Re: [RFC/RFT PATCH 10/19] x86/kvm: Use RIP-relative addressing

Ard Biesheuvel
2026-01-20T20:54:42Z

On Tue, 20 Jan 2026 at 20:44, David Laight <david.laight.linux@gmail.com> wrote:
>
> On Tue, 20 Jan 2026 09:04:26 -0800
> Sean Christopherson <seanjc@google.com> wrote:
>
> > On Thu, Jan 08, 2026, Ard Biesheuvel wrote:
> > > Replace absolute references in inline asm with RIP-relative ones, to
> > > avoid the need for relocation fixups at boot time. This is a
> > > prerequisite for PIE linking, which only permits 64-bit wide
> > > loader-visible absolute references.
> > >
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > ---
> > > arch/x86/kernel/kvm.c | 5 +++--
> > > 1 file changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > > index df78ddee0abb..1a0335f328e1 100644
> > > --- a/arch/x86/kernel/kvm.c
> > > +++ b/arch/x86/kernel/kvm.c
> > > @@ -807,8 +807,9 @@ extern bool __raw_callee_save___kvm_vcpu_is_preempted(long);
> > > * restoring to/from the stack.
> > > */
> > > #define PV_VCPU_PREEMPTED_ASM \
> > > - "movq __per_cpu_offset(,%rdi,8), %rax\n\t" \
> > > - "cmpb $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax)\n\t" \
> > > + "0:leaq 0b(%rip), %rax\n\t" \
> >
> > Please use something other than '0' for the label, it took me forever (and looking
> > at disassembly) to realize "0b" was just a backwards label and not some fancy
> > syntax I didn't know.
>
> I remember taking a while to grok that as well.
>
> Can't you just use . as in:
> leaq .(%rip), %rax
>

How would the other two instructions referring to '0b' in their
immediates refer to '.' in that case?