# Building Julia (Detailed)

## Downloading the Julia source code

If you are behind a firewall, you may need to use the `https` protocol instead of the `git` protocol:

```sh
git config --global url."https://".insteadOf git://
```

Be sure to also configure your system to use the appropriate proxy
settings, e.g. by setting the `https_proxy` and `http_proxy`
variables.

## Building Julia

When compiled the first time, the build will automatically download
pre-built [external
dependencies](#Required-Build-Tools-and-External-Libraries). If you
prefer to build all the dependencies on your own, or are building on a system that cannot
access the network during the build process, add the following in `Make.user`:

```
USE_BINARYBUILDER=0
```

Building Julia requires 5GiB of disk space when building all dependencies and approximately 4GiB of virtual memory.

To perform a parallel build, use `make -j N` and supply the maximum
number of concurrent processes. If the defaults in the build do not work for you, and
you need to set specific make parameters, you can save them in
`Make.user`, and place the file in the root of your Julia source. The
build will automatically check for the existence of `Make.user` and
use it if it exists.

You can create out-of-tree builds of Julia by specifying `make
O=<build-directory> configure` on the command line. This will create a
directory mirror, with all of the necessary Makefiles to build Julia,
in the specified directory. These builds will share the source files
in Julia and `deps/srccache`. Each out-of-tree build directory can
have its own `Make.user` file to override the global `Make.user` file
in the top-level folder. After modifying the `Make.user` file if necessary,
build using: `make -C <build-directory>`.

If everything works correctly, there will be a symlink to
the julia executable in the build directory which can be run as:
```sh
./julia
```
The actual executable is in `<build-directory>/usr/bin`.
After running this, you will see a Julia banner and an
interactive prompt into which you can enter expressions for
evaluation. (Errors related to libraries might be caused by old,
incompatible libraries sitting around in your PATH. In this case, try
moving the `julia` directory earlier in the PATH). Note that most of
the instructions above apply to unix systems.

To run julia from anywhere you can:
- add an alias (in `bash`: `echo "alias julia='<build-directory>/usr/bin/julia'" >> ~/.bashrc && source ~/.bashrc`), or

- add a soft link to the `julia` executable in the `<build-directory>/usr/bin` directory to `/usr/local/bin` (or any suitable directory already in your path), or

- add the `julia` directory to your executable path for this shell session (in `bash`: `export PATH="$(pwd):$PATH"` ; in `csh` or `tcsh`:
`set path= ( $path $cwd )` ), or

- add the `julia` directory to your executable path permanently (e.g. in `.bash_profile`), or

- write `prefix=/path/to/install/folder` into `Make.user` and then run `make install`. If there is a version of Julia already installed in this folder, you should delete it before running `make install`.

Some of the options you can set to control the build of Julia are listed and documented at the beginning of the file `Make.inc`, but you should never edit it for this purpose, use `Make.user` instead.

Julia's Makefiles define convenient automatic rules called `print-<VARNAME>` for printing the value of variables, replacing `<VARNAME>` with the name of the variable to print the value of.
For example
```console
$ make print-JULIA_PRECOMPILE
JULIA_PRECOMPILE=1
```
These rules are useful for debugging purposes.

Now you should be able to run Julia like this:

    julia

If you are building a Julia package for distribution on Linux, macOS,
or Windows, take a look at the detailed notes in
[distributing.md](https://github.com/JuliaLang/julia/blob/master/doc/src/devdocs/build/distributing.md).

## Updating an existing source tree

If you have previously downloaded `julia` using `git clone`, you can update the
existing source tree using `git pull` rather than starting anew:
```sh
cd julia
git pull && make
```
Assuming that you had made no changes to the source tree that will conflict
with upstream updates, these commands will trigger a build to update to the
latest version.

## General troubleshooting

1. Over time, the base library may accumulate enough changes such that the
   bootstrapping process in building the system image will fail. If this
   happens, the build may fail with an error like

   ```sh
    *** This error is usually fixed by running 'make clean'. If the error persists, try 'make cleanall' ***
   ```

   As described, running `make clean && make` is usually sufficient.
   Occasionally, the stronger cleanup done by `make cleanall` is needed.

