1% Building the JDK 2 3## TL;DR (Instructions for the Impatient) 4 5If you are eager to try out building the JDK, these simple steps works most of 6the time. They assume that you have installed Git (and Cygwin if running 7on Windows) and cloned the top-level JDK repository that you want to build. 8 9 1. [Get the complete source code](#getting-the-source-code): \ 10 `git clone https://git.openjdk.java.net/jdk/` 11 12 2. [Run configure](#running-configure): \ 13 `bash configure` 14 15 If `configure` fails due to missing dependencies (to either the 16 [toolchain](#native-compiler-toolchain-requirements), [build tools]( 17 #build-tools-requirements), [external libraries]( 18 #external-library-requirements) or the [boot JDK](#boot-jdk-requirements)), 19 most of the time it prints a suggestion on how to resolve the situation on 20 your platform. Follow the instructions, and try running `bash configure` 21 again. 22 23 3. [Run make](#running-make): \ 24 `make images` 25 26 4. Verify your newly built JDK: \ 27 `./build/*/images/jdk/bin/java -version` 28 29 5. [Run basic tests](##running-tests): \ 30 `make run-test-tier1` 31 32If any of these steps failed, or if you want to know more about build 33requirements or build functionality, please continue reading this document. 34 35## Introduction 36 37The JDK is a complex software project. Building it requires a certain amount of 38technical expertise, a fair number of dependencies on external software, and 39reasonably powerful hardware. 40 41If you just want to use the JDK and not build it yourself, this document is not 42for you. See for instance [OpenJDK installation]( 43http://openjdk.java.net/install) for some methods of installing a prebuilt 44JDK. 45 46## Getting the Source Code 47 48Make sure you are getting the correct version. As of JDK 10, the source is no 49longer split into separate repositories so you only need to clone one single 50repository. At the [OpenJDK Git site](https://git.openjdk.java.net/) you 51can see a list of all available repositories. If you want to build an older version, 52e.g. JDK 11, it is recommended that you get the `jdk11u` repo, which contains 53incremental updates, instead of the `jdk11` repo, which was frozen at JDK 11 GA. 54 55If you are new to Git, a good place to start is the book [Pro 56Git](https://git-scm.com/book/en/v2). The rest of this document 57assumes a working knowledge of Git. 58 59### Special Considerations 60 61For a smooth building experience, it is recommended that you follow these rules 62on where and how to check out the source code. 63 64 * Do not check out the source code in a path which contains spaces. Chances 65 are the build will not work. This is most likely to be an issue on Windows 66 systems. 67 68 * Do not check out the source code in a path which has a very long name or is 69 nested many levels deep. Chances are you will hit an OS limitation during 70 the build. 71 72 * Put the source code on a local disk, not a network share. If possible, use 73 an SSD. The build process is very disk intensive, and having slow disk 74 access will significantly increase build times. If you need to use a 75 network share for the source code, see below for suggestions on how to keep 76 the build artifacts on a local disk. 77 78 * On Windows, if using [Cygwin](#cygwin), extra care must be taken to make sure 79 the environment is consistent. It is recommended that you follow this 80 procedure: 81 82 * Create the directory that is going to contain the top directory of the 83 JDK clone by using the `mkdir` command in the Cygwin bash shell. 84 That is, do *not* create it using Windows Explorer. This will ensure 85 that it will have proper Cygwin attributes, and that it's children will 86 inherit those attributes. 87 88 * Do not put the JDK clone in a path under your Cygwin home 89 directory. This is especially important if your user name contains 90 spaces and/or mixed upper and lower case letters. 91 92 * You need to install a git client. You have two choices, Cygwin git or 93 Git for Windows. Unfortunately there are pros and cons with each choice. 94 95 * The Cygwin `git` client has no line ending issues and understands 96 Cygwin paths (which are used throughout the JDK build system). 97 However, it does not currently work well with the Skara CLI tooling. 98 Please see the [Skara wiki on Git clients]( 99 https://wiki.openjdk.java.net/display/SKARA/Skara#Skara-Git) for 100 up-to-date information about the Skara git client support. 101 102 * The [Git for Windows](https://gitforwindows.org) client has issues 103 with line endings, and do not understand Cygwin paths. It does work 104 well with the Skara CLI tooling, however. To alleviate the line ending 105 problems, make sure you set `core.autocrlf` to `false` (this is asked 106 during installation). 107 108 Failure to follow this procedure might result in hard-to-debug build 109 problems. 110 111## Build Hardware Requirements 112 113The JDK is a massive project, and require machines ranging from decent to 114powerful to be able to build in a reasonable amount of time, or to be able to 115complete a build at all. 116 117We *strongly* recommend usage of an SSD disk for the build, since disk speed is 118one of the limiting factors for build performance. 119 120### Building on x86 121 122At a minimum, a machine with 2-4 cores is advisable, as well as 2-4 GB of RAM. 123(The more cores to use, the more memory you need.) At least 6 GB of free disk 124space is required. 125 126Even for 32-bit builds, it is recommended to use a 64-bit build machine, and 127instead create a 32-bit target using `--with-target-bits=32`. 128 129### Building on aarch64 130 131At a minimum, a machine with 8 cores is advisable, as well as 8 GB of RAM. 132(The more cores to use, the more memory you need.) At least 6 GB of free disk 133space is required. 134 135If you do not have access to sufficiently powerful hardware, it is also 136possible to use [cross-compiling](#cross-compiling). 137 138### Building on 32-bit arm 139 140This is not recommended. Instead, see the section on [Cross-compiling]( 141#cross-compiling). 142 143## Operating System Requirements 144 145The mainline JDK project supports Linux, macOS, AIX and Windows. 146Support for other operating system, e.g. BSD, exists in separate "port" 147projects. 148 149In general, the JDK can be built on a wide range of versions of these operating 150systems, but the further you deviate from what is tested on a daily basis, the 151more likely you are to run into problems. 152 153This table lists the OS versions used by Oracle when building the JDK. Such 154information is always subject to change, but this table is up to date at the 155time of writing. 156 157 Operating system Vendor/version used 158 ----------------- ------------------------------------------------------- 159 Linux Oracle Enterprise Linux 6.4 / 7.6 160 macOS Mac OS X 10.13 (High Sierra) 161 Windows Windows Server 2012 R2 162 163The double version numbers for Linux are due to the hybrid model 164used at Oracle, where header files and external libraries from an older version 165are used when building on a more modern version of the OS. 166 167The Build Group has a wiki page with [Supported Build Platforms]( 168https://wiki.openjdk.java.net/display/Build/Supported+Build+Platforms). From 169time to time, this is updated by contributors to list successes or failures of 170building on different platforms. 171 172### Windows 173 174Windows XP is not a supported platform, but all newer Windows should be able to 175build the JDK. 176 177On Windows, it is important that you pay attention to the instructions in the 178[Special Considerations](#special-considerations). 179 180Windows is the only non-POSIX OS supported by the JDK, and as such, requires 181some extra care. A POSIX support layer is required to build on Windows. 182Currently, the only supported such layers are Cygwin and Windows Subsystem for 183Linux (WSL). (Msys is no longer supported due to a too old bash; msys2 would 184likely be possible to support in a future version but that would require effort 185to implement.) 186 187Internally in the build system, all paths are represented as Unix-style paths, 188e.g. `/cygdrive/c/git/jdk/Makefile` rather than `C:\git\jdk\Makefile`. This 189rule also applies to input to the build system, e.g. in arguments to 190`configure`. So, use `--with-msvcr-dll=/cygdrive/c/msvcr100.dll` rather than 191`--with-msvcr-dll=c:\msvcr100.dll`. For details on this conversion, see the section 192on [Fixpath](#fixpath). 193 194#### Cygwin 195 196A functioning [Cygwin](http://www.cygwin.com/) environment is required for 197building the JDK on Windows. If you have a 64-bit OS, we strongly recommend 198using the 64-bit version of Cygwin. 199 200**Note:** Cygwin has a model of continuously updating all packages without any 201easy way to install or revert to a specific version of a package. This means 202that whenever you add or update a package in Cygwin, you might (inadvertently) 203update tools that are used by the JDK build process, and that can cause 204unexpected build problems. 205 206The JDK requires GNU Make 4.0 or greater in Cygwin. This is usually not a 207problem, since Cygwin currently only distributes GNU Make at a version above 2084.0. 209 210Apart from the basic Cygwin installation, the following packages must also be 211installed: 212 213 * `autoconf` 214 * `make` 215 * `zip` 216 * `unzip` 217 218Often, you can install these packages using the following command line: 219``` 220<path to Cygwin setup>/setup-x86_64 -q -P autoconf -P make -P unzip -P zip 221``` 222 223Unfortunately, Cygwin can be unreliable in certain circumstances. If you 224experience build tool crashes or strange issues when building on Windows, 225please check the Cygwin FAQ on the ["BLODA" list]( 226https://cygwin.com/faq/faq.html#faq.using.bloda) and the section on [fork() 227failures](https://cygwin.com/faq/faq.html#faq.using.fixing-fork-failures). 228 229#### Windows Subsystem for Linux (WSL) 230 231Windows 10 1809 or newer is supported due to a dependency on the wslpath utility 232and support for environment variable sharing through WSLENV. Version 1803 can 233work but intermittent build failures have been observed. 