building.md revision 2773:48ae1d50d393
1% Building OpenJDK 2 3## TL;DR (Instructions for the Impatient) 4 5If you are eager to try out building OpenJDK, these simple steps works most of 6the time. They assume that you have installed Mercurial (and Cygwin if running 7on Windows) and cloned the top-level OpenJDK repository that you want to build. 8 9 1. [Get the complete source code](#getting-the-source-code): \ 10 `bash get_source.sh` 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), [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. 21 22 3. [Run make](#running-make): \ 23 `make images` 24 25 4. Verify your newly built JDK: \ 26 `./build/*/images/jdk/bin/java -version` 27 28 5. [Run basic tests](##running-tests): \ 29 `make run-test-tier1` 30 31If any of these steps failed, or if you want to know more about build 32requirements or build functionality, please continue reading this document. 33 34## Introduction 35 36OpenJDK is a complex software project. Building it requires a certain amount of 37technical expertise, a fair number of dependencies on external software, and 38reasonably powerful hardware. 39 40If you just want to use OpenJDK and not build it yourself, this document is not 41for you. See for instance [OpenJDK installation]( 42http://openjdk.java.net/install) for some methods of installing a prebuilt 43OpenJDK. 44 45## Getting the Source Code 46 47OpenJDK uses [Mercurial](http://www.mercurial-scm.org) for source control. The 48source 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 50repositories to be able to build OpenJDK. To assist you in dealing with this 51somewhat unusual arrangement, there are multiple tools available, which are 52explained below. 53 54In any case, make sure you are getting the correct version. At the [OpenJDK 55Mercurial server](http://hg.openjdk.java.net/) you can see a list of all 56available forests. If you want to build an older version, e.g. JDK 8, it is 57recommended that you get the `jdk8u` forest, which contains incremental 58updates, instead of the `jdk8` forest, which was frozen at JDK 8 GA. 59 60If you are new to Mercurial, a good place to start is the [Mercurial Beginner's 61Guide](http://www.mercurial-scm.org/guide). The rest of this document assumes a 62working knowledge of Mercurial. 63 64### Special Considerations 65 66For a smooth building experience, it is recommended that you follow these rules 67on where and how to check out the source code. 68 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. 72 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. 76 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. 82 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: 86 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. 92 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. 96 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. 100 101 Failure to follow this procedure might result in hard-to-debug build 102 problems. 103 104### Using get\_source.sh 105 106The simplest way to get the entire forest is probably to clone the top-level 107repository and then run the `get_source.sh` script, like this: 108 109``` 110hg clone http://hg.openjdk.java.net/jdk9/jdk9 111cd jdk9 112bash get_source.sh 113``` 114 115The first time this is run, it will clone all the sub-repositories. Any 116subsequent execution of the script will update all sub-repositories to the 117latest revision. 118 119### Using hgforest.sh 120 121The `hgforest.sh` script is more expressive than `get_source.sh`. It takes any 122number of arguments, and runs `hg` with those arguments on each sub-repository 123in the forest. The `get_source.sh` script is basically a simple wrapper that 124runs either `hgforest.sh clone` or `hgforest.sh pull -u`. 125 126 * 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 ``` 132 133 * Pulling and updating the forest: 134 ``` 135 bash common/bin/hgforest.sh pull -u 136 ``` 137 138 * Merging over the entire forest: 139 ``` 140 bash common/bin/hgforest.sh merge 141 ``` 142 143### Using the Trees Extension 144 145The trees extension is a Mercurial add-on that helps you deal with the forest. 146More information is available on the [Code Tools trees page]( 147http://openjdk.java.net/projects/code-tools/trees). 148 149#### Installing the Extension 150 151Install the extension by cloning `http://hg.openjdk.java.net/code-tools/trees` 152and updating your `.hgrc` file. Here's one way to do this: 153 154``` 155cd ~ 156mkdir hg-ext 157cd hg-ext 158hg clone http://hg.openjdk.java.net/code-tools/trees 159cat << EOT >> ~/.hgrc 160[extensions] 161trees=~/hg-ext/trees/trees.py 162EOT 163``` 164 165#### Initializing the Tree 166 167The trees extension needs to know the structure of the forest. If you have 168already cloned the entire forest using another method, you can initialize the 169forest like this: 170 171``` 172hg tconf --set --walk --depth 173``` 174 175Or 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: 177 178``` 179hg tclone http://hg.openjdk.java.net/jdk9/jdk9 180``` 181 182In this case, the forest will be properly initialized from the start. 183 184#### Other Operations 185 186The trees extensions supplement many common operations with a trees version by 187prefixing a `t` to the normal Mercurial command, e.g. `tcommit`, `tstatus` or 188`tmerge`. For instance, to update the entire forest: 189 190``` 191hg tpull -u 192``` 193 194## Build Hardware Requirements 195 196OpenJDK is a massive project, and require machines ranging from decent to 197powerful to be able to build in a reasonable amount of time, or to be able to 198complete a build at all. 199 200We *strongly* recommend usage of an SSD disk for the build, since disk speed is 201one of the limiting factors for build performance. 202 203### Building on x86 204 205At 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 207space is required (8 GB minimum for building on Solaris). 208 209Even for 32-bit builds, it is recommended to use a 64-bit build machine, and 210instead create a 32-bit target using `--with-target-bits=32`. 211 212### Building on sparc 213 214At a minimum, a machine with 4 cores is advisable, as well as 4 GB of RAM. (The 215more cores to use, the more memory you need.) At least 8 GB of free disk space 216is required. 217 218### Building on arm/aarch64 219 220This is not recommended. Instead, see the section on [Cross-compiling]( 221#cross-compiling). 222 223## Operating System Requirements 224 225The mainline OpenJDK project supports Linux, Solaris, macOS, AIX and Windows. 226Support for other operating system, e.g. BSD, exists in separate "port" 227projects. 228 229In general, OpenJDK can be built on a wide range of versions of these operating 230systems, but the further you deviate from what is tested on a daily basis, the 231more likely you are to run into problems. 232 233This table lists the OS versions used by Oracle when building JDK 9. Such 234information is always subject to change, but this table is up to date at the 235time of writing. 236 237 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 243 244The double version numbers for Linux, Solaris and macOS is due to the hybrid 245model used at Oracle, where header files and external libraries from an older 246version is used when building on a more modern version of the OS. 247 248The Build Group has a wiki page with [Supported Build Platforms]( 249https://wiki.openjdk.java.net/display/Build/Supported+Build+Platforms). From 250time to time, this is updated by the community to list successes or failures of 251building on different platforms. 252 253### Windows 254 255Windows XP is not a supported platform, but all newer Windows should be able to 256build OpenJDK. 257 258On Windows, it is important that you pay attention to the instructions in the 259[Special Considerations](#special-considerations). 260 261Windows is the only non-POSIX OS supported by OpenJDK, and as such, requires 262some extra care. A POSIX support layer is required to build on Windows. For 263OpenJDK 9, the only supported such layer is Cygwin. (Msys is no longer 264supported 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 266require a community effort to implement.) 267 268Internally in the build system, all paths are represented as Unix-style paths, 269e.g. `/cygdrive/c/hg/jdk9/Makefile` rather than `C:\hg\jdk9\Makefile`. This 270rule 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 273on [Fixpath](#fixpath). 274 275#### Cygwin 276 277A functioning [Cygwin](http://www.cygwin.com/) environment is thus required for 278building OpenJDK on Windows. If you have a 64-bit OS, we strongly recommend 279using the 64-bit version of Cygwin. 280 281**Note:** Cygwin has a model of continuously updating all packages without any 282easy way to install or revert to a specific version of a package. This means 283that whenever you add or update a package in Cygwin, you might (inadvertently) 284update tools that are used by the OpenJDK build process, and that can cause 285unexpected build problems. 286 287OpenJDK requires GNU Make 4.0 or greater on Windows. This is usually not a 288problem, since Cygwin currently only distributes GNU Make at a version above 2894.0. 290 291Apart from the basic Cygwin installation, the following packages must also be 292installed: 293 294 * `make` 295 * `zip` 296 * `unzip` 297 298Often, 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``` 302 303Unfortunately, Cygwin can be unreliable in certain circumstances. If you 304experience build tool crashes or strange issues when building on Windows, 305please check the Cygwin FAQ on the ["BLODA" list]( 306https://cygwin.com/faq/faq.html#faq.using.bloda) and the section on [fork() 307failures](https://cygwin.com/faq/faq.html#faq.using.fixing-fork-failures). 308 309### Solaris 310 311See `make/devkit/solaris11.1-package-list.txt` for a list of recommended 312packages to install when building on Solaris. The versions specified in this 313list is the versions used by the daily builds at Oracle, and is likely to work 314properly. 315 316Older versions of Solaris shipped a broken version of `objcopy`. At least 317version 2.21.1 is needed, which is provided by Solaris 11 Update 1. Objcopy is 318needed if you want to have external debug symbols. Please make sure you are 319using at least version 2.21.1 of objcopy, or that you disable external debug 320symbols. 321 322### macOS 323 324Apple is using a quite aggressive scheme of pushing OS updates, and coupling 325these updates with required updates of Xcode. Unfortunately, this makes it 326difficult for a project like OpenJDK to keep pace with a continuously updated 327machine running macOS. See the section on [Apple Xcode](#apple-xcode) on some 328strategies to deal with this. 329 330It is recommended that you use at least Mac OS X 10.9 (Mavericks). At the time 331of writing, OpenJDK has been successfully compiled on macOS versions up to 33210.12.5 (Sierra), using XCode 8.3.2 and `--disable-warnings-as-errors`. 333 334The standard macOS environment contains the basic tooling needed to build, but 335for external libraries a package manager is recommended. OpenJDK uses 336[homebrew](https://brew.sh/) in the examples, but feel free to use whatever 337manager you want (or none). 338 339### Linux 340 341It is often not much problem to build OpenJDK on Linux. The only general advice 342is to try to use the compilers, external libraries and header files as provided 343by your distribution. 344 345The basic tooling is provided as part of the core operating system, but you 346will most likely need to install developer packages. 347 348For apt-based distributions (Debian, Ubuntu, etc), try this: 349``` 350sudo apt-get install build-essential 351``` 352 353For rpm-based distributions (Fedora, Red Hat, etc), try this: 354``` 355sudo yum groupinstall "Development Tools" 356``` 357 358### AIX 359 360The regular builds by SAP is using AIX version 7.1, but AIX 5.3 is also 361supported. See the [OpenJDK PowerPC Port Status Page]( 362http://cr.openjdk.java.net/~simonis/ppc-aix-port) for details. 363 364## Native Compiler (Toolchain) Requirements 365 366Large portions of OpenJDK consists of native code, that needs to be compiled to 367be able to run on the target platform. In theory, toolchain and operating 368system should be independent factors, but in practice there's more or less a 369one-to-one correlation between target operating system and toolchain. 370 371 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 378 379Please see the individual sections on the toolchains for version 380recommendations. As a reference, these versions of the toolchains are used, at 381the time of writing, by Oracle for the daily builds of OpenJDK. It should be 382possible to compile OpenJDK with both older and newer versions, but the closer 383you stay to this list, the more likely you are to compile successfully without 384issues. 385 386 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 4 392 393### gcc 394 395The minimum accepted version of gcc is 4.7. Older versions will generate a warning 396by `configure` and are unlikely to work. 397 398OpenJDK 9 includes patches that should allow gcc 6 to compile, but this should 399be considered experimental. 400 401In general, any version between these two should be usable. 402 403### clang 404 405The minimum accepted version of clang is 3.2. Older versions will not be 406accepted by `configure`. 407 408To use clang instead of gcc on Linux, use `--with-toolchain-type=clang`. 409 410### Apple Xcode 411 412The oldest supported version of Xcode is 5. 413 414You will need the Xcode command lines developers tools to be able to build 415OpenJDK. (Actually, *only* the command lines tools are needed, not the IDE.) 416The simplest way to install these is to run: 417``` 418xcode-select --install 419``` 420 421It is advisable to keep an older version of Xcode for building OpenJDK when 422updating Xcode. This [blog page]( 423http://iosdevelopertips.com/xcode/install-multiple-versions-of-xcode.html) has 424good suggestions on managing multiple Xcode versions. To use a specific version 425of 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` 428 429If you have recently (inadvertently) updated your OS and/or Xcode version, and 430OpenJDK can no longer be built, please see the section on [Problems with the 431Build Environment](#problems-with-the-build-environment), and [Getting 432Help](#getting-help) to find out if there are any recent, non-merged patches 433available for this update. 434 435### Oracle Solaris Studio 436 437The 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 439configure. 440 441The Solaris Studio installation should contain at least these packages: 442 443 Package Version 444 -------------------------------------------------- ------------- 445 developer/solarisstudio-124/backend 12.4-1.0.6.0 446 developer/solarisstudio-124/c++ 12.4-1.0.10.0 447 developer/solarisstudio-124/cc 12.4-1.0.4.0 448 developer/solarisstudio-124/library/c++-libs 12.4-1.0.10.0 449 developer/solarisstudio-124/library/math-libs 12.4-1.0.0.1 450 developer/solarisstudio-124/library/studio-gccrt 12.4-1.0.0.1 451 developer/solarisstudio-124/studio-common 12.4-1.0.0.1 452 developer/solarisstudio-124/studio-ja 12.4-1.0.0.1 453 developer/solarisstudio-124/studio-legal 12.4-1.0.0.1 454 developer/solarisstudio-124/studio-zhCN 12.4-1.0.0.1 455 456Compiling with Solaris Studio can sometimes be finicky. This is the exact 457version used by Oracle, which worked correctly at the time of writing: 458``` 459$ cc -V 460cc: Sun C 5.13 SunOS_i386 2014/10/20 461$ CC -V 462CC: Sun C++ 5.13 SunOS_i386 151846-10 2015/10/30 463``` 464 465### Microsoft Visual Studio 466 467The minimum accepted version of Visual Studio is 2010. Older versions will not 468be accepted by `configure`. The maximum accepted version of Visual Studio is 4692013. 470 471If you have multiple versions of Visual Studio installed, `configure` will by 472default pick the latest. You can request a specific version to be used by 473setting `--with-toolchain-version`, e.g. `--with-toolchain-version=2010`. 474 475If you get `LINK: fatal error LNK1123: failure during conversion to COFF: file 476invalid` when building using Visual Studio 2010, you have encountered 477[KB2757355](http://support.microsoft.com/kb/2757355), a bug triggered by a 478specific installation order. However, the solution suggested by the KB article 479does not always resolve the problem. See [this stackoverflow discussion]( 480https://stackoverflow.com/questions/10888391) for other suggestions. 481 482### IBM XL C/C++ 483 484The regular builds by SAP is using version 12.1, described as `IBM XL C/C++ for 485AIX, V12.1 (5765-J02, 5725-C72) Version: 12.01.0000.0017`. 486 487See the [OpenJDK PowerPC Port Status Page]( 488http://cr.openjdk.java.net/~simonis/ppc-aix-port) for details. 