2. New versions of external dependencies may be introduced which may
   occasionally cause conflicts with existing builds of older versions.

   a. Special `make` targets exist to help wipe the existing build of a
      dependency. For example, `make -C deps clean-llvm` will clean out the
      existing build of `llvm` so that `llvm` will be rebuilt from the
      downloaded source distribution the next time `make` is called.
      `make -C deps distclean-llvm` is a stronger wipe which will also delete
      the downloaded source distribution, ensuring that a fresh copy of the
      source distribution will be downloaded and that any new patches will be
      applied the next time `make` is called.

   b. To delete existing binaries of `julia` and all its dependencies,
      delete the `./usr` directory _in the source tree_.

3. If you've updated macOS recently, be sure to run `xcode-select --install` to update the command line tools.
   Otherwise, you could run into errors for missing headers and libraries, such as
   ```ld: library not found for -lcrt1.10.6.o```.

4. If you've moved the source directory, you might get errors such as
    ```CMake Error: The current CMakeCache.txt directory ... is different than the directory ... where     CMakeCache.txt was created.```, in which case you may delete the offending dependency under `deps`

5. In extreme cases, you may wish to reset the source tree to a pristine state.
   The following git commands may be helpful:

   ```sh
    git reset --hard #Forcibly remove any changes to any files under version control
    git clean -x -f -d #Forcibly remove any file or directory not under version control
   ```

   _To avoid losing work, make sure you know what these commands do before you
   run them. `git` will not be able to undo these changes!_

## Platform-Specific Notes

Notes for various operating systems:

* [Linux](https://github.com/JuliaLang/julia/blob/master/doc/src/devdocs/build/linux.md)
* [macOS](https://github.com/JuliaLang/julia/blob/master/doc/src/devdocs/build/macos.md)
* [Windows](https://github.com/JuliaLang/julia/blob/master/doc/src/devdocs/build/windows.md)
* [FreeBSD](https://github.com/JuliaLang/julia/blob/master/doc/src/devdocs/build/freebsd.md)

Notes for various architectures:

* [ARM](https://github.com/JuliaLang/julia/blob/master/doc/src/devdocs/build/arm.md)
* [RISC-V](https://github.com/JuliaLang/julia/blob/master/doc/src/devdocs/build/riscv.md)

## Required Build Tools and External Libraries

Building Julia requires that the following software be installed:

- **[GNU make](https://www.gnu.org/software/make)**                — building dependencies.
- **[gcc & g++](https://gcc.gnu.org)** (>= 7.1) or **[Clang](https://clang.llvm.org)** (>= 5.0, >= 9.3 for Apple Clang) — compiling and linking C, C++.
  - On Linux with g++, the static version of libstdc++ is also required.  If it is unavailable, set `USE_RT_STATIC_LIBSTDCXX=0` in `Make.user`.
- **[libatomic](https://gcc.gnu.org)**          — provided by **[gcc]** and needed to support atomic operations.
- **[python](https://www.python.org/)** (>=2.7)          — needed to build LLVM.
- **[gfortran](https://gcc.gnu.org/fortran/)**                — compiling and linking Fortran libraries.
- **[perl](https://www.perl.org)**                    — preprocessing of header files of libraries.
- **[wget](https://www.gnu.org/software/wget)**, **[curl](https://curl.se)**, or **[fetch](https://www.freebsd.org/cgi/man.cgi?fetch(1))** (FreeBSD) — to automatically download external libraries.
- **[m4](https://www.gnu.org/software/m4)**                      — needed to build GMP.
- **[awk](https://www.gnu.org/software/gawk)**                     — helper tool for Makefiles.
- **[patch](https://www.gnu.org/software/patch)**                   — for modifying source code.
- **[cmake](https://www.cmake.org)** (>= 3.4.3)        — needed to build `libgit2`.
- **[pkg-config](https://www.freedesktop.org/wiki/Software/pkg-config/)**              — needed to build `libgit2` correctly, especially for proxy support.
- **[powershell](https://docs.microsoft.com/en-us/powershell/scripting/wmf/overview)** (>= 3.0)     — necessary only on Windows.
- **[which](https://carlowood.github.io/which/)**                   — needed for checking build dependencies.
- **[diffutils](https://www.gnu.org/software/diffutils/)**                   - `cmp` is used by the makefiles

On Debian-based distributions (e.g. Ubuntu), you can easily install them with `apt-get`:
```
sudo apt-get install build-essential libatomic1 python3 gfortran perl wget m4 cmake pkg-config curl
```

