llvm dev - Feb 2017 - Users of MIPS and PowerPC backends in production-class projects?

Hi,

I'd like to experiment with the MIPS and PowerPC backends, but,
considering that they aren't widely used processors, I'd like to start
with the same environment (OS/ABI/linker) used by the people who work
with these backends.

So, what OS/ABI/linker use the people who use these backends for
production work?

Thanks!!

For PowerPC, common uses are on little endian systems running Linux. The
ABI used on such systems is the ELF v2 ABI and both the GNU linker and GOLD
are in widespread use as far as I'm aware. Big endian systems running Linux
are somewhat common but they use the ELF v1 ABI and mostly the GNU linker.
I will defer to Hal Finkel (on Cc) for use on larger distributed systems as
well as to others for use of the PowerPC back end on 32-bit and embedded
processors.

On Wed, Feb 22, 2017 at 10:48 AM, ardi via llvm-dev <llvm-dev at
lists.llvm.org
> wrote:
> Hi,
>
> I'd like to experiment with the MIPS and PowerPC backends, but,
> considering that they aren't widely used processors, I'd like to
start
> with the same environment (OS/ABI/linker) used by the people who work
> with these backends.
>
> So, what OS/ABI/linker use the people who use these backends for
> production work?
>
> Thanks!!
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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For MIPS, the common OSes would be Linux/FreeBSD/NetBSD/OpenBSD.

Endianness is somewhat variable as many MIPS designs have big endian and
little endian variants. Typically you can assume big endian but little endian is
fairly common as well.

For the ABI would be O32 for 32 bit MIPS and N64 for 64 bit MIPS. There is
another ABI, N32 which fulfils a similar role as X32 for x86_64 i.e. 32bit
pointers
with 64 integers. This is what stock GCC targets by default for mips64. LLVM for
mips64 targets N64 by default for historical reasons.

Historically, MIPS has had other ABIs defined for it, such as GNU's EABI and
it's
64 bit variant and O64. You can stick with O32/N64/N32 as most of the OS
distributions will only use those ABIs.

The usual linker would be the GNU linker and GOLD. LLD is in a good shape for
MIPS.

For baremetal / embedded / kernel environments, the tools and ABIS are the
same but you compile code as non-pic and use custom linker scripts and
startup code tailored to the environment.

Thanks,
Simon
> -----Original Message-----
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of
ardi
> via llvm-dev
> Sent: 22 February 2017 09:48
> To: llvm-dev
> Subject: [llvm-dev] Users of MIPS and PowerPC backends in production-class
> projects?
> 
> Hi,
> 
> I'd like to experiment with the MIPS and PowerPC backends, but,
considering
> that they aren't widely used processors, I'd like to start with the
same
> environment (OS/ABI/linker) used by the people who work with these
> backends.
> 
> So, what OS/ABI/linker use the people who use these backends for
> production work?
> 
> Thanks!!
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

We're still working to get FreeBSD fully building for PowerPC with
clang, and have been in a state of "almost there" for some time now.
There are two methods of doing so, one is using the in-tree binutils
(2.17.50+patches), which has been patched to support newer relocations
LLVM generates; the other is using an external toolchain binutils
(2.25?).  We've had luck with both, and will be looking at lld in the
future as well.

- Justin

On Wed, Feb 22, 2017 at 3:48 AM, ardi via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Hi,
>
> I'd like to experiment with the MIPS and PowerPC backends, but,
> considering that they aren't widely used processors, I'd like to
start
> with the same environment (OS/ABI/linker) used by the people who work
> with these backends.
>
> So, what OS/ABI/linker use the people who use these backends for
> production work?
>
> Thanks!!
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

Is the MIPS backend production-ready for any (or all) of the OSs you
mention? As I said, I'd like to start using the MIPS and PowerPC backends
with an OS/linker where they are most reliable.

In the case of PowerPC, from the comments I conclude there's people
successfully using the backend in Linux. OTOH, FreeBSD is "almost
there",
and not sure about NetBSD and OpenBSD.

