% Building the JDK
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.
-
Get the complete source code:
git clone https://git.openjdk.java.net/jdk/ -
Run configure:
bash configureIf
configurefails due to missing dependencies (to either the toolchain, build tools, external libraries or the boot JDK), most of the time it prints a suggestion on how to resolve the situation on your platform. Follow the instructions, and try runningbash configureagain. -
Run make:
make images -
Verify your newly built JDK:
./build/*/images/jdk/bin/java -version -
Run basic tests:
make run-test-tier1
If any of these steps failed, or if you want to know more about build requirements or build functionality, please continue reading this document.
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.
If you just want to use the JDK and not build it yourself, this document is not for you. See for instance OpenJDK installation for some methods of installing a prebuilt JDK.
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 OpenJDK Git site 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 jdk11u repo, which contains
incremental updates, instead of the jdk11 repo, which was frozen at JDK 11 GA.
If you are new to Git, a good place to start is the book Pro Git. The rest of this document assumes a working knowledge of Git.
For a smooth building experience, it is recommended that you follow these rules on where and how to check out the source code.
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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.
-
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.
-
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.
-
On Windows, if using Cygwin, extra care must be taken to make sure the environment is consistent. It is recommended that you follow this procedure:
-
Create the directory that is going to contain the top directory of the JDK clone by using the
mkdircommand in the Cygwin bash shell. That is, do not create it using Windows Explorer. This will ensure that it will have proper Cygwin attributes, and that it's children will inherit those attributes. -
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.
-
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.
-
The Cygwin
gitclient 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 Skara wiki on Git clients for up-to-date information about the Skara git client support. -
The Git for Windows 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
core.autocrlftofalse(this is asked during installation).
-
Failure to follow this procedure might result in hard-to-debug build problems.
-
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.
We strongly recommend usage of an SSD disk for the build, since disk speed is one of the limiting factors for build performance.
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.
Even for 32-bit builds, it is recommended to use a 64-bit build machine, and
instead create a 32-bit target using --with-target-bits=32.
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.
If you do not have access to sufficiently powerful hardware, it is also possible to use cross-compiling.
This is not recommended. Instead, see the section on Cross-compiling.
The mainline JDK project supports Linux, macOS, AIX and Windows. Support for other operating system, e.g. BSD, exists in separate "port" projects.
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.
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.
Operating system Vendor/version used
Linux Oracle Enterprise Linux 6.4 / 7.6 macOS Mac OS X 10.13 (High Sierra) Windows Windows Server 2012 R2
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.
The Build Group has a wiki page with Supported Build Platforms. From time to time, this is updated by contributors to list successes or failures of building on different platforms.
Windows XP is not a supported platform, but all newer Windows should be able to build the JDK.
On Windows, it is important that you pay attention to the instructions in the Special Considerations.
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 and Windows Subsystem for Linux (WSL). (Msys is no longer supported due to a too old bash; msys2 would likely be possible to support in a future version but that would require effort to implement.)
Internally in the build system, all paths are represented as Unix-style paths,
e.g. /cygdrive/c/git/jdk/Makefile rather than C:\git\jdk\Makefile. This
rule also applies to input to the build system, e.g. in arguments to
configure. So, use --with-msvcr-dll=/cygdrive/c/msvcr100.dll rather than
--with-msvcr-dll=c:\msvcr100.dll. For details on this conversion, see the section
on Fixpath.
A functioning Cygwin 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.
Note: 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.
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.
Apart from the basic Cygwin installation, the following packages must also be installed:
autoconfmakezipunzip
Often, you can install these packages using the following command line:
<path to Cygwin setup>/setup-x86_64 -q -P autoconf -P make -P unzip -P zip
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 "BLODA" list and the section on fork() failures.
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.
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
--build=x86_64-unknown-linux-gnu --host=x86_64-unknown-linux-gnu to
configure.
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.
Note that while it's possible to build on WSL, testing is still not fully supported.
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 Apple Xcode on some strategies to deal with this.
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).
The standard macOS environment contains the basic tooling needed to build, but for external libraries a package manager is recommended. The JDK uses homebrew in the examples, but feel free to use whatever manager you want (or none).
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.
The basic tooling is provided as part of the core operating system, but you will most likely need to install developer packages.
For apt-based distributions (Debian, Ubuntu, etc), try this:
sudo apt-get install build-essential
For rpm-based distributions (Fedora, Red Hat, etc), try this:
sudo yum groupinstall "Development Tools"
For Alpine Linux, aside from basic tooling, install the GNU versions of some programs:
sudo apk add build-base bash grep zip
Please consult the AIX section of the Supported Build Platforms OpenJDK Build Wiki page for details about which versions of AIX are supported.
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.
Operating system Supported toolchain
Linux gcc, clang macOS Apple Xcode (using clang) AIX IBM XL C/C++ Windows Microsoft Visual Studio
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.
Operating system Toolchain version
Linux gcc 10.2.0 macOS Apple Xcode 10.1 (using clang 10.0.0) Windows Microsoft Visual Studio 2019 update 16.7.2
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.
The minimum accepted version of gcc is 5.0. Older versions will generate a warning
by configure and are unlikely to work.
The JDK is currently known to be able to compile with at least version 10.2 of gcc.
In general, any version between these two should be usable.
The minimum accepted version of clang is 3.5. Older versions will not be
accepted by configure.
To use clang instead of gcc on Linux, use --with-toolchain-type=clang.
The oldest supported version of Xcode is 8.
