Re: [PATCH] selftests: kvm: remove reassignment of non-absolute variables

[Bill Wendling <morbo@google.com>]

On Thu, Dec 10, 2020 at 5:07 PM Sean Christopherson <seanjc@google.com> wrote:
> On Thu, Dec 10, 2020, Bill Wendling wrote:
> > On Thu, Dec 10, 2020 at 4:50 PM Sean Christopherson <seanjc@google.com> wrote:
> > > On Wed, Dec 09, 2020, Bill Wendling wrote:
> > > > Clang's integrated assembler does not allow symbols with non-absolute
> > > > values to be reassigned. Modify the interrupt entry loop macro to be
> > > > compatible with IAS by using a label and an offset.
> > > >
> > > > Cc: Jian Cai <caij2003@gmail.com>
> > > > Signed-off-by: Bill Wendling <morbo@google.com>
> > > > References: https://lore.kernel.org/lkml/20200714233024.1789985-1-caij2003@gmail.com/
> > > > ---
> > > >  tools/testing/selftests/kvm/lib/x86_64/handlers.S | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/tools/testing/selftests/kvm/lib/x86_64/handlers.S b/tools/testing/selftests/kvm/lib/x86_64/handlers.S
> > > > index aaf7bc7d2ce1..3f9181e9a0a7 100644
> > > > --- a/tools/testing/selftests/kvm/lib/x86_64/handlers.S
> > > > +++ b/tools/testing/selftests/kvm/lib/x86_64/handlers.S
> > > > @@ -54,9 +54,9 @@ idt_handlers:
> > > >       .align 8
> > > >
> > > >       /* Fetch current address and append it to idt_handlers. */
> > > > -     current_handler = .
> > > > +0 :
> > > >  .pushsection .rodata
> > > > -.quad current_handler
> > > > +     .quad 0b
> > >
> > > Bit of a silly nit: can we use a named label, or at least a non-zero shorthand?
> > > It's really easy to misread "0b" as zeroing out the value, at least for me.
> > >
> > I don't believe that will work. If I rename "0 :" to something more
> > concrete, like ".Lcurrent :", then the label's redefined because of
> > the ".rept". If I assign the "0b" to something, we're back with the
> > unmodified code, which clang issues an error for:
> >
> > <instantiation>:3500:6: error: invalid reassignment of non-absolute variable 'x'
> >  x = 0b
> >      ^
> > <instantiation>:2:2: note: while in macro instantiation
> >  .rept 255 - 18 + 1
>
> Boo.  I assume 1: and 1b work?  Or my KVM favorite "666:" :-)  That's enough to
> at least make me pause and actually read the code.
>
Ah! I missed the second part of your message (about the non-zero
shorthand). That should work. Sorry about that. :-) Should I submit a
new version of this patch?

-bw