Re: [RFC PATCH] x86/sev: x86/sev: enforce PC-relative addressing in clang

[Kevin Loughlin]

On Wed, Jan 10, 2024 at 5:37 AM Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
>
> Similar issues was fixed before with fixup_pointer() tricks. Have you
> tried looking this direction.
>
> Relevant thread starting with:
>
> https://lore.kernel.org/all/20210920192341.maue7db4lcbdn46x@xxxxxxxxxxxxxxxxx

Yes, I considered using `fixup_pointer()` as well, and I agree that it
remains a valid option to solve this problem. I just now mentioned the
primary downside to using `fixup_pointer()` in my response to Andi
(https://lore.kernel.org/lkml/CAGdbjmJcQeLWroBkbRC-cFQ6OuMHONsGLzpUrrA5k3uc8Rzkmw@xxxxxxxxxxxxxx/).
Namely, we would have to pass around `physaddr` from `__startup64()`
to any functions wanting to use `fixup_pointer()`). However, we should
be able to get around needing `physaddr` by using something like the
`GET_RIP_RELATIVE_PTR()` macro that I proposed in the same reply
(forthcoming in v2 of this RFC PATCH).