On Red Hat-based distributions (e.g. Fedora, CentOS), you can install them with `yum`:
```
sudo dnf install gcc gcc-c++ gcc-gfortran python3 perl wget m4 cmake pkgconfig curl which diffutils libatomic libstdc++-static
```

Julia uses the following external libraries, which are automatically
downloaded (or in a few cases, included in the Julia source
repository) and then compiled from source the first time you run
`make`. The specific version numbers of these libraries that Julia
uses are listed in [`deps/$(libname).version`](https://github.com/JuliaLang/julia/blob/master/deps/):

- **[LLVM](https://www.llvm.org)** (15.0 + [patches](https://github.com/JuliaLang/llvm-project/tree/julia-release/15.x)) — compiler infrastructure (see [note below](#llvm)).
- **[FemtoLisp](https://github.com/JeffBezanson/femtolisp)**            — packaged with Julia source, and used to implement the compiler front-end.
- **[libuv](https://github.com/JuliaLang/libuv)**  (custom fork) — portable, high-performance event-based I/O library.
- **[OpenLibm](https://github.com/JuliaLang/openlibm)**             — portable libm library containing elementary math functions.
- **[DSFMT](https://github.com/MersenneTwister-Lab/dSFMT)**                — fast Mersenne Twister pseudorandom number generator library.
- **[OpenBLAS](https://github.com/xianyi/OpenBLAS)**             — fast, open, and maintained [basic linear algebra subprograms (BLAS)]
- **[LAPACK](https://www.netlib.org/lapack)**               — library of linear algebra routines for solving systems of simultaneous linear equations, least-squares solutions of linear systems of equations, eigenvalue problems, and singular value problems.
- **[MKL](https://software.intel.com/en-us/articles/intel-mkl)** (optional)       – OpenBLAS and LAPACK may be replaced by Intel's MKL library.
- **[SuiteSparse](https://people.engr.tamu.edu/davis/suitesparse.html)**          — library of linear algebra routines for sparse matrices.
- **[PCRE](https://www.pcre.org)**                 — Perl-compatible regular expressions library.
- **[GMP](https://gmplib.org)**                  — GNU multiple precision arithmetic library, needed for `BigInt` support.
- **[MPFR](https://www.mpfr.org)**                 — GNU multiple precision floating point library, needed for arbitrary precision floating point (`BigFloat`) support.
- **[libgit2](https://libgit2.org/)**              — Git linkable library, used by Julia's package manager.
- **[curl](https://curl.se)**                 — libcurl provides download and proxy support.
- **[libssh2](https://www.libssh2.org)**              — library for SSH transport, used by libgit2 for packages with SSH remotes.
- **[OpenSSL](https://www.openssl.org/)**              — library used for cryptography and transport layer security, used by libgit2 and libssh2.
- **[utf8proc](https://julialang.org/utf8proc/)**             — a library for processing UTF-8 encoded Unicode strings.
- **[LLVM libunwind](https://www.nongnu.org/libunwind)**       — LLVM's fork of [libunwind], a library that determines the call-chain of a program.
- **[ITTAPI](https://github.com/intel/ittapi)**               — Intel's Instrumentation and Tracing Technology and Just-In-Time API.

## Build dependencies

If you already have one or more of these packages installed on your system, you can prevent Julia from compiling duplicates of these libraries by passing `USE_SYSTEM_...=1` to `make` or adding the line to `Make.user`. The complete list of possible flags can be found in `Make.inc`.

Please be aware that this procedure is not officially supported, as it introduces additional variability into the installation and versioning of the dependencies, and is recommended only for system package maintainers. Unexpected compile errors may result, as the build system will do no further checking to ensure the proper packages are installed.

### LLVM

The most complicated dependency is LLVM, for which we require additional patches from upstream (LLVM is not backward compatible).

For packaging Julia with LLVM, we recommend either:
 - bundling a Julia-only LLVM library inside the Julia package, or
 - adding the patches to the LLVM package of the distribution.
   * A complete list of patches is available on [Github](https://github.com/JuliaLang/llvm-project) see the `julia-release/18.x` branch.
   * The remaining patches are all upstream bug fixes, and have been contributed into upstream LLVM.

Using an unpatched or different version of LLVM will result in errors and/or poor performance.
You can build a different version of LLVM from a remote Git repository with the following options in the `Make.user` file:

