[llvm-bugs] [Bug 32805] New: nopl %ebx is not recognized as valid assembly

via llvm-bugs llvm-bugs at lists.llvm.org
Wed Apr 26 08:27:02 PDT 2017


            Bug ID: 32805
           Summary: nopl %ebx is not recognized as valid assembly
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: Pidgeot18 at gmail.com
                CC: llvm-bugs at lists.llvm.org

$ echo "nopl %ebx" | llvm-mc
<stdin>:1:6: error: invalid operand for instruction
nopl %ebx

$ echo "nopl %ebx" | as && objdump -d a.out

a.out:     file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <.text>:
   0:   0f 1f c3                nop    %ebx

Although the manual recommends that the multi-byte sequences use only the
memory forms, I don't see much of a reason to ignore the register forms for the
Mod/RM byte.

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