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[Bug gas/26685] Error: invalid register operand size for `movdir64b'

From: hjl.tools at gmail dot com
Subject: [Bug gas/26685] Error: invalid register operand size for `movdir64b'
Date: Thu, 01 Oct 2020 11:44:06 +0000


--- Comment #6 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Jan Beulich from comment #5)
> (In reply to H.J. Lu from comment #4)
> > This specific case came from
> > 
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97257
> > 
> > The address prefix changes the register operand in these instructions.
> > (%rip) is a special case.
> Which address prefix? There's not enough data in that bug for me to
> understand. But in any event, it's gcc producing wrong code then, and hence
> the issue should be fixed there, rather than silently "correcting" ambiguous
> code in gas.

In these instructions, the 0x67 prefix applies to the address prefix.
The address prefix should be extracted from the register operand, similar

     if (i.tm.operand_types[0].bitfield.instance == Accum
          || i.operands == 1)
          /* The address size override prefix changes the size of the
             first operand.  */
          if (flag_code == CODE_64BIT
              && i.op[0].regs->reg_type.bitfield.word)
              as_bad (_("16-bit addressing unavailable for `%s'"),
              return 0;

          if ((flag_code == CODE_32BIT
               ? i.op[0].regs->reg_type.bitfield.word
               : i.op[0].regs->reg_type.bitfield.dword)
              && !add_prefix (ADDR_PREFIX_OPCODE))
            return 0;

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