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Re: [PATCH] x86-64: correct segment override prefix generation
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Jan Beulich <JBeulich at suse dot com>
- Cc: binutils at sourceware dot org
- Date: Mon, 30 Jul 2012 10:03:44 -0700
- Subject: Re: [PATCH] x86-64: correct segment override prefix generation
- References: <500EDB2202000078000903AF@nat28.tlf.novell.com>
On Tue, Jul 24, 2012 at 8:28 AM, Jan Beulich <JBeulich@suse.com> wrote:
> Despite them being ignored by the CPU, gas issues segment override
> prefixes for other than FS/GS in 64-bit mode. If doing so at all, it
> should clearly do this correctly. Determining the default segment,
> however, requires to take into consideration RegRex (so far, RSP, RBP,
> R12, and R13 were all treated equally here).
>
> 2012-07-24 Jan Beulich <jbeulich@suse.com>
>
> * config/tc-i386-intel.c (build_modrm_byte): Split determining
> default segment from figuring out encoding. Honor RegRex for
> the former.
>
> --- a/gas/config/tc-i386.c
> +++ b/gas/config/tc-i386.c
> @@ -5733,18 +5733,14 @@ build_modrm_byte (void)
> i.sib.base = i.base_reg->reg_num;
> /* x86-64 ignores REX prefix bit here to avoid decoder
> complications. */
> - if ((i.base_reg->reg_num & 7) == EBP_REG_NUM)
> - {
> + if (!(i.base_reg->reg_flags & RegRex)
> + && (i.base_reg->reg_num == EBP_REG_NUM
> + || i.base_reg->reg_num == ESP_REG_NUM))
> default_seg = &ss;
> - if (i.disp_operands == 0)
> - {
> - fake_zero_displacement = 1;
> - i.types[op].bitfield.disp8 = 1;
> - }
> - }
> - else if (i.base_reg->reg_num == ESP_REG_NUM)
> + if (i.base_reg->reg_num == 5 && i.disp_operands == 0)
> {
> - default_seg = &ss;
> + fake_zero_displacement = 1;
> + i.types[op].bitfield.disp8 = 1;
> }
> i.sib.scale = i.log2_scale_factor;
> if (i.index_reg == 0)
>
Please provide a testcase to show the correct behavior.
Thanks.
--
H.J.