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   * `SPEC_FILTER`
 875 
 876 ## Running Tests
 877 
 878 Most of the JDK tests are using the [JTReg](http://openjdk.java.net/jtreg)
 879 test framework. Make sure that your configuration knows where to find your
 880 installation of JTReg. If this is not picked up automatically, use the
 881 `--with-jtreg=<path to jtreg home>` option to point to the JTReg framework.
 882 Note that this option should point to the JTReg home, i.e. the top directory,
 883 containing `lib/jtreg.jar` etc.
 884 
 885 The [Adoption Group](https://wiki.openjdk.java.net/display/Adoption) provides
 886 recent builds of jtreg [here](
 887 https://adopt-openjdk.ci.cloudbees.com/job/jtreg/lastSuccessfulBuild/artifact).
 888 Download the latest `.tar.gz` file, unpack it, and point `--with-jtreg` to the
 889 `jtreg` directory that you just unpacked.
 890 
 891 To execute the most basic tests (tier 1), use:
 892 ```
 893 make run-test-tier1
 894 ```
 895 
 896 For more details on how to run tests, please see the [Testing
 897 the JDK](testing.html) document.
 898 
 899 ## Cross-compiling
 900 
 901 Cross-compiling means using one platform (the *build* platform) to generate
 902 output that can ran on another platform (the *target* platform).
 903 
 904 The typical reason for cross-compiling is that the build is performed on a more
 905 powerful desktop computer, but the resulting binaries will be able to run on a
 906 different, typically low-performing system. Most of the complications that
 907 arise when building for embedded is due to this separation of *build* and
 908 *target* systems.
 909 
 910 This requires a more complex setup and build procedure. This section assumes
 911 you are familiar with cross-compiling in general, and will only deal with the
 912 particularities of cross-compiling the JDK. If you are new to cross-compiling,
 913 please see the [external links at Wikipedia](
 914 https://en.wikipedia.org/wiki/Cross_compiler#External_links) for a good start
 915 on reading materials.
 916 
 917 Cross-compiling the JDK requires you to be able to build both for the build
 918 platform and for the target platform. The reason for the former is that we need
 919 to build and execute tools during the build process, both native tools and Java
 920 tools.
 921 
 922 If all you want to do is to compile a 32-bit version, for the same OS, on a
 923 64-bit machine, consider using `--with-target-bits=32` instead of doing a
 924 full-blown cross-compilation. (While this surely is possible, it's a lot more
 925 work and will take much longer to build.)
 926 
 927 ### Cross compiling the easy way with OpenJDK devkits
 928 
 929 The OpenJDK build system provides out-of-the box support for creating and using
 930 so called devkits. A `devkit` is basically a collection of a cross-compiling
 931 toolchain and a sysroot environment which can easily be used together with the
 932 `--with-devkit` configure option to cross compile the OpenJDK. On Linux/x86_64,
 933 the following command:
 934 ```
 935 bash configure --with-devkit=<devkit-path> --openjdk-target=ppc64-linux-gnu && make
 936 ```
 937 
 938 will configure and build OpenJDK for Linux/ppc64 assuming that `<devkit-path>`
 939 points to a Linux/x86_64 to Linux/ppc64 devkit.
 940 
 941 Devkits can be created from the `make/devkit` directory by executing:
 942 ```
 943 make [ TARGETS="<TARGET_TRIPLET>+" ] [ BASE_OS=<OS> ] [ BASE_OS_VERSION=<VER> ]
 944 ```
 945 
 946 where `TARGETS` contains one or more `TARGET_TRIPLET`s of the form
 947 described in [section 3.4 of the GNU Autobook](
 948 https://sourceware.org/autobook/autobook/autobook_17.html). If no
 949 targets are given, a native toolchain for the current platform will be
 950 created. Currently, at least the following targets are known to work:
 951 
 952  Supported devkit targets
 953  -------------------------
 954  x86_64-linux-gnu
 955  aarch64-linux-gnu
 956  arm-linux-gnueabihf
 957  ppc64-linux-gnu
 958  ppc64le-linux-gnu
 959  s390x-linux-gnu
 960 
 961 `BASE_OS` must be one of "OEL6" for Oracle Enterprise Linux 6 or
 962 "Fedora" (if not specified "OEL6" will be the default). If the base OS
 963 is "Fedora" the corresponding Fedora release can be specified with the
 964 help of the `BASE_OS_VERSION` option (with "27" as default version).
 965 If the build is successful, the new devkits can be found in the
 966 `build/devkit/result` subdirectory:
 967 ```
 968 cd make/devkit
 969 make TARGETS="ppc64le-linux-gnu aarch64-linux-gnu" BASE_OS=Fedora BASE_OS_VERSION=21
 970 ls -1 ../../build/devkit/result/
 971 x86_64-linux-gnu-to-aarch64-linux-gnu
 972 x86_64-linux-gnu-to-ppc64le-linux-gnu
 973 ```
 974 
 975 Notice that devkits are not only useful for targeting different build
 976 platforms. Because they contain the full build dependencies for a
 977 system (i.e. compiler and root file system), they can easily be used
 978 to build well-known, reliable and reproducible build environments. You
 979 can for example create and use a devkit with GCC 7.3 and a Fedora 12
 980 sysroot environment (with glibc 2.11) on Ubuntu 14.04 (which doesn't
 981 have GCC 7.3 by default) to produce OpenJDK binaries which will run on
 982 all Linux systems with runtime libraries newer than the ones from
 983 Fedora 12 (e.g. Ubuntu 16.04, SLES 11 or RHEL 6).
 984 
 985 ### Boot JDK and Build JDK
 986 
 987 When cross-compiling, make sure you use a boot JDK that runs on the *build*
 988 system, and not on the *target* system.
