1 % Building the JDK
   2 
   3 ## TL;DR (Instructions for the Impatient)
   4 
   5 If you are eager to try out building the JDK, these simple steps works most of
   6 the time. They assume that you have installed Mercurial (and Cygwin if running
   7 on Windows) and cloned the top-level JDK repository that you want to build.
   8 
   9  1. [Get the complete source code](#getting-the-source-code): \
  10     `hg clone http://hg.openjdk.java.net/jdk/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 
  32 If any of these steps failed, or if you want to know more about build
  33 requirements or build functionality, please continue reading this document.
  34 
  35 ## Introduction
  36 
  37 The JDK is a complex software project. Building it requires a certain amount of
  38 technical expertise, a fair number of dependencies on external software, and
  39 reasonably powerful hardware.
  40 
  41 If you just want to use the JDK and not build it yourself, this document is not
  42 for you. See for instance [OpenJDK installation](
  43 http://openjdk.java.net/install) for some methods of installing a prebuilt
  44 JDK.
  45 
  46 ## Getting the Source Code
  47 
  48 Make sure you are getting the correct version. As of JDK 10, the source is no
  49 longer split into separate repositories so you only need to clone one single
  50 repository. At the [OpenJDK Mercurial server](http://hg.openjdk.java.net/) you
  51 can see a list of all available repositories. If you want to build an older version,
  52 e.g. JDK 8, it is recommended that you get the `jdk8u` forest, which contains
  53 incremental updates, instead of the `jdk8` forest, which was frozen at JDK 8 GA.
  54 
  55 If you are new to Mercurial, a good place to start is the [Mercurial Beginner's
  56 Guide](http://www.mercurial-scm.org/guide). The rest of this document assumes a
  57 working knowledge of Mercurial.
  58 
  59 ### Special Considerations
  60 
  61 For a smooth building experience, it is recommended that you follow these rules
  62 on 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       * Clone the JDK repository using the Cygwin command line `hg` client
  93         as instructed in this document. That is, do *not* use another Mercurial
  94         client such as TortoiseHg.
  95 
  96     Failure to follow this procedure might result in hard-to-debug build
  97     problems.
  98 
  99 ## Build Hardware Requirements
 100 
 101 The JDK is a massive project, and require machines ranging from decent to
 102 powerful to be able to build in a reasonable amount of time, or to be able to
 103 complete a build at all.
 104 
 105 We *strongly* recommend usage of an SSD disk for the build, since disk speed is
 106 one of the limiting factors for build performance.
 107 
 108 ### Building on x86
 109 
 110 At a minimum, a machine with 2-4 cores is advisable, as well as 2-4 GB of RAM.
 111 (The more cores to use, the more memory you need.) At least 6 GB of free disk
 112 space is required (8 GB minimum for building on Solaris).
 113 
 114 Even for 32-bit builds, it is recommended to use a 64-bit build machine, and
 115 instead create a 32-bit target using `--with-target-bits=32`.
 116 
 117 ### Building on sparc
 118 
 119 At a minimum, a machine with 4 cores is advisable, as well as 4 GB of RAM. (The
 120 more cores to use, the more memory you need.) At least 8 GB of free disk space
 121 is required.
 122 
 123 ### Building on aarch64
 124 
 125 At a minimum, a machine with 8 cores is advisable, as well as 8 GB of RAM.
 126 (The more cores to use, the more memory you need.) At least 6 GB of free disk
 127 space is required.
 128 
 129 If you do not have access to sufficiently powerful hardware, it is also
 130 possible to use [cross-compiling](#cross-compiling).
 131 
 132 ### Building on 32-bit arm
 133 
 134 This is not recommended. Instead, see the section on [Cross-compiling](
 135 #cross-compiling).
 136 
 137 ## Operating System Requirements
 138 
 139 The mainline JDK project supports Linux, Solaris, macOS, AIX and Windows.
 140 Support for other operating system, e.g. BSD, exists in separate "port"
 141 projects.
 142 
 143 In general, the JDK can be built on a wide range of versions of these operating
 144 systems, but the further you deviate from what is tested on a daily basis, the
 145 more likely you are to run into problems.
 146 
 147 This table lists the OS versions used by Oracle when building the JDK. Such
 148 information is always subject to change, but this table is up to date at the
 149 time of writing.
 150 
 151  Operating system   Vendor/version used
 152  -----------------  -------------------------------------------------------
 153  Linux              Oracle Enterprise Linux 6.4 / 7.6
 154  Solaris            Solaris 11.3 SRU 20
 155  macOS              Mac OS X 10.13 (High Sierra)
 156  Windows            Windows Server 2012 R2
 157 
 158 The double version numbers for Linux and Solaris are due to the hybrid model
 159 used at Oracle, where header files and external libraries from an older version
 160 are used when building on a more modern version of the OS.
 161 
 162 The Build Group has a wiki page with [Supported Build Platforms](
 163 https://wiki.openjdk.java.net/display/Build/Supported+Build+Platforms). From
 164 time to time, this is updated by contributors to list successes or failures of
 165 building on different platforms.
 166 
 167 ### Windows
 168 
 169 Windows XP is not a supported platform, but all newer Windows should be able to
 170 build the JDK.
 171 
 172 On Windows, it is important that you pay attention to the instructions in the
 173 [Special Considerations](#special-considerations).
 174 
 175 Windows is the only non-POSIX OS supported by the JDK, and as such, requires
 176 some extra care. A POSIX support layer is required to build on Windows.
 177 Currently, the only supported such layers are Cygwin and Windows Subsystem for
 178 Linux (WSL). (Msys is no longer supported due to a too old bash; msys2 would
 179 likely be possible to support in a future version but that would require effort
 180 to implement.)
 181 
 182 Internally in the build system, all paths are represented as Unix-style paths,
 183 e.g. `/cygdrive/c/hg/jdk9/Makefile` rather than `C:\hg\jdk9\Makefile`. This
 184 rule also applies to input to the build system, e.g. in arguments to
 185 `configure`. So, use `--with-msvcr-dll=/cygdrive/c/msvcr100.dll` rather than
 186 `--with-msvcr-dll=c:\msvcr100.dll`. For details on this conversion, see the section
 187 on [Fixpath](#fixpath).
 188 
 189 #### Cygwin
 190 
 191 A functioning [Cygwin](http://www.cygwin.com/) environment is required for
 192 building the JDK on Windows. If you have a 64-bit OS, we strongly recommend
 193 using the 64-bit version of Cygwin.
 194 
 195 **Note:** Cygwin has a model of continuously updating all packages without any
 196 easy way to install or revert to a specific version of a package. This means
 197 that whenever you add or update a package in Cygwin, you might (inadvertently)
 198 update tools that are used by the JDK build process, and that can cause
 199 unexpected build problems.
 200 
 201 The JDK requires GNU Make 4.0 or greater in Cygwin. This is usually not a
 202 problem, since Cygwin currently only distributes GNU Make at a version above
 203 4.0.
 204 
 205 Apart from the basic Cygwin installation, the following packages must also be
 206 installed:
 207 
 208   * `autoconf`
 209   * `make`
 210   * `zip`
 211   * `unzip`
 212 
 213 Often, you can install these packages using the following command line:
 214 ```
 215 <path to Cygwin setup>/setup-x86_64 -q -P autoconf -P make -P unzip -P zip
 216 ```
 217 
 218 Unfortunately, Cygwin can be unreliable in certain circumstances. If you
 219 experience build tool crashes or strange issues when building on Windows,
 220 please check the Cygwin FAQ on the ["BLODA" list](
 221 https://cygwin.com/faq/faq.html#faq.using.bloda) and the section on [fork()
 222 failures](https://cygwin.com/faq/faq.html#faq.using.fixing-fork-failures).
 223 
 224 #### Windows Subsystem for Linux (WSL)
 225 
 226 Windows 10 1809 or newer is supported due to a dependency on the wslpath utility
 227 and support for environment variable sharing through WSLENV. Version 1803 can
 228 work but intermittent build failures have been observed.
 229 
 230 It's possible to build both Windows and Linux binaries from WSL. To build
 231 Windows binaries, you must use a Windows boot JDK (located in a
 232 Windows-accessible directory). To build Linux binaries, you must use a Linux
 233 boot JDK. The default behavior is to build for Windows. To build for Linux, pass
 234 `--build=x86_64-unknown-linux-gnu --host=x86_64-unknown-linux-gnu` to
 235 `configure`.
 236 
 237 If building Windows binaries, the source code must be located in a Windows-
 238 accessible directory. This is because Windows executables (such as Visual Studio
 239 and the boot JDK) must be able to access the source code. Also, the drive where
 240 the source is stored must be mounted as case-insensitive by changing either
 241 /etc/fstab or /etc/wsl.conf in WSL. Individual directories may be corrected
 242 using the fsutil tool in case the source was cloned before changing the mount
 243 options.
 244 
 245 Note that while it's possible to build on WSL, testing is still not fully
 246 supported.
 247 
 248 ### Solaris
 249 
 250 See `make/devkit/solaris11.1-package-list.txt` for a list of recommended
 251 packages to install when building on Solaris. The versions specified in this
 252 list is the versions used by the daily builds at Oracle, and is likely to work
 253 properly.
 254 
 255 Older versions of Solaris shipped a broken version of `objcopy`. At least
 256 version 2.21.1 is needed, which is provided by Solaris 11 Update 1. Objcopy is
 257 needed if you want to have external debug symbols. Please make sure you are
 258 using at least version 2.21.1 of objcopy, or that you disable external debug
 259 symbols.
 260 
 261 ### macOS
 262 
 263 Apple is using a quite aggressive scheme of pushing OS updates, and coupling
 264 these updates with required updates of Xcode. Unfortunately, this makes it
 265 difficult for a project such as the JDK to keep pace with a continuously updated
 266 machine running macOS. See the section on [Apple Xcode](#apple-xcode) on some
 267 strategies to deal with this.
 268 
 269 It is recommended that you use at least Mac OS X 10.13 (High Sierra). At the time
 270 of writing, the JDK has been successfully compiled on macOS 10.12 (Sierra).
 271 
 272 The standard macOS environment contains the basic tooling needed to build, but
 273 for external libraries a package manager is recommended. The JDK uses
 274 [homebrew](https://brew.sh/) in the examples, but feel free to use whatever
 275 manager you want (or none).
 276 
 277 ### Linux
 278 
 279 It is often not much problem to build the JDK on Linux. The only general advice
 280 is to try to use the compilers, external libraries and header files as provided
 281 by your distribution.
