This project contains scripts and patches to cross compile and package packages for
the [Termux](http://termux.com/) Android application.
Overview
========
In a non-rooted Android device an app such as Termux may not write to system locations,
which is why every package is installed inside the private file area of the Termux app:
PREFIX=/data/data/com.termux/files/usr
For simplicity while developing and building, the build scripts here assume that a /data
folder is reserved for use on the host builder, which requires setup:
sudo mkdir /data
sudo chown $USER /data
The basic flow is then to run "./build-package.sh $PKG", which
- Sets up a patched stand-alone Android NDK toolchain
- Reads packages/$PKG/build.sh to find out where to find the source code of the
package and how to build it.
- Applies all patches in packages/$PKG/\*.patch
- Builds the package and installs it to $PREFIX
- Packages the package in one or more .dpkg files for distribution
Reading and following build-package.sh is the best way to understand what's going on here.
Additional utilities are contained here:
- build-all.sh, used for building all packages in the correct order (using buildorder.py)
- check-pie.sh, used for verifying that all binaries are using PIE, which is required for Android 5+
- check-versions.sh, used for checking for package updates
- clean-rebuild-all.sh, used for doing a clean rebuild of all packages (takes a couple of hours)
- list-packages.sh, used for listing all packages with a one-line summary
Resources about cross-compiling packages
========================================
* [Linux From Scratch](http://www.linuxfromscratch.org/blfs/view/svn/index.html)
* [Beyond Linux From Scratch](http://www.linuxfromscratch.org/blfs/view/svn/)
* [Cross-Compiled Linux From Scratch](http://cross-lfs.org/view/svn/x86_64-64/)
* [OpenWrt](https://openwrt.org/), an embedded Linx distribution, contains [patches and build scripts](https://dev.openwrt.org/browser/packages)
* http://dan.drown.org/android contains [patches for cross-compiling to Android](http://dan.drown.org/android/src/) as well as [work notes](http://dan.drown.org/android/worknotes.html), including a modified dynamic linker to avoid messing with LD_LIBRARY_PATH.
* [CCTools](http://cctools.info/index.php?title=Main_Page) is an Android native IDE containing [patches for several programs](https://code.google.com/p/cctools/source/browse/#svn%2Ftrunk%2Fcctools-repo%2Fpatches) and [a bug tracker](https://code.google.com/p/cctools/issues/list).
* [BotBrew](http://botbrew.com/) was a package manager for rooted devices with [sources on github](https://github.com/jyio/botbrew). Based on opkg and was transitioning to apt.
* [Kivy recipes](https://github.com/kivy/python-for-android/tree/master/recipes) contains recipes for building packages for Android.
Common porting problems
=======================
* The Android bionic libc does not have iconv and gettext/libintl functionality built in. A package from the NDK, libandroid-support,
contains these and may be used by all packages.
* "error: z: no archive symbol table (run ranlib)" usually means that the build machines libz is used instead of the one for cross compilation, due to the builder library -L path being setup incorrectly
* rindex(3) is defined in <strings.h> but does not exist in NDK, but strrchr(3) from <string.h> is preferred anyway
*<sys/termios.h> does not exist, but <termios.h> is the standard location.
*<sys/fcntl.h> does not exist, but <fcntl.h> is the standard location.
* glob(3) system function (glob.h) - not in bionic, but use the libglob package
* undefined reference to 'rpl_malloc' and/or 'rpl_realloc': These functions are added by some autoconf setups
when it fails to detect 0-safe malloc and realloc during cross-compilating. Avoided by defining
1. They are not preprocessor #define:s so cannot be checked for with #ifdef RTLD_GLOBAL (dln.c in ruby does this)
2. They differ in value from glibc ones, so cannot be hardcoded in files (DLFCN.py in python does this)
3. They are missing some values (RTLD_BINDING_MASK, RTLD_NOLOAD, ...)
RPATH, LD_LIBRARY_PATH AND RUNPATH
==================================
On desktop linux the linker searches for shared libraries in:
1. RPATH - a list of directories which is linked into the executable, supported on most UNIX systems. It is ignored if RUNPATH is present.
2. LD_LIBRARY_PATH - an environment variable which holds a list of directories
3. RUNPATH - same as RPATH, but searched after LD_LIBRARY_PATH, supported only on most recent UNIX systems, e.g. on most current Linux systems
The Android linker (/system/bin/linker) does not support RPATH or RUNPATH, so we set LD_LIBRARY_PATH=$USR/lib and try to avoid building
useless rpath entries with --disable-rpath configure flags.
Another option to avoid depending on LD_LIBRARY_PATH would be supplying a custom linker - this is not done due to the overhead of maintaining a custom linker.
Warnings about unused DT entries
================================
Starting from 5.1 the Android linker warns about VERNEED (0x6FFFFFFE) and VERNEEDNUM (0x6FFFFFFF) ELF dynamic sections:
WARNING: linker: $BINARY: unused DT entry: type 0x6ffffffe arg ...
WARNING: linker: $BINARY: unused DT entry: type 0x6fffffff arg ...
These may come from version scripts in a Makefile such as:
