Re: [PATCH] xen/arm: Remove most of the *_VIRT_END defines

[Julien Grall <julien@xxxxxxx>]

Hi Wei,

On 24/05/2022 09:16, Wei Chen wrote:
> > > It seems you prefer to point _end to the address after the end. Even
> > > though we got rid of the macro definition of _END. But we didn't agree
> > > on how to use it. For me, when I first saw
> > > "end = start + LIVEPATCH_VMAP_SIZE" I subconsciously think the -1 is
> > > missing here. I even added a comment, but removed it when I reached
> > > to this line : )
> > > May be it's better to place some code guide for END in code comment
> > > in the SIZE definition, otherwise, we may have different point addresses
> > > of _end functions.
> > I think it is quite common to have size being the actual size and not size
> > -1.
> > END is clearly the last address of the area but SIZE should be the number
> > of bytes in the area so I think Julien here is right.
> Maybe I didn't describe it clearly : )
> I agree with the SIZE that Julien has done. My concern is that, should we
> need a guide line for how to use the SIZE to calculate END
It is not possible to have a guideline at the moment because we are not 
consistent how "END" is defined in Xen.
This is also why I want to get rid of "END" completely. It is more 
difficult (to not say impossible) to interpret (start, size) differently.
As I wrote in the commit message, I haven't yet addressed the common 
part (there work is a lot more consequent). But I wanted at least to 
start to get rid of some and push the use of "end" as far as possible.
> For example, in this patch, Julien is using END=START+SIZE, then END is
> pointing to the address after the end. But for me, I intend to use
> END=START+SIZE-1, because I want the END point to the last address.
Same here.

> Over time, when there are a lot of get_xxx_end functions in the code,
> their actual meanings will be different, just as confusing as the previous
> macro definitions
My plan is to get rid of get_XXX_end completely and instead return 
start, size.
This is only the first part of the work. I need this one start 
reshuffling the memory layout because I want to be able to use (start, 
size) consistently in the layout.
Cheers,

--
Julien Grall