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

David Laight
2026-01-20T19:44:01Z

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

shame the assembler doesn't understand:
movq %rip, %rax
(maybe it does...)

David