Re: [ARM] Allow MOV/MOV.W to accept all possible immediates

[Jiong Wang <jiong.wang@foss.arm.com>]

On 05/01/17 13:59, Jiong Wang wrote:
> On 05/01/17 10:49, Szabolcs Nagy wrote:
>> adding the reporter to cc and rich because it broke musl.
>>
>> On 05/01/17 10:45, Szabolcs Nagy wrote:
>>> On 01/11/16 12:21, Jiong Wang wrote:
>>>> Hi,
>>>>
>>>>    AArch32 MOV Rd, #imm should accept all immediates which can be 
>>>> encoded into
>>>> available encoding, A1/A2 for ARM, T1/T2/T3 for Thumb/Thumb2, and 
>>>> MOV is the
>>>> preferred disassembly syntax.  See latest ARM Architecture 
>>>> Reference Manual for
>>>> ARMv8-A, section F6.1.108 and for ARMv8-M, section C2.4.89.
>>>>
>>>>    The same for MOV.W under Thumb mode.  It should try all possible 
>>>> 32-bit Thumb
>>>> encoding instead of T2 only.
>>>>
>>>>    This patch let MOV/MOV.W accept more immediate formats while 
>>>> their currently
>>>> supported immediate formats are not affected, so there is no 
>>>> backward compatibility
>>>> issue, also this patch haven't touched the disassembler.
>>>>
>>>>    I think this patch brings GAS closer to ARM Architecture 
>>>> Reference Manual.
>>>>
>>>>    OK for master?
>>>>
>>>> gas/
>>>> 2016-11-01  Jiong Wang  <jiong.wang@arm.com>
>>>>                            * config/tc-arm.c (SBIT_SHIFT): New.
>>>>          (T2_SBIT_SHIFT): Likewise.
>>>>          (t32_insn_ok): Return TRUE for MOV in ARMv8-M Baseline.
>>>>          (md_apply_fix): Try UINT16 encoding when ARM/Thumb 
>>>> modified immediate
>>>>          encoding failed.
>>>>          * testsuite/gas/arm/archv6t2-bad.s: New error case.
>>>>          * testsuite/gas/arm/archv6t2-bad.l: New error match.
>>>>          * testsuite/gas/arm/archv6t2.s: New testcase.
>>>>          * testsuite/gas/arm/archv6t2.d: New expected result.
>>>>          * testsuite/gas/arm/archv8m.s: New testcase
>>>>          * testsuite/gas/arm/archv8m-base.d: New expected result.
>>>>          * testsuite/gas/arm/archv8m-main.d: Likewise.
>>>>          * testsuite/gas/arm/archv8m-main-dsp-1.d: Likewise.
>>> this caused
>>>
>>> $ cat bug.s
>>> .syntax unified
>>> .text
>>> .arch armv7-a
>>>     mov r3,#1
>>>
>>> .arch armv4t
>>> .eabi_attribute 6,2
>>>     bx lr
>>>
>>> $ arm-none-linux-gnueabihf-as -mthumb bug.s
>>> bug.s: Assembler messages:
>>> bug.s:4: Error: invalid constant (1) after fixup
>>>
>>> previously this worked, but i'm not sure if the mix
>>> of .arch directives and .syntax unified is valid here.
>
> It looks to me the failure is caused by the second ".arch armv4t" 
> overrides the
> first ".arch armv7-a", therefore the arch feature is lowerd to armv4t in
> assembler fixup stage.  While "mov r3, #1" under thumb mode is only 
> allowed
> with ARMv6T2.
>
> This patch tightend the check from
>
>       if (fixP->fx_r_type == BFD_RELOC_ARM_T32_IMMEDIATE
>           || fixP->fx_r_type == BFD_RELOC_ARM_T32_ADD_IMM)
>
> into:
>
>       if ((fixP->fx_r_type == BFD_RELOC_ARM_T32_IMMEDIATE
>            && ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v6t2))
>           || fixP->fx_r_type == BFD_RELOC_ARM_T32_ADD_IMM)
>
>
> thus the sequences in bug.s is not allowed.

Does .object_arch works for you? It seems you want the final object arch 
adjusted.

https://sourceware.org/ml/binutils/2006-09/msg00054.html

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