1 % Building OpenJDK
   3 ## TL;DR (Instructions for the Impatient)
   5 If you are eager to try out building OpenJDK, these simple steps works most of
   6 the time. They assume that you have installed Mercurial (and Cygwin if running
   7 on Windows) and cloned the top-level OpenJDK repository that you want to build.
   9  1. [Get the complete source code](#getting-the-source-code): \
  10     `bash get_source.sh`
  12  2. [Run configure](#running-configure): \
  13     `bash configure`
  15     If `configure` fails due to missing dependencies (to either the
  16     [toolchain](#native-compiler-toolchain-requirements), [external libraries](
  17     #external-library-requirements) or the [boot JDK](#boot-jdk-requirements)),
  18     most of the time it prints a suggestion on how to resolve the situation on
  19     your platform. Follow the instructions, and try running `bash configure`
  20     again.
  22  3. [Run make](#running-make): \
  23     `make images`
  25  4. Verify your newly built JDK: \
  26     `./build/*/images/jdk/bin/java -version`
  28  5. [Run basic tests](##running-tests): \
  29     `make run-test-tier1`
  31 If any of these steps failed, or if you want to know more about build
  32 requirements or build functionality, please continue reading this document.
  34 ## Introduction
  36 OpenJDK is a complex software project. Building it requires a certain amount of
  37 technical expertise, a fair number of dependencies on external software, and
  38 reasonably powerful hardware.
  40 If you just want to use OpenJDK and not build it yourself, this document is not
  41 for you. See for instance [OpenJDK installation](
  42 http://openjdk.java.net/install) for some methods of installing a prebuilt
  43 OpenJDK.
  45 ## Getting the Source Code
  47 OpenJDK uses [Mercurial](http://www.mercurial-scm.org) for source control. The
  48 source code is contained not in a single Mercurial repository, but in a tree
  49 ("forest") of interrelated repositories. You will need to check out all of the
  50 repositories to be able to build OpenJDK. To assist you in dealing with this
  51 somewhat unusual arrangement, there are multiple tools available, which are
  52 explained below.
  54 In any case, make sure you are getting the correct version. At the [OpenJDK
  55 Mercurial server](http://hg.openjdk.java.net/) you can see a list of all
  56 available forests. If you want to build an older version, e.g. JDK 8, it is
  57 recommended that you get the `jdk8u` forest, which contains incremental
  58 updates, instead of the `jdk8` forest, which was frozen at JDK 8 GA.
  60 If you are new to Mercurial, a good place to start is the [Mercurial Beginner's
  61 Guide](http://www.mercurial-scm.org/guide). The rest of this document assumes a
  62 working knowledge of Mercurial.
  64 ### Special Considerations
  66 For a smooth building experience, it is recommended that you follow these rules
  67 on where and how to check out the source code.
  69   * Do not check out the source code in a path which contains spaces. Chances
  70     are the build will not work. This is most likely to be an issue on Windows
  71     systems.
  73   * Do not check out the source code in a path which has a very long name or is
  74     nested many levels deep. Chances are you will hit an OS limitation during
  75     the build.
  77   * Put the source code on a local disk, not a network share. If possible, use
  78     an SSD. The build process is very disk intensive, and having slow disk
  79     access will significantly increase build times. If you need to use a
  80     network share for the source code, see below for suggestions on how to keep
  81     the build artifacts on a local disk.
  83   * On Windows, extra care must be taken to make sure the [Cygwin](#cygwin)
  84     environment is consistent. It is recommended that you follow this
  85     procedure:
  87       * Create the directory that is going to contain the top directory of the
  88         OpenJDK clone by using the `mkdir` command in the Cygwin bash shell.
  89         That is, do *not* create it using Windows Explorer. This will ensure
  90         that it will have proper Cygwin attributes, and that it's children will
  91         inherit those attributes.
  93       * Do not put the OpenJDK clone in a path under your Cygwin home
  94         directory. This is especially important if your user name contains
  95         spaces and/or mixed upper and lower case letters.
  97       * Clone the OpenJDK repository using the Cygwin command line `hg` client
  98         as instructed in this document. That is, do *not* use another Mercurial
  99         client such as TortoiseHg.
 101     Failure to follow this procedure might result in hard-to-debug build
 102     problems.
 104 ### Using get\_source.sh
 106 The simplest way to get the entire forest is probably to clone the top-level
 107 repository and then run the `get_source.sh` script, like this:
 109 ```
 110 hg clone http://hg.openjdk.java.net/jdk9/jdk9
 111 cd jdk9
 112 bash get_source.sh
 113 ```
 115 The first time this is run, it will clone all the sub-repositories. Any
 116 subsequent execution of the script will update all sub-repositories to the
 117 latest revision.
 119 ### Using hgforest.sh
 121 The `hgforest.sh` script is more expressive than `get_source.sh`. It takes any
 122 number of arguments, and runs `hg` with those arguments on each sub-repository
 123 in the forest. The `get_source.sh` script is basically a simple wrapper that
 124 runs either `hgforest.sh clone` or `hgforest.sh pull -u`.
 126   * Cloning the forest:
 127     ```
 128     hg clone http://hg.openjdk.java.net/jdk9/jdk9
 129     cd jdk9
 130     bash common/bin/hgforest.sh clone
 131     ```
 133   * Pulling and updating the forest:
 134     ```
 135     bash common/bin/hgforest.sh pull -u
 136     ```
 138   * Merging over the entire forest:
 139     ```
 140     bash common/bin/hgforest.sh merge
 141     ```
 143 ### Using the Trees Extension
 145 The trees extension is a Mercurial add-on that helps you deal with the forest.
 146 More information is available on the [Code Tools trees page](
 147 http://openjdk.java.net/projects/code-tools/trees).
 149 #### Installing the Extension
 151 Install the extension by cloning `http://hg.openjdk.java.net/code-tools/trees`
 152 and updating your `.hgrc` file. Here's one way to do this:
 154 ```
 155 cd ~
 156 mkdir hg-ext
 157 cd hg-ext
 158 hg clone http://hg.openjdk.java.net/code-tools/trees
 159 cat << EOT >> ~/.hgrc
 160 [extensions]
 161 trees=~/hg-ext/trees/trees.py
 162 EOT
 163 ```
 165 #### Initializing the Tree
 167 The trees extension needs to know the structure of the forest. If you have
 168 already cloned the entire forest using another method, you can initialize the
 169 forest like this:
 171 ```
 172 hg tconf --set --walk --depth
 173 ```
 175 Or you can clone the entire forest at once, if you substitute `clone` with
 176 `tclone` when cloning the top-level repository, e.g. like this:
 178 ```
 179 hg tclone http://hg.openjdk.java.net/jdk9/jdk9
 180 ```
 182 In this case, the forest will be properly initialized from the start.
 184 #### Other Operations
 186 The trees extensions supplement many common operations with a trees version by
 187 prefixing a `t` to the normal Mercurial command, e.g. `tcommit`, `tstatus` or
 188 `tmerge`. For instance, to update the entire forest:
 190 ```
 191 hg tpull -u
 192 ```
 194 ## Build Hardware Requirements
 196 OpenJDK is a massive project, and require machines ranging from decent to
 197 powerful to be able to build in a reasonable amount of time, or to be able to
 198 complete a build at all.
 200 We *strongly* recommend usage of an SSD disk for the build, since disk speed is
 201 one of the limiting factors for build performance.
 203 ### Building on x86
 205 At a minimum, a machine with 2-4 cores is advisable, as well as 2-4 GB of RAM.
 206 (The more cores to use, the more memory you need.) At least 6 GB of free disk
 207 space is required (8 GB minimum for building on Solaris).
 209 Even for 32-bit builds, it is recommended to use a 64-bit build machine, and
 210 instead create a 32-bit target using `--with-target-bits=32`.
 212 ### Building on sparc
 214 At a minimum, a machine with 4 cores is advisable, as well as 4 GB of RAM. (The
 215 more cores to use, the more memory you need.) At least 8 GB of free disk space
 216 is required.
 218 ### Building on arm/aarch64
 220 This is not recommended. Instead, see the section on [Cross-compiling](
 221 #cross-compiling).
 223 ## Operating System Requirements
 225 The mainline OpenJDK project supports Linux, Solaris, macOS, AIX and Windows.
 226 Support for other operating system, e.g. BSD, exists in separate "port"
 227 projects.
 229 In general, OpenJDK can be built on a wide range of versions of these operating
 230 systems, but the further you deviate from what is tested on a daily basis, the
 231 more likely you are to run into problems.
 233 This table lists the OS versions used by Oracle when building JDK 9. Such
 234 information is always subject to change, but this table is up to date at the
 235 time of writing.
 237  Operating system   Vendor/version used
 238  -----------------  -------------------------------------------------------
 239  Linux              Oracle Enterprise Linux 6.4 / 7.1 (using kernel 3.8.13)
 240  Solaris            Solaris 11.1 SRU 21.4.1 / 11.2 SRU 5.5
 241  macOS              Mac OS X 10.9 (Mavericks) / 10.10 (Yosemite)
 242  Windows            Windows Server 2012 R2
 244 The double version numbers for Linux, Solaris and macOS is due to the hybrid
 245 model used at Oracle, where header files and external libraries from an older
 246 version is used when building on a more modern version of the OS.
 248 The Build Group has a wiki page with [Supported Build Platforms](
 249 https://wiki.openjdk.java.net/display/Build/Supported+Build+Platforms). From
 250 time to time, this is updated by the community to list successes or failures of
 251 building on different platforms.
 253 ### Windows
 255 Windows XP is not a supported platform, but all newer Windows should be able to
 256 build OpenJDK.
 258 On Windows, it is important that you pay attention to the instructions in the
 259 [Special Considerations](#special-considerations).
 261 Windows is the only non-POSIX OS supported by OpenJDK, and as such, requires
 262 some extra care. A POSIX support layer is required to build on Windows. For
 263 OpenJDK 9, the only supported such layer is Cygwin. (Msys is no longer
 264 supported due to a too old bash; msys2 and the new Windows Subsystem for Linux
 265 (WSL) would likely be possible to support in a future version but that would
 266 require a community effort to implement.)
 268 Internally in the build system, all paths are represented as Unix-style paths,
 269 e.g. `/cygdrive/c/hg/jdk9/Makefile` rather than `C:\hg\jdk9\Makefile`. This
 270 rule also applies to input to the build system, e.g. in arguments to
 271 `configure`. So, use `--with-freetype=/cygdrive/c/freetype` rather than
 272 `--with-freetype=c:\freetype`. For details on this conversion, see the section
 273 on [Fixpath](#fixpath).
 275 #### Cygwin
 277 A functioning [Cygwin](http://www.cygwin.com/) environment is thus required for
 278 building OpenJDK on Windows. If you have a 64-bit OS, we strongly recommend
 279 using the 64-bit version of Cygwin.
 281 **Note:** Cygwin has a model of continuously updating all packages without any
 282 easy way to install or revert to a specific version of a package. This means
 283 that whenever you add or update a package in Cygwin, you might (inadvertently)
 284 update tools that are used by the OpenJDK build process, and that can cause
 285 unexpected build problems.
 287 OpenJDK requires GNU Make 4.0 or greater on Windows. This is usually not a
 288 problem, since Cygwin currently only distributes GNU Make at a version above
 289 4.0.
 291 Apart from the basic Cygwin installation, the following packages must also be
 292 installed:
 294   * `make`
 295   * `zip`
 296   * `unzip`
 298 Often, you can install these packages using the following command line:
 299 ```
 300 <path to Cygwin setup>/setup-x86_64 -q -P make -P unzip -P zip
 301 ```
 303 Unfortunately, Cygwin can be unreliable in certain circumstances. If you
 304 experience build tool crashes or strange issues when building on Windows,
 305 please check the Cygwin FAQ on the ["BLODA" list](
 306 https://cygwin.com/faq/faq.html#faq.using.bloda) and the section on [fork()
 307 failures](https://cygwin.com/faq/faq.html#faq.using.fixing-fork-failures).
 309 ### Solaris
 311 See `make/devkit/solaris11.1-package-list.txt` for a list of recommended
 312 packages to install when building on Solaris. The versions specified in this
 313 list is the versions used by the daily builds at Oracle, and is likely to work
 314 properly.
 316 Older versions of Solaris shipped a broken version of `objcopy`. At least
 317 version 2.21.1 is needed, which is provided by Solaris 11 Update 1. Objcopy is
 318 needed if you want to have external debug symbols. Please make sure you are
 319 using at least version 2.21.1 of objcopy, or that you disable external debug
 320 symbols.
 322 ### macOS
 324 Apple is using a quite aggressive scheme of pushing OS updates, and coupling
 325 these updates with required updates of Xcode. Unfortunately, this makes it
 326 difficult for a project like OpenJDK to keep pace with a continuously updated
 327 machine running macOS. See the section on [Apple Xcode](#apple-xcode) on some
 328 strategies to deal with this.
 330 It is recommended that you use at least Mac OS X 10.9 (Mavericks). At the time
 331 of writing, OpenJDK has been successfully compiled on macOS versions up to
 332 10.12.5 (Sierra), using XCode 8.3.2 and `--disable-warnings-as-errors`.
 334 The standard macOS environment contains the basic tooling needed to build, but
 335 for external libraries a package manager is recommended. OpenJDK uses
 336 [homebrew](https://brew.sh/) in the examples, but feel free to use whatever
 337 manager you want (or none).
 339 ### Linux
 341 It is often not much problem to build OpenJDK on Linux. The only general advice
 342 is to try to use the compilers, external libraries and header files as provided
 343 by your distribution.
 345 The basic tooling is provided as part of the core operating system, but you
 346 will most likely need to install developer packages.
 348 For apt-based distributions (Debian, Ubuntu, etc), try this:
 349 ```
 350 sudo apt-get install build-essential
 351 ```
 353 For rpm-based distributions (Fedora, Red Hat, etc), try this:
 354 ```
 355 sudo yum groupinstall "Development Tools"
 356 ```
 358 ### AIX
 360 The regular builds by SAP is using AIX version 7.1, but AIX 5.3 is also
 361 supported. See the [OpenJDK PowerPC Port Status Page](
 362 http://cr.openjdk.java.net/~simonis/ppc-aix-port) for details.
 364 ## Native Compiler (Toolchain) Requirements
 366 Large portions of OpenJDK consists of native code, that needs to be compiled to
 367 be able to run on the target platform. In theory, toolchain and operating
 368 system should be independent factors, but in practice there's more or less a
 369 one-to-one correlation between target operating system and toolchain.
 371  Operating system   Supported toolchain
 372  ------------------ -------------------------
 373  Linux              gcc, clang
 374  macOS              Apple Xcode (using clang)
 375  Solaris            Oracle Solaris Studio
 376  AIX                IBM XL C/C++
 377  Windows            Microsoft Visual Studio
 379 Please see the individual sections on the toolchains for version
 380 recommendations. As a reference, these versions of the toolchains are used, at
 381 the time of writing, by Oracle for the daily builds of OpenJDK. It should be
 382 possible to compile OpenJDK with both older and newer versions, but the closer
 383 you stay to this list, the more likely you are to compile successfully without
 384 issues.
 386  Operating system   Toolchain version
 387  ------------------ -------------------------------------------------------
 388  Linux              gcc 4.9.2
 389  macOS              Apple Xcode 6.3 (using clang 6.1.0)
 390  Solaris            Oracle Solaris Studio 12.4 (with compiler version 5.13)
 391  Windows            Microsoft Visual Studio 2013 update 4
 393 ### gcc
 395 The minimum accepted version of gcc is 4.7. Older versions will generate a warning 
 396 by `configure` and are unlikely to work.
 398 OpenJDK 9 includes patches that should allow gcc 6 to compile, but this should
 399 be considered experimental.
 401 In general, any version between these two should be usable.
 403 ### clang
 405 The minimum accepted version of clang is 3.2. Older versions will not be
 406 accepted by `configure`.
 408 To use clang instead of gcc on Linux, use `--with-toolchain-type=clang`.
 410 ### Apple Xcode
 412 The oldest supported version of Xcode is 5.
 414 You will need the Xcode command lines developers tools to be able to build
 415 OpenJDK. (Actually, *only* the command lines tools are needed, not the IDE.)
 416 The simplest way to install these is to run:
 417 ```
 418 xcode-select --install
 419 ```
 421 It is advisable to keep an older version of Xcode for building OpenJDK when
 422 updating Xcode. This [blog page](
 423 http://iosdevelopertips.com/xcode/install-multiple-versions-of-xcode.html) has
 424 good suggestions on managing multiple Xcode versions. To use a specific version
 425 of Xcode, use `xcode-select -s` before running `configure`, or use
 426 `--with-toolchain-path` to point to the version of Xcode to use, e.g.
 427 `configure --with-toolchain-path=/Applications/Xcode5.app/Contents/Developer/usr/bin`
 429 If you have recently (inadvertently) updated your OS and/or Xcode version, and
 430 OpenJDK can no longer be built, please see the section on [Problems with the
 431 Build Environment](#problems-with-the-build-environment), and [Getting
 432 Help](#getting-help) to find out if there are any recent, non-merged patches
 433 available for this update.
 435 ### Oracle Solaris Studio
 437 The minimum accepted version of the Solaris Studio compilers is 5.13
 438 (corresponding to Solaris Studio 12.4). Older versions will not be accepted by
 439 configure.
 441 The Solaris Studio installation should contain at least these packages:
 443  Package                                            Version
 444  -------------------------------------------------- -------------
 445  developer/solarisstudio-124/backend                12.4-
 446  developer/solarisstudio-124/c++                    12.4-
 447  developer/solarisstudio-124/cc                     12.4-
 448  developer/solarisstudio-124/library/c++-libs       12.4-
 449  developer/solarisstudio-124/library/math-libs      12.4-
 450  developer/solarisstudio-124/library/studio-gccrt   12.4-
 451  developer/solarisstudio-124/studio-common          12.4-
 452  developer/solarisstudio-124/studio-ja              12.4-
 453  developer/solarisstudio-124/studio-legal           12.4-
 454  developer/solarisstudio-124/studio-zhCN            12.4-
 456 Compiling with Solaris Studio can sometimes be finicky. This is the exact
 457 version used by Oracle, which worked correctly at the time of writing:
 458 ```
 459 $ cc -V
 460 cc: Sun C 5.13 SunOS_i386 2014/10/20
 461 $ CC -V
 462 CC: Sun C++ 5.13 SunOS_i386 151846-10 2015/10/30
 463 ```
 465 ### Microsoft Visual Studio
 467 The minimum accepted version of Visual Studio is 2010. Older versions will not
 468 be accepted by `configure`. The maximum accepted version of Visual Studio is
 469 2013.
 471 If you have multiple versions of Visual Studio installed, `configure` will by
 472 default pick the latest. You can request a specific version to be used by
 473 setting `--with-toolchain-version`, e.g. `--with-toolchain-version=2010`.
 475 If you get `LINK: fatal error LNK1123: failure during conversion to COFF: file
 476 invalid` when building using Visual Studio 2010, you have encountered
 477 [KB2757355](http://support.microsoft.com/kb/2757355), a bug triggered by a
 478 specific installation order. However, the solution suggested by the KB article
 479 does not always resolve the problem. See [this stackoverflow discussion](
 480 https://stackoverflow.com/questions/10888391) for other suggestions.
 482 ### IBM XL C/C++
 484 The regular builds by SAP is using version 12.1, described as `IBM XL C/C++ for
 485 AIX, V12.1 (5765-J02, 5725-C72) Version: 12.01.0000.0017`.
 487 See the [OpenJDK PowerPC Port Status Page](
 488 http://cr.openjdk.java.net/~simonis/ppc-aix-port) for details.