234 235It's possible to build both Windows and Linux binaries from WSL. To build 236Windows binaries, you must use a Windows boot JDK (located in a 237Windows-accessible directory). To build Linux binaries, you must use a Linux 238boot JDK. The default behavior is to build for Windows. To build for Linux, pass 239`--build=x86_64-unknown-linux-gnu --host=x86_64-unknown-linux-gnu` to 240`configure`. 241 242If building Windows binaries, the source code must be located in a Windows- 243accessible directory. This is because Windows executables (such as Visual Studio 244and the boot JDK) must be able to access the source code. Also, the drive where 245the source is stored must be mounted as case-insensitive by changing either 246/etc/fstab or /etc/wsl.conf in WSL. Individual directories may be corrected 247using the fsutil tool in case the source was cloned before changing the mount 248options. 249 250Note that while it's possible to build on WSL, testing is still not fully 251supported. 252 253### macOS 254 255Apple is using a quite aggressive scheme of pushing OS updates, and coupling 256these updates with required updates of Xcode. Unfortunately, this makes it 257difficult for a project such as the JDK to keep pace with a continuously updated 258machine running macOS. See the section on [Apple Xcode](#apple-xcode) on some 259strategies to deal with this. 260 261It is recommended that you use at least Mac OS X 10.13 (High Sierra). At the time 262of writing, the JDK has been successfully compiled on macOS 10.12 (Sierra). 263 264The standard macOS environment contains the basic tooling needed to build, but 265for external libraries a package manager is recommended. The JDK uses 266[homebrew](https://brew.sh/) in the examples, but feel free to use whatever 267manager you want (or none). 268 269### Linux 270 271It is often not much problem to build the JDK on Linux. The only general advice 272is to try to use the compilers, external libraries and header files as provided 273by your distribution. 274 275The basic tooling is provided as part of the core operating system, but you 276will most likely need to install developer packages. 277 278For apt-based distributions (Debian, Ubuntu, etc), try this: 279``` 280sudo apt-get install build-essential 281``` 282 283For rpm-based distributions (Fedora, Red Hat, etc), try this: 284``` 285sudo yum groupinstall "Development Tools" 286``` 287 288For Alpine Linux, aside from basic tooling, install the GNU versions of some 289programs: 290 291``` 292sudo apk add build-base bash grep zip 293``` 294 295### AIX 296 297Please consult the AIX section of the [Supported Build Platforms]( 298https://wiki.openjdk.java.net/display/Build/Supported+Build+Platforms) OpenJDK 299Build Wiki page for details about which versions of AIX are supported. 300 301## Native Compiler (Toolchain) Requirements 302 303Large portions of the JDK consists of native code, that needs to be compiled to 304be able to run on the target platform. In theory, toolchain and operating 305system should be independent factors, but in practice there's more or less a 306one-to-one correlation between target operating system and toolchain. 307 308 Operating system Supported toolchain 309 ------------------ ------------------------- 310 Linux gcc, clang 311 macOS Apple Xcode (using clang) 312 AIX IBM XL C/C++ 313 Windows Microsoft Visual Studio 314 315Please see the individual sections on the toolchains for version 316recommendations. As a reference, these versions of the toolchains are used, at 317the time of writing, by Oracle for the daily builds of the JDK. It should be 318possible to compile the JDK with both older and newer versions, but the closer 319you stay to this list, the more likely you are to compile successfully without 320issues. 321 322 Operating system Toolchain version 323 ------------------ ------------------------------------------------------- 324 Linux gcc 10.2.0 325 macOS Apple Xcode 10.1 (using clang 10.0.0) 326 Windows Microsoft Visual Studio 2019 update 16.7.2 327 328All compilers are expected to be able to compile to the C99 language standard, 329as some C99 features are used in the source code. Microsoft Visual Studio 330doesn't fully support C99 so in practice shared code is limited to using C99 331features that it does support. 332 333### gcc 334 335The minimum accepted version of gcc is 5.0. Older versions will generate a warning 336by `configure` and are unlikely to work. 337 338The JDK is currently known to be able to compile with at least version 10.2 of 339gcc. 340 341In general, any version between these two should be usable. 342 343### clang 344 345The minimum accepted version of clang is 3.5. Older versions will not be 346accepted by `configure`. 347 348To use clang instead of gcc on Linux, use `--with-toolchain-type=clang`. 349 350### Apple Xcode 351 352The oldest supported version of Xcode is 8. 353 354You will need the Xcode command lines developers tools to be able to build 355the JDK. (Actually, *only* the command lines tools are needed, not the IDE.) 356The simplest way to install these is to run: 357``` 358xcode-select --install 359``` 360 361It is advisable to keep an older version of Xcode for building the JDK when 362updating Xcode. This [blog page]( 363http://iosdevelopertips.com/xcode/install-multiple-versions-of-xcode.html) has 364good suggestions on managing multiple Xcode versions. To use a specific version 365of Xcode, use `xcode-select -s` before running `configure`, or use 366`--with-toolchain-path` to point to the version of Xcode to use, e.g. 367`configure --with-toolchain-path=/Applications/Xcode8.app/Contents/Developer/usr/bin` 368 369If you have recently (inadvertently) updated your OS and/or Xcode version, and 370the JDK can no longer be built, please see the section on [Problems with the 371Build Environment](#problems-with-the-build-environment), and [Getting 372Help](#getting-help) to find out if there are any recent, non-merged patches 373available for this update. 374 375### Microsoft Visual Studio 376 377The minimum accepted version of Visual Studio is 2017. Older versions will not 378be accepted by `configure` and will not work. The maximum accepted 379version of Visual Studio is 2019. 380 381If you have multiple versions of Visual Studio installed, `configure` will by 382default pick the latest. You can request a specific version to be used by 383setting `--with-toolchain-version`, e.g. `--with-toolchain-version=2017`. 384 385### IBM XL C/C++ 386 387Please consult the AIX section of the [Supported Build Platforms]( 388https://wiki.openjdk.java.net/display/Build/Supported+Build+Platforms) OpenJDK 389Build Wiki page for details about which versions of XLC are supported. 390 391 392## Boot JDK Requirements 393 394Paradoxically, building the JDK requires a pre-existing JDK. This is called the 395"boot JDK". The boot JDK does not, however, have to be a JDK built directly from 396the source code available in the OpenJDK Community. If you are porting the JDK 397to a new platform, chances are that there already exists another JDK for that 398platform that is usable as boot JDK. 399 400The rule of thumb is that the boot JDK for building JDK major version *N* 401should be a JDK of major version *N-1*, so for building JDK 9 a JDK 8 would be 402suitable as boot JDK. However, the JDK should be able to "build itself", so an 403up-to-date build of the current JDK source is an acceptable alternative. If 404you are following the *N-1* rule, make sure you've got the latest update 405version, since JDK 8 GA might not be able to build JDK 9 on all platforms. 406 407Early in the release cycle, version *N-1* may not yet have been released. In 408that case, the preferred boot JDK will be version *N-2* until version *N-1* 409is available. 410 411If the boot JDK is not automatically detected, or the wrong JDK is picked, use 412`--with-boot-jdk` to point to the JDK to use. 413 414### Getting JDK binaries 415 416JDK binaries for Linux, Windows and macOS can be downloaded from 417[jdk.java.net](http://jdk.java.net). An alternative is to download the 418[Oracle JDK](http://www.oracle.com/technetwork/java/javase/downloads). Another 419is the [Adopt OpenJDK Project](https://adoptopenjdk.net/), which publishes 420experimental prebuilt binaries for various platforms. 421 422On Linux you can also get a JDK from the Linux distribution. On apt-based 423distros (like Debian and Ubuntu), `sudo apt-get install openjdk-<VERSION>-jdk` 424is typically enough to install a JDK \<VERSION\>. On rpm-based distros (like 425Fedora and Red Hat), try `sudo yum install java-<VERSION>-openjdk-devel`. 426 427## External Library Requirements 428 429Different platforms require different external libraries. In general, libraries 430are not optional - that is, they are either required or not used. 431 432If a required library is not detected by `configure`, you need to provide the 433path to it. There are two forms of the `configure` arguments to point to an 434external library: `--with-<LIB>=<path>` or `--with-<LIB>-include=<path to 435include> --with-<LIB>-lib=<path to lib>`. The first variant is more concise, 436but require the include files and library files to reside in a default 437hierarchy under this directory. In most cases, it works fine. 438 439As a fallback, the second version allows you to point to the include directory 440and the lib directory separately. 441 442### FreeType 443 444FreeType2 from [The FreeType Project](http://www.freetype.org/) is not required 445on any platform. The exception is on Unix-based platforms when configuring such 446that the build artifacts will reference a system installed library, 447rather than bundling the JDK's own copy. 448 449 * To install on an apt-based Linux, try running `sudo apt-get install 450 libfreetype6-dev`. 451 * To install on an rpm-based Linux, try running `sudo yum install 452 freetype-devel`. 453 * To install on Alpine Linux, try running `sudo apk add freetype-dev`. 454 * To install on macOS, try running `brew install freetype`. 455 456Use `--with-freetype-include=<path>` and `--with-freetype-lib=<path>` 457if `configure` does not automatically locate the platform FreeType files. 458 459### CUPS 460 461CUPS, [Common UNIX Printing System](http://www.cups.org) header files are 462required on all platforms, except Windows. Often these files are provided by 463your operating system. 464 465 * To install on an apt-based Linux, try running `sudo apt-get install 466 libcups2-dev`. 