llvm dev - Dec 2014 - [LLVMdev] Newbee question: LLVM backend regression tests for thumb1 targets on simulator possible?

On 12/16/14 9:32 AM, Bjoern Haase wrote:
> Am 16.12.2014 15:27, schrieb Jonathan Roelofs:
>> I'm working on a baremetal cross toolchain, and I would like to set
up such a
>> buildbot. There are several pieces needed before that can happen
though, and
>> the important one is remote testing support in LIT (which I'm
working on)...
>> in due time :)
>>
>> Jon
> This would be perfect.
>
> Actually, you suggested to use
>
>  > $qemu-system-arm -semihosting -M integratorcp -cpu cortex-m0 -kernel
a.out
>
> You have some special version of qemu? My default distribution's qemu
package
> did not have a cortex-M0 nor has qemu head freshly taken from git:
Oh, maybe I'm thinking of an internal build of qemu. Sorry about
that.
>
> $ qemu-arm -cpu ?
> Available CPUs:
>    arm926  arm946 arm1026  arm1136  arm1136-r2 arm1176  arm11mpcore
cortex-m3
> cortex-a8
>    cortex-a8-r2 cortex-a9 cortex-a15 ti925t pxa250 sa1100 sa1110 pxa255
pxa260
>    pxa261 pxa262 pxa270 pxa270-a0 pxa270-a1 pxa270-b0 pxa270-b1 xa270-c0
>    pxa270-c5 any
>
> Still your procedure will work, just by using the m3 instead :-).
Yeah, that should work for the most part, unless you emit thumb2 instructions 
(which will work on cortex-m3, but not m0). The list of them is pretty small 
though IIRC, so maybe you can write a script that disassembles & checks for
them.
>
> Yours,
>
> Björn.
-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded

> > $ qemu-arm -cpu ?
> > Available CPUs:
> >    arm926  arm946 arm1026  arm1136  arm1136-r2 arm1176  arm11mpcore
> > cortex-m3
> > cortex-a8
> >    cortex-a8-r2 cortex-a9 cortex-a15 ti925t pxa250 sa1100 sa1110
> pxa255 pxa260
> >    pxa261 pxa262 pxa270 pxa270-a0 pxa270-a1 pxa270-b0 pxa270-b1 xa270-
> c0
> >    pxa270-c5 any
> >
> > Still your procedure will work, just by using the m3 instead :-).
> Yeah, that should work for the most part, unless you emit thumb2
> instructions (which will work on cortex-m3, but not m0). The list of
> them is pretty small though IIRC, so maybe you can write a script that
> disassembles & checks for them.
Cortex-M0 implements the v6m architecture.
Cortex-M3 implements the v7m architecture.

Having had a quick look at the v6m and the v7m ARMARM's, next to the
extra instructions v7m supports, I think the main other difference
that's very relevant for a code generator is that v6m always generates
a fault when an unaligned access occurs, whereas v7m can support unaligned
accesses for many of the load and store instructions. I think it'd
be important to set the CCR register on the v7m simulation so that
it always generates an alignment fault in case there's an unaligned
access, i.e. setting CCR.UNALIGN_TRP to 1.

To check that clang indeed only produces v6m instructions when
telling it to target Cortex-m0, I think we could rely on LLVM's
MC layer correctly modelling if an instruction is part of v6m or not,
as our internal MC Hammer test suite[1] has finally, since about 1
month ago, started passing completely for the v6m architecture.
Potentially, just making sure that a build with assertions enabled
would result in an assertion failure being triggered when a non-v6m
instruction gets emitted could be good enough, as a starting point?

Thanks,

Kristof

[1] http://llvm.org/devmtg/2012-04-12/Slides/Richard_Barton.pdf

> To check that clang indeed only produces v6m instructions when
> telling it to target Cortex-m0, I think we could rely on LLVM's
> MC layer correctly modelling if an instruction is part of v6m or not,
> as our internal MC Hammer test suite[1] has finally, since about 1
> month ago, started passing completely for the v6m architecture.
> Potentially, just making sure that a build with assertions enabled
> would result in an assertion failure being triggered when a non-v6m
> instruction gets emitted could be good enough, as a starting point?
Yes. That would be better. Tim was musing about doing that the last time I ran 
into the v4t lo->lo copy thing.

Jon

-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded