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, extra care must be taken to make sure the [Cygwin](#cygwin)
  79     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 / 7.1 (using kernel 3.8.13)
 154  Solaris            Solaris 11.1 SRU 21.4.1 / 11.2 SRU 5.5
 155  macOS              Mac OS X 10.9 (Mavericks) / 10.10 (Yosemite)
 156  Windows            Windows Server 2012 R2
 157 
 158 The double version numbers for Linux, Solaris and macOS is due to the hybrid
 159 model used at Oracle, where header files and external libraries from an older
 160 version 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 layer is Cygwin. (Msys is no longer
 178 supported due to a too old bash; msys2 and the new Windows Subsystem for Linux
 179 (WSL) would likely be possible to support in a future version but that would
 180 require effort 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 thus 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 on Windows. 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 ### Solaris
 225 
 226 See `make/devkit/solaris11.1-package-list.txt` for a list of recommended
 227 packages to install when building on Solaris. The versions specified in this
 228 list is the versions used by the daily builds at Oracle, and is likely to work
 229 properly.
 230 
 231 Older versions of Solaris shipped a broken version of `objcopy`. At least
 232 version 2.21.1 is needed, which is provided by Solaris 11 Update 1. Objcopy is
 233 needed if you want to have external debug symbols. Please make sure you are
 234 using at least version 2.21.1 of objcopy, or that you disable external debug
 235 symbols.
 236 
 237 ### macOS
 238 
 239 Apple is using a quite aggressive scheme of pushing OS updates, and coupling
 240 these updates with required updates of Xcode. Unfortunately, this makes it
 241 difficult for a project such as the JDK to keep pace with a continuously updated
 242 machine running macOS. See the section on [Apple Xcode](#apple-xcode) on some
 243 strategies to deal with this.
 244 
 245 It is recommended that you use at least Mac OS X 10.13 (High Sierra). At the time
 246 of writing, the JDK has been successfully compiled on macOS 10.12 (Sierra).
 247 
 248 The standard macOS environment contains the basic tooling needed to build, but
 249 for external libraries a package manager is recommended. The JDK uses
 250 [homebrew](https://brew.sh/) in the examples, but feel free to use whatever
 251 manager you want (or none).
 252 
 253 ### Linux
 254 
 255 It is often not much problem to build the JDK on Linux. The only general advice
 256 is to try to use the compilers, external libraries and header files as provided
 257 by your distribution.
 258 
 259 The basic tooling is provided as part of the core operating system, but you
 260 will most likely need to install developer packages.
 261 
 262 For apt-based distributions (Debian, Ubuntu, etc), try this:
 263 ```
 264 sudo apt-get install build-essential
 265 ```
 266 
 267 For rpm-based distributions (Fedora, Red Hat, etc), try this:
 268 ```
 269 sudo yum groupinstall "Development Tools"
 270 ```
 271 
 272 ### AIX
 273 
 274 The regular builds by SAP is using AIX version 7.1, but AIX 5.3 is also
 275 supported. See the [OpenJDK PowerPC Port Status Page](
 276 http://cr.openjdk.java.net/~simonis/ppc-aix-port) for details.
 277 
 278 ## Native Compiler (Toolchain) Requirements
 279 
 280 Large portions of the JDK consists of native code, that needs to be compiled to
 281 be able to run on the target platform. In theory, toolchain and operating
 282 system should be independent factors, but in practice there's more or less a
 283 one-to-one correlation between target operating system and toolchain.
 284 
 285  Operating system   Supported toolchain
 286  ------------------ -------------------------
 287  Linux              gcc, clang
 288  macOS              Apple Xcode (using clang)
 289  Solaris            Oracle Solaris Studio
 290  AIX                IBM XL C/C++
 291  Windows            Microsoft Visual Studio
 292 
 293 Please see the individual sections on the toolchains for version
 294 recommendations. As a reference, these versions of the toolchains are used, at
 295 the time of writing, by Oracle for the daily builds of the JDK. It should be
 296 possible to compile the JDK with both older and newer versions, but the closer
 297 you stay to this list, the more likely you are to compile successfully without
 298 issues.
 299 
 300  Operating system   Toolchain version
 301  ------------------ -------------------------------------------------------
 302  Linux              gcc 7.3.0
 303  macOS              Apple Xcode 9.4 (using clang 9.1.0)
 304  Solaris            Oracle Solaris Studio 12.4 (with compiler version 5.13)
 305  Windows            Microsoft Visual Studio 2017 update 15.5.5
 306 
 307 ### gcc
 308 
 309 The minimum accepted version of gcc is 4.8. Older versions will generate a warning
 310 by `configure` and are unlikely to work.