467 * To install on an rpm-based Linux, try running `sudo yum install 468 cups-devel`. 469 * To install on Alpine Linux, try running `sudo apk add cups-dev`. 470 471Use `--with-cups=<path>` if `configure` does not properly locate your CUPS 472files. 473 474### X11 475 476Certain [X11](http://www.x.org/) libraries and include files are required on 477Linux. 478 479 * To install on an apt-based Linux, try running `sudo apt-get install 480 libx11-dev libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev`. 481 * To install on an rpm-based Linux, try running `sudo yum install 482 libXtst-devel libXt-devel libXrender-devel libXrandr-devel libXi-devel`. 483 * To install on Alpine Linux, try running `sudo apk add libx11-dev 484 libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev`. 485 486Use `--with-x=<path>` if `configure` does not properly locate your X11 files. 487 488### ALSA 489 490ALSA, [Advanced Linux Sound Architecture](https://www.alsa-project.org/) is 491required on Linux. At least version 0.9.1 of ALSA is required. 492 493 * To install on an apt-based Linux, try running `sudo apt-get install 494 libasound2-dev`. 495 * To install on an rpm-based Linux, try running `sudo yum install 496 alsa-lib-devel`. 497 * To install on Alpine Linux, try running `sudo apk add alsa-lib-dev`. 498 499Use `--with-alsa=<path>` if `configure` does not properly locate your ALSA 500files. 501 502### libffi 503 504libffi, the [Portable Foreign Function Interface Library]( 505http://sourceware.org/libffi) is required when building the Zero version of 506Hotspot. 507 508 * To install on an apt-based Linux, try running `sudo apt-get install 509 libffi-dev`. 510 * To install on an rpm-based Linux, try running `sudo yum install 511 libffi-devel`. 512 * To install on Alpine Linux, try running `sudo apk add libffi-dev`. 513 514Use `--with-libffi=<path>` if `configure` does not properly locate your libffi 515files. 516 517## Build Tools Requirements 518 519### Autoconf 520 521The JDK requires [Autoconf](http://www.gnu.org/software/autoconf) on all 522platforms. At least version 2.69 is required. 523 524 * To install on an apt-based Linux, try running `sudo apt-get install 525 autoconf`. 526 * To install on an rpm-based Linux, try running `sudo yum install 527 autoconf`. 528 * To install on Alpine Linux, try running `sudo apk add autoconf`. 529 * To install on macOS, try running `brew install autoconf`. 530 * To install on Windows, try running `<path to Cygwin setup>/setup-x86_64 -q 531 -P autoconf`. 532 533If `configure` has problems locating your installation of autoconf, you can 534specify it using the `AUTOCONF` environment variable, like this: 535 536``` 537AUTOCONF=<path to autoconf> configure ... 538``` 539 540### GNU Make 541 542The JDK requires [GNU Make](http://www.gnu.org/software/make). No other flavors 543of make are supported. 544 545At least version 3.81 of GNU Make must be used. For distributions supporting 546GNU Make 4.0 or above, we strongly recommend it. GNU Make 4.0 contains useful 547functionality to handle parallel building (supported by `--with-output-sync`) 548and speed and stability improvements. 549 550Note that `configure` locates and verifies a properly functioning version of 551`make` and stores the path to this `make` binary in the configuration. If you 552start a build using `make` on the command line, you will be using the version 553of make found first in your `PATH`, and not necessarily the one stored in the 554configuration. This initial make will be used as "bootstrap make", and in a 555second stage, the make located by `configure` will be called. Normally, this 556will present no issues, but if you have a very old `make`, or a non-GNU Make 557`make` in your path, this might cause issues. 558 559If you want to override the default make found by `configure`, use the `MAKE` 560configure variable, e.g. `configure MAKE=/opt/gnu/make`. 561 562### GNU Bash 563 564The JDK requires [GNU Bash](http://www.gnu.org/software/bash). No other shells 565are supported. 566 567At least version 3.2 of GNU Bash must be used. 568 569## Running Configure 570 571To build the JDK, you need a "configuration", which consists of a directory 572where to store the build output, coupled with information about the platform, 573the specific build machine, and choices that affect how the JDK is built. 574 575The configuration is created by the `configure` script. The basic invocation of 576the `configure` script looks like this: 577 578``` 579bash configure [options] 580``` 581 582This will create an output directory containing the configuration and setup an 583area for the build result. This directory typically looks like 584`build/linux-x64-server-release`, but the actual name depends on your specific 585configuration. (It can also be set directly, see [Using Multiple 586Configurations](#using-multiple-configurations)). This directory is referred to 587as `$BUILD` in this documentation. 588 589`configure` will try to figure out what system you are running on and where all 590necessary build components are. If you have all prerequisites for building 591installed, it should find everything. If it fails to detect any component 592automatically, it will exit and inform you about the problem. 593 594Some command line examples: 595 596 * Create a 32-bit build for Windows with FreeType2 in `C:\freetype-i586`: 597 ``` 598 bash configure --with-freetype=/cygdrive/c/freetype-i586 --with-target-bits=32 599 ``` 600 601 * Create a debug build with the `server` JVM and DTrace enabled: 602 ``` 603 bash configure --enable-debug --with-jvm-variants=server --enable-dtrace 604 ``` 605 606### Common Configure Arguments 607 608Here follows some of the most common and important `configure` argument. 609 610To get up-to-date information on *all* available `configure` argument, please 611run: 612``` 613bash configure --help 614``` 615 616(Note that this help text also include general autoconf options, like 617`--dvidir`, that is not relevant to the JDK. To list only JDK-specific 618features, use `bash configure --help=short` instead.) 619 620#### Configure Arguments for Tailoring the Build 621 622 * `--enable-debug` - Set the debug level to `fastdebug` (this is a shorthand 623 for `--with-debug-level=fastdebug`) 624 * `--with-debug-level=<level>` - Set the debug level, which can be `release`, 625 `fastdebug`, `slowdebug` or `optimized`. Default is `release`. `optimized` 626 is variant of `release` with additional Hotspot debug code. 627 * `--with-native-debug-symbols=<method>` - Specify if and how native debug 628 symbols should be built. Available methods are `none`, `internal`, 629 `external`, `zipped`. Default behavior depends on platform. See [Native 630 Debug Symbols](#native-debug-symbols) for more details. 631 * `--with-version-string=<string>` - Specify the version string this build 632 will be identified with. 633 * `--with-version-<part>=<value>` - A group of options, where `<part>` can be 634 any of `pre`, `opt`, `build`, `major`, `minor`, `security` or `patch`. Use 635 these options to modify just the corresponding part of the version string 636 from the default, or the value provided by `--with-version-string`. 637 * `--with-jvm-variants=<variant>[,<variant>...]` - Build the specified variant 638 (or variants) of Hotspot. Valid variants are: `server`, `client`, 639 `minimal`, `core`, `zero`, `custom`. Note that not all 640 variants are possible to combine in a single build. 641 * `--enable-jvm-feature-<feature>` or `--disable-jvm-feature-<feature>` - 642 Include (or exclude) `<feature>` as a JVM feature in Hotspot. You can also 643 specify a list of features to be enabled, separated by space or comma, as 644 `--with-jvm-features=<feature>[,<feature>...]`. If you prefix `<feature>` 645 with a `-`, it will be disabled. These options will modify the default list 646 of features for the JVM variant(s) you are building. For the `custom` JVM 647 variant, the default list is empty. A complete list of valid JVM features 648 can be found using `bash configure --help`. 649 * `--with-target-bits=<bits>` - Create a target binary suitable for running 650 on a `<bits>` platform. Use this to create 32-bit output on a 64-bit build 651 platform, instead of doing a full cross-compile. (This is known as a 652 *reduced* build.) 653 654On Linux, BSD and AIX, it is possible to override where Java by default 655searches for runtime/JNI libraries. This can be useful in situations where 656there is a special shared directory for system JNI libraries. This setting 657can in turn be overridden at runtime by setting the `java.library.path` property. 658 659 * `--with-jni-libpath=<path>` - Use the specified path as a default 660 when searching for runtime libraries. 661 662#### Configure Arguments for Native Compilation 663 664 * `--with-devkit=<path>` - Use this devkit for compilers, tools and resources 665 * `--with-sysroot=<path>` - Use this directory as sysroot 666 * `--with-extra-path=<path>[;<path>]` - Prepend these directories to the 667 default path when searching for all kinds of binaries 668 * `--with-toolchain-path=<path>[;<path>]` - Prepend these directories when 669 searching for toolchain binaries (compilers etc) 670 * `--with-extra-cflags=<flags>` - Append these flags when compiling JDK C 671 files 672 * `--with-extra-cxxflags=<flags>` - Append these flags when compiling JDK C++ 673 files 674 * `--with-extra-ldflags=<flags>` - Append these flags when linking JDK 675 libraries 676 677#### Configure Arguments for External Dependencies 678 679 * `--with-boot-jdk=<path>` - Set the path to the [Boot JDK]( 680 #boot-jdk-requirements) 681 * `--with-freetype=<path>` - Set the path to [FreeType](#freetype) 682 * `--with-cups=<path>` - Set the path to [CUPS](#cups) 683 * `--with-x=<path>` - Set the path to [X11](#x11) 684 * `--with-alsa=<path>` - Set the path to [ALSA](#alsa) 685 * `--with-libffi=<path>` - Set the path to [libffi](#libffi) 686 * `--with-jtreg=<path>` - Set the path to JTReg. See [Running Tests]( 687 #running-tests) 688 689Certain third-party libraries used by the JDK (libjpeg, giflib, libpng, lcms 690and zlib) are included in the JDK repository. The default behavior of the 691JDK build is to use the included ("bundled") versions of libjpeg, giflib, 692libpng and lcms. 693For zlib, the system lib (if present) is used except on Windows and AIX. 694However the bundled libraries may be replaced by an external version. 