[LLVMbugs] [Bug 10806] New: [x86 disassembler] vldmxcsr disassembled incorrectly

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon Aug 29 15:01:08 PDT 2011


           Summary: [x86 disassembler] vldmxcsr disassembled incorrectly
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: kkhoo at perfwizard.com
                CC: llvmbugs at cs.uiuc.edu

According to the "Intel® 64 and IA-32 Architectures Software Developer’s Manual
Volume 2 (2A & 2B): Instruction Set Reference, A-Z", p. 3-571:


"LZ" in the above spec is defined on p. 3-5:
If VEX.LZ is present in the opcode column: The VEX.L must be encoded to be 0B,
an #UD occurs if VEX.L is not zero.

$ echo '0xc5 0xf0 0xae 0x11'| ./llvm-mc -disassemble -triple="x86_64"
        ldmxcsr DWORD PTR [RCX]

$ echo '0xc4 0xc1 0x70 0xae 0x11'| ./llvm-mc -disassemble -triple="x86_64"
        ldmxcsr DWORD PTR [R9]

When the 'L' bit is not set, the disassembler (using trunk r138250) is showing
"ldmxcsr" instead of the expected "vldmxcsr".

With the 'L' bit set, the mnemonic shows the leading 'v', but this should be
undefined according to the Intel spec:
$ echo '0xc5 0xf4 0xae 0x11'| ./llvm-mc -disassemble -triple="x86_64"
        vldmxcsr        DWORD PTR [RCX]

$ echo '0xc4 0xc1 0x74 0xae 0x11'| ./llvm-mc -disassemble -triple="x86_64"
        vldmxcsr        DWORD PTR [R9]

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