 311 
 312 The JDK is currently known to be able to compile with at least version 7.4 of
 313 gcc.
 314 
 315 In general, any version between these two should be usable.
 316 
 317 ### clang
 318 
 319 The minimum accepted version of clang is 3.2. Older versions will not be
 320 accepted by `configure`.
 321 
 322 To use clang instead of gcc on Linux, use `--with-toolchain-type=clang`.
 323 
 324 ### Apple Xcode
 325 
 326 The oldest supported version of Xcode is 8.
 327 
 328 You will need the Xcode command lines developers tools to be able to build
 329 the JDK. (Actually, *only* the command lines tools are needed, not the IDE.)
 330 The simplest way to install these is to run:
 331 ```
 332 xcode-select --install
 333 ```
 334 
 335 It is advisable to keep an older version of Xcode for building the JDK when
 336 updating Xcode. This [blog page](
 337 http://iosdevelopertips.com/xcode/install-multiple-versions-of-xcode.html) has
 338 good suggestions on managing multiple Xcode versions. To use a specific version
 339 of Xcode, use `xcode-select -s` before running `configure`, or use
 340 `--with-toolchain-path` to point to the version of Xcode to use, e.g.
 341 `configure --with-toolchain-path=/Applications/Xcode8.app/Contents/Developer/usr/bin`
 342 
 343 If you have recently (inadvertently) updated your OS and/or Xcode version, and
 344 the JDK can no longer be built, please see the section on [Problems with the
 345 Build Environment](#problems-with-the-build-environment), and [Getting
 346 Help](#getting-help) to find out if there are any recent, non-merged patches
 347 available for this update.
 348 
 349 ### Oracle Solaris Studio
 350 
 351 The minimum accepted version of the Solaris Studio compilers is 5.13
 352 (corresponding to Solaris Studio 12.4). Older versions will not be accepted by
 353 configure.
 354 
 355 The Solaris Studio installation should contain at least these packages:
 356 
 357  Package                                            Version
 358  -------------------------------------------------- -------------
 359  developer/solarisstudio-124/backend                12.4-1.0.6.0
 360  developer/solarisstudio-124/c++                    12.4-1.0.10.0
 361  developer/solarisstudio-124/cc                     12.4-1.0.4.0
 362  developer/solarisstudio-124/library/c++-libs       12.4-1.0.10.0
 363  developer/solarisstudio-124/library/math-libs      12.4-1.0.0.1
 364  developer/solarisstudio-124/library/studio-gccrt   12.4-1.0.0.1
 365  developer/solarisstudio-124/studio-common          12.4-1.0.0.1
 366  developer/solarisstudio-124/studio-ja              12.4-1.0.0.1
 367  developer/solarisstudio-124/studio-legal           12.4-1.0.0.1
 368  developer/solarisstudio-124/studio-zhCN            12.4-1.0.0.1
 369 
 370 Compiling with Solaris Studio can sometimes be finicky. This is the exact
 371 version used by Oracle, which worked correctly at the time of writing:
 372 ```
 373 $ cc -V
 374 cc: Sun C 5.13 SunOS_i386 2014/10/20
 375 $ CC -V
 376 CC: Sun C++ 5.13 SunOS_i386 151846-10 2015/10/30
 377 ```
 378 
 379 ### Microsoft Visual Studio
 380 
 381 The minimum accepted version of Visual Studio is 2010. Older versions will not
 382 be accepted by `configure`. The maximum accepted version of Visual Studio is
 383 2017. Versions older than 2017 are unlikely to continue working for long.
 384 
 385 If you have multiple versions of Visual Studio installed, `configure` will by
 386 default pick the latest. You can request a specific version to be used by
 387 setting `--with-toolchain-version`, e.g. `--with-toolchain-version=2015`.
 388 
 389 If you get `LINK: fatal error LNK1123: failure during conversion to COFF: file
 390 invalid` when building using Visual Studio 2010, you have encountered
 391 [KB2757355](http://support.microsoft.com/kb/2757355), a bug triggered by a
 392 specific installation order. However, the solution suggested by the KB article
 393 does not always resolve the problem. See [this stackoverflow discussion](
 394 https://stackoverflow.com/questions/10888391) for other suggestions.
