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<h1 class="title">Building the JDK</h1>
</header>
<nav id="TOC" role="doc-toc">
<ul>
<li><a href="#tldr-instructions-for-the-impatient"
id="toc-tldr-instructions-for-the-impatient">TL;DR (Instructions for the
Impatient)</a></li>
<li><a href="#introduction" id="toc-introduction">Introduction</a></li>
<li><a href="#getting-the-source-code"
id="toc-getting-the-source-code">Getting the Source Code</a>
<ul>
<li><a href="#special-considerations"
id="toc-special-considerations">Special Considerations</a></li>
</ul></li>
<li><a href="#build-hardware-requirements"
id="toc-build-hardware-requirements">Build Hardware Requirements</a>
<ul>
<li><a href="#building-on-x86" id="toc-building-on-x86">Building on
x86</a></li>
<li><a href="#building-on-aarch64" id="toc-building-on-aarch64">Building
on aarch64</a></li>
<li><a href="#building-on-32-bit-arm"
id="toc-building-on-32-bit-arm">Building on 32-bit arm</a></li>
</ul></li>
<li><a href="#operating-system-requirements"
id="toc-operating-system-requirements">Operating System Requirements</a>
<ul>
<li><a href="#windows" id="toc-windows">Windows</a></li>
<li><a href="#macos" id="toc-macos">macOS</a></li>
<li><a href="#linux" id="toc-linux">Linux</a></li>
<li><a href="#aix" id="toc-aix">AIX</a></li>
</ul></li>
<li><a href="#native-compiler-toolchain-requirements"
id="toc-native-compiler-toolchain-requirements">Native Compiler
(Toolchain) Requirements</a>
<ul>
<li><a href="#gcc" id="toc-gcc">gcc</a></li>
<li><a href="#clang" id="toc-clang">clang</a></li>
<li><a href="#apple-xcode" id="toc-apple-xcode">Apple Xcode</a></li>
<li><a href="#microsoft-visual-studio"
id="toc-microsoft-visual-studio">Microsoft Visual Studio</a></li>
<li><a href="#ibm-xl-cc" id="toc-ibm-xl-cc">IBM XL C/C++</a></li>
</ul></li>
<li><a href="#boot-jdk-requirements" id="toc-boot-jdk-requirements">Boot
JDK Requirements</a>
<ul>
<li><a href="#getting-jdk-binaries"
id="toc-getting-jdk-binaries">Getting JDK binaries</a></li>
</ul></li>
<li><a href="#external-library-requirements"
id="toc-external-library-requirements">External Library Requirements</a>
<ul>
<li><a href="#freetype" id="toc-freetype">FreeType</a></li>
<li><a href="#cups" id="toc-cups">CUPS</a></li>
<li><a href="#x11" id="toc-x11">X11</a></li>
<li><a href="#alsa" id="toc-alsa">ALSA</a></li>
<li><a href="#libffi" id="toc-libffi">libffi</a></li>
</ul></li>
<li><a href="#build-tools-requirements"
id="toc-build-tools-requirements">Build Tools Requirements</a>
<ul>
<li><a href="#autoconf" id="toc-autoconf">Autoconf</a></li>
<li><a href="#gnu-make" id="toc-gnu-make">GNU Make</a></li>
<li><a href="#gnu-bash" id="toc-gnu-bash">GNU Bash</a></li>
</ul></li>
<li><a href="#running-configure" id="toc-running-configure">Running
Configure</a>
<ul>
<li><a href="#common-configure-arguments"
id="toc-common-configure-arguments">Common Configure Arguments</a></li>
<li><a href="#configure-control-variables"
id="toc-configure-control-variables">Configure Control
Variables</a></li>
</ul></li>
<li><a href="#running-make" id="toc-running-make">Running Make</a>
<ul>
<li><a href="#common-make-targets" id="toc-common-make-targets">Common
Make Targets</a></li>
<li><a href="#make-control-variables"
id="toc-make-control-variables">Make Control Variables</a></li>
</ul></li>
<li><a href="#running-tests" id="toc-running-tests">Running
Tests</a></li>
<li><a href="#signing" id="toc-signing">Signing</a>
<ul>
<li><a href="#macos-1" id="toc-macos-1">macOS</a></li>
</ul></li>
<li><a href="#cross-compiling"
id="toc-cross-compiling">Cross-compiling</a>
<ul>
<li><a href="#cross-compiling-the-easy-way-with-openjdk-devkits"
id="toc-cross-compiling-the-easy-way-with-openjdk-devkits">Cross
compiling the easy way with OpenJDK devkits</a></li>
<li><a href="#boot-jdk-and-build-jdk"
id="toc-boot-jdk-and-build-jdk">Boot JDK and Build JDK</a></li>
<li><a href="#specifying-the-target-platform"
id="toc-specifying-the-target-platform">Specifying the Target
Platform</a></li>
<li><a href="#toolchain-considerations"
id="toc-toolchain-considerations">Toolchain Considerations</a></li>
<li><a href="#native-libraries" id="toc-native-libraries">Native
Libraries</a></li>
<li><a href="#cross-compiling-with-debian-sysroots"
id="toc-cross-compiling-with-debian-sysroots">Cross compiling with
Debian sysroots</a></li>
<li><a href="#building-for-armaarch64"
id="toc-building-for-armaarch64">Building for ARM/aarch64</a></li>
<li><a href="#building-for-risc-v" id="toc-building-for-risc-v">Building
for RISC-V</a></li>
<li><a href="#building-for-musl" id="toc-building-for-musl">Building for
musl</a></li>
<li><a href="#verifying-the-build"
id="toc-verifying-the-build">Verifying the Build</a></li>
</ul></li>
<li><a href="#build-performance" id="toc-build-performance">Build
Performance</a>
<ul>
<li><a href="#disk-speed" id="toc-disk-speed">Disk Speed</a></li>
<li><a href="#virus-checking" id="toc-virus-checking">Virus
Checking</a></li>
<li><a href="#ccache" id="toc-ccache">Ccache</a></li>
<li><a href="#precompiled-headers"
id="toc-precompiled-headers">Precompiled Headers</a></li>
<li><a href="#icecc-icecream" id="toc-icecc-icecream">Icecc /
icecream</a></li>
<li><a href="#using-the-javac-server"
id="toc-using-the-javac-server">Using the javac server</a></li>
<li><a href="#building-the-right-target"
id="toc-building-the-right-target">Building the Right Target</a></li>
</ul></li>
<li><a href="#troubleshooting"
id="toc-troubleshooting">Troubleshooting</a>
<ul>
<li><a href="#locating-the-source-of-the-error"
id="toc-locating-the-source-of-the-error">Locating the Source of the
Error</a></li>
<li><a href="#fixing-unexpected-build-failures"
id="toc-fixing-unexpected-build-failures">Fixing Unexpected Build
Failures</a></li>
<li><a href="#specific-build-issues"
id="toc-specific-build-issues">Specific Build Issues</a></li>
<li><a href="#getting-help" id="toc-getting-help">Getting Help</a></li>
</ul></li>
<li><a href="#reproducible-builds"
id="toc-reproducible-builds">Reproducible Builds</a></li>
<li><a href="#hints-and-suggestions-for-advanced-users"
id="toc-hints-and-suggestions-for-advanced-users">Hints and Suggestions
for Advanced Users</a>
<ul>
<li><a href="#bash-completion" id="toc-bash-completion">Bash
Completion</a></li>
<li><a href="#using-multiple-configurations"
id="toc-using-multiple-configurations">Using Multiple
Configurations</a></li>
<li><a href="#handling-reconfigurations"
id="toc-handling-reconfigurations">Handling Reconfigurations</a></li>
<li><a href="#using-fine-grained-make-targets"
id="toc-using-fine-grained-make-targets">Using Fine-Grained Make
Targets</a></li>
</ul></li>
<li><a href="#understanding-the-build-system"
id="toc-understanding-the-build-system">Understanding the Build
System</a>
<ul>
<li><a href="#configurations"
id="toc-configurations">Configurations</a></li>
<li><a href="#build-output-structure"
id="toc-build-output-structure">Build Output Structure</a></li>
<li><a href="#fixpath" id="toc-fixpath">Fixpath</a></li>
<li><a href="#native-debug-symbols" id="toc-native-debug-symbols">Native
Debug Symbols</a></li>
<li><a href="#autoconf-details" id="toc-autoconf-details">Autoconf
Details</a></li>
<li><a href="#developing-the-build-system-itself"
id="toc-developing-the-build-system-itself">Developing the Build System
Itself</a></li>
</ul></li>
<li><a href="#contributing-to-the-jdk"
id="toc-contributing-to-the-jdk">Contributing to the JDK</a></li>
<li><a href="#editing-this-document"
id="toc-editing-this-document">Editing this document</a></li>
</ul>
</nav>
<h2 id="tldr-instructions-for-the-impatient">TL;DR (Instructions for the
Impatient)</h2>
<p>If you are eager to try out building the JDK, these simple steps
works most of the time. They assume that you have installed Git (and
Cygwin if running on Windows) and cloned the top-level JDK repository
that you want to build.</p>
<ol type="1">
<li><p><a href="#getting-the-source-code">Get the complete source
code</a>:<br />
<code>git clone https://git.openjdk.org/jdk/</code></p></li>
<li><p><a href="#running-configure">Run configure</a>:<br />
<code>bash configure</code></p>
<p>If <code>configure</code> fails due to missing dependencies (to
either the <a
href="#native-compiler-toolchain-requirements">toolchain</a>, <a
href="#build-tools-requirements">build tools</a>, <a
href="#external-library-requirements">external libraries</a> or the <a
href="#boot-jdk-requirements">boot JDK</a>), most of the time it prints
a suggestion on how to resolve the situation on your platform. Follow
the instructions, and try running <code>bash configure</code>
again.</p></li>
<li><p><a href="#running-make">Run make</a>:<br />
<code>make images</code></p></li>
<li><p>Verify your newly built JDK:<br />
<code>./build/*/images/jdk/bin/java -version</code></p></li>
<li><p><a href="##running-tests">Run basic tests</a>:<br />
<code>make run-test-tier1</code></p></li>
</ol>
<p>If any of these steps failed, or if you want to know more about build
requirements or build functionality, please continue reading this
document.</p>
<h2 id="introduction">Introduction</h2>
<p>The JDK is a complex software project. Building it requires a certain
amount of technical expertise, a fair number of dependencies on external
software, and reasonably powerful hardware.</p>
<p>If you just want to use the JDK and not build it yourself, this
document is not for you. See for instance <a
href="http://openjdk.org/install">OpenJDK installation</a> for some
methods of installing a prebuilt JDK.</p>
<h2 id="getting-the-source-code">Getting the Source Code</h2>
<p>Make sure you are getting the correct version. As of JDK 10, the
source is no longer split into separate repositories so you only need to
clone one single repository. At the <a
href="https://git.openjdk.org/">OpenJDK Git site</a> you can see a list
of all available repositories. If you want to build an older version,
e.g. JDK 11, it is recommended that you get the <code>jdk11u</code>
repo, which contains incremental updates, instead of the
<code>jdk11</code> repo, which was frozen at JDK 11 GA.</p>
<p>If you are new to Git, a good place to start is the book <a
href="https://git-scm.com/book/en/v2">Pro Git</a>. The rest of this
document assumes a working knowledge of Git.</p>
<h3 id="special-considerations">Special Considerations</h3>
<p>For a smooth building experience, it is recommended that you follow
these rules on where and how to check out the source code.</p>
<ul>
<li><p>Do not check out the source code in a path which contains spaces.
Chances are the build will not work. This is most likely to be an issue
on Windows systems.</p></li>
<li><p>Do not check out the source code in a path which has a very long
name or is nested many levels deep. Chances are you will hit an OS
limitation during the build.</p></li>
<li><p>Put the source code on a local disk, not a network share. If
possible, use an SSD. The build process is very disk intensive, and
having slow disk access will significantly increase build times. If you
need to use a network share for the source code, see below for
suggestions on how to keep the build artifacts on a local disk.</p></li>
<li><p>On Windows, if using <a href="#cygwin">Cygwin</a>, extra care
must be taken to make sure the environment is consistent. It is
recommended that you follow this procedure:</p>
<ul>
<li><p>Create the directory that is going to contain the top directory
of the JDK clone by using the <code>mkdir</code> command in the Cygwin
bash shell. That is, do <em>not</em> create it using Windows Explorer.
This will ensure that it will have proper Cygwin attributes, and that
it's children will inherit those attributes.</p></li>
<li><p>Do not put the JDK clone in a path under your Cygwin home
directory. This is especially important if your user name contains
spaces and/or mixed upper and lower case letters.</p></li>
<li><p>You need to install a git client. You have two choices, Cygwin
git or Git for Windows. Unfortunately there are pros and cons with each
choice.</p>
<ul>
<li><p>The Cygwin <code>git</code> client has no line ending issues and
understands Cygwin paths (which are used throughout the JDK build
system). However, it does not currently work well with the Skara CLI
tooling. Please see the <a
href="https://wiki.openjdk.org/display/SKARA/Skara#Skara-Git">Skara wiki
on Git clients</a> for up-to-date information about the Skara git client
support.</p></li>
<li><p>The <a href="https://gitforwindows.org">Git for Windows</a>
client has issues with line endings, and do not understand Cygwin paths.