489 490## Boot JDK Requirements 491 492Paradoxically, 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 494porting OpenJDK to a new platform, chances are that there already exists 495another JDK for that platform that is usable as boot JDK. 496 497The rule of thumb is that the boot JDK for building JDK major version *N* 498should be an JDK of major version *N-1*, so for building JDK 9 a JDK 8 would be 499suitable as boot JDK. However, OpenJDK should be able to "build itself", so an 500up-to-date build of the current OpenJDK source is an acceptable alternative. If 501you are following the *N-1* rule, make sure you got the latest update version, 502since JDK 8 GA might not be able to build JDK 9 on all platforms. 503 504If 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. 506 507### JDK 8 on Linux 508 509On apt-based distros (like Debian and Ubuntu), `sudo apt-get install 510openjdk-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`. 512 513### JDK 8 on Windows 514 515No pre-compiled binaries of OpenJDK 8 are readily available for Windows at the 516time of writing. An alternative is to download the [Oracle JDK]( 517http://www.oracle.com/technetwork/java/javase/downloads). Another is the [Adopt 518OpenJDK Project](https://adoptopenjdk.net/), which publishes experimental 519prebuilt binaries for Windows. 520 521### JDK 8 on macOS 522 523No pre-compiled binaries of OpenJDK 8 are readily available for macOS at the 524time of writing. An alternative is to download the [Oracle JDK]( 525http://www.oracle.com/technetwork/java/javase/downloads), or to install it 526using `brew cask install java`. Another option is the [Adopt OpenJDK Project]( 527https://adoptopenjdk.net/), which publishes experimental prebuilt binaries for 528macOS. 529 530### JDK 8 on AIX 531 532No pre-compiled binaries of OpenJDK 8 are readily available for AIX at the 533time of writing. A starting point for working with OpenJDK on AIX is 534the [PowerPC/AIX Port Project](http://openjdk.java.net/projects/ppc-aix-port/). 535 536## External Library Requirements 537 538Different platforms require different external libraries. In general, libraries 539are not optional - that is, they are either required or not used. 540 541If a required library is not detected by `configure`, you need to provide the 542path to it. There are two forms of the `configure` arguments to point to an 543external library: `--with-<LIB>=<path>` or `--with-<LIB>-include=<path to 544include> --with-<LIB>-lib=<path to lib>`. The first variant is more concise, 545but require the include files an library files to reside in a default hierarchy 546under this directory. In most cases, it works fine. 547 548As a fallback, the second version allows you to point to the include directory 549and the lib directory separately. 550 551### FreeType 552 553FreeType2 from [The FreeType Project](http://www.freetype.org/) is required on 554all platforms. At least version 2.3 is required. 555 556 * 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). 563 564Use `--with-freetype=<path>` if `configure` does not properly locate your 565FreeType files. 566 567#### Building FreeType on Windows 568 569On Windows, there is no readily available compiled version of FreeType. OpenJDK 570can help you compile FreeType from source. Download the FreeType sources and 571unpack them into an arbitrary directory: 572 573``` 574wget http://download.savannah.gnu.org/releases/freetype/freetype-2.5.3.tar.gz 575tar -xzf freetype-2.5.3.tar.gz 576``` 577 578Then run `configure` with `--with-freetype-src=<freetype_src>`. This will 579automatically build the freetype library into `<freetype_src>/lib64` for 64-bit 580builds or into `<freetype_src>/lib32` for 32-bit builds. Afterwards you can 581always use `--with-freetype-include=<freetype_src>/include` and 582`--with-freetype-lib=<freetype_src>/lib[32|64]` for other builds. 583 584Alternatively you can unpack the sources like this to use the default 585directory: 586 587``` 588tar --one-top-level=$HOME/freetype --strip-components=1 -xzf freetype-2.5.3.tar.gz 589``` 590 591### CUPS 592 593CUPS, [Common UNIX Printing System](http://www.cups.org) header files are 594required on all platforms, except Windows. Often these files are provided by 595your operating system. 596 597 * 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`. 602 603Use `--with-cups=<path>` if `configure` does not properly locate your CUPS 604files. 605 606### X11 607 608Certain [X11](http://www.x.org/) libraries and include files are required on 609Linux and Solaris. 610 611 * 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`. 621 622Use `--with-x=<path>` if `configure` does not properly locate your X11 files. 623 624### ALSA 625 626ALSA, [Advanced Linux Sound Architecture](https://www.alsa-project.org/) is 627required on Linux. At least version 0.9.1 of ALSA is required. 628 629 * 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`. 633 634Use `--with-alsa=<path>` if `configure` does not properly locate your ALSA 635files. 636 637### libffi 638 639libffi, the [Portable Foreign Function Interface Library]( 640http://sourceware.org/libffi) is required when building the Zero version of 641Hotspot. 642 643 * 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`. 647 648Use `--with-libffi=<path>` if `configure` does not properly locate your libffi 649files. 650 651## Other Tooling Requirements 652 653### GNU Make 654 655OpenJDK requires [GNU Make](http://www.gnu.org/software/make). No other flavors 656of make are supported. 657 658At least version 3.81 of GNU Make must be used. For distributions supporting 659GNU Make 4.0 or above, we strongly recommend it. GNU Make 4.0 contains useful 660functionality to handle parallel building (supported by `--with-output-sync`) 661and speed and stability improvements. 662 663Note 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 665start a build using `make` on the command line, you will be using the version 666of make found first in your `PATH`, and not necessarily the one stored in the 667configuration. This initial make will be used as "bootstrap make", and in a 668second stage, the make located by `configure` will be called. Normally, this 669will 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. 671 672If you want to override the default make found by `configure`, use the `MAKE` 673configure variable, e.g. `configure MAKE=/opt/gnu/make`. 674 675On Solaris, it is common to call the GNU version of make by using `gmake`. 676 677### GNU Bash 678 679OpenJDK requires [GNU Bash](http://www.gnu.org/software/bash). No other shells 680are supported. 681 682At least version 3.2 of GNU Bash must be used. 683 684### Autoconf 685 686If you want to modify the build system itself, you need to install [Autoconf]( 687http://www.gnu.org/software/autoconf). 688 689However, if you only need to build OpenJDK or if you only edit the actual 690OpenJDK source files, there is no dependency on autoconf, since the source 691distribution includes a pre-generated `configure` shell script. 692 693See the section on [Autoconf Details](#autoconf-details) for details on how 694OpenJDK uses autoconf. This is especially important if you plan to contribute 695changes to OpenJDK that modifies the build system. 696 697## Running Configure 698 699To build OpenJDK, you need a "configuration", which consists of a directory 700where to store the build output, coupled with information about the platform, 701the specific build machine, and choices that affect how OpenJDK is built. 702 703The configuration is created by the `configure` script. The basic invocation of 704the `configure` script looks like this: 705 706``` 707bash configure [options] 708``` 709 710This will create an output directory containing the configuration and setup an 711area for the build result. This directory typically looks like 712`build/linux-x64-normal-server-release`, but the actual name depends on your 713specific configuration. (It can also be set directly, see [Using Multiple 714Configurations](#using-multiple-configurations)). This directory is referred to 715as `$BUILD` in this documentation. 716 717`configure` will try to figure out what system you are running on and where all 718necessary build components are. If you have all prerequisites for building 719installed, it should find everything. If it fails to detect any component 720automatically, it will exit and inform you about the problem. 721 722Some command line examples: 723 724 * 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 ``` 728 729 * Create a debug build with the `server` JVM and DTrace enabled: 730 ``` 731 bash configure --enable-debug --with-jvm-variants=server --enable-dtrace 732 ``` 733 734### Common Configure Arguments 735 736Here follows some of the most common and important `configure` argument. 737 738To get up-to-date information on *all* available `configure` argument, please 739run: 740``` 741bash configure --help 742``` 743 744(Note that this help text also include general autoconf options, like 745`--dvidir`, that is not relevant to OpenJDK. To list only OpenJDK specific 746features, use `bash configure --help=short` instead.) 747 748#### Configure Arguments for Tailoring the Build 749 750 * `--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.) 778 779#### Configure Arguments for Native Compilation 780 781 * `--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 793 794#### Configure Arguments for External Dependencies 795 796 * `--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) 805 806Certain third-party libraries used by OpenJDK (libjpeg, giflib, libpng, lcms 807and zlib) are included in the OpenJDK repository. The default behavior of the 808OpenJDK build is to use this version of these libraries, but they might be 809replaced by an external version. To do so, specify `system` as the `<source>` 810option in these arguments. (The default is `bundled`). 811 812 * `--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 817 818On Linux, it is possible to select either static or dynamic linking of the C++ 819runtime. The default is static linking, with dynamic linking as fallback if the 820static library is not found. 821 822 * `--with-stdc++lib=<method>` - Use the specified method (`static`, `dynamic` 823 or `default`) for linking the C++ runtime. 824 825### Configure Control Variables 826 827It is possible to control certain aspects of `configure` by overriding the 828value of `configure` variables, either on the command line or in the 829environment. 830 831Normally, this is **not recommended**. If used improperly, it can lead to a 832broken configuration. Unless you're well versed in the build system, this is 833hard to use properly. Therefore, `configure` will print a warning if this is 834detected. 835 836However, there are a few `configure` variables, known as *control variables* 837that are supposed to be overriden on the command line. These are variables that 838describe the location of tools needed by the build, like `MAKE` or `GREP`. If 839any such variable is specified, `configure` will use that value instead of 840trying to autodetect the tool. For instance, `bash configure 841MAKE=/opt/gnumake4.0/bin/make`. 842 843If a configure argument exists, use that instead, e.g. use `--with-jtreg` 844instead of setting `JTREGEXE`. 845 846Also note that, despite what autoconf claims, setting `CFLAGS` will not 847accomplish anything. Instead use `--with-extra-cflags` (and similar for 848`cxxflags` and `ldflags`). 849 850## Running Make 851 852When you have a proper configuration, all you need to do to build OpenJDK is to 853run `make`. (But see the warning at [GNU Make](#gnu-make) about running the 854correct version of make.) 855 856When running `make` without any arguments, the default target is used, which is 857the same as running `make default` or `make jdk`. This will build a minimal (or 858roughly minimal) set of compiled output (known as an "exploded image") needed 859for a developer to actually execute the newly built JDK. The idea is that in an 860incremental development fashion, when doing a normal make, you should only 861spend time recompiling what's changed (making it purely incremental) and only 862do the work that's needed to actually run and test your code. 863 864The output of the exploded image resides in `$BUILD/jdk`. You can test the 865newly built JDK like this: `$BUILD/jdk/bin/java -version`. 866 867### Common Make Targets 868 869Apart from the default target, here are some common make targets: 870 871 * `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 882 883Run `make help` to get an up-to-date list of important make targets and make 884control variables. 885 886It is possible to build just a single module, a single phase, or a single phase 887of a single module, by creating make targets according to these followin 888patterns. 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. 891 892 * `<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 896 897Similarly, it is possible to clean just a part of the build by creating make 898targets according to these patterns: 899 900 * `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 906 907### Make Control Variables 908 909It is possible to control `make` behavior by overriding the value of `make` 910variables, either on the command line or in the environment. 911 912Normally, this is **not recommended**. If used improperly, it can lead to a 913broken build. Unless you're well versed in the build system, this is hard to 914use properly. Therefore, `make` will print a warning if this is detected. 915 916However, there are a few `make` variables, known as *control variables* that 917are supposed to be overriden on the command line. These make up the "make time" 918configuration, as opposed to the "configure time" configuration. 919 920#### General Make Control Variables 921 922 * `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) 928 929#### Test Make Control Variables 930 931These make control variables only make sense when running tests. Please see 932[Testing OpenJDK](testing.html) for details. 933 934 * `TEST` 935 * `TEST_JOBS` 936 * `JTREG` 937 * `GTEST` 938 939#### Advanced Make Control Variables 940 941These advanced make control variables can be potentially unsafe. See [Hints and 942Suggestions for Advanced Users](#hints-and-suggestions-for-advanced-users) and 943[Understanding the Build System](#understanding-the-build-system) for details. 944 945 * `SPEC` 946 * `CONF_CHECK` 947 * `COMPARE_BUILD` 948 * `JDK_FILTER` 949 950## Running Tests 951 952Most of the OpenJDK tests are using the [JTReg](http://openjdk.java.net/jtreg) 953test framework. Make sure that your configuration knows where to find your 954installation 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. 956Note that this option should point to the JTReg home, i.e. the top directory, 957containing `lib/jtreg.jar` etc. 958 959To execute the most basic tests (tier 1), use: 960``` 961make run-test-tier1 962``` 963 964For more details on how to run tests, please see the [Testing 965OpenJDK](testing.html) document. 966 967## Cross-compiling 968 969Cross-compiling means using one platform (the *build* platform) to generate 970output that can ran on another platform (the *target* platform). 971 972The typical reason for cross-compiling is that the build is performed on a more 973powerful desktop computer, but the resulting binaries will be able to run on a 974different, typically low-performing system. Most of the complications that 975arise when building for embedded is due to this separation of *build* and 976*target* systems. 977 978This requires a more complex setup and build procedure. This section assumes 979you are familiar with cross-compiling in general, and will only deal with the 980particularities of cross-compiling OpenJDK. If you are new to cross-compiling, 981please see the [external links at Wikipedia]( 982https://en.wikipedia.org/wiki/Cross_compiler#External_links) for a good start 983on reading materials. 984 985Cross-compiling OpenJDK requires you to be able to build both for the build 986platform and for the target platform. The reason for the former is that we need 987to build and execute tools during the build process, both native tools and Java 988tools. 989 990If all you want to do is to compile a 32-bit version, for the same OS, on a 99164-bit machine, consider using `--with-target-bits=32` instead of doing a 992full-blown cross-compilation. (While this surely is possible, it's a lot more 993work and will take much longer to build.) 994 995### Boot JDK and Build JDK 996 997When cross-compiling, make sure you use a boot JDK that runs on the *build* 998system, and not on the *target* system. 999 1000To be able to build, we need a "Build JDK", which is a JDK built from the 1001current sources (that is, the same as the end result of the entire build 1002process), 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 1004building JDK 9.) 1005 1006The build process will create a minimal Build JDK for you, as part of building. 1007To speed up the build, you can use `--with-build-jdk` to `configure` to point 1008to a pre-built Build JDK. Please note that the build result is unpredictable, 1009and can possibly break in subtle ways, if the Build JDK does not **exactly** 1010match the current sources. 