 395 
 396 ### IBM XL C/C++
 397 
 398 The regular builds by SAP is using version 12.1, described as `IBM XL C/C++ for
 399 AIX, V12.1 (5765-J02, 5725-C72) Version: 12.01.0000.0017`.
 400 
 401 See the [OpenJDK PowerPC Port Status Page](
 402 http://cr.openjdk.java.net/~simonis/ppc-aix-port) for details.
 403 
 404 ## Boot JDK Requirements
 405 
 406 Paradoxically, building the JDK requires a pre-existing JDK. This is called the
 407 "boot JDK". The boot JDK does not, however, have to be a JDK built directly from
 408 the source code available in the OpenJDK Community.  If you are porting the JDK
 409 to a new platform, chances are that there already exists another JDK for that
 410 platform that is usable as boot JDK.
 411 
 412 The rule of thumb is that the boot JDK for building JDK major version *N*
 413 should be a JDK of major version *N-1*, so for building JDK 9 a JDK 8 would be
 414 suitable as boot JDK. However, the JDK should be able to "build itself", so an
 415 up-to-date build of the current JDK source is an acceptable alternative. If
 416 you are following the *N-1* rule, make sure you've got the latest update
 417 version, since JDK 8 GA might not be able to build JDK 9 on all platforms.
 418 
 419 Early in the release cycle, version *N-1* may not yet have been released. In
 420 that case, the preferred boot JDK will be version *N-2* until version *N-1*
 421 is available.
 422 
 423 If the boot JDK is not automatically detected, or the wrong JDK is picked, use
 424 `--with-boot-jdk` to point to the JDK to use.
 425 
 426 ### Getting JDK binaries
 427 
 428 JDK binaries for Linux, Windows and macOS can be downloaded from
 429 [jdk.java.net](http://jdk.java.net). An alternative is to download the
 430 [Oracle JDK](http://www.oracle.com/technetwork/java/javase/downloads). Another
 431 is the [Adopt OpenJDK Project](https://adoptopenjdk.net/), which publishes
 432 experimental prebuilt binaries for various platforms.
 433 
 434 On Linux you can also get a JDK from the Linux distribution. On apt-based
 435 distros (like Debian and Ubuntu), `sudo apt-get install openjdk-<VERSION>-jdk`
 436 is typically enough to install a JDK \<VERSION\>. On rpm-based distros (like
 437 Fedora and Red Hat), try `sudo yum install java-<VERSION>-openjdk-devel`.
 438 
 439 ## External Library Requirements
 440 
 441 Different platforms require different external libraries. In general, libraries
 442 are not optional - that is, they are either required or not used.
 443 
 444 If a required library is not detected by `configure`, you need to provide the
 445 path to it. There are two forms of the `configure` arguments to point to an
 446 external library: `--with-<LIB>=<path>` or `--with-<LIB>-include=<path to
 447 include> --with-<LIB>-lib=<path to lib>`. The first variant is more concise,
 448 but require the include files an library files to reside in a default hierarchy
 449 under this directory. In most cases, it works fine.
 450 
 451 As a fallback, the second version allows you to point to the include directory
 452 and the lib directory separately.
 453 
 454 ### FreeType
 455 
 456 FreeType2 from [The FreeType Project](http://www.freetype.org/) is not required
 457 on any platform. The exception is on Unix-based platforms when configuring such
 458 that the build artifacts will reference a system installed library,
 459 rather than bundling the JDK’s own copy.
 460 
 461   * To install on an apt-based Linux, try running `sudo apt-get install
 462     libfreetype6-dev`.
 463   * To install on an rpm-based Linux, try running `sudo yum install
 464     freetype-devel`.
 465   * To install on Solaris, try running `pkg install system/library/freetype-2`.
 466 
 467 Use `--with-freetype-include=<path>` and `--with-freetype-lib=<path>`
 468 if `configure` does not automatically locate the platform FreeType files.
 469 
 470 ### CUPS
 471 
 472 CUPS, [Common UNIX Printing System](http://www.cups.org) header files are
 473 required on all platforms, except Windows. Often these files are provided by
 474 your operating system.
 475 
 476   * To install on an apt-based Linux, try running `sudo apt-get install
 477     libcups2-dev`.
 478   * To install on an rpm-based Linux, try running `sudo yum install
 479     cups-devel`.
 480   * To install on Solaris, try running `pkg install print/cups`.
 481 
 482 Use `--with-cups=<path>` if `configure` does not properly locate your CUPS
 483 files.
 484 
 485 ### X11
 486 
 487 Certain [X11](http://www.x.org/) libraries and include files are required on
 488 Linux and Solaris.
 489 
 490   * To install on an apt-based Linux, try running `sudo apt-get install
 491     libx11-dev libxext-dev libxrender-dev libxtst-dev libxt-dev`.