 282 
 283 The basic tooling is provided as part of the core operating system, but you
 284 will most likely need to install developer packages.
 285 
 286 For apt-based distributions (Debian, Ubuntu, etc), try this:
 287 ```
 288 sudo apt-get install build-essential
 289 ```
 290 
 291 For rpm-based distributions (Fedora, Red Hat, etc), try this:
 292 ```
 293 sudo yum groupinstall "Development Tools"
 294 ```
 295 
 296 ### AIX
 297 
 298 Please consult the AIX section of the [Supported Build Platforms](
 299 https://wiki.openjdk.java.net/display/Build/Supported+Build+Platforms) OpenJDK
 300 Build Wiki page for details about which versions of AIX are supported.
 301 
 302 ## Native Compiler (Toolchain) Requirements
 303 
 304 Large portions of the JDK consists of native code, that needs to be compiled to
 305 be able to run on the target platform. In theory, toolchain and operating
 306 system should be independent factors, but in practice there's more or less a
 307 one-to-one correlation between target operating system and toolchain.
 308 
 309  Operating system   Supported toolchain
 310  ------------------ -------------------------
 311  Linux              gcc, clang
 312  macOS              Apple Xcode (using clang)
 313  Solaris            Oracle Solaris Studio
 314  AIX                IBM XL C/C++
 315  Windows            Microsoft Visual Studio
 316 
 317 Please see the individual sections on the toolchains for version
 318 recommendations. As a reference, these versions of the toolchains are used, at
 319 the time of writing, by Oracle for the daily builds of the JDK. It should be
 320 possible to compile the JDK with both older and newer versions, but the closer
 321 you stay to this list, the more likely you are to compile successfully without
 322 issues.
 323 
 324  Operating system   Toolchain version
 325  ------------------ -------------------------------------------------------
 326  Linux              gcc 8.2.0
 327  macOS              Apple Xcode 10.1 (using clang 10.0.0)
 328  Solaris            Oracle Solaris Studio 12.6 (with compiler version 5.15)
 329  Windows            Microsoft Visual Studio 2017 update 15.9.6
 330 
 331 All compilers are expected to be able to compile to the C99 language standard,
 332 as some C99 features are used in the source code. Microsoft Visual Studio
 333 doesn't fully support C99 so in practice shared code is limited to using C99
 334 features that it does support.
 335 
 336 ### gcc
 337 
 338 The minimum accepted version of gcc is 4.8. Older versions will generate a warning
 339 by `configure` and are unlikely to work.
 340 
 341 The JDK is currently known to be able to compile with at least version 7.4 of
 342 gcc.
 343 
 344 In general, any version between these two should be usable.
 345 
 346 ### clang
 347 
 348 The minimum accepted version of clang is 3.2. Older versions will not be
 349 accepted by `configure`.
 350 
 351 To use clang instead of gcc on Linux, use `--with-toolchain-type=clang`.
 352 
 353 ### Apple Xcode
 354 
 355 The oldest supported version of Xcode is 8.
 356 
 357 You will need the Xcode command lines developers tools to be able to build
 358 the JDK. (Actually, *only* the command lines tools are needed, not the IDE.)
 359 The simplest way to install these is to run:
 360 ```
 361 xcode-select --install
 362 ```
 363 
 364 It is advisable to keep an older version of Xcode for building the JDK when
 365 updating Xcode. This [blog page](
 366 http://iosdevelopertips.com/xcode/install-multiple-versions-of-xcode.html) has
 367 good suggestions on managing multiple Xcode versions. To use a specific version
 368 of Xcode, use `xcode-select -s` before running `configure`, or use
 369 `--with-toolchain-path` to point to the version of Xcode to use, e.g.
 370 `configure --with-toolchain-path=/Applications/Xcode8.app/Contents/Developer/usr/bin`
 371 
 372 If you have recently (inadvertently) updated your OS and/or Xcode version, and
 373 the JDK can no longer be built, please see the section on [Problems with the
 374 Build Environment](#problems-with-the-build-environment), and [Getting
 375 Help](#getting-help) to find out if there are any recent, non-merged patches
 376 available for this update.
 377 
 378 ### Oracle Solaris Studio
 379 
 380 The minimum accepted version of the Solaris Studio compilers is 5.13
 381 (corresponding to Solaris Studio 12.4). Older versions will not be accepted by
 382 configure.
 383 
 384 The Solaris Studio installation should contain at least these packages:
 385 
 386  Package                                            Version
 387  -------------------------------------------------- -------------
 388  developer/solarisstudio-124/backend                12.4-1.0.6.0
 389  developer/solarisstudio-124/c++                    12.4-1.0.10.0
 390  developer/solarisstudio-124/cc                     12.4-1.0.4.0
 391  developer/solarisstudio-124/library/c++-libs       12.4-1.0.10.0
 392  developer/solarisstudio-124/library/math-libs      12.4-1.0.0.1
 393  developer/solarisstudio-124/library/studio-gccrt   12.4-1.0.0.1
 394  developer/solarisstudio-124/studio-common          12.4-1.0.0.1
 395  developer/solarisstudio-124/studio-ja              12.4-1.0.0.1
 396  developer/solarisstudio-124/studio-legal           12.4-1.0.0.1
 397  developer/solarisstudio-124/studio-zhCN            12.4-1.0.0.1
 398 
 399 Compiling with Solaris Studio can sometimes be finicky. This is the exact
 400 version used by Oracle, which worked correctly at the time of writing:
 401 ```
 402 $ cc -V
 403 cc: Sun C 5.13 SunOS_i386 2014/10/20
 404 $ CC -V
 405 CC: Sun C++ 5.13 SunOS_i386 151846-10 2015/10/30
 406 ```
 407 
 408 ### Microsoft Visual Studio
 409 
 410 The minimum accepted version of Visual Studio is 2010. Older versions will not
 411 be accepted by `configure`. The maximum accepted version of Visual Studio is
 412 2019. Versions older than 2017 are unlikely to continue working for long.
 413 
 414 If you have multiple versions of Visual Studio installed, `configure` will by
 415 default pick the latest. You can request a specific version to be used by
 416 setting `--with-toolchain-version`, e.g. `--with-toolchain-version=2015`.
 417 
 418 If you get `LINK: fatal error LNK1123: failure during conversion to COFF: file
 419 invalid` when building using Visual Studio 2010, you have encountered
 420 [KB2757355](http://support.microsoft.com/kb/2757355), a bug triggered by a
 421 specific installation order. However, the solution suggested by the KB article
 422 does not always resolve the problem. See [this stackoverflow discussion](
 423 https://stackoverflow.com/questions/10888391) for other suggestions.
 424 
 425 ### IBM XL C/C++
 426 
 427 Please consult the AIX section of the [Supported Build Platforms](
 428 https://wiki.openjdk.java.net/display/Build/Supported+Build+Platforms) OpenJDK
 429 Build Wiki page for details about which versions of XLC are supported.
 430 
 431 
 432 ## Boot JDK Requirements
 433 
 434 Paradoxically, building the JDK requires a pre-existing JDK. This is called the
 435 "boot JDK". The boot JDK does not, however, have to be a JDK built directly from
 436 the source code available in the OpenJDK Community.  If you are porting the JDK
 437 to a new platform, chances are that there already exists another JDK for that
 438 platform that is usable as boot JDK.
 439 
 440 The rule of thumb is that the boot JDK for building JDK major version *N*
 441 should be a JDK of major version *N-1*, so for building JDK 9 a JDK 8 would be
 442 suitable as boot JDK. However, the JDK should be able to "build itself", so an
 443 up-to-date build of the current JDK source is an acceptable alternative. If
 444 you are following the *N-1* rule, make sure you've got the latest update
 445 version, since JDK 8 GA might not be able to build JDK 9 on all platforms.
 446 
 447 Early in the release cycle, version *N-1* may not yet have been released. In
 448 that case, the preferred boot JDK will be version *N-2* until version *N-1*
 449 is available.
 450 
 451 If the boot JDK is not automatically detected, or the wrong JDK is picked, use
 452 `--with-boot-jdk` to point to the JDK to use.
 453 
 454 ### Getting JDK binaries
 455 
 456 JDK binaries for Linux, Windows and macOS can be downloaded from
 457 [jdk.java.net](http://jdk.java.net). An alternative is to download the
 458 [Oracle JDK](http://www.oracle.com/technetwork/java/javase/downloads). Another
 459 is the [Adopt OpenJDK Project](https://adoptopenjdk.net/), which publishes
 460 experimental prebuilt binaries for various platforms.
 461 
 462 On Linux you can also get a JDK from the Linux distribution. On apt-based
 463 distros (like Debian and Ubuntu), `sudo apt-get install openjdk-<VERSION>-jdk`
 464 is typically enough to install a JDK \<VERSION\>. On rpm-based distros (like
 465 Fedora and Red Hat), try `sudo yum install java-<VERSION>-openjdk-devel`.
 466 
 467 ## External Library Requirements
 468 
 469 Different platforms require different external libraries. In general, libraries
 470 are not optional - that is, they are either required or not used.
 471 
 472 If a required library is not detected by `configure`, you need to provide the
 473 path to it. There are two forms of the `configure` arguments to point to an
 474 external library: `--with-<LIB>=<path>` or `--with-<LIB>-include=<path to
 475 include> --with-<LIB>-lib=<path to lib>`. The first variant is more concise,
 476 but require the include files an library files to reside in a default hierarchy
 477 under this directory. In most cases, it works fine.
 478 
 479 As a fallback, the second version allows you to point to the include directory
 480 and the lib directory separately.
 481 
 482 ### FreeType
 483 
 484 FreeType2 from [The FreeType Project](http://www.freetype.org/) is not required
 485 on any platform. The exception is on Unix-based platforms when configuring such
 486 that the build artifacts will reference a system installed library,
 487 rather than bundling the JDK’s own copy.
 488 
 489   * To install on an apt-based Linux, try running `sudo apt-get install
 490     libfreetype6-dev`.
 491   * To install on an rpm-based Linux, try running `sudo yum install
 492     freetype-devel`.
 493   * To install on Solaris, try running `pkg install system/library/freetype-2`.
 494 
 495 Use `--with-freetype-include=<path>` and `--with-freetype-lib=<path>`
 496 if `configure` does not automatically locate the platform FreeType files.
 497 
 498 ### CUPS
 499 
 500 CUPS, [Common UNIX Printing System](http://www.cups.org) header files are
 501 required on all platforms, except Windows. Often these files are provided by
 502 your operating system.
