This directory contains a number of shell scripts, which we will
call the "dev-scripts", that are only used to develop the NDK
itself, i.e. they are un-needed when using ndk-build to build
applicative native code.

Their purpose is to handle various sophisticated issues:

  - rebuilding host cross-toolchains for our supported CPU ABIs

  - rebuilding other required host tools (e.g. ndk-stack) from sources

  - rebuilding all target-specific prebuilt binaries from sources
    (this requires working host cross-toolchains)

  - packaging final NDK release tarballs, including adding samples
    and documentation which normally live in $NDK/../development/ndk

This document is here to explain how to use these dev-scripts and how
everything is architected / designed, in case you want to maintain it.


I. Organization:
----------------

First, a small description of the NDK's overall directory structure:

  $NDK/build/core
    Contains the main NDK build system used when 'ndk-build'.
    Relies heavily on GNU Make 3.81+ but isn't used by any of the
    scripts described here.

  $NDK/build/tools
    Contains all the dev-scripts that are described in this document.
    More on this later.

  $NDK/sources/host-tools/
    Contains sources of various libraries or programs that will be
    compiled to generate useful host programs for the final NDK
    installation. For example, $NDK/sources/host-tools/ndk-stack/
    contains the sources of the 'ndk-stack' program.

  $NDK/sources/cxx-stl/
    Contains the sources of various C++ runtime and libraries that
    can be used with 'ndk-build'. See docs/CPLUSPLUS-SUPPORT.html for
    more details.

  $NDK/sources/cxx-stl/gabi++/
    Contains the sources of the GAbi++ C++ runtime library. Note that
    the dev-script 'build-gabi++.sh' can be used to generate prebuilt
    libraries from these sources, that will be copied under this
    directory.

  $NDK/sources/cxx-stl/stlport/
    Contains the sources of a port of STLport that can be used with ndk-build.
    The dev-script 'build-stlport.sh' can be used to generate prebuilt
    libraries from these sources, that will be copied under this directory.

  $NDK/sources/cxx-stl/gnu-libstdc++/
    This directory doesn't contain sources at all, only an Android.mk.
    The dev-script 'build-gnu-libstdc++.sh' is used to generate prebuilt
    libraries from the sources that are located in the toolchain source
    tree instead.

  $NDK/sources/cxx-stl/system/
    This directory contains a few headers used to use the native system
    Android C++ runtime (with _very_ limited capabilites), a.k.a.
    /system/lib/libstdc++.so. The prebuilt version of this library is
    generated by the 'gen-platform.sh' dev-script described later, but
    it never placed in this directory.

  $NDK/sources/android/libthread_db/
    This directory contains the sources of the libthread_db implementation
    that is linked into the prebuilt target gdbserver binary. Note that two
    versions are provided, corresponding to different versions of gdb.

    The sources are customized versions of the ones found under
    $ANDROID/bionic/libthread_db. They contain various changes used to
    deal with platform bugs.

  $NDK/sources/
    The rest of $NDK/sources/ is used to store the sources of helper
    libraries used with 'ndk-build'. For example, the 'cpu-features'
    helper library is under $NDK/sources/android/cpu-features/

  $DEVNDK a.k.a $NDK/../development/ndk
    This directory contains platform-specific files. The reason why it
    it is separate from $NDK is because it is not primarly developed in
    the open.

    More specifically:

    - all $NDK development happens in the public AOSP repository ndk.git

    - any $DEVNDK development that happens in the public AOSP development.git
      repository is auto-merged to the internal tree maintained by Google

    - $DEVNDK developments that are specific to an yet-unreleased version of
      the system happen only in the internal tree. They get back-ported to
      the public tree only when the corresponding system release is
      open-sourced.

    Having two distinct git repositories makes things easier. Also, you
    generally don't want to see the churn that goes in the internal tree
    during development. It's usually not very pretty :)

  $DEVNDK/platforms/android-$PLATFORM, where $PLATFORM is a decimal number
    Contains all files that are specific to a given API level $PLATFORM,
    that were not already defined for the previous API level.

    For example, android-3 corresponds to Android 1.5, and android-4
    corresponds to Android 1.6. The platforms/android-4 directory only
    contains files that are either new or modified, compared to android-3.

  $DEVNDK/platforms/android-$PLATFORM/include/
    Contains all system headers exposed by the NDK for a given platform.
    All these headers are independent from the CPU architecture of target devices.