 492   * To install on an rpm-based Linux, try running `sudo yum install
 493     libXtst-devel libXt-devel libXrender-devel libXi-devel`.
 494   * To install on Solaris, try running `pkg install x11/header/x11-protocols
 495     x11/library/libice x11/library/libpthread-stubs x11/library/libsm
 496     x11/library/libx11 x11/library/libxau x11/library/libxcb
 497     x11/library/libxdmcp x11/library/libxevie x11/library/libxext
 498     x11/library/libxrender x11/library/libxscrnsaver x11/library/libxtst
 499     x11/library/toolkit/libxt`.
 500 
 501 Use `--with-x=<path>` if `configure` does not properly locate your X11 files.
 502 
 503 ### ALSA
 504 
 505 ALSA, [Advanced Linux Sound Architecture](https://www.alsa-project.org/) is
 506 required on Linux. At least version 0.9.1 of ALSA is required.
 507 
 508   * To install on an apt-based Linux, try running `sudo apt-get install
 509     libasound2-dev`.
 510   * To install on an rpm-based Linux, try running `sudo yum install
 511     alsa-lib-devel`.
 512 
 513 Use `--with-alsa=<path>` if `configure` does not properly locate your ALSA
 514 files.
 515 
 516 ### libffi
 517 
 518 libffi, the [Portable Foreign Function Interface Library](
 519 http://sourceware.org/libffi) is required when building the Zero version of
 520 Hotspot.
 521 
 522   * To install on an apt-based Linux, try running `sudo apt-get install
 523     libffi-dev`.
 524   * To install on an rpm-based Linux, try running `sudo yum install
 525     libffi-devel`.
 526 
 527 Use `--with-libffi=<path>` if `configure` does not properly locate your libffi
 528 files.
 529 
 530 ## Build Tools Requirements
 531 
 532 ### Autoconf
 533 
 534 The JDK requires [Autoconf](http://www.gnu.org/software/autoconf) on all
 535 platforms. At least version 2.69 is required.
 536 
 537   * To install on an apt-based Linux, try running `sudo apt-get install
 538     autoconf`.
 539   * To install on an rpm-based Linux, try running `sudo yum install
 540     autoconf`.
 541   * To install on macOS, try running `brew install autoconf`.
 542   * To install on Windows, try running `<path to Cygwin setup>/setup-x86_64 -q
 543     -P autoconf`.
 544 
 545 If `configure` has problems locating your installation of autoconf, you can
 546 specify it using the `AUTOCONF` environment variable, like this:
 547 
 548 ```
 549 AUTOCONF=<path to autoconf> configure ...
 550 ```
 551 
 552 ### GNU Make
 553 
 554 The JDK requires [GNU Make](http://www.gnu.org/software/make). No other flavors
 555 of make are supported.
 556 
 557 At least version 3.81 of GNU Make must be used. For distributions supporting
 558 GNU Make 4.0 or above, we strongly recommend it. GNU Make 4.0 contains useful
 559 functionality to handle parallel building (supported by `--with-output-sync`)
 560 and speed and stability improvements.
 561 
 562 Note that `configure` locates and verifies a properly functioning version of
 563 `make` and stores the path to this `make` binary in the configuration. If you
 564 start a build using `make` on the command line, you will be using the version
 565 of make found first in your `PATH`, and not necessarily the one stored in the
 566 configuration. This initial make will be used as "bootstrap make", and in a
 567 second stage, the make located by `configure` will be called. Normally, this
 568 will present no issues, but if you have a very old `make`, or a non-GNU Make
 569 `make` in your path, this might cause issues.
 570 
 571 If you want to override the default make found by `configure`, use the `MAKE`
 572 configure variable, e.g. `configure MAKE=/opt/gnu/make`.
 573 
 574 On Solaris, it is common to call the GNU version of make by using `gmake`.
 575 
 576 ### GNU Bash
 577 
 578 The JDK requires [GNU Bash](http://www.gnu.org/software/bash). No other shells
 579 are supported.
 580 
 581 At least version 3.2 of GNU Bash must be used.
 582 
 583 ## Running Configure
 584 
 585 To build the JDK, you need a "configuration", which consists of a directory
 586 where to store the build output, coupled with information about the platform,
 587 the specific build machine, and choices that affect how the JDK is built.
