Re: [gentoo-alt] Re: Ideas for this year's Google Summer of Code

[Ruud Koolen]

On Monday 08 April 2013 06:26:07 heroxbd wrote:
> redlizard's gentoo-prefix-libc was tried out and I have revised the
> proposal based on the trial.
>
>     http://www.awa.tohoku.ac.jp/~benda/projects/android.html
>
> Details of how glibc is included in Gentoo Prefix are discussed. A new
> section of bootstraping by cross-compilation is added.
>
> Yours,
> Benda

Nice. A few comments:

> Though we could patch gcc headers to redefine the default standard run time
> linker location, the same ld-wrapper mechanism can be used to inject things
> like "–dynamic-linker=${EPREFIX}/lib/ld-linux.so.2". The latter solution
> will make switching between rpath and prefix-libc variants of Gentoo Prefix
> easier.

Note that gentoo-prefix-libc also has different settings on the compiler 
itself, like not having /usr/include in the default include path. Switching 
linker configurations will not change that.

> It could be hard to bootstrap Gentoo Prefix on Android. One possible way is
> to install a native full distribution and then bootstrap a Gentoo Prefix
> with libc. We could distribute precompiled Gentoo Prefix on Google Play for
> the general public.

Zero_Chaos bootstrapped his install by first unpacking a plain gentoo tarball 
into a chroot, and bootstrapping prefix(-libc) from within that chroot. 
Afterwards, the prefix install could be moved out of the chroot.

> redlizard's gentoo-prefix-libc has cross bootstraping in mind, with the hope
> of running uclibc-based Gentoo Prefix on Android. The details, however,
> still call for much effort.

While the local-libc architecture allows for arbitrary cross compilation 
bootstraps, the current gentoo-prefix-libc bootstrap script only works for 
cross compilations to architectures runtime compatible with the host -- amd64 
to x86, arm hardfp to arm softfp, etc. In other words, the host processor 
should still be able to run the target executables. This can be changed to 
support real cross compilation, but this will probably be a nontrivial 
addition.

> It would be very nice if crossdev could produce cross toolchain in Gentoo
> Prefix by a single command.

I tried the same, and accomplishing this would make the bootstrap process a 
whole lot easier. It would basically reduce the bootstrap-prefix.sh process 
to:

- Manually bootstrap stage1 tools into some temporary directory 
(${EPREFIX}/tmp).
- Manually bootstrap portage into ${EPREFIX}/tmp (!).
- Manually bootstrap crossdev into ${EPREFIX}/tmp.
- Use crossdev to build a cross compiler that targets the desired architecture 
(which need not be runtime-compatible with the host architecture!)
- env PORTAGE_OVERRIDE_EPREFIX=${EPREFIX} emerge -e @system.

-- Ruud