  $DEVNDK/platforms/android-$PLATFORM/arch-$ARCH/
    Contains all files that are specific to a given $PLATFORM level and a
    specific CPU architecture. $ARCH is typically 'arm' or 'x86'

  $DEVNDK/platforms/android-$PLATFORM/arch-$ARCH/include/
    Contains all the architecture-specific headers for a given API level.

  $DEVNDK/platforms/android-$PLATFORM/arch-$ARCH/lib/
    Contains several CPU-specific object files and static libraries that
    are required to build the host cross-toolchains properly.

    Before NDK r7, this also contains prebuilt system shared libraries that
    had been hand-picked from various platform builds. These have been
    replaced by symbol list files instead (see below).

  $DEVNDK/platforms/android-$PLATFORM/arch-$ARCH/symbols/
    Contains, for each system shared library exposed by the NDK, two
    files describing the dynamic symbols it exports, for example, for
    the C library:

       libc.so.functions.txt -> list of exported function names
       libc.so.variables.txt -> list of exported variable names

    These files were introduced in NDK r7 and are used to generate "shell"
    shared libraries that can be used by ndk-build at link time. The shell
    libraries only provide dynamic symbols to 

    These files can be generated from a given platform build using the
    'dev-platform-import.sh' dev-script, described later in this document.

    This is handy to compare which symbols were added between platform
    releases (and check that nothing disappeared).

  $DEVNDK/platforms/android-$PLATFORM/samples/
    Contains samples that are specific to a given API level. These are
    usually copied into $INSTALLED_NDK/samples/ by the 'gen-platforms.sh'
    script.


  $NDK/platforms/
    Note to be confused with $DEVNDK/platforms/, this directory is not
    part of the NDK git directory (and is spefically listed in $NDK/.gitignore)
    but of its final installation.

    Its purpose is to hold the fully expanded platform-specific files.
    This means that, unlike $DEVNDK/platforms/android-$PLATFORM, the
    $NDK/platforms/android-$PLATFORM will contain _all_ the files that
    are specific to API level $PLATFORM.

    Moreover, the directory is organized slightly differently, i.e. as
    toolchain sysroot, i.e. for each supported $PLATFORM and $ARCH values,
    it provides two directories:

       $NDK/platforms/android-$PLATFORM/arch-$ARCH/usr/include
       $NDK/platforms/android-$PLATFORM/arch-$ARCH/usr/lib

    Notice the 'usr' subdirectory here. It is required by GCC to be able
    to use the directories with --with-sysroot. For example, to generate
    binaries that target API level 5 for the arm architecture, one would
    use:

       $TOOLCHAIN_PREFIX-gcc --with-sysroot=$NDK/platforms/android-5/arch-arm

    Where $TOOLCHAIN_PREFIX depends on the exact toolchain being used.

    The dev-script 'gen-platforms.sh' is used to populate $NDK/platforms.
    Note that by default, the script does more, see its detailed description
    below.

Generally, everything dev-script supports the --help option to display a
description of the program and the list of all supported options. Also,
debug traces can be activated by using the --verbose option. Use it several
times to increase the level of verbosity.

Note that all Windows host programs can be built on Linux if you have the
'mingw32' cross-toolchain installed ('apt-get install mingw32' on Debian or
Ubuntu). You will need to add the '--mingw' option when invoking the script.

All dev-scripts rebuilding host programs on Linux and Darwin will only
generate 32-bit programs by default. You can experiment with 64-bit binary
generation by adding the '--try-64' option. Note that as of now, 64-bit
binaries are never distributed as part of official NDK releases.

When building 32-bit Linux host programs, the dev-scripts will look for
$NDK/../prebuilts/gcc/linux-x86/host/i686-linux-glibc2.7-4.6/, which is
part of the Android platform source tree. It is a special toolchain that
ensures that the generated programs can run on old systems like Ubuntu 8.04
that only have GLibc 2.7. Otherwise, the corresponding binaries may not run
due to ABI changes in mor recent versions of GLibc.

This shall always be used to official NDK Linux releases.


II. Host toolchains:
--------------------

The host toolchains are the compiler, linker, debugger and other crucial
programs used to generate machine code for the target Android
system supported by the NDK.


II.1 Getting the toolchain sources:
- - - - - - - - - - - - - - - - - -

The NDK toolchain sources are located under the toolchain/ directly
from the top of the public AOSP repositories. There are actually several
git repositories of interest here:

    binutils/
    build/
    gcc/
    gdb/
    gold/
    gmp/
    mpfr/

The AOSP toolchain/ repository contains sources corresponding to toolchains
that are used to build the Android platform tree. For various reasons, they
need to be slightly patched for use with the NDK.

