From d21a861def3e196110acbd5463f6eca6b27fd142 Mon Sep 17 00:00:00 2001 From: codehelp Date: Tue, 1 Jun 2010 08:12:06 +0000 Subject: [PATCH] This README will be better off in pdebuild-cross. git-svn-id: http://emdebian.org/svn/current@7262 563faec7-e20c-0410-992a-a66f704d0ccd --- README | 115 --------------------------------------------------------- 1 file changed, 115 deletions(-) delete mode 100644 README diff --git a/README b/README deleted file mode 100644 index db1d2b5..0000000 --- a/README +++ /dev/null @@ -1,115 +0,0 @@ - Emdebian Bootstrapping - ====================== - -Cross-building can get very confusing at times. The confusion only increases -when dealing with a chroot. This document tries to cover some of the reasons, -some of the problems and tries to provide some clarity, at least as far as how -chroots can be used in Emdebian. - -There are multiple ways that Emdebian can relate to bootstrapping and chroots. -The most common method of using a chroot within Debian is pbuilder and the -pdebuild wrapper and this is the primary inspiration for using chroots in -Emdebian. Other methods revolve around QEMU or scratchbox and whilst this code -may be able to support such uses later, there are key differences in how and -why this method is separate. - -EMDEBIAN PBUILDER CHROOT MODEL -============================== - -The Debian pbuilder package exists to ensure package dependencies are complete -and to provide an environment to automate package building on all supported -Debian architectures without cluttering the build machine with every library -and dev package in the entire archive. This is particularly useful when -building GUI packages that can have two dozen dependencies or more. In -Emdebian, this separation between the build system packages and the chroot -packages becomes even more useful because cross-building often involves not -only installing the library and -dev package for the build architecture (e.g. -i386/amd64) but also building and installing the same library and -dev package -(with dependencies) in the TARGET architecture, e.g. arm, with apt-cross and -dpkg-cross. The chaos that could result from trying to upgrade the packages on -an Emdebian buildd system with a duplicate set of cross dependencies is truly -scary. - -In the pbuilder model, an Emdebian chroot is the SAME architecture as the -buildd - i386 on i386 etc. This mimics how emdebian-tools normally work. -Packages are then downloaded, patched and cross-built for the target -architecture, just as outside the chroot. This model, the pbuilder model of an -emdebian chroot, concentrates on dependencies rather than the actual -cross-building process. Inside such a chroot, cache files are used as normal to -avoid having to run the cross-compiled code during the build. - -The Emdebian chroot is similar in size to a normal Debian pbuilder chroot, -mainly because it is a full build environment, not an installation environment. - -This directory contains my experiments with debootstrap, using this pbuilder -model, trying to make a complete Emdebian cross-building environment that can -be compressed to a base.tgz. Changes to the chroot can be discarded, just as -with pbuilder, allowing dependencies to be tested. The main benefit is that -packages can be built without having to install long chains of cross -dependencies via apt-cross or dpkg-cross on the main system. To me, it's the -only way to cross-build GUI suites like GPE against a background of changing -dependencies. - -In the pbuilder model, Emdebian builds a chroot for the build architecture -(amd64/i386 etc.) - except that it will run emdebian-tools instead of pbuilder -to create the arm binaries (or whichever architecture is the dpkg-cross -default). I expect the same code to work for arm chroots on amd64 etc, but -mechanisms already exist for those so it's not the priority. - -In order to make best use of the existing pbuilder code, these are shell scripts -whereas the rest of emdebian-tools uses perl. - -DEPENDENCIES ------------- - -To emdebianise and cross-build packages, the chroot needs to install -emdebian-tools. This brings in the majority of dependencies to support building -Debian and Emdebian packages. This (current sample) code uses part of the -pbuilder source so that the eventual chroots behave as similarly as possible to -pbuilder and pdebuild in Debian. Therefore, the emdebian pbuilder chroot is NOT -designed or intended to be installed on any embedded device - it is intended for -cross-building packages for Emdebian only. See the SLIND installer for more -information or the emsandbox script in emdebian-tools. - -empdebuild depends on pbuilder and installing emdebian-tools within a chroot -causes pbuilder to be installed inside the chroot. Whilst empdebuild and emsandbox -could be split out into a separate package to prevent pbuilder being needed inside -the chroot, there are corner cases where this can be useful providing sufficient -care is taken. - -DIFFERENCES TO PBUILDER ------------------------ - -1. emdebian-tools handles the 'installaptlines' subroutine. -2. emdebian-tools dependencies handle the installation of build-essential dpkg-dev - and apt that pbuilder normally does separately. -3. emdebian-tools handles the BUILDPLACE via debconf. -4. Other embootstrap options are hardcoded - BUILDRESULT is placed in BUILDPLACE, - APTCACHE also and APTCACHEHARDLINK is set to yes. -5. emdebian-tools provides the emdebianised source package and patches. - -EMDEBIAN NATIVE CHROOT MODEL -============================ - -The same code should also be able to create a native chroot so that the -cross-built packages can be installed alongside each other for more testing. -These chroots have already been tested and instructions exist in the Wiki: -http://wiki.debian.org/EmDebian/CrossDebootstrap - -Trying to cross-build inside scratchbox limits you to where scratchbox will -install which is only certain architectures. emdebian-tools is about -cross-building Debian packages using normal Debian tools on a normal Debian -system. Emdebian and emdebian-tools are designed to make building inside -scratchbox redundant because it simply isn't sufficiently flexible. A -scratchbox2 has been mooted but nothing has happened yet. - -Cross-build using normal tools (maybe using the chroot as above) and then test -either on a native device or via scratchbox if you really have to. - -An Emdebian native chroot would be an arm chroot running on an amd64 system - -indeed it would need to support creation of a chroot *for* any supported Debian -architecture and be able to create and run that chroot *on* any supported -Debian architecture. - -This is only the first draft - if there are areas that need further clarification -or updating, please email the debian-embedded mailing list.