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Re: [PATCH 3/9] x86: correct MPX insn w/o base or index encoding in 16-bit mode
On Wed, Mar 4, 2020 at 3:50 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 04.03.2020 12:45, H.J. Lu wrote:
> > On Wed, Mar 4, 2020 at 1:38 AM Jan Beulich <jbeulich@suse.com> wrote:
> >> --- a/gas/config/tc-i386.c
> >> +++ b/gas/config/tc-i386.c
> >> @@ -10297,6 +10297,21 @@ i386_addressing_mode (void)
> >>
> >> if (i.prefix[ADDR_PREFIX])
> >> addr_mode = flag_code == CODE_32BIT ? CODE_16BIT : CODE_32BIT;
> >> + else if (flag_code == CODE_16BIT
> >> + && current_templates->start->cpu_flags.bitfield.cpumpx
> >> + /* Avoid replacing the "16-bit addressing not allowed" diagnostic
> >> + from md_assemble() by "is not a valid base/index expression"
> >> + when there is a base and/or index. */
> >> + && !i.types[this_operand].bitfield.baseindex)
> >> + {
> >> + /* MPX insn memory operands with neither base nor index must be forced
> >> + to use 32-bit addressing in 16-bit mode. */
> >> + addr_mode = CODE_32BIT;
> >> + i.prefix[ADDR_PREFIX] = ADDR_PREFIX_OPCODE;
> >> + ++i.prefixes;
> >> + gas_assert (!i.types[this_operand].bitfield.disp16);
> >> + gas_assert (!i.types[this_operand].bitfield.disp32);
> >> + }
> >> else
> >> {
> >
> > Since MPX isn't available in 16-bit mode, should they be disallowed?
>
> How is it not available? As per my understanding, one just needs
> to use 32-bit addressing.
0x67 prefix is special for MPX. It can't be used as address prefix on MPX
instructions.
> > Given that MPX has been deprecated, I prefer an error here.
>
> The use of "here" is confusing - just for the broken case (no
> base/index), or for MPX insns in general? (Asking just in case
> my understanding expressed above is wrong.)
flag_code == CODE_16BIT && current_templates->start->cpu_flags.bitfield.cpumpx
should be an error.
--
H.J.