 989 
 990 To be able to build, we need a "Build JDK", which is a JDK built from the
 991 current sources (that is, the same as the end result of the entire build
 992 process), but able to run on the *build* system, and not the *target* system.
 993 (In contrast, the Boot JDK should be from an older release, e.g. JDK 8 when
 994 building JDK 9.)
 995 
 996 The build process will create a minimal Build JDK for you, as part of building.
 997 To speed up the build, you can use `--with-build-jdk` to `configure` to point
 998 to a pre-built Build JDK. Please note that the build result is unpredictable,
 999 and can possibly break in subtle ways, if the Build JDK does not **exactly**
1000 match the current sources.
1001 
1002 ### Specifying the Target Platform
1003 
1004 You *must* specify the target platform when cross-compiling. Doing so will also
1005 automatically turn the build into a cross-compiling mode. The simplest way to
1006 do this is to use the `--openjdk-target` argument, e.g.
1007 `--openjdk-target=arm-linux-gnueabihf`. or `--openjdk-target=aarch64-oe-linux`.
1008 This will automatically set the `--build`, `--host` and `--target` options for
1009 autoconf, which can otherwise be confusing. (In autoconf terminology, the
1010 "target" is known as "host", and "target" is used for building a Canadian
1011 cross-compiler.)
1012 
1013 ### Toolchain Considerations
1014 
1015 You will need two copies of your toolchain, one which generates output that can
1016 run on the target system (the normal, or *target*, toolchain), and one that
1017 generates output that can run on the build system (the *build* toolchain). Note
1018 that cross-compiling is only supported for gcc at the time being. The gcc
1019 standard is to prefix cross-compiling toolchains with the target denominator.
1020 If you follow this standard, `configure` is likely to pick up the toolchain
1021 correctly.
1022 
1023 The *build* toolchain will be autodetected just the same way the normal
1024 *build*/*target* toolchain will be autodetected when not cross-compiling. If
1025 this is not what you want, or if the autodetection fails, you can specify a
1026 devkit containing the *build* toolchain using `--with-build-devkit` to
1027 `configure`, or by giving `BUILD_CC` and `BUILD_CXX` arguments.
1028 
1029 It is often helpful to locate the cross-compilation tools, headers and
1030 libraries in a separate directory, outside the normal path, and point out that
1031 directory to `configure`. Do this by setting the sysroot (`--with-sysroot`) and
1032 appending the directory when searching for cross-compilations tools
1033 (`--with-toolchain-path`). As a compact form, you can also use `--with-devkit`
1034 to point to a single directory, if it is correctly setup. (See `basics.m4` for
1035 details.)
1036 
1037 If you are unsure what toolchain and versions to use, these have been proved
1038 working at the time of writing:
1039 
1040   * [aarch64](
1041 https://releases.linaro.org/archive/13.11/components/toolchain/binaries/gcc-linaro-aarch64-linux-gnu-4.8-2013.11_linux.tar.xz)
1042   * [arm 32-bit hardware floating  point](
1043 https://launchpad.net/linaro-toolchain-unsupported/trunk/2012.09/+download/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux.tar.bz2)
1044 
1045 ### Native Libraries
1046 
1047 You will need copies of external native libraries for the *target* system,
1048 present on the *build* machine while building.
1049 
1050 Take care not to replace the *build* system's version of these libraries by
1051 mistake, since that can render the *build* machine unusable.
1052 
1053 Make sure that the libraries you point to (ALSA, X11, etc) are for the
1054 *target*, not the *build*, platform.
1055 
1056 #### ALSA
1057 
1058 You will need alsa libraries suitable for your *target* system. For most cases,
1059 using Debian's pre-built libraries work fine.
1060 
1061 Note that alsa is needed even if you only want to build a headless JDK.
1062 
1063   * Go to [Debian Package Search](https://www.debian.org/distrib/packages) and
1064     search for the `libasound2` and `libasound2-dev` packages for your *target*
1065     system. Download them to /tmp.
1066 
1067   * Install the libraries into the cross-compilation toolchain. For instance:
1068 ```
1069 cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc
1070 dpkg-deb -x /tmp/libasound2_1.0.25-4_armhf.deb .
1071 dpkg-deb -x /tmp/libasound2-dev_1.0.25-4_armhf.deb .
1072 ```
1073 
1074   * If alsa is not properly detected by `configure`, you can point it out by
1075     `--with-alsa`.
1076 
1077 #### X11
1078 
1079 You will need X11 libraries suitable for your *target* system. For most cases,
1080 using Debian's pre-built libraries work fine.
1081 
1082 Note that X11 is needed even if you only want to build a headless JDK.
1083 
1084   * Go to [Debian Package Search](https://www.debian.org/distrib/packages),
1085     search for the following packages for your *target* system, and download them
1086     to /tmp/target-x11:
1087       * libxi
1088       * libxi-dev
1089       * x11proto-core-dev
1090       * x11proto-input-dev
1091       * x11proto-kb-dev
1092       * x11proto-render-dev
1093       * x11proto-xext-dev
1094       * libice-dev
1095       * libxrender
1096       * libxrender-dev
1097       * libxrandr-dev
1098       * libsm-dev
1099       * libxt-dev
1100       * libx11
1101       * libx11-dev
1102       * libxtst
1103       * libxtst-dev
1104       * libxext
1105       * libxext-dev
1106 
1107   * Install the libraries into the cross-compilation toolchain. For instance:
1108     ```
1109     cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc/usr
1110     mkdir X11R6
1111     cd X11R6
1112     for deb in /tmp/target-x11/*.deb ; do dpkg-deb -x $deb . ; done
1113     mv usr/* .
1114     cd lib
1115     cp arm-linux-gnueabihf/* .
