[Nasm-bugs] [Bug 3392681] New: movdir64b causes panic

noreply-nasm at dev.nasm.us noreply-nasm at dev.nasm.us
Sat Jun 20 18:45:36 PDT 2020


            Bug ID: 3392681
           Summary: movdir64b causes panic
           Product: NASM
           Version: 2.14.xx
          Hardware: PC
                OS: Linux
            Status: OPEN
          Severity: normal
          Priority: Medium
         Component: Assembler
          Assignee: nobody at nasm.us
          Reporter: philip.lantz at intel.com
                CC: chang.seok.bae at intel.com, gorcunov at gmail.com,
                    hpa at zytor.com, nasm-bugs at nasm.us
     Obtained from: Build from source archive using configure

Use of movdir64b instruction causes nasm to panic.

$ cat n.s
        bits    64
        movdir64b rax, [rdi]

$ nasm -f elf64 n.s
n.s:2: panic: assertion data.insoffs == insn_size failed at asm/assemble.c:754

$ nasm -version
NASM version 2.14.02 compiled on Jun 20 2020

Based on a little investigation, it seems that the calcsize function
incorrectly thinks that a REX prefix is required and calculates the size of the
instruction as 6 instead of 5.

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