Messages in this thread | | | From | Andy Lutomirski <> | Date | Fri, 23 Dec 2016 17:57:12 -0800 | Subject | Re: [v2 1/7] x86/mpx: Do not use SIB index if index points to R/ESP |
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On Fri, Dec 23, 2016 at 5:37 PM, Ricardo Neri <ricardo.neri-calderon@linux.intel.com> wrote: > Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software > Developer's Manual volume 2A states that when memory addressing is used > (i.e., mod part of ModR/M is not 3), a SIB byte is used and the index of > the SIB byte points to the R/ESP (i.e.,index = 4), the index should not be > used in the computation of the memory address. > > An example of such instruction could be > > insn -0x80(%rsp) > > This is represented as: > > [opcode] 4c 24 80 > > ModR/M: mod: 1, reg: 1: r/m: 4 (R/ESP) > SIB 24: sc: 0, index: 100 (R/ESP), base(R/ESP): 100 > Displacement -0x80 > > The correct address is (base) + displacement; no index is used. > > Care is taken to allow R12 to be used as index, which is a valid scenario.
Since I have no idea what this patch has to do with the rest of the series, I'll ask a question:
Why isn't this code in the standard x86 instruction decoder? Is the decoder similarly buggy?
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