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

[Ramana Radhakrishnan <ramana dot gcc at googlemail dot com>]

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.

 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
>>
>
>