For most people the best way to obtain an environment for building packages is by using Docker. This should work everywhere Docker is supported (replace `/` with `\` if using Windows) and ensures an up to date build environment that is tested by other package builders.
Note that building packages can take up a lot of space (especially if `build-all.sh` is used to build all packages) and you may need to [increase the base device size](http://www.projectatomic.io/blog/2016/03/daemon_option_basedevicesize/) if running with a storage driver using a small base size of 10 GB.
Build environment without Docker
================================
If you can't run Docker you can use a Ubuntu 16.10 installation (either by installing a virtual maching guest or on direct hardware) by using the below scripts:
- Run `scripts/setup-ubuntu.sh` to install required packages and setup the `/data/` folder.
- Run `scripts/setup-android-sdk.sh` to install the Android SDK and NDK at `$HOME/lib/android-{sdk,ndk}`.
There is also a [Vagrantfile](scripts/Vagrantfile) available as a shortcut for setting up an Ubuntu installation with the above steps applied.
* The Android bionic libc does not have iconv and gettext/libintl functionality built in. A `libandroid-support` package 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
* SYSV shared memory is not supported by the kernel. A `libandroid-shmem` package, which emulates SYSV shared memory on top of the [ashmem](http://elinux.org/Android_Kernel_Features#ashmem) shared memory system, is available. Use it with `LDFLAGS+=" -landroid-shmem`.
1. They are not preprocessor #define:s so cannot be checked for with `#ifdef RTLD_GLOBAL`. Termux patches this to #define values for compatibility with several packages.
The Android dynamic linker is located at `/system/bin/linker` (32-bit) or `/system/bin/linker64` (64-bit). Here are source links to different versions of the linker:
- The linker warns about unused [dynamic section entries](https://docs.oracle.com/cd/E23824_01/html/819-0690/chapter6-42444.html) with a `WARNING: linker: $BINARY: unused DT entry: type ${VALUE_OF_d_tag}` message.
- The supported types of dynamic section entries has increased over time.
- The Termux build system uses [termux-elf-cleaner](https://github.com/termux/termux-elf-cleaner) to strip away unused ELF entries causing the above mentioned linker warnings.
- Symbol versioning is supported only as of Android 6.0, so is stripped away.
-`DT_RPATH`, the list of directories where the linker should look for shared libraries, is not supported, so is stripped away.
-`DT_RUNPATH`, the same as above but looked at after `LD_LIBRARY_PATH`, is supported only from Android 7.0, so is stripped away.
- Symbol visibility when opening shared libraries using `dlopen()` works differently. On a normal linker, when an executable linking against a shared library libA dlopen():s another shared library libB, the symbols of libA are exposed to libB without libB needing to link against libA explicitly. This does not work with the Android linker, which can break plug-in systems where the main executable dlopen():s a plug-in which doesn't explicitly link against some shared libraries already linked to by the executable. See [the relevant NDK issue](https://github.com/android-ndk/ndk/issues/201) for more information.
