Messages in this thread | | | From | Sami Tolvanen <> | Date | Tue, 17 May 2022 13:36:14 -0700 | Subject | Re: [RFC PATCH v2 20/21] x86: Add support for CONFIG_CFI_CLANG |
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On Mon, May 16, 2022 at 11:44 PM Peter Zijlstra <peterz@infradead.org> wrote: > > 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?
No, this won't change register allocation, but I will have to ensure that the compiler won't do any unnecessary register shuffling for the check itself.
Sami
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