695To do so, specify `system` as the `<source>` option in these arguments. 696(The default is `bundled`). 697 698 * `--with-libjpeg=<source>` - Use the specified source for libjpeg 699 * `--with-giflib=<source>` - Use the specified source for giflib 700 * `--with-libpng=<source>` - Use the specified source for libpng 701 * `--with-lcms=<source>` - Use the specified source for lcms 702 * `--with-zlib=<source>` - Use the specified source for zlib 703 704On Linux, it is possible to select either static or dynamic linking of the C++ 705runtime. The default is static linking, with dynamic linking as fallback if the 706static library is not found. 707 708 * `--with-stdc++lib=<method>` - Use the specified method (`static`, `dynamic` 709 or `default`) for linking the C++ runtime. 710 711### Configure Control Variables 712 713It is possible to control certain aspects of `configure` by overriding the 714value of `configure` variables, either on the command line or in the 715environment. 716 717Normally, this is **not recommended**. If used improperly, it can lead to a 718broken configuration. Unless you're well versed in the build system, this is 719hard to use properly. Therefore, `configure` will print a warning if this is 720detected. 721 722However, there are a few `configure` variables, known as *control variables* 723that are supposed to be overridden on the command line. These are variables that 724describe the location of tools needed by the build, like `MAKE` or `GREP`. If 725any such variable is specified, `configure` will use that value instead of 726trying to autodetect the tool. For instance, `bash configure 727MAKE=/opt/gnumake4.0/bin/make`. 728 729If a configure argument exists, use that instead, e.g. use `--with-jtreg` 730instead of setting `JTREGEXE`. 731 732Also note that, despite what autoconf claims, setting `CFLAGS` will not 733accomplish anything. Instead use `--with-extra-cflags` (and similar for 734`cxxflags` and `ldflags`). 735 736## Running Make 737 738When you have a proper configuration, all you need to do to build the JDK is to 739run `make`. (But see the warning at [GNU Make](#gnu-make) about running the 740correct version of make.) 741 742When running `make` without any arguments, the default target is used, which is 743the same as running `make default` or `make jdk`. This will build a minimal (or 744roughly minimal) set of compiled output (known as an "exploded image") needed 745for a developer to actually execute the newly built JDK. The idea is that in an 746incremental development fashion, when doing a normal make, you should only 747spend time recompiling what's changed (making it purely incremental) and only 748do the work that's needed to actually run and test your code. 749 750The output of the exploded image resides in `$BUILD/jdk`. You can test the 751newly built JDK like this: `$BUILD/jdk/bin/java -version`. 752 753### Common Make Targets 754 755Apart from the default target, here are some common make targets: 756 757 * `hotspot` - Build all of hotspot (but only hotspot) 758 * `hotspot-<variant>` - Build just the specified jvm variant 759 * `images` or `product-images` - Build the JDK image 760 * `docs` or `docs-image` - Build the documentation image 761 * `test-image` - Build the test image 762 * `all` or `all-images` - Build all images (product, docs and test) 763 * `bootcycle-images` - Build images twice, second time with newly built JDK 764 (good for testing) 765 * `clean` - Remove all files generated by make, but not those generated by 766 configure 767 * `dist-clean` - Remove all files, including configuration 768 769Run `make help` to get an up-to-date list of important make targets and make 770control variables. 771 772It is possible to build just a single module, a single phase, or a single phase 773of a single module, by creating make targets according to these followin 774patterns. A phase can be either of `gensrc`, `gendata`, `copy`, `java`, 775`launchers`, or `libs`. See [Using Fine-Grained Make Targets]( 776#using-fine-grained-make-targets) for more details about this functionality. 777 778 * `<phase>` - Build the specified phase and everything it depends on 779 * `<module>` - Build the specified module and everything it depends on 780 * `<module>-<phase>` - Compile the specified phase for the specified module 781 and everything it depends on 782 783Similarly, it is possible to clean just a part of the build by creating make 784targets according to these patterns: 785 786 * `clean-<outputdir>` - Remove the subdir in the output dir with the name 787 * `clean-<phase>` - Remove all build results related to a certain build 788 phase 789 * `clean-<module>` - Remove all build results related to a certain module 790 * `clean-<module>-<phase>` - Remove all build results related to a certain 791 module and phase 792 793### Make Control Variables 794 795It is possible to control `make` behavior by overriding the value of `make` 796variables, either on the command line or in the environment. 797 798Normally, this is **not recommended**. If used improperly, it can lead to a 799broken build. Unless you're well versed in the build system, this is hard to 800use properly. Therefore, `make` will print a warning if this is detected. 801 802However, there are a few `make` variables, known as *control variables* that 803are supposed to be overridden on the command line. These make up the "make time" 804configuration, as opposed to the "configure time" configuration. 805 806#### General Make Control Variables 807 808 * `JOBS` - Specify the number of jobs to build with. See [Build 809 Performance](#build-performance). 810 * `LOG` - Specify the logging level and functionality. See [Checking the 811 Build Log File](#checking-the-build-log-file) 812 * `CONF` and `CONF_NAME` - Selecting the configuration(s) to use. See [Using 813 Multiple Configurations](#using-multiple-configurations) 814 815#### Test Make Control Variables 816 817These make control variables only make sense when running tests. Please see 818[Testing the JDK](testing.html) for details. 819 820 * `TEST` 821 * `TEST_JOBS` 822 * `JTREG` 823 * `GTEST` 824 825#### Advanced Make Control Variables 826 827These advanced make control variables can be potentially unsafe. See [Hints and 828Suggestions for Advanced Users](#hints-and-suggestions-for-advanced-users) and 829[Understanding the Build System](#understanding-the-build-system) for details. 830 831 * `SPEC` 832 * `CONF_CHECK` 833 * `COMPARE_BUILD` 834 * `JDK_FILTER` 835 * `SPEC_FILTER` 836 837## Running Tests 838 839Most of the JDK tests are using the [JTReg](http://openjdk.java.net/jtreg) 840test framework. Make sure that your configuration knows where to find your 841installation of JTReg. If this is not picked up automatically, use the 842`--with-jtreg=<path to jtreg home>` option to point to the JTReg framework. 843Note that this option should point to the JTReg home, i.e. the top directory, 844containing `lib/jtreg.jar` etc. 845 846The [Adoption Group](https://wiki.openjdk.java.net/display/Adoption) provides 847recent builds of jtreg [here]( 848https://ci.adoptopenjdk.net/view/Dependencies/job/jtreg/lastSuccessfulBuild/artifact). 849Download the latest `.tar.gz` file, unpack it, and point `--with-jtreg` to the 850`jtreg` directory that you just unpacked. 851 852Building of Hotspot Gtest suite requires the source code of Google Test framework. 853The top directory, which contains both `googletest` and `googlemock` 854directories, should be specified via `--with-gtest`. 855The supported version of Google Test is 1.8.1, whose source code can be obtained: 856 857 * by downloading and unpacking the source bundle from [here](https://github.com/google/googletest/releases/tag/release-1.8.1) 858 * or by checking out `release-1.8.1` tag of `googletest` project: `git clone -b release-1.8.1 https://github.com/google/googletest` 859 860To execute the most basic tests (tier 1), use: 861``` 862make run-test-tier1 863``` 864 865For more details on how to run tests, please see the [Testing 866the JDK](testing.html) document. 867 868## Cross-compiling 869 870Cross-compiling means using one platform (the *build* platform) to generate 871output that can ran on another platform (the *target* platform). 872 873The typical reason for cross-compiling is that the build is performed on a more 874powerful desktop computer, but the resulting binaries will be able to run on a 875different, typically low-performing system. Most of the complications that 876arise when building for embedded is due to this separation of *build* and 877*target* systems. 878 879This requires a more complex setup and build procedure. This section assumes 880you are familiar with cross-compiling in general, and will only deal with the 881particularities of cross-compiling the JDK. If you are new to cross-compiling, 882please see the [external links at Wikipedia]( 883https://en.wikipedia.org/wiki/Cross_compiler#External_links) for a good start 884on reading materials. 885 886Cross-compiling the JDK requires you to be able to build both for the build 887platform and for the target platform. The reason for the former is that we need 888to build and execute tools during the build process, both native tools and Java 889tools. 890 891If all you want to do is to compile a 32-bit version, for the same OS, on a 89264-bit machine, consider using `--with-target-bits=32` instead of doing a 893full-blown cross-compilation. (While this surely is possible, it's a lot more 894work and will take much longer to build.) 895 896### Cross compiling the easy way with OpenJDK devkits 897 898The OpenJDK build system provides out-of-the box support for creating and using 899so called devkits. A `devkit` is basically a collection of a cross-compiling 900toolchain and a sysroot environment which can easily be used together with the 901`--with-devkit` configure option to cross compile the OpenJDK. On Linux/x86_64, 902the following command: 903``` 904bash configure --with-devkit=<devkit-path> --openjdk-target=ppc64-linux-gnu && make 905``` 906 907will configure and build OpenJDK for Linux/ppc64 assuming that `<devkit-path>` 908points to a Linux/x86_64 to Linux/ppc64 devkit. 