 503 
 504   * To install on an apt-based Linux, try running `sudo apt-get install
 505     libcups2-dev`.
 506   * To install on an rpm-based Linux, try running `sudo yum install
 507     cups-devel`.
 508   * To install on Solaris, try running `pkg install print/cups`.
 509 
 510 Use `--with-cups=<path>` if `configure` does not properly locate your CUPS
 511 files.
 512 
 513 ### X11
 514 
 515 Certain [X11](http://www.x.org/) libraries and include files are required on
 516 Linux and Solaris.
 517 
 518   * To install on an apt-based Linux, try running `sudo apt-get install
 519     libx11-dev libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev`.
 520   * To install on an rpm-based Linux, try running `sudo yum install
 521     libXtst-devel libXt-devel libXrender-devel libXrandr-devel libXi-devel`.
 522   * To install on Solaris, try running `pkg install x11/header/x11-protocols
 523     x11/library/libice x11/library/libpthread-stubs x11/library/libsm
 524     x11/library/libx11 x11/library/libxau x11/library/libxcb
 525     x11/library/libxdmcp x11/library/libxevie x11/library/libxext
 526     x11/library/libxrender x11/library/libxrandr x11/library/libxscrnsaver
 527     x11/library/libxtst x11/library/toolkit/libxt`.
 528 
 529 Use `--with-x=<path>` if `configure` does not properly locate your X11 files.
 530 
 531 ### ALSA
 532 
 533 ALSA, [Advanced Linux Sound Architecture](https://www.alsa-project.org/) is
 534 required on Linux. At least version 0.9.1 of ALSA is required.
 535 
 536   * To install on an apt-based Linux, try running `sudo apt-get install
 537     libasound2-dev`.
 538   * To install on an rpm-based Linux, try running `sudo yum install
 539     alsa-lib-devel`.
 540 
 541 Use `--with-alsa=<path>` if `configure` does not properly locate your ALSA
 542 files.
 543 
 544 ### libffi
 545 
 546 libffi, the [Portable Foreign Function Interface Library](
 547 http://sourceware.org/libffi) is required when building the Zero version of
 548 Hotspot.
 549 
 550   * To install on an apt-based Linux, try running `sudo apt-get install
 551     libffi-dev`.
 552   * To install on an rpm-based Linux, try running `sudo yum install
 553     libffi-devel`.
 554 
 555 Use `--with-libffi=<path>` if `configure` does not properly locate your libffi
 556 files.
 557 
 558 ## Build Tools Requirements
 559 
 560 ### Autoconf
 561 
 562 The JDK requires [Autoconf](http://www.gnu.org/software/autoconf) on all
 563 platforms. At least version 2.69 is required.
 564 
 565   * To install on an apt-based Linux, try running `sudo apt-get install
 566     autoconf`.
 567   * To install on an rpm-based Linux, try running `sudo yum install
 568     autoconf`.
 569   * To install on macOS, try running `brew install autoconf`.
 570   * To install on Windows, try running `<path to Cygwin setup>/setup-x86_64 -q
 571     -P autoconf`.
 572 
 573 If `configure` has problems locating your installation of autoconf, you can
 574 specify it using the `AUTOCONF` environment variable, like this:
 575 
 576 ```
 577 AUTOCONF=<path to autoconf> configure ...
 578 ```
 579 
 580 ### GNU Make
 581 
 582 The JDK requires [GNU Make](http://www.gnu.org/software/make). No other flavors
 583 of make are supported.
 584 
 585 At least version 3.81 of GNU Make must be used. For distributions supporting
 586 GNU Make 4.0 or above, we strongly recommend it. GNU Make 4.0 contains useful
 587 functionality to handle parallel building (supported by `--with-output-sync`)
 588 and speed and stability improvements.
 589 
 590 Note that `configure` locates and verifies a properly functioning version of
 591 `make` and stores the path to this `make` binary in the configuration. If you
 592 start a build using `make` on the command line, you will be using the version
 593 of make found first in your `PATH`, and not necessarily the one stored in the
 594 configuration. This initial make will be used as "bootstrap make", and in a
 595 second stage, the make located by `configure` will be called. Normally, this
 596 will present no issues, but if you have a very old `make`, or a non-GNU Make
 597 `make` in your path, this might cause issues.
 598 
 599 If you want to override the default make found by `configure`, use the `MAKE`
 600 configure variable, e.g. `configure MAKE=/opt/gnu/make`.
 601 
 602 On Solaris, it is common to call the GNU version of make by using `gmake`.
 603 
 604 ### GNU Bash
 605 
 606 The JDK requires [GNU Bash](http://www.gnu.org/software/bash). No other shells
 607 are supported.
 608 
 609 At least version 3.2 of GNU Bash must be used.
 610 
 611 ## Running Configure
 612 
 613 To build the JDK, you need a "configuration", which consists of a directory
 614 where to store the build output, coupled with information about the platform,
 615 the specific build machine, and choices that affect how the JDK is built.
 616 
 617 The configuration is created by the `configure` script. The basic invocation of
 618 the `configure` script looks like this:
 619 
 620 ```
 621 bash configure [options]
 622 ```
 623 
 624 This will create an output directory containing the configuration and setup an
 625 area for the build result. This directory typically looks like
 626 `build/linux-x64-normal-server-release`, but the actual name depends on your
 627 specific configuration. (It can also be set directly, see [Using Multiple
 628 Configurations](#using-multiple-configurations)). This directory is referred to
 629 as `$BUILD` in this documentation.
 630 
 631 `configure` will try to figure out what system you are running on and where all
 632 necessary build components are. If you have all prerequisites for building
 633 installed, it should find everything. If it fails to detect any component
 634 automatically, it will exit and inform you about the problem.
 635 
 636 Some command line examples:
 637 
 638   * Create a 32-bit build for Windows with FreeType2 in `C:\freetype-i586`:
 639     ```
 640     bash configure --with-freetype=/cygdrive/c/freetype-i586 --with-target-bits=32
 641     ```
 642 
 643   * Create a debug build with the `server` JVM and DTrace enabled:
 644     ```
 645     bash configure --enable-debug --with-jvm-variants=server --enable-dtrace
 646     ```
 647 
 648 ### Common Configure Arguments
 649 
 650 Here follows some of the most common and important `configure` argument.
 651 
 652 To get up-to-date information on *all* available `configure` argument, please
 653 run:
 654 ```
 655 bash configure --help
 656 ```
 657 
 658 (Note that this help text also include general autoconf options, like
 659 `--dvidir`, that is not relevant to the JDK. To list only JDK-specific
 660 features, use `bash configure --help=short` instead.)
 661 
 662 #### Configure Arguments for Tailoring the Build
 663 
 664   * `--enable-debug` - Set the debug level to `fastdebug` (this is a shorthand
 665     for `--with-debug-level=fastdebug`)
 666   * `--with-debug-level=<level>` - Set the debug level, which can be `release`,
 667     `fastdebug`, `slowdebug` or `optimized`. Default is `release`. `optimized`
 668     is variant of `release` with additional Hotspot debug code.
 669   * `--with-native-debug-symbols=<method>` - Specify if and how native debug
 670     symbols should be built. Available methods are `none`, `internal`,
 671     `external`, `zipped`. Default behavior depends on platform. See [Native
 672     Debug Symbols](#native-debug-symbols) for more details.
 673   * `--with-version-string=<string>` - Specify the version string this build
 674     will be identified with.
 675   * `--with-version-<part>=<value>` - A group of options, where `<part>` can be
 676     any of `pre`, `opt`, `build`, `major`, `minor`, `security` or `patch`. Use
 677     these options to modify just the corresponding part of the version string
 678     from the default, or the value provided by `--with-version-string`.
 679   * `--with-jvm-variants=<variant>[,<variant>...]` - Build the specified variant
 680     (or variants) of Hotspot. Valid variants are: `server`, `client`,
 681     `minimal`, `core`, `zero`, `custom`. Note that not all
 682     variants are possible to combine in a single build.
 683   * `--with-jvm-features=<feature>[,<feature>...]` - Use the specified JVM
 684     features when building Hotspot. The list of features will be enabled on top
 685     of the default list. For the `custom` JVM variant, this default list is
 686     empty. A complete list of available JVM features can be found using `bash
 687     configure --help`.
 688   * `--with-target-bits=<bits>` - Create a target binary suitable for running
 689     on a `<bits>` platform. Use this to create 32-bit output on a 64-bit build
 690     platform, instead of doing a full cross-compile. (This is known as a
 691     *reduced* build.)
 692 
 693 On Linux, BSD and AIX, it is possible to override where Java by default
 694 searches for runtime/JNI libraries. This can be useful in situations where
 695 there is a special shared directory for system JNI libraries. This setting
 696 can in turn be overriden at runtime by setting the `java.library.path` property.
 697 
 698   * `--with-jni-libpath=<path>` - Use the specified path as a default
 699   when searching for runtime libraries.
 700 
 701 #### Configure Arguments for Native Compilation
 702 
 703   * `--with-devkit=<path>` - Use this devkit for compilers, tools and resources
 704   * `--with-sysroot=<path>` - Use this directory as sysroot
 705   * `--with-extra-path=<path>[;<path>]` - Prepend these directories to the
 706     default path when searching for all kinds of binaries
 707   * `--with-toolchain-path=<path>[;<path>]` - Prepend these directories when
 708     searching for toolchain binaries (compilers etc)
 709   * `--with-extra-cflags=<flags>` - Append these flags when compiling JDK C
 710     files
 711   * `--with-extra-cxxflags=<flags>` - Append these flags when compiling JDK C++
 712     files
 713   * `--with-extra-ldflags=<flags>` - Append these flags when linking JDK
 714     libraries
 715 
 716 #### Configure Arguments for External Dependencies
 717 
 718   * `--with-boot-jdk=<path>` - Set the path to the [Boot JDK](
 719     #boot-jdk-requirements)
 720   * `--with-freetype=<path>` - Set the path to [FreeType](#freetype)
 721   * `--with-cups=<path>` - Set the path to [CUPS](#cups)
 722   * `--with-x=<path>` - Set the path to [X11](#x11)
 723   * `--with-alsa=<path>` - Set the path to [ALSA](#alsa)
 724   * `--with-libffi=<path>` - Set the path to [libffi](#libffi)
 725   * `--with-jtreg=<path>` - Set the path to JTReg. See [Running Tests](
 726     #running-tests)
 727 
 728 Certain third-party libraries used by the JDK (libjpeg, giflib, libpng, lcms
 729 and zlib) are included in the JDK repository. The default behavior of the
 730 JDK build is to use the included ("bundled") versions of libjpeg, giflib,
 731 libpng and lcms.