1116     ```
1117 
1118     You can ignore the following messages. These libraries are not needed to
1119     successfully complete a full JDK build.
1120     ```
1121     cp: cannot stat `arm-linux-gnueabihf/libICE.so': No such file or directory
1122     cp: cannot stat `arm-linux-gnueabihf/libSM.so': No such file or directory
1123     cp: cannot stat `arm-linux-gnueabihf/libXt.so': No such file or directory
1124     ```
1125 
1126   * If the X11 libraries are not properly detected by `configure`, you can
1127     point them out by `--with-x`.
1128 
1129 ### Creating And Using Sysroots With qemu-deboostrap
1130 
1131 Fortunately, you can create sysroots for foreign architectures with tools
1132 provided by your OS. On Debian/Ubuntu systems, one could use `qemu-deboostrap` to
1133 create the *target* system chroot, which would have the native libraries and headers
1134 specific to that *target* system. After that, we can use the cross-compiler on the *build*
1135 system, pointing into chroot to get the build dependencies right. This allows building
1136 for foreign architectures with native compilation speed.
1137 
1138 For example, cross-compiling to AArch64 from x86_64 could be done like this:
1139 
1140   * Install cross-compiler on the *build* system:
1141 ```
1142 apt install g++-aarch64-linux-gnu gcc-aarch64-linux-gnu
1143 ```
1144 
1145   * Create chroot on the *build* system, configuring it for *target* system:
1146 ```
1147 sudo qemu-debootstrap --arch=arm64 --verbose \
1148        --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 \
1149        --resolve-deps jessie /chroots/arm64 http://httpredir.debian.org/debian/
1150 ```
1151 
1152   * Configure and build with newly created chroot as sysroot/toolchain-path:
1153 ```
1154 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/
1155 make images
1156 ls build/linux-aarch64-normal-server-release/
1157 ```
1158 
1159 The build does not create new files in that chroot, so it can be reused for multiple builds
1160 without additional cleanup.
1161 
1162 Architectures that are known to successfully cross-compile like this are:
1163 
1164   Target        `CC`                      `CXX`                       `--arch=...`  `--openjdk-target=...`
1165   ------------  ------------------------- --------------------------- ------------- -----------------------
1166   x86           default                   default                     i386          i386-linux-gnu
1167   armhf         gcc-arm-linux-gnueabihf   g++-arm-linux-gnueabihf     armhf         arm-linux-gnueabihf
1168   aarch64       gcc-aarch64-linux-gnu     g++-aarch64-linux-gnu       arm64         aarch64-linux-gnu
1169   ppc64el       gcc-powerpc64le-linux-gnu g++-powerpc64le-linux-gnu   ppc64el       powerpc64le-linux-gnu
1170   s390x         gcc-s390x-linux-gnu       g++-s390x-linux-gnu         s390x         s390x-linux-gnu
1171 
1172 Additional architectures might be supported by Debian/Ubuntu Ports.
1173 
1174 ### Building for ARM/aarch64
1175 
1176 A common cross-compilation target is the ARM CPU. When building for ARM, it is
1177 useful to set the ABI profile. A number of pre-defined ABI profiles are
1178 available using `--with-abi-profile`: arm-vfp-sflt, arm-vfp-hflt, arm-sflt,
1179 armv5-vfp-sflt, armv6-vfp-hflt. Note that soft-float ABIs are no longer
1180 properly supported by the JDK.
1181 
1182 ### Verifying the Build
1183 
1184 The build will end up in a directory named like
1185 `build/linux-arm-normal-server-release`.
1186 
1187 Inside this build output directory, the `images/jdk` will contain the newly
1188 built JDK, for your *target* system.
1189 
1190 Copy these folders to your *target* system. Then you can run e.g.
1191 `images/jdk/bin/java -version`.
1192 
1193 ## Build Performance
1194 
1195 Building the JDK requires a lot of horsepower. Some of the build tools can be
1196 adjusted to utilize more or less of resources such as parallel threads and
1197 memory. The `configure` script analyzes your system and selects reasonable
1198 values for such options based on your hardware. If you encounter resource
1199 problems, such as out of memory conditions, you can modify the detected values
1200 with:
1201 
1202   * `--with-num-cores` -- number of cores in the build system, e.g.
1203     `--with-num-cores=8`.
1204 
1205   * `--with-memory-size` -- memory (in MB) available in the build system, e.g.
1206     `--with-memory-size=1024`
1207 
1208 You can also specify directly the number of build jobs to use with
1209 `--with-jobs=N` to `configure`, or `JOBS=N` to `make`. Do not use the `-j` flag
1210 to `make`. In most cases it will be ignored by the makefiles, but it can cause
1211 problems for some make targets.
1212 
1213 It might also be necessary to specify the JVM arguments passed to the Boot JDK,
1214 using e.g. `--with-boot-jdk-jvmargs="-Xmx8G"`. Doing so will override the
1215 default JVM arguments passed to the Boot JDK.
1216 
1217 At the end of a successful execution of `configure`, you will get a performance
1218 summary, indicating how well the build will perform. Here you will also get
1219 performance hints. If you want to build fast, pay attention to those!
1220 
1221 If you want to tweak build performance, run with `make LOG=info` to get a build
1222 time summary at the end of the build process.
1223 
1224 ### Disk Speed
1225 
1226 If you are using network shares, e.g. via NFS, for your source code, make sure
1227 the build directory is situated on local disk (e.g. by `ln -s
1228 /localdisk/jdk-build $JDK-SHARE/build`). The performance penalty is extremely
1229 high for building on a network share; close to unusable.
1230 
1231 Also, make sure that your build tools (including Boot JDK and toolchain) is
1232 located on a local disk and not a network share.