 588 
 589 The configuration is created by the `configure` script. The basic invocation of
 590 the `configure` script looks like this:
 591 
 592 ```
 593 bash configure [options]
 594 ```
 595 
 596 This will create an output directory containing the configuration and setup an
 597 area for the build result. This directory typically looks like
 598 `build/linux-x64-normal-server-release`, but the actual name depends on your
 599 specific configuration. (It can also be set directly, see [Using Multiple
 600 Configurations](#using-multiple-configurations)). This directory is referred to
 601 as `$BUILD` in this documentation.
 602 
 603 `configure` will try to figure out what system you are running on and where all
 604 necessary build components are. If you have all prerequisites for building
 605 installed, it should find everything. If it fails to detect any component
 606 automatically, it will exit and inform you about the problem.
 607 
 608 Some command line examples:
 609 
 610   * Create a 32-bit build for Windows with FreeType2 in `C:\freetype-i586`:
 611     ```
 612     bash configure --with-freetype=/cygdrive/c/freetype-i586 --with-target-bits=32
 613     ```
 614 
 615   * Create a debug build with the `server` JVM and DTrace enabled:
 616     ```
 617     bash configure --enable-debug --with-jvm-variants=server --enable-dtrace
 618     ```
 619 
 620 ### Common Configure Arguments
 621 
 622 Here follows some of the most common and important `configure` argument.
 623 
 624 To get up-to-date information on *all* available `configure` argument, please
 625 run:
 626 ```
 627 bash configure --help
 628 ```
 629 
 630 (Note that this help text also include general autoconf options, like
 631 `--dvidir`, that is not relevant to the JDK. To list only JDK-specific
 632 features, use `bash configure --help=short` instead.)
 633 
 634 #### Configure Arguments for Tailoring the Build
 635 
 636   * `--enable-debug` - Set the debug level to `fastdebug` (this is a shorthand
 637     for `--with-debug-level=fastdebug`)
 638   * `--with-debug-level=<level>` - Set the debug level, which can be `release`,
 639     `fastdebug`, `slowdebug` or `optimized`. Default is `release`. `optimized`
 640     is variant of `release` with additional Hotspot debug code.
 641   * `--with-native-debug-symbols=<method>` - Specify if and how native debug
 642     symbols should be built. Available methods are `none`, `internal`,
 643     `external`, `zipped`. Default behavior depends on platform. See [Native
 644     Debug Symbols](#native-debug-symbols) for more details.
 645   * `--with-version-string=<string>` - Specify the version string this build
 646     will be identified with.
 647   * `--with-version-<part>=<value>` - A group of options, where `<part>` can be
 648     any of `pre`, `opt`, `build`, `major`, `minor`, `security` or `patch`. Use
 649     these options to modify just the corresponding part of the version string
 650     from the default, or the value provided by `--with-version-string`.
 651   * `--with-jvm-variants=<variant>[,<variant>...]` - Build the specified variant
 652     (or variants) of Hotspot. Valid variants are: `server`, `client`,
 653     `minimal`, `core`, `zero`, `custom`. Note that not all
 654     variants are possible to combine in a single build.
 655   * `--with-jvm-features=<feature>[,<feature>...]` - Use the specified JVM
 656     features when building Hotspot. The list of features will be enabled on top
 657     of the default list. For the `custom` JVM variant, this default list is
 658     empty. A complete list of available JVM features can be found using `bash
 659     configure --help`.
 660   * `--with-target-bits=<bits>` - Create a target binary suitable for running
 661     on a `<bits>` platform. Use this to create 32-bit output on a 64-bit build
 662     platform, instead of doing a full cross-compile. (This is known as a
 663     *reduced* build.)
 664 
 665 #### Configure Arguments for Native Compilation
 666 
 667   * `--with-devkit=<path>` - Use this devkit for compilers, tools and resources
 668   * `--with-sysroot=<path>` - Use this directory as sysroot
 669   * `--with-extra-path=<path>[;<path>]` - Prepend these directories to the
 670     default path when searching for all kinds of binaries
 671   * `--with-toolchain-path=<path>[;<path>]` - Prepend these directories when
 672     searching for toolchain binaries (compilers etc)
 673   * `--with-extra-cflags=<flags>` - Append these flags when compiling JDK C
 674     files
 675   * `--with-extra-cxxflags=<flags>` - Append these flags when compiling JDK C++
 676     files
 677   * `--with-extra-ldflags=<flags>` - Append these flags when linking JDK
 678     libraries
 679 
 680 #### Configure Arguments for External Dependencies
 681 
 682   * `--with-boot-jdk=<path>` - Set the path to the [Boot JDK](
 683     #boot-jdk-requirements)
 684   * `--with-freetype=<path>` - Set the path to [FreeType](#freetype)
 685   * `--with-cups=<path>` - Set the path to [CUPS](#cups)
 686   * `--with-x=<path>` - Set the path to [X11](#x11)
 687   * `--with-alsa=<path>` - Set the path to [ALSA](#alsa)
 688   * `--with-libffi=<path>` - Set the path to [libffi](#libffi)
 689   * `--with-jtreg=<path>` - Set the path to JTReg. See [Running Tests](
 690     #running-tests)
 691 
 692 Certain third-party libraries used by the JDK (libjpeg, giflib, libpng, lcms
 693 and zlib) are included in the JDK repository. The default behavior of the
 694 JDK build is to use this version of these libraries, but they might be
 695 replaced by an external version. To do so, specify `system` as the `<source>`
 696 option in these arguments. (The default is `bundled`).