1011 1012### Specifying the Target Platform 1013 1014You *must* specify the target platform when cross-compiling. Doing so will also 1015automatically turn the build into a cross-compiling mode. The simplest way to 1016do this is to use the `--openjdk-target` argument, e.g. 1017`--openjdk-target=arm-linux-gnueabihf`. or `--openjdk-target=aarch64-oe-linux`. 1018This will automatically set the `--build`, `--host` and `--target` options for 1019autoconf, which can otherwise be confusing. (In autoconf terminology, the 1020"target" is known as "host", and "target" is used for building a Canadian 1021cross-compiler.) 1022 1023### Toolchain Considerations 1024 1025You will need two copies of your toolchain, one which generates output that can 1026run on the target system (the normal, or *target*, toolchain), and one that 1027generates output that can run on the build system (the *build* toolchain). Note 1028that cross-compiling is only supported for gcc at the time being. The gcc 1029standard is to prefix cross-compiling toolchains with the target denominator. 1030If you follow this standard, `configure` is likely to pick up the toolchain 1031correctly. 1032 1033The *build* toolchain will be autodetected just the same way the normal 1034*build*/*target* toolchain will be autodetected when not cross-compiling. If 1035this is not what you want, or if the autodetection fails, you can specify a 1036devkit containing the *build* toolchain using `--with-build-devkit` to 1037`configure`, or by giving `BUILD_CC` and `BUILD_CXX` arguments. 1038 1039It is often helpful to locate the cross-compilation tools, headers and 1040libraries in a separate directory, outside the normal path, and point out that 1041directory to `configure`. Do this by setting the sysroot (`--with-sysroot`) and 1042appending the directory when searching for cross-compilations tools 1043(`--with-toolchain-path`). As a compact form, you can also use `--with-devkit` 1044to point to a single directory, if it is correctly setup. (See `basics.m4` for 1045details.) 1046 1047If you are unsure what toolchain and versions to use, these have been proved 1048working at the time of writing: 1049 1050 * [aarch64]( 1051https://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]( 1053https://launchpad.net/linaro-toolchain-unsupported/trunk/2012.09/+download/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux.tar.bz2) 1054 1055### Native Libraries 1056 1057You will need copies of external native libraries for the *target* system, 1058present on the *build* machine while building. 1059 1060Take care not to replace the *build* system's version of these libraries by 1061mistake, since that can render the *build* machine unusable. 1062 1063Make sure that the libraries you point to (ALSA, X11, etc) are for the 1064*target*, not the *build*, platform. 1065 1066#### ALSA 1067 1068You will need alsa libraries suitable for your *target* system. For most cases, 1069using Debian's pre-built libraries work fine. 1070 1071Note that alsa is needed even if you only want to build a headless JDK. 1072 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. 1076 1077 * Install the libraries into the cross-compilation toolchain. For instance: 1078``` 1079cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc 1080dpkg-deb -x /tmp/libasound2_1.0.25-4_armhf.deb . 1081dpkg-deb -x /tmp/libasound2-dev_1.0.25-4_armhf.deb . 1082``` 1083 1084 * If alsa is not properly detected by `configure`, you can point it out by 1085 `--with-alsa`. 1086 1087#### X11 1088 1089You will need X11 libraries suitable for your *target* system. For most cases, 1090using Debian's pre-built libraries work fine. 1091 1092Note that X11 is needed even if you only want to build a headless JDK. 1093 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 1115 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 ``` 1126 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 ``` 1134 1135 * If the X11 libraries are not properly detected by `configure`, you can 1136 point them out by `--with-x`. 1137 1138### Building for ARM/aarch64 1139 1140A common cross-compilation target is the ARM CPU. When building for ARM, it is 1141useful to set the ABI profile. A number of pre-defined ABI profiles are 1142available using `--with-abi-profile`: arm-vfp-sflt, arm-vfp-hflt, arm-sflt, 1143armv5-vfp-sflt, armv6-vfp-hflt. Note that soft-float ABIs are no longer 1144properly supported on OpenJDK. 1145 1146OpenJDK contains two different ports for the aarch64 platform, one is the 1147original aarch64 port from the [AArch64 Port Project]( 1148http://openjdk.java.net/projects/aarch64-port) and one is a 64-bit version of 1149the Oracle contributed ARM port. When targeting aarch64, by the default the 1150original 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. 1153 1154### Verifying the Build 1155 1156The build will end up in a directory named like 1157`build/linux-arm-normal-server-release`. 1158 1159Inside this build output directory, the `images/jdk` and `images/jre` will 1160contain the newly built JDK and JRE, respectively, for your *target* system. 1161 1162Copy these folders to your *target* system. Then you can run e.g. 1163`images/jdk/bin/java -version`. 1164 1165## Build Performance 1166 1167Building OpenJDK requires a lot of horsepower. Some of the build tools can be 1168adjusted to utilize more or less of resources such as parallel threads and 1169memory. The `configure` script analyzes your system and selects reasonable 1170values for such options based on your hardware. If you encounter resource 1171problems, such as out of memory conditions, you can modify the detected values 1172with: 1173 1174 * `--with-num-cores` -- number of cores in the build system, e.g. 1175 `--with-num-cores=8`. 1176 1177 * `--with-memory-size` -- memory (in MB) available in the build system, e.g. 1178 `--with-memory-size=1024` 1179 1180You 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 1182to `make`. In most cases it will be ignored by the makefiles, but it can cause 1183problems for some make targets. 1184 1185It might also be necessary to specify the JVM arguments passed to the Boot JDK, 1186using e.g. `--with-boot-jdk-jvmargs="-Xmx8G"`. Doing so will override the 1187default JVM arguments passed to the Boot JDK. 1188 1189At the end of a successful execution of `configure`, you will get a performance 1190summary, indicating how well the build will perform. Here you will also get 1191performance hints. If you want to build fast, pay attention to those! 1192 1193If you want to tweak build performance, run with `make LOG=info` to get a build 1194time summary at the end of the build process. 1195 1196### Disk Speed 1197 1198If you are using network shares, e.g. via NFS, for your source code, make sure 1199the build directory is situated on local disk (e.g. by `ln -s 1200/localdisk/jdk-build $JDK-SHARE/build`). The performance penalty is extremely 1201high for building on a network share; close to unusable. 1202 1203Also, make sure that your build tools (including Boot JDK and toolchain) is 1204located on a local disk and not a network share. 1205 1206As has been stressed elsewhere, do use SSD for source code and build directory, 1207as well as (if possible) the build tools. 1208 1209### Virus Checking 1210 1211The use of virus checking software, especially on Windows, can *significantly* 1212slow down building of OpenJDK. If possible, turn off such software, or exclude 1213the directory containing the OpenJDK source code from on-the-fly checking. 1214 1215### Ccache 1216 1217The OpenJDK build supports building with ccache when using gcc or clang. Using 1218ccache can radically speed up compilation of native code if you often rebuild 1219the same sources. Your milage may vary however, so we recommend evaluating it 1220for yourself. To enable it, make sure it's on the path and configure with 1221`--enable-ccache`. 1222 1223### Precompiled Headers 1224 1225By default, the Hotspot build uses preccompiled headers (PCH) on the toolchains 1226were it is properly supported (clang, gcc, and Visual Studio). Normally, this 1227speeds up the build process, but in some circumstances, it can actually slow 1228things down. 1229 1230You can experiment by disabling precompiled headers using 1231`--disable-precompiled-headers`. 1232 1233### Icecc / icecream 1234 1235[icecc/icecream](http://github.com/icecc/icecream) is a simple way to setup a 1236distributed compiler network. If you have multiple machines available for 1237building OpenJDK, you can drastically cut individual build times by utilizing 1238it. 1239 1240To use, setup an icecc network, and install icecc on the build machine. Then 1241run `configure` using `--enable-icecc`. 