1233 
1234 As has been stressed elsewhere, do use SSD for source code and build directory,
1235 as well as (if possible) the build tools.
1236 
1237 ### Virus Checking
1238 
1239 The use of virus checking software, especially on Windows, can *significantly*
1240 slow down building of the JDK. If possible, turn off such software, or exclude
1241 the directory containing the JDK source code from on-the-fly checking.
1242 
1243 ### Ccache
1244 
1245 The JDK build supports building with ccache when using gcc or clang. Using
1246 ccache can radically speed up compilation of native code if you often rebuild
1247 the same sources. Your milage may vary however, so we recommend evaluating it
1248 for yourself. To enable it, make sure it's on the path and configure with
1249 `--enable-ccache`.
1250 
1251 ### Precompiled Headers
1252 
1253 By default, the Hotspot build uses preccompiled headers (PCH) on the toolchains
1254 were it is properly supported (clang, gcc, and Visual Studio). Normally, this
1255 speeds up the build process, but in some circumstances, it can actually slow
1256 things down.
1257 
1258 You can experiment by disabling precompiled headers using
1259 `--disable-precompiled-headers`.
1260 
1261 ### Icecc / icecream
1262 
1263 [icecc/icecream](http://github.com/icecc/icecream) is a simple way to setup a
1264 distributed compiler network. If you have multiple machines available for
1265 building the JDK, you can drastically cut individual build times by utilizing
1266 it.
1267 
1268 To use, setup an icecc network, and install icecc on the build machine. Then
1269 run `configure` using `--enable-icecc`.
1270 
1271 ### Using sjavac
1272 
1273 To speed up Java compilation, especially incremental compilations, you can try
1274 the experimental sjavac compiler by using `--enable-sjavac`.
1275 
1276 ### Building the Right Target
1277 
1278 Selecting the proper target to build can have dramatic impact on build time.
1279 For normal usage, `jdk` or the default target is just fine. You only need to
1280 build `images` for shipping, or if your tests require it.
1281 
1282 See also [Using Fine-Grained Make Targets](#using-fine-grained-make-targets) on
1283 how to build an even smaller subset of the product.
1284 
1285 ## Troubleshooting
1286 
1287 If your build fails, it can sometimes be difficult to pinpoint the problem or
1288 find a proper solution.
1289 
1290 ### Locating the Source of the Error
1291 
1292 When a build fails, it can be hard to pinpoint the actual cause of the error.
1293 In a typical build process, different parts of the product build in parallel,
1294 with the output interlaced.
1295 
1296 #### Build Failure Summary
1297 
1298 To help you, the build system will print a failure summary at the end. It looks
1299 like this:
1300 
1301 ```
1302 ERROR: Build failed for target 'hotspot' in configuration 'linux-x64' (exit code 2)
1303 
1304 === Output from failing command(s) repeated here ===
1305 * For target hotspot_variant-server_libjvm_objs_psMemoryPool.o:
1306 /localhome/hg/jdk9-sandbox/hotspot/src/share/vm/services/psMemoryPool.cpp:1:1: error: 'failhere' does not name a type
1307    ... (rest of output omitted)
1308 
1309 * All command lines available in /localhome/hg/jdk9-sandbox/build/linux-x64/make-support/failure-logs.
1310 === End of repeated output ===
1311 
1312 === Make failed targets repeated here ===
1313 lib/CompileJvm.gmk:207: recipe for target '/localhome/hg/jdk9-sandbox/build/linux-x64/hotspot/variant-server/libjvm/objs/psMemoryPool.o' failed
1314 make/Main.gmk:263: recipe for target 'hotspot-server-libs' failed
1315 === End of repeated output ===
1316 
1317 Hint: Try searching the build log for the name of the first failed target.
1318 Hint: If caused by a warning, try configure --disable-warnings-as-errors.
1319 ```
1320 
1321 Let's break it down! First, the selected configuration, and the top-level
1322 target you entered on the command line that caused the failure is printed.
1323 
1324 Then, between the `Output from failing command(s) repeated here` and `End of
1325 repeated output` the first lines of output (stdout and stderr) from the actual
1326 failing command is repeated. In most cases, this is the error message that
1327 caused the build to fail. If multiple commands were failing (this can happen in
1328 a parallel build), output from all failed commands will be printed here.
1329 
1330 The path to the `failure-logs` directory is printed. In this file you will find
1331 a `<target>.log` file that contains the output from this command in its
1332 entirety, and also a `<target>.cmd`, which contain the complete command line
1333 used for running this command. You can re-run the failing command by executing
1334 `. <path to failure-logs>/<target>.cmd` in your shell.
1335 
1336 Another way to trace the failure is to follow the chain of make targets, from
1337 top-level targets to individual file targets. Between `Make failed targets
1338 repeated here` and `End of repeated output` the output from make showing this
1339 chain is repeated. The first failed recipe will typically contain the full path
1340 to the file in question that failed to compile. Following lines will show a
1341 trace of make targets why we ended up trying to compile that file.
1342 
1343 Finally, some hints are given on how to locate the error in the complete log.
1344 In this example, we would try searching the log file for "`psMemoryPool.o`".
1345 Another way to quickly locate make errors in the log is to search for "`]
1346 Error`" or "`***`".
1347 
1348 Note that the build failure summary will only help you if the issue was a
1349 compilation failure or similar. If the problem is more esoteric, or is due to
1350 errors in the build machinery, you will likely get empty output logs, and `No
1351 indication of failed target found` instead of the make target chain.
1352 
1353 #### Checking the Build Log File
1354 
1355 The output (stdout and stderr) from the latest build is always stored in
1356 `$BUILD/build.log`. The previous build log is stored as `build.log.old`. This
1357 means that it is not necessary to redirect the build output yourself if you
1358 want to process it.
