Add README.cross
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Tor Lillqvist
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README.cross
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Cross-compiling LibreOffice
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===========================
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Notes on cross-compiling LibreOffice, written by Tor Lillqvist
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<tlillqvist@novell.com> <tml@iki.fi> in May, 2011.
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Cross-compilation of LibreOffice is not possible yet. Some initial
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work is done, "baby steps", but a lot remains. This work is highly
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experimental and done mostly in my own spare time just for the hacking
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pleasure. No promise, explicit or implied, is given that it will ever
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be finished.
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Searching for information about cross-compilation of OpenOffice.org
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(the predecessor of LibreOffice) you will find information about what
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actually was not cross-compilation, but using QEMU.
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The cross-compilation experimentation is going on for three platforms:
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Windows, iOS and Android. This work is being done on the master branch
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of LibreOffice. Some other people have talked about setting up a
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separate branch for Android work, or even separate clones at github. I
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am not interested in that.
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General
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-------
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In GNU Autoconf terminology, "build" is the platform on which you are
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running a build on some software and "host" is the platform on which
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the software you are building will run. Only in the specific case of
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building compilers and other programming tools is the term "target"
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used to indicate the platform for which the tools your are building
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will produce code. As LibreOffice is not a compiler, the "target" term
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should not be used in the context of cross-compilation.
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(For a case where all three of "build", "host" and "target" are
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different: consider a gcc cross-compiler running on Windows, producing
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code for Android, where the cross-compiler itself was built on
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Linux. (This is a real case.) An interesting tidbit is that such
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configurations are called "Canadian Cross".)
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Even though the LibreOffice build mechanism is highly unorthodox, the
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configure script takes the normal --build and --host options like any
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GNU Autoconf -based configure script. To cross-compile, you basically
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need just to specify a suitable --host option and things should work
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out nicely. In practise, some more details might be needed. See
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examples below.
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What is so hard, then?
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----------------------
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Despite the fact that the configure script takes normal --build and
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--host options, that is just the beginning. In practise a lot of work
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was necessary to separate tests for "host" and "build" platforms in
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the configure script. See the git log for details. And the reasonably
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"standard" configure.in is just the top level; when we get down to the
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actual makefilery used to build the bits of LibreOffice, it gets much
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worse.
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Windows
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-------
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There is some support in LibreOffice already (from OpenOffice.org) for
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building it locally on Windows but with the GNU tool-chain, i.e. what
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is commonly known as MinGW. But as far as I know, that work has never
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attempted cross-compilation.
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This OOo-originated MinGW support attempts to support both running
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Cygwin gcc in its -mno-cygwin mode, and a native MinGW compiler. The
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-mno-cygwin mechanism in the Cygwin gcc is rapidly being obsoleted, if
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it isn't already, and I have not attempted to check that it keeps
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working. Ditto for native MinGW; if one compiles natively on Windows,
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why not use Microsoft's compiler, as OOo/LO has been build for Windows
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all the time using that and it works fine. In my opinion, it makes
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sense to use MinGW only for cross-compilation. (Because of obvious
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benefits like speed improvement, easier automation in systems like the
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openSUSE Build Servce, etc.)
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MinGW is available as cross-build toolchains pre-packaged in more or
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less official packages for many Linux distros including Debian, Fedora
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and openSUSE. Personally I use the mingw32 packages in the openSUSE
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Build Service, running on openSUSE.
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It is somewhat unclear how well thought-out the conditionals and code
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for MinGW inside the LibreOffice code actually is. The little I have
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seen of it seems a bit randomish, with copy-pasting haveing been
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preferred to factoring out differences.