 732 For zlib, the system lib (if present) is used except on Windows and AIX.
 733 However the bundled libraries may be replaced by an external version.
 734 To do so, specify `system` as the `<source>` option in these arguments.
 735 (The default is `bundled`).
 736 
 737   * `--with-libjpeg=<source>` - Use the specified source for libjpeg
 738   * `--with-giflib=<source>` - Use the specified source for giflib
 739   * `--with-libpng=<source>` - Use the specified source for libpng
 740   * `--with-lcms=<source>` - Use the specified source for lcms
 741   * `--with-zlib=<source>` - Use the specified source for zlib
 742 
 743 On Linux, it is possible to select either static or dynamic linking of the C++
 744 runtime. The default is static linking, with dynamic linking as fallback if the
 745 static library is not found.
 746 
 747   * `--with-stdc++lib=<method>` - Use the specified method (`static`, `dynamic`
 748     or `default`) for linking the C++ runtime.
 749 
 750 ### Configure Control Variables
 751 
 752 It is possible to control certain aspects of `configure` by overriding the
 753 value of `configure` variables, either on the command line or in the
 754 environment.
 755 
 756 Normally, this is **not recommended**. If used improperly, it can lead to a
 757 broken configuration. Unless you're well versed in the build system, this is
 758 hard to use properly. Therefore, `configure` will print a warning if this is
 759 detected.
 760 
 761 However, there are a few `configure` variables, known as *control variables*
 762 that are supposed to be overriden on the command line. These are variables that
 763 describe the location of tools needed by the build, like `MAKE` or `GREP`. If
 764 any such variable is specified, `configure` will use that value instead of
 765 trying to autodetect the tool. For instance, `bash configure
 766 MAKE=/opt/gnumake4.0/bin/make`.
 767 
 768 If a configure argument exists, use that instead, e.g. use `--with-jtreg`
 769 instead of setting `JTREGEXE`.
 770 
 771 Also note that, despite what autoconf claims, setting `CFLAGS` will not
 772 accomplish anything. Instead use `--with-extra-cflags` (and similar for
 773 `cxxflags` and `ldflags`).
 774 
 775 ## Running Make
 776 
 777 When you have a proper configuration, all you need to do to build the JDK is to
 778 run `make`. (But see the warning at [GNU Make](#gnu-make) about running the
 779 correct version of make.)
 780 
 781 When running `make` without any arguments, the default target is used, which is
 782 the same as running `make default` or `make jdk`. This will build a minimal (or
 783 roughly minimal) set of compiled output (known as an "exploded image") needed
 784 for a developer to actually execute the newly built JDK. The idea is that in an
 785 incremental development fashion, when doing a normal make, you should only
 786 spend time recompiling what's changed (making it purely incremental) and only
 787 do the work that's needed to actually run and test your code.
 788 
 789 The output of the exploded image resides in `$BUILD/jdk`. You can test the
 790 newly built JDK like this: `$BUILD/jdk/bin/java -version`.
 791 
 792 ### Common Make Targets
 793 
 794 Apart from the default target, here are some common make targets:
 795 
 796   * `hotspot` - Build all of hotspot (but only hotspot)
 797   * `hotspot-<variant>` - Build just the specified jvm variant
 798   * `images` or `product-images` - Build the JDK image
 799   * `docs` or `docs-image` - Build the documentation image
 800   * `test-image` - Build the test image
 801   * `all` or `all-images` - Build all images (product, docs and test)
 802   * `bootcycle-images` - Build images twice, second time with newly built JDK
 803     (good for testing)
 804   * `clean` - Remove all files generated by make, but not those generated by
 805     configure
 806   * `dist-clean` - Remove all files, including configuration
 807 
 808 Run `make help` to get an up-to-date list of important make targets and make
 809 control variables.
 810 
 811 It is possible to build just a single module, a single phase, or a single phase
 812 of a single module, by creating make targets according to these followin
 813 patterns. A phase can be either of `gensrc`, `gendata`, `copy`, `java`,
 814 `launchers`, `libs` or `rmic`. See [Using Fine-Grained Make Targets](
 815 #using-fine-grained-make-targets) for more details about this functionality.
 816 
 817   * `<phase>` - Build the specified phase and everything it depends on
 818   * `<module>` - Build the specified module and everything it depends on
 819   * `<module>-<phase>` - Compile the specified phase for the specified module
 820     and everything it depends on
 821 
 822 Similarly, it is possible to clean just a part of the build by creating make
 823 targets according to these patterns:
 824 
 825   * `clean-<outputdir>` - Remove the subdir in the output dir with the name
 826   * `clean-<phase>` - Remove all build results related to a certain build
 827     phase
 828   * `clean-<module>` - Remove all build results related to a certain module
 829   * `clean-<module>-<phase>` - Remove all build results related to a certain
 830     module and phase
 831 
 832 ### Make Control Variables
 833 
 834 It is possible to control `make` behavior by overriding the value of `make`
 835 variables, either on the command line or in the environment.
 836 
 837 Normally, this is **not recommended**. If used improperly, it can lead to a
 838 broken build. Unless you're well versed in the build system, this is hard to
 839 use properly. Therefore, `make` will print a warning if this is detected.
 840 
 841 However, there are a few `make` variables, known as *control variables* that
 842 are supposed to be overriden on the command line. These make up the "make time"
 843 configuration, as opposed to the "configure time" configuration.
 844 
 845 #### General Make Control Variables
 846 
 847   * `JOBS` - Specify the number of jobs to build with. See [Build
 848     Performance](#build-performance).
 849   * `LOG` - Specify the logging level and functionality. See [Checking the
 850     Build Log File](#checking-the-build-log-file)
 851   * `CONF` and `CONF_NAME` - Selecting the configuration(s) to use. See [Using
 852     Multiple Configurations](#using-multiple-configurations)
 853 
 854 #### Test Make Control Variables
 855 
 856 These make control variables only make sense when running tests. Please see
 857 [Testing the JDK](testing.html) for details.
 858 
 859   * `TEST`
 860   * `TEST_JOBS`
 861   * `JTREG`
 862   * `GTEST`
 863 
 864 #### Advanced Make Control Variables
 865 
 866 These advanced make control variables can be potentially unsafe. See [Hints and
 867 Suggestions for Advanced Users](#hints-and-suggestions-for-advanced-users) and
 868 [Understanding the Build System](#understanding-the-build-system) for details.
 869 
 870   * `SPEC`
 871   * `CONF_CHECK`
 872   * `COMPARE_BUILD`
 873   * `JDK_FILTER`
 874 
 875 ## Running Tests
 876 
 877 Most of the JDK tests are using the [JTReg](http://openjdk.java.net/jtreg)
 878 test framework. Make sure that your configuration knows where to find your
 879 installation of JTReg. If this is not picked up automatically, use the
 880 `--with-jtreg=<path to jtreg home>` option to point to the JTReg framework.
 881 Note that this option should point to the JTReg home, i.e. the top directory,
 882 containing `lib/jtreg.jar` etc.
 883 
 884 The [Adoption Group](https://wiki.openjdk.java.net/display/Adoption) provides
 885 recent builds of jtreg [here](
 886 https://adopt-openjdk.ci.cloudbees.com/job/jtreg/lastSuccessfulBuild/artifact).
 887 Download the latest `.tar.gz` file, unpack it, and point `--with-jtreg` to the
 888 `jtreg` directory that you just unpacked.
 889 
 890 To execute the most basic tests (tier 1), use:
 891 ```
 892 make run-test-tier1
 893 ```
 894 
 895 For more details on how to run tests, please see the [Testing
 896 the JDK](testing.html) document.
 897 
 898 ## Cross-compiling
 899 
 900 Cross-compiling means using one platform (the *build* platform) to generate
 901 output that can ran on another platform (the *target* platform).
 902 
 903 The typical reason for cross-compiling is that the build is performed on a more
 904 powerful desktop computer, but the resulting binaries will be able to run on a
 905 different, typically low-performing system. Most of the complications that
 906 arise when building for embedded is due to this separation of *build* and
 907 *target* systems.
 908 
 909 This requires a more complex setup and build procedure. This section assumes
 910 you are familiar with cross-compiling in general, and will only deal with the
 911 particularities of cross-compiling the JDK. If you are new to cross-compiling,
 912 please see the [external links at Wikipedia](
 913 https://en.wikipedia.org/wiki/Cross_compiler#External_links) for a good start
 914 on reading materials.
 915 
 916 Cross-compiling the JDK requires you to be able to build both for the build
 917 platform and for the target platform. The reason for the former is that we need
 918 to build and execute tools during the build process, both native tools and Java
 919 tools.
 920 
 921 If all you want to do is to compile a 32-bit version, for the same OS, on a
 922 64-bit machine, consider using `--with-target-bits=32` instead of doing a
 923 full-blown cross-compilation. (While this surely is possible, it's a lot more
 924 work and will take much longer to build.)
 925 
 926 ### Cross compiling the easy way with OpenJDK devkits
 927 
 928 The OpenJDK build system provides out-of-the box support for creating and using
 929 so called devkits. A `devkit` is basically a collection of a cross-compiling
 930 toolchain and a sysroot environment which can easily be used together with the
 931 `--with-devkit` configure option to cross compile the OpenJDK. On Linux/x86_64,
 932 the following command:
 933 ```
 934 bash configure --with-devkit=<devkit-path> --openjdk-target=ppc64-linux-gnu && make
 935 ```
 936 
 937 will configure and build OpenJDK for Linux/ppc64 assuming that `<devkit-path>`
 938 points to a Linux/x86_64 to Linux/ppc64 devkit.
 939 
 940 Devkits can be created from the `make/devkit` directory by executing:
 941 ```
 942 make [ TARGETS="<TARGET_TRIPLET>+" ] [ BASE_OS=<OS> ] [ BASE_OS_VERSION=<VER> ]
 943 ```
 944 
 945 where `TARGETS` contains one or more `TARGET_TRIPLET`s of the form
 946 described in [section 3.4 of the GNU Autobook](
 947 https://sourceware.org/autobook/autobook/autobook_17.html). If no
 948 targets are given, a native toolchain for the current platform will be
 949 created. Currently, at least the following targets are known to work:
 950 
 951  Supported devkit targets
 952  -------------------------
 953  x86_64-linux-gnu
 954  aarch64-linux-gnu
 955  arm-linux-gnueabihf
 956  ppc64-linux-gnu
 957  ppc64le-linux-gnu
 958  s390x-linux-gnu
 959 
 960 `BASE_OS` must be one of "OEL6" for Oracle Enterprise Linux 6 or
 961 "Fedora" (if not specified "OEL6" will be the default). If the base OS
 962 is "Fedora" the corresponding Fedora release can be specified with the
 963 help of the `BASE_OS_VERSION` option (with "27" as default version).