1359 
1360 You can increase the verbosity of the log file, by the `LOG` control variable
1361 to `make`. If you want to see the command lines used in compilations, use
1362 `LOG=cmdlines`. To increase the general verbosity, use `LOG=info`, `LOG=debug`
1363 or `LOG=trace`. Both of these can be combined with `cmdlines`, e.g.
1364 `LOG=info,cmdlines`. The `debug` log level will show most shell commands
1365 executed by make, and `trace` will show all. Beware that both these log levels
1366 will produce a massive build log!
1367 
1368 ### Fixing Unexpected Build Failures
1369 
1370 Most of the time, the build will fail due to incorrect changes in the source
1371 code.
1372 
1373 Sometimes the build can fail with no apparent changes that have caused the
1374 failure. If this is the first time you are building the JDK on this particular
1375 computer, and the build fails, the problem is likely with your build
1376 environment. But even if you have previously built the JDK with success, and it
1377 now fails, your build environment might have changed (perhaps due to OS
1378 upgrades or similar). But most likely, such failures are due to problems with
1379 the incremental rebuild.
1380 
1381 #### Problems with the Build Environment
1382 
1383 Make sure your configuration is correct. Re-run `configure`, and look for any
1384 warnings. Warnings that appear in the middle of the `configure` output is also
1385 repeated at the end, after the summary. The entire log is stored in
1386 `$BUILD/configure.log`.
1387 
1388 Verify that the summary at the end looks correct. Are you indeed using the Boot
1389 JDK and native toolchain that you expect?
1390 
1391 By default, the JDK has a strict approach where warnings from the compiler is
1392 considered errors which fail the build. For very new or very old compiler
1393 versions, this can trigger new classes of warnings, which thus fails the build.
1394 Run `configure` with `--disable-warnings-as-errors` to turn of this behavior.
1395 (The warnings will still show, but not make the build fail.)
1396 
1397 #### Problems with Incremental Rebuilds
1398 
1399 Incremental rebuilds mean that when you modify part of the product, only the
1400 affected parts get rebuilt. While this works great in most cases, and
1401 significantly speed up the development process, from time to time complex
1402 interdependencies will result in an incorrect build result. This is the most
1403 common cause for unexpected build problems.
1404 
1405 Here are a suggested list of things to try if you are having unexpected build
1406 problems. Each step requires more time than the one before, so try them in
1407 order. Most issues will be solved at step 1 or 2.
1408 
1409  1. Make sure your repository is up-to-date
1410 
1411     Run `hg pull -u` to make sure you have the latest changes.
1412 
1413  2. Clean build results
1414 
1415     The simplest way to fix incremental rebuild issues is to run `make clean`.
1416     This will remove all build results, but not the configuration or any build
1417     system support artifacts. In most cases, this will solve build errors
1418     resulting from incremental build mismatches.
1419 
1420  3. Completely clean the build directory.
1421 
1422     If this does not work, the next step is to run `make dist-clean`, or
1423     removing the build output directory (`$BUILD`). This will clean all
1424     generated output, including your configuration. You will need to re-run
1425     `configure` after this step. A good idea is to run `make
1426     print-configuration` before running `make dist-clean`, as this will print
1427     your current `configure` command line. Here's a way to do this:
1428 
1429     ```
1430     make print-configuration > current-configuration
1431     make dist-clean
1432     bash configure $(cat current-configuration)
1433     make
1434     ```
1435 
1436  4. Re-clone the Mercurial repository
1437 
1438     Sometimes the Mercurial repository gets in a state that causes the product
1439     to be un-buildable. In such a case, the simplest solution is often the
1440     "sledgehammer approach": delete the entire repository, and re-clone it.
1441     If you have local changes, save them first to a different location using
1442     `hg export`.
1443 
1444 ### Specific Build Issues
1445 
1446 #### Clock Skew
1447 
1448 If you get an error message like this:
1449 ```
1450 File 'xxx' has modification time in the future.
1451 Clock skew detected. Your build may be incomplete.
1452 ```
1453 then the clock on your build machine is out of sync with the timestamps on the
1454 source files. Other errors, apparently unrelated but in fact caused by the
1455 clock skew, can occur along with the clock skew warnings. These secondary
1456 errors may tend to obscure the fact that the true root cause of the problem is
1457 an out-of-sync clock.
1458 
1459 If you see these warnings, reset the clock on the build machine, run `make
1460 clean` and restart the build.
1461 
1462 #### Out of Memory Errors
1463 
1464 On Solaris, you might get an error message like this:
1465 ```
1466 Trouble writing out table to disk
1467 ```
1468 To solve this, increase the amount of swap space on your build machine.
1469 
1470 On Windows, you might get error messages like this:
1471 ```
1472 fatal error - couldn't allocate heap
1473 cannot create ... Permission denied
1474 spawn failed
1475 ```
1476 This can be a sign of a Cygwin problem. See the information about solving
1477 problems in the [Cygwin](#cygwin) section. Rebooting the computer might help
1478 temporarily.
1479 
1480 ### Getting Help
1481 
1482 If none of the suggestions in this document helps you, or if you find what you
1483 believe is a bug in the build system, please contact the Build Group by sending
1484 a mail to [build-dev@openjdk.java.net](mailto:build-dev@openjdk.java.net).
1485 Please include the relevant parts of the configure and/or build log.
1486 
1487 If you need general help or advice about developing for the JDK, you can also
1488 contact the Adoption Group. See the section on [Contributing to OpenJDK](
1489 #contributing-to-openjdk) for more information.
1490 
1491 ## Hints and Suggestions for Advanced Users
1492 
1493 ### Setting Up a Repository for Pushing Changes (defpath)
1494 
1495 To help you prepare a proper push path for a Mercurial repository, there exists
1496 a useful tool known as [defpath](
1497 http://openjdk.java.net/projects/code-tools/defpath). It will help you setup a
1498 proper push path for pushing changes to the JDK.
