On Tue, Apr 25, 2017 at 07:04:20PM -0700, Ricardo Neri wrote: > For the specific case of ModRM.mod being 0, I feel I need to clarify > that REX.B is not decoded and if SIB.base is %r13 the base is also 0.
Well, that all doesn't matter. The rule is this: ModRM.mod == 00b and ModRM.r/m == 101b -> effective address: disp32 See Table 2-2. "32-Bit Addressing Forms with the ModR/M Byte" in the SDM. So the base register is not used. How that base register is specified then doesn't matter (undecoded REX bits or not). > This comment adds clarity because REX.X is decoded when determining > SIB.index. Well, that's a different thing. The REX bits participating in the SIB fields don't matter about this particular case. We only want to say that we're returning a disp32 without a base register and the comment should keep it simple without extraneous information. I know, you want to mention what Table 2-5. "Special Cases of REX Encodings" says but we should avoid unnecessary content in the comment. People who want details can stare at the manuals - the comment should only document what that particular case is. Btw, you could write it even better: if (!X86_MODRM_MOD(insn->modrm.value) && X86_MODRM_RM(insn->modrm.value) == 5) and then it is basically a 1:1 copy of the rule from Table 2-2. -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) -- -- To unsubscribe from this list: send the line "unsubscribe linux-msdos" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html