Re: [PATCH] x86emul: fix SYSENTER/SYSCALL switching into 64-bit mode

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 10/02/2021 14:18, Jan Beulich wrote:
> On 10.02.2021 15:02, Andrew Cooper wrote:
>> On 10/02/2021 13:54, Jan Beulich wrote:
>>> Just like considered in the post-description
>>> remark, we could drop the conditional part from sysexit's
>>> setting of _regs.r(ip), and _then_ we would indeed need a
>>> respective change there, for the truncation to happen at
>>> complete_insn:.
>> I think it would look odd changing just rip and not rsp truncation.
> Yes, this was another consideration of mine as well. But it
> is a fact that we treat rip and rsp differently in this
> regard. Perhaps generated code overall could benefit from
> treating rsp more like rip, but this would need careful
> looking at all the involved pieces - especially in cases
> where the updated stack pointer gets further used we may
> not be able to defer the truncation to complete_insn:.

There are other differences.  rip gets updated on every instruction,
while rsp does not.  We also have instructions with (possibly multiple)
rsp-relative memory references which need truncating individually to get
proper behaviour.

~Andrew