909 910Devkits can be created from the `make/devkit` directory by executing: 911``` 912make [ TARGETS="<TARGET_TRIPLET>+" ] [ BASE_OS=<OS> ] [ BASE_OS_VERSION=<VER> ] 913``` 914 915where `TARGETS` contains one or more `TARGET_TRIPLET`s of the form 916described in [section 3.4 of the GNU Autobook]( 917https://sourceware.org/autobook/autobook/autobook_17.html). If no 918targets are given, a native toolchain for the current platform will be 919created. Currently, at least the following targets are known to work: 920 921 Supported devkit targets 922 ------------------------- 923 x86_64-linux-gnu 924 aarch64-linux-gnu 925 arm-linux-gnueabihf 926 ppc64-linux-gnu 927 ppc64le-linux-gnu 928 s390x-linux-gnu 929 930`BASE_OS` must be one of "OEL6" for Oracle Enterprise Linux 6 or 931"Fedora" (if not specified "OEL6" will be the default). If the base OS 932is "Fedora" the corresponding Fedora release can be specified with the 933help of the `BASE_OS_VERSION` option (with "27" as default version). 934If the build is successful, the new devkits can be found in the 935`build/devkit/result` subdirectory: 936``` 937cd make/devkit 938make TARGETS="ppc64le-linux-gnu aarch64-linux-gnu" BASE_OS=Fedora BASE_OS_VERSION=21 939ls -1 ../../build/devkit/result/ 940x86_64-linux-gnu-to-aarch64-linux-gnu 941x86_64-linux-gnu-to-ppc64le-linux-gnu 942``` 943 944Notice that devkits are not only useful for targeting different build 945platforms. Because they contain the full build dependencies for a 946system (i.e. compiler and root file system), they can easily be used 947to build well-known, reliable and reproducible build environments. You 948can for example create and use a devkit with GCC 7.3 and a Fedora 12 949sysroot environment (with glibc 2.11) on Ubuntu 14.04 (which doesn't 950have GCC 7.3 by default) to produce OpenJDK binaries which will run on 951all Linux systems with runtime libraries newer than the ones from 952Fedora 12 (e.g. Ubuntu 16.04, SLES 11 or RHEL 6). 953 954### Boot JDK and Build JDK 955 956When cross-compiling, make sure you use a boot JDK that runs on the *build* 957system, and not on the *target* system. 958 959To be able to build, we need a "Build JDK", which is a JDK built from the 960current sources (that is, the same as the end result of the entire build 961process), but able to run on the *build* system, and not the *target* system. 962(In contrast, the Boot JDK should be from an older release, e.g. JDK 8 when 963building JDK 9.) 964 965The build process will create a minimal Build JDK for you, as part of building. 966To speed up the build, you can use `--with-build-jdk` to `configure` to point 967to a pre-built Build JDK. Please note that the build result is unpredictable, 968and can possibly break in subtle ways, if the Build JDK does not **exactly** 969match the current sources. 970 971### Specifying the Target Platform 972 973You *must* specify the target platform when cross-compiling. Doing so will also 974automatically turn the build into a cross-compiling mode. The simplest way to 975do this is to use the `--openjdk-target` argument, e.g. 976`--openjdk-target=arm-linux-gnueabihf`. or `--openjdk-target=aarch64-oe-linux`. 977This will automatically set the `--build`, `--host` and `--target` options for 978autoconf, which can otherwise be confusing. (In autoconf terminology, the 979"target" is known as "host", and "target" is used for building a Canadian 980cross-compiler.) 981 982### Toolchain Considerations 983 984You will need two copies of your toolchain, one which generates output that can 985run on the target system (the normal, or *target*, toolchain), and one that 986generates output that can run on the build system (the *build* toolchain). Note 987that cross-compiling is only supported for gcc at the time being. The gcc 988standard is to prefix cross-compiling toolchains with the target denominator. 989If you follow this standard, `configure` is likely to pick up the toolchain 990correctly. 991 992The *build* toolchain will be autodetected just the same way the normal 993*build*/*target* toolchain will be autodetected when not cross-compiling. If 994this is not what you want, or if the autodetection fails, you can specify a 995devkit containing the *build* toolchain using `--with-build-devkit` to 996`configure`, or by giving `BUILD_CC` and `BUILD_CXX` arguments. 997 998It is often helpful to locate the cross-compilation tools, headers and 999libraries in a separate directory, outside the normal path, and point out that 1000directory to `configure`. Do this by setting the sysroot (`--with-sysroot`) and 1001appending the directory when searching for cross-compilations tools 1002(`--with-toolchain-path`). As a compact form, you can also use `--with-devkit` 1003to point to a single directory, if it is correctly setup. (See `basics.m4` for 1004details.) 1005 1006### Native Libraries 1007 1008You will need copies of external native libraries for the *target* system, 1009present on the *build* machine while building. 1010 1011Take care not to replace the *build* system's version of these libraries by 1012mistake, since that can render the *build* machine unusable. 1013 1014Make sure that the libraries you point to (ALSA, X11, etc) are for the 1015*target*, not the *build*, platform. 1016 1017#### ALSA 1018 1019You will need alsa libraries suitable for your *target* system. For most cases, 1020using Debian's pre-built libraries work fine. 1021 1022Note that alsa is needed even if you only want to build a headless JDK. 1023 1024 * Go to [Debian Package Search](https://www.debian.org/distrib/packages) and 1025 search for the `libasound2` and `libasound2-dev` packages for your *target* 1026 system. Download them to /tmp. 1027 1028 * Install the libraries into the cross-compilation toolchain. For instance: 1029``` 1030cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc 1031dpkg-deb -x /tmp/libasound2_1.0.25-4_armhf.deb . 1032dpkg-deb -x /tmp/libasound2-dev_1.0.25-4_armhf.deb . 1033``` 1034 1035 * If alsa is not properly detected by `configure`, you can point it out by 1036 `--with-alsa`. 1037 1038#### X11 1039 1040You will need X11 libraries suitable for your *target* system. For most cases, 1041using Debian's pre-built libraries work fine. 1042 1043Note that X11 is needed even if you only want to build a headless JDK. 1044 1045 * Go to [Debian Package Search](https://www.debian.org/distrib/packages), 1046 search for the following packages for your *target* system, and download them 1047 to /tmp/target-x11: 1048 * libxi 1049 * libxi-dev 1050 * x11proto-core-dev 1051 * x11proto-input-dev 1052 * x11proto-kb-dev 1053 * x11proto-render-dev 1054 * x11proto-xext-dev 1055 * libice-dev 1056 * libxrender 1057 * libxrender-dev 1058 * libxrandr-dev 1059 * libsm-dev 1060 * libxt-dev 1061 * libx11 1062 * libx11-dev 1063 * libxtst 1064 * libxtst-dev 1065 * libxext 1066 * libxext-dev 1067 1068 * Install the libraries into the cross-compilation toolchain. For instance: 1069 ``` 1070 cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc/usr 1071 mkdir X11R6 1072 cd X11R6 1073 for deb in /tmp/target-x11/*.deb ; do dpkg-deb -x $deb . ; done 1074 mv usr/* . 1075 cd lib 1076 cp arm-linux-gnueabihf/* . 1077 ``` 1078 1079 You can ignore the following messages. These libraries are not needed to 1080 successfully complete a full JDK build. 1081 ``` 1082 cp: cannot stat `arm-linux-gnueabihf/libICE.so': No such file or directory 1083 cp: cannot stat `arm-linux-gnueabihf/libSM.so': No such file or directory 1084 cp: cannot stat `arm-linux-gnueabihf/libXt.so': No such file or directory 1085 ``` 1086 1087 * If the X11 libraries are not properly detected by `configure`, you can 1088 point them out by `--with-x`. 1089 1090### Creating And Using Sysroots With qemu-deboostrap 1091 1092Fortunately, you can create sysroots for foreign architectures with tools 1093provided by your OS. On Debian/Ubuntu systems, one could use `qemu-deboostrap` to 1094create the *target* system chroot, which would have the native libraries and headers 1095specific to that *target* system. After that, we can use the cross-compiler on the *build* 1096system, pointing into chroot to get the build dependencies right. This allows building 1097for foreign architectures with native compilation speed. 1098 1099For example, cross-compiling to AArch64 from x86_64 could be done like this: 1100 1101 * Install cross-compiler on the *build* system: 1102 ``` 1103 apt install g++-aarch64-linux-gnu gcc-aarch64-linux-gnu 1104 ``` 1105 1106 * Create chroot on the *build* system, configuring it for *target* system: 1107 ``` 1108 sudo qemu-debootstrap \ 1109 --arch=arm64 \ 1110 --verbose \ 1111 --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 \ 1112 --resolve-deps \ 1113 buster \ 1114 ~/sysroot-arm64 \ 1115 http://httpredir.debian.org/debian/ 1116 ``` 1117 1118 * Make sure the symlinks inside the newly created chroot point to proper locations: 1119 ``` 1120 sudo chroot ~/sysroot-arm64 symlinks -cr . 1121 ``` 1122 1123 * Configure and build with newly created chroot as sysroot/toolchain-path: 1124 ``` 1125 CC=aarch64-linux-gnu-gcc CXX=aarch64-linux-gnu-g++ sh ./configure \ 1126 --openjdk-target=aarch64-linux-gnu \ 1127 --with-sysroot=~/sysroot-arm64 \ 1128 --with-toolchain-path=~/sysroot-arm64 \ 1129 --with-freetype-lib=~/sysroot-arm64/usr/lib/aarch64-linux-gnu/ \ 1130 --with-freetype-include=~/sysroot-arm64/usr/include/freetype2/ \ 1131 --x-libraries=~/sysroot-arm64/usr/lib/aarch64-linux-gnu/ 1132 make images 1133 ls build/linux-aarch64-server-release/ 1134 ``` 1135 1136The build does not create new files in that chroot, so it can be reused for multiple builds 1137without additional cleanup. 1138 1139Architectures that are known to successfully cross-compile like this are: 1140 1141 Target `CC` `CXX` `--arch=...` `--openjdk-target=...` 1142 ------------ ------------------------- --------------------------- ------------- ----------------------- 1143 x86 default default i386 i386-linux-gnu 1144 armhf gcc-arm-linux-gnueabihf g++-arm-linux-gnueabihf armhf arm-linux-gnueabihf 1145 aarch64 gcc-aarch64-linux-gnu g++-aarch64-linux-gnu arm64 aarch64-linux-gnu 1146 ppc64el gcc-powerpc64le-linux-gnu g++-powerpc64le-linux-gnu ppc64el powerpc64le-linux-gnu 1147 s390x gcc-s390x-linux-gnu g++-s390x-linux-gnu s390x s390x-linux-gnu 1148 1149Additional architectures might be supported by Debian/Ubuntu Ports. 