CuBox-i: compile+install on laptop then move system on SD

[Matte88]

Hi all!

I just received from SoliRun a CuBox-i4Pro and I found this wiki entry: http://wiki.gentoo.org/wiki/Cubox-i

Is there a way to install Gentoo on laptop's hdd, compiling locally in my laptop (Intel 2nd gen i3) using the power of its CPU and then simply move the whole installed system on the SD card and then boot the Cubox?

Asking this because:
a) I want to speed up the whole process using the much powered CPU of my laptop instead of the CuBOX CPU;
b) read/write operations on SD card reduced at minimum

Thanks!
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[Hu]

If the CuBox had a compatible CPU, this would be as easy as installing a chroot. Since it does not, you will need to cross-compile all the relevant packages and install them into a separate area on the host. Some packages do not cross-compile easily or at all.

[Matte88]

So... The ARM on which I'd like having Gentoo running is this the CuBox-i4Pro http://www.solid-run.com/products/cubox-i-mini-computer/cubox-i-specifications/.

Can you please tell me something about this cross-compiling and what are the "risks" of packages that couldn't be installed at all?

I read something about on internet and I also found this link: http://landley.net/aboriginal/presentation.html but I think I didn't understand cross-compiling at all...
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[Hu]

Some packages have badly designed build systems that assume they can use the same compiler both to build the code to be installed and to build helpers that are run during the build. Such systems fail when cross-compiling because the code to be installed and the code to run during the build require different CPU architectures. Generally, if the cross-compile build completes successfully, then the resulting code should run correctly.

[Matte88]

Just a little update of my working in progress now (on my host, I set "~amd64" globally).
W A R N I N G: the post DOESN'T give you instructions to get the work done; I'm working on it.

So, one could start from the wiki: https://wiki.gentoo.org/wiki/Cubox-i.

Knowing the fact I'm a total n00b, I'll write here some steps that I discovered they are needed (but not written in the wiki).

https://wiki.gentoo.org/wiki/Cubox-i#Installing_Crossdev:

[NeddySeagoon]

Matte88,

Pure cross compiling is fairly broken. Hu has told you why.

When you ran crossdev to generate your cross toolchain you got a free /usr/<target> which is an empty gentoo root directory for four target.
In theory you can run emerge-wrapper, set make.conf in /usr/<target> then cross compile whatever you want into /usr/<target>.
Eventually you write /usr/<target> to / on your SD card and everything justworks.

Messing about with assorted Raspberry Pis, I've found that the path of least resistance is cross distcc.
This is where your arm board does some of the building but much of the hard work is done by a more powerful system.

There is another usually slower alternative. QEMU can emulate your arm CPU.
On your laptop, you put the arm stage3 into /usr/<target> (don't mess that up). Now you can chroot into /usr/<target> (where the arm code is) and QEMU will emulate your arm CPU in software and execute the arm code ... on your AMD/Intel laptop.
The drawback is that software emulation of a CPU is slow.

I've glossed over that a little but its documented on the wiki.
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Regards,

NeddySeagoon

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