netdev - Re: [Intel-wired-lan] [PATCH iwl-net] idpf: avoid compiler padding in virtchnl2

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Date: Thu, 4 Jan 2024 14:15:16 -0800
From: "Linga, Pavan Kumar" <pavan.kumar.linga@...el.com>
To: Paul Menzel <pmenzel@...gen.mpg.de>
CC: <intel-wired-lan@...ts.osuosl.org>, <netdev@...r.kernel.org>,
	<przemyslaw.kitszel@...el.com>, Emil Tantilov <emil.s.tantilov@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-net] idpf: avoid compiler padding in
 virtchnl2_ptype struct



On 12/28/2023 9:39 AM, Linga, Pavan Kumar wrote:
> 
> 
> On 12/27/2023 1:45 PM, Paul Menzel wrote:
>> Dear Pavan,
>>
>>
>> Thank you for yoru patch.
>>
>> Am 27.12.23 um 18:37 schrieb Pavan Kumar Linga:
>>> Config option in arm random config file
>>
>> Sorry, I do not understand this part of the sentence. What Kconfig 
>> option was selected exactly causing this behavior.
>>
>  > Apologies as I couldn't find the config option that was causing this. As
> the driver compilation with arm rand config was failing, posted the fix 
> first. Will debug further to find the config option that resulted in 
> this failure. Thanks for the review.
>

After further debug, found that the arm random config was using OABI 
(old ABI) which was inferred from the compiler option '-mabi=apcs-gnu'. 
kconfig option 'CONFIG_AEABI' is related to this and was disabled by 
default in the config file.

Static assertion check passed when compiled the driver with 
'CONFIG_AEABI' enabled. The check also passed on explicitly changing the 
compiler option to '-mabi=aapcs-linux'. I will update the commit message 
with this info.

Regards,
Pavan

>>> is causing the compiler
>>> to add padding. Avoid it by using "__packed" structure attribute
>>> for virtchnl2_ptype struct.
>>
>> Did the compiler emit a warning? If so, please paste it.
>>
> 
> Here is the compiler error and also will update the commit message with 
> the error:
> 
> 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);
>           | ^~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Regards,
> Pavan
> 
>>> Fixes: 0d7502a9b4a7 ("virtchnl: add virtchnl version 2 ops")
>>> Reported-by: kernel test robot <lkp@...el.com>
>>> Closes: 
>>> https://lore.kernel.org/oe-kbuild-all/202312220250.ufEm8doQ-lkp@intel.com
>>> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
>>> Signed-off-by: Pavan Kumar Linga <pavan.kumar.linga@...el.com>
>>> ---
>>>   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);
>>>   /**
>>
>> Reviewed-by: Paul Menzel <pmenzel@...gen.mpg.de>
>>
>>
>>
>> Kind regards,
>>
>> Paul
>