 490 ## Boot JDK Requirements
 492 Paradoxically, building OpenJDK requires a pre-existing JDK. This is called the
 493 "boot JDK". The boot JDK does not have to be OpenJDK, though. If you are
 494 porting OpenJDK to a new platform, chances are that there already exists
 495 another JDK for that platform that is usable as boot JDK.
 497 The rule of thumb is that the boot JDK for building JDK major version *N*
 498 should be an JDK of major version *N-1*, so for building JDK 9 a JDK 8 would be
 499 suitable as boot JDK. However, OpenJDK should be able to "build itself", so an
 500 up-to-date build of the current OpenJDK source is an acceptable alternative. If
 501 you are following the *N-1* rule, make sure you got the latest update version,
 502 since JDK 8 GA might not be able to build JDK 9 on all platforms.
 504 If the Boot JDK is not automatically detected, or the wrong JDK is picked, use
 505 `--with-boot-jdk` to point to the JDK to use.
 507 ### JDK 8 on Linux
 509 On apt-based distros (like Debian and Ubuntu), `sudo apt-get install
 510 openjdk-8-jdk` is typically enough to install OpenJDK 8. On rpm-based distros
 511 (like Fedora and Red Hat), try `sudo yum install java-1.8.0-openjdk-devel`.
 513 ### JDK 8 on Windows
 515 No pre-compiled binaries of OpenJDK 8 are readily available for Windows at the
 516 time of writing. An alternative is to download the [Oracle JDK](
 517 http://www.oracle.com/technetwork/java/javase/downloads). Another is the [Adopt
 518 OpenJDK Project](https://adoptopenjdk.net/), which publishes experimental
 519 prebuilt binaries for Windows.
 521 ### JDK 8 on macOS
 523 No pre-compiled binaries of OpenJDK 8 are readily available for macOS at the
 524 time of writing. An alternative is to download the [Oracle JDK](
 525 http://www.oracle.com/technetwork/java/javase/downloads), or to install it
 526 using `brew cask install java`. Another option is the [Adopt OpenJDK Project](
 527 https://adoptopenjdk.net/), which publishes experimental prebuilt binaries for
 528 macOS.
 530 ### JDK 8 on AIX
 532 No pre-compiled binaries of OpenJDK 8 are readily available for AIX at the
 533 time of writing. A starting point for working with OpenJDK on AIX is
 534 the [PowerPC/AIX Port Project](http://openjdk.java.net/projects/ppc-aix-port/).
 536 ## External Library Requirements
 538 Different platforms require different external libraries. In general, libraries
 539 are not optional - that is, they are either required or not used.
 541 If a required library is not detected by `configure`, you need to provide the
 542 path to it. There are two forms of the `configure` arguments to point to an
 543 external library: `--with-<LIB>=<path>` or `--with-<LIB>-include=<path to
 544 include> --with-<LIB>-lib=<path to lib>`. The first variant is more concise,
 545 but require the include files an library files to reside in a default hierarchy
 546 under this directory. In most cases, it works fine.
 548 As a fallback, the second version allows you to point to the include directory
 549 and the lib directory separately.
 551 ### FreeType
 553 FreeType2 from [The FreeType Project](http://www.freetype.org/) is required on
 554 all platforms. At least version 2.3 is required.
 556   * To install on an apt-based Linux, try running `sudo apt-get install
 557     libcups2-dev`.
 558   * To install on an rpm-based Linux, try running `sudo yum install
 559     cups-devel`.
 560   * To install on Solaris, try running `pkg install system/library/freetype-2`.
 561   * To install on macOS, try running `brew install freetype`.
 562   * To install on Windows, see [below](#building-freetype-on-windows).
 564 Use `--with-freetype=<path>` if `configure` does not properly locate your
 565 FreeType files.
 567 #### Building FreeType on Windows
 569 On Windows, there is no readily available compiled version of FreeType. OpenJDK
 570 can help you compile FreeType from source. Download the FreeType sources and
 571 unpack them into an arbitrary directory:
 573 ```
 574 wget http://download.savannah.gnu.org/releases/freetype/freetype-2.5.3.tar.gz
 575 tar -xzf freetype-2.5.3.tar.gz
 576 ```
 578 Then run `configure` with `--with-freetype-src=<freetype_src>`. This will
 579 automatically build the freetype library into `<freetype_src>/lib64` for 64-bit
 580 builds or into `<freetype_src>/lib32` for 32-bit builds. Afterwards you can
 581 always use `--with-freetype-include=<freetype_src>/include` and
 582 `--with-freetype-lib=<freetype_src>/lib[32|64]` for other builds.
 584 Alternatively you can unpack the sources like this to use the default
 585 directory:
 587 ```
 588 tar --one-top-level=$HOME/freetype --strip-components=1 -xzf freetype-2.5.3.tar.gz
 589 ```
 591 ### CUPS
 593 CUPS, [Common UNIX Printing System](http://www.cups.org) header files are
 594 required on all platforms, except Windows. Often these files are provided by
 595 your operating system.
 597   * To install on an apt-based Linux, try running `sudo apt-get install
 598     libcups2-dev`.
 599   * To install on an rpm-based Linux, try running `sudo yum install
 600     cups-devel`.
 601   * To install on Solaris, try running `pkg install print/cups`.
 603 Use `--with-cups=<path>` if `configure` does not properly locate your CUPS
 604 files.
 606 ### X11
 608 Certain [X11](http://www.x.org/) libraries and include files are required on
 609 Linux and Solaris.
 611   * To install on an apt-based Linux, try running `sudo apt-get install
 612     libx11-dev libxext-dev libxrender-dev libxtst-dev libxt-dev`.
 613   * To install on an rpm-based Linux, try running `sudo yum install
 614     libXtst-devel libXt-devel libXrender-devel libXi-devel`.
 615   * To install on Solaris, try running `pkg install x11/header/x11-protocols
 616     x11/library/libice x11/library/libpthread-stubs x11/library/libsm
 617     x11/library/libx11 x11/library/libxau x11/library/libxcb
 618     x11/library/libxdmcp x11/library/libxevie x11/library/libxext
 619     x11/library/libxrender x11/library/libxscrnsaver x11/library/libxtst
 620     x11/library/toolkit/libxt`.
 622 Use `--with-x=<path>` if `configure` does not properly locate your X11 files.
 624 ### ALSA
 626 ALSA, [Advanced Linux Sound Architecture](https://www.alsa-project.org/) is
 627 required on Linux. At least version 0.9.1 of ALSA is required.
 629   * To install on an apt-based Linux, try running `sudo apt-get install
 630     libasound2-dev`.
 631   * To install on an rpm-based Linux, try running `sudo yum install
 632     alsa-lib-devel`.
 634 Use `--with-alsa=<path>` if `configure` does not properly locate your ALSA
 635 files.
 637 ### libffi
 639 libffi, the [Portable Foreign Function Interface Library](
 640 http://sourceware.org/libffi) is required when building the Zero version of
 641 Hotspot.
 643   * To install on an apt-based Linux, try running `sudo apt-get install
 644     libffi-dev`.
 645   * To install on an rpm-based Linux, try running `sudo yum install
 646     libffi-devel`.
 648 Use `--with-libffi=<path>` if `configure` does not properly locate your libffi
 649 files.
 651 ## Other Tooling Requirements
 653 ### GNU Make
 655 OpenJDK requires [GNU Make](http://www.gnu.org/software/make). No other flavors
 656 of make are supported.
 658 At least version 3.81 of GNU Make must be used. For distributions supporting
 659 GNU Make 4.0 or above, we strongly recommend it. GNU Make 4.0 contains useful
 660 functionality to handle parallel building (supported by `--with-output-sync`)
 661 and speed and stability improvements.
 663 Note that `configure` locates and verifies a properly functioning version of
 664 `make` and stores the path to this `make` binary in the configuration. If you
 665 start a build using `make` on the command line, you will be using the version
 666 of make found first in your `PATH`, and not necessarily the one stored in the
 667 configuration. This initial make will be used as "bootstrap make", and in a
 668 second stage, the make located by `configure` will be called. Normally, this
 669 will present no issues, but if you have a very old `make`, or a non-GNU Make
 670 `make` in your path, this might cause issues.
 672 If you want to override the default make found by `configure`, use the `MAKE`
 673 configure variable, e.g. `configure MAKE=/opt/gnu/make`.
 675 On Solaris, it is common to call the GNU version of make by using `gmake`.
 677 ### GNU Bash
 679 OpenJDK requires [GNU Bash](http://www.gnu.org/software/bash). No other shells
 680 are supported.
 682 At least version 3.2 of GNU Bash must be used.
 684 ### Autoconf
 686 If you want to modify the build system itself, you need to install [Autoconf](
 687 http://www.gnu.org/software/autoconf).
 689 However, if you only need to build OpenJDK or if you only edit the actual
 690 OpenJDK source files, there is no dependency on autoconf, since the source
 691 distribution includes a pre-generated `configure` shell script.
 693 See the section on [Autoconf Details](#autoconf-details) for details on how
 694 OpenJDK uses autoconf. This is especially important if you plan to contribute
 695 changes to OpenJDK that modifies the build system.
 697 ## Running Configure
 699 To build OpenJDK, you need a "configuration", which consists of a directory
 700 where to store the build output, coupled with information about the platform,
 701 the specific build machine, and choices that affect how OpenJDK is built.
 703 The configuration is created by the `configure` script. The basic invocation of
 704 the `configure` script looks like this:
 706 ```
 707 bash configure [options]
 708 ```
 710 This will create an output directory containing the configuration and setup an
 711 area for the build result. This directory typically looks like
 712 `build/linux-x64-normal-server-release`, but the actual name depends on your
 713 specific configuration. (It can also be set directly, see [Using Multiple
 714 Configurations](#using-multiple-configurations)). This directory is referred to
 715 as `$BUILD` in this documentation.
