[LLVMbugs] [Bug 10724] New: [x86 disassembler] vcvtsd2si disassembled incorrectly

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Aug 23 14:12:44 PDT 2011


           Summary: [x86 disassembler] vcvtsd2si 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

>From the "Intel® 64 and IA-32 Architectures Software Developer’s Manual
Volume 2 (2A & 2B): Instruction Set Reference, A-Z", p. 3-264:

VEX.LIG.F2.0F.W0 2D /r
VCVTSD2SI r32, xmm1/m64

VEX.LIG.F2.0F.W1 2D /r
VCVTSD2SI r64, xmm1/m64

'VCVTSD2SI' can be specified with either the 2- or 3-byte VEX prefix (clang on
correctly assembles the following):

vcvtsd2si %xmm0, %eax
vcvtsd2si %xmm0, %rax

The object file shows:
C5 FB 2D C0 
C4 E1 FB 2D C0 

But using llvm-mc built from trunk r138250 produces the wrong output
for these byte sequences:

$ echo '0xc5 0xfb 0x2d 0xc0'| ./llvm-mc -disassemble -triple="x86_64"
        cvtsd2si        EAX, XMM0

$ echo '0xc5 0xff 0x2d 0xc0'| ./llvm-mc -disassemble -triple="x86_64"
        cvtsd2si        EAX, XMM0

$ echo '0xc4 0xe1 0xf7 0x2d 0xc0'| ./llvm-mc -disassemble -triple="x86_64"
        cvtsd2si        RAX, XMM0

The mnemonic is missing the leading 'v' in all of these cases. The mnemonic is
correct for the 3-byte VEX prefix with the 'L' bit set:

$ echo '0xc4 0xe1 0xfb 0x2d 0xc0'| ./llvm-mc -disassemble -triple="x86_64"
        vcvtsd2si       RAX, XMM0

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