You will need the Xcode command lines developers tools to be able to build the JDK. (Actually, only the command lines tools are needed, not the IDE.) The simplest way to install these is to run:
xcode-select --install
It is advisable to keep an older version of Xcode for building the JDK when
updating Xcode. This blog page has
good suggestions on managing multiple Xcode versions. To use a specific version
of Xcode, use xcode-select -s before running configure, or use
--with-toolchain-path to point to the version of Xcode to use, e.g.
configure --with-toolchain-path=/Applications/Xcode8.app/Contents/Developer/usr/bin
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 Problems with the Build Environment, and Getting Help to find out if there are any recent, non-merged patches available for this update.
The minimum accepted version of Visual Studio is 2017. Older versions will not
be accepted by configure and will not work. The maximum accepted
version of Visual Studio is 2019.
If you have multiple versions of Visual Studio installed, configure will by
default pick the latest. You can request a specific version to be used by
setting --with-toolchain-version, e.g. --with-toolchain-version=2017.
If you have Visual Studio installed but configure fails to detect it, it may
be because of spaces in path.
Please consult the AIX section of the Supported Build Platforms OpenJDK Build Wiki page for details about which versions of XLC are supported.
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.
The rule of thumb is that the boot JDK for building JDK major version N should be a JDK of major version N-1, 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 N-1 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.
Early in the release cycle, version N-1 may not yet have been released. In that case, the preferred boot JDK will be version N-2 until version N-1 is available.
If the boot JDK is not automatically detected, or the wrong JDK is picked, use
--with-boot-jdk to point to the JDK to use.
JDK binaries for Linux, Windows and macOS can be downloaded from jdk.java.net. An alternative is to download the Oracle JDK. Another is the Adopt OpenJDK Project, which publishes experimental prebuilt binaries for various platforms.
On Linux you can also get a JDK from the Linux distribution. On apt-based
distros (like Debian and Ubuntu), sudo apt-get install openjdk-<VERSION>-jdk
is typically enough to install a JDK <VERSION>. On rpm-based distros (like
Fedora and Red Hat), try sudo yum install java-<VERSION>-openjdk-devel.
Different platforms require different external libraries. In general, libraries are not optional - that is, they are either required or not used.
If a required library is not detected by configure, you need to provide the
path to it. There are two forms of the configure arguments to point to an
external library: --with-<LIB>=<path> or --with-<LIB>-include=<path to include> --with-<LIB>-lib=<path to lib>. 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.
As a fallback, the second version allows you to point to the include directory and the lib directory separately.
FreeType2 from The FreeType Project 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.
- To install on an apt-based Linux, try running
sudo apt-get install libfreetype6-dev. - To install on an rpm-based Linux, try running
sudo yum install freetype-devel. - To install on Alpine Linux, try running
sudo apk add freetype-dev. - To install on macOS, try running
brew install freetype.
Use --with-freetype-include=<path> and --with-freetype-lib=<path>
if configure does not automatically locate the platform FreeType files.
CUPS, Common UNIX Printing System header files are required on all platforms, except Windows. Often these files are provided by your operating system.
- To install on an apt-based Linux, try running
sudo apt-get install libcups2-dev. - To install on an rpm-based Linux, try running
sudo yum install cups-devel. - To install on Alpine Linux, try running
sudo apk add cups-dev.
Use --with-cups=<path> if configure does not properly locate your CUPS
files.
Certain X11 libraries and include files are required on Linux.
- To install on an apt-based Linux, try running
sudo apt-get install libx11-dev libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev. - To install on an rpm-based Linux, try running
sudo yum install libXtst-devel libXt-devel libXrender-devel libXrandr-devel libXi-devel. - To install on Alpine Linux, try running
sudo apk add libx11-dev libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev.
Use --with-x=<path> if configure does not properly locate your X11 files.
ALSA, Advanced Linux Sound Architecture is required on Linux. At least version 0.9.1 of ALSA is required.
- To install on an apt-based Linux, try running
sudo apt-get install libasound2-dev. - To install on an rpm-based Linux, try running
sudo yum install alsa-lib-devel. - To install on Alpine Linux, try running
sudo apk add alsa-lib-dev.
Use --with-alsa=<path> if configure does not properly locate your ALSA
files.
libffi, the Portable Foreign Function Interface Library is required when building the Zero version of Hotspot.
- To install on an apt-based Linux, try running
sudo apt-get install libffi-dev. - To install on an rpm-based Linux, try running
sudo yum install libffi-devel. - To install on Alpine Linux, try running
sudo apk add libffi-dev.
Use --with-libffi=<path> if configure does not properly locate your libffi
files.
The JDK requires Autoconf on all platforms. At least version 2.69 is required.
- To install on an apt-based Linux, try running
sudo apt-get install autoconf. - To install on an rpm-based Linux, try running
sudo yum install autoconf. - To install on Alpine Linux, try running
sudo apk add autoconf. - To install on macOS, try running
brew install autoconf. - To install on Windows, try running
<path to Cygwin setup>/setup-x86_64 -q -P autoconf.
If configure has problems locating your installation of autoconf, you can
specify it using the AUTOCONF environment variable, like this:
AUTOCONF=<path to autoconf> configure ...
The JDK requires GNU Make. No other flavors of make are supported.
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 --with-output-sync)
and speed and stability improvements.
Note that configure locates and verifies a properly functioning version of
make and stores the path to this make binary in the configuration. If you
start a build using make on the command line, you will be using the version
of make found first in your PATH, 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 configure will be called. Normally, this
will present no issues, but if you have a very old make, or a non-GNU Make
make in your path, this might cause issues.