 717 `configure` will try to figure out what system you are running on and where all
 718 necessary build components are. If you have all prerequisites for building
 719 installed, it should find everything. If it fails to detect any component
 720 automatically, it will exit and inform you about the problem.
 722 Some command line examples:
 724   * Create a 32-bit build for Windows with FreeType2 in `C:\freetype-i586`:
 725     ```
 726     bash configure --with-freetype=/cygdrive/c/freetype-i586 --with-target-bits=32
 727     ```
 729   * Create a debug build with the `server` JVM and DTrace enabled:
 730     ```
 731     bash configure --enable-debug --with-jvm-variants=server --enable-dtrace
 732     ```
 734 ### Common Configure Arguments
 736 Here follows some of the most common and important `configure` argument.
 738 To get up-to-date information on *all* available `configure` argument, please
 739 run:
 740 ```
 741 bash configure --help
 742 ```
 744 (Note that this help text also include general autoconf options, like
 745 `--dvidir`, that is not relevant to OpenJDK. To list only OpenJDK specific
 746 features, use `bash configure --help=short` instead.)
 748 #### Configure Arguments for Tailoring the Build
 750   * `--enable-debug` - Set the debug level to `fastdebug` (this is a shorthand
 751     for `--with-debug-level=fastdebug`)
 752   * `--with-debug-level=<level>` - Set the debug level, which can be `release`,
 753     `fastdebug`, `slowdebug` or `optimized`. Default is `release`. `optimized`
 754     is variant of `release` with additional Hotspot debug code.
 755   * `--with-native-debug-symbols=<method>` - Specify if and how native debug
 756     symbols should be built. Available methods are `none`, `internal`,
 757     `external`, `zipped`. Default behavior depends on platform. See [Native
 758     Debug Symbols](#native-debug-symbols) for more details.
 759   * `--with-version-string=<string>` - Specify the version string this build
 760     will be identified with.
 761   * `--with-version-<part>=<value>` - A group of options, where `<part>` can be
 762     any of `pre`, `opt`, `build`, `major`, `minor`, `security` or `patch`. Use
 763     these options to modify just the corresponding part of the version string
 764     from the default, or the value provided by `--with-version-string`.
 765   * `--with-jvm-variants=<variant>[,<variant>...]` - Build the specified variant
 766     (or variants) of Hotspot. Valid variants are: `server`, `client`,
 767     `minimal`, `core`, `zero`, `zeroshark`, `custom`. Note that not all
 768     variants are possible to combine in a single build.
 769   * `--with-jvm-features=<feature>[,<feature>...]` - Use the specified JVM
 770     features when building Hotspot. The list of features will be enabled on top
 771     of the default list. For the `custom` JVM variant, this default list is
 772     empty. A complete list of available JVM features can be found using `bash
 773     configure --help`.
 774   * `--with-target-bits=<bits>` - Create a target binary suitable for running
 775     on a `<bits>` platform. Use this to create 32-bit output on a 64-bit build
 776     platform, instead of doing a full cross-compile. (This is known as a
 777     *reduced* build.)
 779 #### Configure Arguments for Native Compilation
 781   * `--with-devkit=<path>` - Use this devkit for compilers, tools and resources
 782   * `--with-sysroot=<path>` - Use this directory as sysroot
 783   * `--with-extra-path=<path>[;<path>]` - Prepend these directories to the
 784     default path when searching for all kinds of binaries
 785   * `--with-toolchain-path=<path>[;<path>]` - Prepend these directories when
 786     searching for toolchain binaries (compilers etc)
 787   * `--with-extra-cflags=<flags>` - Append these flags when compiling JDK C
 788     files
 789   * `--with-extra-cxxflags=<flags>` - Append these flags when compiling JDK C++
 790     files
 791   * `--with-extra-ldflags=<flags>` - Append these flags when linking JDK
 792     libraries
 794 #### Configure Arguments for External Dependencies
 796   * `--with-boot-jdk=<path>` - Set the path to the [Boot JDK](
 797     #boot-jdk-requirements)
 798   * `--with-freetype=<path>` - Set the path to [FreeType](#freetype)
 799   * `--with-cups=<path>` - Set the path to [CUPS](#cups)
 800   * `--with-x=<path>` - Set the path to [X11](#x11)
 801   * `--with-alsa=<path>` - Set the path to [ALSA](#alsa)
 802   * `--with-libffi=<path>` - Set the path to [libffi](#libffi)
 803   * `--with-jtreg=<path>` - Set the path to JTReg. See [Running Tests](
 804     #running-tests)
 806 Certain third-party libraries used by OpenJDK (libjpeg, giflib, libpng, lcms
 807 and zlib) are included in the OpenJDK repository. The default behavior of the
 808 OpenJDK build is to use this version of these libraries, but they might be
 809 replaced by an external version. To do so, specify `system` as the `<source>`
 810 option in these arguments. (The default is `bundled`).
 812   * `--with-libjpeg=<source>` - Use the specified source for libjpeg
 813   * `--with-giflib=<source>` - Use the specified source for giflib
 814   * `--with-libpng=<source>` - Use the specified source for libpng
 815   * `--with-lcms=<source>` - Use the specified source for lcms
 816   * `--with-zlib=<source>` - Use the specified source for zlib
 818 On Linux, it is possible to select either static or dynamic linking of the C++
 819 runtime. The default is static linking, with dynamic linking as fallback if the
 820 static library is not found.
 822   * `--with-stdc++lib=<method>` - Use the specified method (`static`, `dynamic`
 823     or `default`) for linking the C++ runtime.
 825 ### Configure Control Variables
 827 It is possible to control certain aspects of `configure` by overriding the
 828 value of `configure` variables, either on the command line or in the
 829 environment.
 831 Normally, this is **not recommended**. If used improperly, it can lead to a
 832 broken configuration. Unless you're well versed in the build system, this is
 833 hard to use properly. Therefore, `configure` will print a warning if this is
 834 detected.
 836 However, there are a few `configure` variables, known as *control variables*
 837 that are supposed to be overriden on the command line. These are variables that
 838 describe the location of tools needed by the build, like `MAKE` or `GREP`. If
 839 any such variable is specified, `configure` will use that value instead of
 840 trying to autodetect the tool. For instance, `bash configure
 841 MAKE=/opt/gnumake4.0/bin/make`.
 843 If a configure argument exists, use that instead, e.g. use `--with-jtreg`
 844 instead of setting `JTREGEXE`.
 846 Also note that, despite what autoconf claims, setting `CFLAGS` will not
 847 accomplish anything. Instead use `--with-extra-cflags` (and similar for
 848 `cxxflags` and `ldflags`).
 850 ## Running Make
 852 When you have a proper configuration, all you need to do to build OpenJDK is to
 853 run `make`. (But see the warning at [GNU Make](#gnu-make) about running the
 854 correct version of make.)
 856 When running `make` without any arguments, the default target is used, which is
 857 the same as running `make default` or `make jdk`. This will build a minimal (or
 858 roughly minimal) set of compiled output (known as an "exploded image") needed
 859 for a developer to actually execute the newly built JDK. The idea is that in an
 860 incremental development fashion, when doing a normal make, you should only
 861 spend time recompiling what's changed (making it purely incremental) and only
 862 do the work that's needed to actually run and test your code.
 864 The output of the exploded image resides in `$BUILD/jdk`. You can test the
 865 newly built JDK like this: `$BUILD/jdk/bin/java -version`.
 867 ### Common Make Targets
 869 Apart from the default target, here are some common make targets:
 871   * `hotspot` - Build all of hotspot (but only hotspot)
 872   * `hotspot-<variant>` - Build just the specified jvm variant
 873   * `images` or `product-images` - Build the JRE and JDK images
 874   * `docs` or `docs-image` - Build the documentation image
 875   * `test-image` - Build the test image
 876   * `all` or `all-images` - Build all images (product, docs and test)
 877   * `bootcycle-images` - Build images twice, second time with newly built JDK
 878     (good for testing)
 879   * `clean` - Remove all files generated by make, but not those generated by
 880     configure
 881   * `dist-clean` - Remove all files, including configuration
 883 Run `make help` to get an up-to-date list of important make targets and make
 884 control variables.
 886 It is possible to build just a single module, a single phase, or a single phase
 887 of a single module, by creating make targets according to these followin
 888 patterns. A phase can be either of `gensrc`, `gendata`, `copy`, `java`,
 889 `launchers`, `libs` or `rmic`. See [Using Fine-Grained Make Targets](
 890 #using-fine-grained-make-targets) for more details about this functionality.
 892   * `<phase>` - Build the specified phase and everything it depends on
 893   * `<module>` - Build the specified module and everything it depends on
 894   * `<module>-<phase>` - Compile the specified phase for the specified module
 895     and everything it depends on
 897 Similarly, it is possible to clean just a part of the build by creating make
 898 targets according to these patterns:
 900   * `clean-<outputdir>` - Remove the subdir in the output dir with the name
 901   * `clean-<phase>` - Remove all build results related to a certain build
 902     phase
 903   * `clean-<module>` - Remove all build results related to a certain module
 904   * `clean-<module>-<phase>` - Remove all build results related to a certain
 905     module and phase
 907 ### Make Control Variables
 909 It is possible to control `make` behavior by overriding the value of `make`
 910 variables, either on the command line or in the environment.
 912 Normally, this is **not recommended**. If used improperly, it can lead to a
 913 broken build. Unless you're well versed in the build system, this is hard to
 914 use properly. Therefore, `make` will print a warning if this is detected.
 916 However, there are a few `make` variables, known as *control variables* that
 917 are supposed to be overriden on the command line. These make up the "make time"
 918 configuration, as opposed to the "configure time" configuration.
 920 #### General Make Control Variables
 922   * `JOBS` - Specify the number of jobs to build with. See [Build
 923     Performance](#build-performance).
 924   * `LOG` - Specify the logging level and functionality. See [Checking the
 925     Build Log File](#checking-the-build-log-file)
 926   * `CONF` and `CONF_NAME` - Selecting the configuration(s) to use. See [Using
 927     Multiple Configurations](#using-multiple-configurations)
 929 #### Test Make Control Variables
 931 These make control variables only make sense when running tests. Please see
 932 [Testing OpenJDK](testing.html) for details.
