Re: Cross-building and debugging

[Baurzhan Ismagulov <ibr@radix50.net>]

Hello Andrea,

On Mon, Oct 30, 2017 at 01:34:19AM -0700, andrea.marson.dave@gmail.com wrote:
> IIUC, when using Isar it is implicitly assumed that the user applications 
> are natively built on the target.

The current implementation builds user applications natively in buildchroot
using qemu on the host. This was a customer requirement to avoid having to
tweak Debian packages which one may happen to want to rebuild and which don't
support cross-building.

That said, Isar's predecessor is based on cross-building, which is state of the
art in Emdebian and has its advantages in certain use cases.


> If, for any reason, this is not possibile, one has to cross-build the 
> applications.
> Which approach do you recommend to set up the cross-build environment, in 
> order to make it work smoothly with Isar?

Basically, it worked like this:

1. Install cross-toolchain (e.g., gcc-arm-linux-gnueabihf) into buildchroot.

2. Modify the package's debian/rules for cross-building (e.g., pass the right
   --host=arm-linux-gnueabihf to ./configure).

3. Cross-build (e.g., call dpkg-buildpackage with --arch=arm or similar).

I don't remember the details, so the quotations above are not literal.

There is a branch
https://github.com/ilbers/isar/tree/lenormf/develop-l20170602-dpkg-cross which
should support cross-building. We plan to refine it and propose for
integration into master.

Till then, you might use the current qemu approach or look at the branch above
(will probably require some hacking). If you can share your use case, maybe we
could suggest something. E.g., GLIB doesn't cross-compile out of the box due to
configure failing to run test programs for the target; supplying the test
results to configure pre-canned in a file makes it happy.


With kind regards,
Baurzhan.