If you want to override the default make found by configure, use the MAKE
configure variable, e.g. configure MAKE=/opt/gnu/make.
The JDK requires GNU Bash. No other shells are supported.
At least version 3.2 of GNU Bash must be used.
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.
The configuration is created by the configure script. The basic invocation of
the configure script looks like this:
bash configure [options]
This will create an output directory containing the configuration and setup an
area for the build result. This directory typically looks like
build/linux-x64-server-release, but the actual name depends on your specific
configuration. (It can also be set directly, see Using Multiple
Configurations). This directory is referred to
as $BUILD in this documentation.
configure 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.
Some command line examples:
-
Create a 32-bit build for Windows with FreeType2 in
C:\freetype-i586:bash configure --with-freetype=/cygdrive/c/freetype-i586 --with-target-bits=32 -
Create a debug build with the
serverJVM and DTrace enabled:bash configure --enable-debug --with-jvm-variants=server --enable-dtrace
Here follows some of the most common and important configure argument.
To get up-to-date information on all available configure argument, please
run:
bash configure --help
(Note that this help text also include general autoconf options, like
--dvidir, that is not relevant to the JDK. To list only JDK-specific
features, use bash configure --help=short instead.)
--enable-debug- Set the debug level tofastdebug(this is a shorthand for--with-debug-level=fastdebug)--with-debug-level=<level>- Set the debug level, which can berelease,fastdebug,slowdebugoroptimized. Default isrelease.optimizedis variant ofreleasewith additional Hotspot debug code.--with-native-debug-symbols=<method>- Specify if and how native debug symbols should be built. Available methods arenone,internal,external,zipped. Default behavior depends on platform. See Native Debug Symbols for more details.--with-version-string=<string>- Specify the version string this build will be identified with.--with-version-<part>=<value>- A group of options, where<part>can be any ofpre,opt,build,major,minor,securityorpatch. Use these options to modify just the corresponding part of the version string from the default, or the value provided by--with-version-string.--with-jvm-variants=<variant>[,<variant>...]- Build the specified variant (or variants) of Hotspot. Valid variants are:server,client,minimal,core,zero,custom. Note that not all variants are possible to combine in a single build.--enable-jvm-feature-<feature>or--disable-jvm-feature-<feature>- Include (or exclude)<feature>as a JVM feature in Hotspot. You can also specify a list of features to be enabled, separated by space or comma, as--with-jvm-features=<feature>[,<feature>...]. If you prefix<feature>with a-, it will be disabled. These options will modify the default list of features for the JVM variant(s) you are building. For thecustomJVM variant, the default list is empty. A complete list of valid JVM features can be found usingbash configure --help.--with-target-bits=<bits>- Create a target binary suitable for running on a<bits>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 reduced build.)
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 java.library.path property.
--with-jni-libpath=<path>- Use the specified path as a default when searching for runtime libraries.
--with-devkit=<path>- Use this devkit for compilers, tools and resources--with-sysroot=<path>- Use this directory as sysroot--with-extra-path=<path>[;<path>]- Prepend these directories to the default path when searching for all kinds of binaries--with-toolchain-path=<path>[;<path>]- Prepend these directories when searching for toolchain binaries (compilers etc)--with-extra-cflags=<flags>- Append these flags when compiling JDK C files--with-extra-cxxflags=<flags>- Append these flags when compiling JDK C++ files--with-extra-ldflags=<flags>- Append these flags when linking JDK libraries
--with-boot-jdk=<path>- Set the path to the Boot JDK--with-freetype=<path>- Set the path to FreeType--with-cups=<path>- Set the path to CUPS--with-x=<path>- Set the path to X11--with-alsa=<path>- Set the path to ALSA--with-libffi=<path>- Set the path to libffi--with-jtreg=<path>- Set the path to JTReg. See Running Tests
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 system as the <source> option in these arguments.
(The default is bundled).
--with-libjpeg=<source>- Use the specified source for libjpeg--with-giflib=<source>- Use the specified source for giflib--with-libpng=<source>- Use the specified source for libpng--with-lcms=<source>- Use the specified source for lcms--with-zlib=<source>- Use the specified source for zlib
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.
--with-stdc++lib=<method>- Use the specified method (static,dynamicordefault) for linking the C++ runtime.
It is possible to control certain aspects of configure by overriding the
value of configure variables, either on the command line or in the
environment.
Normally, this is not recommended. 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, configure will print a warning if this is
detected.
However, there are a few configure variables, known as control variables
that are supposed to be overridden on the command line. These are variables that
describe the location of tools needed by the build, like MAKE or GREP. If
any such variable is specified, configure will use that value instead of
trying to autodetect the tool. For instance, bash configure MAKE=/opt/gnumake4.0/bin/make.
If a configure argument exists, use that instead, e.g. use --with-jtreg
instead of setting JTREGEXE.
Also note that, despite what autoconf claims, setting CFLAGS will not
accomplish anything. Instead use --with-extra-cflags (and similar for
cxxflags and ldflags).
When you have a proper configuration, all you need to do to build the JDK is to
run make. (But see the warning at GNU Make about running the
correct version of make.)
When running make without any arguments, the default target is used, which is
the same as running make default or make jdk. 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.
The output of the exploded image resides in $BUILD/jdk. You can test the
newly built JDK like this: $BUILD/jdk/bin/java -version.