It does work well with the Skara CLI tooling, however. To alleviate the
line ending problems, make sure you set <code>core.autocrlf</code> to
<code>false</code> (this is asked during installation).</p></li>
</ul></li>
</ul>
<p>Failure to follow this procedure might result in hard-to-debug build
problems.</p></li>
</ul>
<h2 id="build-hardware-requirements">Build Hardware Requirements</h2>
<p>The JDK is a massive project, and require machines ranging from
decent to powerful to be able to build in a reasonable amount of time,
or to be able to complete a build at all.</p>
<p>We <em>strongly</em> recommend usage of an SSD disk for the build,
since disk speed is one of the limiting factors for build
performance.</p>
<h3 id="building-on-x86">Building on x86</h3>
<p>At a minimum, a machine with 2-4 cores is advisable, as well as 2-4
GB of RAM. (The more cores to use, the more memory you need.) At least 6
GB of free disk space is required.</p>
<p>Even for 32-bit builds, it is recommended to use a 64-bit build
machine, and instead create a 32-bit target using
<code>--with-target-bits=32</code>.</p>
<h3 id="building-on-aarch64">Building on aarch64</h3>
<p>At a minimum, a machine with 8 cores is advisable, as well as 8 GB of
RAM. (The more cores to use, the more memory you need.) At least 6 GB of
free disk space is required.</p>
<p>If you do not have access to sufficiently powerful hardware, it is
also possible to use <a href="#cross-compiling">cross-compiling</a>.</p>
<h4 id="branch-protection">Branch Protection</h4>
<p>In order to use Branch Protection features in the VM,
<code>--enable-branch-protection</code> must be used. This option
requires C++ compiler support (GCC 9.1.0+ or Clang 10+). The resulting
build can be run on both machines with and without support for branch
protection in hardware. Branch Protection is only supported for Linux
targets.</p>
<h3 id="building-on-32-bit-arm">Building on 32-bit arm</h3>
<p>This is not recommended. Instead, see the section on <a
href="#cross-compiling">Cross-compiling</a>.</p>
<h2 id="operating-system-requirements">Operating System
Requirements</h2>
<p>The mainline JDK project supports Linux, macOS, AIX and Windows.
Support for other operating system, e.g. BSD, exists in separate "port"
projects.</p>
<p>In general, the JDK can be built on a wide range of versions of these
operating systems, but the further you deviate from what is tested on a
daily basis, the more likely you are to run into problems.</p>
<p>This table lists the OS versions used by Oracle when building the
JDK. Such information is always subject to change, but this table is up
to date at the time of writing.</p>
<table>
<thead>
<tr class="header">
<th>Operating system</th>
<th>Vendor/version used</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td>Linux</td>
<td>Oracle Enterprise Linux 6.4 / 7.6</td>
</tr>
<tr class="even">
<td>macOS</td>
<td>Mac OS X 10.13 (High Sierra)</td>
</tr>
<tr class="odd">
<td>Windows</td>
<td>Windows Server 2012 R2</td>
</tr>
</tbody>
</table>
<p>The double version numbers for Linux are due to the hybrid model used
at Oracle, where header files and external libraries from an older
version are used when building on a more modern version of the OS.</p>
<p>The Build Group has a wiki page with <a
href="https://wiki.openjdk.org/display/Build/Supported+Build+Platforms">Supported
Build Platforms</a>. From time to time, this is updated by contributors
to list successes or failures of building on different platforms.</p>
<h3 id="windows">Windows</h3>
<p>Windows XP is not a supported platform, but all newer Windows should
be able to build the JDK.</p>
<p>On Windows, it is important that you pay attention to the
instructions in the <a href="#special-considerations">Special
Considerations</a>.</p>
<p>Windows is the only non-POSIX OS supported by the JDK, and as such,
requires some extra care. A POSIX support layer is required to build on
Windows. Currently, the only supported such layers are Cygwin, Windows
Subsystem for Linux (WSL), and MSYS2. (MSYS is no longer supported due
to an outdated bash; While OpenJDK can be built with MSYS2, support for
it is still experimental, so build failures and unusual errors are not
uncommon.)</p>
<p>Internally in the build system, all paths are represented as
Unix-style paths, e.g. <code>/cygdrive/c/git/jdk/Makefile</code> rather
than <code>C:\git\jdk\Makefile</code>. This rule also applies to input
to the build system, e.g. in arguments to <code>configure</code>. So,
use <code>--with-msvcr-dll=/cygdrive/c/msvcr100.dll</code> rather than
<code>--with-msvcr-dll=c:\msvcr100.dll</code>. For details on this
conversion, see the section on <a href="#fixpath">Fixpath</a>.</p>
<h4 id="cygwin">Cygwin</h4>
<p>A functioning <a href="http://www.cygwin.com/">Cygwin</a> environment
is required for building the JDK on Windows. If you have a 64-bit OS, we
strongly recommend using the 64-bit version of Cygwin.</p>
<p><strong>Note:</strong> Cygwin has a model of continuously updating
all packages without any easy way to install or revert to a specific
version of a package. This means that whenever you add or update a
package in Cygwin, you might (inadvertently) update tools that are used
by the JDK build process, and that can cause unexpected build
problems.</p>
<p>The JDK requires GNU Make 4.0 or greater in Cygwin. This is usually
not a problem, since Cygwin currently only distributes GNU Make at a
version above 4.0.</p>
<p>Apart from the basic Cygwin installation, the following packages must
also be installed:</p>
<ul>
<li><code>autoconf</code></li>
<li><code>make</code></li>
<li><code>zip</code></li>
<li><code>unzip</code></li>
</ul>
<p>Often, you can install these packages using the following command
line:</p>
<pre><code>&lt;path to Cygwin setup&gt;/setup-x86_64 -q -P autoconf -P make -P unzip -P zip</code></pre>
<p>Unfortunately, Cygwin can be unreliable in certain circumstances. If
you experience build tool crashes or strange issues when building on
Windows, please check the Cygwin FAQ on the <a
href="https://cygwin.com/faq/faq.html#faq.using.bloda">"BLODA" list</a>
and the section on <a
href="https://cygwin.com/faq/faq.html#faq.using.fixing-fork-failures">fork()
failures</a>.</p>
<h4 id="windows-subsystem-for-linux-wsl">Windows Subsystem for Linux
(WSL)</h4>
<p>Windows 10 1809 or newer is supported due to a dependency on the
wslpath utility and support for environment variable sharing through
WSLENV. Version 1803 can work but intermittent build failures have been
observed.</p>
<p>It's possible to build both Windows and Linux binaries from WSL. To
build Windows binaries, you must use a Windows boot JDK (located in a
Windows-accessible directory). To build Linux binaries, you must use a
Linux boot JDK. The default behavior is to build for Windows. To build
for Linux, pass
<code>--build=x86_64-unknown-linux-gnu --openjdk-target=x86_64-unknown-linux-gnu</code>
to <code>configure</code>.</p>
<p>If building Windows binaries, the source code must be located in a
Windows- accessible directory. This is because Windows executables (such
as Visual Studio and the boot JDK) must be able to access the source
code. Also, the drive where the source is stored must be mounted as
case-insensitive by changing either /etc/fstab or /etc/wsl.conf in WSL.
Individual directories may be corrected using the fsutil tool in case
the source was cloned before changing the mount options.</p>
<p>Note that while it's possible to build on WSL, testing is still not
fully supported.</p>
<h3 id="macos">macOS</h3>
<p>Apple is using a quite aggressive scheme of pushing OS updates, and
coupling these updates with required updates of Xcode. Unfortunately,
this makes it difficult for a project such as the JDK to keep pace with
a continuously updated machine running macOS. See the section on <a
href="#apple-xcode">Apple Xcode</a> on some strategies to deal with
this.</p>
<p>It is recommended that you use at least Mac OS X 10.13 (High Sierra).
At the time of writing, the JDK has been successfully compiled on macOS
10.12 (Sierra).</p>
<p>The standard macOS environment contains the basic tooling needed to
build, but for external libraries a package manager is recommended. The
JDK uses <a href="https://brew.sh/">homebrew</a> in the examples, but
feel free to use whatever manager you want (or none).</p>
<h3 id="linux">Linux</h3>
<p>It is often not much problem to build the JDK on Linux. The only
general advice is to try to use the compilers, external libraries and
header files as provided by your distribution.</p>
<p>The basic tooling is provided as part of the core operating system,
but you will most likely need to install developer packages.</p>
<p>For apt-based distributions (Debian, Ubuntu, etc), try this:</p>
<pre><code>sudo apt-get install build-essential</code></pre>
<p>For rpm-based distributions (Fedora, Red Hat, etc), try this:</p>
<pre><code>sudo yum groupinstall &quot;Development Tools&quot;</code></pre>
<p>For Alpine Linux, aside from basic tooling, install the GNU versions
of some programs:</p>
<pre><code>sudo apk add build-base bash grep zip</code></pre>
<h3 id="aix">AIX</h3>
<p>Please consult the AIX section of the <a
href="https://wiki.openjdk.org/display/Build/Supported+Build+Platforms">Supported
Build Platforms</a> OpenJDK Build Wiki page for details about which
versions of AIX are supported.</p>
<h2 id="native-compiler-toolchain-requirements">Native Compiler
(Toolchain) Requirements</h2>
<p>Large portions of the JDK consists of native code, that needs to be
compiled to be able to run on the target platform. In theory, toolchain
and operating system should be independent factors, but in practice
there's more or less a one-to-one correlation between target operating
system and toolchain. There are ongoing efforts to loosen this strict
coupling between compiler and operating system (see <a
href="https://bugs.openjdk.org/browse/JDK-8288293">JDK-8288293</a>) but
it will likely be a very long time before this goal can be realized.</p>
<table>
<thead>
<tr class="header">
<th>Operating system</th>
<th>Supported toolchain</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td>Linux</td>
<td>gcc, clang</td>
</tr>
<tr class="even">
<td>macOS</td>
<td>Apple Xcode (using clang)</td>
</tr>
<tr class="odd">
<td>AIX</td>
<td>IBM XL C/C++</td>
</tr>
<tr class="even">
<td>Windows</td>
<td>Microsoft Visual Studio</td>
</tr>
</tbody>
</table>
<p>Please see the individual sections on the toolchains for version
recommendations. As a reference, these versions of the toolchains are
used, at the time of writing, by Oracle for the daily builds of the JDK.
It should be possible to compile the JDK with both older and newer
versions, but the closer you stay to this list, the more likely you are
to compile successfully without issues.</p>
<table>
<thead>
<tr class="header">
<th>Operating system</th>
<th>Toolchain version</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td>Linux</td>
<td>gcc 11.2.0</td>
</tr>
<tr class="even">
<td>macOS</td>
<td>Apple Xcode 10.1 (using clang 10.0.0)</td>
</tr>
<tr class="odd">
<td>Windows</td>
<td>Microsoft Visual Studio 2022 update 17.1.0</td>
</tr>
</tbody>
</table>
<p>All compilers are expected to be able to compile to the C99 language
standard, as some C99 features are used in the source code. Microsoft
Visual Studio doesn't fully support C99 so in practice shared code is
limited to using C99 features that it does support.</p>
<h3 id="gcc">gcc</h3>
<p>The minimum accepted version of gcc is 5.0. Older versions will
generate a warning by <code>configure</code> and are unlikely to
work.</p>
<p>The JDK is currently known to be able to compile with at least
version 11.2 of gcc.</p>
<p>In general, any version between these two should be usable.</p>
<h3 id="clang">clang</h3>
<p>The minimum accepted version of clang is 3.5. Older versions will not
be accepted by <code>configure</code>.</p>
<p>To use clang instead of gcc on Linux, use
<code>--with-toolchain-type=clang</code>.</p>
<h3 id="apple-xcode">Apple Xcode</h3>
<p>The oldest supported version of Xcode is 8.</p>
<p>You will need the Xcode command line developer tools to be able to
build the JDK. (Actually, <em>only</em> the command line tools are
needed, not the IDE.) The simplest way to install these is to run:</p>
<pre><code>xcode-select --install</code></pre>
<p>When updating Xcode, it is advisable to keep an older version for
building the JDK. To use a specific version of Xcode you have multiple
options:</p>
<ul>
<li>Use <code>xcode-select -s</code> before running
<code>configure</code>, e.g.
<code>xcode-select -s /Applications/Xcode13.1.app</code>. The drawback
is that the setting is system wide and you may have to revert it after
an OpenJDK build.</li>
<li>Use configure option <code>--with-xcode-path</code>, e.g.
<code>configure --with-xcode-path=/Applications/Xcode13.1.app</code>
This allows using a specific Xcode version for an OpenJDK build,
independently of the active Xcode version by
<code>xcode-select</code>.</li>
</ul>
<p>If you have recently (inadvertently) updated your OS and/or Xcode
version, and the JDK can no longer be built, please see the section on
<a href="#problems-with-the-build-environment">Problems with the Build
Environment</a>, and <a href="#getting-help">Getting Help</a> to find
out if there are any recent, non-merged patches available for this
update.</p>
<h3 id="microsoft-visual-studio">Microsoft Visual Studio</h3>
<p>The minimum accepted version is Visual Studio 2019 version 16.8.
(Note that this version is often presented as "MSVC 14.28", and reported
by cl.exe as 19.28.) Older versions will not be accepted by
<code>configure</code> and will not work. The maximum accepted version
of Visual Studio is 2022.</p>
<p>If you have multiple versions of Visual Studio installed,
<code>configure</code> will by default pick the latest. You can request
a specific version to be used by setting
<code>--with-toolchain-version</code>, e.g.
<code>--with-toolchain-version=2022</code>.</p>
<p>If you have Visual Studio installed but <code>configure</code> fails
to detect it, it may be because of <a href="#spaces-in-path">spaces in
path</a>.</p>
<h3 id="ibm-xl-cc">IBM XL C/C++</h3>
<p>Please consult the AIX section of the <a
href="https://wiki.openjdk.org/display/Build/Supported+Build+Platforms">Supported
Build Platforms</a> OpenJDK Build Wiki page for details about which
versions of XLC are supported.</p>
<h2 id="boot-jdk-requirements">Boot JDK Requirements</h2>
<p>Paradoxically, building the JDK requires a pre-existing JDK. This is
called the "boot JDK". The boot JDK does not, however, have to be a JDK
built directly from the source code available in the OpenJDK Community.
