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Re: [PATCH ARM/THUMB1] unified syntax MOV with both low register emitting unpredictable code
- From: Richard Earnshaw <rearnsha at arm dot com>
- To: Thomas Klein <th dot r dot klein at web dot de>
- Cc: Matthew Gretton-Dann <Matthew dot Gretton-Dann at arm dot com>, "binutils at sourceware dot org" <binutils at sourceware dot org>
- Date: Thu, 17 Nov 2011 09:57:05 +0000
- Subject: Re: [PATCH ARM/THUMB1] unified syntax MOV with both low register emitting unpredictable code
- References: <4EC17845.6090901@web.de> <4EC2819D.2060901@arm.com> <4EC2F185.1020709@web.de>
On 15/11/11 23:11, Thomas Klein wrote:
> On 11/15/11 15:13, Matthew Gretton-Dann wrote:
>> On 14/11/11 20:21, Thomas Klein wrote:
>>> + if (low_regs&& !ARM_CPU_HAS_FEATURE (selected_cpu,
>>> arm_ext_v6t2))
>>
>> This test is incorrect - you want to check for arm_ext_v6, as all v6
>> variants whether Thumb-1 or Thumb-2 allow low registers in this
>> instruction.
>>
>>> + {
>>
>> Some regression tests would be good here.
>
> Correction and tests attached.
> Is this OK.
>
This is incorrect. There is no pre-v6 Thumb1 'MOV lo, lo' instruction
in unified syntax and the assembler should fault it; it shouldn't try to
use a flag setting insn.
R.
> Regards
> Thomas
>
>
>
> diff.out
>
>
> Index: gas/config/tc-arm.c
> ===================================================================
> RCS file: /cvs/src/src/gas/config/tc-arm.c,v
> retrieving revision 1.504
> diff -u -p -r1.504 tc-arm.c
> --- gas/config/tc-arm.c 7 Nov 2011 16:20:47 -0000 1.504
> +++ gas/config/tc-arm.c 15 Nov 2011 22:11:53 -0000
> @@ -10913,10 +10913,24 @@ do_t_mov_cmp (void)
> switch (inst.instruction)
> {
> case T_MNEM_mov:
> - inst.instruction = T_OPCODE_MOV_HR;
> - inst.instruction |= (Rn & 0x8) << 4;
> - inst.instruction |= (Rn & 0x7);
> - inst.instruction |= Rm << 3;
> + if (low_regs && !ARM_CPU_HAS_FEATURE (selected_cpu, arm_ext_v6))
> + {
> + as_warn (_("MOV r%u,r%u is not permitted on this architecture "
> + "using ADDS r%u,r%u,#0 instead"),Rn,Rm,Rn,Rm);
> + /* In v4t or v5t a move of two lowregs produces
> + unpredictable results. Encode this the same way as in
> + non unified syntax.*/
> + inst.instruction = T_OPCODE_ADD_I3;
> + inst.instruction |= Rn;
> + inst.instruction |= Rm << 3;
> + }
> + else
> + {
> + inst.instruction = T_OPCODE_MOV_HR;
> + inst.instruction |= (Rn & 0x8) << 4;
> + inst.instruction |= (Rn & 0x7);
> + inst.instruction |= Rm << 3;
> + }
> break;
>
> case T_MNEM_movs:
> Index: gas/testsuite/gas/arm/thumb1_unified.d
> ===================================================================
> RCS file: /cvs/src/src/gas/testsuite/gas/arm/thumb1_unified.d,v
> retrieving revision 1.3
> diff -u -p -r1.3 thumb1_unified.d
> --- gas/testsuite/gas/arm/thumb1_unified.d 30 Jun 2009 11:57:05 -0000 1.3
> +++ gas/testsuite/gas/arm/thumb1_unified.d 15 Nov 2011 22:11:54 -0000
> @@ -5,6 +5,7 @@
>
> Disassembly of section .text:
> 0[0-9a-f]+ <[^>]+> 200c movs r0, #12
> +0[0-9a-f]+ <[^>]+> 1c1a adds r2, r3, #0
> 0[0-9a-f]+ <[^>]+> 1cd1 adds r1, r2, #3
> 0[0-9a-f]+ <[^>]+> 1ed1 subs r1, r2, #3
> 0[0-9a-f]+ <[^>]+> 3364 adds r3, #100.*
> @@ -18,3 +19,6 @@ Disassembly of section .text:
> 0[0-9a-f]+ <[^>]+> b081 sub sp, #4
> 0[0-9a-f]+ <[^>]+> af01 add r7, sp, #4
> 0[0-9a-f]+ <[^>]+> 4251 negs r1, r2
> +0[0-9a-f]+ <[^>]+> 46c0 nop.*
> +0[0-9a-f]+ <[^>]+> 461a mov r2, r3
> +0[0-9a-f]+ <[^>]+> 46c0 nop.*
> Index: gas/testsuite/gas/arm/thumb1_unified.s
> ===================================================================
> RCS file: /cvs/src/src/gas/testsuite/gas/arm/thumb1_unified.s,v
> retrieving revision 1.1
> diff -u -p -r1.1 thumb1_unified.s
> --- gas/testsuite/gas/arm/thumb1_unified.s 19 Apr 2007 17:08:21 -0000 1.1
> +++ gas/testsuite/gas/arm/thumb1_unified.s 15 Nov 2011 22:11:54 -0000
> @@ -4,6 +4,7 @@
> .thumb
> foo:
> movs r0, #12
> +mov r2, r3
> adds r1, r2, #3
> subs r1, r2, #3
> adds r3, r3, #0x64
> @@ -21,5 +22,10 @@ add r7, sp, #4
> rsbs r1, r2, #0
>
> .align 2
> +
> +.arch armv6
> +.thumb
> bar:
> +mov r2, r3
> +.align 2
>
>
>
> ChangeLog
>
>
> 2011-11-15 Thomas Klein <th.r.klein@web.de>
>
> * config/tc-arm.c (do_t_mov_cmp): Encode low register mov for arch v4t
> and v5t the same way as in non unified syntax form.