[PATCH][ARM][gas] Warn on deprecated ldm r<n>, {..., sp,...} and ldm r<n>, {...,lr,pc,...} forms

[Kyrill Tkachov]

On 20/01/15 10:10, Kyrill Tkachov wrote:
> On 14/01/15 11:32, Ramana Radhakrishnan wrote:
>> On Wed, Jan 14, 2015 at 11:12 AM, Richard Earnshaw <rearnsha@arm.com> wrote:
>>> On 14/01/15 10:24, Kyrill Tkachov wrote:
>>>> Hi all,
>>>>
>>>> ARMv7-A deprecates ldm instructions that use the SP register in their list
>>>> as well as ldm instructions that use both LR and PC. GAS should warn
>>>> about them.
>>>>
>>>> This patch adds a warning for these forms.
>>>> Tests are added/updated.
>>>>
>>>> Tested check-gas in arm-none-eabi and I've had it sitting in my tree
>>>> being tested
>>>> with gcc for a few months now.
>>>>
>>>> What do people think?
>>>>
>>> I think firstly, that we should use as_tsktsk for deprecations, rather
>>> than warnings.
>> as_tsktsk would be better but we need to change a whole load of
>> deprecations to this form rather than warnings in the ARM port. I
>> don't think all our other deprecations use tsktsk. I think we need to
>> move people on when they use this on v7-a and newer revisions of the
>> architecture.
> Shall we go the way of as_tsktsk then and convert the other deprecation
> warnings to as_tsktsk.

That should have been a question :)

Kyrill

> I do see some deprecations using as_tsktsk and some using
> as_warn.
>
> Kyrill
>
>>    I don't like hiding these behind flags or folks will not fix their
>> issues without the compiler or assembler warning / shouting at them.
>>
>>> I'm still somewhat concerned about the use of SP in LDM lists.  This is
>>> going to make any legacy ABI code generated by GCC (-mapcs-frame) very
>>> verbose.  I don't expect we will want to fix GCC to avoid this sequence.
>> Personally I think (not very strongly) we should fix GCC to avoid this
>> sequence if we can and then deprecate all uses of mapcs-frame.
>> Unfortunately it's one of these options that appears to linger on in
>> build systems for no apparently good reason.
>>
>> Ramana
>>
>>> I'd like opinions from others on this one...
>>>
>>> R.
>>>
>>>> Thanks,
>>>> Kyrill
>>>>
>>>> [gas/]
>>>> 2015-01-14  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>>>
>>>>        * config/tc-arm.c (encode_ldmstm): Add deprecation warning when
>>>>        SP or both LR and PC are used in ldm register list.
>>>>
>>>> [gas/testsuite]
>>>> 2015-01-14  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>>>
>>>>        * gas/cfi/cfi-arm-1.s: Change usage of sp to ip in 'ldmea'.
>>>>        * gas/arm/arm-ldm-bad.s: New file.
>>>>        * gas/arm/arm-ldm-bad.d: Likewise.
>>>>        * gas/arm/arm-ldm-bad.l: Likewise.
>>>>
>>>>
>>>> arm-gas-ldm-warnings.patch
>>>>
>>>>
>>>> commit 945c748ad5075d3d0e7d54e6258d8ab9bcf5fa36
>>>> Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
>>>> Date:   Mon Jun 30 17:28:56 2014 +0100
>>>>
>>>>       [ARM][gas] ldm sp warnings
>>>>
>>>> diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
>>>> index ce0532b..5755b4b 100644
>>>> --- a/gas/config/tc-arm.c
>>>> +++ b/gas/config/tc-arm.c
>>>> @@ -8130,6 +8130,15 @@ encode_ldmstm(int from_push_pop_mnem)
>>>>         }
>>>>        }
>>>>
>>>> +  if (inst.instruction & LOAD_BIT
>>>> +      && ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v7a))
>>>> +    {
>>>> +      if (range & (1 << REG_SP))
>>>> +        as_warn (_("usage of SP in register list is deprecated"));
>>>> +      else if (range & (1 << REG_PC) && range & (1 << REG_LR))
>>>> +        as_warn (_("usage of both LR and PC in register list is deprecated"));
>>>> +    }
>>>> +
>>>>      /* If PUSH/POP has only one register, then use the A2 encoding.  */
>>>>      one_reg = only_one_reg_in_list (range);
>>>>      if (from_push_pop_mnem && one_reg >= 0)
>>>> diff --git a/gas/testsuite/gas/arm/arm-ldm-bad.d b/gas/testsuite/gas/arm/arm-ldm-bad.d
>>>> new file mode 100644
>>>> index 0000000..8ce6a54
>>>> --- /dev/null
>>>> +++ b/gas/testsuite/gas/arm/arm-ldm-bad.d
>>>> @@ -0,0 +1,3 @@
>>>> +#name: ARM ldm/stm warnings
>>>> +#as: -march=armv7-a
>>>> +#error-output: arm-ldm-bad.l
>>>> diff --git a/gas/testsuite/gas/arm/arm-ldm-bad.l b/gas/testsuite/gas/arm/arm-ldm-bad.l
>>>> new file mode 100644
>>>> index 0000000..1609594
>>>> --- /dev/null
>>>> +++ b/gas/testsuite/gas/arm/arm-ldm-bad.l
>>>> @@ -0,0 +1,5 @@
>>>> +[^:]*: Assembler messages:
>>>> +[^:]*:4: Warning: usage of both LR and PC in register list is deprecated
>>>> +[^:]*:5: Warning: usage of both LR and PC in register list is deprecated
>>>> +[^:]*:6: Warning: usage of SP in register list is deprecated
>>>> +[^:]*:7: Warning: usage of SP in register list is deprecated
>>>> diff --git a/gas/testsuite/gas/arm/arm-ldm-bad.s b/gas/testsuite/gas/arm/arm-ldm-bad.s
>>>> new file mode 100644
>>>> index 0000000..d16cf5d
>>>> --- /dev/null
>>>> +++ b/gas/testsuite/gas/arm/arm-ldm-bad.s
>>>> @@ -0,0 +1,7 @@
>>>> +     .global entry
>>>> +     .text
>>>> +entry:
>>>> +     ldm sp, {r4-r7,r11,lr,pc}
>>>> +     ldm sp!, {r4-r7,r11,lr,pc}
>>>> +     ldm r1, {r4-r7,sp}
>>>> +     ldm r1!, {r4-r7,sp}
>>>> diff --git a/gas/testsuite/gas/cfi/cfi-arm-1.s b/gas/testsuite/gas/cfi/cfi-arm-1.s
>>>> index d962442..481f4f2 100644
>>>> --- a/gas/testsuite/gas/cfi/cfi-arm-1.s
>>>> +++ b/gas/testsuite/gas/cfi/cfi-arm-1.s
>>>> @@ -23,7 +23,7 @@ foo:
>>>>         .cfi_offset r1,  -16
>>>>         .cfi_offset s1,  -20
>>>>         .cfi_offset d11, -48
>>>> -
>>>> -     ldmea   fp, {fp, sp, pc}
>>>> +
>>>> +     ldmea   fp, {fp, ip, pc}
>>>>         .cfi_endproc
>>>>         .size   foo, .-foo
>>>>
>
>