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

[Kyrill Tkachov <kyrylo dot tkachov at arm dot com>]

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