 934   * `TEST`
 935   * `TEST_JOBS`
 936   * `JTREG`
 937   * `GTEST`
 939 #### Advanced Make Control Variables
 941 These advanced make control variables can be potentially unsafe. See [Hints and
 942 Suggestions for Advanced Users](#hints-and-suggestions-for-advanced-users) and
 943 [Understanding the Build System](#understanding-the-build-system) for details.
 945   * `SPEC`
 946   * `CONF_CHECK`
 947   * `COMPARE_BUILD`
 948   * `JDK_FILTER`
 950 ## Running Tests
 952 Most of the OpenJDK tests are using the [JTReg](http://openjdk.java.net/jtreg)
 953 test framework. Make sure that your configuration knows where to find your
 954 installation of JTReg. If this is not picked up automatically, use the
 955 `--with-jtreg=<path to jtreg home>` option to point to the JTReg framework.
 956 Note that this option should point to the JTReg home, i.e. the top directory,
 957 containing `lib/jtreg.jar` etc.
 959 To execute the most basic tests (tier 1), use:
 960 ```
 961 make run-test-tier1
 962 ```
 964 For more details on how to run tests, please see the [Testing
 965 OpenJDK](testing.html) document.
 967 ## Cross-compiling
 969 Cross-compiling means using one platform (the *build* platform) to generate
 970 output that can ran on another platform (the *target* platform).
 972 The typical reason for cross-compiling is that the build is performed on a more
 973 powerful desktop computer, but the resulting binaries will be able to run on a
 974 different, typically low-performing system. Most of the complications that
 975 arise when building for embedded is due to this separation of *build* and
 976 *target* systems.
 978 This requires a more complex setup and build procedure. This section assumes
 979 you are familiar with cross-compiling in general, and will only deal with the
 980 particularities of cross-compiling OpenJDK. If you are new to cross-compiling,
 981 please see the [external links at Wikipedia](
 982 https://en.wikipedia.org/wiki/Cross_compiler#External_links) for a good start
 983 on reading materials.
 985 Cross-compiling OpenJDK requires you to be able to build both for the build
 986 platform and for the target platform. The reason for the former is that we need
 987 to build and execute tools during the build process, both native tools and Java
 988 tools.
 990 If all you want to do is to compile a 32-bit version, for the same OS, on a
 991 64-bit machine, consider using `--with-target-bits=32` instead of doing a
 992 full-blown cross-compilation. (While this surely is possible, it's a lot more
 993 work and will take much longer to build.)
 995 ### Boot JDK and Build JDK
 997 When cross-compiling, make sure you use a boot JDK that runs on the *build*
 998 system, and not on the *target* system.
1000 To be able to build, we need a "Build JDK", which is a JDK built from the
1001 current sources (that is, the same as the end result of the entire build
1002 process), but able to run on the *build* system, and not the *target* system.
1003 (In contrast, the Boot JDK should be from an older release, e.g. JDK 8 when
1004 building JDK 9.)
1006 The build process will create a minimal Build JDK for you, as part of building.
1007 To speed up the build, you can use `--with-build-jdk` to `configure` to point
1008 to a pre-built Build JDK. Please note that the build result is unpredictable,
1009 and can possibly break in subtle ways, if the Build JDK does not **exactly**
1010 match the current sources.
1012 ### Specifying the Target Platform
1014 You *must* specify the target platform when cross-compiling. Doing so will also
1015 automatically turn the build into a cross-compiling mode. The simplest way to
1016 do this is to use the `--openjdk-target` argument, e.g.
1017 `--openjdk-target=arm-linux-gnueabihf`. or `--openjdk-target=aarch64-oe-linux`.
1018 This will automatically set the `--build`, `--host` and `--target` options for
1019 autoconf, which can otherwise be confusing. (In autoconf terminology, the
1020 "target" is known as "host", and "target" is used for building a Canadian
1021 cross-compiler.)
1023 ### Toolchain Considerations
1025 You will need two copies of your toolchain, one which generates output that can
1026 run on the target system (the normal, or *target*, toolchain), and one that
1027 generates output that can run on the build system (the *build* toolchain). Note
1028 that cross-compiling is only supported for gcc at the time being. The gcc
1029 standard is to prefix cross-compiling toolchains with the target denominator.
1030 If you follow this standard, `configure` is likely to pick up the toolchain
1031 correctly.
1033 The *build* toolchain will be autodetected just the same way the normal
1034 *build*/*target* toolchain will be autodetected when not cross-compiling. If
1035 this is not what you want, or if the autodetection fails, you can specify a
1036 devkit containing the *build* toolchain using `--with-build-devkit` to
1037 `configure`, or by giving `BUILD_CC` and `BUILD_CXX` arguments.
1039 It is often helpful to locate the cross-compilation tools, headers and
1040 libraries in a separate directory, outside the normal path, and point out that
1041 directory to `configure`. Do this by setting the sysroot (`--with-sysroot`) and
1042 appending the directory when searching for cross-compilations tools
1043 (`--with-toolchain-path`). As a compact form, you can also use `--with-devkit`
1044 to point to a single directory, if it is correctly setup. (See `basics.m4` for
1045 details.)
1047 If you are unsure what toolchain and versions to use, these have been proved
1048 working at the time of writing:
1050   * [aarch64](
1051 https://releases.linaro.org/archive/13.11/components/toolchain/binaries/gcc-linaro-aarch64-linux-gnu-4.8-2013.11_linux.tar.xz)
1052   * [arm 32-bit hardware floating  point](
1053 https://launchpad.net/linaro-toolchain-unsupported/trunk/2012.09/+download/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux.tar.bz2)
1055 ### Native Libraries
1057 You will need copies of external native libraries for the *target* system,
1058 present on the *build* machine while building.
1060 Take care not to replace the *build* system's version of these libraries by
1061 mistake, since that can render the *build* machine unusable.
1063 Make sure that the libraries you point to (ALSA, X11, etc) are for the
1064 *target*, not the *build*, platform.
1066 #### ALSA
1068 You will need alsa libraries suitable for your *target* system. For most cases,
1069 using Debian's pre-built libraries work fine.
1071 Note that alsa is needed even if you only want to build a headless JDK.
1073   * Go to [Debian Package Search](https://www.debian.org/distrib/packages) and
1074     search for the `libasound2` and `libasound2-dev` packages for your *target*
1075     system. Download them to /tmp.
1077   * Install the libraries into the cross-compilation toolchain. For instance:
1078 ```
1079 cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc
1080 dpkg-deb -x /tmp/libasound2_1.0.25-4_armhf.deb .
1081 dpkg-deb -x /tmp/libasound2-dev_1.0.25-4_armhf.deb .
1082 ```
1084   * If alsa is not properly detected by `configure`, you can point it out by
1085     `--with-alsa`.
1087 #### X11
1089 You will need X11 libraries suitable for your *target* system. For most cases,
1090 using Debian's pre-built libraries work fine.
1092 Note that X11 is needed even if you only want to build a headless JDK.
1094   * Go to [Debian Package Search](https://www.debian.org/distrib/packages),
1095     search for the following packages for your *target* system, and download them
1096     to /tmp/target-x11:
1097       * libxi
1098       * libxi-dev
1099       * x11proto-core-dev
1100       * x11proto-input-dev
1101       * x11proto-kb-dev
1102       * x11proto-render-dev
1103       * x11proto-xext-dev
1104       * libice-dev
1105       * libxrender
1106       * libxrender-dev
1107       * libsm-dev
1108       * libxt-dev
1109       * libx11
1110       * libx11-dev
1111       * libxtst
1112       * libxtst-dev
1113       * libxext
1114       * libxext-dev
1116   * Install the libraries into the cross-compilation toolchain. For instance:
1117     ```
1118     cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc/usr
1119     mkdir X11R6
1120     cd X11R6
1121     for deb in /tmp/target-x11/*.deb ; do dpkg-deb -x $deb . ; done
1122     mv usr/* .
1123     cd lib
1124     cp arm-linux-gnueabihf/* .
1125     ```
1127     You can ignore the following messages. These libraries are not needed to
1128     successfully complete a full JDK build.
1129     ```
1130     cp: cannot stat `arm-linux-gnueabihf/libICE.so': No such file or directory
1131     cp: cannot stat `arm-linux-gnueabihf/libSM.so': No such file or directory
1132     cp: cannot stat `arm-linux-gnueabihf/libXt.so': No such file or directory
1133     ```
1135   * If the X11 libraries are not properly detected by `configure`, you can
1136     point them out by `--with-x`.
1138 ### Building for ARM/aarch64
1140 A common cross-compilation target is the ARM CPU. When building for ARM, it is
1141 useful to set the ABI profile. A number of pre-defined ABI profiles are
1142 available using `--with-abi-profile`: arm-vfp-sflt, arm-vfp-hflt, arm-sflt,
1143 armv5-vfp-sflt, armv6-vfp-hflt. Note that soft-float ABIs are no longer
1144 properly supported on OpenJDK.
1146 OpenJDK contains two different ports for the aarch64 platform, one is the
1147 original aarch64 port from the [AArch64 Port Project](
1148 http://openjdk.java.net/projects/aarch64-port) and one is a 64-bit version of
1149 the Oracle contributed ARM port. When targeting aarch64, by the default the
1150 original aarch64 port is used. To select the Oracle ARM 64 port, use
1151 `--with-cpu-port=arm64`. Also set the corresponding value (`aarch64` or
1152 `arm64`) to --with-abi-profile, to ensure a consistent build.
1154 ### Verifying the Build
1156 The build will end up in a directory named like
1157 `build/linux-arm-normal-server-release`.
1159 Inside this build output directory, the `images/jdk` and `images/jre` will
1160 contain the newly built JDK and JRE, respectively, for your *target* system.
