### Usage

To build dependencies for the current arch+OS:

    make

To build for another arch/OS:

    make HOST=host-platform-triplet

For example:

    make HOST=x86_64-w64-mingw32 -j4

**Bitcoin Core's configure script by default will ignore the depends output.** In
order for it to pick up libraries, tools, and settings from the depends build,
you must point it at the appropriate `--prefix` directory generated by the
build. In the above example, a prefix dir named x86_64-w64-mingw32 will be
created. To use it for Bitcoin:

    ./configure --prefix=$PWD/depends/x86_64-w64-mingw32

Common `host-platform-triplets` for cross compilation are:

- `i686-pc-linux-gnu` for Linux 32 bit
- `x86_64-pc-linux-gnu` for x86 Linux
- `x86_64-w64-mingw32` for Win64
- `x86_64-apple-darwin16` for macOS
- `arm-linux-gnueabihf` for Linux ARM 32 bit
- `aarch64-linux-gnu` for Linux ARM 64 bit
- `powerpc64-linux-gnu` for Linux POWER 64-bit (big endian)
- `powerpc64le-linux-gnu` for Linux POWER 64-bit (little endian)
- `riscv32-linux-gnu` for Linux RISC-V 32 bit
- `riscv64-linux-gnu` for Linux RISC-V 64 bit
- `s390x-linux-gnu` for Linux S390X
- `armv7a-linux-android` for Android ARM 32 bit
- `aarch64-linux-android` for Android ARM 64 bit
- `i686-linux-android` for Android x86 32 bit
- `x86_64-linux-android` for Android x86 64 bit

The paths are automatically configured and no other options are needed unless targeting [Android](#Android).

### Install the required dependencies: Ubuntu & Debian

#### For macOS cross compilation

    sudo apt-get install curl librsvg2-bin libtiff-tools bsdmainutils cmake imagemagick libcap-dev libz-dev libbz2-dev python3-setuptools

#### For Win64 cross compilation

- see [build-windows.md](../doc/build-windows.md#cross-compilation-for-ubuntu-and-windows-subsystem-for-linux)

#### For linux (including i386, ARM) cross compilation

Common linux dependencies:

    sudo apt-get install make automake cmake curl g++-multilib libtool binutils-gold bsdmainutils pkg-config python3 patch

For linux ARM cross compilation:

    sudo apt-get install g++-arm-linux-gnueabihf binutils-arm-linux-gnueabihf

For linux AARCH64 cross compilation:

    sudo apt-get install g++-aarch64-linux-gnu binutils-aarch64-linux-gnu

For linux POWER 64-bit cross compilation (there are no packages for 32-bit):

    sudo apt-get install g++-powerpc64-linux-gnu binutils-powerpc64-linux-gnu g++-powerpc64le-linux-gnu binutils-powerpc64le-linux-gnu

For linux RISC-V 64-bit cross compilation (there are no packages for 32-bit):

    sudo apt-get install g++-riscv64-linux-gnu binutils-riscv64-linux-gnu

RISC-V known issue: gcc-7.3.0 and gcc-7.3.1 result in a broken `test_bitcoin` executable (see https://github.com/bitcoin/bitcoin/pull/13543),
this is apparently fixed in gcc-8.1.0.

For linux S390X cross compilation:

    sudo apt-get install g++-s390x-linux-gnu binutils-s390x-linux-gnu

### Dependency Options
The following can be set when running make: make FOO=bar

    SOURCES_PATH: downloaded sources will be placed here
    BASE_CACHE: built packages will be placed here
    SDK_PATH: Path where sdk's can be found (used by macOS)
    FALLBACK_DOWNLOAD_PATH: If a source file can't be fetched, try here before giving up
    NO_QT: Don't download/build/cache qt and its dependencies
    NO_QR: Don't download/build/cache packages needed for enabling qrencode
    NO_ZMQ: Don't download/build/cache packages needed for enabling zeromq
    NO_WALLET: Don't download/build/cache libs needed to enable the wallet
    NO_UPNP: Don't download/build/cache packages needed for enabling upnp
    DEBUG: disable some optimizations and enable more runtime checking
    HOST_ID_SALT: Optional salt to use when generating host package ids
    BUILD_ID_SALT: Optional salt to use when generating build package ids

If some packages are not built, for example `make NO_WALLET=1`, the appropriate
options will be passed to bitcoin's configure. In this case, `--disable-wallet`.

### Additional targets

    download: run 'make download' to fetch all sources without building them
    download-osx: run 'make download-osx' to fetch all sources needed for macOS builds
    download-win: run 'make download-win' to fetch all sources needed for win builds
    download-linux: run 'make download-linux' to fetch all sources needed for linux builds


### Android

Before proceeding with an Android build one needs to get the [Android SDK](https://developer.android.com/studio) and use the "SDK Manager" tool to download the NDK and one or more "Platform packages" (these are Android versions and have a corresponding API level).
In order to build `ANDROID_API_LEVEL` (API level corresponding to the Android version targeted, e.g. Android 9.0 Pie is 28 and its "Platform package" needs to be available) and `ANDROID_TOOLCHAIN_BIN` (path to toolchain binaries depending on the platform the build is being performed on) need to be set.

API levels from 24 to 29 have been tested to work.

If the build includes Qt, environment variables `ANDROID_SDK` and `ANDROID_NDK` need to be set as well but can otherwise be omitted.
This is an example command for a default build with no disabled dependencies:

    ANDROID_SDK=/home/user/Android/Sdk ANDROID_NDK=/home/user/Android/Sdk/ndk-bundle make HOST=aarch64-linux-android ANDROID_API_LEVEL=28 ANDROID_TOOLCHAIN_BIN=/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin

### Other documentation

- [description.md](description.md): General description of the depends system
- [packages.md](packages.md): Steps for adding packages