All patches are located under $NDK/build/tools/toolchain-patches/

The script 'download-toolchain-sources.sh' can be used to download and patch
the toolchain sources from the server. You simply need to give it the name of
a destination directory, for example:

  $NDK/build/tools/download-toolchain-sources.sh /tmp/ndk-$USER/src

Note that this process can take several minutes. If you happen to already
have a clone of the repo toolchain/ tree, you can speed this up considerably
using the --git-reference or --git-base option. See --help for more options
and details.

Note, to create a local toolchain repo:

   mkdir -p /tmp/ndk-$USER/toolchain
   cd /tmp/ndk-$USER/toolchain
   repo init https://android.googlesource.com/toolchain/manifest.git
   repo sync

then use with:

  $NDK/build/tools/download-toolchain-sources.sh \
       --git-reference=/tmp/ndk-$USER/toolchain \
       /tmp/ndk-$USER/src


The script doesn't simply copy the current HEAD of the toolchain
repositories. Instead, it will checkout the sources as they were
at a given known date, defined as TOOLCHAIN_GIT_DATE in 'prebuilt-common.sh'.

If you adjust TOOLCHAIN_GIT_DATE, verify that all patches still apply
correctly, you might need to remove patches if they have been integrated
into the toolchain/ repositories.

Note: you can avoid the patching with the --no-patches option to
'download-toolchain-patches.sh', and later use 'patch-sources.sh' manually
to verify that the patches apply cleanly.

The toolchains binaries are typically placed under the directory
$NDK/toolchains/$NAME/prebuilt/$SYSTEM, where $NAME is the toolchain name's
full name (e.g. arm-linux-androideabi-4.4.3), and $SYSTEM is the name of the
host system it is meant to run on (e.g. 'linux-x86', 'windows' or 'darwin-x86')


I.2. Building the toolchains:
- - - - - - - - - - - - - - -

After downloading and patching the toolchain sources, you will need to build
a proper "sysroot" directory before being able to configure/build them.

A sysroot is a directory containing system headers and libraries that the
compiler will use to build a few required target-specific binaries (e.g. libgcc.a)

To do that, use:

   $NDK/build/tools/gen-platforms.sh --minimal

This will populate $NDK/platforms/ with just the files necessary to rebuild the
toolchains. Note that without the --minimal option, the script will fail without
prebuilt toolchain binaries.

Once the sysroots are in place, use 'build-gcc.sh' by providing the path
to the toolchain sources root directory, a destination NDK installation
directory to build, and the full toolchain name.

For example, to rebuild the arm and x86 prebuilt toolchain binaries in the
current NDK directory (which can be handy if you want to later use them to
rebuild other target prebuilts or run tests), do:

   $NDK/build/tools/build-gcc.sh /tmp/ndk-$USER/src $NDK arm-linux-androideabi-4.4.3
   $NDK/build/tools/build-gcc.sh /tmp/ndk-$USER/src $NDK x86-4.4.3

Here, we assume you downloaded the toolchain sources in /tmp/ndk-$USER/src
as described in the previous section.

This operation can take some time. The script automatically performs a parallel
build to speed up the build on multi-core machine (use the -j<number> option to
control this), but the GCC sources are very large, so expect to wait a few
minutes.

For the record, on a 2.4 GHz Xeon with 16 Hyper-threaded cores and 12GB of
memory, rebuilding each toolchain takes between 2 and 4 minutes.

You need to be on Linux to build the Windows binaries, using the "mingw32"
cross-toolchain (install it with "apt-get install mingw32" on Ubuntu). To do so
use the "--mingw" option, as in:

    $NDK/build/tools/build-gcc.sh --mingw \
        /tmp/ndk-$USER/src $NDK arm-linux-androideabi-4.4.3

    $NDK/build/tools/build-gcc.sh --mingw \
        /tmp/ndk-$USER/src $NDK x86-4.4.3

The corresponding binaries are installed under $NDK/toolchains/$NAME/prebuilt/windows
Note that these are native Windows programs, not Cygwin ones.

Building the Windows toolchains under MSys and Cygwin is completely unsupported
and highly un-recommended: even if it works, it will probably take several
hours, even on a powerful machine :-(

The Darwin binaries must be generated on a Darwin machine. Note that the script
will try to use the 10.5 XCode SDK if it is installed on your system. This
ensures that the generated binaries run on Leopard, even if you're building
on a more recent version of the system.

Once you've completed your builds, you should be able to generate the other
target-specific prebuilts.


III. Target-specific prebuilt binaries:
---------------------------------------

A final NDK installation comes with a lot of various target-specific prebuilt
binaries that must be generated from sources once you have working host toolchains.