 964 If the build is successful, the new devkits can be found in the
 965 `build/devkit/result` subdirectory:
 966 ```
 967 cd make/devkit
 968 make TARGETS="ppc64le-linux-gnu aarch64-linux-gnu" BASE_OS=Fedora BASE_OS_VERSION=21
 969 ls -1 ../../build/devkit/result/
 970 x86_64-linux-gnu-to-aarch64-linux-gnu
 971 x86_64-linux-gnu-to-ppc64le-linux-gnu
 972 ```
 973 
 974 Notice that devkits are not only useful for targeting different build
 975 platforms. Because they contain the full build dependencies for a
 976 system (i.e. compiler and root file system), they can easily be used
 977 to build well-known, reliable and reproducible build environments. You
 978 can for example create and use a devkit with GCC 7.3 and a Fedora 12
 979 sysroot environment (with glibc 2.11) on Ubuntu 14.04 (which doesn't
 980 have GCC 7.3 by default) to produce OpenJDK binaries which will run on
 981 all Linux systems with runtime libraries newer than the ones from
 982 Fedora 12 (e.g. Ubuntu 16.04, SLES 11 or RHEL 6).
 983 
 984 ### Boot JDK and Build JDK
 985 
 986 When cross-compiling, make sure you use a boot JDK that runs on the *build*
 987 system, and not on the *target* system.
 988 
 989 To be able to build, we need a "Build JDK", which is a JDK built from the
 990 current sources (that is, the same as the end result of the entire build
 991 process), but able to run on the *build* system, and not the *target* system.
 992 (In contrast, the Boot JDK should be from an older release, e.g. JDK 8 when
 993 building JDK 9.)
 994 
 995 The build process will create a minimal Build JDK for you, as part of building.
 996 To speed up the build, you can use `--with-build-jdk` to `configure` to point
 997 to a pre-built Build JDK. Please note that the build result is unpredictable,
 998 and can possibly break in subtle ways, if the Build JDK does not **exactly**
 999 match the current sources.
1000 
1001 ### Specifying the Target Platform
1002 
1003 You *must* specify the target platform when cross-compiling. Doing so will also
1004 automatically turn the build into a cross-compiling mode. The simplest way to
1005 do this is to use the `--openjdk-target` argument, e.g.
1006 `--openjdk-target=arm-linux-gnueabihf`. or `--openjdk-target=aarch64-oe-linux`.
1007 This will automatically set the `--build`, `--host` and `--target` options for
1008 autoconf, which can otherwise be confusing. (In autoconf terminology, the
1009 "target" is known as "host", and "target" is used for building a Canadian
1010 cross-compiler.)
1011 
1012 ### Toolchain Considerations
1013 
1014 You will need two copies of your toolchain, one which generates output that can
1015 run on the target system (the normal, or *target*, toolchain), and one that
1016 generates output that can run on the build system (the *build* toolchain). Note
1017 that cross-compiling is only supported for gcc at the time being. The gcc
1018 standard is to prefix cross-compiling toolchains with the target denominator.
1019 If you follow this standard, `configure` is likely to pick up the toolchain
1020 correctly.
1021 
1022 The *build* toolchain will be autodetected just the same way the normal
1023 *build*/*target* toolchain will be autodetected when not cross-compiling. If
1024 this is not what you want, or if the autodetection fails, you can specify a
1025 devkit containing the *build* toolchain using `--with-build-devkit` to
1026 `configure`, or by giving `BUILD_CC` and `BUILD_CXX` arguments.
1027 
1028 It is often helpful to locate the cross-compilation tools, headers and
1029 libraries in a separate directory, outside the normal path, and point out that
1030 directory to `configure`. Do this by setting the sysroot (`--with-sysroot`) and
1031 appending the directory when searching for cross-compilations tools
1032 (`--with-toolchain-path`). As a compact form, you can also use `--with-devkit`
1033 to point to a single directory, if it is correctly setup. (See `basics.m4` for
1034 details.)
1035 
1036 If you are unsure what toolchain and versions to use, these have been proved
1037 working at the time of writing:
1038 
1039   * [aarch64](
1040 https://releases.linaro.org/archive/13.11/components/toolchain/binaries/gcc-linaro-aarch64-linux-gnu-4.8-2013.11_linux.tar.xz)
1041   * [arm 32-bit hardware floating  point](
1042 https://launchpad.net/linaro-toolchain-unsupported/trunk/2012.09/+download/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux.tar.bz2)
1043 
1044 ### Native Libraries
1045 
1046 You will need copies of external native libraries for the *target* system,
1047 present on the *build* machine while building.
1048 
1049 Take care not to replace the *build* system's version of these libraries by
1050 mistake, since that can render the *build* machine unusable.
1051 
1052 Make sure that the libraries you point to (ALSA, X11, etc) are for the
1053 *target*, not the *build*, platform.
1054 
1055 #### ALSA
1056 
1057 You will need alsa libraries suitable for your *target* system. For most cases,
1058 using Debian's pre-built libraries work fine.
1059 
1060 Note that alsa is needed even if you only want to build a headless JDK.
1061 
1062   * Go to [Debian Package Search](https://www.debian.org/distrib/packages) and
1063     search for the `libasound2` and `libasound2-dev` packages for your *target*
1064     system. Download them to /tmp.
1065 
1066   * Install the libraries into the cross-compilation toolchain. For instance:
1067 ```
1068 cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc
1069 dpkg-deb -x /tmp/libasound2_1.0.25-4_armhf.deb .
1070 dpkg-deb -x /tmp/libasound2-dev_1.0.25-4_armhf.deb .
1071 ```
1072 
1073   * If alsa is not properly detected by `configure`, you can point it out by
1074     `--with-alsa`.
1075 
1076 #### X11
1077 
1078 You will need X11 libraries suitable for your *target* system. For most cases,
1079 using Debian's pre-built libraries work fine.
1080 
1081 Note that X11 is needed even if you only want to build a headless JDK.
1082 
1083   * Go to [Debian Package Search](https://www.debian.org/distrib/packages),
1084     search for the following packages for your *target* system, and download them
1085     to /tmp/target-x11:
1086       * libxi
1087       * libxi-dev
1088       * x11proto-core-dev
1089       * x11proto-input-dev
1090       * x11proto-kb-dev
1091       * x11proto-render-dev
1092       * x11proto-xext-dev
1093       * libice-dev
1094       * libxrender
1095       * libxrender-dev
1096       * libxrandr-dev
1097       * libsm-dev
1098       * libxt-dev
1099       * libx11
1100       * libx11-dev
1101       * libxtst
1102       * libxtst-dev
1103       * libxext
1104       * libxext-dev
1105 
1106   * Install the libraries into the cross-compilation toolchain. For instance:
1107     ```
1108     cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc/usr
1109     mkdir X11R6
1110     cd X11R6
1111     for deb in /tmp/target-x11/*.deb ; do dpkg-deb -x $deb . ; done
1112     mv usr/* .
1113     cd lib
1114     cp arm-linux-gnueabihf/* .
1115     ```
1116 
1117     You can ignore the following messages. These libraries are not needed to
1118     successfully complete a full JDK build.
1119     ```
1120     cp: cannot stat `arm-linux-gnueabihf/libICE.so': No such file or directory
1121     cp: cannot stat `arm-linux-gnueabihf/libSM.so': No such file or directory
1122     cp: cannot stat `arm-linux-gnueabihf/libXt.so': No such file or directory
1123     ```
1124 
1125   * If the X11 libraries are not properly detected by `configure`, you can
1126     point them out by `--with-x`.
1127 
1128 ### Creating And Using Sysroots With qemu-deboostrap
1129 
1130 Fortunately, you can create sysroots for foreign architectures with tools
1131 provided by your OS. On Debian/Ubuntu systems, one could use `qemu-deboostrap` to
1132 create the *target* system chroot, which would have the native libraries and headers
1133 specific to that *target* system. After that, we can use the cross-compiler on the *build*
1134 system, pointing into chroot to get the build dependencies right. This allows building
1135 for foreign architectures with native compilation speed.
1136 
1137 For example, cross-compiling to AArch64 from x86_64 could be done like this:
1138 
1139   * Install cross-compiler on the *build* system:
1140 ```
1141 apt install g++-aarch64-linux-gnu gcc-aarch64-linux-gnu
1142 ```
1143 
1144   * Create chroot on the *build* system, configuring it for *target* system:
1145 ```
1146 sudo qemu-debootstrap --arch=arm64 --verbose \
1147        --include=fakeroot,build-essential,libx11-dev,libxext-dev,libxrender-dev,libxrandr-dev,libxtst-dev,libxt-dev,libcups2-dev,libfontconfig1-dev,libasound2-dev,libfreetype6-dev,libpng12-dev \
1148        --resolve-deps jessie /chroots/arm64 http://httpredir.debian.org/debian/
1149 ```
1150 
1151   * Configure and build with newly created chroot as sysroot/toolchain-path:
1152 ```
1153 CC=aarch64-linux-gnu-gcc CXX=aarch64-linux-gnu-g++ sh ./configure --openjdk-target=aarch64-linux-gnu --with-sysroot=/chroots/arm64/ --with-toolchain-path=/chroots/arm64/
1154 make images
1155 ls build/linux-aarch64-normal-server-release/
1156 ```
1157 
1158 The build does not create new files in that chroot, so it can be reused for multiple builds
1159 without additional cleanup.
