llvm dev - Aug 2017 - Cross compiling C++ program

You may also take a look at the ELLCC project (www.ellcc.org
<http://www.ellcc.org/>). As far as I understand it they produce and
package cross toolchains for a number of popular targets.

- Matthias
> On Aug 4, 2017, at 12:54 PM, Jonathan Roelofs via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> 
> 
> On 8/4/17 1:14 PM, Goran Mekić via llvm-dev wrote:
>> On Thu, Aug 03, 2017 at 08:22:24AM -0600, Jonathan Roelofs wrote:
>>> IIUC, you don't want to cross compile llvm itself (which is
what those
>>> instructions are for), but instead you want to *use* llvm to cross
compile
>>> things.
>>> 
>>> To build your sysroot, you'll need to cross-build:
>>> 
>>>   1) A libc. Good choices for that for baremetal are: newlib or
musl.
>>>   2) Builtins. In llvm, that's provided in the compiler-rt
repo. Otherwise
>>> you can use libgcc from an arm-none-eabi-gcc toolchain.
>>>   3) If you want c++, you'll also need:
>>>      3A) c++ abi library. llvm provides this as libcxxabi.
There's also
>>> libsupc++, and libcxxrt, depending on what licenses you're
comfortable with.
>>>      3B) An unwinder. llvm provides libunwind. There's also one
packaged in
>>> libgcc_s (depending on how it was built), and another from the old
HP
>>> libunwind project (different codebase, but same name as the llvm
one).
>>>      3C) A c++ standard library. llvm provides this as libcxx.
There's also
>>> libstdc++.
>>> 
>>> 
>>> To start with, I recommend using the cmake cache in:
>>> $clang_src/cmake/caches/BaremetalARM.cmake. You'll want the
stuff in it that
>>> references the armv7em-none-eabi triple. To use it, do something
like:
>>> 
>>> $  cmake -G <build system>
>>> -DBAREMETAL_ARMV7EM_SYSROOT=path/to/your/v7em/sysroot -C
>>> path/to/BaremetalARM.cmake [other CMake Options]
>>> 
>>> Assuming your sysroot has libc headers in it, that should get you a
clang
>>> that's capable of compiling basic things, which you can use to
build all the
>>> libraries above.
>>> 
>>> 
>>> Jon
>> Hello,
>> Your input was very valuable, but I must be too noob so I have to ask.
I tried to read as much as I could about musl, compiler-rt and libunwind to
understand what are those libs and I decided to go with a "relexed"
licenced alternatives. :o) If I got it right, the order of repos I need to
compile is:
>> - musl
>> - compiler-rt
>> - libcxxabi
>> - libunwind
>> - libcxx
>> - clang (with the suggestion about baremetal cache)
> 
> 
> Not quite. You'll need clang built in order to build the other things.
(I guess you could use your existing toolchain to do that, but IIUC, you want to
use clang for all of it & bootstrap a full clang-based toolchain). For that,
the usual order is to:
> 
> 1) Pick a directory as your sysroot
> 2) Install the libc headers there (without having built it)
> 3) Build clang w/ baremetal cache, pointing it at the partially built
sysroot.
> 4) Build your libc.
> 4A) Test your libc.
> 4B) Install your libc in your sysroot.
> 5) Build libcxxabi. (it's build needs to know where the source for
libcxx lives)
> 5A) Test libcxxabi. (testing it requires knowing where source for libcxx
lives. use remote executors & linker scripts to run on your board, or in
qemu)
> 5B) Install libcxxabi in your sysroot.
> 6) Build libunwind.
> 6A) Test libunwind. (testing it requires knowing where source for libcxx
lives. use remote executors & linker scripts to run on your board, or in
qemu)
> 6B) Install libunwind in your sysroot.
> 7) Build libcxx.
> 7A) Test libcxx. (use remote executors & linker scripts to run on your
board, or in qemu)
> 7B) Install libcxx in your sysroot.
> 
> 
> A note on linker scripts: support for them in lld is still a bit rough
around the edges, so you may want to use the linker that comes with your board
(presumably binutils ld).