1499 
1500 Install the extension by cloning
1501 `http://hg.openjdk.java.net/code-tools/defpath` and updating your `.hgrc` file.
1502 Here's one way to do this:
1503 
1504 ```
1505 cd ~
1506 mkdir hg-ext
1507 cd hg-ext
1508 hg clone http://hg.openjdk.java.net/code-tools/defpath
1509 cat << EOT >> ~/.hgrc
1510 [extensions]
1511 defpath=~/hg-ext/defpath/defpath.py
1512 EOT
1513 ```
1514 
1515 You can now setup a proper push path using:
1516 ```
1517 hg defpath -d -u <your OpenJDK username>
1518 ```
1519 
1520 ### Bash Completion
1521 
1522 The `configure` and `make` commands tries to play nice with bash command-line
1523 completion (using `<tab>` or `<tab><tab>`). To use this functionality, make
1524 sure you enable completion in your `~/.bashrc` (see instructions for bash in
1525 your operating system).
1526 
1527 Make completion will work out of the box, and will complete valid make targets.
1528 For instance, typing `make jdk-i<tab>` will complete to `make jdk-image`.
1529 
1530 The `configure` script can get completion for options, but for this to work you
1531 need to help `bash` on the way. The standard way of running the script, `bash
1532 configure`, will not be understood by bash completion. You need `configure` to
1533 be the command to run. One way to achieve this is to add a simple helper script
1534 to your path:
1535 
1536 ```
1537 cat << EOT > /tmp/configure
1538 #!/bin/bash
1539 if [ \$(pwd) = \$(cd \$(dirname \$0); pwd) ] ; then
1540   echo >&2 "Abort: Trying to call configure helper recursively"
1541   exit 1
1542 fi
1543 
1544 bash \$PWD/configure "\$@"
1545 EOT
1546 chmod +x /tmp/configure
1547 sudo mv /tmp/configure /usr/local/bin
1548 ```
1549 
1550 Now `configure --en<tab>-dt<tab>` will result in `configure --enable-dtrace`.
1551 
1552 ### Using Multiple Configurations
1553 
1554 You can have multiple configurations for a single source repository. When you
1555 create a new configuration, run `configure --with-conf-name=<name>` to create a
1556 configuration with the name `<name>`. Alternatively, you can create a directory
1557 under `build` and run `configure` from there, e.g. `mkdir build/<name> && cd
1558 build/<name> && bash ../../configure`.
1559 
1560 Then you can build that configuration using `make CONF_NAME=<name>` or `make
1561 CONF=<pattern>`, where `<pattern>` is a substring matching one or several
1562 configurations, e.g. `CONF=debug`. The special empty pattern (`CONF=`) will
1563 match *all* available configuration, so `make CONF= hotspot` will build the
1564 `hotspot` target for all configurations. Alternatively, you can execute `make`
1565 in the configuration directory, e.g. `cd build/<name> && make`.
1566 
1567 ### Handling Reconfigurations
1568 
1569 If you update the repository and part of the configure script has changed, the
1570 build system will force you to re-run `configure`.
1571 
1572 Most of the time, you will be fine by running `configure` again with the same
1573 arguments as the last time, which can easily be performed by `make
1574 reconfigure`. To simplify this, you can use the `CONF_CHECK` make control
1575 variable, either as `make CONF_CHECK=auto`, or by setting an environment
1576 variable. For instance, if you add `export CONF_CHECK=auto` to your `.bashrc`
1577 file, `make` will always run `reconfigure` automatically whenever the configure
1578 script has changed.
1579 
1580 You can also use `CONF_CHECK=ignore` to skip the check for a needed configure
1581 update. This might speed up the build, but comes at the risk of an incorrect
1582 build result. This is only recommended if you know what you're doing.
1583 
1584 From time to time, you will also need to modify the command line to `configure`
1585 due to changes. Use `make print-configure` to show the command line used for
1586 your current configuration.
1587 
1588 ### Using Fine-Grained Make Targets
1589 
1590 The default behavior for make is to create consistent and correct output, at
1591 the expense of build speed, if necessary.
1592 
1593 If you are prepared to take some risk of an incorrect build, and know enough of
1594 the system to understand how things build and interact, you can speed up the
1595 build process considerably by instructing make to only build a portion of the
1596 product.
1597 
1598 #### Building Individual Modules
1599 
1600 The safe way to use fine-grained make targets is to use the module specific
1601 make targets. All source code in the JDK is organized so it belongs to a
1602 module, e.g. `java.base` or `jdk.jdwp.agent`. You can build only a specific
1603 module, by giving it as make target: `make jdk.jdwp.agent`. If the specified
1604 module depends on other modules (e.g. `java.base`), those modules will be built
1605 first.
1606 
1607 You can also specify a set of modules, just as you can always specify a set of
1608 make targets: `make jdk.crypto.cryptoki jdk.crypto.ec jdk.crypto.mscapi
1609 jdk.crypto.ucrypto`
1610 
1611 #### Building Individual Module Phases
1612 
1613 The build process for each module is divided into separate phases. Not all
1614 modules need all phases. Which are needed depends on what kind of source code
1615 and other artifact the module consists of. The phases are:
1616 
1617   * `gensrc` (Generate source code to compile)
1618   * `gendata` (Generate non-source code artifacts)
1619   * `copy` (Copy resource artifacts)
1620   * `java` (Compile Java code)
1621   * `launchers` (Compile native executables)
1622   * `libs` (Compile native libraries)
1623   * `rmic` (Run the `rmic` tool)
1624 
1625 You can build only a single phase for a module by using the notation
1626 `$MODULE-$PHASE`. For instance, to build the `gensrc` phase for `java.base`,
1627 use `make java.base-gensrc`.