If you are porting the JDK to a new platform, chances are that there
already exists another JDK for that platform that is usable as boot
JDK.</p>
<p>The rule of thumb is that the boot JDK for building JDK major version
<em>N</em> should be a JDK of major version <em>N-1</em>, so for
building JDK 9 a JDK 8 would be suitable as boot JDK. However, the JDK
should be able to "build itself", so an up-to-date build of the current
JDK source is an acceptable alternative. If you are following the
<em>N-1</em> rule, make sure you've got the latest update version, since
JDK 8 GA might not be able to build JDK 9 on all platforms.</p>
<p>Early in the release cycle, version <em>N-1</em> may not yet have
been released. In that case, the preferred boot JDK will be version
<em>N-2</em> until version <em>N-1</em> is available.</p>
<p>If the boot JDK is not automatically detected, or the wrong JDK is
picked, use <code>--with-boot-jdk</code> to point to the JDK to use.</p>
<h3 id="getting-jdk-binaries">Getting JDK binaries</h3>
<p>JDK binaries for Linux, Windows and macOS can be downloaded from <a
href="http://jdk.java.net">jdk.java.net</a>. An alternative is to
download the <a
href="http://www.oracle.com/technetwork/java/javase/downloads">Oracle
JDK</a>. Another is the <a href="https://adoptopenjdk.net/">Adopt
OpenJDK Project</a>, which publishes experimental prebuilt binaries for
various platforms.</p>
<p>On Linux you can also get a JDK from the Linux distribution. On
apt-based distros (like Debian and Ubuntu),
<code>sudo apt-get install openjdk-&lt;VERSION&gt;-jdk</code> is
typically enough to install a JDK &lt;VERSION&gt;. On rpm-based distros
(like Fedora and Red Hat), try
<code>sudo yum install java-&lt;VERSION&gt;-openjdk-devel</code>.</p>
<h2 id="external-library-requirements">External Library
Requirements</h2>
<p>Different platforms require different external libraries. In general,
libraries are not optional - that is, they are either required or not
used.</p>
<p>If a required library is not detected by <code>configure</code>, you
need to provide the path to it. There are two forms of the
<code>configure</code> arguments to point to an external library:
<code>--with-&lt;LIB&gt;=&lt;path&gt;</code> or
<code>--with-&lt;LIB&gt;-include=&lt;path to include&gt; --with-&lt;LIB&gt;-lib=&lt;path to lib&gt;</code>.
The first variant is more concise, but require the include files and
library files to reside in a default hierarchy under this directory. In
most cases, it works fine.</p>
<p>As a fallback, the second version allows you to point to the include
directory and the lib directory separately.</p>
<h3 id="freetype">FreeType</h3>
<p>FreeType2 from <a href="http://www.freetype.org/">The FreeType
Project</a> is not required on any platform. The exception is on
Unix-based platforms when configuring such that the build artifacts will
reference a system installed library, rather than bundling the JDK's own
copy.</p>
<ul>
<li>To install on an apt-based Linux, try running
<code>sudo apt-get install     libfreetype6-dev</code>.</li>
<li>To install on an rpm-based Linux, try running
<code>sudo yum install     freetype-devel</code>.</li>
<li>To install on Alpine Linux, try running
<code>sudo apk add freetype-dev</code>.</li>
<li>To install on macOS, try running
<code>brew install freetype</code>.</li>
</ul>
<p>Use <code>--with-freetype-include=&lt;path&gt;</code> and
<code>--with-freetype-lib=&lt;path&gt;</code> if <code>configure</code>
does not automatically locate the platform FreeType files.</p>
<h3 id="cups">CUPS</h3>
<p>CUPS, <a href="http://www.cups.org">Common UNIX Printing System</a>
header files are required on all platforms, except Windows. Often these
files are provided by your operating system.</p>
<ul>
<li>To install on an apt-based Linux, try running
<code>sudo apt-get install     libcups2-dev</code>.</li>
<li>To install on an rpm-based Linux, try running
<code>sudo yum install     cups-devel</code>.</li>
<li>To install on Alpine Linux, try running
<code>sudo apk add cups-dev</code>.</li>
</ul>
<p>Use <code>--with-cups=&lt;path&gt;</code> if <code>configure</code>
does not properly locate your CUPS files.</p>
<h3 id="x11">X11</h3>
<p>Certain <a href="http://www.x.org/">X11</a> libraries and include
files are required on Linux.</p>
<ul>
<li>To install on an apt-based Linux, try running
<code>sudo apt-get install     libx11-dev libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev</code>.</li>
<li>To install on an rpm-based Linux, try running
<code>sudo yum install     libXtst-devel libXt-devel libXrender-devel libXrandr-devel libXi-devel</code>.</li>
<li>To install on Alpine Linux, try running
<code>sudo apk add libx11-dev     libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev</code>.</li>
</ul>
<p>Use <code>--with-x=&lt;path&gt;</code> if <code>configure</code> does
not properly locate your X11 files.</p>
<h3 id="alsa">ALSA</h3>
<p>ALSA, <a href="https://www.alsa-project.org/">Advanced Linux Sound
Architecture</a> is required on Linux. At least version 0.9.1 of ALSA is
required.</p>
<ul>
<li>To install on an apt-based Linux, try running
<code>sudo apt-get install     libasound2-dev</code>.</li>
<li>To install on an rpm-based Linux, try running
<code>sudo yum install     alsa-lib-devel</code>.</li>
<li>To install on Alpine Linux, try running
<code>sudo apk add alsa-lib-dev</code>.</li>
</ul>
<p>Use <code>--with-alsa=&lt;path&gt;</code> if <code>configure</code>
does not properly locate your ALSA files.</p>
<h3 id="libffi">libffi</h3>
<p>libffi, the <a href="http://sourceware.org/libffi">Portable Foreign
Function Interface Library</a> is required when building the Zero
version of Hotspot.</p>
<ul>
<li>To install on an apt-based Linux, try running
<code>sudo apt-get install     libffi-dev</code>.</li>
<li>To install on an rpm-based Linux, try running
<code>sudo yum install     libffi-devel</code>.</li>
<li>To install on Alpine Linux, try running
<code>sudo apk add libffi-dev</code>.</li>
</ul>
<p>Use <code>--with-libffi=&lt;path&gt;</code> if <code>configure</code>
does not properly locate your libffi files.</p>
<h2 id="build-tools-requirements">Build Tools Requirements</h2>
<h3 id="autoconf">Autoconf</h3>
<p>The JDK requires <a
href="http://www.gnu.org/software/autoconf">Autoconf</a> on all
platforms. At least version 2.69 is required.</p>
<ul>
<li>To install on an apt-based Linux, try running
<code>sudo apt-get install     autoconf</code>.</li>
<li>To install on an rpm-based Linux, try running
<code>sudo yum install     autoconf</code>.</li>
<li>To install on Alpine Linux, try running
<code>sudo apk add autoconf</code>.</li>
<li>To install on macOS, try running
<code>brew install autoconf</code>.</li>
<li>To install on Windows, try running
<code>&lt;path to Cygwin setup&gt;/setup-x86_64 -q     -P autoconf</code>.</li>
</ul>
<p>If <code>configure</code> has problems locating your installation of
autoconf, you can specify it using the <code>AUTOCONF</code> environment
variable, like this:</p>
<pre><code>AUTOCONF=&lt;path to autoconf&gt; configure ...</code></pre>
<h3 id="gnu-make">GNU Make</h3>
<p>The JDK requires <a href="http://www.gnu.org/software/make">GNU
Make</a>. No other flavors of make are supported.</p>
<p>At least version 3.81 of GNU Make must be used. For distributions
supporting GNU Make 4.0 or above, we strongly recommend it. GNU Make 4.0
contains useful functionality to handle parallel building (supported by
<code>--with-output-sync</code>) and speed and stability
improvements.</p>
<p>Note that <code>configure</code> locates and verifies a properly
functioning version of <code>make</code> and stores the path to this
<code>make</code> binary in the configuration. If you start a build
using <code>make</code> on the command line, you will be using the
version of make found first in your <code>PATH</code>, and not
necessarily the one stored in the configuration. This initial make will
be used as "bootstrap make", and in a second stage, the make located by
<code>configure</code> will be called. Normally, this will present no
issues, but if you have a very old <code>make</code>, or a non-GNU Make
<code>make</code> in your path, this might cause issues.</p>
<p>If you want to override the default make found by
<code>configure</code>, use the <code>MAKE</code> configure variable,
e.g. <code>configure MAKE=/opt/gnu/make</code>.</p>
<h3 id="gnu-bash">GNU Bash</h3>
<p>The JDK requires <a href="http://www.gnu.org/software/bash">GNU
Bash</a>. No other shells are supported.</p>
<p>At least version 3.2 of GNU Bash must be used.</p>
<h2 id="running-configure">Running Configure</h2>
<p>To build the JDK, you need a "configuration", which consists of a
directory where to store the build output, coupled with information
about the platform, the specific build machine, and choices that affect
how the JDK is built.</p>
<p>The configuration is created by the <code>configure</code> script.
The basic invocation of the <code>configure</code> script looks like
this:</p>
<pre><code>bash configure [options]</code></pre>
<p>This will create an output directory containing the configuration and
setup an area for the build result. This directory typically looks like
<code>build/linux-x64-server-release</code>, but the actual name depends
on your specific configuration. (It can also be set directly, see <a
href="#using-multiple-configurations">Using Multiple
Configurations</a>). This directory is referred to as
<code>$BUILD</code> in this documentation.</p>
<p><code>configure</code> will try to figure out what system you are
running on and where all necessary build components are. If you have all
prerequisites for building installed, it should find everything. If it
fails to detect any component automatically, it will exit and inform you
about the problem.</p>
<p>Some command line examples:</p>
<ul>
<li><p>Create a 32-bit build for Windows with FreeType2 in
<code>C:\freetype-i586</code>:
<code>bash configure --with-freetype=/cygdrive/c/freetype-i586 --with-target-bits=32</code></p></li>
<li><p>Create a debug build with the <code>server</code> JVM and DTrace
enabled:
<code>bash configure --enable-debug --with-jvm-variants=server --enable-dtrace</code></p></li>
</ul>
<h3 id="common-configure-arguments">Common Configure Arguments</h3>
<p>Here follows some of the most common and important
<code>configure</code> argument.</p>
<p>To get up-to-date information on <em>all</em> available
<code>configure</code> argument, please run:</p>
<pre><code>bash configure --help</code></pre>
<p>(Note that this help text also include general autoconf options, like
<code>--dvidir</code>, that is not relevant to the JDK. To list only
JDK-specific features, use <code>bash configure --help=short</code>
instead.)</p>
<h4 id="configure-arguments-for-tailoring-the-build">Configure Arguments
for Tailoring the Build</h4>
<ul>
<li><code>--enable-debug</code> - Set the debug level to
<code>fastdebug</code> (this is a shorthand for
<code>--with-debug-level=fastdebug</code>)</li>
<li><code>--with-debug-level=&lt;level&gt;</code> - Set the debug level,
which can be <code>release</code>, <code>fastdebug</code>,
<code>slowdebug</code> or <code>optimized</code>. Default is
<code>release</code>. <code>optimized</code> is variant of
<code>release</code> with additional Hotspot debug code.</li>
<li><code>--with-native-debug-symbols=&lt;method&gt;</code> - Specify if
and how native debug symbols should be built. Available methods are
<code>none</code>, <code>internal</code>, <code>external</code>,
<code>zipped</code>. Default behavior depends on platform. See <a
href="#native-debug-symbols">Native Debug Symbols</a> for more
details.</li>
<li><code>--with-version-string=&lt;string&gt;</code> - Specify the
version string this build will be identified with.</li>
<li><code>--with-version-&lt;part&gt;=&lt;value&gt;</code> - A group of
options, where <code>&lt;part&gt;</code> can be any of <code>pre</code>,
<code>opt</code>, <code>build</code>, <code>major</code>,
<code>minor</code>, <code>security</code> or <code>patch</code>. Use
these options to modify just the corresponding part of the version
string from the default, or the value provided by
<code>--with-version-string</code>.</li>
<li><code>--with-jvm-variants=&lt;variant&gt;[,&lt;variant&gt;...]</code>
- Build the specified variant (or variants) of Hotspot. Valid variants
are: <code>server</code>, <code>client</code>, <code>minimal</code>,
<code>core</code>, <code>zero</code>, <code>custom</code>. Note that not
all variants are possible to combine in a single build.</li>
<li><code>--enable-jvm-feature-&lt;feature&gt;</code> or
<code>--disable-jvm-feature-&lt;feature&gt;</code> - Include (or
exclude) <code>&lt;feature&gt;</code> as a JVM feature in Hotspot. You
can also specify a list of features to be enabled, separated by space or
comma, as
<code>--with-jvm-features=&lt;feature&gt;[,&lt;feature&gt;...]</code>.