```make
# Force source build of LLVM
USE_BINARYBUILDER_LLVM = 0
# Use Git for fetching LLVM source code
# this is either `1` to get all of them
DEPS_GIT = 1
# or a space-separated list of specific dependencies to download with git
DEPS_GIT = llvm

# Other useful options:
#URL of the Git repository you want to obtain LLVM from:
#  LLVM_GIT_URL = ...
#Name of the alternate branch to clone from git
#  LLVM_BRANCH = julia-16.0.6-0
#SHA hash of the alternate commit to check out automatically
#  LLVM_SHA1 = $(LLVM_BRANCH)
#List of LLVM targets to build. It is strongly recommended to keep at least all the
#default targets listed in `deps/llvm.mk`, even if you don't necessarily need all of them.
#  LLVM_TARGETS = ...
#Use ccache for faster recompilation in case you need to restart a build.
#  USECCACHE = 1
#  CMAKE_GENERATOR=Ninja
#  LLVM_ASSERTIONS=1
#  LLVM_DEBUG=Symbols
```

The various build phases are controlled by specific files:
 * `deps/llvm.version` : touch or change to checkout a new version, `make get-llvm check-llvm`
 * `deps/srccache/llvm/source-extracted` : result of `make extract-llvm`
 * `deps/llvm/build_Release*/build-configured` : result of `make configure-llvm`
 * `deps/llvm/build_Release*/build-configured` : result of `make compile-llvm`
 * `usr-staging/llvm/build_Release*.tgz` : result of `make stage-llvm` (regenerate with `make reinstall-llvm`)
 * `usr/manifest/llvm` : result of `make install-llvm` (regenerate with `make uninstall-llvm`)
 * `make version-check-llvm` : runs every time to warn the user if there are local modifications

Though Julia can be built with newer LLVM versions, support for this should be regarded as experimental and not suitable for packaging.

### libuv

Julia uses a custom fork of libuv. It is a small dependency, and can be safely bundled in the same package as Julia, and will not conflict with the system library. Julia builds should _not_ try to use the system libuv.

### BLAS and LAPACK

As a high-performance numerical language, Julia should be linked to a multi-threaded BLAS and LAPACK, such as OpenBLAS or ATLAS, which will provide much better performance than the reference `libblas` implementations which may be default on some systems.

## Source distributions of releases

Each pre-release and release of Julia has a "full" source distribution and a "light" source
distribution.

The full source distribution contains the source code for Julia and all dependencies so
that it can be built from source without an internet connection. The light source
distribution does not include the source code of dependencies.

For example, `julia-1.0.0.tar.gz` is the light source distribution for the `v1.0.0` release
of Julia, while `julia-1.0.0-full.tar.gz` is the full source distribution.

## Building Julia from source with a Git checkout of a stdlib

If you need to build Julia from source with a Git checkout of a stdlib, then use `make DEPS_GIT=NAME_OF_STDLIB` when building Julia.

For example, if you need to build Julia from source with a Git checkout of Pkg, then use `make DEPS_GIT=Pkg` when building Julia. The `Pkg` repo is in `stdlib/Pkg`, and created initially with a detached `HEAD`. If you're doing this from a pre-existing Julia repository, you may need to `make clean` beforehand.

If you need to build Julia from source with Git checkouts of more than one stdlib, then `DEPS_GIT` should be a space-separated list of the stdlib names. For example, if you need to build Julia from source with a Git checkout of Pkg, Tar, and Downloads, then use `make DEPS_GIT='Pkg Tar Downloads'` when building Julia.

## Building an "assert build" of Julia

An "assert build" of Julia is a build that was built with both `FORCE_ASSERTIONS=1` and
`LLVM_ASSERTIONS=1`. To build an assert build, define both of the following variables
in your `Make.user` file:

```
FORCE_ASSERTIONS=1
LLVM_ASSERTIONS=1
```

Please note that assert builds of Julia will be slower than regular (non-assert) builds.

## Building a debug build of Julia

A full debug build of Julia can be built with `make debug`.  This builds a debug
version of `libjulia` and uses it to bootstrap the compiler, before creating a
system image with debug symbols enabled.  This can take more than 15 minutes.

Although it may result in some differences, a debug build can be built much
quicker by bootstrapping from a release build:

```sh
$ make julia-src-release julia-sysbase-release
$ make julia-sysimg-debug CROSS_BOOTSTRAP_JULIA=$PWD/usr/bin/julia CROSS_BOOTSTRAP_SYSBASE=$PWD/usr/lib/julia/sysbase.so
```

## Building 32-bit Julia on a 64-bit machine

Occasionally, bugs specific to 32-bit architectures may arise, and when this happens it is useful to be able to debug the problem on your local machine. Since most modern 64-bit systems support running programs built for 32-bit ones, if you don't have to recompile Julia from source (e.g. you mainly need to inspect the behavior of a 32-bit Julia without having to touch the C code), you can likely use a 32-bit build of Julia for your system that you can obtain from the [official downloads page](https://julialang.org/downloads/).
However, if you do need to recompile Julia from source one option is to use a Docker container of a 32-bit system. At least for now, building a 32-bit version of Julia is relatively straightforward using [ubuntu 32-bit docker images](https://hub.docker.com/r/i386/ubuntu). In brief, after setting up `docker` here are the required steps:

```sh
$ docker pull i386/ubuntu
$ docker run --platform i386 -i -t i386/ubuntu /bin/bash
```

At this point you should be in a 32-bit machine console (note that `uname` reports the host architecture, so will still say 64-bit, but this will not affect the Julia build). You can add packages and compile code; when you `exit`, all the changes will be lost, so be sure to finish your analysis in a single session or set up a copy/pastable script you can use to set up your environment.

From this point, you should

```sh
# apt update
```
(Note that `sudo` isn't installed, but neither is it necessary since you are running as `root`, so you can omit `sudo` from all commands.)

Then add all the [build dependencies](#required-build-tools-and-external-libraries), a console-based editor of your choice, `git`, and anything else you'll need (e.g., `gdb`, `rr`, etc). Pick a directory to work in and `git clone` Julia, check out the branch you wish to debug, and build Julia as usual.


## Update the version number of a dependency

There are two types of builds
1. Build everything (`deps/` and `src/`) from source code.
    (Add `USE_BINARYBUILDER=0` to `Make.user`, see [Building Julia](#building-julia))
2. Build from source (`src/`) with pre-compiled dependencies (default)

When you want to update the version number of a dependency in `deps/`,
you may want to use the following checklist:

```md
### Check list

Version numbers:
- [ ] `deps/$(libname).version`: `LIBNAME_VER`, `LIBNAME_BRANCH`, `LIBNAME_SHA1` and `LIBNAME_JLL_VER`
- [ ] `stdlib/$(LIBNAME_JLL_NAME)_jll/Project.toml`: `version`

Checksum:
- [ ] `deps/checksums/$(libname)`
- [ ] `deps/checksums/$(LIBNAME_JLL_NAME)-*/`: `md5` and `sha512`

Patches:
- [ ] `deps/$(libname).mk`
- [ ] `deps/patches/$(libname)-*.patch`
```

Note:
- For specific dependencies, some items in the checklist may not exist.
- For checksum file, it may be **a single file** without a suffix, or **a folder** containing two files.


### Example: `OpenLibm`

1. Update Version numbers in `deps/openlibm.version`
    - `OPENLIBM_VER := 0.X.Y`
    - `OPENLIBM_BRANCH = v0.X.Y`
    - `OPENLIBM_SHA1 = new-sha1-hash`
2. Update Version number in `stdlib/OpenLibm_jll/Project.toml`
    - `version = "0.X.Y+0"`
3. Update checksums in `deps/checksums/openlibm`
    - `make -f contrib/refresh_checksums.mk openlibm`
4. Check if the patch files `deps/patches/openlibm-*.patch` exist
    - if patches don't exist, skip.
    - if patches exist, check if they have been merged into the new version and need to be removed.
        When deleting a patch, remember to modify the corresponding Makefile file (`deps/openlibm.mk`).