> 
>> If you know any doc on how to get clang++ compile for any bare metal
arm, I'll be glad to RTFM. :o)
> 
> Sorry, I don't have a doc for that. We're getting closer to making
it work "out of the tin", but it's not there yet. We (wearing my
CodeSourcery hat) are working on it, but it's going to take some time before
it "just works" upstream.
> 
> 
> Jon
> 
>> _______________________________________________
>> 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>
> 
> -- 
> Jon Roelofs
> jonathan at codesourcery.com <mailto:jonathan at codesourcery.com>
> CodeSourcery / Mentor Embedded / Siemens
> _______________________________________________
> 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>
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On 8/4/17 3:04 PM, Matthias Braun wrote:
> You may also take a look at the ELLCC project (www.ellcc.org 
> <http://www.ellcc.org>). As far as I understand it they produce and 
> package cross toolchains for a number of popular targets.
AFAIU, ELLCC doesn't support baremetal. It only has linux targets.


Jon
>
> - Matthias
>
>> On Aug 4, 2017, at 12:54 PM, Jonathan Roelofs via llvm-dev 
>> <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
>>
>>
>>
>> On 8/4/17 1:14 PM, Goran Mekić via llvm-dev wrote:
>>> On Thu, Aug 03, 2017 at 08:22:24AM -0600, Jonathan Roelofs wrote:
>>>> IIUC, you don't want to cross compile llvm itself (which is
what those
>>>> instructions are for), but instead you want to *use* llvm to
cross
>>>> compile
>>>> things.
>>>>
>>>> To build your sysroot, you'll need to cross-build:
>>>>
>>>>   1) A libc. Good choices for that for baremetal are: newlib or
musl.
>>>>   2) Builtins. In llvm, that's provided in the compiler-rt
repo.
>>>> Otherwise
>>>> you can use libgcc from an arm-none-eabi-gcc toolchain.
>>>>   3) If you want c++, you'll also need:
>>>>      3A) c++ abi library. llvm provides this as libcxxabi.
There's also
>>>> libsupc++, and libcxxrt, depending on what licenses you're 
>>>> comfortable with.
>>>>      3B) An unwinder. llvm provides libunwind. There's also
one
>>>> packaged in
>>>> libgcc_s (depending on how it was built), and another from the
old HP
>>>> libunwind project (different codebase, but same name as the
llvm one).
>>>>      3C) A c++ standard library. llvm provides this as libcxx. 
>>>> There's also
>>>> libstdc++.
>>>>
>>>>
>>>> To start with, I recommend using the cmake cache in:
>>>> $clang_src/cmake/caches/BaremetalARM.cmake. You'll want the
stuff
>>>> in it that
>>>> references the armv7em-none-eabi triple. To use it, do
something like:
>>>>
>>>> $  cmake -G <build system>
>>>> -DBAREMETAL_ARMV7EM_SYSROOT=path/to/your/v7em/sysroot -C
>>>> path/to/BaremetalARM.cmake [other CMake Options]
>>>>
>>>> Assuming your sysroot has libc headers in it, that should get
you a
>>>> clang
>>>> that's capable of compiling basic things, which you can use
to
>>>> build all the
>>>> libraries above.
>>>>
>>>>
>>>> Jon
>>> Hello,
>>> Your input was very valuable, but I must be too noob so I have to 
>>> ask. I tried to read as much as I could about musl, compiler-rt and
>>> libunwind to understand what are those libs and I decided to go
with
>>> a "relexed" licenced alternatives. :o) If I got it right,
the order
>>> of repos I need to compile is:
>>> - musl
>>> - compiler-rt
>>> - libcxxabi
>>> - libunwind
>>> - libcxx
>>> - clang (with the suggestion about baremetal cache)
>>
>>
>> Not quite. You'll need clang built in order to build the other 
>> things. (I guess you could use your existing toolchain to do that, 
>> but IIUC, you want to use clang for all of it & bootstrap a full 
>> clang-based toolchain). For that, the usual order is to:
>>
>> 1) Pick a directory as your sysroot
>> 2) Install the libc headers there (without having built it)
>> 3) Build clang w/ baremetal cache, pointing it at the partially built 
>> sysroot.
