Q: How do I add $PACKAGE to my system image's root filesystem?
Q: I added my uClibc patch to sources/patches but it didn't do anything, what's wrong?
The project provides development and test environments for lots of different hardware platforms, based on busybox and uClibc and configured to run under QEMU.
Most people want to do one of three things:
Download a prebuilt system image, boot it up under the emulator, and compile stuff natively for a target.
Go here and download the appropriate system-image-$ARCH.tar.bz2 for your $TARGET, extract it, cd into it, and ./run-emulator.sh to boot it under qemu.
Alternately, you can run the script ./development-environment.sh, which is a wrapper around run-emulator.sh that feeds QEMU extra options to add memory (256 megs) and writeable disk space (a blank 2 gigabyte disk image mounted on /home) to provide a more capable development environment.
The system images contain native compiler toolchains, but if you install distccd on the host and add the appropriate cross compiler to your host's $PATH, the ./run-emulator.sh script will detect this and set up the system image to automatically use distcc to call out to the cross compiler through the virtual network, speeding up native builds significantly.
Build your own cross compilers and system images from source, using the build scripts.
Go to the downloads directory, grab the most recent release tarball, extract it, and run ./build.sh to list the available targets. The run ./build.sh $TARGET to compile the one you like. The results wind up in the "build" directory.
The build scripts are written in bash, and fairly extensively commented. All the scripts at the top level are designed to be run directly, and build.sh is just a wrapper script that calls them in order. The less commonly used scripts in sources/more are also designed to be run directly.
A large number of variables can be set to configure the build, either by modifying the file "config" (which documents them all) or by exporting them as environment variables.
To grab the latest development version of the build scripts out of the source control system, go to the mercurial archive. If you don't want to install mercurial, you can grab a tarball of the current code at any time.
Download a prebuilt cross compiler and cross-compile stuff with it.
Go here and download the appropriate cross-compiler-$TARGET.tar.bz2 for your $TARGET, extract it, add its "bin" directory to your $PATH, and use the appropriate $TARGET-cc and $TARGET-ld and so on to compile your program. (The tool names have prefixes so they can be in the same $PATH as your host's existing compiler.)
If all else fails, look at the pretty screenshots.
A: Yup. The name changed shortly before the 1.0 release in 2010.
If you're really bored, there's a page on the history of the project, which includes the rationale for the name change.
A: Use the rw-system-image instead of the system-image. This gives you a writeable root filesystem with enough extra space to install your package in.
FWL builds squashfs images by default, and the prebuilt binary tarballs in the downloads/binaries directory are built with the default values. Squashfs is a read-only compressed filesystem, which means it's pretty durable (you never need to fsck it), but also a bit limiting. The dev-environment.sh script attaches a 2 gigabyte ext2 image to /dev/hdb (which is mounted on /home) so you always have writeable space to build stuff in, but that doesn't let you modify the root filesystem on /dev/hda: you can't install packages you build into /bin and such on a read-only root filesystem.
The "SYSIMAGE_TYPE" and "SYSIMAGE_HDA_MEGS" config entries let you change the default system image type generated by the system-image.sh script. You can edit the file "config" or specify them as environment variables, ala:
SYSIMAGE_TYPE=ext2 SYSIMAGE_HDA_MEGS=2048 ./build.sh $TARGET
That creates a 2 gigabyte ext2 image, which you can boot into and install packages natively under, using the "./run-from-build.sh $TARGET" script. If you've already built a system image, you can repackage the existing root filesystem by just running system-image.sh (instead of the whole build.sh). As always, your new system image is created in the "build" subdirectory.
Note: since this is a writeable image, you'll have to fsck it. You can also use "tune2fs -j" to turn it into an ext3 image.
(You can also use the BUILD_RW_SYSTEM_IMAGE environment variable, which tells build.sh to package the system image two ways, creating a rw-system-image tarball with the above options.)
A: You're using Ubuntu, aren't you? You need to install "qemu-kvm-extras" to get the non-x86 targets.
The Ubuntu developers have packaged qemu in an actively
misleading "interesting" way. They've confused the emulator QEMU
with the virtualizer KVM.
QEMU is an emulator that supports multiple hardware targets, translating the target code into host code a page at a time. KVM stands for Kernel Virtualization Module, a kernel module which allows newer x86 chips with support for the "VT" extension to run x86 code in a virtual container.
The KVM project started life as a fork of QEMU (replacing QEMU's CPU emulation with a kernel module providing VT virtualization support, but using QEMU's device emulation for I/O), but KVM only ever offered a small subset of the functionality of QEMU, and current versions of QEMU have merged KVM support into the base package. (QEMU 0.11.0 can automatically detect and use the KVM module as an accelerator, where appropriate.)
It's a bit like the X11 project providing a "drm" module (for 3D acceleration and such), which was integrated upstream into the Linux kernel. The Linux kernel was never part of the X11 project, and vice versa, and pretending the two projects were the same thing would be wrong.
That said, on Ubuntu the "qemu" package is an alias for "qemu-kvm", a package which only supports i386 and x86_64 (because that's all KVM supports when running on an x86 PC). In order to install the rest of qemu (support for emulating arm, mips, powerpc, sh4, and so on), you need to install the "qemu-kvm-extras" package (which despite the name has nothing whatsoever to do with KVM).
Support for non-x86 targets is part of the base package when you build QEMU from source. If you ignore Ubuntu's packaging insanity and build QEMU from source, you shouldn't have to worry about this strangely named artificial split.
The Linux filesystem is case sensitive, so the patch has to start with "uClibc-" with a capital C.
Because you skipped the host-tools.sh step, and because installing a package on the host isn't the same as installing it on the target.
Even though host-tools.sh is technically an optional step, your host has to be carefully set up to work without it.
Not only does host-tools.sh add prerequisite packages your build requires, it _removes_ everything else from the path that might change the behavior of the build. Without this, the ./configure stages of various packages will detect that libtool exists, or that the host has Python or Perl installed, and configure the packages to make use of things that the cross compiler's headers and libraries don't have, and that the target root filesystem may not have installed.