Debian PowerPC e500v2 port, part 6

This is part of the Debian PowerPC e500 porting effort, the series on my blog starts at: "How to bootstrap a new Debian port"

Well, after all that work building new packages I figured it was time to see how far I could get at building a chroot filesystem and upgrading it to be current.  I'll be doing all of my work in "/srv/stuff", but you can use any volume you would like with several gigs of free disk space.

The first step is building a chroot with the most recent historical snapshot of the Debian-Ports archive that actually still worked, taken on 2011-04-03, at 00:58:02 GMT.  Note that the "unstable" and "experimental" archives don't include sources (see "omitdebsrc=true" below) as those must only be binary builds of upstream Debian sources.  The "unreleased" archive does include sources, as that is intended for packages which need temporary patches to build.

NOTE: I spent a few hours trying various ways to get the multistrap to pull some packages from the current archives (including my fresh-built stuff), but so much stuff was uninstallable (especially Perl stuff) that I determined it was less work to install an old archive and try to upgrade by hand.

First I created "/srv/stuff/e500chroot.multistrap.conf":
  [General]
  arch=powerpcspe
  directory=/srv/stuff/e500chroot/
  noauth=true
  cleanup=true
  unpack=true
  aptsources=Old-Unstable Old-Experimental Old-Unreleased
  bootstrap=Old-Unstable Old-Experimental Old-Unreleased


  [Old-Unstable]
  packages=build-essential debhelper fakeroot sbuild masqmail
  source=http://snapshot.debian.org/archive/debian/ports/20110403T005802Z/
  suite=unstable
  omitdebsrc=true

  [Old-Experimental]
  packages=
  source=http://snapshot.debian.org/archive/debian/ports/20110403T005802Z/
  suite=experimental
  omitdebsrc=true

  [Old-Unreleased]
  packages=
  source=http://snapshot.debian.org/archive/debian/ports/20110403T005802Z/
  suite=unreleased

Then I wrote "/srv/stuff/setup-e500chroot.sh" to copy QEMU into the chroot before starting the multistrap process:
  #! /bin/sh


  set -e


  CHROOT=/srv/stuff/e500chroot
  MULTISTRAP_CONF=/srv/stuff/e500chroot.multistrap.conf


  install -d "${CHROOT}/usr/bin"
  install -t "${CHROOT}/usr/bin" "/usr/bin/qemu-ppc-static"
  install -d "${CHROOT}/usr/local/bin" "/usr/local/bin/qemu-e500v2-static"


  exec multistrap -f "${MULTISTRAP_CONF}"


I ran my multistrap wrapper script and waited about 5-10 minutes for the download and file extraction to complete.


WARNING: The chroot is NOT DONE YET!!!  It has been unpacked, but none of the packages have been configured yet (with "dpkg --configure -a"), because that needs to be run on the target system.


I tried to do the testing entirely on my amd64 workstation using the the QEMU procedure I described in "Using qemu-user-static to help the Debian e500 bootstrap".  Unfortunately I almost immediately started getting "Illegal instruction" exceptions out of QEMU; it looks like it might be fixed by this patch to qemu-ppc but I don't really feel like trying to rebuild all of QEMU for that.

So I need to get the files onto one of my actual HWW-1U-1A boards.  Fortunately for me, I have an old build of an initramfs (based on busybox and a few other things) which lets me do a very-basic NFS boot.  Unfortunately for anyone trying to do this over again, I don't have the original sources for that initramfs so I can't actually distribute it.  In that situation I strongly recommend formatting a plain old SATA disk with ext4 to do the multistrap onto; then just connect the disk to your hardware.

NOTE: This assumes that you already have an existing kernel you can boot on your hardware (probably from U-Boot) with everything you need built in.  Eventually you will need to switch to a Debian-standard kernel, don't worry about it for now.

Once I finish getting NFS and TFTP working I'll be back with another post.

