[PATCH 4/5] x86-64: special case LEA when determining signedness of displacement

[H.J. Lu]

On Thu, Apr 22, 2021 at 1:40 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> LEA behavior without a 64-bit destination is independent of address size
> - in particular LEA with 32-bit addressing and 64-bit destination is the
> same as LEA with 64-bit addressing and 32-bit destination. IOW checking
> merely i.prefix[ADDR_PREFIX] is insufficient. This also means wrong
> relocation types (R_X86_64_32S when R_X86_64_32 is needed) were used so
> far in such cases.

Do you have a testcase for the wrong relocation type?

> Note that in one case in build_modrm_byte() the 64-bit check came too
> early altogether, and hence gets dropped in favor of the one included in
> the new helper. This is benign to non-64-bit code from all I can tell,
> but the failure to clear disp16 could have been a latent problem.
>
> gas/
> 2021-04-XX  Jan Beulich  <jbeulich@suse.com>
>
>         * config/tc-i386.c (want_disp32): New.
>         (md_assemble): Use it.
>         (optimize_disp): Likewise.
>         (build_modrm_byte): Likewise.
>
> --- a/gas/config/tc-i386.c
> +++ b/gas/config/tc-i386.c
> @@ -3555,6 +3555,16 @@ tc_i386_fix_adjustable (fixS *fixP ATTRI
>    return 1;
>  }
>
> +static INLINE bool
> +want_disp32 (const insn_template *t)
> +{
> +  return flag_code != CODE_64BIT
> +        || i.prefix[ADDR_PREFIX]
> +        || (t->base_opcode == 0x8d
> +            && t->opcode_modifier.opcodespace == SPACE_BASE
> +            && !i.types[1].bitfield.qword);
> +}
> +
>  static int
>  intel_float_operand (const char *mnemonic)
>  {
> @@ -4740,7 +4750,7 @@ md_assemble (char *line)
>    if (i.imm_operands)
>      optimize_imm ();
>
> -  if (i.disp_operands && flag_code == CODE_64BIT && !i.prefix[ADDR_PREFIX])
> +  if (i.disp_operands && !want_disp32 (current_templates->start))
>      {
>        for (j = 0; j < i.operands; ++j)
>         {
> @@ -5748,7 +5758,7 @@ optimize_disp (void)
>  #ifdef BFD64
>             else if (flag_code == CODE_64BIT)
>               {
> -               if (i.prefix[ADDR_PREFIX]
> +               if (want_disp32 (current_templates->start)
>                     && fits_in_unsigned_long (op_disp))
>                   i.types[op].bitfield.disp32 = 1;
>
> @@ -8108,7 +8118,7 @@ build_modrm_byte (void)
>                   i.types[op].bitfield.disp8 = 0;
>                   i.types[op].bitfield.disp16 = 0;
>                   i.types[op].bitfield.disp64 = 0;
> -                 if (flag_code != CODE_64BIT || i.prefix[ADDR_PREFIX])
> +                 if (want_disp32 (&i.tm))
>                     {
>                       /* Must be 32 bit */
>                       i.types[op].bitfield.disp32 = 1;
> @@ -8159,7 +8169,7 @@ build_modrm_byte (void)
>                       i.rm.regmem = ESCAPE_TO_TWO_BYTE_ADDRESSING;
>                       i.sib.base = NO_BASE_REGISTER;
>                       i.sib.index = NO_INDEX_REGISTER;
> -                     newdisp = (!i.prefix[ADDR_PREFIX] ? disp32s : disp32);
> +                     newdisp = (want_disp32(&i.tm) ? disp32 : disp32s);
>                     }
>                   else if ((flag_code == CODE_16BIT)
>                            ^ (i.prefix[ADDR_PREFIX] != 0))
> @@ -8188,7 +8198,7 @@ build_modrm_byte (void)
>                   i.types[op].bitfield.disp8 = 0;
>                   i.types[op].bitfield.disp16 = 0;
>                   i.types[op].bitfield.disp64 = 0;
> -                 if (flag_code != CODE_64BIT || i.prefix[ADDR_PREFIX])
> +                 if (want_disp32 (&i.tm))
>                     {
>                       /* Must be 32 bit */
>                       i.types[op].bitfield.disp32 = 1;
> @@ -8263,12 +8273,11 @@ build_modrm_byte (void)
>             }
>           else /* i.base_reg and 32/64 bit mode  */
>             {
> -             if (flag_code == CODE_64BIT
> -                 && operand_type_check (i.types[op], disp))
> +             if (operand_type_check (i.types[op], disp))
>                 {
>                   i.types[op].bitfield.disp16 = 0;
>                   i.types[op].bitfield.disp64 = 0;
> -                 if (i.prefix[ADDR_PREFIX] == 0)
> +                 if (!want_disp32 (&i.tm))
>                     {
>                       i.types[op].bitfield.disp32 = 0;
>                       i.types[op].bitfield.disp32s = 1;
>


-- 
H.J.