1162 Copy these folders to your *target* system. Then you can run e.g.
1163 `images/jdk/bin/java -version`.
1165 ## Build Performance
1167 Building OpenJDK requires a lot of horsepower. Some of the build tools can be
1168 adjusted to utilize more or less of resources such as parallel threads and
1169 memory. The `configure` script analyzes your system and selects reasonable
1170 values for such options based on your hardware. If you encounter resource
1171 problems, such as out of memory conditions, you can modify the detected values
1172 with:
1174   * `--with-num-cores` -- number of cores in the build system, e.g.
1175     `--with-num-cores=8`.
1177   * `--with-memory-size` -- memory (in MB) available in the build system, e.g.
1178     `--with-memory-size=1024`
1180 You can also specify directly the number of build jobs to use with
1181 `--with-jobs=N` to `configure`, or `JOBS=N` to `make`. Do not use the `-j` flag
1182 to `make`. In most cases it will be ignored by the makefiles, but it can cause
1183 problems for some make targets.
1185 It might also be necessary to specify the JVM arguments passed to the Boot JDK,
1186 using e.g. `--with-boot-jdk-jvmargs="-Xmx8G"`. Doing so will override the
1187 default JVM arguments passed to the Boot JDK.
1189 At the end of a successful execution of `configure`, you will get a performance
1190 summary, indicating how well the build will perform. Here you will also get
1191 performance hints. If you want to build fast, pay attention to those!
1193 If you want to tweak build performance, run with `make LOG=info` to get a build
1194 time summary at the end of the build process.
1196 ### Disk Speed
1198 If you are using network shares, e.g. via NFS, for your source code, make sure
1199 the build directory is situated on local disk (e.g. by `ln -s
1200 /localdisk/jdk-build $JDK-SHARE/build`). The performance penalty is extremely
1201 high for building on a network share; close to unusable.
1203 Also, make sure that your build tools (including Boot JDK and toolchain) is
1204 located on a local disk and not a network share.
1206 As has been stressed elsewhere, do use SSD for source code and build directory,
1207 as well as (if possible) the build tools.
1209 ### Virus Checking
1211 The use of virus checking software, especially on Windows, can *significantly*
1212 slow down building of OpenJDK. If possible, turn off such software, or exclude
1213 the directory containing the OpenJDK source code from on-the-fly checking.
1215 ### Ccache
1217 The OpenJDK build supports building with ccache when using gcc or clang. Using
1218 ccache can radically speed up compilation of native code if you often rebuild
1219 the same sources. Your milage may vary however, so we recommend evaluating it
1220 for yourself. To enable it, make sure it's on the path and configure with
1221 `--enable-ccache`.
1223 ### Precompiled Headers
1225 By default, the Hotspot build uses preccompiled headers (PCH) on the toolchains
1226 were it is properly supported (clang, gcc, and Visual Studio). Normally, this
1227 speeds up the build process, but in some circumstances, it can actually slow
1228 things down.
1230 You can experiment by disabling precompiled headers using
1231 `--disable-precompiled-headers`.
1233 ### Icecc / icecream
1235 [icecc/icecream](http://github.com/icecc/icecream) is a simple way to setup a
1236 distributed compiler network. If you have multiple machines available for
1237 building OpenJDK, you can drastically cut individual build times by utilizing
1238 it.
1240 To use, setup an icecc network, and install icecc on the build machine. Then
1241 run `configure` using `--enable-icecc`.
1243 ### Using sjavac
1245 To speed up Java compilation, especially incremental compilations, you can try
1246 the experimental sjavac compiler by using `--enable-sjavac`.
1248 ### Building the Right Target
1250 Selecting the proper target to build can have dramatic impact on build time.
1251 For normal usage, `jdk` or the default target is just fine. You only need to
1252 build `images` for shipping, or if your tests require it.
1254 See also [Using Fine-Grained Make Targets](#using-fine-grained-make-targets) on
1255 how to build an even smaller subset of the product.
1257 ## Troubleshooting
1259 If your build fails, it can sometimes be difficult to pinpoint the problem or
1260 find a proper solution.
1262 ### Locating the Source of the Error
1264 When a build fails, it can be hard to pinpoint the actual cause of the error.
1265 In a typical build process, different parts of the product build in parallel,
1266 with the output interlaced.
1268 #### Build Failure Summary
1270 To help you, the build system will print a failure summary at the end. It looks
1271 like this:
1273 ```
1274 ERROR: Build failed for target 'hotspot' in configuration 'linux-x64' (exit code 2)
1276 === Output from failing command(s) repeated here ===
1277 * For target hotspot_variant-server_libjvm_objs_psMemoryPool.o:
1278 /localhome/hg/jdk9-sandbox/hotspot/src/share/vm/services/psMemoryPool.cpp:1:1: error: 'failhere' does not name a type
1279    ... (rest of output omitted)
1281 * All command lines available in /localhome/hg/jdk9-sandbox/build/linux-x64/make-support/failure-logs.
1282 === End of repeated output ===
1284 === Make failed targets repeated here ===
1285 lib/CompileJvm.gmk:207: recipe for target '/localhome/hg/jdk9-sandbox/build/linux-x64/hotspot/variant-server/libjvm/objs/psMemoryPool.o' failed
1286 make/Main.gmk:263: recipe for target 'hotspot-server-libs' failed
1287 === End of repeated output ===
1289 Hint: Try searching the build log for the name of the first failed target.
1290 Hint: If caused by a warning, try configure --disable-warnings-as-errors.
1291 ```
1293 Let's break it down! First, the selected configuration, and the top-level
1294 target you entered on the command line that caused the failure is printed.
1296 Then, between the `Output from failing command(s) repeated here` and `End of
1297 repeated output` the first lines of output (stdout and stderr) from the actual
1298 failing command is repeated. In most cases, this is the error message that
1299 caused the build to fail. If multiple commands were failing (this can happen in
1300 a parallel build), output from all failed commands will be printed here.
1302 The path to the `failure-logs` directory is printed. In this file you will find
1303 a `<target>.log` file that contains the output from this command in its
1304 entirety, and also a `<target>.cmd`, which contain the complete command line
1305 used for running this command. You can re-run the failing command by executing
1306 `. <path to failure-logs>/<target>.cmd` in your shell.
1308 Another way to trace the failure is to follow the chain of make targets, from
1309 top-level targets to individual file targets. Between `Make failed targets
1310 repeated here` and `End of repeated output` the output from make showing this
1311 chain is repeated. The first failed recipe will typically contain the full path
1312 to the file in question that failed to compile. Following lines will show a
1313 trace of make targets why we ended up trying to compile that file.
1315 Finally, some hints are given on how to locate the error in the complete log.
1316 In this example, we would try searching the log file for "`psMemoryPool.o`".
1317 Another way to quickly locate make errors in the log is to search for "`]
1318 Error`" or "`***`".
1320 Note that the build failure summary will only help you if the issue was a
1321 compilation failure or similar. If the problem is more esoteric, or is due to
1322 errors in the build machinery, you will likely get empty output logs, and `No
1323 indication of failed target found` instead of the make target chain.
1325 #### Checking the Build Log File
1327 The output (stdout and stderr) from the latest build is always stored in
1328 `$BUILD/build.log`. The previous build log is stored as `build.log.old`. This
1329 means that it is not necessary to redirect the build output yourself if you
1330 want to process it.
1332 You can increase the verbosity of the log file, by the `LOG` control variable
1333 to `make`. If you want to see the command lines used in compilations, use
1334 `LOG=cmdlines`. To increase the general verbosity, use `LOG=info`, `LOG=debug`
1335 or `LOG=trace`. Both of these can be combined with `cmdlines`, e.g.
1336 `LOG=info,cmdlines`. The `debug` log level will show most shell commands
1337 executed by make, and `trace` will show all. Beware that both these log levels
1338 will produce a massive build log!
1340 ### Fixing Unexpected Build Failures
1342 Most of the time, the build will fail due to incorrect changes in the source
1343 code.
1345 Sometimes the build can fail with no apparent changes that have caused the
1346 failure. If this is the first time you are building OpenJDK on this particular
1347 computer, and the build fails, the problem is likely with your build
1348 environment. But even if you have previously built OpenJDK with success, and it
1349 now fails, your build environment might have changed (perhaps due to OS
1350 upgrades or similar). But most likely, such failures are due to problems with
1351 the incremental rebuild.
1353 #### Problems with the Build Environment
1355 Make sure your configuration is correct. Re-run `configure`, and look for any
1356 warnings. Warnings that appear in the middle of the `configure` output is also
1357 repeated at the end, after the summary. The entire log is stored in
1358 `$BUILD/configure.log`.
1360 Verify that the summary at the end looks correct. Are you indeed using the Boot
1361 JDK and native toolchain that you expect?
1363 By default, OpenJDK has a strict approach where warnings from the compiler is
1364 considered errors which fail the build. For very new or very old compiler
1365 versions, this can trigger new classes of warnings, which thus fails the build.
1366 Run `configure` with `--disable-warnings-as-errors` to turn of this behavior.
1367 (The warnings will still show, but not make the build fail.)
1369 #### Problems with Incremental Rebuilds
1371 Incremental rebuilds mean that when you modify part of the product, only the
1372 affected parts get rebuilt. While this works great in most cases, and
1373 significantly speed up the development process, from time to time complex
1374 interdependencies will result in an incorrect build result. This is the most
1375 common cause for unexpected build problems, together with inconsistencies
1376 between the different Mercurial repositories in the forest.
1378 Here are a suggested list of things to try if you are having unexpected build
1379 problems. Each step requires more time than the one before, so try them in
1380 order. Most issues will be solved at step 1 or 2.
1382  1. Make sure your forest is up-to-date
1384     Run `bash get_source.sh` to make sure you have the latest version of all
1385     repositories.