If you prefix <code>&lt;feature&gt;</code> with a <code>-</code>, it
will be disabled. These options will modify the default list of features
for the JVM variant(s) you are building. For the <code>custom</code> JVM
variant, the default list is empty. A complete list of valid JVM
features can be found using <code>bash configure --help</code>.</li>
<li><code>--with-target-bits=&lt;bits&gt;</code> - Create a target
binary suitable for running on a <code>&lt;bits&gt;</code> platform. Use
this to create 32-bit output on a 64-bit build platform, instead of
doing a full cross-compile. (This is known as a <em>reduced</em>
build.)</li>
</ul>
<p>On Linux, BSD and AIX, it is possible to override where Java by
default searches for runtime/JNI libraries. This can be useful in
situations where there is a special shared directory for system JNI
libraries. This setting can in turn be overridden at runtime by setting
the <code>java.library.path</code> property.</p>
<ul>
<li><code>--with-jni-libpath=&lt;path&gt;</code> - Use the specified
path as a default when searching for runtime libraries.</li>
</ul>
<h4 id="configure-arguments-for-native-compilation">Configure Arguments
for Native Compilation</h4>
<ul>
<li><code>--with-devkit=&lt;path&gt;</code> - Use this devkit for
compilers, tools and resources</li>
<li><code>--with-sysroot=&lt;path&gt;</code> - Use this directory as
sysroot</li>
<li><code>--with-extra-path=&lt;path&gt;[;&lt;path&gt;]</code> - Prepend
these directories to the default path when searching for all kinds of
binaries</li>
<li><code>--with-toolchain-path=&lt;path&gt;[;&lt;path&gt;]</code> -
Prepend these directories when searching for toolchain binaries
(compilers etc)</li>
<li><code>--with-extra-cflags=&lt;flags&gt;</code> - Append these flags
when compiling JDK C files</li>
<li><code>--with-extra-cxxflags=&lt;flags&gt;</code> - Append these
flags when compiling JDK C++ files</li>
<li><code>--with-extra-ldflags=&lt;flags&gt;</code> - Append these flags
when linking JDK libraries</li>
</ul>
<h4 id="configure-arguments-for-external-dependencies">Configure
Arguments for External Dependencies</h4>
<ul>
<li><code>--with-boot-jdk=&lt;path&gt;</code> - Set the path to the <a
href="#boot-jdk-requirements">Boot JDK</a></li>
<li><code>--with-freetype=&lt;path&gt;</code> - Set the path to <a
href="#freetype">FreeType</a></li>
<li><code>--with-cups=&lt;path&gt;</code> - Set the path to <a
href="#cups">CUPS</a></li>
<li><code>--with-x=&lt;path&gt;</code> - Set the path to <a
href="#x11">X11</a></li>
<li><code>--with-alsa=&lt;path&gt;</code> - Set the path to <a
href="#alsa">ALSA</a></li>
<li><code>--with-libffi=&lt;path&gt;</code> - Set the path to <a
href="#libffi">libffi</a></li>
<li><code>--with-jtreg=&lt;path&gt;</code> - Set the path to JTReg. See
<a href="#running-tests">Running Tests</a></li>
</ul>
<p>Certain third-party libraries used by the JDK (libjpeg, giflib,
libpng, lcms and zlib) are included in the JDK repository. The default
behavior of the JDK build is to use the included ("bundled") versions of
libjpeg, giflib, libpng and lcms. For zlib, the system lib (if present)
is used except on Windows and AIX. However the bundled libraries may be
replaced by an external version. To do so, specify <code>system</code>
as the <code>&lt;source&gt;</code> option in these arguments. (The
default is <code>bundled</code>).</p>
<ul>
<li><code>--with-libjpeg=&lt;source&gt;</code> - Use the specified
source for libjpeg</li>
<li><code>--with-giflib=&lt;source&gt;</code> - Use the specified source
for giflib</li>
<li><code>--with-libpng=&lt;source&gt;</code> - Use the specified source
for libpng</li>
<li><code>--with-lcms=&lt;source&gt;</code> - Use the specified source
for lcms</li>
<li><code>--with-zlib=&lt;source&gt;</code> - Use the specified source
for zlib</li>
</ul>
<p>On Linux, it is possible to select either static or dynamic linking
of the C++ runtime. The default is static linking, with dynamic linking
as fallback if the static library is not found.</p>
<ul>
<li><code>--with-stdc++lib=&lt;method&gt;</code> - Use the specified
method (<code>static</code>, <code>dynamic</code> or
<code>default</code>) for linking the C++ runtime.</li>
</ul>
<h3 id="configure-control-variables">Configure Control Variables</h3>
<p>It is possible to control certain aspects of <code>configure</code>
by overriding the value of <code>configure</code> variables, either on
the command line or in the environment.</p>
<p>Normally, this is <strong>not recommended</strong>. If used
improperly, it can lead to a broken configuration. Unless you're well
versed in the build system, this is hard to use properly. Therefore,
<code>configure</code> will print a warning if this is detected.</p>
<p>However, there are a few <code>configure</code> variables, known as
<em>control variables</em> that are supposed to be overridden on the
command line. These are variables that describe the location of tools
needed by the build, like <code>MAKE</code> or <code>GREP</code>. If any
such variable is specified, <code>configure</code> will use that value
instead of trying to autodetect the tool. For instance,
<code>bash configure MAKE=/opt/gnumake4.0/bin/make</code>.</p>
<p>If a configure argument exists, use that instead, e.g. use
<code>--with-jtreg</code> instead of setting <code>JTREGEXE</code>.</p>
<p>Also note that, despite what autoconf claims, setting
<code>CFLAGS</code> will not accomplish anything. Instead use
<code>--with-extra-cflags</code> (and similar for <code>cxxflags</code>
and <code>ldflags</code>).</p>
<h2 id="running-make">Running Make</h2>
<p>When you have a proper configuration, all you need to do to build the
JDK is to run <code>make</code>. (But see the warning at <a
href="#gnu-make">GNU Make</a> about running the correct version of
make.)</p>
<p>When running <code>make</code> without any arguments, the default
target is used, which is the same as running <code>make default</code>
or <code>make jdk</code>. This will build a minimal (or roughly minimal)
set of compiled output (known as an "exploded image") needed for a
developer to actually execute the newly built JDK. The idea is that in
an incremental development fashion, when doing a normal make, you should
only spend time recompiling what's changed (making it purely
incremental) and only do the work that's needed to actually run and test
your code.</p>
<p>The output of the exploded image resides in <code>$BUILD/jdk</code>.
You can test the newly built JDK like this:
<code>$BUILD/jdk/bin/java -version</code>.</p>
<h3 id="common-make-targets">Common Make Targets</h3>
<p>Apart from the default target, here are some common make targets:</p>
<ul>
<li><code>hotspot</code> - Build all of hotspot (but only hotspot)</li>
<li><code>hotspot-&lt;variant&gt;</code> - Build just the specified jvm
variant</li>
<li><code>images</code> or <code>product-images</code> - Build the JDK
image</li>
<li><code>docs</code> or <code>docs-image</code> - Build the
documentation image</li>
<li><code>test-image</code> - Build the test image</li>
<li><code>all</code> or <code>all-images</code> - Build all images
(product, docs and test)</li>
<li><code>bootcycle-images</code> - Build images twice, second time with
newly built JDK (good for testing)</li>
<li><code>clean</code> - Remove all files generated by make, but not
those generated by configure</li>
<li><code>dist-clean</code> - Remove all files, including
configuration</li>
</ul>
<p>Run <code>make help</code> to get an up-to-date list of important
make targets and make control variables.</p>
<p>It is possible to build just a single module, a single phase, or a
single phase of a single module, by creating make targets according to
these followin patterns. A phase can be either of <code>gensrc</code>,
<code>gendata</code>, <code>copy</code>, <code>java</code>,
<code>launchers</code>, or <code>libs</code>. See <a
href="#using-fine-grained-make-targets">Using Fine-Grained Make
Targets</a> for more details about this functionality.</p>
<ul>
<li><code>&lt;phase&gt;</code> - Build the specified phase and
everything it depends on</li>
<li><code>&lt;module&gt;</code> - Build the specified module and
everything it depends on</li>
<li><code>&lt;module&gt;-&lt;phase&gt;</code> - Compile the specified
phase for the specified module and everything it depends on</li>
</ul>
<p>Similarly, it is possible to clean just a part of the build by
creating make targets according to these patterns:</p>
<ul>
<li><code>clean-&lt;outputdir&gt;</code> - Remove the subdir in the
output dir with the name</li>
<li><code>clean-&lt;phase&gt;</code> - Remove all build results related
to a certain build phase</li>
<li><code>clean-&lt;module&gt;</code> - Remove all build results related
to a certain module</li>
<li><code>clean-&lt;module&gt;-&lt;phase&gt;</code> - Remove all build
results related to a certain module and phase</li>
</ul>
<h3 id="make-control-variables">Make Control Variables</h3>
<p>It is possible to control <code>make</code> behavior by overriding
the value of <code>make</code> variables, either on the command line or
in the environment.</p>
<p>Normally, this is <strong>not recommended</strong>. If used
improperly, it can lead to a broken build. Unless you're well versed in
the build system, this is hard to use properly. Therefore,
<code>make</code> will print a warning if this is detected.</p>
<p>However, there are a few <code>make</code> variables, known as
<em>control variables</em> that are supposed to be overridden on the
command line. These make up the "make time" configuration, as opposed to
the "configure time" configuration.</p>
<h4 id="general-make-control-variables">General Make Control
Variables</h4>
<ul>
<li><code>JOBS</code> - Specify the number of jobs to build with. See <a
href="#build-performance">Build Performance</a>.</li>
<li><code>LOG</code> - Specify the logging level and functionality. See
<a href="#checking-the-build-log-file">Checking the Build Log
File</a></li>
<li><code>CONF</code> and <code>CONF_NAME</code> - Selecting the
configuration(s) to use. See <a
href="#using-multiple-configurations">Using Multiple
Configurations</a></li>
</ul>
<h4 id="test-make-control-variables">Test Make Control Variables</h4>
<p>These make control variables only make sense when running tests.
Please see <strong>Testing the JDK</strong> (<a
href="testing.html">html</a>, <a href="testing.md">markdown</a>) for
details.</p>
<ul>
<li><code>TEST</code></li>
<li><code>TEST_JOBS</code></li>
<li><code>JTREG</code></li>
<li><code>GTEST</code></li>
</ul>
<h4 id="advanced-make-control-variables">Advanced Make Control
Variables</h4>
<p>These advanced make control variables can be potentially unsafe. See
<a href="#hints-and-suggestions-for-advanced-users">Hints and
Suggestions for Advanced Users</a> and <a
href="#understanding-the-build-system">Understanding the Build
System</a> for details.</p>
<ul>
<li><code>SPEC</code></li>
<li><code>CONF_CHECK</code></li>
<li><code>COMPARE_BUILD</code></li>
<li><code>JDK_FILTER</code></li>
<li><code>SPEC_FILTER</code></li>
</ul>
<h2 id="running-tests">Running Tests</h2>
<p>Most of the JDK tests are using the <a
href="http://openjdk.org/jtreg">JTReg</a> test framework. Make sure that
your configuration knows where to find your installation of JTReg. If
this is not picked up automatically, use the
<code>--with-jtreg=&lt;path to jtreg home&gt;</code> option to point to
the JTReg framework. Note that this option should point to the JTReg
home, i.e. the top directory, containing <code>lib/jtreg.jar</code>
etc.</p>
<p>The <a href="https://wiki.openjdk.org/display/Adoption">Adoption
Group</a> provides recent builds of jtreg <a
href="https://ci.adoptium.net/view/Dependencies/job/dependency_pipeline/lastSuccessfulBuild/artifact/jtreg/">here</a>.
Download the latest <code>.tar.gz</code> file, unpack it, and point
<code>--with-jtreg</code> to the <code>jtreg</code> directory that you
just unpacked.</p>
<p>Building of Hotspot Gtest suite requires the source code of Google
Test framework. The top directory, which contains both
<code>googletest</code> and <code>googlemock</code> directories, should
be specified via <code>--with-gtest</code>. The minimum supported
version of Google Test is 1.13.0, whose source code can be obtained:</p>
<ul>
<li>by downloading and unpacking the source bundle from <a
href="https://github.com/google/googletest/releases/tag/v1.13.0">here</a></li>
<li>or by checking out <code>v1.13.0</code> tag of
<code>googletest</code> project:
<code>git clone -b v1.13.0 https://github.com/google/googletest</code></li>
</ul>
<p>To execute the most basic tests (tier 1), use:</p>
<pre><code>make run-test-tier1</code></pre>
<p>For more details on how to run tests, please see <strong>Testing the
JDK</strong> (<a href="testing.html">html</a>, <a
href="testing.md">markdown</a>).</p>
<h2 id="signing">Signing</h2>
<h3 id="macos-1">macOS</h3>
<p>Modern versions of macOS require applications to be signed and
notarizied before distribution. See Apple's documentation for more
background on what this means and how it works. To help support this,
the JDK build can be configured to automatically sign all native
binaries, and the JDK bundle, with all the options needed for successful
notarization, as well as all the entitlements required by the JDK. To
enable <code>hardened</code> signing, use configure parameter
<code>--with-macosx-codesign=hardened</code> and configure the signing
identity you wish to use with
<code>--with-macosx-codesign-identity=&lt;identity&gt;</code>. The
identity refers to a signing identity from Apple that needs to be
preinstalled on the build host.</p>
<p>When not signing for distribution with the hardened option, the JDK
build will still attempt to perform <code>adhoc</code> signing to add
the special entitlement <code>com.apple.security.get-task-allow</code>
to each binary. This entitlement is required to be able to dump core
files from a process. Note that adding this entitlement makes the build
invalid for notarization, so it is only added when signing in
<code>debug</code> mode. To explicitly enable this kind of adhoc
signing, use configure parameter
<code>--with-macosx-codesign=debug</code>. It will be enabled by default
in most cases.</p>
<p>It's also possible to completely disable any explicit codesign
operations done by the JDK build using the configure parameter
<code>--without-macosx-codesign</code>. The exact behavior then depends
on the architecture. For macOS on x64, it (at least at the time of this
writing) results in completely unsigned binaries that should still work
fine for development and debugging purposes. On aarch64, the Xcode
linker will apply a default "adhoc" signing, without any entitlements.
