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

[Richard Earnshaw <rearnsha at arm dot com>]

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.

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.

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
>