1387  2. Clean build results
1389     The simplest way to fix incremental rebuild issues is to run `make clean`.
1390     This will remove all build results, but not the configuration or any build
1391     system support artifacts. In most cases, this will solve build errors
1392     resulting from incremental build mismatches.
1394  3. Completely clean the build directory.
1396     If this does not work, the next step is to run `make dist-clean`, or
1397     removing the build output directory (`$BUILD`). This will clean all
1398     generated output, including your configuration. You will need to re-run
1399     `configure` after this step. A good idea is to run `make
1400     print-configuration` before running `make dist-clean`, as this will print
1401     your current `configure` command line. Here's a way to do this:
1403     ```
1404     make print-configuration > current-configuration
1405     make dist-clean
1406     bash configure $(cat current-configuration)
1407     make
1408     ```
1410  4. Re-clone the Mercurial forest
1412     Sometimes the Mercurial repositories themselves gets in a state that causes
1413     the product to be un-buildable. In such a case, the simplest solution is
1414     often the "sledgehammer approach": delete the entire forest, and re-clone
1415     it. If you have local changes, save them first to a different location
1416     using `hg export`.
1418 ### Specific Build Issues
1420 #### Clock Skew
1422 If you get an error message like this:
1423 ```
1424 File 'xxx' has modification time in the future.
1425 Clock skew detected. Your build may be incomplete.
1426 ```
1427 then the clock on your build machine is out of sync with the timestamps on the
1428 source files. Other errors, apparently unrelated but in fact caused by the
1429 clock skew, can occur along with the clock skew warnings. These secondary
1430 errors may tend to obscure the fact that the true root cause of the problem is
1431 an out-of-sync clock.
1433 If you see these warnings, reset the clock on the build machine, run `make
1434 clean` and restart the build.
1436 #### Out of Memory Errors
1438 On Solaris, you might get an error message like this:
1439 ```
1440 Trouble writing out table to disk
1441 ```
1442 To solve this, increase the amount of swap space on your build machine.
1444 On Windows, you might get error messages like this:
1445 ```
1446 fatal error - couldn't allocate heap
1447 cannot create ... Permission denied
1448 spawn failed
1449 ```
1450 This can be a sign of a Cygwin problem. See the information about solving
1451 problems in the [Cygwin](#cygwin) section. Rebooting the computer might help
1452 temporarily.
1454 ### Getting Help
1456 If none of the suggestions in this document helps you, or if you find what you
1457 believe is a bug in the build system, please contact the Build Group by sending
1458 a mail to [build-dev@openjdk.java.net](mailto:build-dev@openjdk.java.net).
1459 Please include the relevant parts of the configure and/or build log.
1461 If you need general help or advice about developing for OpenJDK, you can also
1462 contact the Adoption Group. See the section on [Contributing to OpenJDK](
1463 #contributing-to-openjdk) for more information.
1465 ## Hints and Suggestions for Advanced Users
1467 ### Setting Up a Forest for Pushing Changes (defpath)
1469 To help you prepare a proper push path for a Mercurial repository, there exists
1470 a useful tool known as [defpath](
1471 http://openjdk.java.net/projects/code-tools/defpath). It will help you setup a
1472 proper push path for pushing changes to OpenJDK.
1474 Install the extension by cloning
1475 `http://hg.openjdk.java.net/code-tools/defpath` and updating your `.hgrc` file.
1476 Here's one way to do this:
1478 ```
1479 cd ~
1480 mkdir hg-ext
1481 cd hg-ext
1482 hg clone http://hg.openjdk.java.net/code-tools/defpath
1483 cat << EOT >> ~/.hgrc
1484 [extensions]
1485 defpath=~/hg-ext/defpath/defpath.py
1486 EOT
1487 ```
1489 You can now setup a proper push path using:
1490 ```
1491 hg defpath -d -u <your OpenJDK username>
1492 ```
1494 If you also have the `trees` extension installed in Mercurial, you will
1495 automatically get a `tdefpath` command, which is even more useful. By running
1496 `hg tdefpath -du <username>` in the top repository of your forest, all repos
1497 will get setup automatically. This is the recommended usage.
1499 ### Bash Completion
1501 The `configure` and `make` commands tries to play nice with bash command-line
1502 completion (using `<tab>` or `<tab><tab>`). To use this functionality, make
1503 sure you enable completion in your `~/.bashrc` (see instructions for bash in
1504 your operating system).
1506 Make completion will work out of the box, and will complete valid make targets.
1507 For instance, typing `make jdk-i<tab>` will complete to `make jdk-image`.
1509 The `configure` script can get completion for options, but for this to work you
1510 need to help `bash` on the way. The standard way of running the script, `bash
1511 configure`, will not be understood by bash completion. You need `configure` to
1512 be the command to run. One way to achieve this is to add a simple helper script
1513 to your path:
1515 ```
1516 cat << EOT > /tmp/configure
1517 #!/bin/bash
1518 if [ \$(pwd) = \$(cd \$(dirname \$0); pwd) ] ; then
1519   echo >&2 "Abort: Trying to call configure helper recursively"
1520   exit 1
1521 fi
1523 bash \$PWD/configure "\$@"
1524 EOT
1525 chmod +x /tmp/configure
1526 sudo mv /tmp/configure /usr/local/bin
1527 ```
1529 Now `configure --en<tab>-dt<tab>` will result in `configure --enable-dtrace`.
1531 ### Using Multiple Configurations
1533 You can have multiple configurations for a single source forest. When you
1534 create a new configuration, run `configure --with-conf-name=<name>` to create a
1535 configuration with the name `<name>`. Alternatively, you can create a directory
1536 under `build` and run `configure` from there, e.g. `mkdir build/<name> && cd
1537 build/<name> && bash ../../configure`.
1539 Then you can build that configuration using `make CONF_NAME=<name>` or `make
1540 CONF=<pattern>`, where `<pattern>` is a substring matching one or several
1541 configurations, e.g. `CONF=debug`. The special empty pattern (`CONF=`) will
1542 match *all* available configuration, so `make CONF= hotspot` will build the
1543 `hotspot` target for all configurations. Alternatively, you can execute `make`
1544 in the configuration directory, e.g. `cd build/<name> && make`.
1546 ### Handling Reconfigurations
1548 If you update the forest and part of the configure script has changed, the
1549 build system will force you to re-run `configure`.
1551 Most of the time, you will be fine by running `configure` again with the same
1552 arguments as the last time, which can easily be performed by `make
1553 reconfigure`. To simplify this, you can use the `CONF_CHECK` make control
1554 variable, either as `make CONF_CHECK=auto`, or by setting an environment
1555 variable. For instance, if you add `export CONF_CHECK=auto` to your `.bashrc`
1556 file, `make` will always run `reconfigure` automatically whenever the configure
1557 script has changed.
1559 You can also use `CONF_CHECK=ignore` to skip the check for a needed configure
1560 update. This might speed up the build, but comes at the risk of an incorrect
1561 build result. This is only recommended if you know what you're doing.
1563 From time to time, you will also need to modify the command line to `configure`
1564 due to changes. Use `make print-configure` to show the command line used for
1565 your current configuration.
1567 ### Using Fine-Grained Make Targets
1569 The default behavior for make is to create consistent and correct output, at
1570 the expense of build speed, if necessary.
1572 If you are prepared to take some risk of an incorrect build, and know enough of
1573 the system to understand how things build and interact, you can speed up the
1574 build process considerably by instructing make to only build a portion of the
1575 product.
1577 #### Building Individual Modules
1579 The safe way to use fine-grained make targets is to use the module specific
1580 make targets. All source code in JDK 9 is organized so it belongs to a module,
1581 e.g. `java.base` or `jdk.jdwp.agent`. You can build only a specific module, by
1582 giving it as make target: `make jdk.jdwp.agent`. If the specified module
1583 depends on other modules (e.g. `java.base`), those modules will be built first.
1585 You can also specify a set of modules, just as you can always specify a set of
1586 make targets: `make jdk.crypto.cryptoki jdk.crypto.ec jdk.crypto.mscapi
1587 jdk.crypto.ucrypto`
1589 #### Building Individual Module Phases
1591 The build process for each module is divided into separate phases. Not all
1592 modules need all phases. Which are needed depends on what kind of source code
1593 and other artifact the module consists of. The phases are:
1595   * `gensrc` (Generate source code to compile)
1596   * `gendata` (Generate non-source code artifacts)
1597   * `copy` (Copy resource artifacts)
1598   * `java` (Compile Java code)
1599   * `launchers` (Compile native executables)
1600   * `libs` (Compile native libraries)
1601   * `rmic` (Run the `rmic` tool)
1603 You can build only a single phase for a module by using the notation
1604 `$MODULE-$PHASE`. For instance, to build the `gensrc` phase for `java.base`,
1605 use `make java.base-gensrc`.
1607 Note that some phases may depend on others, e.g. `java` depends on `gensrc` (if
1608 present). Make will build all needed prerequisites before building the
1609 requested phase.
1611 #### Skipping the Dependency Check
1613 When using an iterative development style with frequent quick rebuilds, the
1614 dependency check made by make can take up a significant portion of the time
1615 spent on the rebuild. In such cases, it can be useful to bypass the dependency
1616 check in make.
1618 > **Note that if used incorrectly, this can lead to a broken build!**
1620 To achieve this, append `-only` to the build target. For instance, `make
1621 jdk.jdwp.agent-java-only` will *only* build the `java` phase of the
1622 `jdk.jdwp.agent` module. If the required dependencies are not present, the
1623 build can fail. On the other hand, the execution time measures in milliseconds.
1625 A useful pattern is to build the first time normally (e.g. `make
1626 jdk.jdwp.agent`) and then on subsequent builds, use the `-only` make target.
1628 #### Rebuilding Part of java.base (JDK\_FILTER)
1630 If you are modifying files in `java.base`, which is the by far largest module
1631 in OpenJDK, then you need to rebuild all those files whenever a single file has
1632 changed. (This inefficiency will hopefully be addressed in JDK 10.)
