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Re: [PATCH, v2] 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: Tue, 7 Aug 2012 06:44:21 -0700
- Subject: Re: [PATCH, v2] x86-64: correct segment override prefix generation
- References: <500EDB2202000078000903AF@nat28.tlf.novell.com> <CAMe9rOr2HedB_bmSAX+ji23N2tBzYDPaV12XFWJxF=TaekPiwA@mail.gmail.com> <50210AD602000078000932B3@nat28.tlf.novell.com>
On Tue, Aug 7, 2012 at 3:32 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>> On 30.07.12 at 19:03, "H.J. Lu" <hjl.tools@gmail.com> wrote:
>> Please provide a testcase to show the correct behavior.
>
> Here you go.
>
> Jan
>
> 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).
>
> gas/
> 2012-08-07 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.
>
> gas/testsuite/
> 2012-08-07 Jan Beulich <jbeulich@suse.com>
>
> * gas/i386/x86-64-segovr.{s,l}: New.
> * gas/i386/i386.exp: Run new test.
>
> --- 2012-08-07/gas/config/tc-i386.c 2012-07-31 09:45:03.000000000 +0200
> +++ 2012-08-07/gas/config/tc-i386.c 2012-08-07 12:13:39.000000000 +0200
> @@ -5729,18 +5729,14 @@ 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)
Please use EBP_REG_NUM instead 5 here.
> {
> - 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)
> --- 2012-08-07/gas/testsuite/gas/i386/i386.exp 2012-07-24 14:52:59.000000000 +0200
> +++ 2012-08-07/gas/testsuite/gas/i386/i386.exp 2012-08-07 12:13:39.000000000 +0200
> @@ -311,6 +311,7 @@ if [expr ([istarget "i*86-*-*"] || [ista
> run_dump_test "x86-64-stack-suffix"
> run_list_test "x86-64-inval" "-al"
> run_list_test "x86-64-segment" "-al"
> + run_dump_test "x86-64-segovr"
> run_list_test "x86-64-inval-seg" "-al"
> run_dump_test "x86-64-branch"
> run_dump_test "x86-64-relax-1"
> --- 2012-08-07/gas/testsuite/gas/i386/x86-64-segovr.d 1970-01-01 01:00:00.000000000 +0100
> +++ 2012-08-07/gas/testsuite/gas/i386/x86-64-segovr.d 2012-08-03 14:06:44.000000000 +0200
> @@ -0,0 +1,41 @@
> +#objdump: -dw
> +#name: x86-64 segment overrides
> +
> +.*: +file format .*
> +
> +Disassembly of section .text:
> +
> +0+ <segovr>:
> +[ ]*[a-f0-9]+: 8b 00[ ]+mov[ ]+\(%rax\),%eax
> +[ ]*[a-f0-9]+: 8b 01[ ]+mov[ ]+\(%rcx\),%eax
> +[ ]*[a-f0-9]+: 8b 02[ ]+mov[ ]+\(%rdx\),%eax
> +[ ]*[a-f0-9]+: 8b 03[ ]+mov[ ]+\(%rbx\),%eax
> +[ ]*[a-f0-9]+: 3e 8b 04 24[ ]+mov[ ]+%ds:\(%rsp\),%eax
> +[ ]*[a-f0-9]+: 3e 8b 45 00[ ]+mov[ ]+%ds:((0x)?0)?\(%rbp\),%eax
> +[ ]*[a-f0-9]+: 8b 06[ ]+mov[ ]+\(%rsi\),%eax
> +[ ]*[a-f0-9]+: 8b 07[ ]+mov[ ]+\(%rdi\),%eax
> +[ ]*[a-f0-9]+: 41 8b 00[ ]+mov[ ]+\(%r8\),%eax
> +[ ]*[a-f0-9]+: 41 8b 01[ ]+mov[ ]+\(%r9\),%eax
> +[ ]*[a-f0-9]+: 41 8b 02[ ]+mov[ ]+\(%r10\),%eax
> +[ ]*[a-f0-9]+: 41 8b 03[ ]+mov[ ]+\(%r11\),%eax
> +[ ]*[a-f0-9]+: 41 8b 04 24[ ]+mov[ ]+\(%r12\),%eax
> +[ ]*[a-f0-9]+: 41 8b 45 00[ ]+mov[ ]+((0x)?0)?\(%r13\),%eax
> +[ ]*[a-f0-9]+: 41 8b 06[ ]+mov[ ]+\(%r14\),%eax
> +[ ]*[a-f0-9]+: 41 8b 07[ ]+mov[ ]+\(%r15\),%eax
> +[ ]*[a-f0-9]+: 36 8b 00[ ]+mov[ ]+%ss:\(%rax\),%eax
> +[ ]*[a-f0-9]+: 36 8b 01[ ]+mov[ ]+%ss:\(%rcx\),%eax
> +[ ]*[a-f0-9]+: 36 8b 02[ ]+mov[ ]+%ss:\(%rdx\),%eax
> +[ ]*[a-f0-9]+: 36 8b 03[ ]+mov[ ]+%ss:\(%rbx\),%eax
> +[ ]*[a-f0-9]+: 8b 04 24[ ]+mov[ ]+\(%rsp\),%eax
> +[ ]*[a-f0-9]+: 8b 45 00[ ]+mov[ ]+((0x)?0)?\(%rbp\),%eax
> +[ ]*[a-f0-9]+: 36 8b 06[ ]+mov[ ]+%ss:\(%rsi\),%eax
> +[ ]*[a-f0-9]+: 36 8b 07[ ]+mov[ ]+%ss:\(%rdi\),%eax
> +[ ]*[a-f0-9]+: 36 41 8b 00[ ]+mov[ ]+%ss:\(%r8\),%eax
> +[ ]*[a-f0-9]+: 36 41 8b 01[ ]+mov[ ]+%ss:\(%r9\),%eax
> +[ ]*[a-f0-9]+: 36 41 8b 02[ ]+mov[ ]+%ss:\(%r10\),%eax
> +[ ]*[a-f0-9]+: 36 41 8b 03[ ]+mov[ ]+%ss:\(%r11\),%eax
> +[ ]*[a-f0-9]+: 36 41 8b 04 24[ ]+mov[ ]+%ss:\(%r12\),%eax
> +[ ]*[a-f0-9]+: 36 41 8b 45 00[ ]+mov[ ]+%ss:((0x)?0)?\(%r13\),%eax
> +[ ]*[a-f0-9]+: 36 41 8b 06[ ]+mov[ ]+%ss:\(%r14\),%eax
> +[ ]*[a-f0-9]+: 36 41 8b 07[ ]+mov[ ]+%ss:\(%r15\),%eax
> +#pass
> --- 2012-08-07/gas/testsuite/gas/i386/x86-64-segovr.s 1970-01-01 01:00:00.000000000 +0100
> +++ 2012-08-07/gas/testsuite/gas/i386/x86-64-segovr.s 2012-08-03 13:54:08.000000000 +0200
> @@ -0,0 +1,9 @@
> +# 64bit segment overrides
> +
> + .text
> +segovr:
> +.irp seg, ds, ss
> + .irp reg, ax, cx, dx, bx, sp, bp, si, di, 8, 9, 10, 11, 12, 13, 14, 15
> + mov %\seg:(%r\reg), %eax
> + .endr
> +.endr
>
>
OK with the EBP_REG_NUM change above if Linux x86-64 kernel
compiles and runs.
Thanks.
--
H.J.