Apart from the default target, here are some common make targets:
hotspot- Build all of hotspot (but only hotspot)hotspot-<variant>- Build just the specified jvm variantimagesorproduct-images- Build the JDK imagedocsordocs-image- Build the documentation imagetest-image- Build the test imageallorall-images- Build all images (product, docs and test)bootcycle-images- Build images twice, second time with newly built JDK (good for testing)clean- Remove all files generated by make, but not those generated by configuredist-clean- Remove all files, including configuration
Run make help to get an up-to-date list of important make targets and make
control variables.
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 gensrc, gendata, copy, java,
launchers, or libs. See Using Fine-Grained Make Targets for more details about this functionality.
<phase>- Build the specified phase and everything it depends on<module>- Build the specified module and everything it depends on<module>-<phase>- Compile the specified phase for the specified module and everything it depends on
Similarly, it is possible to clean just a part of the build by creating make targets according to these patterns:
clean-<outputdir>- Remove the subdir in the output dir with the nameclean-<phase>- Remove all build results related to a certain build phaseclean-<module>- Remove all build results related to a certain moduleclean-<module>-<phase>- Remove all build results related to a certain module and phase
It is possible to control make behavior by overriding the value of make
variables, either on the command line or in the environment.
Normally, this is not recommended. 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, make will print a warning if this is detected.
However, there are a few make variables, known as control variables that
are supposed to be overridden on the command line. These make up the "make time"
configuration, as opposed to the "configure time" configuration.
JOBS- Specify the number of jobs to build with. See Build Performance.LOG- Specify the logging level and functionality. See Checking the Build Log FileCONFandCONF_NAME- Selecting the configuration(s) to use. See Using Multiple Configurations
These make control variables only make sense when running tests. Please see Testing the JDK (html, markdown) for details.
TESTTEST_JOBSJTREGGTEST
These advanced make control variables can be potentially unsafe. See Hints and Suggestions for Advanced Users and Understanding the Build System for details.
SPECCONF_CHECKCOMPARE_BUILDJDK_FILTERSPEC_FILTER
Most of the JDK tests are using the JTReg
test framework. Make sure that your configuration knows where to find your
installation of JTReg. If this is not picked up automatically, use the
--with-jtreg=<path to jtreg home> option to point to the JTReg framework.
Note that this option should point to the JTReg home, i.e. the top directory,
containing lib/jtreg.jar etc.
The Adoption Group provides
recent builds of jtreg here.
Download the latest .tar.gz file, unpack it, and point --with-jtreg to the
jtreg directory that you just unpacked.
Building of Hotspot Gtest suite requires the source code of Google Test framework.
The top directory, which contains both googletest and googlemock
directories, should be specified via --with-gtest.
The supported version of Google Test is 1.8.1, whose source code can be obtained:
- by downloading and unpacking the source bundle from here
- or by checking out
release-1.8.1tag ofgoogletestproject:git clone -b release-1.8.1 https://github.com/google/googletest
To execute the most basic tests (tier 1), use:
make run-test-tier1
For more details on how to run tests, please see Testing the JDK (html, markdown).
Cross-compiling means using one platform (the build platform) to generate output that can ran on another platform (the target platform).
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 build and target systems.
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 external links at Wikipedia for a good start on reading materials.
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.
If all you want to do is to compile a 32-bit version, for the same OS, on a
64-bit machine, consider using --with-target-bits=32 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.)
The OpenJDK build system provides out-of-the box support for creating and using
so called devkits. A devkit is basically a collection of a cross-compiling
toolchain and a sysroot environment which can easily be used together with the
--with-devkit configure option to cross compile the OpenJDK. On Linux/x86_64,
the following command:
bash configure --with-devkit=<devkit-path> --openjdk-target=ppc64-linux-gnu && make
will configure and build OpenJDK for Linux/ppc64 assuming that <devkit-path>
points to a Linux/x86_64 to Linux/ppc64 devkit.
Devkits can be created from the make/devkit directory by executing:
make [ TARGETS="<TARGET_TRIPLET>+" ] [ BASE_OS=<OS> ] [ BASE_OS_VERSION=<VER> ]
where TARGETS contains one or more TARGET_TRIPLETs of the form
described in section 3.4 of the GNU Autobook. 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:
x86_64-linux-gnu aarch64-linux-gnu arm-linux-gnueabihf ppc64-linux-gnu ppc64le-linux-gnu s390x-linux-gnu
BASE_OS 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 BASE_OS_VERSION option (with "27" as default version).
If the build is successful, the new devkits can be found in the
build/devkit/result subdirectory:
cd make/devkit
make TARGETS="ppc64le-linux-gnu aarch64-linux-gnu" 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
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).
When cross-compiling, make sure you use a boot JDK that runs on the build system, and not on the target system.
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 build system, and not the target system. (In contrast, the Boot JDK should be from an older release, e.g. JDK 8 when building JDK 9.)
The build process will create a minimal Build JDK for you, as part of building.
To speed up the build, you can use --with-build-jdk to configure 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 exactly
match the current sources.
You must 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 --openjdk-target argument, e.g.
--openjdk-target=arm-linux-gnueabihf. or --openjdk-target=aarch64-oe-linux.
This will automatically set the --build, --host and --target 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.)
You will need two copies of your toolchain, one which generates output that can
run on the target system (the normal, or target, toolchain), and one that
generates output that can run on the build system (the build 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, configure is likely to pick up the toolchain
correctly.
The build toolchain will be autodetected just the same way the normal
build/target 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 build toolchain using --with-build-devkit to
configure, or by giving BUILD_CC and BUILD_CXX arguments.
