Changing my toolchain architecture (in gentoo)

Question

This is somewhat gentoo-specific, so I'll explain it in that context, then try to abstract it to a generic linux machine.

I accidently set my CHOST to "i686-pc-linux-gnu" in the beginning, not paying attention, when my machine is a Athlon64. I would like to change it to "x86_64-pc-linux-gnu". There is a guide for this. It doesn't work.

The first step is "Recompile binutils, then recompile gcc"

Here's the problem illustrated:

1. Compile binutils using gcc - this succeeds producing new as, ar, and the like files
2. This breaks gcc. gcc is now trying to use the new /usr/bin/as - but it can't work with them
3. Since gcc can't compile anything, I can't compile gcc. I have to revert as, ar, etc; then revert the CHOST change, and recompile binutils.

So I tried the following:

1. back up as, ar, etc
2. Compile binutils, rendering gcc inoperabe
3. link ar, as, etc to the old versions I backed up
4. try to compile gcc

The gcc compile fails with:

/usr/x86_64-pc-linux-gnu/bin/ld: skipping incompatible /usr/lib/libc.so when searching for -lc
/usr/x86_64-pc-linux-gnu/bin/ld: skipping incompatible /usr/lib/libc.a when searching for -lc
/usr/x86_64-pc-linux-gnu/bin/ld: cannot find -lc
collect2: ld returned 1 exit status

This is a glibc error (completing the chain).

So it seems:

1. for gcc to compile it has a dependency on the new version glibc
2. for gcc to run, binutils must be the older version

The steps I haven't tried, because it's so complicated I wanted to get opinions first, are:

1. compile binutils under new architecture,
2. relink as, ar, etc to old executables
3. compile new glibc with old-gcc and old-binutils
4. compile new-gcc with old-gcc and old-binutils but new-glibc
5. relink as, ars, etc to new-binutils
6. recompile everything like a boss

Is there any chance of #4 above working? Do I have any hope of accomplishing this without a complete reinstall?

Answer 1

As far as I know it is not possible. Please remember that toolchain does not exist in vaccum and is interlinked.

What might work is to build cross-compiler of new infrastructure but I really doubt it - the "atomicity" on update of glibc will break everything.

I would advice backup & reinstall of system.

Answer 2

Have you tried downloading the amd64 stage3 tarball and using the copy of gcc with that?

Answer 3

If your kernel is 64-bit (and so you can run 64-bit binaries), you can start a new x86_64 Gentoo install in a chroot, following the usual instructions. I've done similar before — effectively a reinstall, but while still running the old system. If you don't have a spare block device to install to, you can use a subdirectory and either boot with init=chroot\040/new\040/bin/sinit or drop down to a minimal environment to shuffle directories around.

If your kernel is 32-bit, find a 64-bit kernel or build a cross-compiler to 64-bit to build a 64-bit kernel, boot it, then see above.