III.1.: Preparation of platform sysroots:
- - - - - - - - - - - - - - - - - - - - -

Each target prebuilt is handled by a specific dev-script. HOWEVER, all these script
require that you generate a fully populated $NDK/platforms/ directory first. To do
that, simply run:

  $NDK/gen-platforms.sh

Note that we used this script with the --minimal option to generate the host
toolchains. That's because without this flag, the script will also auto-generate
tiny versions of the system shared libraries that will be used at link-time when
building our target prebuilts.

III.2.: Generation of gdbserver:
- - - - - - - - - - - - - - - - -

A target-specific 'gdbserver' binary is required. This is a small program
that is run on the device through 'ndk-gdb' during debugging. For a variety
of technical reasons, it must be copied into a debuggable project's output
directory when 'ndk-build' is called.

The prebuilt binary is placed under $NDK/toolchains/$NAME/prebuilt/gdbserver
in the final NDK installation. You can generate with 'build-gdbserver.sh' and
takes the same parameters than 'build-gcc.sh'. So one can do:

  $NDK/build/tools/build-gcc.sh  /tmp/ndk-$USER/src $NDK arm-linux-androideabi-4.4.3
  $NDK/build/tools/build-gcc.sh  /tmp/ndk-$USER/src $NDK x86-4.4.3


III.3. Generating C++ runtime prebuilt binaries:
- - - - - - - - - - - - - - - - - - - - - - - -

Sources and support files for several C++ runtimes / standard libraries are
provided under $NDK/sources/cxx-stl/. Several dev-scripts are provided to
rebuild their binaries. The scripts place them to their respective location
(e.g. the GAbi++ binaries will go to $NDK/sources/cxx-stl/gabi++/libs/)
unless you use the --out-dir=<path> option.

Note that:

  - each script will generate the binaries for all the CPU ABIs supported by
    the NDK, e.g. armeabi, armeabi-v7a and x86. You can restrict them using
    the --abis=<list> option though.

  - the GNU libstdc++ dev-script requires the path to the toolchain sources,
    since this is where the library's sources are located.

An example usage would be:

  $NDK/build/tools/build-gabi++.sh
  $NDK/build/tools/build-stlport.sh
  $NDK/build/tools/build-gnu-libstdc++.sh /tmp/ndk-$USER/src

Note that generating the STLport and GNU libstdc++ binaries can take a
few minutes. You can follow the build by using the --verbose option to display
what's going on.


IV. Other host prebuilt binaries:
---------------------------------

There are a few other host prebuilt binaries that are needed for a full
NDK installation. Their sources are typically installed under
$NDK/sources/host-tools/

Note that the corresponding dev-script recognize the --mingw and --try-64
options described at the end of section I above.


IV.1.: Building 'ndk-stack':
- - - - - - - - - - - - - -

The 'build-ndk-stack.sh' script can be used to rebuild the 'ndk-stack'
helper host program. See docs/NDK-STACK.html for a usage description.
To build it, just do:

  $NDK/build/tools/build-ndk-stack.sh


V. Packaging all prebuilts:
---------------------------

Generating all the prebuilt binaries takes a lot of time and is no fun.
To avoid doing it again and again, it is useful to place all the generated
files aside in special tarballs.

Most dev-scripts generating them typically support a --package-dir=<path>
option to do this, where <path> points to a directory that will store
compressed tarballs of the generated binaries.

For example, to build and package the GAbi++ binaries, use:

  $NDK/build/tools/build-gabi++.sh --package-dir=/tmp/ndk-$USER/prebuilt/

In NDK r7, this will actually create three tarballs (one per supported ABI),
under the directory /tmp/ndk-$USER/prebuilt/, i.e.:

  gabi++-libs-armeabi.tar.bz2
  gabi++-libs-armeabi-v7a.tar.bz2
  gabi++-libs-x86.tar.bz2

Note that these tarballs are built to be uncompressed from the top-level
of an existing NDK install tree.

Similarly, to rebuild the STLport binaries and package them:

  $NDK/build/tools/build-stlport.sh --package-dir=/tmp/ndk-$USER/prebuilt

A dev-script is provided to rebuild _and_ package all prebuilts. It is called
'rebuild-all-prebuilt.sh'. Note that by default, it will automatically
invoke 'download-toolchain-sources.sh', and place the prebuilt tarballs
under /tmp/ndk-$USER/prebuilt-$DATE, where $DATE is the current date in
ISO format (e.g. 20110915 for the 15th of September of 2011).

