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Re: [PATCH v2 13/13] SUPPORT.md: write down restriction of 32-bit tool stacks

Hi Jan,

On 15/07/2021 07:38, Jan Beulich wrote:
On 14.07.2021 20:16, Julien Grall wrote:
On 05/07/2021 16:18, Jan Beulich wrote:
Let's try to avoid giving the impression that 32-bit tool stacks are as
capable as 64-bit ones.

Would you be able to provide a few examples of the known issues in the
commit message? This would be helpful for anyone to understand why we
decided to drop the support.

Not sure how useful this is going to be.

It would at least be useful to me, so I can make an informed decision. I suspect it would also be for anyone reading it in the future. This is rather frustrating to find commit message with barely any rationale and no-one remembering why this was done...

I vaguely recall a discussion about 64-bit hypercall ([1]). I assume the decision to drop support is related to it, but I have no way to prove it from the commit message.

It is also not clear why adding the restriction is the way to go...

This would be pointing at the
declarations / definitions of various tool stack internal variables or
structure fields. Which also is why ...

... is this because such issues are too widespread in libxc/libxl to fix it in long term?

At least on Arm, we tried to design the hypercall ABI in such a way that
it should be possible to use a 32-bit toolstack.

... keeping the ABI tidy in this regard didn't help at all (albeit it
of course was a prereq to writing a tool stack that would be capable).


[1] https://lore.kernel.org/xen-devel/71b8a4f1-9c18-36e7-56b1-3f1b1dabddd6@xxxxxxxx/

Julien Grall



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