Re: [RFC PATCH v2 20/21] x86: Add support for CONFIG_CFI_CLANG

Peter Zijlstra
2022-05-17T06:44:19Z

On Mon, May 16, 2022 at 03:03:02PM -0700, Sami Tolvanen wrote:
> On Mon, May 16, 2022 at 2:44 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Mon, May 16, 2022 at 09:32:55PM +0000, David Laight wrote:
> >
> > > > The compiler always generates this specific instruction sequence.
> > >
> > > Yes, but there are several ways to encode 'cmpl imm,-6(reg)'.
> >
> > Yes, but we don't care. This *always* uses the 32bit immediate form.
> > Even if the immediate is small.
>
> Yes, that part is not a problem, but it's a valid point that LLVM
> might not always use r8-r15 here, so I will have to check for the REX
> prefix before blindly attempting to decode the instruction.

LLVM has always used r11 for indirect calls, will that change?