Such a build does not allow dumping core files.</p>
<p>The default mode "auto" will try for <code>hardened</code> signing if
the debug level is <code>release</code> and either the default identity
or the specified identity is valid. If hardened isn't possible, then
<code>debug</code> signing is chosen if it works. If nothing works, the
codesign build step is disabled.</p>
<h2 id="cross-compiling">Cross-compiling</h2>
<p>Cross-compiling means using one platform (the <em>build</em>
platform) to generate output that can ran on another platform (the
<em>target</em> platform).</p>
<p>The typical reason for cross-compiling is that the build is performed
on a more powerful desktop computer, but the resulting binaries will be
able to run on a different, typically low-performing system. Most of the
complications that arise when building for embedded is due to this
separation of <em>build</em> and <em>target</em> systems.</p>
<p>This requires a more complex setup and build procedure. This section
assumes you are familiar with cross-compiling in general, and will only
deal with the particularities of cross-compiling the JDK. If you are new
to cross-compiling, please see the <a
href="https://en.wikipedia.org/wiki/Cross_compiler#External_links">external
links at Wikipedia</a> for a good start on reading materials.</p>
<p>Cross-compiling the JDK requires you to be able to build both for the
build platform and for the target platform. The reason for the former is
that we need to build and execute tools during the build process, both
native tools and Java tools.</p>
<p>If all you want to do is to compile a 32-bit version, for the same
OS, on a 64-bit machine, consider using
<code>--with-target-bits=32</code> instead of doing a full-blown
cross-compilation. (While this surely is possible, it's a lot more work
and will take much longer to build.)</p>
<h3 id="cross-compiling-the-easy-way-with-openjdk-devkits">Cross
compiling the easy way with OpenJDK devkits</h3>
<p>The OpenJDK build system provides out-of-the box support for creating
and using so called devkits. A <code>devkit</code> is basically a
collection of a cross-compiling toolchain and a sysroot environment
which can easily be used together with the <code>--with-devkit</code>
configure option to cross compile the OpenJDK. On Linux/x86_64, the
following command:</p>
<pre><code>bash configure --with-devkit=&lt;devkit-path&gt; --openjdk-target=ppc64-linux-gnu &amp;&amp; make</code></pre>
<p>will configure and build OpenJDK for Linux/ppc64 assuming that
<code>&lt;devkit-path&gt;</code> points to a Linux/x86_64 to Linux/ppc64
devkit.</p>
<p>Devkits can be created from the <code>make/devkit</code> directory by
executing:</p>
<pre><code>make [ TARGETS=&quot;&lt;TARGET_TRIPLET&gt;+&quot; ] [ BASE_OS=&lt;OS&gt; ] [ BASE_OS_VERSION=&lt;VER&gt; ]</code></pre>
<p>where <code>TARGETS</code> contains one or more
<code>TARGET_TRIPLET</code>s of the form described in <a
href="https://sourceware.org/autobook/autobook/autobook_17.html">section
3.4 of the GNU Autobook</a>. If no targets are given, a native toolchain
for the current platform will be created. Currently, at least the
following targets are known to work:</p>
<table>
<thead>
<tr class="header">
<th>Supported devkit targets</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td>x86_64-linux-gnu</td>
</tr>
<tr class="even">
<td>aarch64-linux-gnu</td>
</tr>
<tr class="odd">
<td>arm-linux-gnueabihf</td>
</tr>
<tr class="even">
<td>ppc64-linux-gnu</td>
</tr>
<tr class="odd">
<td>ppc64le-linux-gnu</td>
</tr>
<tr class="even">
<td>s390x-linux-gnu</td>
</tr>
</tbody>
</table>
<p><code>BASE_OS</code> must be one of "OEL6" for Oracle Enterprise
Linux 6 or "Fedora" (if not specified "OEL6" will be the default). If
the base OS is "Fedora" the corresponding Fedora release can be
specified with the help of the <code>BASE_OS_VERSION</code> option (with
"27" as default version). If the build is successful, the new devkits
can be found in the <code>build/devkit/result</code> subdirectory:</p>
<pre><code>cd make/devkit
make TARGETS=&quot;ppc64le-linux-gnu aarch64-linux-gnu&quot; BASE_OS=Fedora BASE_OS_VERSION=21
ls -1 ../../build/devkit/result/
x86_64-linux-gnu-to-aarch64-linux-gnu
x86_64-linux-gnu-to-ppc64le-linux-gnu</code></pre>
<p>Notice that devkits are not only useful for targeting different build
platforms. Because they contain the full build dependencies for a system
(i.e. compiler and root file system), they can easily be used to build
well-known, reliable and reproducible build environments. You can for
example create and use a devkit with GCC 7.3 and a Fedora 12 sysroot
environment (with glibc 2.11) on Ubuntu 14.04 (which doesn't have GCC
7.3 by default) to produce OpenJDK binaries which will run on all Linux
systems with runtime libraries newer than the ones from Fedora 12 (e.g.
Ubuntu 16.04, SLES 11 or RHEL 6).</p>
<h3 id="boot-jdk-and-build-jdk">Boot JDK and Build JDK</h3>
<p>When cross-compiling, make sure you use a boot JDK that runs on the
<em>build</em> system, and not on the <em>target</em> system.</p>
<p>To be able to build, we need a "Build JDK", which is a JDK built from
the current sources (that is, the same as the end result of the entire
build process), but able to run on the <em>build</em> system, and not
the <em>target</em> system. (In contrast, the Boot JDK should be from an
older release, e.g. JDK 8 when building JDK 9.)</p>
<p>The build process will create a minimal Build JDK for you, as part of
building. To speed up the build, you can use
<code>--with-build-jdk</code> to <code>configure</code> to point to a
pre-built Build JDK. Please note that the build result is unpredictable,
and can possibly break in subtle ways, if the Build JDK does not
<strong>exactly</strong> match the current sources.</p>
<h3 id="specifying-the-target-platform">Specifying the Target
Platform</h3>
<p>You <em>must</em> specify the target platform when cross-compiling.
Doing so will also automatically turn the build into a cross-compiling
mode. The simplest way to do this is to use the
<code>--openjdk-target</code> argument, e.g.
<code>--openjdk-target=arm-linux-gnueabihf</code>. or
<code>--openjdk-target=aarch64-oe-linux</code>. This will automatically
set the <code>--host</code> and <code>--target</code> options for
autoconf, which can otherwise be confusing. (In autoconf terminology,
the "target" is known as "host", and "target" is used for building a
Canadian cross-compiler.)</p>
<p>If <code>--build</code> has not been explicitly passed to configure,
<code>--openjdk-target</code> will autodetect the build platform and
internally set the flag automatically, otherwise the platform that was
explicitly passed to <code>--build</code> will be used instead.</p>
<h3 id="toolchain-considerations">Toolchain Considerations</h3>
<p>You will need two copies of your toolchain, one which generates
output that can run on the target system (the normal, or
<em>target</em>, toolchain), and one that generates output that can run
on the build system (the <em>build</em> toolchain). Note that
cross-compiling is only supported for gcc at the time being. The gcc
standard is to prefix cross-compiling toolchains with the target
denominator. If you follow this standard, <code>configure</code> is
likely to pick up the toolchain correctly.</p>
<p>The <em>build</em> toolchain will be autodetected just the same way
the normal <em>build</em>/<em>target</em> toolchain will be autodetected
when not cross-compiling. If this is not what you want, or if the
autodetection fails, you can specify a devkit containing the
<em>build</em> toolchain using <code>--with-build-devkit</code> to
<code>configure</code>, or by giving <code>BUILD_CC</code> and
<code>BUILD_CXX</code> arguments.</p>
<p>It is often helpful to locate the cross-compilation tools, headers
and libraries in a separate directory, outside the normal path, and
point out that directory to <code>configure</code>. Do this by setting
the sysroot (<code>--with-sysroot</code>) and appending the directory
when searching for cross-compilations tools
(<code>--with-toolchain-path</code>). As a compact form, you can also
use <code>--with-devkit</code> to point to a single directory, if it is
correctly setup. (See <code>basics.m4</code> for details.)</p>
<h3 id="native-libraries">Native Libraries</h3>
<p>You will need copies of external native libraries for the
<em>target</em> system, present on the <em>build</em> machine while
building.</p>
<p>Take care not to replace the <em>build</em> system's version of these
libraries by mistake, since that can render the <em>build</em> machine
unusable.</p>
<p>Make sure that the libraries you point to (ALSA, X11, etc) are for
the <em>target</em>, not the <em>build</em>, platform.</p>
<h4 id="alsa-1">ALSA</h4>
<p>You will need alsa libraries suitable for your <em>target</em>
system. For most cases, using Debian's pre-built libraries work
fine.</p>
<p>Note that alsa is needed even if you only want to build a headless
JDK.</p>
<ul>
<li><p>Go to <a href="https://www.debian.org/distrib/packages">Debian
Package Search</a> and search for the <code>libasound2</code> and
<code>libasound2-dev</code> packages for your <em>target</em> system.
Download them to /tmp.</p></li>
<li><p>Install the libraries into the cross-compilation toolchain. For
instance:</p></li>
</ul>
<pre><code>cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc
dpkg-deb -x /tmp/libasound2_1.0.25-4_armhf.deb .
dpkg-deb -x /tmp/libasound2-dev_1.0.25-4_armhf.deb .</code></pre>
<ul>
<li>If alsa is not properly detected by <code>configure</code>, you can
point it out by <code>--with-alsa</code>.</li>
</ul>
<h4 id="x11-1">X11</h4>
<p>You will need X11 libraries suitable for your <em>target</em> system.
For most cases, using Debian's pre-built libraries work fine.</p>
<p>Note that X11 is needed even if you only want to build a headless
JDK.</p>
<ul>
<li><p>Go to <a href="https://www.debian.org/distrib/packages">Debian
Package Search</a>, search for the following packages for your
<em>target</em> system, and download them to /tmp/target-x11:</p>
<ul>
<li>libxi</li>
<li>libxi-dev</li>
<li>x11proto-core-dev</li>
<li>x11proto-input-dev</li>
<li>x11proto-kb-dev</li>
<li>x11proto-render-dev</li>
<li>x11proto-xext-dev</li>
<li>libice-dev</li>
<li>libxrender</li>
<li>libxrender-dev</li>
<li>libxrandr-dev</li>
<li>libsm-dev</li>
<li>libxt-dev</li>
<li>libx11</li>
<li>libx11-dev</li>
<li>libxtst</li>
<li>libxtst-dev</li>
<li>libxext</li>
<li>libxext-dev</li>
</ul></li>
<li><p>Install the libraries into the cross-compilation toolchain. For
instance:</p>
<pre><code>    cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc/usr
    mkdir X11R6
    cd X11R6
    for deb in /tmp/target-x11/*.deb ; do dpkg-deb -x $deb . ; done
    mv usr/* .
    cd lib
    cp arm-linux-gnueabihf/* .