1628 
1629 Note that some phases may depend on others, e.g. `java` depends on `gensrc` (if
1630 present). Make will build all needed prerequisites before building the
1631 requested phase.
1632 
1633 #### Skipping the Dependency Check
1634 
1635 When using an iterative development style with frequent quick rebuilds, the
1636 dependency check made by make can take up a significant portion of the time
1637 spent on the rebuild. In such cases, it can be useful to bypass the dependency
1638 check in make.
1639 
1640 > **Note that if used incorrectly, this can lead to a broken build!**
1641 
1642 To achieve this, append `-only` to the build target. For instance, `make
1643 jdk.jdwp.agent-java-only` will *only* build the `java` phase of the
1644 `jdk.jdwp.agent` module. If the required dependencies are not present, the
1645 build can fail. On the other hand, the execution time measures in milliseconds.
1646 
1647 A useful pattern is to build the first time normally (e.g. `make
1648 jdk.jdwp.agent`) and then on subsequent builds, use the `-only` make target.
1649 
1650 #### Rebuilding Part of java.base (JDK\_FILTER)
1651 
1652 If you are modifying files in `java.base`, which is the by far largest module
1653 in the JDK, then you need to rebuild all those files whenever a single file has
1654 changed. (This inefficiency will hopefully be addressed in JDK 10.)
1655 
1656 As a hack, you can use the make control variable `JDK_FILTER` to specify a
1657 pattern that will be used to limit the set of files being recompiled. For
1658 instance, `make java.base JDK_FILTER=javax/crypto` (or, to combine methods,
1659 `make java.base-java-only JDK_FILTER=javax/crypto`) will limit the compilation
1660 to files in the `javax.crypto` package.
1661 
1662 ### Learn About Mercurial
1663 
1664 To become an efficient JDK developer, it is recommended that you invest in
1665 learning Mercurial properly. Here are some links that can get you started:
1666 
1667   * [Mercurial for git users](http://www.mercurial-scm.org/wiki/GitConcepts)
1668   * [The official Mercurial tutorial](http://www.mercurial-scm.org/wiki/Tutorial)
1669   * [hg init](http://hginit.com/)
1670   * [Mercurial: The Definitive Guide](http://hgbook.red-bean.com/read/)
1671 
1672 ## Understanding the Build System
1673 
1674 This section will give you a more technical description on the details of the
1675 build system.
1676 
1677 ### Configurations
1678 
1679 The build system expects to find one or more configuration. These are
1680 technically defined by the `spec.gmk` in a subdirectory to the `build`
1681 subdirectory. The `spec.gmk` file is generated by `configure`, and contains in
1682 principle the configuration (directly or by files included by `spec.gmk`).
1683 
1684 You can, in fact, select a configuration to build by pointing to the `spec.gmk`
1685 file with the `SPEC` make control variable, e.g. `make SPEC=$BUILD/spec.gmk`.
1686 While this is not the recommended way to call `make` as a user, it is what is
1687 used under the hood by the build system.
1688 
1689 ### Build Output Structure
1690 
1691 The build output for a configuration will end up in `build/<configuration
1692 name>`, which we refer to as `$BUILD` in this document. The `$BUILD` directory
1693 contains the following important directories:
1694 
1695 ```
1696 buildtools/
1697 configure-support/
1698 hotspot/
1699 images/
1700 jdk/
1701 make-support/
1702 support/
1703 test-results/
1704 test-support/
1705 ```
1706 
1707 This is what they are used for:
1708 
1709   * `images`: This is the directory were the output of the `*-image` make
1710     targets end up. For instance, `make jdk-image` ends up in `images/jdk`.
1711 
1712   * `jdk`: This is the "exploded image". After `make jdk`, you will be able to
1713     launch the newly built JDK by running `$BUILD/jdk/bin/java`.
1714 
1715   * `test-results`: This directory contains the results from running tests.
1716 
1717   * `support`: This is an area for intermediate files needed during the build,
1718     e.g. generated source code, object files and class files. Some noteworthy
1719     directories in `support` is `gensrc`, which contains the generated source
1720     code, and the `modules_*` directories, which contains the files in a
1721     per-module hierarchy that will later be collapsed into the `jdk` directory
1722     of the exploded image.
1723 
1724   * `buildtools`: This is an area for tools compiled for the build platform
1725     that are used during the rest of the build.
1726 
1727   * `hotspot`: This is an area for intermediate files needed when building
1728     hotspot.
1729 
1730   * `configure-support`, `make-support` and `test-support`: These directories
1731     contain files that are needed by the build system for `configure`, `make`
1732     and for running tests.
1733 
1734 ### Fixpath
1735 
1736 Windows path typically look like `C:\User\foo`, while Unix paths look like
1737 `/home/foo`. Tools with roots from Unix often experience issues related to this
1738 mismatch when running on Windows.
1739 
1740 In the JDK build, we always use Unix paths internally, and only just before
1741 calling a tool that does not understand Unix paths do we convert them to
1742 Windows paths.
1743 
1744 This conversion is done by the `fixpath` tool, which is a small wrapper that
1745 modifies unix-style paths to Windows-style paths in command lines. Fixpath is
1746 compiled automatically by `configure`.
1747 
1748 ### Native Debug Symbols
1749 
1750 Native libraries and executables can have debug symbol (and other debug
1751 information) associated with them. How this works is very much platform
1752 dependent, but a common problem is that debug symbol information takes a lot of
1753 disk space, but is rarely needed by the end user.
1754 
1755 The JDK supports different methods on how to handle debug symbols. The
1756 method used is selected by `--with-native-debug-symbols`, and available methods
1757 are `none`, `internal`, `external`, `zipped`.
