[Xen-devel] struct vcpu_guest_core_reg stable ABI?

[Julien Grall <julien.grall@xxxxxxx>]

Hi all,

It looks like the structures vcpu_guest_core_regs and vcpu_guest_context 
does not correctly reflect the AArch64 state. For instance, all Arm64 
system registers (e.g sctlr, cpsr, spsr_el1) should be 64-bit wide not 
32-bit wide.
On ARMv8.0, some of the registers have only the low 32-bit defined, the 
rest is RES0. RES0 only means they are reserved for future use, it does 
not mean they can be ignored. Newer revision (such as ARMv8.0-SSBS) 
actually began to define bit in the top 32-bit.
This means that the structures vcpu_guest_core_regs and 
vcpu_guest_context would not be able to store the top 32-bit and 
therefore misrepresenting the hardware.
From my understanding, vcpu_guest_context is defined between the tools 
and Xen. So it would be possible to modify it without caring on backward 
compatibly.
Howerver, struct vcpu_guest_core_reg seems to be outside of the #ifdef. 
So I assume it is part of the stable ABI. Am I correct?
Do you have any suggestion how this could safely be extended?

Cheers,

--
Julien Grall

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