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 configure. Do this by setting the sysroot (--with-sysroot) and
appending the directory when searching for cross-compilations tools
(--with-toolchain-path). As a compact form, you can also use --with-devkit
to point to a single directory, if it is correctly setup. (See basics.m4 for
details.)
You will need copies of external native libraries for the target system, present on the build machine while building.
Take care not to replace the build system's version of these libraries by mistake, since that can render the build machine unusable.
Make sure that the libraries you point to (ALSA, X11, etc) are for the target, not the build, platform.
You will need alsa libraries suitable for your target system. For most cases, using Debian's pre-built libraries work fine.
Note that alsa is needed even if you only want to build a headless JDK.
-
Go to Debian Package Search and search for the
libasound2andlibasound2-devpackages for your target system. Download them to /tmp. -
Install the libraries into the cross-compilation toolchain. For instance:
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 .
- If alsa is not properly detected by
configure, you can point it out by--with-alsa.
You will need X11 libraries suitable for your target system. For most cases, using Debian's pre-built libraries work fine.
Note that X11 is needed even if you only want to build a headless JDK.
-
Go to Debian Package Search, search for the following packages for your target system, and download them to /tmp/target-x11:
- libxi
- libxi-dev
- x11proto-core-dev
- x11proto-input-dev
- x11proto-kb-dev
- x11proto-render-dev
- x11proto-xext-dev
- libice-dev
- libxrender
- libxrender-dev
- libxrandr-dev
- libsm-dev
- libxt-dev
- libx11
- libx11-dev
- libxtst
- libxtst-dev
- libxext
- libxext-dev
-
Install the libraries into the cross-compilation toolchain. For instance:
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.
cp: cannot stat `arm-linux-gnueabihf/libICE.so': No such file or directory cp: cannot stat `arm-linux-gnueabihf/libSM.so': No such file or directory cp: cannot stat `arm-linux-gnueabihf/libXt.so': No such file or directory -
If the X11 libraries are not properly detected by
configure, you can point them out by--with-x.
Fortunately, you can create sysroots for foreign architectures with tools
provided by your OS. On Debian/Ubuntu systems, one could use qemu-deboostrap to
create the target system chroot, which would have the native libraries and headers
specific to that target system. After that, we can use the cross-compiler on the build
system, pointing into chroot to get the build dependencies right. This allows building
for foreign architectures with native compilation speed.
For example, cross-compiling to AArch64 from x86_64 could be done like this:
-
Install cross-compiler on the build system:
apt install g++-aarch64-linux-gnu gcc-aarch64-linux-gnu -
Create chroot on the build system, configuring it for target system:
sudo qemu-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/ -
Make sure the symlinks inside the newly created chroot point to proper locations:
sudo chroot ~/sysroot-arm64 symlinks -cr . -
Configure and build with newly created chroot as sysroot/toolchain-path:
sh ./configure \ --openjdk-target=aarch64-linux-gnu \ --with-sysroot=~/sysroot-arm64 make images ls build/linux-aarch64-server-release/
The build does not create new files in that chroot, so it can be reused for multiple builds without additional cleanup.
The build system should automatically detect the toolchain paths and dependencies, but sometimes it might require a little nudge with:
-
Native compilers: override
CCorCXXfor./configure -
Freetype lib location: override
--with-freetype-lib, for example${sysroot}/usr/lib/${target}/ -
Freetype includes location: override
--with-freetype-includefor example${sysroot}/usr/include/freetype2/ -
X11 libraries location: override
--x-libraries, for example${sysroot}/usr/lib/${target}/
Architectures that are known to successfully cross-compile like this are:
Target Debian tree Debian arch --openjdk-target=... --with-jvm-variants=...
x86 buster i386 i386-linux-gnu (all) arm buster armhf arm-linux-gnueabihf (all) aarch64 buster arm64 aarch64-linux-gnu (all) ppc64le buster ppc64el powerpc64le-linux-gnu (all) s390x buster s390x s390x-linux-gnu (all) mipsle buster mipsel mipsel-linux-gnu zero mips64le buster mips64el mips64el-linux-gnueabi64 zero armel buster arm arm-linux-gnueabi zero ppc sid powerpc powerpc-linux-gnu zero ppc64be sid ppc64 powerpc64-linux-gnu (all) m68k sid m68k m68k-linux-gnu zero alpha sid alpha alpha-linux-gnu zero sh4 sid sh4 sh4-linux-gnu zero
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 --with-abi-profile: 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.
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 build system.
A devkit suitable for most target CPU architectures can be obtained from
musl.cc. After installing the required packages in the
sysroot, configure the build with --openjdk-target:
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
and run make normally.
The build will end up in a directory named like
build/linux-arm-normal-server-release.
Inside this build output directory, the images/jdk will contain the newly
built JDK, for your target system.
Copy these folders to your target system. Then you can run e.g.
images/jdk/bin/java -version.
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 configure 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:
-
--with-num-cores-- number of cores in the build system, e.g.--with-num-cores=8. -
--with-memory-size-- memory (in MB) available in the build system, e.g.--with-memory-size=1024
You can also specify directly the number of build jobs to use with
--with-jobs=N to configure, or JOBS=N to make. Do not use the -j flag
to make. In most cases it will be ignored by the makefiles, but it can cause
problems for some make targets.
It might also be necessary to specify the JVM arguments passed to the Boot JDK,
using e.g. --with-boot-jdk-jvmargs="-Xmx8G". Doing so will override the
default JVM arguments passed to the Boot JDK.
At the end of a successful execution of configure, 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!