1150 1151### Building for ARM/aarch64 1152 1153A common cross-compilation target is the ARM CPU. When building for ARM, it is 1154useful to set the ABI profile. A number of pre-defined ABI profiles are 1155available using `--with-abi-profile`: arm-vfp-sflt, arm-vfp-hflt, arm-sflt, 1156armv5-vfp-sflt, armv6-vfp-hflt. Note that soft-float ABIs are no longer 1157properly supported by the JDK. 1158 1159### Building for musl 1160 1161Just like it's possible to cross-compile for a different CPU, it's possible to 1162cross-compile for musl libc on a glibc-based *build* system. 1163A devkit suitable for most target CPU architectures can be obtained from 1164[musl.cc](https://musl.cc). After installing the required packages in the 1165sysroot, configure the build with `--openjdk-target`: 1166 1167``` 1168sh ./configure --with-jvm-variants=server \ 1169--with-boot-jdk=$BOOT_JDK \ 1170--with-build-jdk=$BUILD_JDK \ 1171--openjdk-target=x86_64-unknown-linux-musl \ 1172--with-devkit=$DEVKIT \ 1173--with-sysroot=$SYSROOT 1174``` 1175 1176and run `make` normally. 1177 1178### Verifying the Build 1179 1180The build will end up in a directory named like 1181`build/linux-arm-normal-server-release`. 1182 1183Inside this build output directory, the `images/jdk` will contain the newly 1184built JDK, for your *target* system. 1185 1186Copy these folders to your *target* system. Then you can run e.g. 1187`images/jdk/bin/java -version`. 1188 1189## Build Performance 1190 1191Building the JDK requires a lot of horsepower. Some of the build tools can be 1192adjusted to utilize more or less of resources such as parallel threads and 1193memory. The `configure` script analyzes your system and selects reasonable 1194values for such options based on your hardware. If you encounter resource 1195problems, such as out of memory conditions, you can modify the detected values 1196with: 1197 1198 * `--with-num-cores` -- number of cores in the build system, e.g. 1199 `--with-num-cores=8`. 1200 1201 * `--with-memory-size` -- memory (in MB) available in the build system, e.g. 1202 `--with-memory-size=1024` 1203 1204You can also specify directly the number of build jobs to use with 1205`--with-jobs=N` to `configure`, or `JOBS=N` to `make`. Do not use the `-j` flag 1206to `make`. In most cases it will be ignored by the makefiles, but it can cause 1207problems for some make targets. 1208 1209It might also be necessary to specify the JVM arguments passed to the Boot JDK, 1210using e.g. `--with-boot-jdk-jvmargs="-Xmx8G"`. Doing so will override the 1211default JVM arguments passed to the Boot JDK. 1212 1213At the end of a successful execution of `configure`, you will get a performance 1214summary, indicating how well the build will perform. Here you will also get 1215performance hints. If you want to build fast, pay attention to those! 1216 1217If you want to tweak build performance, run with `make LOG=info` to get a build 1218time summary at the end of the build process. 1219 1220### Disk Speed 1221 1222If you are using network shares, e.g. via NFS, for your source code, make sure 1223the build directory is situated on local disk (e.g. by `ln -s 1224/localdisk/jdk-build $JDK-SHARE/build`). The performance penalty is extremely 1225high for building on a network share; close to unusable. 1226 1227Also, make sure that your build tools (including Boot JDK and toolchain) is 1228located on a local disk and not a network share. 1229 1230As has been stressed elsewhere, do use SSD for source code and build directory, 1231as well as (if possible) the build tools. 1232 1233### Virus Checking 1234 1235The use of virus checking software, especially on Windows, can *significantly* 1236slow down building of the JDK. If possible, turn off such software, or exclude 1237the directory containing the JDK source code from on-the-fly checking. 1238 1239### Ccache 1240 1241The JDK build supports building with ccache when using gcc or clang. Using 1242ccache can radically speed up compilation of native code if you often rebuild 1243the same sources. Your milage may vary however, so we recommend evaluating it 1244for yourself. To enable it, make sure it's on the path and configure with 1245`--enable-ccache`. 1246 1247### Precompiled Headers 1248 1249By default, the Hotspot build uses preccompiled headers (PCH) on the toolchains 1250were it is properly supported (clang, gcc, and Visual Studio). Normally, this 1251speeds up the build process, but in some circumstances, it can actually slow 1252things down. 1253 1254You can experiment by disabling precompiled headers using 1255`--disable-precompiled-headers`. 1256 1257### Icecc / icecream 1258 1259[icecc/icecream](http://github.com/icecc/icecream) is a simple way to setup a 1260distributed compiler network. If you have multiple machines available for 1261building the JDK, you can drastically cut individual build times by utilizing 1262it. 1263 1264To use, setup an icecc network, and install icecc on the build machine. Then 1265run `configure` using `--enable-icecc`. 1266 1267### Using sjavac 1268 1269To speed up Java compilation, especially incremental compilations, you can try 1270the experimental sjavac compiler by using `--enable-sjavac`. 1271 1272### Building the Right Target 1273 1274Selecting the proper target to build can have dramatic impact on build time. 1275For normal usage, `jdk` or the default target is just fine. You only need to 1276build `images` for shipping, or if your tests require it. 1277 1278See also [Using Fine-Grained Make Targets](#using-fine-grained-make-targets) on 1279how to build an even smaller subset of the product. 1280 1281## Troubleshooting 1282 1283If your build fails, it can sometimes be difficult to pinpoint the problem or 1284find a proper solution. 1285 1286### Locating the Source of the Error 1287 1288When a build fails, it can be hard to pinpoint the actual cause of the error. 1289In a typical build process, different parts of the product build in parallel, 1290with the output interlaced. 1291 1292#### Build Failure Summary 1293 1294To help you, the build system will print a failure summary at the end. It looks 1295like this: 1296 1297``` 1298ERROR: Build failed for target 'hotspot' in configuration 'linux-x64' (exit code 2) 1299 1300=== Output from failing command(s) repeated here === 1301* For target hotspot_variant-server_libjvm_objs_psMemoryPool.o: 1302/localhome/git/jdk-sandbox/hotspot/src/share/vm/services/psMemoryPool.cpp:1:1: error: 'failhere' does not name a type 1303 ... (rest of output omitted) 1304 1305* All command lines available in /localhome/git/jdk-sandbox/build/linux-x64/make-support/failure-logs. 1306=== End of repeated output === 1307 1308=== Make failed targets repeated here === 1309lib/CompileJvm.gmk:207: recipe for target '/localhome/git/jdk-sandbox/build/linux-x64/hotspot/variant-server/libjvm/objs/psMemoryPool.o' failed 1310make/Main.gmk:263: recipe for target 'hotspot-server-libs' failed 1311=== End of repeated output === 1312 1313Hint: Try searching the build log for the name of the first failed target. 1314Hint: If caused by a warning, try configure --disable-warnings-as-errors. 1315``` 1316 1317Let's break it down! First, the selected configuration, and the top-level 1318target you entered on the command line that caused the failure is printed. 1319 1320Then, between the `Output from failing command(s) repeated here` and `End of 1321repeated output` the first lines of output (stdout and stderr) from the actual 1322failing command is repeated. In most cases, this is the error message that 1323caused the build to fail. If multiple commands were failing (this can happen in 1324a parallel build), output from all failed commands will be printed here. 1325 1326The path to the `failure-logs` directory is printed. In this file you will find 1327a `<target>.log` file that contains the output from this command in its 1328entirety, and also a `<target>.cmd`, which contain the complete command line 1329used for running this command. You can re-run the failing command by executing 1330`. <path to failure-logs>/<target>.cmd` in your shell. 1331 1332Another way to trace the failure is to follow the chain of make targets, from 1333top-level targets to individual file targets. Between `Make failed targets 1334repeated here` and `End of repeated output` the output from make showing this 1335chain is repeated. The first failed recipe will typically contain the full path 1336to the file in question that failed to compile. Following lines will show a 1337trace of make targets why we ended up trying to compile that file. 1338 1339Finally, some hints are given on how to locate the error in the complete log. 1340In this example, we would try searching the log file for "`psMemoryPool.o`". 1341Another way to quickly locate make errors in the log is to search for "`] 1342Error`" or "`***`". 1343 1344Note that the build failure summary will only help you if the issue was a 1345compilation failure or similar. If the problem is more esoteric, or is due to 1346errors in the build machinery, you will likely get empty output logs, and `No 1347indication of failed target found` instead of the make target chain. 1348 1349#### Checking the Build Log File 1350 1351The output (stdout and stderr) from the latest build is always stored in 1352`$BUILD/build.log`. The previous build log is stored as `build.log.old`. This 1353means that it is not necessary to redirect the build output yourself if you 1354want to process it. 1355 1356You can increase the verbosity of the log file, by the `LOG` control variable 1357to `make`. If you want to see the command lines used in compilations, use 1358`LOG=cmdlines`. To increase the general verbosity, use `LOG=info`, `LOG=debug` 1359or `LOG=trace`. Both of these can be combined with `cmdlines`, e.g. 1360`LOG=info,cmdlines`. The `debug` log level will show most shell commands 1361executed by make, and `trace` will show all. Beware that both these log levels 1362will produce a massive build log! 1363 1364### Fixing Unexpected Build Failures 1365 1366Most of the time, the build will fail due to incorrect changes in the source 1367code. 1368 1369Sometimes the build can fail with no apparent changes that have caused the 1370failure. If this is the first time you are building the JDK on this particular 1371computer, and the build fails, the problem is likely with your build 1372environment. But even if you have previously built the JDK with success, and it 1373now fails, your build environment might have changed (perhaps due to OS 1374upgrades or similar). But most likely, such failures are due to problems with 1375the incremental rebuild. 