 697 
 698   * `--with-libjpeg=<source>` - Use the specified source for libjpeg
 699   * `--with-giflib=<source>` - Use the specified source for giflib
 700   * `--with-libpng=<source>` - Use the specified source for libpng
 701   * `--with-lcms=<source>` - Use the specified source for lcms
 702   * `--with-zlib=<source>` - Use the specified source for zlib
 703 
 704 On Linux, it is possible to select either static or dynamic linking of the C++
 705 runtime. The default is static linking, with dynamic linking as fallback if the
 706 static library is not found.
 707 
 708   * `--with-stdc++lib=<method>` - Use the specified method (`static`, `dynamic`
 709     or `default`) for linking the C++ runtime.
 710 
 711 ### Configure Control Variables
 712 
 713 It is possible to control certain aspects of `configure` by overriding the
 714 value of `configure` variables, either on the command line or in the
 715 environment.
 716 
 717 Normally, this is **not recommended**. If used improperly, it can lead to a
 718 broken configuration. Unless you're well versed in the build system, this is
 719 hard to use properly. Therefore, `configure` will print a warning if this is
 720 detected.
 721 
 722 However, there are a few `configure` variables, known as *control variables*
 723 that are supposed to be overriden on the command line. These are variables that
 724 describe the location of tools needed by the build, like `MAKE` or `GREP`. If
 725 any such variable is specified, `configure` will use that value instead of
 726 trying to autodetect the tool. For instance, `bash configure
 727 MAKE=/opt/gnumake4.0/bin/make`.
 728 
 729 If a configure argument exists, use that instead, e.g. use `--with-jtreg`
 730 instead of setting `JTREGEXE`.
 731 
 732 Also note that, despite what autoconf claims, setting `CFLAGS` will not
 733 accomplish anything. Instead use `--with-extra-cflags` (and similar for
 734 `cxxflags` and `ldflags`).
 735 
 736 ## Running Make
 737 
 738 When you have a proper configuration, all you need to do to build the JDK is to
 739 run `make`. (But see the warning at [GNU Make](#gnu-make) about running the
 740 correct version of make.)
 741 
 742 When running `make` without any arguments, the default target is used, which is
 743 the same as running `make default` or `make jdk`. This will build a minimal (or
 744 roughly minimal) set of compiled output (known as an "exploded image") needed
 745 for a developer to actually execute the newly built JDK. The idea is that in an
 746 incremental development fashion, when doing a normal make, you should only
 747 spend time recompiling what's changed (making it purely incremental) and only
 748 do the work that's needed to actually run and test your code.
 749 
 750 The output of the exploded image resides in `$BUILD/jdk`. You can test the
 751 newly built JDK like this: `$BUILD/jdk/bin/java -version`.
 752 
 753 ### Common Make Targets
 754 
 755 Apart from the default target, here are some common make targets:
 756 
 757   * `hotspot` - Build all of hotspot (but only hotspot)
 758   * `hotspot-<variant>` - Build just the specified jvm variant
 759   * `images` or `product-images` - Build the JDK image
 760   * `docs` or `docs-image` - Build the documentation image
 761   * `test-image` - Build the test image
 762   * `all` or `all-images` - Build all images (product, docs and test)
 763   * `bootcycle-images` - Build images twice, second time with newly built JDK
 764     (good for testing)
 765   * `clean` - Remove all files generated by make, but not those generated by
 766     configure
 767   * `dist-clean` - Remove all files, including configuration
 768 
 769 Run `make help` to get an up-to-date list of important make targets and make
 770 control variables.
