August 02
On Wednesday, 2 August 2017 at 21:39:00 UTC, Oleg B wrote:
> On Wednesday, 2 August 2017 at 03:28:48 UTC, Joakim wrote:
> Thank you! I found -L/usr/lib64 switch in /etc/ldc2.conf. In .ldc/ldc2.conf I configure build for arm and it's work!

Great!

> Question about it: why '.ldc'? Why not '.config/' dir?

No idea, maybe that should be updated.

>> See this previous post for an example:
>>
>> http://forum.dlang.org/post/skdqeursuheqdsermmwh@forum.dlang.org
>
> Cool! But I don't understand how it use through dub. Dub don't know about any arch expect x86(_64). If add dflags "-march=arm" or something like this in dub.sdl it applies only for building package, not for dependencies. Building without dub is some painful for me and it's not useful to change .ldc/ldc2.conf when need arm and when need x86... Maybe I do something wrong?

So you want to compile dub packages for ARM using a ldc cross-compiler on x86?  While dub works fine natively on ARM, I don't think it supports switching back and forth between natively compiling and cross-compiling yet.  You may be able to configure it another way by writing a config file at ~/.dub/settings.json, like this:
{
    "defaultCompiler" : "/home/oleg/ldc-arm-cross/bin/ldc2"
}

This would need to be an ldc cross-compiler with the armhf triple enabled by default, ie you'd have to compile llvm with that default triple.  Then, when you want to compile for x86, simply change the defaultCompiler or move the settings.json.

I think this should trick dub into cross-compiling everything for ARM, but I've never tried it.  The alternative might be patching dub so that you could use the same ldc build for both native and cross-compilation, rather than swapping out two different compilers like this.

>> We're working on making it much simpler to cross-compile the stdlib for the next ldc 1.4 beta, see kinke's latest patch here:
>>
>> https://github.com/ldc-developers/ldc/pull/2253
>
> I'm looking forward to full cross-building. It's plained? Or always be need external cross-linker?

There has been some work on integrating lld, the llvm linker, but I don't know if we'll ever ship it, so maybe it'll always require getting that.

>> I'm not sure how well your approach will work, as the ldc 1.4 stdlib may not work with ldc 1.3.  I'll be submitting a PR soon that should make it even easier, so you may want to wait for the next 1.4 beta instead.
>
> Can't wait 1.4 beta, business does not wait =)

In that case, you can follow the instructions here for Android/ARM, but modify them for linux/armhf to create your own cross-compiler:

https://wiki.dlang.org/Build_LDC_for_Android

Don't use that llvm patch for Android, but use the llvm default triple you need for your arm board.  You will have to change the C flags from the ldc patch for your platform, but don't need the rest of it.  You don't have to checkout the 1.3 branch, if you want 1.4, and no need for the Phobos patch.  If you want to build the test runners, no need for the druntime test runner patch, though one test in std.random will likely fail for you.

If you want to make it easier to use the ldc toolchain for cross-compiling, you may want to engage kinke or one of the other ldc devs in some consulting work, as I believe they do similar consulting work for Weka.io.
August 03
On Wednesday, 2 August 2017 at 21:39:00 UTC, Oleg B wrote:
> But I don't understand how it use through dub. Dub don't know about any arch expect x86(_64). If add dflags "-march=arm" or something like this in dub.sdl it applies only for building package, not for dependencies. Building without dub is some painful for me and it's not useful to change .ldc/ldc2.conf when need arm and when need x86... Maybe I do something wrong?

The currently intended way is to augment your LDC config file on a per-triple basis. See step 4 in https://github.com/ldc-developers/ldc/pull/2142#issuecomment-304472412. Use `ldc2 -mtriple=... -v` to check the real triple (displayed in the config line), in your case probably `arm--linux-gnueabihf`, and add a config file section for it, by copying the default section and tweaking the lib directories. Specifying a compatible `-mtriple` in the LDC command line is then enough.
I don't use dub, so I don't know what's missing for full cross-compilation support.

> I'm looking forward to full cross-building. It's plained? Or always be need external cross-linker?

It's already built-in for Windows MSVC targets since LDC v1.3 (`-link-internally` switch). I opened a PR to integrate LLD for ELF and Mach-O targets as well: https://github.com/ldc-developers/ldc/pull/2203. It's completely untested, so guys like you experimenting with it are very welcome. Needs LLVM >= 5.0 incl. LLD.
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