1376 1377#### Problems with the Build Environment 1378 1379Make sure your configuration is correct. Re-run `configure`, and look for any 1380warnings. Warnings that appear in the middle of the `configure` output is also 1381repeated at the end, after the summary. The entire log is stored in 1382`$BUILD/configure.log`. 1383 1384Verify that the summary at the end looks correct. Are you indeed using the Boot 1385JDK and native toolchain that you expect? 1386 1387By default, the JDK has a strict approach where warnings from the compiler is 1388considered errors which fail the build. For very new or very old compiler 1389versions, this can trigger new classes of warnings, which thus fails the build. 1390Run `configure` with `--disable-warnings-as-errors` to turn of this behavior. 1391(The warnings will still show, but not make the build fail.) 1392 1393#### Problems with Incremental Rebuilds 1394 1395Incremental rebuilds mean that when you modify part of the product, only the 1396affected parts get rebuilt. While this works great in most cases, and 1397significantly speed up the development process, from time to time complex 1398interdependencies will result in an incorrect build result. This is the most 1399common cause for unexpected build problems. 1400 1401Here are a suggested list of things to try if you are having unexpected build 1402problems. Each step requires more time than the one before, so try them in 1403order. Most issues will be solved at step 1 or 2. 1404 1405 1. Make sure your repository is up-to-date 1406 1407 Run `git pull origin master` to make sure you have the latest changes. 1408 1409 2. Clean build results 1410 1411 The simplest way to fix incremental rebuild issues is to run `make clean`. 1412 This will remove all build results, but not the configuration or any build 1413 system support artifacts. In most cases, this will solve build errors 1414 resulting from incremental build mismatches. 1415 1416 3. Completely clean the build directory. 1417 1418 If this does not work, the next step is to run `make dist-clean`, or 1419 removing the build output directory (`$BUILD`). This will clean all 1420 generated output, including your configuration. You will need to re-run 1421 `configure` after this step. A good idea is to run `make 1422 print-configuration` before running `make dist-clean`, as this will print 1423 your current `configure` command line. Here's a way to do this: 1424 1425 ``` 1426 make print-configuration > current-configuration 1427 make dist-clean 1428 bash configure $(cat current-configuration) 1429 make 1430 ``` 1431 1432 4. Re-clone the Git repository 1433 1434 Sometimes the Git repository gets in a state that causes the product 1435 to be un-buildable. In such a case, the simplest solution is often the 1436 "sledgehammer approach": delete the entire repository, and re-clone it. 1437 If you have local changes, save them first to a different location using 1438 `git format-patch`. 1439 1440### Specific Build Issues 1441 1442#### Clock Skew 1443 1444If you get an error message like this: 1445``` 1446File 'xxx' has modification time in the future. 1447Clock skew detected. Your build may be incomplete. 1448``` 1449then the clock on your build machine is out of sync with the timestamps on the 1450source files. Other errors, apparently unrelated but in fact caused by the 1451clock skew, can occur along with the clock skew warnings. These secondary 1452errors may tend to obscure the fact that the true root cause of the problem is 1453an out-of-sync clock. 1454 1455If you see these warnings, reset the clock on the build machine, run `make 1456clean` and restart the build. 1457 1458#### Out of Memory Errors 1459 1460On Windows, you might get error messages like this: 1461``` 1462fatal error - couldn't allocate heap 1463cannot create ... Permission denied 1464spawn failed 1465``` 1466This can be a sign of a Cygwin problem. See the information about solving 1467problems in the [Cygwin](#cygwin) section. Rebooting the computer might help 1468temporarily. 1469 1470### Getting Help 1471 1472If none of the suggestions in this document helps you, or if you find what you 1473believe is a bug in the build system, please contact the Build Group by sending 1474a mail to [build-dev@openjdk.java.net](mailto:build-dev@openjdk.java.net). 1475Please include the relevant parts of the configure and/or build log. 1476 1477If you need general help or advice about developing for the JDK, you can also 1478contact the Adoption Group. See the section on [Contributing to OpenJDK]( 1479#contributing-to-openjdk) for more information. 1480 1481## Hints and Suggestions for Advanced Users 1482 1483### Bash Completion 1484 1485The `configure` and `make` commands tries to play nice with bash command-line 1486completion (using `<tab>` or `<tab><tab>`). To use this functionality, make 1487sure you enable completion in your `~/.bashrc` (see instructions for bash in 1488your operating system). 1489 1490Make completion will work out of the box, and will complete valid make targets. 1491For instance, typing `make jdk-i<tab>` will complete to `make jdk-image`. 1492 1493The `configure` script can get completion for options, but for this to work you 1494need to help `bash` on the way. The standard way of running the script, `bash 1495configure`, will not be understood by bash completion. You need `configure` to 1496be the command to run. One way to achieve this is to add a simple helper script 1497to your path: 1498 1499``` 1500cat << EOT > /tmp/configure 1501#!/bin/bash 1502if [ \$(pwd) = \$(cd \$(dirname \$0); pwd) ] ; then 1503 echo >&2 "Abort: Trying to call configure helper recursively" 1504 exit 1 1505fi 1506 1507bash \$PWD/configure "\$@" 1508EOT 1509chmod +x /tmp/configure 1510sudo mv /tmp/configure /usr/local/bin 1511``` 1512 1513Now `configure --en<tab>-dt<tab>` will result in `configure --enable-dtrace`. 1514 1515### Using Multiple Configurations 1516 1517You can have multiple configurations for a single source repository. When you 1518create a new configuration, run `configure --with-conf-name=<name>` to create a 1519configuration with the name `<name>`. Alternatively, you can create a directory 1520under `build` and run `configure` from there, e.g. `mkdir build/<name> && cd 1521build/<name> && bash ../../configure`. 1522 1523Then you can build that configuration using `make CONF_NAME=<name>` or `make 1524CONF=<pattern>`, where `<pattern>` is a substring matching one or several 1525configurations, e.g. `CONF=debug`. The special empty pattern (`CONF=`) will 1526match *all* available configuration, so `make CONF= hotspot` will build the 1527`hotspot` target for all configurations. Alternatively, you can execute `make` 1528in the configuration directory, e.g. `cd build/<name> && make`. 1529 1530### Handling Reconfigurations 1531 1532If you update the repository and part of the configure script has changed, the 1533build system will force you to re-run `configure`. 1534 1535Most of the time, you will be fine by running `configure` again with the same 1536arguments as the last time, which can easily be performed by `make 1537reconfigure`. To simplify this, you can use the `CONF_CHECK` make control 1538variable, either as `make CONF_CHECK=auto`, or by setting an environment 1539variable. For instance, if you add `export CONF_CHECK=auto` to your `.bashrc` 1540file, `make` will always run `reconfigure` automatically whenever the configure 1541script has changed. 1542 1543You can also use `CONF_CHECK=ignore` to skip the check for a needed configure 1544update. This might speed up the build, but comes at the risk of an incorrect 1545build result. This is only recommended if you know what you're doing. 1546 1547From time to time, you will also need to modify the command line to `configure` 1548due to changes. Use `make print-configure` to show the command line used for 1549your current configuration. 1550 1551### Using Fine-Grained Make Targets 1552 1553The default behavior for make is to create consistent and correct output, at 1554the expense of build speed, if necessary. 1555 1556If you are prepared to take some risk of an incorrect build, and know enough of 1557the system to understand how things build and interact, you can speed up the 1558build process considerably by instructing make to only build a portion of the 1559product. 1560 1561#### Building Individual Modules 1562 1563The safe way to use fine-grained make targets is to use the module specific 1564make targets. All source code in the JDK is organized so it belongs to a 1565module, e.g. `java.base` or `jdk.jdwp.agent`. You can build only a specific 1566module, by giving it as make target: `make jdk.jdwp.agent`. If the specified 1567module depends on other modules (e.g. `java.base`), those modules will be built 1568first. 1569 1570You can also specify a set of modules, just as you can always specify a set of 1571make targets: `make jdk.crypto.cryptoki jdk.crypto.ec jdk.crypto.mscapi` 1572 1573#### Building Individual Module Phases 1574 1575The build process for each module is divided into separate phases. Not all 1576modules need all phases. Which are needed depends on what kind of source code 1577and other artifact the module consists of. The phases are: 1578 1579 * `gensrc` (Generate source code to compile) 1580 * `gendata` (Generate non-source code artifacts) 1581 * `copy` (Copy resource artifacts) 1582 * `java` (Compile Java code) 1583 * `launchers` (Compile native executables) 1584 * `libs` (Compile native libraries) 1585 1586You can build only a single phase for a module by using the notation 1587`$MODULE-$PHASE`. For instance, to build the `gensrc` phase for `java.base`, 1588use `make java.base-gensrc`. 1589 1590Note that some phases may depend on others, e.g. `java` depends on `gensrc` (if 1591present). Make will build all needed prerequisites before building the 1592requested phase. 1593 1594#### Skipping the Dependency Check 1595 1596When using an iterative development style with frequent quick rebuilds, the 1597dependency check made by make can take up a significant portion of the time 1598spent on the rebuild. In such cases, it can be useful to bypass the dependency 1599check in make. 1600 1601> **Note that if used incorrectly, this can lead to a broken build!