If you want to tweak build performance, run with make LOG=info to get a build
time summary at the end of the build process.
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 ln -s /localdisk/jdk-build $JDK-SHARE/build). The performance penalty is extremely
high for building on a network share; close to unusable.
Also, make sure that your build tools (including Boot JDK and toolchain) is located on a local disk and not a network share.
As has been stressed elsewhere, do use SSD for source code and build directory, as well as (if possible) the build tools.
The use of virus checking software, especially on Windows, can significantly 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.
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
--enable-ccache.
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.
You can experiment by disabling precompiled headers using
--disable-precompiled-headers.
icecc/icecream 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.
To use, setup an icecc network, and install icecc on the build machine. Then
run configure using --enable-icecc.
To speed up Java compilation, especially incremental compilations, you can try
the experimental sjavac compiler by using --enable-sjavac.
Selecting the proper target to build can have dramatic impact on build time.
For normal usage, jdk or the default target is just fine. You only need to
build images for shipping, or if your tests require it.
See also Using Fine-Grained Make Targets on how to build an even smaller subset of the product.
If your build fails, it can sometimes be difficult to pinpoint the problem or find a proper solution.
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.
To help you, the build system will print a failure summary at the end. It looks like this:
ERROR: Build failed for target 'hotspot' in configuration 'linux-x64' (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: 'failhere' 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 '/localhome/git/jdk-sandbox/build/linux-x64/hotspot/variant-server/libjvm/objs/psMemoryPool.o' failed
make/Main.gmk:263: recipe for target 'hotspot-server-libs' 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.
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.
Then, between the Output from failing command(s) repeated here and End of repeated output 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.
The path to the failure-logs directory is printed. In this file you will find
a <target>.log file that contains the output from this command in its
entirety, and also a <target>.cmd, which contain the complete command line
used for running this command. You can re-run the failing command by executing
. <path to failure-logs>/<target>.cmd in your shell.
Another way to trace the failure is to follow the chain of make targets, from
top-level targets to individual file targets. Between Make failed targets repeated here and End of repeated output 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.
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 "psMemoryPool.o".
Another way to quickly locate make errors in the log is to search for "] Error" or "***".
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 No indication of failed target found instead of the make target chain.
The output (stdout and stderr) from the latest build is always stored in
$BUILD/build.log. The previous build log is stored as build.log.old. This
means that it is not necessary to redirect the build output yourself if you
want to process it.
You can increase the verbosity of the log file, by the LOG control variable
to make. If you want to see the command lines used in compilations, use
LOG=cmdlines. To increase the general verbosity, use LOG=info, LOG=debug
or LOG=trace. Both of these can be combined with cmdlines, e.g.
LOG=info,cmdlines. The debug log level will show most shell commands
executed by make, and trace will show all. Beware that both these log levels
will produce a massive build log!
Most of the time, the build will fail due to incorrect changes in the source code.
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.
Make sure your configuration is correct. Re-run configure, and look for any
warnings. Warnings that appear in the middle of the configure output is also
repeated at the end, after the summary. The entire log is stored in
$BUILD/configure.log.
Verify that the summary at the end looks correct. Are you indeed using the Boot JDK and native toolchain that you expect?
By default, the JDK has a strict approach where warnings from the compiler is
considered errors which fail the build. For very new or very old compiler
versions, this can trigger new classes of warnings, which thus fails the build.
Run configure with --disable-warnings-as-errors to turn of this behavior.
(The warnings will still show, but not make the build fail.)
Incremental rebuilds mean that when you modify part of the product, only the affected parts get rebuilt. While this works great in most cases, and significantly speed up the development process, from time to time complex interdependencies will result in an incorrect build result. This is the most common cause for unexpected build problems.
Here are a suggested list of things to try if you are having unexpected build problems. Each step requires more time than the one before, so try them in order. Most issues will be solved at step 1 or 2.
-
Make sure your repository is up-to-date
Run
git pull origin masterto make sure you have the latest changes. -
Clean build results
The simplest way to fix incremental rebuild issues is to run
make clean. This will remove all build results, but not the configuration or any build system support artifacts. In most cases, this will solve build errors resulting from incremental build mismatches. -
Completely clean the build directory.
If this does not work, the next step is to run
make dist-clean, or removing the build output directory ($BUILD). This will clean all generated output, including your configuration. You will need to re-runconfigureafter this step. A good idea is to runmake print-configurationbefore runningmake dist-clean, as this will print your currentconfigurecommand line. Here's a way to do this:make print-configuration > current-configuration make dist-clean bash configure $(cat current-configuration) make -
Re-clone the Git repository
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
git format-patch.
If you get an error message like this:
File 'xxx' has modification time in the future.
Clock skew detected. Your build may be incomplete.
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.
If you see these warnings, reset the clock on the build machine, run make clean and restart the build.
On Windows, you might get error messages like this:
fatal error - couldn't allocate heap
cannot create ... Permission denied
spawn failed
This can be a sign of a Cygwin problem. See the information about solving problems in the Cygwin section. Rebooting the computer might help temporarily.
On Windows, when configuring, fixpath.sh may report that some directory
names have spaces. Usually, it assumes those directories have
short paths.
You can run fsutil file setshortname in cmd on certain directories, such as
Microsoft Visual Studio or Windows Kits, to assign arbitrary short paths so
configure can access them.
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 [email protected]. Please include the relevant parts of the configure and/or build log.
If you need general help or advice about developing for the JDK, you can also contact the Adoption Group. See the section on Contributing to OpenJDK for more information.