1634 As a hack, you can use the make control variable `JDK_FILTER` to specify a
1635 pattern that will be used to limit the set of files being recompiled. For
1636 instance, `make java.base JDK_FILTER=javax/crypto` (or, to combine methods,
1637 `make java.base-java-only JDK_FILTER=javax/crypto`) will limit the compilation
1638 to files in the `javax.crypto` package.
1640 ### Learn About Mercurial
1642 To become an efficient OpenJDK developer, it is recommended that you invest in
1643 learning Mercurial properly. Here are some links that can get you started:
1645   * [Mercurial for git users](http://www.mercurial-scm.org/wiki/GitConcepts)
1646   * [The official Mercurial tutorial](http://www.mercurial-scm.org/wiki/Tutorial)
1647   * [hg init](http://hginit.com/)
1648   * [Mercurial: The Definitive Guide](http://hgbook.red-bean.com/read/)
1650 ## Understanding the Build System
1652 This section will give you a more technical description on the details of the
1653 build system.
1655 ### Configurations
1657 The build system expects to find one or more configuration. These are
1658 technically defined by the `spec.gmk` in a subdirectory to the `build`
1659 subdirectory. The `spec.gmk` file is generated by `configure`, and contains in
1660 principle the configuration (directly or by files included by `spec.gmk`).
1662 You can, in fact, select a configuration to build by pointing to the `spec.gmk`
1663 file with the `SPEC` make control variable, e.g. `make SPEC=$BUILD/spec.gmk`.
1664 While this is not the recommended way to call `make` as a user, it is what is
1665 used under the hood by the build system.
1667 ### Build Output Structure
1669 The build output for a configuration will end up in `build/<configuration
1670 name>`, which we refer to as `$BUILD` in this document. The `$BUILD` directory
1671 contains the following important directories:
1673 ```
1674 buildtools/
1675 configure-support/
1676 hotspot/
1677 images/
1678 jdk/
1679 make-support/
1680 support/
1681 test-results/
1682 test-support/
1683 ```
1685 This is what they are used for:
1687   * `images`: This is the directory were the output of the `*-image` make
1688     targets end up. For instance, `make jdk-image` ends up in `images/jdk`.
1690   * `jdk`: This is the "exploded image". After `make jdk`, you will be able to
1691     launch the newly built JDK by running `$BUILD/jdk/bin/java`.
1693   * `test-results`: This directory contains the results from running tests.
1695   * `support`: This is an area for intermediate files needed during the build,
1696     e.g. generated source code, object files and class files. Some noteworthy
1697     directories in `support` is `gensrc`, which contains the generated source
1698     code, and the `modules_*` directories, which contains the files in a
1699     per-module hierarchy that will later be collapsed into the `jdk` directory
1700     of the exploded image.
1702   * `buildtools`: This is an area for tools compiled for the build platform
1703     that are used during the rest of the build.
1705   * `hotspot`: This is an area for intermediate files needed when building
1706     hotspot.
1708   * `configure-support`, `make-support` and `test-support`: These directories
1709     contain files that are needed by the build system for `configure`, `make`
1710     and for running tests.
1712 ### Fixpath
1714 Windows path typically look like `C:\User\foo`, while Unix paths look like
1715 `/home/foo`. Tools with roots from Unix often experience issues related to this
1716 mismatch when running on Windows.
1718 In the OpenJDK build, we always use Unix paths internally, and only just before
1719 calling a tool that does not understand Unix paths do we convert them to
1720 Windows paths.
1722 This conversion is done by the `fixpath` tool, which is a small wrapper that
1723 modifies unix-style paths to Windows-style paths in command lines. Fixpath is
1724 compiled automatically by `configure`.
1726 ### Native Debug Symbols
1728 Native libraries and executables can have debug symbol (and other debug
1729 information) associated with them. How this works is very much platform
1730 dependent, but a common problem is that debug symbol information takes a lot of
1731 disk space, but is rarely needed by the end user.
1733 The OpenJDK supports different methods on how to handle debug symbols. The
1734 method used is selected by `--with-native-debug-symbols`, and available methods
1735 are `none`, `internal`, `external`, `zipped`.
1737   * `none` means that no debug symbols will be generated during the build.
1739   * `internal` means that debug symbols will be generated during the build, and
1740     they will be stored in the generated binary.
1742   * `external` means that debug symbols will be generated during the build, and
1743     after the compilation, they will be moved into a separate `.debuginfo` file.
1744     (This was previously known as FDS, Full Debug Symbols).
1746   * `zipped` is like `external`, but the .debuginfo file will also be zipped
1747     into a `.diz` file.
1749 When building for distribution, `zipped` is a good solution. Binaries built
1750 with `internal` is suitable for use by developers, since they facilitate
1751 debugging, but should be stripped before distributed to end users.
1753 ### Autoconf Details
1755 The `configure` script is based on the autoconf framework, but in some details
1756 deviate from a normal autoconf `configure` script.
1758 The `configure` script in the top level directory of OpenJDK is just a thin
1759 wrapper that calls `common/autoconf/configure`. This in turn provides
1760 functionality that is not easily expressed in the normal Autoconf framework,
1761 and then calls into the core of the `configure` script, which is the
1762 `common/autoconf/generated-configure.sh` file.
1764 As the name implies, this file is generated by Autoconf. It is checked in after
1765 regeneration, to alleviate the common user to have to install Autoconf.
1767 The build system will detect if the Autoconf source files have changed, and
1768 will trigger a regeneration of `common/autoconf/generated-configure.sh` if
1769 needed. You can also manually request such an update by `bash
1770 common/autoconf/autogen.sh`.
1772 If you make changes to the build system that requires a re-generation, note the
1773 following:
1775   * You must use *exactly* version 2.69 of autoconf for your patch to be
1776     accepted. This is to avoid spurious changes in the generated file. Note
1777     that Ubuntu 16.04 ships a patched version of autoconf which claims to be
1778     2.69, but is not.
1780   * You do not need to include the generated file in reviews.
1782   * If the generated file needs updating, the Oracle JDK closed counter-part
1783     will also need to be updated. It is very much appreciated if you ask for an
1784     Oracle engineer to sponsor your push so this can be made in tandem.
1786 ### Developing the Build System Itself
1788 This section contains a few remarks about how to develop for the build system
1789 itself. It is not relevant if you are only making changes in the product source
1790 code.
1792 While technically using `make`, the make source files of the OpenJDK does not
1793 resemble most other Makefiles. Instead of listing specific targets and actions
1794 (perhaps using patterns), the basic modus operandi is to call a high-level
1795 function (or properly, macro) from the API in `make/common`. For instance, to
1796 compile all classes in the `jdk.internal.foo` package in the `jdk.foo` module,
1797 a call like this would be made:
1799 ```
1800 $(eval $(call SetupJavaCompilation, BUILD_FOO_CLASSES, \
1802     SRC := $(JDK_TOPDIR)/src/jkd.foo/share/classes, \
1803     INCLUDES := jdk/internal/foo, \
1804     BIN := $(SUPPORT_OUTPUTDIR)/foo_classes, \
1805 ))
1806 ```
1808 By encapsulating and expressing the high-level knowledge of *what* should be
1809 done, rather than *how* it should be done (as is normal in Makefiles), we can
1810 build a much more powerful and flexible build system.
1812 Correct dependency tracking is paramount. Sloppy dependency tracking will lead
1813 to improper parallelization, or worse, race conditions.
1815 To test for/debug race conditions, try running `make JOBS=1` and `make
1816 JOBS=100` and see if it makes any difference. (It shouldn't).
1818 To compare the output of two different builds and see if, and how, they differ,
1819 run `$BUILD1/compare.sh -o $BUILD2`, where `$BUILD1` and `$BUILD2` are the two
1820 builds you want to compare.
1822 To automatically build two consecutive versions and compare them, use
1823 `COMPARE_BUILD`. The value of `COMPARE_BUILD` is a set of variable=value
1824 assignments, like this:
1825 ```
1826 make COMPARE_BUILD=CONF=--enable-new-hotspot-feature:MAKE=hotspot
1827 ```
1828 See `make/InitSupport.gmk` for details on how to use `COMPARE_BUILD`.
1830 To analyze build performance, run with `LOG=trace` and check `$BUILD/build-trace-time.log`.
1831 Use `JOBS=1` to avoid parallelism.
1833 Please check that you adhere to the [Code Conventions for the Build System](
1834 http://openjdk.java.net/groups/build/doc/code-conventions.html) before
1835 submitting patches. Also see the section in [Autoconf Details](
1836 #autoconf-details) about the generated configure script.
1838 ## Contributing to OpenJDK
1840 So, now you've build your OpenJDK, and made your first patch, and want to
1841 contribute it back to the OpenJDK community.
1843 First of all: Thank you! We gladly welcome your contribution to the OpenJDK.
1844 However, please bear in mind that OpenJDK is a massive project, and we must ask
1845 you to follow our rules and guidelines to be able to accept your contribution.
1847 The official place to start is the ['How to contribute' page](
1848 http://openjdk.java.net/contribute/). There is also an official (but somewhat
1849 outdated and skimpy on details) [Developer's Guide](
1850 http://openjdk.java.net/guide/).
1852 If this seems overwhelming to you, the Adoption Group is there to help you! A
1853 good place to start is their ['New Contributor' page](
1854 https://wiki.openjdk.java.net/display/Adoption/New+Contributor), or start
1855 reading the comprehensive [Getting Started Kit](
1856 https://adoptopenjdk.gitbooks.io/adoptopenjdk-getting-started-kit/en/). The
1857 Adoption Group will also happily answer any questions you have about
1858 contributing. Contact them by [mail](
1859 http://mail.openjdk.java.net/mailman/listinfo/adoption-discuss) or [IRC](
1860 http://openjdk.java.net/irc/).
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1863 # Override styles from the base CSS file that are not ideal for this document.
1864 header-includes:
1865  - '<style type="text/css">pre, code, tt { color: #1d6ae5; }</style>'
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