>> 4) Build your libc.
>> 4A) Test your libc.
>> 4B) Install your libc in your sysroot.
>> 5) Build libcxxabi. (it's build needs to know where the source for 
>> libcxx lives)
>> 5A) Test libcxxabi. (testing it requires knowing where source for 
>> libcxx lives. use remote executors & linker scripts to run on your 
>> board, or in qemu)
>> 5B) Install libcxxabi in your sysroot.
>> 6) Build libunwind.
>> 6A) Test libunwind. (testing it requires knowing where source for 
>> libcxx lives. use remote executors & linker scripts to run on your 
>> board, or in qemu)
>> 6B) Install libunwind in your sysroot.
>> 7) Build libcxx.
>> 7A) Test libcxx. (use remote executors & linker scripts to run on 
>> your board, or in qemu)
>> 7B) Install libcxx in your sysroot.
>>
>>
>> A note on linker scripts: support for them in lld is still a bit 
>> rough around the edges, so you may want to use the linker that comes 
>> with your board (presumably binutils ld).
>>
>>> If you know any doc on how to get clang++ compile for any bare
metal
>>> arm, I'll be glad to RTFM. :o)
>>
>> Sorry, I don't have a doc for that. We're getting closer to
making it
>> work "out of the tin", but it's not there yet. We
(wearing my
>> CodeSourcery hat) are working on it, but it's going to take some
time
>> before it "just works" upstream.
>>
>>
>> Jon
>>
>>> _______________________________________________
>>> 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
>>
>> --
>> Jon Roelofs
>> jonathan at codesourcery.com <mailto:jonathan at
codesourcery.com>
>> CodeSourcery / Mentor Embedded / Siemens
>> _______________________________________________
>> 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
>
-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded / Siemens

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On Fri, Aug 04, 2017 at 02:04:17PM -0700, Matthias Braun
wrote:
> You may also take a look at the ELLCC project (www.ellcc.org
<http://www.ellcc.org/>). As far as I understand it they produce and
package cross toolchains for a number of popular targets.
>
> - Matthias
I am talking with him on IRC to try to make ELLCC run on FreeBSD via Linux
emulation and maybe get started with that.
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On 08/04/2017 04:34 PM, Jonathan Roelofs via llvm-dev
wrote:
>
>
>
> On 8/4/17 3:04 PM, Matthias Braun wrote:
>> You may also take a look at the ELLCC project (www.ellcc.org
>> <http://www.ellcc.org>). As far as I understand it they produce
and
>> package cross toolchains for a number of popular targets.
>
> AFAIU, ELLCC doesn't support baremetal. It only has linux targets.
>
>
> Jon
>
ELLCC has been used for baremetal stuff, but it takes some work. I'm
looking at adding NuttX support, which will make baremetal much easier.

-Rich
>>
>> - Matthias
>>
>>> On Aug 4, 2017, at 12:54 PM, Jonathan Roelofs via llvm-dev
>>> <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
>>>
>>>
>>>
>>> On 8/4/17 1:14 PM, Goran Mekić via llvm-dev wrote:
>>>> On Thu, Aug 03, 2017 at 08:22:24AM -0600, Jonathan Roelofs
wrote:
>>>>> IIUC, you don't want to cross compile llvm itself
(which is what those
>>>>> instructions are for), but instead you want to *use* llvm
to cross
>>>>> compile
>>>>> things.
>>>>>
>>>>> To build your sysroot, you'll need to cross-build:
>>>>>
>>>>>   1) A libc. Good choices for that for baremetal are:
newlib or musl.
>>>>>   2) Builtins. In llvm, that's provided in the
compiler-rt repo.
>>>>> Otherwise
>>>>> you can use libgcc from an arm-none-eabi-gcc toolchain.
>>>>>   3) If you want c++, you'll also need:
>>>>>      3A) c++ abi library. llvm provides this as libcxxabi.
There's
>>>>> also
>>>>> libsupc++, and libcxxrt, depending on what licenses
you're
>>>>> comfortable with.