1160 
1161 Architectures that are known to successfully cross-compile like this are:
1162 
1163   Target        `CC`                      `CXX`                       `--arch=...`  `--openjdk-target=...`
1164   ------------  ------------------------- --------------------------- ------------- -----------------------
1165   x86           default                   default                     i386          i386-linux-gnu
1166   armhf         gcc-arm-linux-gnueabihf   g++-arm-linux-gnueabihf     armhf         arm-linux-gnueabihf
1167   aarch64       gcc-aarch64-linux-gnu     g++-aarch64-linux-gnu       arm64         aarch64-linux-gnu
1168   ppc64el       gcc-powerpc64le-linux-gnu g++-powerpc64le-linux-gnu   ppc64el       powerpc64le-linux-gnu
1169   s390x         gcc-s390x-linux-gnu       g++-s390x-linux-gnu         s390x         s390x-linux-gnu
1170 
1171 Additional architectures might be supported by Debian/Ubuntu Ports.
1172 
1173 ### Building for ARM/aarch64
1174 
1175 A common cross-compilation target is the ARM CPU. When building for ARM, it is
1176 useful to set the ABI profile. A number of pre-defined ABI profiles are
1177 available using `--with-abi-profile`: arm-vfp-sflt, arm-vfp-hflt, arm-sflt,
1178 armv5-vfp-sflt, armv6-vfp-hflt. Note that soft-float ABIs are no longer
1179 properly supported by the JDK.
1180 
1181 ### Verifying the Build
1182 
1183 The build will end up in a directory named like
1184 `build/linux-arm-normal-server-release`.
1185 
1186 Inside this build output directory, the `images/jdk` will contain the newly
1187 built JDK, for your *target* system.
1188 
1189 Copy these folders to your *target* system. Then you can run e.g.
1190 `images/jdk/bin/java -version`.
1191 
1192 ## Build Performance
1193 
1194 Building the JDK requires a lot of horsepower. Some of the build tools can be
1195 adjusted to utilize more or less of resources such as parallel threads and
1196 memory. The `configure` script analyzes your system and selects reasonable
1197 values for such options based on your hardware. If you encounter resource
1198 problems, such as out of memory conditions, you can modify the detected values
1199 with:
1200 
1201   * `--with-num-cores` -- number of cores in the build system, e.g.
1202     `--with-num-cores=8`.
1203 
1204   * `--with-memory-size` -- memory (in MB) available in the build system, e.g.
1205     `--with-memory-size=1024`
1206 
1207 You can also specify directly the number of build jobs to use with
1208 `--with-jobs=N` to `configure`, or `JOBS=N` to `make`. Do not use the `-j` flag
1209 to `make`. In most cases it will be ignored by the makefiles, but it can cause
1210 problems for some make targets.
1211 
1212 It might also be necessary to specify the JVM arguments passed to the Boot JDK,
1213 using e.g. `--with-boot-jdk-jvmargs="-Xmx8G"`. Doing so will override the
1214 default JVM arguments passed to the Boot JDK.
1215 
1216 At the end of a successful execution of `configure`, you will get a performance
1217 summary, indicating how well the build will perform. Here you will also get
1218 performance hints. If you want to build fast, pay attention to those!
1219 
1220 If you want to tweak build performance, run with `make LOG=info` to get a build
1221 time summary at the end of the build process.
1222 
1223 ### Disk Speed
1224 
1225 If you are using network shares, e.g. via NFS, for your source code, make sure
1226 the build directory is situated on local disk (e.g. by `ln -s
1227 /localdisk/jdk-build $JDK-SHARE/build`). The performance penalty is extremely
1228 high for building on a network share; close to unusable.
1229 
1230 Also, make sure that your build tools (including Boot JDK and toolchain) is
1231 located on a local disk and not a network share.
1232 
1233 As has been stressed elsewhere, do use SSD for source code and build directory,
1234 as well as (if possible) the build tools.
1235 
1236 ### Virus Checking
1237 
1238 The use of virus checking software, especially on Windows, can *significantly*
1239 slow down building of the JDK. If possible, turn off such software, or exclude
1240 the directory containing the JDK source code from on-the-fly checking.
1241 
1242 ### Ccache
1243 
1244 The JDK build supports building with ccache when using gcc or clang. Using
1245 ccache can radically speed up compilation of native code if you often rebuild
1246 the same sources. Your milage may vary however, so we recommend evaluating it
1247 for yourself. To enable it, make sure it's on the path and configure with
1248 `--enable-ccache`.
1249 
1250 ### Precompiled Headers
1251 
1252 By default, the Hotspot build uses preccompiled headers (PCH) on the toolchains
1253 were it is properly supported (clang, gcc, and Visual Studio). Normally, this
1254 speeds up the build process, but in some circumstances, it can actually slow
1255 things down.
1256 
1257 You can experiment by disabling precompiled headers using
1258 `--disable-precompiled-headers`.
1259 
1260 ### Icecc / icecream
1261 
1262 [icecc/icecream](http://github.com/icecc/icecream) is a simple way to setup a
1263 distributed compiler network. If you have multiple machines available for
1264 building the JDK, you can drastically cut individual build times by utilizing
1265 it.
1266 
1267 To use, setup an icecc network, and install icecc on the build machine. Then
1268 run `configure` using `--enable-icecc`.
1269 
1270 ### Using sjavac
1271 
1272 To speed up Java compilation, especially incremental compilations, you can try
1273 the experimental sjavac compiler by using `--enable-sjavac`.
1274 
1275 ### Building the Right Target
1276 
1277 Selecting the proper target to build can have dramatic impact on build time.
1278 For normal usage, `jdk` or the default target is just fine. You only need to
1279 build `images` for shipping, or if your tests require it.
1280 
1281 See also [Using Fine-Grained Make Targets](#using-fine-grained-make-targets) on
1282 how to build an even smaller subset of the product.
1283 
1284 ## Troubleshooting
1285 
1286 If your build fails, it can sometimes be difficult to pinpoint the problem or
1287 find a proper solution.
1288 
1289 ### Locating the Source of the Error
1290 
1291 When a build fails, it can be hard to pinpoint the actual cause of the error.
1292 In a typical build process, different parts of the product build in parallel,
1293 with the output interlaced.
1294 
1295 #### Build Failure Summary
1296 
1297 To help you, the build system will print a failure summary at the end. It looks
1298 like this:
1299 
1300 ```
1301 ERROR: Build failed for target 'hotspot' in configuration 'linux-x64' (exit code 2)
1302 
1303 === Output from failing command(s) repeated here ===
1304 * For target hotspot_variant-server_libjvm_objs_psMemoryPool.o:
1305 /localhome/hg/jdk9-sandbox/hotspot/src/share/vm/services/psMemoryPool.cpp:1:1: error: 'failhere' does not name a type
1306    ... (rest of output omitted)
1307 
1308 * All command lines available in /localhome/hg/jdk9-sandbox/build/linux-x64/make-support/failure-logs.
1309 === End of repeated output ===
1310 
1311 === Make failed targets repeated here ===
1312 lib/CompileJvm.gmk:207: recipe for target '/localhome/hg/jdk9-sandbox/build/linux-x64/hotspot/variant-server/libjvm/objs/psMemoryPool.o' failed
1313 make/Main.gmk:263: recipe for target 'hotspot-server-libs' failed
1314 === End of repeated output ===
1315 
1316 Hint: Try searching the build log for the name of the first failed target.
1317 Hint: If caused by a warning, try configure --disable-warnings-as-errors.
1318 ```
1319 
1320 Let's break it down! First, the selected configuration, and the top-level
1321 target you entered on the command line that caused the failure is printed.
1322 
1323 Then, between the `Output from failing command(s) repeated here` and `End of
1324 repeated output` the first lines of output (stdout and stderr) from the actual
1325 failing command is repeated. In most cases, this is the error message that
1326 caused the build to fail. If multiple commands were failing (this can happen in
1327 a parallel build), output from all failed commands will be printed here.
1328 
1329 The path to the `failure-logs` directory is printed. In this file you will find
1330 a `<target>.log` file that contains the output from this command in its
1331 entirety, and also a `<target>.cmd`, which contain the complete command line
1332 used for running this command. You can re-run the failing command by executing
1333 `. <path to failure-logs>/<target>.cmd` in your shell.
1334 
1335 Another way to trace the failure is to follow the chain of make targets, from
1336 top-level targets to individual file targets. Between `Make failed targets
1337 repeated here` and `End of repeated output` the output from make showing this
1338 chain is repeated. The first failed recipe will typically contain the full path
1339 to the file in question that failed to compile. Following lines will show a
1340 trace of make targets why we ended up trying to compile that file.
1341 
1342 Finally, some hints are given on how to locate the error in the complete log.
1343 In this example, we would try searching the log file for "`psMemoryPool.o`".
1344 Another way to quickly locate make errors in the log is to search for "`]
1345 Error`" or "`***`".
1346 
1347 Note that the build failure summary will only help you if the issue was a
1348 compilation failure or similar. If the problem is more esoteric, or is due to
1349 errors in the build machinery, you will likely get empty output logs, and `No
1350 indication of failed target found` instead of the make target chain.
1351 
1352 #### Checking the Build Log File
1353 
1354 The output (stdout and stderr) from the latest build is always stored in
1355 `$BUILD/build.log`. The previous build log is stored as `build.log.old`. This
1356 means that it is not necessary to redirect the build output yourself if you
1357 want to process it.
1358 
1359 You can increase the verbosity of the log file, by the `LOG` control variable
1360 to `make`. If you want to see the command lines used in compilations, use
1361 `LOG=cmdlines`. To increase the general verbosity, use `LOG=info`, `LOG=debug`
1362 or `LOG=trace`. Both of these can be combined with `cmdlines`, e.g.
1363 `LOG=info,cmdlines`. The `debug` log level will show most shell commands
1364 executed by make, and `trace` will show all. Beware that both these log levels
1365 will produce a massive build log!
1366 
1367 ### Fixing Unexpected Build Failures
1368 
1369 Most of the time, the build will fail due to incorrect changes in the source
1370 code.
1371 
1372 Sometimes the build can fail with no apparent changes that have caused the
1373 failure. If this is the first time you are building the JDK on this particular
1374 computer, and the build fails, the problem is likely with your build
1375 environment. But even if you have previously built the JDK with success, and it
1376 now fails, your build environment might have changed (perhaps due to OS
1377 upgrades or similar). But most likely, such failures are due to problems with
1378 the incremental rebuild.
1379 
1380 #### Problems with the Build Environment
1381 
1382 Make sure your configuration is correct. Re-run `configure`, and look for any
1383 warnings. Warnings that appear in the middle of the `configure` output is also
1384 repeated at the end, after the summary. The entire log is stored in
1385 `$BUILD/configure.log`.
1386 
1387 Verify that the summary at the end looks correct. Are you indeed using the Boot
1388 JDK and native toolchain that you expect?
1389 
1390 By default, the JDK has a strict approach where warnings from the compiler is
1391 considered errors which fail the build. For very new or very old compiler
1392 versions, this can trigger new classes of warnings, which thus fails the build.