    ```

You can ignore the following messages. These libraries are not needed to
successfully complete a full JDK build.</code></pre>
<p>cp: cannot stat
<code>arm-linux-gnueabihf/libICE.so': No such file or directory cp: cannot stat</code>arm-linux-gnueabihf/libSM.so':
No such file or directory cp: cannot stat
`arm-linux-gnueabihf/libXt.so': No such file or directory ```</p></li>
<li><p>If the X11 libraries are not properly detected by
<code>configure</code>, you can point them out by
<code>--with-x</code>.</p></li>
</ul>
<h3 id="cross-compiling-with-debian-sysroots">Cross compiling with
Debian sysroots</h3>
<p>Fortunately, you can create sysroots for foreign architectures with
tools provided by your OS. On Debian/Ubuntu systems, one could use
<code>debootstrap</code> to create the <em>target</em> system chroot,
which would have the native libraries and headers specific to that
<em>target</em> system. After that, we can use the cross-compiler on the
<em>build</em> system, pointing into chroot to get the build
dependencies right. This allows building for foreign architectures with
native compilation speed.</p>
<p>For example, cross-compiling to AArch64 from x86_64 could be done
like this:</p>
<ul>
<li><p>Install cross-compiler on the <em>build</em> system:
<code>apt install g++-aarch64-linux-gnu gcc-aarch64-linux-gnu</code></p></li>
<li><p>Create chroot on the <em>build</em> system, configuring it for
<em>target</em> system:
<code>sudo debootstrap \       --arch=arm64 \       --verbose \       --include=fakeroot,symlinks,build-essential,libx11-dev,libxext-dev,libxrender-dev,libxrandr-dev,libxtst-dev,libxt-dev,libcups2-dev,libfontconfig1-dev,libasound2-dev,libfreetype6-dev,libpng-dev,libffi-dev \       --resolve-deps \       buster \       ~/sysroot-arm64 \       http://httpredir.debian.org/debian/     # If the target architecture is `riscv64`,     # the path should be `debian-ports` instead of `debian`.</code></p></li>
<li><p>Make sure the symlinks inside the newly created chroot point to
proper locations:
<code>sudo chroot ~/sysroot-arm64 symlinks -cr .</code></p></li>
<li><p>Configure and build with newly created chroot as
sysroot/toolchain-path:
<code>sh ./configure \       --openjdk-target=aarch64-linux-gnu \       --with-sysroot=~/sysroot-arm64     make images     ls build/linux-aarch64-server-release/</code></p></li>
</ul>
<p>The build does not create new files in that chroot, so it can be
reused for multiple builds without additional cleanup.</p>
<p>The build system should automatically detect the toolchain paths and
dependencies, but sometimes it might require a little nudge with:</p>
<ul>
<li><p>Native compilers: override <code>CC</code> or <code>CXX</code>
for <code>./configure</code></p></li>
<li><p>Freetype lib location: override <code>--with-freetype-lib</code>,
for example <code>${sysroot}/usr/lib/${target}/</code></p></li>
<li><p>Freetype includes location: override
<code>--with-freetype-include</code> for example
<code>${sysroot}/usr/include/freetype2/</code></p></li>
<li><p>X11 libraries location: override <code>--x-libraries</code>, for
example <code>${sysroot}/usr/lib/${target}/</code></p></li>
</ul>
<p>Architectures that are known to successfully cross-compile like this
are:</p>
<table>
<colgroup>
<col style="width: 13%" />
<col style="width: 13%" />
<col style="width: 15%" />
<col style="width: 27%" />
<col style="width: 29%" />
</colgroup>
<thead>
<tr class="header">
<th>Target</th>
<th>Debian tree</th>
<th>Debian arch</th>
<th><code>--openjdk-target=...</code></th>
<th><code>--with-jvm-variants=...</code></th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td>x86</td>
<td>buster</td>
<td>i386</td>
<td>i386-linux-gnu</td>
<td>(all)</td>
</tr>
<tr class="even">
<td>arm</td>
<td>buster</td>
<td>armhf</td>
<td>arm-linux-gnueabihf</td>
<td>(all)</td>
</tr>
<tr class="odd">
<td>aarch64</td>
<td>buster</td>
<td>arm64</td>
<td>aarch64-linux-gnu</td>
<td>(all)</td>
</tr>
<tr class="even">
<td>ppc64le</td>
<td>buster</td>
<td>ppc64el</td>
<td>powerpc64le-linux-gnu</td>
<td>(all)</td>
</tr>
<tr class="odd">
<td>s390x</td>
<td>buster</td>
<td>s390x</td>
<td>s390x-linux-gnu</td>
<td>(all)</td>
</tr>
<tr class="even">
<td>mipsle</td>
<td>buster</td>
<td>mipsel</td>
<td>mipsel-linux-gnu</td>
<td>zero</td>
</tr>
<tr class="odd">
<td>mips64le</td>
<td>buster</td>
<td>mips64el</td>
<td>mips64el-linux-gnueabi64</td>
<td>zero</td>
</tr>
<tr class="even">
<td>armel</td>
<td>buster</td>
<td>arm</td>
<td>arm-linux-gnueabi</td>
<td>zero</td>
</tr>
<tr class="odd">
<td>ppc</td>
<td>sid</td>
<td>powerpc</td>
<td>powerpc-linux-gnu</td>
<td>zero</td>
</tr>
<tr class="even">
<td>ppc64be</td>
<td>sid</td>
<td>ppc64</td>
<td>powerpc64-linux-gnu</td>
<td>(all)</td>
</tr>
<tr class="odd">
<td>m68k</td>
<td>sid</td>
<td>m68k</td>
<td>m68k-linux-gnu</td>
<td>zero</td>
</tr>
<tr class="even">
<td>alpha</td>
<td>sid</td>
<td>alpha</td>
<td>alpha-linux-gnu</td>
<td>zero</td>
</tr>
<tr class="odd">
<td>sh4</td>
<td>sid</td>
<td>sh4</td>
<td>sh4-linux-gnu</td>
<td>zero</td>
</tr>
<tr class="even">
<td>riscv64</td>
<td>sid</td>
<td>riscv64</td>
<td>riscv64-linux-gnu</td>
<td>(all)</td>
</tr>
</tbody>
</table>
<h3 id="building-for-armaarch64">Building for ARM/aarch64</h3>
<p>A common cross-compilation target is the ARM CPU. When building for
ARM, it is useful to set the ABI profile. A number of pre-defined ABI
profiles are available using <code>--with-abi-profile</code>:
arm-vfp-sflt, arm-vfp-hflt, arm-sflt, armv5-vfp-sflt, armv6-vfp-hflt.
Note that soft-float ABIs are no longer properly supported by the
JDK.</p>
<h3 id="building-for-risc-v">Building for RISC-V</h3>
<p>The RISC-V community provides a basic <a
href="https://github.com/riscv-collab/riscv-gnu-toolchain">GNU compiler
toolchain</a>, but the <a href="#External-Library-Requirements">external
libraries</a> required by OpenJDK complicate the building process. The
placeholder <code>&lt;toolchain-installed-path&gt;</code> shown below is
the path where you want to install the toolchain.</p>
<ul>
<li><p>Install the RISC-V GNU compiler toolchain:
<code>git clone --recursive https://github.com/riscv-collab/riscv-gnu-toolchain     cd riscv-gnu-toolchain     ./configure --prefix=&lt;toolchain-installed-path&gt;     make linux     export PATH=&lt;toolchain-installed-path&gt;/bin:$PATH</code></p></li>
<li><p>Cross-compile all the required libraries:
<code># An example for libffi     git clone https://github.com/libffi/libffi     cd libffi     ./configure --host=riscv64-unknown-linux-gnu --prefix=&lt;toolchain-installed-path&gt;/sysroot/usr     make     make install</code></p></li>
<li><p>Configure and build OpenJDK:
<code>bash configure \       --with-boot-jdk=$BOOT_JDK \       --openjdk-target=riscv64-linux-gnu \       --with-sysroot=&lt;toolchain-installed-path&gt;/sysroot \       --with-toolchain-path=&lt;toolchain-installed-path&gt;/bin \       --with-extra-path=&lt;toolchain-installed-path&gt;/bin     make images</code></p></li>
</ul>
<h3 id="building-for-musl">Building for musl</h3>
<p>Just like it's possible to cross-compile for a different CPU, it's
possible to cross-compile for musl libc on a glibc-based <em>build</em>
system. A devkit suitable for most target CPU architectures can be
obtained from <a href="https://musl.cc">musl.cc</a>. After installing
the required packages in the sysroot, configure the build with
<code>--openjdk-target</code>:</p>
<pre><code>sh ./configure --with-jvm-variants=server \
--with-boot-jdk=$BOOT_JDK \
--with-build-jdk=$BUILD_JDK \
--openjdk-target=x86_64-unknown-linux-musl \
--with-devkit=$DEVKIT \
--with-sysroot=$SYSROOT</code></pre>
<p>and run <code>make</code> normally.</p>
<h3 id="verifying-the-build">Verifying the Build</h3>
<p>The build will end up in a directory named like
<code>build/linux-arm-normal-server-release</code>.</p>
<p>Inside this build output directory, the <code>images/jdk</code> will
contain the newly built JDK, for your <em>target</em> system.</p>
<p>Copy these folders to your <em>target</em> system. Then you can run
e.g. <code>images/jdk/bin/java -version</code>.</p>
<h2 id="build-performance">Build Performance</h2>
<p>Building the JDK requires a lot of horsepower. Some of the build
tools can be adjusted to utilize more or less of resources such as
parallel threads and memory. The <code>configure</code> script analyzes
your system and selects reasonable values for such options based on your
hardware. If you encounter resource problems, such as out of memory
conditions, you can modify the detected values with:</p>
<ul>
<li><p><code>--with-num-cores</code> -- number of cores in the build
system, e.g. <code>--with-num-cores=8</code>.</p></li>
<li><p><code>--with-memory-size</code> -- memory (in MB) available in
the build system, e.g. <code>--with-memory-size=1024</code></p></li>
</ul>
<p>You can also specify directly the number of build jobs to use with
<code>--with-jobs=N</code> to <code>configure</code>, or
<code>JOBS=N</code> to <code>make</code>. Do not use the <code>-j</code>
flag to <code>make</code>. In most cases it will be ignored by the
makefiles, but it can cause problems for some make targets.</p>
<p>It might also be necessary to specify the JVM arguments passed to the
Boot JDK, using e.g. <code>--with-boot-jdk-jvmargs="-Xmx8G"</code>.
Doing so will override the default JVM arguments passed to the Boot
JDK.</p>
<p>At the end of a successful execution of <code>configure</code>, you
will get a performance summary, indicating how well the build will
perform. Here you will also get performance hints. If you want to build
fast, pay attention to those!</p>
<p>If you want to tweak build performance, run with
<code>make LOG=info</code> to get a build time summary at the end of the
build process.</p>
<h3 id="disk-speed">Disk Speed</h3>
<p>If you are using network shares, e.g. via NFS, for your source code,
make sure the build directory is situated on local disk (e.g. by
<code>ln -s /localdisk/jdk-build $JDK-SHARE/build</code>). The
performance penalty is extremely high for building on a network share;
close to unusable.</p>
<p>Also, make sure that your build tools (including Boot JDK and
toolchain) is located on a local disk and not a network share.</p>
<p>As has been stressed elsewhere, do use SSD for source code and build
directory, as well as (if possible) the build tools.</p>
<h3 id="virus-checking">Virus Checking</h3>
<p>The use of virus checking software, especially on Windows, can
<em>significantly</em> slow down building of the JDK. If possible, turn
off such software, or exclude the directory containing the JDK source
code from on-the-fly checking.</p>
<h3 id="ccache">Ccache</h3>
<p>The JDK build supports building with ccache when using gcc or clang.
Using ccache can radically speed up compilation of native code if you
often rebuild the same sources. Your milage may vary however, so we
recommend evaluating it for yourself. To enable it, make sure it's on
the path and configure with <code>--enable-ccache</code>.</p>
<h3 id="precompiled-headers">Precompiled Headers</h3>
<p>By default, the Hotspot build uses preccompiled headers (PCH) on the
toolchains were it is properly supported (clang, gcc, and Visual
Studio). Normally, this speeds up the build process, but in some
circumstances, it can actually slow things down.</p>
<p>You can experiment by disabling precompiled headers using
<code>--disable-precompiled-headers</code>.</p>
<h3 id="icecc-icecream">Icecc / icecream</h3>
<p><a href="http://github.com/icecc/icecream">icecc/icecream</a> is a
simple way to setup a distributed compiler network. If you have multiple
machines available for building the JDK, you can drastically cut
individual build times by utilizing it.</p>
<p>To use, setup an icecc network, and install icecc on the build
machine. Then run <code>configure</code> using
<code>--enable-icecc</code>.</p>
<h3 id="using-the-javac-server">Using the javac server</h3>
<p>To speed up compilation of Java code, especially during incremental
compilations, the javac server is automatically enabled in the
configuration step by default. To explicitly enable or disable the javac
server, use either <code>--enable-javac-server</code> or
<code>--disable-javac-server</code>.</p>
<h3 id="building-the-right-target">Building the Right Target</h3>
<p>Selecting the proper target to build can have dramatic impact on
build time. For normal usage, <code>jdk</code> or the default target is
just fine. You only need to build <code>images</code> for shipping, or
if your tests require it.</p>
<p>See also <a href="#using-fine-grained-make-targets">Using
Fine-Grained Make Targets</a> on how to build an even smaller subset of
the product.</p>
<h2 id="troubleshooting">Troubleshooting</h2>
<p>If your build fails, it can sometimes be difficult to pinpoint the
problem or find a proper solution.</p>
<h3 id="locating-the-source-of-the-error">Locating the Source of the
Error</h3>
<p>When a build fails, it can be hard to pinpoint the actual cause of
the error. In a typical build process, different parts of the product
build in parallel, with the output interlaced.</p>
<h4 id="build-failure-summary">Build Failure Summary</h4>
<p>To help you, the build system will print a failure summary at the
end. It looks like this:</p>
<pre><code>ERROR: Build failed for target &#39;hotspot&#39; in configuration &#39;linux-x64&#39; (exit code 2)

=== Output from failing command(s) repeated here ===
* For target hotspot_variant-server_libjvm_objs_psMemoryPool.o:
/localhome/git/jdk-sandbox/hotspot/src/share/vm/services/psMemoryPool.cpp:1:1: error: &#39;failhere&#39; does not name a type
   ... (rest of output omitted)

* All command lines available in /localhome/git/jdk-sandbox/build/linux-x64/make-support/failure-logs.
=== End of repeated output ===

=== Make failed targets repeated here ===
lib/CompileJvm.gmk:207: recipe for target &#39;/localhome/git/jdk-sandbox/build/linux-x64/hotspot/variant-server/libjvm/objs/psMemoryPool.o&#39; failed
make/Main.gmk:263: recipe for target &#39;hotspot-server-libs&#39; failed
=== End of repeated output ===

Hint: Try searching the build log for the name of the first failed target.
Hint: If caused by a warning, try configure --disable-warnings-as-errors.</code></pre>
<p>Let's break it down! First, the selected configuration, and the
top-level target you entered on the command line that caused the failure
is printed.</p>
<p>Then, between the
<code>Output from failing command(s) repeated here</code> and
<code>End of repeated output</code> the first lines of output (stdout
and stderr) from the actual failing command is repeated. In most cases,
this is the error message that caused the build to fail. If multiple
commands were failing (this can happen in a parallel build), output from
all failed commands will be printed here.</p>
<p>The path to the <code>failure-logs</code> directory is printed. In
this file you will find a <code>&lt;target&gt;.log</code> file that
contains the output from this command in its entirety, and also a
<code>&lt;target&gt;.cmd</code>, which contain the complete command line
used for running this command. You can re-run the failing command by
executing <code>. &lt;path to failure-logs&gt;/&lt;target&gt;.cmd</code>
in your shell.</p>
<p>Another way to trace the failure is to follow the chain of make
targets, from top-level targets to individual file targets. Between
<code>Make failed targets repeated here</code> and
<code>End of repeated output</code> the output from make showing this
chain is repeated. The first failed recipe will typically contain the
full path to the file in question that failed to compile. Following
lines will show a trace of make targets why we ended up trying to
compile that file.</p>
<p>Finally, some hints are given on how to locate the error in the
complete log. In this example, we would try searching the log file for
"<code>psMemoryPool.o</code>". Another way to quickly locate make errors
in the log is to search for "<code>] Error</code>" or
"<code>***</code>".</p>
<p>Note that the build failure summary will only help you if the issue
was a compilation failure or similar. If the problem is more esoteric,
or is due to errors in the build machinery, you will likely get empty
output logs, and <code>No indication of failed target found</code>
instead of the make target chain.</p>
<h4 id="checking-the-build-log-file">Checking the Build Log File</h4>
<p>The output (stdout and stderr) from the latest build is always stored
in <code>$BUILD/build.log</code>. The previous build log is stored as
<code>build.log.old</code>. This means that it is not necessary to
redirect the build output yourself if you want to process it.</p>
<p>You can increase the verbosity of the log file, by the
<code>LOG</code> control variable to <code>make</code>. If you want to
see the command lines used in compilations, use
<code>LOG=cmdlines</code>. To increase the general verbosity, use
<code>LOG=info</code>, <code>LOG=debug</code> or <code>LOG=trace</code>.
