On 1/7/21 11:38 PM, Jakub Kicinski wrote:
> On Thu, 7 Jan 2021 22:17:15 +0100 Marc Kleine-Budde wrote:
>>> +struct __packed tcan4x5x_buf_cmd {
>>> + u8 cmd;
>>> + __be16 addr;
>>> + u8 len;
>>> +};
>>
>> This has to be packed, as I assume the compiler would add some space after
>> the
>> "u8 cmd" to align the __be16 naturally.
>
> Ack, packing this one makes sense.
>
>>> +struct __packed tcan4x5x_map_buf {
>>> + struct tcan4x5x_buf_cmd cmd;
>>> + u8 data[256 * sizeof(u32)];
>>> +} ____cacheline_aligned;
>>
>> Due to the packing of the struct tcan4x5x_buf_cmd it should have a length of
>> 4
>> bytes. Without __packed, will the "u8 data" come directly after the cmd?
>
> Yup, u8 with no alignment attribute will follow the previous
> field with no holes.Ack, without __packed, there's no diff in the objdump on arm. Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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