[LLVMbugs] [Bug 10097] New: MCDisassembler is unable to decode XOR r32, r/m32

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Jun 7 13:20:19 PDT 2011


           Summary: MCDisassembler is unable to decode XOR r32,r/m32
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: karl.vogel at gmail.com
                CC: llvmbugs at cs.uiuc.edu

The MCDisassembler is unable to decode the XOR r32,r/m32 variant. It only knows
the XOR r/m32,r32 variant.

$ echo "0x31 0xc0"|./bin/llvm-mc --disassemble
    xorl    %eax, %eax
$ echo "0x33 0xc0"|./bin/llvm-mc --disassemble
<stdin>:1:1: warning: invalid instruction encoding
0x33 0xc0

both are valid opcode sequences. (cfr. Intel(R) 64 and IA-32 Architectures
Software Developer's Manual, Volume 2 (2A & 2B) - Vol 2B p4-515).

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