[llvm-dev] Level of support for ARM LLD

[Peter Smith via llvm-dev]

Hello Sumonto,

There are several upstream build bots that run the Arm specific LLD
tests. You can find these tests in the lld/test/ELF directory, they
all start with arm. At Linaro we are planning to set up a build-bot,
modelled on the equivalent AArch64 one that does a 2 stage build of
clang with LLD as the linker, this will also include running the test
suite.

For the ELF port; the major Arm specific features that it is missing are:
- Full support for BuildAttributes.
- Big Endian support.
- Support for older Architectures such as Arm v4, v5 and v6.
- Errata fixes supported by ld.bfd such as the cortex-a8.

I do have some plans to improve support for BuildAttributes as these
are important for embedded systems. I've got some downstream patches
for v5 and v6 support (limit branch range, and use different
instructions in stubs), however I don't think anyone has actually
needed support yet. Big endian support is a little trickier than for
other architectures as the linker needs to endian reverse all the
instructions. There isn't much use of Big Endian on Arm outside of
networking though so getting access to hardware to test on is
difficult. I'm not planning on adding the errata fixes as these are
quite disruptive and the affected CPUs are now quite old and not in
wide use.

Peter


On 27 February 2018 at 03:04, Sumonto Ghosh via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Is there a regression bot with a list of tests or alike
>
> Thanks
>
> On Mon, Feb 26, 2018 at 4:19 PM Rafael Avila de Espindola
> <rafael.espindola at gmail.com> wrote:
>>
>> I think ARM ELF is pretty good. I was able to link clang with it some
>> time ago and it now has support for thunks.
>>
>> Cheers,
>> Rafael
>>
>>
>> Sumonto Ghosh <sumonto.ghosh at gmail.com> writes:
>>
>> > Thanks Rafael, wondering as of what is the level of support for ARM and
>> > is
>> > it close to production quality?
>> >
>> > Thanks
>> >
>> > On Mon, Feb 26, 2018 at 2:06 PM, Rafael Avila de Espindola <
>> > rafael.espindola at gmail.com> wrote:
>> >
>> >> Not sure there is an official POC, you are probably better off asking
>> >> whatever question you have directly on the list.
>> >>
>> >> Cheers,
>> >> Rafael
>> >>
>> >> Sumonto Ghosh via llvm-dev <llvm-dev at lists.llvm.org> writes:
>> >>
>> >> > Hi,
>> >> > Could someone please connect me to the POC for ARM support on LLD
>> >> >
>> >> >
>> >> > Thanks
>> >> > _______________________________________________
>> >> > LLVM Developers mailing list
>> >> > llvm-dev at lists.llvm.org
>> >> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >>
>
> --
> Thanks
>
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