** 1602 1603To achieve this, append `-only` to the build target. For instance, `make 1604jdk.jdwp.agent-java-only` will *only* build the `java` phase of the 1605`jdk.jdwp.agent` module. If the required dependencies are not present, the 1606build can fail. On the other hand, the execution time measures in milliseconds. 1607 1608A useful pattern is to build the first time normally (e.g. `make 1609jdk.jdwp.agent`) and then on subsequent builds, use the `-only` make target. 1610 1611#### Rebuilding Part of java.base (JDK\_FILTER) 1612 1613If you are modifying files in `java.base`, which is the by far largest module 1614in the JDK, then you need to rebuild all those files whenever a single file has 1615changed. (This inefficiency will hopefully be addressed in JDK 10.) 1616 1617As a hack, you can use the make control variable `JDK_FILTER` to specify a 1618pattern that will be used to limit the set of files being recompiled. For 1619instance, `make java.base JDK_FILTER=javax/crypto` (or, to combine methods, 1620`make java.base-java-only JDK_FILTER=javax/crypto`) will limit the compilation 1621to files in the `javax.crypto` package. 1622 1623## Understanding the Build System 1624 1625This section will give you a more technical description on the details of the 1626build system. 1627 1628### Configurations 1629 1630The build system expects to find one or more configuration. These are 1631technically defined by the `spec.gmk` in a subdirectory to the `build` 1632subdirectory. The `spec.gmk` file is generated by `configure`, and contains in 1633principle the configuration (directly or by files included by `spec.gmk`). 1634 1635You can, in fact, select a configuration to build by pointing to the `spec.gmk` 1636file with the `SPEC` make control variable, e.g. `make SPEC=$BUILD/spec.gmk`. 1637While this is not the recommended way to call `make` as a user, it is what is 1638used under the hood by the build system. 1639 1640### Build Output Structure 1641 1642The build output for a configuration will end up in `build/<configuration 1643name>`, which we refer to as `$BUILD` in this document. The `$BUILD` directory 1644contains the following important directories: 1645 1646``` 1647buildtools/ 1648configure-support/ 1649hotspot/ 1650images/ 1651jdk/ 1652make-support/ 1653support/ 1654test-results/ 1655test-support/ 1656``` 1657 1658This is what they are used for: 1659 1660 * `images`: This is the directory were the output of the `*-image` make 1661 targets end up. For instance, `make jdk-image` ends up in `images/jdk`. 1662 1663 * `jdk`: This is the "exploded image". After `make jdk`, you will be able to 1664 launch the newly built JDK by running `$BUILD/jdk/bin/java`. 1665 1666 * `test-results`: This directory contains the results from running tests. 1667 1668 * `support`: This is an area for intermediate files needed during the build, 1669 e.g. generated source code, object files and class files. Some noteworthy 1670 directories in `support` is `gensrc`, which contains the generated source 1671 code, and the `modules_*` directories, which contains the files in a 1672 per-module hierarchy that will later be collapsed into the `jdk` directory 1673 of the exploded image. 1674 1675 * `buildtools`: This is an area for tools compiled for the build platform 1676 that are used during the rest of the build. 1677 1678 * `hotspot`: This is an area for intermediate files needed when building 1679 hotspot. 1680 1681 * `configure-support`, `make-support` and `test-support`: These directories 1682 contain files that are needed by the build system for `configure`, `make` 1683 and for running tests. 1684 1685### Fixpath 1686 1687Windows path typically look like `C:\User\foo`, while Unix paths look like 1688`/home/foo`. Tools with roots from Unix often experience issues related to this 1689mismatch when running on Windows. 1690 1691In the JDK build, we always use Unix paths internally, and only just before 1692calling a tool that does not understand Unix paths do we convert them to 1693Windows paths. 1694 1695This conversion is done by the `fixpath` tool, which is a small wrapper that 1696modifies unix-style paths to Windows-style paths in command lines. Fixpath is 1697compiled automatically by `configure`. 1698 1699### Native Debug Symbols 1700 1701Native libraries and executables can have debug symbol (and other debug 1702information) associated with them. How this works is very much platform 1703dependent, but a common problem is that debug symbol information takes a lot of 1704disk space, but is rarely needed by the end user. 1705 1706The JDK supports different methods on how to handle debug symbols. The 1707method used is selected by `--with-native-debug-symbols`, and available methods 1708are `none`, `internal`, `external`, `zipped`. 1709 1710 * `none` means that no debug symbols will be generated during the build. 1711 1712 * `internal` means that debug symbols will be generated during the build, and 1713 they will be stored in the generated binary. 1714 1715 * `external` means that debug symbols will be generated during the build, and 1716 after the compilation, they will be moved into a separate `.debuginfo` file. 1717 (This was previously known as FDS, Full Debug Symbols). 1718 1719 * `zipped` is like `external`, but the .debuginfo file will also be zipped 1720 into a `.diz` file. 1721 1722When building for distribution, `zipped` is a good solution. Binaries built 1723with `internal` is suitable for use by developers, since they facilitate 1724debugging, but should be stripped before distributed to end users. 1725 1726### Autoconf Details 1727 1728The `configure` script is based on the autoconf framework, but in some details 1729deviate from a normal autoconf `configure` script. 1730 1731The `configure` script in the top level directory of the JDK is just a thin 1732wrapper that calls `make/autoconf/configure`. This in turn will run `autoconf` 1733to create the runnable (generated) configure script, as 1734`.build/generated-configure.sh`. Apart from being responsible for the 1735generation of the runnable script, the `configure` script also provides 1736functionality that is not easily expressed in the normal Autoconf framework. As 1737part of this functionality, the generated script is called. 1738 1739The build system will detect if the Autoconf source files have changed, and 1740will trigger a regeneration of the generated script if needed. You can also 1741manually request such an update by `bash configure autogen`. 1742 1743In previous versions of the JDK, the generated script was checked in at 1744`make/autoconf/generated-configure.sh`. This is no longer the case. 1745 1746### Developing the Build System Itself 1747 1748This section contains a few remarks about how to develop for the build system 1749itself. It is not relevant if you are only making changes in the product source 1750code. 1751 1752While technically using `make`, the make source files of the JDK does not 1753resemble most other Makefiles. Instead of listing specific targets and actions 1754(perhaps using patterns), the basic modus operandi is to call a high-level 1755function (or properly, macro) from the API in `make/common`. For instance, to 1756compile all classes in the `jdk.internal.foo` package in the `jdk.foo` module, 1757a call like this would be made: 1758 1759``` 1760$(eval $(call SetupJavaCompilation, BUILD_FOO_CLASSES, \ 1761 SETUP := GENERATE_OLDBYTECODE, \ 1762 SRC := $(TOPDIR)/src/jkd.foo/share/classes, \ 1763 INCLUDES := jdk/internal/foo, \ 1764 BIN := $(SUPPORT_OUTPUTDIR)/foo_classes, \ 1765)) 1766``` 1767 1768By encapsulating and expressing the high-level knowledge of *what* should be 1769done, rather than *how* it should be done (as is normal in Makefiles), we can 1770build a much more powerful and flexible build system. 1771 1772Correct dependency tracking is paramount. Sloppy dependency tracking will lead 1773to improper parallelization, or worse, race conditions. 1774 1775To test for/debug race conditions, try running `make JOBS=1` and `make 1776JOBS=100` and see if it makes any difference. (It shouldn't). 1777 1778To compare the output of two different builds and see if, and how, they differ, 1779run `$BUILD1/compare.sh -o $BUILD2`, where `$BUILD1` and `$BUILD2` are the two 1780builds you want to compare. 1781 1782To automatically build two consecutive versions and compare them, use 1783`COMPARE_BUILD`. The value of `COMPARE_BUILD` is a set of variable=value 1784assignments, like this: 1785``` 1786make COMPARE_BUILD=CONF=--enable-new-hotspot-feature:MAKE=hotspot 1787``` 1788See `make/InitSupport.gmk` for details on how to use `COMPARE_BUILD`. 1789 1790To analyze build performance, run with `LOG=trace` and check `$BUILD/build-trace-time.log`. 1791Use `JOBS=1` to avoid parallelism. 1792 1793Please check that you adhere to the [Code Conventions for the Build System]( 1794http://openjdk.java.net/groups/build/doc/code-conventions.html) before 1795submitting patches. 1796 1797## Contributing to the JDK 1798 1799So, now you've built your JDK, and made your first patch, and want to 1800contribute it back to the OpenJDK Community. 1801 1802First of all: Thank you! We gladly welcome your contribution. 1803However, please bear in mind that the JDK is a massive project, and we must ask 1804you to follow our rules and guidelines to be able to accept your contribution. 1805 1806The official place to start is the ['How to contribute' page]( 1807http://openjdk.java.net/contribute/). There is also an official (but somewhat 1808outdated and skimpy on details) [Developer's Guide]( 1809http://openjdk.java.net/guide/). 1810 1811If this seems overwhelming to you, the Adoption Group is there to help you! A 1812good place to start is their ['New Contributor' page]( 1813https://wiki.openjdk.java.net/display/Adoption/New+Contributor), or start 1814reading the comprehensive [Getting Started Kit]( 1815https://adoptopenjdk.gitbooks.io/adoptopenjdk-getting-started-kit/en/). The 1816Adoption Group will also happily answer any questions you have about 1817contributing. Contact them by [mail]( 1818http://mail.openjdk.java.net/mailman/listinfo/adoption-discuss) or [IRC]( 1819http://openjdk.java.net/irc/). 1820 1821--- 1822# Override styles from the base CSS file that are not ideal for this document. 1823header-includes: 1824 - '<style type="text/css">pre, code, tt { color: #1d6ae5; }</style>' 1825--- 1826