In the case of MIPS, would Linux be the most reliable choice, or is any BSD
flavour already using the backend successfully?

Thanks!

ardi



On Wednesday, February 22, 2017, Simon Dardis <Simon.Dardis at imgtec.com>
wrote:
> For MIPS, the common OSes would be Linux/FreeBSD/NetBSD/OpenBSD.
>
> Endianness is somewhat variable as many MIPS designs have big endian and
> little endian variants. Typically you can assume big endian but little
> endian is
> fairly common as well.
>
> For the ABI would be O32 for 32 bit MIPS and N64 for 64 bit MIPS. There is
> another ABI, N32 which fulfils a similar role as X32 for x86_64 i.e. 32bit
> pointers
> with 64 integers. This is what stock GCC targets by default for mips64.
> LLVM for
> mips64 targets N64 by default for historical reasons.
>
> Historically, MIPS has had other ABIs defined for it, such as GNU's
EABI
> and it's
> 64 bit variant and O64. You can stick with O32/N64/N32 as most of the OS
> distributions will only use those ABIs.
>
> The usual linker would be the GNU linker and GOLD. LLD is in a good shape
> for
> MIPS.
>
> For baremetal / embedded / kernel environments, the tools and ABIS are the
> same but you compile code as non-pic and use custom linker scripts and
> startup code tailored to the environment.
>
> Thanks,
> Simon
>
> > -----Original Message-----
> > From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org
<javascript:;>]
> On Behalf Of ardi
> > via llvm-dev
> > Sent: 22 February 2017 09:48
> > To: llvm-dev
> > Subject: [llvm-dev] Users of MIPS and PowerPC backends in
> production-class
> > projects?
> >
> > Hi,
> >
> > I'd like to experiment with the MIPS and PowerPC backends, but,
> considering
> > that they aren't widely used processors, I'd like to start
with the same
> > environment (OS/ABI/linker) used by the people who work with these
> > backends.
> >
> > So, what OS/ABI/linker use the people who use these backends for
> > production work?
> >
> > Thanks!!
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org <javascript:;>
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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On 02/22/2017 04:56 AM, Nemanja Ivanovic wrote:
> For PowerPC, common uses are on little endian systems running Linux. 
> The ABI used on such systems is the ELF v2 ABI and both the GNU linker 
> and GOLD are in widespread use as far as I'm aware. Big endian systems 
> running Linux are somewhat common but they use the ELF v1 ABI and 
> mostly the GNU linker.
> I will defer to Hal Finkel (on Cc) for use on larger distributed 
> systems as well
We use the LLVM/PowerPC on big-Endian PPC64/Linux using recent binutils 
in production (on POWER7 and the BG/Q).

  -Hal
> as to others for use of the PowerPC back end on 32-bit and embedded 
> processors.
>
> On Wed, Feb 22, 2017 at 10:48 AM, ardi via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
>
>     Hi,
>
>     I'd like to experiment with the MIPS and PowerPC backends, but,
>     considering that they aren't widely used processors, I'd like
to start
>     with the same environment (OS/ABI/linker) used by the people who work
>     with these backends.
>
>     So, what OS/ABI/linker use the people who use these backends for
>     production work?
>
>     Thanks!!
>     _______________________________________________
>     LLVM Developers mailing list
>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>     http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>     <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>
>
-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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Hi Ardi,

> So, what OS/ABI/linker use the people who use these backends for
> production work?
>
W.R.T production use of llvm ppc, we make extensive use of the ppc backend
in the HPC (High Performance Computing, i.e. "Supercomputers")
community
since clang tends to produce much better quality code for C++ than IBM
xlC.  Most all of these are Linux + gcc linker.  The ones that aren't Linux
are the BlueGene/Q which use a custom OS just for that machine, but those
are using a special port that Argonne National Labs maintains (bgclang), so
that's likely less of a concern for you.  Moving forward virtually all the
ppc platforms of concern are Linux, littel endian, i.e. ppc64le, mostly
power8 and power9.

- Chuck
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