1242 1243### Using sjavac 1244 1245To speed up Java compilation, especially incremental compilations, you can try 1246the experimental sjavac compiler by using `--enable-sjavac`. 1247 1248### Building the Right Target 1249 1250Selecting the proper target to build can have dramatic impact on build time. 1251For normal usage, `jdk` or the default target is just fine. You only need to 1252build `images` for shipping, or if your tests require it. 1253 1254See also [Using Fine-Grained Make Targets](#using-fine-grained-make-targets) on 1255how to build an even smaller subset of the product. 1256 1257## Troubleshooting 1258 1259If your build fails, it can sometimes be difficult to pinpoint the problem or 1260find a proper solution. 1261 1262### Locating the Source of the Error 1263 1264When a build fails, it can be hard to pinpoint the actual cause of the error. 1265In a typical build process, different parts of the product build in parallel, 1266with the output interlaced. 1267 1268#### Build Failure Summary 1269 1270To help you, the build system will print a failure summary at the end. It looks 1271like this: 1272 1273``` 1274ERROR: Build failed for target 'hotspot' in configuration 'linux-x64' (exit code 2) 1275 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) 1280 1281* All command lines available in /localhome/hg/jdk9-sandbox/build/linux-x64/make-support/failure-logs. 1282=== End of repeated output === 1283 1284=== Make failed targets repeated here === 1285lib/CompileJvm.gmk:207: recipe for target '/localhome/hg/jdk9-sandbox/build/linux-x64/hotspot/variant-server/libjvm/objs/psMemoryPool.o' failed 1286make/Main.gmk:263: recipe for target 'hotspot-server-libs' failed 1287=== End of repeated output === 1288 1289Hint: Try searching the build log for the name of the first failed target. 1290Hint: If caused by a warning, try configure --disable-warnings-as-errors. 1291``` 1292 1293Let's break it down! First, the selected configuration, and the top-level 1294target you entered on the command line that caused the failure is printed. 1295 1296Then, between the `Output from failing command(s) repeated here` and `End of 1297repeated output` the first lines of output (stdout and stderr) from the actual 1298failing command is repeated. In most cases, this is the error message that 1299caused the build to fail. If multiple commands were failing (this can happen in 1300a parallel build), output from all failed commands will be printed here. 1301 1302The path to the `failure-logs` directory is printed. In this file you will find 1303a `<target>.log` file that contains the output from this command in its 1304entirety, and also a `<target>.cmd`, which contain the complete command line 1305used for running this command. You can re-run the failing command by executing 1306`. <path to failure-logs>/<target>.cmd` in your shell. 1307 1308Another way to trace the failure is to follow the chain of make targets, from 1309top-level targets to individual file targets. Between `Make failed targets 1310repeated here` and `End of repeated output` the output from make showing this 1311chain is repeated. The first failed recipe will typically contain the full path 1312to the file in question that failed to compile. Following lines will show a 1313trace of make targets why we ended up trying to compile that file. 1314 1315Finally, some hints are given on how to locate the error in the complete log. 1316In this example, we would try searching the log file for "`psMemoryPool.o`". 1317Another way to quickly locate make errors in the log is to search for "`] 1318Error`" or "`***`". 1319 1320Note that the build failure summary will only help you if the issue was a 1321compilation failure or similar. If the problem is more esoteric, or is due to 1322errors in the build machinery, you will likely get empty output logs, and `No 1323indication of failed target found` instead of the make target chain. 1324 1325#### Checking the Build Log File 1326 1327The 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 1329means that it is not necessary to redirect the build output yourself if you 1330want to process it. 1331 1332You can increase the verbosity of the log file, by the `LOG` control variable 1333to `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` 1335or `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 1337executed by make, and `trace` will show all. Beware that both these log levels 1338will produce a massive build log! 1339 1340### Fixing Unexpected Build Failures 1341 1342Most of the time, the build will fail due to incorrect changes in the source 1343code. 1344 1345Sometimes the build can fail with no apparent changes that have caused the 1346failure. If this is the first time you are building OpenJDK on this particular 1347computer, and the build fails, the problem is likely with your build 1348environment. But even if you have previously built OpenJDK with success, and it 1349now fails, your build environment might have changed (perhaps due to OS 1350upgrades or similar). But most likely, such failures are due to problems with 1351the incremental rebuild. 1352 1353#### Problems with the Build Environment 1354 1355Make sure your configuration is correct. Re-run `configure`, and look for any 1356warnings. Warnings that appear in the middle of the `configure` output is also 1357repeated at the end, after the summary. The entire log is stored in 1358`$BUILD/configure.log`. 1359 1360Verify that the summary at the end looks correct. Are you indeed using the Boot 1361JDK and native toolchain that you expect? 1362 1363By default, OpenJDK has a strict approach where warnings from the compiler is 1364considered errors which fail the build. For very new or very old compiler 1365versions, this can trigger new classes of warnings, which thus fails the build. 1366Run `configure` with `--disable-warnings-as-errors` to turn of this behavior. 1367(The warnings will still show, but not make the build fail.) 1368 1369#### Problems with Incremental Rebuilds 1370 1371Incremental rebuilds mean that when you modify part of the product, only the 1372affected parts get rebuilt. While this works great in most cases, and 1373significantly speed up the development process, from time to time complex 1374interdependencies will result in an incorrect build result. This is the most 1375common cause for unexpected build problems, together with inconsistencies 1376between the different Mercurial repositories in the forest. 1377 1378Here are a suggested list of things to try if you are having unexpected build 1379problems. Each step requires more time than the one before, so try them in 1380order. Most issues will be solved at step 1 or 2. 1381 1382 1. Make sure your forest is up-to-date 1383 1384 Run `bash get_source.sh` to make sure you have the latest version of all 1385 repositories. 1386 1387 2. Clean build results 1388 1389 The simplest way to fix incremental rebuild issues is to run `make clean`. 1390 This will remove all build results, but not the configuration or any build 1391 system support artifacts. In most cases, this will solve build errors 1392 resulting from incremental build mismatches. 1393 1394 3. Completely clean the build directory. 1395 1396 If this does not work, the next step is to run `make dist-clean`, or 1397 removing the build output directory (`$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: 1402 1403 ``` 1404 make print-configuration > current-configuration 1405 make dist-clean 1406 bash configure $(cat current-configuration) 1407 make 1408 ``` 1409 1410 4. Re-clone the Mercurial forest 1411 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`. 1417 1418### Specific Build Issues 1419 1420#### Clock Skew 1421 1422If you get an error message like this: 1423``` 1424File 'xxx' has modification time in the future. 1425Clock skew detected. Your build may be incomplete. 1426``` 1427then the clock on your build machine is out of sync with the timestamps on the 1428source files. Other errors, apparently unrelated but in fact caused by the 1429clock skew, can occur along with the clock skew warnings. These secondary 1430errors may tend to obscure the fact that the true root cause of the problem is 1431an out-of-sync clock. 1432 1433If you see these warnings, reset the clock on the build machine, run `make 1434clean` and restart the build. 1435 1436#### Out of Memory Errors 1437 1438On Solaris, you might get an error message like this: 1439``` 1440Trouble writing out table to disk 1441``` 1442To solve this, increase the amount of swap space on your build machine. 