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

Kyrill Tkachov kyrylo.tkachov@arm.com
Wed Feb 4 11:52:00 GMT 2015 

On 20/01/15 14:00, Richard Earnshaw wrote:
> On 20/01/15 10:13, Kyrill Tkachov wrote:
>> 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 :)
>>
> Yes, we should be consistent.  And I think tsktsk is the right level for
> these.  We really do understand what the user has asked for, it's just
> that it has *potentially* undefined behaviour at run time.
>
> A separate patch to make the messages consistent would be welcomed.  For
> this patch, just fix it to use tsktsk.

Ok, here it is, using as_tsktsk.
I'll look into moving the other deprecation warnings to tsktsk as well, 
though I guess the -mwarn-deprecated option will be not "technically" 
warning the user, just notifying?

Kyrill

[gas/]
2015-02-04  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

        * config/tc-arm.c (encode_ldmstm): Add deprecation message when
        SP or both LR and PC are used in ldm register list.

[gas/testsuite]
2015-02-04  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.



>
> R.
>
>> 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
>>>>>>
>>>
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