>>>>>      3B) An unwinder. llvm provides libunwind. There's
also one
>>>>> packaged in
>>>>> libgcc_s (depending on how it was built), and another from
the old HP
>>>>> libunwind project (different codebase, but same name as the
llvm one).
>>>>>      3C) A c++ standard library. llvm provides this as
libcxx.
>>>>> There's also
>>>>> libstdc++.
>>>>>
>>>>>
>>>>> To start with, I recommend using the cmake cache in:
>>>>> $clang_src/cmake/caches/BaremetalARM.cmake. You'll want
the stuff
>>>>> in it that
>>>>> references the armv7em-none-eabi triple. To use it, do
something like:
>>>>>
>>>>> $  cmake -G <build system>
>>>>> -DBAREMETAL_ARMV7EM_SYSROOT=path/to/your/v7em/sysroot -C
>>>>> path/to/BaremetalARM.cmake [other CMake Options]
>>>>>
>>>>> Assuming your sysroot has libc headers in it, that should
get you
>>>>> a clang
>>>>> that's capable of compiling basic things, which you can
use to
>>>>> build all the
>>>>> libraries above.
>>>>>
>>>>>
>>>>> Jon
>>>> Hello,
>>>> Your input was very valuable, but I must be too noob so I have
to
>>>> ask. I tried to read as much as I could about musl, compiler-rt
and
>>>> libunwind to understand what are those libs and I decided to go
>>>> with a "relexed" licenced alternatives. :o) If I got
it right, the
>>>> order of repos I need to compile is:
>>>> - musl
>>>> - compiler-rt
>>>> - libcxxabi
>>>> - libunwind
>>>> - libcxx
>>>> - clang (with the suggestion about baremetal cache)
>>>
>>>
>>> Not quite. You'll need clang built in order to build the other
>>> things. (I guess you could use your existing toolchain to do that,
>>> but IIUC, you want to use clang for all of it & bootstrap a
full
>>> clang-based toolchain). For that, the usual order is to:
>>>
>>> 1) Pick a directory as your sysroot
>>> 2) Install the libc headers there (without having built it)
>>> 3) Build clang w/ baremetal cache, pointing it at the partially
>>> built sysroot.
>>> 4) Build your libc.
>>> 4A) Test your libc.
>>> 4B) Install your libc in your sysroot.
>>> 5) Build libcxxabi. (it's build needs to know where the source
for
>>> libcxx lives)
>>> 5A) Test libcxxabi. (testing it requires knowing where source for
>>> libcxx lives. use remote executors & linker scripts to run on
your
>>> board, or in qemu)
>>> 5B) Install libcxxabi in your sysroot.
>>> 6) Build libunwind.
>>> 6A) Test libunwind. (testing it requires knowing where source for
>>> libcxx lives. use remote executors & linker scripts to run on
your
>>> board, or in qemu)
>>> 6B) Install libunwind in your sysroot.
>>> 7) Build libcxx.
>>> 7A) Test libcxx. (use remote executors & linker scripts to run
on
>>> your board, or in qemu)
>>> 7B) Install libcxx in your sysroot.
>>>
>>>
>>> A note on linker scripts: support for them in lld is still a bit
>>> rough around the edges, so you may want to use the linker that
comes
>>> with your board (presumably binutils ld).
>>>
>>>> If you know any doc on how to get clang++ compile for any bare
>>>> metal arm, I'll be glad to RTFM. :o)
>>>
>>> Sorry, I don't have a doc for that. We're getting closer to
making
>>> it work "out of the tin", but it's not there yet. We
(wearing my
>>> CodeSourcery hat) are working on it, but it's going to take
some
>>> time before it "just works" upstream.
>>>
>>>
>>> Jon
>>>
>>>> _______________________________________________
>>>> 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
>>>
>>> -- 
>>> Jon Roelofs
>>> jonathan at codesourcery.com <mailto:jonathan at
codesourcery.com>
>>> CodeSourcery / Mentor Embedded / Siemens
>>> _______________________________________________
>>> 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
>>
>
> -- 
> Jon Roelofs
> jonathan at codesourcery.com
> CodeSourcery / Mentor Embedded / Siemens
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

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