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 Reproducible Builds for more information about the background and reasons for reproducible builds.
Currently, it is not possible to build OpenJDK fully reproducibly, but getting there is an ongoing effort. There are some things you can do to minimize non-determinism and make a larger part of the build reproducible:
- Turn on build system support for reproducible builds
Add the flag --enable-reproducible-build to your configure command line.
This will turn on support for reproducible builds where it could otherwise be
lacking.
- Do not rely on
configure's default adhoc version strings
Default adhoc version strings OPT segment include user name, source directory
and timestamp. You can either override just the OPT segment using
--with-version-opt=<any fixed string>, or you can specify the entire version
string using --with-version-string=<your version>.
- Specify how the build sets
SOURCE_DATE_EPOCH
The JDK build system will set the SOURCE_DATE_EPOCH environment variable
during building, depending on the value of the --with-source-date option for
configure. The default value is updated, which means that
SOURCE_DATE_EPOCH will be set to the current time each time you are running
make.
The SOURCE_DATE_EPOCH environment variable is an industry
standard, that many tools, such as gcc, recognize, and use in place of the
current time when generating output.
For reproducible builds, you need to set this to a fixed value. You can use the
special value version which will use the nominal release date for the current
JDK version, or a value describing a date, either an epoch based timestamp as an
integer, or a valid ISO-8601 date.
Hint: If your build environment already sets SOURCE_DATE_EPOCH, you can
propagate this using --with-source-date=$SOURCE_DATE_EPOCH.
- Specify a hotspot build time
Set a fixed hotspot build time. This will be included in the hotspot library
(libjvm.so or jvm.dll) and defaults to the current time when building
hotspot. Use --with-hotspot-build-time=<any fixed string> for reproducible
builds. It's a string so you don't need to format it specifically, so e.g. n/a
will do. Another solution is to use the SOURCE_DATE_EPOCH variable, e.g.
--with-hotspot-build-time=$(date --date=@$SOURCE_DATE_EPOCH).
- Copyright year
The copyright year in some generated text files are normally set to the current
year. This can be overridden by --with-copyright-year=<year>. For fully
reproducible builds, this needs to be set to a fixed value.
The configure and make commands tries to play nice with bash command-line
completion (using <tab> or <tab><tab>). To use this functionality, make
sure you enable completion in your ~/.bashrc (see instructions for bash in
your operating system).
Make completion will work out of the box, and will complete valid make targets.
For instance, typing make jdk-i<tab> will complete to make jdk-image.
The configure script can get completion for options, but for this to work you
need to help bash on the way. The standard way of running the script, bash configure, will not be understood by bash completion. You need configure to
be the command to run. One way to achieve this is to add a simple helper script
to your path:
cat << EOT > /tmp/configure
#!/bin/bash
if [ \$(pwd) = \$(cd \$(dirname \$0); pwd) ] ; then
echo >&2 "Abort: Trying to call configure helper recursively"
exit 1
fi
bash \$PWD/configure "\$@"
EOT
chmod +x /tmp/configure
sudo mv /tmp/configure /usr/local/bin
Now configure --en<tab>-dt<tab> will result in configure --enable-dtrace.
You can have multiple configurations for a single source repository. When you
create a new configuration, run configure --with-conf-name=<name> to create a
configuration with the name <name>. Alternatively, you can create a directory
under build and run configure from there, e.g. mkdir build/<name> && cd build/<name> && bash ../../configure.
Then you can build that configuration using make CONF_NAME=<name> or make CONF=<pattern>, where <pattern> is a substring matching one or several
configurations, e.g. CONF=debug. The special empty pattern (CONF=) will
match all available configuration, so make CONF= hotspot will build the
hotspot target for all configurations. Alternatively, you can execute make
in the configuration directory, e.g. cd build/<name> && make.
If you update the repository and part of the configure script has changed, the
build system will force you to re-run configure.
Most of the time, you will be fine by running configure again with the same
arguments as the last time, which can easily be performed by make reconfigure. To simplify this, you can use the CONF_CHECK make control
variable, either as make CONF_CHECK=auto, or by setting an environment
variable. For instance, if you add export CONF_CHECK=auto to your .bashrc
file, make will always run reconfigure automatically whenever the configure
script has changed.
You can also use CONF_CHECK=ignore 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.
From time to time, you will also need to modify the command line to configure
due to changes. Use make print-configuration to show the command line used
for your current configuration.
The default behavior for make is to create consistent and correct output, at the expense of build speed, if necessary.
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.
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. java.base or jdk.jdwp.agent. You can build only a specific
module, by giving it as make target: make jdk.jdwp.agent. If the specified
module depends on other modules (e.g. java.base), those modules will be built
first.
You can also specify a set of modules, just as you can always specify a set of
make targets: make jdk.crypto.cryptoki jdk.crypto.ec jdk.crypto.mscapi
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:
gensrc(Generate source code to compile)gendata(Generate non-source code artifacts)copy(Copy resource artifacts)java(Compile Java code)launchers(Compile native executables)libs(Compile native libraries)
You can build only a single phase for a module by using the notation
$MODULE-$PHASE. For instance, to build the gensrc phase for java.base,
use make java.base-gensrc.
Note that some phases may depend on others, e.g. java depends on gensrc (if
present). Make will build all needed prerequisites before building the
requested phase.
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.
Note that if used incorrectly, this can lead to a broken build!
To achieve this, append -only to the build target. For instance, make jdk.jdwp.agent-java-only will only build the java phase of the
jdk.jdwp.agent module. If the required dependencies are not present, the
build can fail. On the other hand, the execution time measures in milliseconds.