Cheers,
Kyle Moffett

Using qemu-user-static to help the Debian e500 bootstrap

This is part of the Debian PowerPC e500 porting effort, the series on my blog starts at: "How to bootstrap a new Debian port"

I was trying to figure out an easy way to do basic testing without directly having access to the hardware and I discovered that QEMU supports several MPC85xx processor variants for its user-mode emulation.  The standard "qemu-user-static" package even allows you to trivially run non-native programs (either in a chroot or on your normal system) without much complexity.

Unfortunately, I could not figure out any way to convince QEMU to pick the right CPU type by default, especially since there might not be any reasonable config files in the chroot.  The solution ended up being to add a second binary alongside the normal "/usr/bin/qemu-ppc-static" file.  I wrote the following short little C program:

  #include <stdlib.h>
  #include <unistd.h>


  #define QEMU_BIN "/usr/bin/qemu-ppc-static"
  #define CPU_TYPE "MPC8548E_v21"


  int main(int argc, char **argv, char **envp)
  {
          int i;


          char **newargv = malloc(sizeof(*newargv) * (argc + 3));
          if (newargv) {
                  newargv[0] = QEMU_BIN;
                  newargv[1] = "-cpu";
                  newargv[2] = CPU_TYPE;
                  for (i = 1; i < argc; i++)
                          newargv[i + 2] = argv[i];
                  execve(QEMU_BIN, newargv, envp);
          }
          exit(255);
  }


Then I compiled it like this and put it in /usr/local/bin: (UPDATE: Fixed options for static compile)
  $ gcc -static -Wall -Wextra -Werror -ggdb3 -o qemu-e500v2-static qemu-e500v2-static.c
  $ sudo install qemu-e500v2-static /usr/local/bin/


Next I installed the Debian package "qemu-user-static" on my dev system and disabled the previously-loaded PPC support: (UPDATE: Diverted somewhere the init script won't find it)
  $ sudo aptitude install qemu-user-static binfmt-support
  $ sudo update-binfmts --package qemu-user-static \
            --remove qemu-ppc /usr/bin/qemu-ppc-static
  $ sudo dpkg-divert --divert /usr/share/binfmt.diverted.qemu-ppc \
            --local --rename --add /usr/share/binfmts/qemu-ppc


Then I needed to modify the existing PPC handler for e500v2 (and my custom C program)
  $ cp /usr/share/binfmt.diverted.qemu-ppc ~/qemu-e500v2.binfmt
  $ vim ~/qemu-e500v2.binfmt

The resulting file should look somewhat like this (the flags/offset/magic/mask are unmodified from the original):

  package <local>

  interpreter /usr/local/bin/qemu-e500v2-static

  flags: OC

  offset: 0

  magic \x7fELF......stuff....

  mask \xff\xff\xff\xff.........stuff.....

Then you just need to load your new version and off you go:
  $ sudo update-binfmts --import ~/qemu-e500v2.binfmt
  $ LD_LIBRARY_PATH=/usr/powerpc-linux-gnuspe/lib \
            /usr/powerpc-linux-gnuspe/lib/ld.so.1
  Usage: ld.so [OPTION]... EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]
  [...]


With the rest of the multiarch support slowly going into Debian, this seems extremely promising to me for being able to avoid a lot of the classic cross-build hassle by doing pretend-native builds with a cross-compiler and a bunch of native headers and other tools.  Eventually you will also be able to have a native-architecture-only chroot with only those two binaries (the qemu-e500v2-static and the qemu-ppc-static) in it.

Unfortunately not enough of multiarch is working yet to really make it 100% feasible, but it should at least allow me to work around many of the egregious cross-compiling bugs by actually being able to run the compiled binaries locally.

On the other hand, if my goal was instead to actually identify and fix such cross-compiling bugs, then I would probably need to disable the qemu binfmt lest I get falsely successful builds.

The more likely use-case is that I will use this to perform some basic testing of my freshly built packages when I don't have direct hardware access.

Cheers,
Kyle Moffett