1393 Run `configure` with `--disable-warnings-as-errors` to turn of this behavior.
1394 (The warnings will still show, but not make the build fail.)
1395 
1396 #### Problems with Incremental Rebuilds
1397 
1398 Incremental rebuilds mean that when you modify part of the product, only the
1399 affected parts get rebuilt. While this works great in most cases, and
1400 significantly speed up the development process, from time to time complex
1401 interdependencies will result in an incorrect build result. This is the most
1402 common cause for unexpected build problems.
1403 
1404 Here are a suggested list of things to try if you are having unexpected build
1405 problems. Each step requires more time than the one before, so try them in
1406 order. Most issues will be solved at step 1 or 2.
1407 
1408  1. Make sure your repository is up-to-date
1409 
1410     Run `hg pull -u` to make sure you have the latest changes.
1411 
1412  2. Clean build results
1413 
1414     The simplest way to fix incremental rebuild issues is to run `make clean`.
1415     This will remove all build results, but not the configuration or any build
1416     system support artifacts. In most cases, this will solve build errors
1417     resulting from incremental build mismatches.
1418 
1419  3. Completely clean the build directory.
1420 
1421     If this does not work, the next step is to run `make dist-clean`, or
1422     removing the build output directory (`$BUILD`). This will clean all
1423     generated output, including your configuration. You will need to re-run
1424     `configure` after this step. A good idea is to run `make
1425     print-configuration` before running `make dist-clean`, as this will print
1426     your current `configure` command line. Here's a way to do this:
1427 
1428     ```
1429     make print-configuration > current-configuration
1430     make dist-clean
1431     bash configure $(cat current-configuration)
1432     make
1433     ```
1434 
1435  4. Re-clone the Mercurial repository
1436 
1437     Sometimes the Mercurial repository gets in a state that causes the product
1438     to be un-buildable. In such a case, the simplest solution is often the
1439     "sledgehammer approach": delete the entire repository, and re-clone it.
1440     If you have local changes, save them first to a different location using
1441     `hg export`.
1442 
1443 ### Specific Build Issues
1444 
1445 #### Clock Skew
1446 
1447 If you get an error message like this:
1448 ```
1449 File 'xxx' has modification time in the future.
1450 Clock skew detected. Your build may be incomplete.
1451 ```
1452 then the clock on your build machine is out of sync with the timestamps on the
1453 source files. Other errors, apparently unrelated but in fact caused by the
1454 clock skew, can occur along with the clock skew warnings. These secondary
1455 errors may tend to obscure the fact that the true root cause of the problem is
1456 an out-of-sync clock.
1457 
1458 If you see these warnings, reset the clock on the build machine, run `make
1459 clean` and restart the build.
1460 
1461 #### Out of Memory Errors
1462 
1463 On Solaris, you might get an error message like this:
1464 ```
1465 Trouble writing out table to disk
1466 ```
1467 To solve this, increase the amount of swap space on your build machine.
1468 
1469 On Windows, you might get error messages like this:
1470 ```
1471 fatal error - couldn't allocate heap
1472 cannot create ... Permission denied
1473 spawn failed
1474 ```
1475 This can be a sign of a Cygwin problem. See the information about solving
1476 problems in the [Cygwin](#cygwin) section. Rebooting the computer might help
1477 temporarily.
1478 
1479 ### Getting Help
1480 
1481 If none of the suggestions in this document helps you, or if you find what you
1482 believe is a bug in the build system, please contact the Build Group by sending
1483 a mail to [build-dev@openjdk.java.net](mailto:build-dev@openjdk.java.net).
1484 Please include the relevant parts of the configure and/or build log.
1485 
1486 If you need general help or advice about developing for the JDK, you can also
1487 contact the Adoption Group. See the section on [Contributing to OpenJDK](
1488 #contributing-to-openjdk) for more information.
1489 
1490 ## Hints and Suggestions for Advanced Users
1491 
1492 ### Setting Up a Repository for Pushing Changes (defpath)
1493 
1494 To help you prepare a proper push path for a Mercurial repository, there exists
1495 a useful tool known as [defpath](
1496 http://openjdk.java.net/projects/code-tools/defpath). It will help you setup a
1497 proper push path for pushing changes to the JDK.
1498 
1499 Install the extension by cloning
1500 `http://hg.openjdk.java.net/code-tools/defpath` and updating your `.hgrc` file.
1501 Here's one way to do this:
1502 
1503 ```
1504 cd ~
1505 mkdir hg-ext
1506 cd hg-ext
1507 hg clone http://hg.openjdk.java.net/code-tools/defpath
1508 cat << EOT >> ~/.hgrc
1509 [extensions]
1510 defpath=~/hg-ext/defpath/defpath.py
1511 EOT
1512 ```
1513 
1514 You can now setup a proper push path using:
1515 ```
1516 hg defpath -d -u <your OpenJDK username>
1517 ```
1518 
1519 ### Bash Completion
1520 
1521 The `configure` and `make` commands tries to play nice with bash command-line
1522 completion (using `<tab>` or `<tab><tab>`). To use this functionality, make
1523 sure you enable completion in your `~/.bashrc` (see instructions for bash in
1524 your operating system).
1525 
1526 Make completion will work out of the box, and will complete valid make targets.
1527 For instance, typing `make jdk-i<tab>` will complete to `make jdk-image`.
1528 
1529 The `configure` script can get completion for options, but for this to work you
1530 need to help `bash` on the way. The standard way of running the script, `bash
1531 configure`, will not be understood by bash completion. You need `configure` to
1532 be the command to run. One way to achieve this is to add a simple helper script
1533 to your path:
1534 
1535 ```
1536 cat << EOT > /tmp/configure
1537 #!/bin/bash
1538 if [ \$(pwd) = \$(cd \$(dirname \$0); pwd) ] ; then
1539   echo >&2 "Abort: Trying to call configure helper recursively"
1540   exit 1
1541 fi
1542 
1543 bash \$PWD/configure "\$@"
1544 EOT
1545 chmod +x /tmp/configure
1546 sudo mv /tmp/configure /usr/local/bin
1547 ```
1548 
1549 Now `configure --en<tab>-dt<tab>` will result in `configure --enable-dtrace`.
1550 
1551 ### Using Multiple Configurations
1552 
1553 You can have multiple configurations for a single source repository. When you
1554 create a new configuration, run `configure --with-conf-name=<name>` to create a
1555 configuration with the name `<name>`. Alternatively, you can create a directory
1556 under `build` and run `configure` from there, e.g. `mkdir build/<name> && cd
1557 build/<name> && bash ../../configure`.
1558 
1559 Then you can build that configuration using `make CONF_NAME=<name>` or `make
1560 CONF=<pattern>`, where `<pattern>` is a substring matching one or several
1561 configurations, e.g. `CONF=debug`. The special empty pattern (`CONF=`) will
1562 match *all* available configuration, so `make CONF= hotspot` will build the
1563 `hotspot` target for all configurations. Alternatively, you can execute `make`
1564 in the configuration directory, e.g. `cd build/<name> && make`.
1565 
1566 ### Handling Reconfigurations
1567 
1568 If you update the repository and part of the configure script has changed, the
1569 build system will force you to re-run `configure`.
1570 
1571 Most of the time, you will be fine by running `configure` again with the same
1572 arguments as the last time, which can easily be performed by `make
1573 reconfigure`. To simplify this, you can use the `CONF_CHECK` make control
1574 variable, either as `make CONF_CHECK=auto`, or by setting an environment
1575 variable. For instance, if you add `export CONF_CHECK=auto` to your `.bashrc`
1576 file, `make` will always run `reconfigure` automatically whenever the configure
1577 script has changed.
1578 
1579 You can also use `CONF_CHECK=ignore` to skip the check for a needed configure
1580 update. This might speed up the build, but comes at the risk of an incorrect
1581 build result. This is only recommended if you know what you're doing.
1582 
1583 From time to time, you will also need to modify the command line to `configure`
1584 due to changes. Use `make print-configure` to show the command line used for
1585 your current configuration.
1586 
1587 ### Using Fine-Grained Make Targets
1588 
1589 The default behavior for make is to create consistent and correct output, at
1590 the expense of build speed, if necessary.
1591 
1592 If you are prepared to take some risk of an incorrect build, and know enough of
1593 the system to understand how things build and interact, you can speed up the
1594 build process considerably by instructing make to only build a portion of the
1595 product.
1596 
1597 #### Building Individual Modules
1598 
1599 The safe way to use fine-grained make targets is to use the module specific
1600 make targets. All source code in the JDK is organized so it belongs to a
1601 module, e.g. `java.base` or `jdk.jdwp.agent`. You can build only a specific
1602 module, by giving it as make target: `make jdk.jdwp.agent`. If the specified
1603 module depends on other modules (e.g. `java.base`), those modules will be built
1604 first.
1605 
1606 You can also specify a set of modules, just as you can always specify a set of
1607 make targets: `make jdk.crypto.cryptoki jdk.crypto.ec jdk.crypto.mscapi
1608 jdk.crypto.ucrypto`
1609 
1610 #### Building Individual Module Phases
1611 
1612 The build process for each module is divided into separate phases. Not all
1613 modules need all phases. Which are needed depends on what kind of source code
1614 and other artifact the module consists of. The phases are:
1615 
1616   * `gensrc` (Generate source code to compile)
1617   * `gendata` (Generate non-source code artifacts)
1618   * `copy` (Copy resource artifacts)
1619   * `java` (Compile Java code)
1620   * `launchers` (Compile native executables)
1621   * `libs` (Compile native libraries)
1622   * `rmic` (Run the `rmic` tool)
1623 
1624 You can build only a single phase for a module by using the notation
1625 `$MODULE-$PHASE`. For instance, to build the `gensrc` phase for `java.base`,
1626 use `make java.base-gensrc`.
1627 
1628 Note that some phases may depend on others, e.g. `java` depends on `gensrc` (if
1629 present). Make will build all needed prerequisites before building the
1630 requested phase.
1631 
1632 #### Skipping the Dependency Check
1633 
1634 When using an iterative development style with frequent quick rebuilds, the
1635 dependency check made by make can take up a significant portion of the time
1636 spent on the rebuild. In such cases, it can be useful to bypass the dependency
1637 check in make.
1638 
1639 > **Note that if used incorrectly, this can lead to a broken build!**
1640 
1641 To achieve this, append `-only` to the build target. For instance, `make
1642 jdk.jdwp.agent-java-only` will *only* build the `java` phase of the
1643 `jdk.jdwp.agent` module. If the required dependencies are not present, the
1644 build can fail. On the other hand, the execution time measures in milliseconds.
