Re: [RFC/RFT PATCH 11/19] x86/rethook: Use RIP-relative reference for fake return address

Ard Biesheuvel
2026-01-08T12:10:19Z

On Thu, 8 Jan 2026 at 13:08, David Laight <david.laight.linux@gmail.com> wrote:
>
> On Thu, 8 Jan 2026 09:25:38 +0000
> Ard Biesheuvel <ardb@kernel.org> wrote:
>
> > Pushing an immediate absolute address to the stack is not permitted when
> > linking x86_64 code in PIE mode. Usually, the address can be taken using
> > a RIP-relative LEA instruction, but this is not possible here as there
> > are no available registers.
> >
> > So instead, take the address into a static global, and push it onto the
> > stack using a RIP-relative memory operand.
>
> The comment implies the address is 'fake'.
> Does that mean it could just be a constant?

It could be, but it isn't, across all architectures.

> Clearly the unwinder would need the same change.
>

Why? The value being pushed is the same.