Il 04/07/2013 13:06, Denys Vlasenko ha scritto: >>> >> - case 0x90 ... 0x97: /* nop / xchg reg, rax */ >>> >> - if (ctxt->dst.addr.reg == reg_rmw(ctxt, VCPU_REGS_RAX)) >>> >> - break; >>> >> + case 0x90: /* nop */ >>> >> + break; >> > This does not work on 64bit and REX prefix. > Can you elaborate? > > 0x90 is special-cased in CPU to be a NOP regardless of bit width. > IOW, xchg %eax,%eax ordinarily would clear upper 32 bits of %rax, > but 0x90 doesn't do that. > > Do you mean that with REX.R==1, 0x90 will refer to R8?
Yes. $ echo 'xchg %rax,%r8' | as $ objdump -d a.out a.out: file format elf64-x86-64 Disassembly of section .text: 0000000000000000 <.text>: 0: 49 90 xchg %rax,%r8 Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
