Re: [PATCH] efi/cper: Fix endianness of PCI class code

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(+ Arnd)

Full patch here: http://marc.info/?l=linux-pci&m=149400953408528

On 6 May 2017 at 10:07, Lukas Wunner <lukas@xxxxxxxxx> wrote:
> On Sat, May 06, 2017 at 08:46:07AM +0100, Ard Biesheuvel wrote:
>> On 5 May 2017 at 19:38, Lukas Wunner <lukas@xxxxxxxxx> wrote:
>> > The CPER parser assumes that the class code is big endian, but at least
>> > on this edk2-derived Intel Purley platform it's little endian:
> [snip]
>> > --- a/include/linux/cper.h
>> > +++ b/include/linux/cper.h
>> > @@ -416,7 +416,7 @@ struct cper_sec_pcie {
>> >         struct {
>> >                 __u16   vendor_id;
>> >                 __u16   device_id;
>> > -               __u8    class_code[3];
>> > +               __u32   class_code:24;
>>
>> I'd like to avoid this change if we can. Couldn't we simply invert the
>> order of p[] above?
>
> Hm, why would you like to avoid it?

Because we shouldn't use bitfields in structs in code that should be
portable across archs with different endiannesses.

>  The class_code element isn't
> referenced anywhere else in the kernel and this isn't a uapi header,
> so the change would only impact out-of-tree drivers.  Not sure if
> any exist which might be interested in CPER parsing.
>

The point is that the change in the struct definition is simply not
necessary, given that inverting the order of p[] already achieves
exactly what we want.
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