1443 1444On Windows, you might get error messages like this: 1445``` 1446fatal error - couldn't allocate heap 1447cannot create ... Permission denied 1448spawn failed 1449``` 1450This can be a sign of a Cygwin problem. See the information about solving 1451problems in the [Cygwin](#cygwin) section. Rebooting the computer might help 1452temporarily. 1453 1454### Getting Help 1455 1456If none of the suggestions in this document helps you, or if you find what you 1457believe is a bug in the build system, please contact the Build Group by sending 1458a mail to [build-dev@openjdk.java.net](mailto:build-dev@openjdk.java.net). 1459Please include the relevant parts of the configure and/or build log. 1460 1461If you need general help or advice about developing for OpenJDK, you can also 1462contact the Adoption Group. See the section on [Contributing to OpenJDK]( 1463#contributing-to-openjdk) for more information. 1464 1465## Hints and Suggestions for Advanced Users 1466 1467### Setting Up a Forest for Pushing Changes (defpath) 1468 1469To help you prepare a proper push path for a Mercurial repository, there exists 1470a useful tool known as [defpath]( 1471http://openjdk.java.net/projects/code-tools/defpath). It will help you setup a 1472proper push path for pushing changes to OpenJDK. 1473 1474Install the extension by cloning 1475`http://hg.openjdk.java.net/code-tools/defpath` and updating your `.hgrc` file. 1476Here's one way to do this: 1477 1478``` 1479cd ~ 1480mkdir hg-ext 1481cd hg-ext 1482hg clone http://hg.openjdk.java.net/code-tools/defpath 1483cat << EOT >> ~/.hgrc 1484[extensions] 1485defpath=~/hg-ext/defpath/defpath.py 1486EOT 1487``` 1488 1489You can now setup a proper push path using: 1490``` 1491hg defpath -d -u <your OpenJDK username> 1492``` 1493 1494If you also have the `trees` extension installed in Mercurial, you will 1495automatically 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 1497will get setup automatically. This is the recommended usage. 1498 1499### Bash Completion 1500 1501The `configure` and `make` commands tries to play nice with bash command-line 1502completion (using `<tab>` or `<tab><tab>`). To use this functionality, make 1503sure you enable completion in your `~/.bashrc` (see instructions for bash in 1504your operating system). 1505 1506Make completion will work out of the box, and will complete valid make targets. 1507For instance, typing `make jdk-i<tab>` will complete to `make jdk-image`. 1508 1509The `configure` script can get completion for options, but for this to work you 1510need to help `bash` on the way. The standard way of running the script, `bash 1511configure`, will not be understood by bash completion. You need `configure` to 1512be the command to run. One way to achieve this is to add a simple helper script 1513to your path: 1514 1515``` 1516cat << EOT > /tmp/configure 1517#!/bin/bash 1518if [ \$(pwd) = \$(cd \$(dirname \$0); pwd) ] ; then 1519 echo >&2 "Abort: Trying to call configure helper recursively" 1520 exit 1 1521fi 1522 1523bash \$PWD/configure "\$@" 1524EOT 1525chmod +x /tmp/configure 1526sudo mv /tmp/configure /usr/local/bin 1527``` 1528 1529Now `configure --en<tab>-dt<tab>` will result in `configure --enable-dtrace`. 1530 1531### Using Multiple Configurations 1532 1533You can have multiple configurations for a single source forest. When you 1534create a new configuration, run `configure --with-conf-name=<name>` to create a 1535configuration with the name `<name>`. Alternatively, you can create a directory 1536under `build` and run `configure` from there, e.g. `mkdir build/<name> && cd 1537build/<name> && bash ../../configure`. 1538 1539Then you can build that configuration using `make CONF_NAME=<name>` or `make 1540CONF=<pattern>`, where `<pattern>` is a substring matching one or several 1541configurations, e.g. `CONF=debug`. The special empty pattern (`CONF=`) will 1542match *all* available configuration, so `make CONF= hotspot` will build the 1543`hotspot` target for all configurations. Alternatively, you can execute `make` 1544in the configuration directory, e.g. `cd build/<name> && make`. 1545 1546### Handling Reconfigurations 1547 1548If you update the forest and part of the configure script has changed, the 1549build system will force you to re-run `configure`. 1550 1551Most of the time, you will be fine by running `configure` again with the same 1552arguments as the last time, which can easily be performed by `make 1553reconfigure`. To simplify this, you can use the `CONF_CHECK` make control 1554variable, either as `make CONF_CHECK=auto`, or by setting an environment 1555variable. For instance, if you add `export CONF_CHECK=auto` to your `.bashrc` 1556file, `make` will always run `reconfigure` automatically whenever the configure 1557script has changed. 1558 1559You can also use `CONF_CHECK=ignore` to skip the check for a needed configure 1560update. This might speed up the build, but comes at the risk of an incorrect 1561build result. This is only recommended if you know what you're doing. 1562 1563From time to time, you will also need to modify the command line to `configure` 1564due to changes. Use `make print-configure` to show the command line used for 1565your current configuration. 1566 1567### Using Fine-Grained Make Targets 1568 1569The default behavior for make is to create consistent and correct output, at 1570the expense of build speed, if necessary. 1571 1572If you are prepared to take some risk of an incorrect build, and know enough of 1573the system to understand how things build and interact, you can speed up the 1574build process considerably by instructing make to only build a portion of the 1575product. 1576 1577#### Building Individual Modules 1578 1579The safe way to use fine-grained make targets is to use the module specific 1580make targets. All source code in JDK 9 is organized so it belongs to a module, 1581e.g. `java.base` or `jdk.jdwp.agent`. You can build only a specific module, by 1582giving it as make target: `make jdk.jdwp.agent`. If the specified module 1583depends on other modules (e.g. `java.base`), those modules will be built first. 1584 1585You can also specify a set of modules, just as you can always specify a set of 1586make targets: `make jdk.crypto.cryptoki jdk.crypto.ec jdk.crypto.mscapi 1587jdk.crypto.ucrypto` 1588 1589#### Building Individual Module Phases 1590 1591The build process for each module is divided into separate phases. Not all 1592modules need all phases. Which are needed depends on what kind of source code 1593and other artifact the module consists of. The phases are: 1594 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) 1602 1603You 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`, 1605use `make java.base-gensrc`. 1606 1607Note that some phases may depend on others, e.g. `java` depends on `gensrc` (if 1608present). Make will build all needed prerequisites before building the 1609requested phase. 1610 1611#### Skipping the Dependency Check 1612 1613When using an iterative development style with frequent quick rebuilds, the 1614dependency check made by make can take up a significant portion of the time 1615spent on the rebuild. In such cases, it can be useful to bypass the dependency 1616check in make. 1617 1618> **Note that if used incorrectly, this can lead to a broken build!** 1619 1620To achieve this, append `-only` to the build target. For instance, `make 1621jdk.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 1623build can fail. On the other hand, the execution time measures in milliseconds. 1624 1625A useful pattern is to build the first time normally (e.g. `make 1626jdk.jdwp.agent`) and then on subsequent builds, use the `-only` make target. 1627 1628#### Rebuilding Part of java.base (JDK\_FILTER) 1629 1630If you are modifying files in `java.base`, which is the by far largest module 1631in OpenJDK, then you need to rebuild all those files whenever a single file has 1632changed. (This inefficiency will hopefully be addressed in JDK 10.) 1633 1634As a hack, you can use the make control variable `JDK_FILTER` to specify a 1635pattern that will be used to limit the set of files being recompiled. For 1636instance, `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 1638to files in the `javax.crypto` package. 1639 1640### Learn About Mercurial 1641 1642To become an efficient OpenJDK developer, it is recommended that you invest in 1643learning Mercurial properly. Here are some links that can get you started: 1644 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/) 1649 1650## Understanding the Build System 1651 1652This section will give you a more technical description on the details of the 1653build system. 