Both of these can be combined with <code>cmdlines</code>, e.g.
<code>LOG=info,cmdlines</code>. The <code>debug</code> log level will
show most shell commands executed by make, and <code>trace</code> will
show all. Beware that both these log levels will produce a massive build
log!</p>
<h3 id="fixing-unexpected-build-failures">Fixing Unexpected Build
Failures</h3>
<p>Most of the time, the build will fail due to incorrect changes in the
source code.</p>
<p>Sometimes the build can fail with no apparent changes that have
caused the failure. If this is the first time you are building the JDK
on this particular computer, and the build fails, the problem is likely
with your build environment. But even if you have previously built the
JDK with success, and it now fails, your build environment might have
changed (perhaps due to OS upgrades or similar). But most likely, such
failures are due to problems with the incremental rebuild.</p>
<h4 id="problems-with-the-build-environment">Problems with the Build
Environment</h4>
<p>Make sure your configuration is correct. Re-run
<code>configure</code>, and look for any warnings. Warnings that appear
in the middle of the <code>configure</code> output is also repeated at
the end, after the summary. The entire log is stored in
<code>$BUILD/configure.log</code>.</p>
<p>Verify that the summary at the end looks correct. Are you indeed
using the Boot JDK and native toolchain that you expect?</p>
<p>By default, the JDK has a strict approach where warnings from the
compiler is considered errors which fail the build. For very new or very
old compiler versions, this can trigger new classes of warnings, which
thus fails the build. Run <code>configure</code> with
<code>--disable-warnings-as-errors</code> to turn of this behavior. (The
warnings will still show, but not make the build fail.)</p>
<h4 id="problems-with-incremental-rebuilds">Problems with Incremental
Rebuilds</h4>
<p>Incremental rebuilds mean that when you modify part of the product,
only the affected parts get rebuilt. While this works great in most
cases, and significantly speed up the development process, from time to
time complex interdependencies will result in an incorrect build result.
This is the most common cause for unexpected build problems.</p>
<p>Here are a suggested list of things to try if you are having
unexpected build problems. Each step requires more time than the one
before, so try them in order. Most issues will be solved at step 1 or
2.</p>
<ol type="1">
<li><p>Make sure your repository is up-to-date</p>
<p>Run <code>git pull origin master</code> to make sure you have the
latest changes.</p></li>
<li><p>Clean build results</p>
<p>The simplest way to fix incremental rebuild issues is to run
<code>make clean</code>. This will remove all build results, but not the
configuration or any build system support artifacts. In most cases, this
will solve build errors resulting from incremental build
mismatches.</p></li>
<li><p>Completely clean the build directory.</p>
<p>If this does not work, the next step is to run
<code>make dist-clean</code>, or removing the build output directory
(<code>$BUILD</code>). This will clean all generated output, including
your configuration. You will need to re-run <code>configure</code> after
this step. A good idea is to run <code>make print-configuration</code>
before running <code>make dist-clean</code>, as this will print your
current <code>configure</code> command line. Here's a way to do
this:</p>
<pre><code>make print-configuration &gt; current-configuration
make dist-clean
bash configure $(cat current-configuration)
make</code></pre></li>
<li><p>Re-clone the Git repository</p>
<p>Sometimes the Git repository gets in a state that causes the product
to be un-buildable. In such a case, the simplest solution is often the
"sledgehammer approach": delete the entire repository, and re-clone it.
If you have local changes, save them first to a different location using
<code>git format-patch</code>.</p></li>
</ol>
<h3 id="specific-build-issues">Specific Build Issues</h3>
<h4 id="clock-skew">Clock Skew</h4>
<p>If you get an error message like this:</p>
<pre><code>File &#39;xxx&#39; has modification time in the future.
Clock skew detected. Your build may be incomplete.</code></pre>
<p>then the clock on your build machine is out of sync with the
timestamps on the source files. Other errors, apparently unrelated but
in fact caused by the clock skew, can occur along with the clock skew
warnings. These secondary errors may tend to obscure the fact that the
true root cause of the problem is an out-of-sync clock.</p>
<p>If you see these warnings, reset the clock on the build machine, run
<code>make clean</code> and restart the build.</p>
<h4 id="out-of-memory-errors">Out of Memory Errors</h4>
<p>On Windows, you might get error messages like this:</p>
<pre><code>fatal error - couldn&#39;t allocate heap
cannot create ... Permission denied
spawn failed</code></pre>
<p>This can be a sign of a Cygwin problem. See the information about
solving problems in the <a href="#cygwin">Cygwin</a> section. Rebooting
the computer might help temporarily.</p>
<h4 id="spaces-in-path">Spaces in Path</h4>
<p>On Windows, when configuring, <code>fixpath.sh</code> may report that
some directory names have spaces. Usually, it assumes those directories
have <a
href="https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/fsutil-8dot3name">short
paths</a>. You can run <code>fsutil file setshortname</code> in
<code>cmd</code> on certain directories, such as
<code>Microsoft Visual Studio</code> or <code>Windows Kits</code>, to
assign arbitrary short paths so <code>configure</code> can access
them.</p>
<h3 id="getting-help">Getting Help</h3>
<p>If none of the suggestions in this document helps you, or if you find
what you believe is a bug in the build system, please contact the Build
Group by sending a mail to <a
href="mailto:build-dev@openjdk.org">build-dev@openjdk.org</a>. Please
include the relevant parts of the configure and/or build log.</p>
<p>If you need general help or advice about developing for the JDK, you
can also contact the Adoption Group. See the section on <a
href="#contributing-to-openjdk">Contributing to OpenJDK</a> for more
information.</p>
<h2 id="reproducible-builds">Reproducible Builds</h2>
<p>Build reproducibility is the property of getting exactly the same
bits out when building, every time, independent on who builds the
product, or where. This is for many reasons a harder goal than it
initially appears, but it is an important goal, for security reasons and
others. Please see <a
href="https://reproducible-builds.org">Reproducible Builds</a> for more
information about the background and reasons for reproducible
builds.</p>
<p>Currently, it is not possible to build OpenJDK fully reproducibly,
but getting there is an ongoing effort.</p>
<p>An absolute prerequisite for building reproducible is to speficy a
fixed build time, since time stamps are embedded in many file formats.
This is done by setting the <code>SOURCE_DATE_EPOCH</code> environment
variable, which is an <a
href="https://reproducible-builds.org/docs/source-date-epoch/">industry
standard</a>, that many tools, such as gcc, recognize, and use in place
of the current time when generating output.</p>
<p>To generate reproducible builds, you must set
<code>SOURCE_DATE_EPOCH</code> before running <code>configure</code>.
The value in <code>SOURCE_DATE_EPOCH</code> will be stored in the
configuration, and used by <code>make</code>. Setting
<code>SOURCE_DATE_EPOCH</code> before running <code>make</code> will
have no effect on the build.</p>
<p>You must also make sure your build does not rely on
<code>configure</code>'s default adhoc version strings. Default adhoc
version strings <code>OPT</code> segment include user name and source
directory. You can either override just the <code>OPT</code> segment
using <code>--with-version-opt=&lt;any fixed string&gt;</code>, or you
can specify the entire version string using
<code>--with-version-string=&lt;your version&gt;</code>.</p>
<p>This is a typical example of how to build the JDK in a reproducible
way:</p>
<pre><code>export SOURCE_DATE_EPOCH=946684800
bash configure --with-version-opt=adhoc
make</code></pre>
<p>Note that regardless if you specify a source date for
<code>configure</code> or not, the JDK build system will set
<code>SOURCE_DATE_EPOCH</code> for all build tools when building. If
<code>--with-source-date</code> has the value <code>current</code>
(which is the default unless <code>SOURCE_DATE_EPOCH</code> is found by
in the environment by <code>configure</code>), the source date value
will be determined at configure time.</p>
<p>There are several aspects of reproducible builds that can be
individually adjusted by <code>configure</code> arguments. If any of
these are given, they will override the value derived from
<code>SOURCE_DATE_EPOCH</code>. These arguments are:</p>
<ul>
<li><p><code>--with-source-date</code></p>
<p>This option controls how the JDK build sets
<code>SOURCE_DATE_EPOCH</code> when building. It can be set to a value
describing a date, either an epoch based timestamp as an integer, or a
valid ISO-8601 date.</p>
<p>It can also be set to one of the special values <code>current</code>,
<code>updated</code> or <code>version</code>. <code>current</code> means
that the time of running <code>configure</code> will be used.
<code>version</code> will use the nominal release date for the current
JDK version. <code>updated</code>, which means that
<code>SOURCE_DATE_EPOCH</code> will be set to the current time each time
you are running <code>make</code>. All choices, except for
<code>updated</code>, will set a fixed value for the source date
timestamp.</p>
<p>When <code>SOURCE_DATE_EPOCH</code> is set, the default value for
<code>--with-source-date</code> will be the value given by
<code>SOURCE_DATE_EPOCH</code>. Otherwise, the default value is
<code>current</code>.</p></li>
<li><p><code>--with-hotspot-build-time</code></p>
<p>This option controls the build time string that will be included in
the hotspot library (<code>libjvm.so</code> or <code>jvm.dll</code>).
When the source date is fixed (e.g. by setting
<code>SOURCE_DATE_EPOCH</code>), the default value for
<code>--with-hotspot-build-time</code> will be an ISO 8601
representation of that time stamp. Otherwise the default value will be
the current time when building hotspot.</p></li>
<li><p><code>--with-copyright-year</code></p>
<p>This option controls the copyright year in some generated text files.
When the source date is fixed (e.g. by setting
<code>SOURCE_DATE_EPOCH</code>), the default value for
<code>--with-copyright-year</code> will be the year of that time stamp.
Otherwise the default is the current year at the time of running
configure. This can be overridden by
<code>--with-copyright-year=&lt;year&gt;</code>.</p></li>
<li><p><code>--enable-reproducible-build</code></p>
<p>This option controls some additional behavior needed to make the
build reproducible. When the source date is fixed (e.g. by setting
<code>SOURCE_DATE_EPOCH</code>), this flag will be turned on by default.
Otherwise, the value is determined by heuristics. If it is explicitly
turned off, the build might not be reproducible.</p></li>
</ul>
<h2 id="hints-and-suggestions-for-advanced-users">Hints and Suggestions
for Advanced Users</h2>
<h3 id="bash-completion">Bash Completion</h3>
<p>The <code>configure</code> and <code>make</code> commands tries to
play nice with bash command-line completion (using
<code>&lt;tab&gt;</code> or <code>&lt;tab&gt;&lt;tab&gt;</code>). To use
this functionality, make sure you enable completion in your
<code>~/.bashrc</code> (see instructions for bash in your operating
system).</p>
<p>Make completion will work out of the box, and will complete valid
make targets. For instance, typing <code>make jdk-i&lt;tab&gt;</code>
will complete to <code>make jdk-image</code>.</p>
<p>The <code>configure</code> script can get completion for options, but
for this to work you need to help <code>bash</code> on the way. The
standard way of running the script, <code>bash configure</code>, will
not be understood by bash completion. You need <code>configure</code> to
be the command to run. One way to achieve this is to add a simple helper
script to your path:</p>
<pre><code>cat &lt;&lt; EOT &gt; /tmp/configure
#!/bin/bash
if [ \$(pwd) = \$(cd \$(dirname \$0); pwd) ] ; then
  echo &gt;&amp;2 &quot;Abort: Trying to call configure helper recursively&quot;
  exit 1
fi

bash \$PWD/configure &quot;\$@&quot;
EOT
chmod +x /tmp/configure
sudo mv /tmp/configure /usr/local/bin</code></pre>
<p>Now <code>configure --en&lt;tab&gt;-dt&lt;tab&gt;</code> will result
in <code>configure --enable-dtrace</code>.</p>
<h3 id="using-multiple-configurations">Using Multiple
Configurations</h3>
<p>You can have multiple configurations for a single source repository.
When you create a new configuration, run
<code>configure --with-conf-name=&lt;name&gt;</code> to create a
configuration with the name <code>&lt;name&gt;</code>. Alternatively,
you can create a directory under <code>build</code> and run
<code>configure</code> from there, e.g.
<code>mkdir build/&lt;name&gt; &amp;&amp; cd build/&lt;name&gt; &amp;&amp; bash ../../configure</code>.</p>
<p>Then you can build that configuration using
<code>make CONF_NAME=&lt;name&gt;</code> or
<code>make CONF=&lt;pattern&gt;</code>, where
<code>&lt;pattern&gt;</code> is a substring matching one or several
configurations, e.g. <code>CONF=debug</code>. The special empty pattern
(<code>CONF=</code>) will match <em>all</em> available configuration, so
<code>make CONF= hotspot</code> will build the <code>hotspot</code>
target for all configurations. Alternatively, you can execute
<code>make</code> in the configuration directory, e.g.