1758 
1759   * `none` means that no debug symbols will be generated during the build.
1760 
1761   * `internal` means that debug symbols will be generated during the build, and
1762     they will be stored in the generated binary.
1763 
1764   * `external` means that debug symbols will be generated during the build, and
1765     after the compilation, they will be moved into a separate `.debuginfo` file.
1766     (This was previously known as FDS, Full Debug Symbols).
1767 
1768   * `zipped` is like `external`, but the .debuginfo file will also be zipped
1769     into a `.diz` file.
1770 
1771 When building for distribution, `zipped` is a good solution. Binaries built
1772 with `internal` is suitable for use by developers, since they facilitate
1773 debugging, but should be stripped before distributed to end users.
1774 
1775 ### Autoconf Details
1776 
1777 The `configure` script is based on the autoconf framework, but in some details
1778 deviate from a normal autoconf `configure` script.
1779 
1780 The `configure` script in the top level directory of the JDK is just a thin
1781 wrapper that calls `make/autoconf/configure`. This in turn will run `autoconf`
1782 to create the runnable (generated) configure script, as
1783 `.build/generated-configure.sh`. Apart from being responsible for the
1784 generation of the runnable script, the `configure` script also provides
1785 functionality that is not easily expressed in the normal Autoconf framework. As
1786 part of this functionality, the generated script is called.
1787 
1788 The build system will detect if the Autoconf source files have changed, and
1789 will trigger a regeneration of the generated script if needed. You can also
1790 manually request such an update by `bash configure autogen`.
1791 
1792 In previous versions of the JDK, the generated script was checked in at
1793 `make/autoconf/generated-configure.sh`. This is no longer the case.
1794 
1795 ### Developing the Build System Itself
1796 
1797 This section contains a few remarks about how to develop for the build system
1798 itself. It is not relevant if you are only making changes in the product source
1799 code.
1800 
1801 While technically using `make`, the make source files of the JDK does not
1802 resemble most other Makefiles. Instead of listing specific targets and actions
1803 (perhaps using patterns), the basic modus operandi is to call a high-level
1804 function (or properly, macro) from the API in `make/common`. For instance, to
1805 compile all classes in the `jdk.internal.foo` package in the `jdk.foo` module,
1806 a call like this would be made:
1807 
1808 ```
1809 $(eval $(call SetupJavaCompilation, BUILD_FOO_CLASSES, \
1810     SETUP := GENERATE_OLDBYTECODE, \
1811     SRC := $(TOPDIR)/src/jkd.foo/share/classes, \
1812     INCLUDES := jdk/internal/foo, \
1813     BIN := $(SUPPORT_OUTPUTDIR)/foo_classes, \
1814 ))
1815 ```
1816 
1817 By encapsulating and expressing the high-level knowledge of *what* should be
1818 done, rather than *how* it should be done (as is normal in Makefiles), we can
1819 build a much more powerful and flexible build system.
1820 
1821 Correct dependency tracking is paramount. Sloppy dependency tracking will lead
1822 to improper parallelization, or worse, race conditions.
1823 
1824 To test for/debug race conditions, try running `make JOBS=1` and `make
1825 JOBS=100` and see if it makes any difference. (It shouldn't).
1826 
1827 To compare the output of two different builds and see if, and how, they differ,
1828 run `$BUILD1/compare.sh -o $BUILD2`, where `$BUILD1` and `$BUILD2` are the two
1829 builds you want to compare.
1830 
1831 To automatically build two consecutive versions and compare them, use
1832 `COMPARE_BUILD`. The value of `COMPARE_BUILD` is a set of variable=value
1833 assignments, like this:
1834 ```
1835 make COMPARE_BUILD=CONF=--enable-new-hotspot-feature:MAKE=hotspot
1836 ```
1837 See `make/InitSupport.gmk` for details on how to use `COMPARE_BUILD`.
1838 
1839 To analyze build performance, run with `LOG=trace` and check `$BUILD/build-trace-time.log`.
1840 Use `JOBS=1` to avoid parallelism.
1841 
1842 Please check that you adhere to the [Code Conventions for the Build System](
1843 http://openjdk.java.net/groups/build/doc/code-conventions.html) before
1844 submitting patches.
1845 
1846 ## Contributing to the JDK
1847 
1848 So, now you've built your JDK, and made your first patch, and want to
1849 contribute it back to the OpenJDK Community.
1850 
1851 First of all: Thank you! We gladly welcome your contribution.
1852 However, please bear in mind that the JDK is a massive project, and we must ask
1853 you to follow our rules and guidelines to be able to accept your contribution.
1854 
1855 The official place to start is the ['How to contribute' page](
1856 http://openjdk.java.net/contribute/). There is also an official (but somewhat
1857 outdated and skimpy on details) [Developer's Guide](
1858 http://openjdk.java.net/guide/).
1859 
1860 If this seems overwhelming to you, the Adoption Group is there to help you! A
1861 good place to start is their ['New Contributor' page](
1862 https://wiki.openjdk.java.net/display/Adoption/New+Contributor), or start
1863 reading the comprehensive [Getting Started Kit](
1864 https://adoptopenjdk.gitbooks.io/adoptopenjdk-getting-started-kit/en/). The
1865 Adoption Group will also happily answer any questions you have about
1866 contributing. Contact them by [mail](
1867 http://mail.openjdk.java.net/mailman/listinfo/adoption-discuss) or [IRC](
1868 http://openjdk.java.net/irc/).
1869 
1870 ---
1871 # Override styles from the base CSS file that are not ideal for this document.
1872 header-includes:
1873  - '<style type="text/css">pre, code, tt { color: #1d6ae5; }</style>'
1874 ---