1654 1655### Configurations 1656 1657The build system expects to find one or more configuration. These are 1658technically defined by the `spec.gmk` in a subdirectory to the `build` 1659subdirectory. The `spec.gmk` file is generated by `configure`, and contains in 1660principle the configuration (directly or by files included by `spec.gmk`). 1661 1662You can, in fact, select a configuration to build by pointing to the `spec.gmk` 1663file with the `SPEC` make control variable, e.g. `make SPEC=$BUILD/spec.gmk`. 1664While this is not the recommended way to call `make` as a user, it is what is 1665used under the hood by the build system. 1666 1667### Build Output Structure 1668 1669The build output for a configuration will end up in `build/<configuration 1670name>`, which we refer to as `$BUILD` in this document. The `$BUILD` directory 1671contains the following important directories: 1672 1673``` 1674buildtools/ 1675configure-support/ 1676hotspot/ 1677images/ 1678jdk/ 1679make-support/ 1680support/ 1681test-results/ 1682test-support/ 1683``` 1684 1685This is what they are used for: 1686 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`. 1689 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`. 1692 1693 * `test-results`: This directory contains the results from running tests. 1694 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. 1701 1702 * `buildtools`: This is an area for tools compiled for the build platform 1703 that are used during the rest of the build. 1704 1705 * `hotspot`: This is an area for intermediate files needed when building 1706 hotspot. 1707 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. 1711 1712### Fixpath 1713 1714Windows 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 1716mismatch when running on Windows. 1717 1718In the OpenJDK build, we always use Unix paths internally, and only just before 1719calling a tool that does not understand Unix paths do we convert them to 1720Windows paths. 1721 1722This conversion is done by the `fixpath` tool, which is a small wrapper that 1723modifies unix-style paths to Windows-style paths in command lines. Fixpath is 1724compiled automatically by `configure`. 1725 1726### Native Debug Symbols 1727 1728Native libraries and executables can have debug symbol (and other debug 1729information) associated with them. How this works is very much platform 1730dependent, but a common problem is that debug symbol information takes a lot of 1731disk space, but is rarely needed by the end user. 1732 1733The OpenJDK supports different methods on how to handle debug symbols. The 1734method used is selected by `--with-native-debug-symbols`, and available methods 1735are `none`, `internal`, `external`, `zipped`. 1736 1737 * `none` means that no debug symbols will be generated during the build. 1738 1739 * `internal` means that debug symbols will be generated during the build, and 1740 they will be stored in the generated binary. 1741 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). 1745 1746 * `zipped` is like `external`, but the .debuginfo file will also be zipped 1747 into a `.diz` file. 1748 1749When building for distribution, `zipped` is a good solution. Binaries built 1750with `internal` is suitable for use by developers, since they facilitate 1751debugging, but should be stripped before distributed to end users. 1752 1753### Autoconf Details 1754 1755The `configure` script is based on the autoconf framework, but in some details 1756deviate from a normal autoconf `configure` script. 1757 1758The `configure` script in the top level directory of OpenJDK is just a thin 1759wrapper that calls `common/autoconf/configure`. This in turn provides 1760functionality that is not easily expressed in the normal Autoconf framework, 1761and then calls into the core of the `configure` script, which is the 1762`common/autoconf/generated-configure.sh` file. 1763 1764As the name implies, this file is generated by Autoconf. It is checked in after 1765regeneration, to alleviate the common user to have to install Autoconf. 1766 1767The build system will detect if the Autoconf source files have changed, and 1768will trigger a regeneration of `common/autoconf/generated-configure.sh` if 1769needed. You can also manually request such an update by `bash 1770common/autoconf/autogen.sh`. 1771 1772If you make changes to the build system that requires a re-generation, note the 1773following: 1774 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. 1779 1780 * You do not need to include the generated file in reviews. 1781 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. 1785 1786### Developing the Build System Itself 1787 1788This section contains a few remarks about how to develop for the build system 1789itself. It is not relevant if you are only making changes in the product source 1790code. 1791 1792While technically using `make`, the make source files of the OpenJDK does not 1793resemble most other Makefiles. Instead of listing specific targets and actions 1794(perhaps using patterns), the basic modus operandi is to call a high-level 1795function (or properly, macro) from the API in `make/common`. For instance, to 1796compile all classes in the `jdk.internal.foo` package in the `jdk.foo` module, 1797a call like this would be made: 1798 1799``` 1800$(eval $(call SetupJavaCompilation, BUILD_FOO_CLASSES, \ 1801 SETUP := GENERATE_OLDBYTECODE, \ 1802 SRC := $(JDK_TOPDIR)/src/jkd.foo/share/classes, \ 1803 INCLUDES := jdk/internal/foo, \ 1804 BIN := $(SUPPORT_OUTPUTDIR)/foo_classes, \ 1805)) 1806``` 1807 1808By encapsulating and expressing the high-level knowledge of *what* should be 1809done, rather than *how* it should be done (as is normal in Makefiles), we can 1810build a much more powerful and flexible build system. 1811 1812Correct dependency tracking is paramount. Sloppy dependency tracking will lead 1813to improper parallelization, or worse, race conditions. 1814 1815To test for/debug race conditions, try running `make JOBS=1` and `make 1816JOBS=100` and see if it makes any difference. (It shouldn't). 1817 1818To compare the output of two different builds and see if, and how, they differ, 1819run `$BUILD1/compare.sh -o $BUILD2`, where `$BUILD1` and `$BUILD2` are the two 1820builds you want to compare. 1821 1822To automatically build two consecutive versions and compare them, use 1823`COMPARE_BUILD`. The value of `COMPARE_BUILD` is a set of variable=value 1824assignments, like this: 1825``` 1826make COMPARE_BUILD=CONF=--enable-new-hotspot-feature:MAKE=hotspot 1827``` 1828See `make/InitSupport.gmk` for details on how to use `COMPARE_BUILD`. 1829 1830To analyze build performance, run with `LOG=trace` and check `$BUILD/build-trace-time.log`. 1831Use `JOBS=1` to avoid parallelism. 1832 1833Please check that you adhere to the [Code Conventions for the Build System]( 1834http://openjdk.java.net/groups/build/doc/code-conventions.html) before 1835submitting patches. Also see the section in [Autoconf Details]( 1836#autoconf-details) about the generated configure script. 1837 1838## Contributing to OpenJDK 1839 1840So, now you've build your OpenJDK, and made your first patch, and want to 1841contribute it back to the OpenJDK community. 1842 1843First of all: Thank you! We gladly welcome your contribution to the OpenJDK. 1844However, please bear in mind that OpenJDK is a massive project, and we must ask 1845you to follow our rules and guidelines to be able to accept your contribution. 1846 1847The official place to start is the ['How to contribute' page]( 1848http://openjdk.java.net/contribute/). There is also an official (but somewhat 1849outdated and skimpy on details) [Developer's Guide]( 1850http://openjdk.java.net/guide/). 1851 1852If this seems overwhelming to you, the Adoption Group is there to help you! A 1853good place to start is their ['New Contributor' page]( 1854https://wiki.openjdk.java.net/display/Adoption/New+Contributor), or start 1855reading the comprehensive [Getting Started Kit]( 1856https://adoptopenjdk.gitbooks.io/adoptopenjdk-getting-started-kit/en/). The 1857Adoption Group will also happily answer any questions you have about 1858contributing. Contact them by [mail]( 1859http://mail.openjdk.java.net/mailman/listinfo/adoption-discuss) or [IRC]( 1860http://openjdk.java.net/irc/). 1861 1862--- 1863# Override styles from the base CSS file that are not ideal for this document. 1864header-includes: 1865 - '<style type="text/css">pre, code, tt { color: #1d6ae5; }</style>' 1866--- 1867