<code>cd build/&lt;name&gt; &amp;&amp; make</code>.</p>
<h3 id="handling-reconfigurations">Handling Reconfigurations</h3>
<p>If you update the repository and part of the configure script has
changed, the build system will force you to re-run
<code>configure</code>.</p>
<p>Most of the time, you will be fine by running <code>configure</code>
again with the same arguments as the last time, which can easily be
performed by <code>make reconfigure</code>. To simplify this, you can
use the <code>CONF_CHECK</code> make control variable, either as
<code>make CONF_CHECK=auto</code>, or by setting an environment
variable. For instance, if you add <code>export CONF_CHECK=auto</code>
to your <code>.bashrc</code> file, <code>make</code> will always run
<code>reconfigure</code> automatically whenever the configure script has
changed.</p>
<p>You can also use <code>CONF_CHECK=ignore</code> to skip the check for
a needed configure update. This might speed up the build, but comes at
the risk of an incorrect build result. This is only recommended if you
know what you're doing.</p>
<p>From time to time, you will also need to modify the command line to
<code>configure</code> due to changes. Use
<code>make print-configuration</code> to show the command line used for
your current configuration.</p>
<h3 id="using-fine-grained-make-targets">Using Fine-Grained Make
Targets</h3>
<p>The default behavior for make is to create consistent and correct
output, at the expense of build speed, if necessary.</p>
<p>If you are prepared to take some risk of an incorrect build, and know
enough of the system to understand how things build and interact, you
can speed up the build process considerably by instructing make to only
build a portion of the product.</p>
<h4 id="building-individual-modules">Building Individual Modules</h4>
<p>The safe way to use fine-grained make targets is to use the module
specific make targets. All source code in the JDK is organized so it
belongs to a module, e.g. <code>java.base</code> or
<code>jdk.jdwp.agent</code>. You can build only a specific module, by
giving it as make target: <code>make jdk.jdwp.agent</code>. If the
specified module depends on other modules (e.g. <code>java.base</code>),
those modules will be built first.</p>
<p>You can also specify a set of modules, just as you can always specify
a set of make targets:
<code>make jdk.crypto.cryptoki jdk.crypto.ec jdk.crypto.mscapi</code></p>
<h4 id="building-individual-module-phases">Building Individual Module
Phases</h4>
<p>The build process for each module is divided into separate phases.
Not all modules need all phases. Which are needed depends on what kind
of source code and other artifact the module consists of. The phases
are:</p>
<ul>
<li><code>gensrc</code> (Generate source code to compile)</li>
<li><code>gendata</code> (Generate non-source code artifacts)</li>
<li><code>copy</code> (Copy resource artifacts)</li>
<li><code>java</code> (Compile Java code)</li>
<li><code>launchers</code> (Compile native executables)</li>
<li><code>libs</code> (Compile native libraries)</li>
</ul>
<p>You can build only a single phase for a module by using the notation
<code>$MODULE-$PHASE</code>. For instance, to build the
<code>gensrc</code> phase for <code>java.base</code>, use
<code>make java.base-gensrc</code>.</p>
<p>Note that some phases may depend on others, e.g. <code>java</code>
depends on <code>gensrc</code> (if present). Make will build all needed
prerequisites before building the requested phase.</p>
<h4 id="skipping-the-dependency-check">Skipping the Dependency
Check</h4>
<p>When using an iterative development style with frequent quick
rebuilds, the dependency check made by make can take up a significant
portion of the time spent on the rebuild. In such cases, it can be
useful to bypass the dependency check in make.</p>
<blockquote>
<p><strong>Note that if used incorrectly, this can lead to a broken
build!</strong></p>
</blockquote>
<p>To achieve this, append <code>-only</code> to the build target. For
instance, <code>make jdk.jdwp.agent-java-only</code> will <em>only</em>
build the <code>java</code> phase of the <code>jdk.jdwp.agent</code>
module. If the required dependencies are not present, the build can
fail. On the other hand, the execution time measures in
milliseconds.</p>
<p>A useful pattern is to build the first time normally (e.g.
<code>make jdk.jdwp.agent</code>) and then on subsequent builds, use the
<code>-only</code> make target.</p>
<h4 id="rebuilding-part-of-java.base-jdk_filter">Rebuilding Part of
java.base (JDK_FILTER)</h4>
<p>If you are modifying files in <code>java.base</code>, which is the by
far largest module in the JDK, then you need to rebuild all those files
whenever a single file has changed. (This inefficiency will hopefully be
addressed in JDK 10.)</p>
<p>As a hack, you can use the make control variable
<code>JDK_FILTER</code> to specify a pattern that will be used to limit
the set of files being recompiled. For instance,
<code>make java.base JDK_FILTER=javax/crypto</code> (or, to combine
methods, <code>make java.base-java-only JDK_FILTER=javax/crypto</code>)
will limit the compilation to files in the <code>javax.crypto</code>
package.</p>
<h2 id="understanding-the-build-system">Understanding the Build
System</h2>
<p>This section will give you a more technical description on the
details of the build system.</p>
<h3 id="configurations">Configurations</h3>
<p>The build system expects to find one or more configuration. These are
technically defined by the <code>spec.gmk</code> in a subdirectory to
the <code>build</code> subdirectory. The <code>spec.gmk</code> file is
generated by <code>configure</code>, and contains in principle the
configuration (directly or by files included by
<code>spec.gmk</code>).</p>
<p>You can, in fact, select a configuration to build by pointing to the
<code>spec.gmk</code> file with the <code>SPEC</code> make control
variable, e.g. <code>make SPEC=$BUILD/spec.gmk</code>. While this is not
the recommended way to call <code>make</code> as a user, it is what is
used under the hood by the build system.</p>
<h3 id="build-output-structure">Build Output Structure</h3>
<p>The build output for a configuration will end up in
<code>build/&lt;configuration name&gt;</code>, which we refer to as
<code>$BUILD</code> in this document. The <code>$BUILD</code> directory
contains the following important directories:</p>
<pre><code>buildtools/
configure-support/
hotspot/
images/
jdk/
make-support/
support/
test-results/
test-support/</code></pre>
<p>This is what they are used for:</p>
<ul>
<li><p><code>images</code>: This is the directory were the output of the
<code>*-image</code> make targets end up. For instance,
<code>make jdk-image</code> ends up in <code>images/jdk</code>.</p></li>
<li><p><code>jdk</code>: This is the "exploded image". After
<code>make jdk</code>, you will be able to launch the newly built JDK by
running <code>$BUILD/jdk/bin/java</code>.</p></li>
<li><p><code>test-results</code>: This directory contains the results
from running tests.</p></li>
<li><p><code>support</code>: This is an area for intermediate files
needed during the build, e.g. generated source code, object files and
class files. Some noteworthy directories in <code>support</code> is
<code>gensrc</code>, which contains the generated source code, and the
<code>modules_*</code> directories, which contains the files in a
per-module hierarchy that will later be collapsed into the
<code>jdk</code> directory of the exploded image.</p></li>
<li><p><code>buildtools</code>: This is an area for tools compiled for
the build platform that are used during the rest of the build.</p></li>
<li><p><code>hotspot</code>: This is an area for intermediate files
needed when building hotspot.</p></li>
<li><p><code>configure-support</code>, <code>make-support</code> and
<code>test-support</code>: These directories contain files that are
needed by the build system for <code>configure</code>, <code>make</code>
and for running tests.</p></li>
</ul>
<h3 id="fixpath">Fixpath</h3>
<p>Windows path typically look like <code>C:\User\foo</code>, while Unix
paths look like <code>/home/foo</code>. Tools with roots from Unix often
experience issues related to this mismatch when running on Windows.</p>
<p>In the JDK build, we always use Unix paths internally, and only just
before calling a tool that does not understand Unix paths do we convert
them to Windows paths.</p>
<p>This conversion is done by the <code>fixpath</code> tool, which is a
small wrapper that modifies unix-style paths to Windows-style paths in
command lines. Fixpath is compiled automatically by
<code>configure</code>.</p>
<h3 id="native-debug-symbols">Native Debug Symbols</h3>
<p>Native libraries and executables can have debug symbol (and other
debug information) associated with them. How this works is very much
platform dependent, but a common problem is that debug symbol
information takes a lot of disk space, but is rarely needed by the end
user.</p>
<p>The JDK supports different methods on how to handle debug symbols.
The method used is selected by <code>--with-native-debug-symbols</code>,
and available methods are <code>none</code>, <code>internal</code>,
<code>external</code>, <code>zipped</code>.</p>
<ul>
<li><p><code>none</code> means that no debug symbols will be generated
during the build.</p></li>
<li><p><code>internal</code> means that debug symbols will be generated
during the build, and they will be stored in the generated
binary.</p></li>
<li><p><code>external</code> means that debug symbols will be generated
during the build, and after the compilation, they will be moved into a
separate <code>.debuginfo</code> file. (This was previously known as
FDS, Full Debug Symbols).</p></li>
<li><p><code>zipped</code> is like <code>external</code>, but the
.debuginfo file will also be zipped into a <code>.diz</code>
file.</p></li>
</ul>
<p>When building for distribution, <code>zipped</code> is a good
solution. Binaries built with <code>internal</code> is suitable for use
by developers, since they facilitate debugging, but should be stripped
before distributed to end users.</p>
<h3 id="autoconf-details">Autoconf Details</h3>
<p>The <code>configure</code> script is based on the autoconf framework,
but in some details deviate from a normal autoconf
<code>configure</code> script.</p>
<p>The <code>configure</code> script in the top level directory of the
JDK is just a thin wrapper that calls
<code>make/autoconf/configure</code>. This in turn will run
<code>autoconf</code> to create the runnable (generated) configure
script, as <code>.build/generated-configure.sh</code>. Apart from being
responsible for the generation of the runnable script, the
<code>configure</code> script also provides functionality that is not
easily expressed in the normal Autoconf framework. As part of this
functionality, the generated script is called.</p>
<p>The build system will detect if the Autoconf source files have
changed, and will trigger a regeneration of the generated script if
needed. You can also manually request such an update by
<code>bash configure autogen</code>.</p>
<p>In previous versions of the JDK, the generated script was checked in
at <code>make/autoconf/generated-configure.sh</code>. This is no longer
the case.</p>
<h3 id="developing-the-build-system-itself">Developing the Build System
Itself</h3>
<p>This section contains a few remarks about how to develop for the
build system itself. It is not relevant if you are only making changes
in the product source code.</p>
<p>While technically using <code>make</code>, the make source files of
the JDK does not resemble most other Makefiles. Instead of listing
specific targets and actions (perhaps using patterns), the basic modus
operandi is to call a high-level function (or properly, macro) from the
API in <code>make/common</code>. For instance, to compile all classes in
the <code>jdk.internal.foo</code> package in the <code>jdk.foo</code>
module, a call like this would be made:</p>
<pre><code>$(eval $(call SetupJavaCompilation, BUILD_FOO_CLASSES, \
    SETUP := GENERATE_OLDBYTECODE, \
    SRC := $(TOPDIR)/src/jkd.foo/share/classes, \
    INCLUDES := jdk/internal/foo, \
    BIN := $(SUPPORT_OUTPUTDIR)/foo_classes, \
))</code></pre>
<p>By encapsulating and expressing the high-level knowledge of
<em>what</em> should be done, rather than <em>how</em> it should be done
(as is normal in Makefiles), we can build a much more powerful and
flexible build system.</p>
<p>Correct dependency tracking is paramount. Sloppy dependency tracking
will lead to improper parallelization, or worse, race conditions.</p>
<p>To test for/debug race conditions, try running
<code>make JOBS=1</code> and <code>make JOBS=100</code> and see if it
makes any difference. (It shouldn't).</p>
<p>To compare the output of two different builds and see if, and how,
they differ, run <code>$BUILD1/compare.sh -o $BUILD2</code>, where
<code>$BUILD1</code> and <code>$BUILD2</code> are the two builds you
want to compare.</p>
<p>To automatically build two consecutive versions and compare them, use
<code>COMPARE_BUILD</code>. The value of <code>COMPARE_BUILD</code> is a
set of variable=value assignments, like this:</p>
<pre><code>make COMPARE_BUILD=CONF=--enable-new-hotspot-feature:MAKE=hotspot</code></pre>
<p>See <code>make/InitSupport.gmk</code> for details on how to use
<code>COMPARE_BUILD</code>.</p>
<p>To analyze build performance, run with <code>LOG=trace</code> and
check <code>$BUILD/build-trace-time.log</code>. Use <code>JOBS=1</code>
to avoid parallelism.</p>
<p>Please check that you adhere to the <a
href="http://openjdk.org/groups/build/doc/code-conventions.html">Code
Conventions for the Build System</a> before submitting patches.</p>
<h2 id="contributing-to-the-jdk">Contributing to the JDK</h2>
<p>So, now you've built your JDK, and made your first patch, and want to
contribute it back to the OpenJDK Community.</p>
<p>First of all: Thank you! We gladly welcome your contribution.
However, please bear in mind that the JDK is a massive project, and we
must ask you to follow our rules and guidelines to be able to accept
your contribution.</p>
<p>The official place to start is the <a
href="http://openjdk.org/contribute/">'How to contribute' page</a>.
There is also an official (but somewhat outdated and skimpy on details)
<a href="http://openjdk.org/guide/">Developer's Guide</a>.</p>
<p>If this seems overwhelming to you, the Adoption Group is there to
help you! A good place to start is their <a
href="https://wiki.openjdk.org/display/Adoption/New+Contributor">'New
Contributor' page</a>, or start reading the comprehensive <a
href="https://adoptopenjdk.gitbooks.io/adoptopenjdk-getting-started-kit/en/">Getting
Started Kit</a>. The Adoption Group will also happily answer any
questions you have about contributing. Contact them by <a
href="http://mail.openjdk.org/mailman/listinfo/adoption-discuss">mail</a>
or <a href="http://openjdk.org/irc/">IRC</a>.</p>
<h2 id="editing-this-document">Editing this document</h2>
<p>If you want to contribute changes to this document, edit
<code>doc/building.md</code> and then run
<code>make update-build-docs</code> to generate the same changes in
<code>doc/building.html</code>.</p>
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