Re: [PATCH v2] docs/misra: document the expected sizes of integer types

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

I haven't fully read the thread. But I wanted to clarify something.

On 21/03/2024 19:03, Stefano Stabellini wrote:
> > > Or possibly unsigned long depending on the parameter.
> > You're contradicting yourself: You mean to advocate for fixed-width types,
> > yet then you suggest "unsigned long".
> No. I explained it in another thread a couple of days ago. There are
> cases where we have fixed-width types but the type changes by
> architecture: 32-bit for 32-bit archs and 64-bit for 64-bit archs.
> Rather than having #ifdefs, which is also an option, that is the one
> case where using "unsigned long" could be a decent compromise. In this
> context "unsigned long" means register size (on ARM we even have
> register_t). Once you pick an architecture, the size is actually meant
> to be fixed. In fact, it is specified in this document. Which is one of
> the reasons why we have to use == in this document and not >=. In
> general, fixed-width types like uint32_t are better because they are
> clearer and unambiguous. When possible I think they should be our first
> choice in ABIs.
"unsigned long" is not fixed in a given architecture. It will change 
base on the data model used by the OS. For instance, for Arm 64-bit, we 
have 3 models: ILP32, LP64, LLP64. Only on LP64, 'unsigned long' is 32-bit.
So effectively unsigned long can't be used in the ABI.

As a side note, Xen will use LP64, hence why we tend to use 'unsigned 
long' to describe 32-bit for Arm32 and 64-bit for Arm64.
Cheers,

--
Julien Grall