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Date: Tue, 17 May 2022 08:44:06 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: David Laight <David.Laight@aculab.com>,
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Subject: Re: [RFC PATCH v2 20/21] x86: Add support for CONFIG_CFI_CLANG
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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?