ("virtchnl: add virtchnl version 2 ops")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202312220250.ufEm8doQ-lkp@intel.com
> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
> Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
> Signed-off-by: Pavan Kumar Linga <pavan.kumar.linga@intel.com>

Reviewed-by: Simon Horman <horms@kernel.org>

Re: [Intel-wired-lan] [PATCH iwl-net v2] idpf: avoid compiler padding in virtchnl2_ptype struct

[Alexander Lobakin]

From: Pavan Kumar Linga <pavan.kumar.linga@intel.com>
Date: Thu,  4 Jan 2024 17:32:32 -0800

> In the arm random config file, kconfig option 'CONFIG_AEABI' is
> disabled which results in adding the compiler flag '-mabi=apcs-gnu'.
> This causes the compiler to add padding in virtchnl2_ptype
> structure to align it to 8 bytes, resulting in the following
> size check failure:

[...]

> diff --git a/drivers/net/ethernet/intel/idpf/virtchnl2.h b/drivers/net/ethernet/intel/idpf/virtchnl2.h
> index 8dc83788972..dd750e6dcd0 100644
> --- a/drivers/net/ethernet/intel/idpf/virtchnl2.h
> +++ b/drivers/net/ethernet/intel/idpf/virtchnl2.h
> @@ -978,7 +978,7 @@ struct virtchnl2_ptype {
>  	u8 proto_id_count;
>  	__le16 pad;
>  	__le16 proto_id[];
> -};
> +} __packed;

Try using `__packed __aligned(sizeof(__le16))`
(or just `__packed __aligned(2)`) here. It may generate more optimized
code than just __packed, as the latter assumes the structure address in
the memory can be `2n + 1`, while it fact it's aligned to 2 bytes.

(another virtchnl2 design fail anyway :D)

>  VIRTCHNL2_CHECK_STRUCT_LEN(6, virtchnl2_ptype);
>  
>  /**

Thanks,
Olek