Re: [GCC, ARM] armv8 linux toolchain asan testcase fail due to stl missing conditional code

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

Hi Shiva,

On 04/06/15 04:13, Shiva Chen wrote:
> Hi, Ramana
>
> Currently, I work for Marvell and the company have copyright assignment on file.
>
> Hi, all
>
> After adding the attribute and rebuild gcc, I got the assembler error message
>
> load_n.s:39: Error: bad instruction `ldrbeq r0,[r0]'
>
> When i look into armv8 ISA document, it seems ldrb Encoding A1 have
> conditional code field.
>
> Does it mean we should also patch assembler or I just miss
> understanding something ?
>
> Following command use to generate load_n.s:
>
> /home/shivac/build-system-trunk/Release/build/armv8-marvell-linux-gnueabihf-hard/gcc-final/./gcc/cc1
> -fpreprocessed load_n.i -quiet -dumpbase load_n.c -march=armv8-a
> -mfloat-abi=hard -mfpu=fp-armv8  -mtls-dialect=gnu -auxbase-strip
> .libs/load_1_.o -g3 -O2 -Wall -Werror -version -fPIC -funwind-tables
> -o load_n.s
>
>
> The test.c is a simple test case to reproduce missing conditional code
> in mmap.c.
>
> Any suggestion ?

I reproduced the assembler failure with your patch.

The reason is that for arm mode we use divided syntax, where the condition field goes in a
different place. So, while ldrbeq r0,[r0] is rejected, ldreqb r0, [r0] works.
Since we always use divided syntax for arm mode, I think you'll need to put the condition field
in the right place depending on arm or thumb mode.
Ugh, this is becoming ugly :(

Kyrill

> Shiva
>
> 2015-06-03 17:29 GMT+08:00 Shiva Chen <shiva0217@gmail.com>:
> > Hi, Ramana
> >
> > I'm not sure what copyright assignment means ?
> >
> > Does it mean the patch have copyright assignment or not ?
> >
> > I update the patch to add "predicable" and  "predicable_short_it"
> > attribute as suggestion.
> >
> > However, I don't have svn write access yet.
> >
> > Shiva
> >
> > 2015-06-03 16:36 GMT+08:00 Kyrill Tkachov <kyrylo.tkachov@arm.com>:
> > > On 03/06/15 09:32, Ramana Radhakrishnan wrote:
> > > > > This pattern is not predicable though, i.e. it doesn't have the
> > > > > "predicable" attribute set to "yes".
> > > > > Therefore the compiler should be trying to branch around here rather than
> > > > > try to do a cond_exec.
> > > > > Why does the generated code above look like it's converted to conditional
> > > > > execution?
> > > > > Could you produce a self-contained reduced testcase for this?
> > > > CCFSM state machine in ARM state.
> > > >
> > > > arm.c (final_prescan_insn).
> > >
> > > Ah ok.
> > > This patch makes sense then.
> > > As Ramana mentioned, please mark the pattern with "predicable" and also set
> > > the "predicable_short_it" attribute to "no" so that it will not be
> > > conditionalised in Thumb2 mode or when -mrestrict-it is enabled.
> > >
> > > Thanks,
> > > Kyrill
> > >
> > >
> > >
> > > > Ramana
> > > >
> > > > > Thanks,
> > > > > Kyrill
> > > > >
> > > > > > @@ -91,9 +91,9 @@
> > > > > >        {
> > > > > >          enum memmodel model = memmodel_from_int (INTVAL (operands[2]));
> > > > > >          if (is_mm_relaxed (model) || is_mm_consume (model) ||
> > > > > > is_mm_acquire (model))
> > > > > > -      return \"str<sync_sfx>\t%1, %0\";
> > > > > > +      return \"str<sync_sfx>%?\t%1, %0\";
> > > > > >          else
> > > > > > -      return \"stl<sync_sfx>\t%1, %0\";
> > > > > > +      return \"stl<sync_sfx>%?\t%1, %0\";
> > > > > >        }
> > > > > >      )