1645 
1646 A useful pattern is to build the first time normally (e.g. `make
1647 jdk.jdwp.agent`) and then on subsequent builds, use the `-only` make target.
1648 
1649 #### Rebuilding Part of java.base (JDK\_FILTER)
1650 
1651 If you are modifying files in `java.base`, which is the by far largest module
1652 in the JDK, then you need to rebuild all those files whenever a single file has
1653 changed. (This inefficiency will hopefully be addressed in JDK 10.)
1654 
1655 As a hack, you can use the make control variable `JDK_FILTER` to specify a
1656 pattern that will be used to limit the set of files being recompiled. For
1657 instance, `make java.base JDK_FILTER=javax/crypto` (or, to combine methods,
1658 `make java.base-java-only JDK_FILTER=javax/crypto`) will limit the compilation
1659 to files in the `javax.crypto` package.
1660 
1661 ### Learn About Mercurial
1662 
1663 To become an efficient JDK developer, it is recommended that you invest in
1664 learning Mercurial properly. Here are some links that can get you started:
1665 
1666   * [Mercurial for git users](http://www.mercurial-scm.org/wiki/GitConcepts)
1667   * [The official Mercurial tutorial](http://www.mercurial-scm.org/wiki/Tutorial)
1668   * [hg init](http://hginit.com/)
1669   * [Mercurial: The Definitive Guide](http://hgbook.red-bean.com/read/)
1670 
1671 ## Understanding the Build System
1672 
1673 This section will give you a more technical description on the details of the
1674 build system.
1675 
1676 ### Configurations
1677 
1678 The build system expects to find one or more configuration. These are
1679 technically defined by the `spec.gmk` in a subdirectory to the `build`
1680 subdirectory. The `spec.gmk` file is generated by `configure`, and contains in
1681 principle the configuration (directly or by files included by `spec.gmk`).
1682 
1683 You can, in fact, select a configuration to build by pointing to the `spec.gmk`
1684 file with the `SPEC` make control variable, e.g. `make SPEC=$BUILD/spec.gmk`.
1685 While this is not the recommended way to call `make` as a user, it is what is
1686 used under the hood by the build system.
1687 
1688 ### Build Output Structure
1689 
1690 The build output for a configuration will end up in `build/<configuration
1691 name>`, which we refer to as `$BUILD` in this document. The `$BUILD` directory
1692 contains the following important directories:
1693 
1694 ```
1695 buildtools/
1696 configure-support/
1697 hotspot/
1698 images/
1699 jdk/
1700 make-support/
1701 support/
1702 test-results/
1703 test-support/
1704 ```
1705 
1706 This is what they are used for:
1707 
1708   * `images`: This is the directory were the output of the `*-image` make
1709     targets end up. For instance, `make jdk-image` ends up in `images/jdk`.
1710 
1711   * `jdk`: This is the "exploded image". After `make jdk`, you will be able to
1712     launch the newly built JDK by running `$BUILD/jdk/bin/java`.
1713 
1714   * `test-results`: This directory contains the results from running tests.
1715 
1716   * `support`: This is an area for intermediate files needed during the build,
1717     e.g. generated source code, object files and class files. Some noteworthy
1718     directories in `support` is `gensrc`, which contains the generated source
1719     code, and the `modules_*` directories, which contains the files in a
1720     per-module hierarchy that will later be collapsed into the `jdk` directory
1721     of the exploded image.
1722 
1723   * `buildtools`: This is an area for tools compiled for the build platform
1724     that are used during the rest of the build.
1725 
1726   * `hotspot`: This is an area for intermediate files needed when building
1727     hotspot.
1728 
1729   * `configure-support`, `make-support` and `test-support`: These directories
1730     contain files that are needed by the build system for `configure`, `make`
1731     and for running tests.
1732 
1733 ### Fixpath
1734 
1735 Windows path typically look like `C:\User\foo`, while Unix paths look like
1736 `/home/foo`. Tools with roots from Unix often experience issues related to this
1737 mismatch when running on Windows.
1738 
1739 In the JDK build, we always use Unix paths internally, and only just before
1740 calling a tool that does not understand Unix paths do we convert them to
1741 Windows paths.
1742 
1743 This conversion is done by the `fixpath` tool, which is a small wrapper that
1744 modifies unix-style paths to Windows-style paths in command lines. Fixpath is
1745 compiled automatically by `configure`.
1746 
1747 ### Native Debug Symbols
1748 
1749 Native libraries and executables can have debug symbol (and other debug
1750 information) associated with them. How this works is very much platform
1751 dependent, but a common problem is that debug symbol information takes a lot of
1752 disk space, but is rarely needed by the end user.
1753 
1754 The JDK supports different methods on how to handle debug symbols. The
1755 method used is selected by `--with-native-debug-symbols`, and available methods
1756 are `none`, `internal`, `external`, `zipped`.
1757 
1758   * `none` means that no debug symbols will be generated during the build.
1759 
1760   * `internal` means that debug symbols will be generated during the build, and
1761     they will be stored in the generated binary.
1762 
1763   * `external` means that debug symbols will be generated during the build, and
1764     after the compilation, they will be moved into a separate `.debuginfo` file.
1765     (This was previously known as FDS, Full Debug Symbols).
1766 
1767   * `zipped` is like `external`, but the .debuginfo file will also be zipped
1768     into a `.diz` file.
1769 
1770 When building for distribution, `zipped` is a good solution. Binaries built
1771 with `internal` is suitable for use by developers, since they facilitate
1772 debugging, but should be stripped before distributed to end users.
1773 
1774 ### Autoconf Details
1775 
1776 The `configure` script is based on the autoconf framework, but in some details
1777 deviate from a normal autoconf `configure` script.
1778 
1779 The `configure` script in the top level directory of the JDK is just a thin
1780 wrapper that calls `make/autoconf/configure`. This in turn will run `autoconf`
1781 to create the runnable (generated) configure script, as
1782 `.build/generated-configure.sh`. Apart from being responsible for the
1783 generation of the runnable script, the `configure` script also provides
1784 functionality that is not easily expressed in the normal Autoconf framework. As
1785 part of this functionality, the generated script is called.
1786 
1787 The build system will detect if the Autoconf source files have changed, and
1788 will trigger a regeneration of the generated script if needed. You can also
1789 manually request such an update by `bash configure autogen`.
1790 
1791 In previous versions of the JDK, the generated script was checked in at
1792 `make/autoconf/generated-configure.sh`. This is no longer the case.
1793 
1794 ### Developing the Build System Itself
1795 
1796 This section contains a few remarks about how to develop for the build system
1797 itself. It is not relevant if you are only making changes in the product source
1798 code.
1799 
1800 While technically using `make`, the make source files of the JDK does not
1801 resemble most other Makefiles. Instead of listing specific targets and actions
1802 (perhaps using patterns), the basic modus operandi is to call a high-level
1803 function (or properly, macro) from the API in `make/common`. For instance, to
1804 compile all classes in the `jdk.internal.foo` package in the `jdk.foo` module,
1805 a call like this would be made:
1806 
1807 ```
1808 $(eval $(call SetupJavaCompilation, BUILD_FOO_CLASSES, \
1809     SETUP := GENERATE_OLDBYTECODE, \
1810     SRC := $(TOPDIR)/src/jkd.foo/share/classes, \
1811     INCLUDES := jdk/internal/foo, \
1812     BIN := $(SUPPORT_OUTPUTDIR)/foo_classes, \
1813 ))
1814 ```
1815 
1816 By encapsulating and expressing the high-level knowledge of *what* should be
1817 done, rather than *how* it should be done (as is normal in Makefiles), we can
1818 build a much more powerful and flexible build system.
1819 
1820 Correct dependency tracking is paramount. Sloppy dependency tracking will lead
1821 to improper parallelization, or worse, race conditions.
1822 
1823 To test for/debug race conditions, try running `make JOBS=1` and `make
1824 JOBS=100` and see if it makes any difference. (It shouldn't).
1825 
1826 To compare the output of two different builds and see if, and how, they differ,
1827 run `$BUILD1/compare.sh -o $BUILD2`, where `$BUILD1` and `$BUILD2` are the two
1828 builds you want to compare.
1829 
1830 To automatically build two consecutive versions and compare them, use
1831 `COMPARE_BUILD`. The value of `COMPARE_BUILD` is a set of variable=value
1832 assignments, like this:
1833 ```
1834 make COMPARE_BUILD=CONF=--enable-new-hotspot-feature:MAKE=hotspot
1835 ```
1836 See `make/InitSupport.gmk` for details on how to use `COMPARE_BUILD`.
1837 
1838 To analyze build performance, run with `LOG=trace` and check `$BUILD/build-trace-time.log`.
1839 Use `JOBS=1` to avoid parallelism.
1840 
1841 Please check that you adhere to the [Code Conventions for the Build System](
1842 http://openjdk.java.net/groups/build/doc/code-conventions.html) before
1843 submitting patches.
1844 
1845 ## Contributing to the JDK
1846 
1847 So, now you've built your JDK, and made your first patch, and want to
1848 contribute it back to the OpenJDK Community.
1849 
1850 First of all: Thank you! We gladly welcome your contribution.
1851 However, please bear in mind that the JDK is a massive project, and we must ask
1852 you to follow our rules and guidelines to be able to accept your contribution.
1853 
1854 The official place to start is the ['How to contribute' page](
1855 http://openjdk.java.net/contribute/). There is also an official (but somewhat
1856 outdated and skimpy on details) [Developer's Guide](
1857 http://openjdk.java.net/guide/).
1858 
1859 If this seems overwhelming to you, the Adoption Group is there to help you! A
1860 good place to start is their ['New Contributor' page](
1861 https://wiki.openjdk.java.net/display/Adoption/New+Contributor), or start
1862 reading the comprehensive [Getting Started Kit](
1863 https://adoptopenjdk.gitbooks.io/adoptopenjdk-getting-started-kit/en/). The
1864 Adoption Group will also happily answer any questions you have about
1865 contributing. Contact them by [mail](
1866 http://mail.openjdk.java.net/mailman/listinfo/adoption-discuss) or [IRC](
1867 http://openjdk.java.net/irc/).
1868 
1869 ---
1870 # Override styles from the base CSS file that are not ideal for this document.
1871 header-includes:
1872  - '<style type="text/css">pre, code, tt { color: #1d6ae5; }</style>'
1873 ---