If you have already downloaded the toolchain sources, use the
--toolchain-src-dir=<path> option to save a few minutes to your rebuild,
as in:

  $NDK/build/tools/rebuild-all-prebuilt.sh \
        --toolchain-src-dir=/tmp/ndk-$USER/src

By default, this only rebuilds the host prebuilds for the current host
system. You can use --mingw to force the generation of Windows binaries on
Linux.

Additionally, you can use the --darwin-ssh=<hostname> option to launch the
build of the Darwin binaries from a Linux machine, by using ssh to access a
remote Darwin machine. The script will package all required sources into a
temporary tarball, copy it to the remote machine, launch the build there,
then copy back all binaries to your own machine.

This means that it is possible to generate the host binaries for all supported
host systems from Linux (provided you have ssh access to a Darwin machine).

Alternatively, you can run 'rebuild-all-prebuilt.sh' on a Darwin machine.

Once you have used the script three times (once per supported host systems),
you should have plenty of files under /tmp/ndk-$USER/prebuilt-$DATE.
For the record, with NDK r7, the list was:


VI. Packaging NDK releases:
---------------------------

Use the 'package-release.sh' dev-script to generate full NDK release packages.
These contain everything needed by a typical NDK user, including:

  - all prebuilt binaries (host toolchains, host tools, target libs, etc...)
  - all samples (including those collected from $DEVNDK/platforms/)
  - all documentation

You need to have a directory containing prebuilt tarballs, as described in
the previous section. You can use it as:

  $NDK/build/tools/package-release.sh  \
      --release=<name>      \
      --systems=<list>      \
      --arch=<list>         \
      --prebuilt-dir=<path>

The --release option is optional and allows you to provide a name for your
generated NDK archive. More specifically, the archive file name will be
something like android-ndk-$RELEASE-$SYSTEM.tar.bz2, where $RELEASE is
the release name, and $SYSTEM the supported host system (e.g. linux-x86).

By default, i.e. without the option, $RELEASE will be set to the current $DATE.

The --systems=<list> is optional, but can be used to limit the number of host
systems you want to generate for. <list> must be a comma-separated list of
system names (from 'linux-x86', 'windows' and 'darwin-x86'). This is useful
if you're working on a experimental feature and don't have the time to
regenerate the host toolchains for all systems. It allows you to generate
an experimental package that you can distribute to third-party for
experimentation.

By default, i.e. without the option, the scripts tries to build NDK archives
for all supported host systems.

The --arch=<list> is also optional, but can be used ot limit the number of
target architectures you want to generate for. <list> must be a comma-separated
list of CPU architectures (e.g. from 'arm' and 'x86'). Without the option,
this will try to build packages that support all architectures.

Finally, --prebuilt-dir=<path> must point to the directory that contains the
prebuilt tarballs described in section V. Following our previous example, one
could use --prebuilt-dir=/tmp/ndk-$USER/prebuilt here.


VI. Testing:
------------

The $NDK/tests directory contains a number of NDK unit-tests that can be
used to verify that the generated NDK packages or the working NDK tree still
behave correctly.

If you have an NDK package archive, you can run the following to run the
test suite against it:

  $NDK/tests/run-tests.sh --package=<ndk-archive>

This will uncompress the NDK archive in a temporary directory, then run all
the tests with it. When all tests have run, the temporary directory is removed
automatically.

You can also point to an existing NDK installation with --ndk=<path>, as in:

  $NDK/tests/run-tests.sh --ndk=<path>

Where <path> points to another NDK installation. The script will run the
test suite present under $NDK/tests/, not the one in the remote NDK directory.

If you don't use any option, the test suite will be run with the current NDK
directory. This can only work if you have generated or unpacked all prebuilt
archives into it before that.

You can get more traces from the tests by using --verbose. Use it twice to see
even more traces.

There are several kinds of tests:

  - 'build tests' are used to test the building capabilities of the NDK.
    I.e. the tests will only use them to check that the NDK build system
    didn't regress. The corresponding generated binaries are never used
    otherwise.

  - 'device tests' are used to test both the build and the behaviour of
    the generated code. If the 'adb' program is in your path, and have
    one device or emulator connected to your host machine, 'run-tests.sh'
    will automatically upload, run and cleanup these tests for you.

    If adb is not in your path, or no device is connected, run-tests.sh
    will simply print a warning and carry on.


Whenever you add a feature to the NDK, or fix a bug, it is recommended to
add a unit test to check the feature or the fix. Use $NDK/tests/build for
build tests, and $NDK/tests/device for device tests.