A useful pattern is to build the first time normally (e.g. make jdk.jdwp.agent) and then on subsequent builds, use the -only make target.
If you are modifying files in java.base, 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.)
As a hack, you can use the make control variable JDK_FILTER to specify a
pattern that will be used to limit the set of files being recompiled. For
instance, make java.base JDK_FILTER=javax/crypto (or, to combine methods,
make java.base-java-only JDK_FILTER=javax/crypto) will limit the compilation
to files in the javax.crypto package.
This section will give you a more technical description on the details of the build system.
The build system expects to find one or more configuration. These are
technically defined by the spec.gmk in a subdirectory to the build
subdirectory. The spec.gmk file is generated by configure, and contains in
principle the configuration (directly or by files included by spec.gmk).
You can, in fact, select a configuration to build by pointing to the spec.gmk
file with the SPEC make control variable, e.g. make SPEC=$BUILD/spec.gmk.
While this is not the recommended way to call make as a user, it is what is
used under the hood by the build system.
The build output for a configuration will end up in build/<configuration name>, which we refer to as $BUILD in this document. The $BUILD directory
contains the following important directories:
buildtools/
configure-support/
hotspot/
images/
jdk/
make-support/
support/
test-results/
test-support/
This is what they are used for:
-
images: This is the directory were the output of the*-imagemake targets end up. For instance,make jdk-imageends up inimages/jdk. -
jdk: This is the "exploded image". Aftermake jdk, you will be able to launch the newly built JDK by running$BUILD/jdk/bin/java. -
test-results: This directory contains the results from running tests. -
support: This is an area for intermediate files needed during the build, e.g. generated source code, object files and class files. Some noteworthy directories insupportisgensrc, which contains the generated source code, and themodules_*directories, which contains the files in a per-module hierarchy that will later be collapsed into thejdkdirectory of the exploded image. -
buildtools: This is an area for tools compiled for the build platform that are used during the rest of the build. -
hotspot: This is an area for intermediate files needed when building hotspot. -
configure-support,make-supportandtest-support: These directories contain files that are needed by the build system forconfigure,makeand for running tests.
Windows path typically look like C:\User\foo, while Unix paths look like
/home/foo. Tools with roots from Unix often experience issues related to this
mismatch when running on Windows.
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.
This conversion is done by the fixpath tool, which is a small wrapper that
modifies unix-style paths to Windows-style paths in command lines. Fixpath is
compiled automatically by configure.
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.
The JDK supports different methods on how to handle debug symbols. The
method used is selected by --with-native-debug-symbols, and available methods
are none, internal, external, zipped.
-
nonemeans that no debug symbols will be generated during the build. -
internalmeans that debug symbols will be generated during the build, and they will be stored in the generated binary. -
externalmeans that debug symbols will be generated during the build, and after the compilation, they will be moved into a separate.debuginfofile. (This was previously known as FDS, Full Debug Symbols). -
zippedis likeexternal, but the .debuginfo file will also be zipped into a.dizfile.
When building for distribution, zipped is a good solution. Binaries built
with internal is suitable for use by developers, since they facilitate
debugging, but should be stripped before distributed to end users.
The configure script is based on the autoconf framework, but in some details
deviate from a normal autoconf configure script.
The configure script in the top level directory of the JDK is just a thin
wrapper that calls make/autoconf/configure. This in turn will run autoconf
to create the runnable (generated) configure script, as
.build/generated-configure.sh. Apart from being responsible for the
generation of the runnable script, the configure script also provides
functionality that is not easily expressed in the normal Autoconf framework. As
part of this functionality, the generated script is called.
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 bash configure autogen.
In previous versions of the JDK, the generated script was checked in at
make/autoconf/generated-configure.sh. This is no longer the case.
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.
While technically using make, 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 make/common. For instance, to
compile all classes in the jdk.internal.foo package in the jdk.foo module,
a call like this would be made:
$(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, \
))
By encapsulating and expressing the high-level knowledge of what should be done, rather than how it should be done (as is normal in Makefiles), we can build a much more powerful and flexible build system.
Correct dependency tracking is paramount. Sloppy dependency tracking will lead to improper parallelization, or worse, race conditions.
To test for/debug race conditions, try running make JOBS=1 and make JOBS=100 and see if it makes any difference. (It shouldn't).
To compare the output of two different builds and see if, and how, they differ,
run $BUILD1/compare.sh -o $BUILD2, where $BUILD1 and $BUILD2 are the two
builds you want to compare.
To automatically build two consecutive versions and compare them, use
COMPARE_BUILD. The value of COMPARE_BUILD is a set of variable=value
assignments, like this:
make COMPARE_BUILD=CONF=--enable-new-hotspot-feature:MAKE=hotspot
See make/InitSupport.gmk for details on how to use COMPARE_BUILD.
To analyze build performance, run with LOG=trace and check $BUILD/build-trace-time.log.
Use JOBS=1 to avoid parallelism.
Please check that you adhere to the Code Conventions for the Build System before submitting patches.
So, now you've built your JDK, and made your first patch, and want to contribute it back to the OpenJDK Community.
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.
The official place to start is the 'How to contribute' page. There is also an official (but somewhat outdated and skimpy on details) Developer's Guide.
If this seems overwhelming to you, the Adoption Group is there to help you! A good place to start is their 'New Contributor' page, or start reading the comprehensive Getting Started Kit. The Adoption Group will also happily answer any questions you have about contributing. Contact them by mail or IRC.
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