 771 
 772 It is possible to build just a single module, a single phase, or a single phase
 773 of a single module, by creating make targets according to these followin
 774 patterns. A phase can be either of `gensrc`, `gendata`, `copy`, `java`,
 775 `launchers`, `libs` or `rmic`. See [Using Fine-Grained Make Targets](
 776 #using-fine-grained-make-targets) for more details about this functionality.
 777 
 778   * `<phase>` - Build the specified phase and everything it depends on
 779   * `<module>` - Build the specified module and everything it depends on
 780   * `<module>-<phase>` - Compile the specified phase for the specified module
 781     and everything it depends on
 782 
 783 Similarly, it is possible to clean just a part of the build by creating make
 784 targets according to these patterns:
 785 
 786   * `clean-<outputdir>` - Remove the subdir in the output dir with the name
 787   * `clean-<phase>` - Remove all build results related to a certain build
 788     phase
 789   * `clean-<module>` - Remove all build results related to a certain module
 790   * `clean-<module>-<phase>` - Remove all build results related to a certain
 791     module and phase
 792 
 793 ### Make Control Variables
 794 
 795 It is possible to control `make` behavior by overriding the value of `make`
 796 variables, either on the command line or in the environment.
 797 
 798 Normally, this is **not recommended**. If used improperly, it can lead to a
 799 broken build. Unless you're well versed in the build system, this is hard to
 800 use properly. Therefore, `make` will print a warning if this is detected.
 801 
 802 However, there are a few `make` variables, known as *control variables* that
 803 are supposed to be overriden on the command line. These make up the "make time"
 804 configuration, as opposed to the "configure time" configuration.
 805 
 806 #### General Make Control Variables
 807 
 808   * `JOBS` - Specify the number of jobs to build with. See [Build
 809     Performance](#build-performance).
 810   * `LOG` - Specify the logging level and functionality. See [Checking the
 811     Build Log File](#checking-the-build-log-file)
 812   * `CONF` and `CONF_NAME` - Selecting the configuration(s) to use. See [Using
 813     Multiple Configurations](#using-multiple-configurations)
 814 
 815 #### Test Make Control Variables
 816 
 817 These make control variables only make sense when running tests. Please see
 818 [Testing the JDK](testing.html) for details.
 819 
 820   * `TEST`
 821   * `TEST_JOBS`
 822   * `JTREG`
 823   * `GTEST`
 824 
 825 #### Advanced Make Control Variables
 826 
 827 These advanced make control variables can be potentially unsafe. See [Hints and
 828 Suggestions for Advanced Users](#hints-and-suggestions-for-advanced-users) and
 829 [Understanding the Build System](#understanding-the-build-system) for details.
 830 
 831   * `SPEC`
 832   * `CONF_CHECK`
 833   * `COMPARE_BUILD`
 834   * `JDK_FILTER`
 835 
 836 ## Running Tests
 837 
 838 Most of the JDK tests are using the [JTReg](http://openjdk.java.net/jtreg)
 839 test framework. Make sure that your configuration knows where to find your
 840 installation of JTReg. If this is not picked up automatically, use the
 841 `--with-jtreg=<path to jtreg home>` option to point to the JTReg framework.
 842 Note that this option should point to the JTReg home, i.e. the top directory,
 843 containing `lib/jtreg.jar` etc.
 844 
 845 The [Adoption Group](https://wiki.openjdk.java.net/display/Adoption) provides
 846 recent builds of jtreg [here](
 847 https://adopt-openjdk.ci.cloudbees.com/job/jtreg/lastSuccessfulBuild/artifact).
 848 Download the latest `.tar.gz` file, unpack it, and point `--with-jtreg` to the
 849 `jtreg` directory that you just unpacked.
 850 
 851 To execute the most basic tests (tier 1), use:
 852 ```
 853 make run-test-tier1
 854 ```
 855 
 856 For more details on how to run tests, please see the [Testing
 857 the JDK](testing.html) document.
 858 
 859 ## Cross-compiling
 860 
 861 Cross-compiling means using one platform (the *build* platform) to generate
 862 output that can ran on another platform (the *target* platform).
 863 
 864 The typical reason for cross-compiling is that the build is performed on a more
 865 powerful desktop computer, but the resulting binaries will be able to run on a
 866 different, typically low-performing system. Most of the complications that
 867 arise when building for embedded is due to this separation of *build* and
 868 *target* systems.