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The autogen.lastrun I use for my MinGW cross-compilation experimentation is:
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CC=ccache i686-w64-mingw32-gcc
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CXX=ccache i686-w64-mingw32-g++
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CC_FOR_BUILD=ccache gcc
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CXX_FOR_BUILD=ccache g++
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--build=x86_64-unknown-linux-gnu
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--host=i686-w64-mingw32
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--with-distro=LibreOfficeWin32
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--disable-build-mozilla
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--disable-ext-nlpsolver
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--disable-ext-pdfimport
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--disable-ext-presenter-console
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--disable-ext-presenter-minimizer
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--disable-ext-report-builder
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--disable-ext-scripting-beanshell
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--disable-ext-scripting-javascript
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--disable-ext-wiki-publisher
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--disable-ext-wiki-publisher
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--disable-mozilla
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--disable-zenity
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--with-external-tar=/mnt/hemulen/ooo/git/master/src
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--with-num-cpus=1
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--with-max-jobs=1
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--with-system-altlinuxhyph
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--with-system-boost
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--with-system-curl
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--with-system-db
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--with-system-expat
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--with-system-hunspell
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--with-system-icu
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--with-system-jpeg
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--with-system-lpsolve
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--with-system-neon
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--with-system-openssl
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--with-system-redland
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--with-system-libwpd
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--with-system-libwps
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--with-system-libwpg
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--with-system-libxml
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--with-system-libxslt
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--with-system-mythes
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--with-system-python
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--with-system-zlib
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--with-vendor=no
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iOS
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---
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iOS is the operating system of Apple's mobile devices. Clearly for a
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device like the iPad it would be totally unacceptable to run a normal
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LibreOffice application with a overlapping windows and mouse-oriented
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GUI widgets. No work has been done (at least publicly) to design a
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touch GUI for LibreOffice, so the work on cross-compiling LibreOffice
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for iOS is extremely experimental, and of course partly pointless;)
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But it is interesting and fun nonetheless.
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Obviously it will make sense to build only a part of LibreOffice's
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code for iOS. Most likely all GUI-oriented code should be left out,
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and some iOS app that eventually wants to use the remaining bits will
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handle all its GUI in a platform-dependent manner. How well it will be
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possible to do such a split remains to be seen. As I said, this is
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highly experimental and just in its baby steps phase.
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Technically, one important special aspect of iOS is that apps are not
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allowed to load own dynamic libraries. (System libraries are used in
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the form of dynamic libraries, just like on MacOSX, of which iOS is a
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variant.) So all the libraries in LibreOffice that normally are shared
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libraries (DLLs on Windows, shared objects (.so) on Linux, dynamic
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libraries on MacOSX (.dylib)) need to be built as static archives
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instead. Obviously this will have some interesting consequences for
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how UNO is implemented and used. None of that has been spared much
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thought yet.
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The Apple tool-chain for iOS cross-building is available only for
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MacOSX, so that is where I have been doing it.
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Here is my autogen.lastrun for iOS:
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CXX=ccache /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/g++-4.2 -arch armv7 -isysroot /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk
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CC=ccache /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc-4.2 -arch armv7 -isysroot /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk
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CC_FOR_BUILD=ccache /Xcode3/usr/bin/gcc-4.0
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CXX_FOR_BUILD=ccache /Xcode3/usr/bin/g++-4.0
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--with-distro=LibreOfficeiOS
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--with-external-tar=/Volumes/ooo/git/master/src
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--with-icu-native-build-root=/Users/tml/lo-macosx/icu/unxmacxi.pro/misc/build/icu/source
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--with-num-cpus=1
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--with-max-jobs=1
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Android
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-------
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I don't know much about Android, but from a technical point of view it
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is a kind of Linux, of course. As far as I know it is allowed for an
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Android app to use shared objects, but if it isn't, then just the same
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approach as used on iOS will need to be used.
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As for the GUI, the same holds as said above for iOS.
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I have done my Android cross-compilation work on Linux (openSUSE in
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particular), but it could as well be done on MacOSX. The Android
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cross-buld tool-chain (the "Native Development Kit", or NDK) is
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available for Linux, MacOSX and Windows. (Trying to cross-compile from
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Windows will probably drive you insane.)
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Here is my autogen.lastrun for Android:
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CC=ccache /home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-gcc --sysroot /home/tml/android-ndk-r5b/platforms/android-9/arch-arm
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CXX=ccache /home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-g++ --sysroot /home/tml/android-ndk-r5b/platforms/android-9/arch-arm
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AR=/home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-ar
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NM=/home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-nm
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OBJDUMP=/home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-objdump
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RANLIB=/home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-ranlib
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STRIP=/home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-strip
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CC_FOR_BUILD=ccache gcc
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CXX_FOR_BUILD=ccache g++
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--build=x86_64-unknown-linux-gnu
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--disable-zenity
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--with-distro=LibreOfficeAndroid
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--with-external-tar=/mnt/hemulen/ooo/git/master/src
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That's all, thank you, and have a nice day. People with commit access,
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feel free to edit this document and add yourself below. Sorry for
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writing now initially from such a personal point of view.
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--Tor Lillqvist <tlillqvist@novell.com>, <tml@iki.fi>
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