 869 
 870 This requires a more complex setup and build procedure. This section assumes
 871 you are familiar with cross-compiling in general, and will only deal with the
 872 particularities of cross-compiling the JDK. If you are new to cross-compiling,
 873 please see the [external links at Wikipedia](
 874 https://en.wikipedia.org/wiki/Cross_compiler#External_links) for a good start
 875 on reading materials.
 876 
 877 Cross-compiling the JDK requires you to be able to build both for the build
 878 platform and for the target platform. The reason for the former is that we need
 879 to build and execute tools during the build process, both native tools and Java
 880 tools.
 881 
 882 If all you want to do is to compile a 32-bit version, for the same OS, on a
 883 64-bit machine, consider using `--with-target-bits=32` instead of doing a
 884 full-blown cross-compilation. (While this surely is possible, it's a lot more
 885 work and will take much longer to build.)
 886 
 887 ### Cross compiling the easy way with OpenJDK devkits
 888 
 889 The OpenJDK build system provides out-of-the box support for creating and using
 890 so called devkits. A `devkit` is basically a collection of a cross-compiling
 891 toolchain and a sysroot environment which can easily be used together with the
 892 `--with-devkit` configure option to cross compile the OpenJDK. On Linux/x86_64,
 893 the following command:
 894 ```
 895 bash configure --with-devkit=<devkit-path> --openjdk-target=ppc64-linux-gnu && make
 896 ```
 897 
 898 will configure and build OpenJDK for Linux/ppc64 assuming that `<devkit-path>`
 899 points to a Linux/x86_64 to Linux/ppc64 devkit.
 900 
 901 Devkits can be created from the `make/devkit` directory by executing:
 902 ```
 903 make [ TARGETS="<TARGET_TRIPLET>+" ] [ BASE_OS=<OS> ] [ BASE_OS_VERSION=<VER> ]
 904 ```
 905 
 906 where `TARGETS` contains one or more `TARGET_TRIPLET`s of the form
 907 described in [section 3.4 of the GNU Autobook](
 908 https://sourceware.org/autobook/autobook/autobook_17.html). If no
 909 targets are given, a native toolchain for the current platform will be
 910 created. Currently, at least the following targets are known to work:
 911 
 912  Supported devkit targets
 913  ------------------------
 914  x86_64-linux-gnu
 915  aarch64-linux-gnu
 916  arm-linux-gnueabihf
 917  ppc64-linux-gnu
 918  ppc64le-linux-gnu
 919  s390x-linux-gnu
 920 
 921 `BASE_OS` must be one of "OEL6" for Oracle Enterprise Linux 6 or
 922 "Fedora" (if not specified "OEL6" will be the default). If the base OS
 923 is "Fedora" the corresponding Fedora release can be specified with the
 924 help of the `BASE_OS_VERSION` option (with "27" as default version).
 925 If the build is successful, the new devkits can be found in the
 926 `build/devkit/result` subdirectory:
 927 ```
 928 cd make/devkit
 929 make TARGETS="ppc64le-linux-gnu aarch64-linux-gnu" BASE_OS=Fedora BASE_OS_VERSION=21
 930 ls -1 ../../build/devkit/result/
 931 x86_64-linux-gnu-to-aarch64-linux-gnu
 932 x86_64-linux-gnu-to-ppc64le-linux-gnu
 933 ```
 934 
 935 Notice that devkits are not only useful for targeting different build
 936 platforms. Because they contain the full build dependencies for a
 937 system (i.e. compiler and root file system), they can easily be used
 938 to build well-known, reliable and reproducible build environments. You
 939 can for example create and use a devkit with GCC 7.3 and a Fedora 12
 940 sysroot environment (with glibc 2.11) on Ubuntu 14.04 (which doesn't
 941 have GCC 7.3 by default) to produce OpenJDK binaries which will run on
 942 all Linux systems with runtime libraries newer than the ones from
 943 Fedora 12 (e.g. Ubuntu 16.04, SLES 11 or RHEL 6).
 944 
 945 ### Boot JDK and Build JDK
 946 
 947 When cross-compiling, make sure you use a boot JDK that runs on the *build*
 948 system, and not on the *target* system.
 949 
 950 To be able to build, we need a "Build JDK", which is a JDK built from the
 951 current sources (that is, the same as the end result of the entire build
 952 process), but able to run on the *build* system, and not the *target* system.
 953 (In contrast, the Boot JDK should be from an older release, e.g. JDK 8 when
 954 building JDK 9.)
 955 
 956 The build process will create a minimal Build JDK for you, as part of building.
 957 To speed up the build, you can use `--with-build-jdk` to `configure` to point
 958 to a pre-built Build JDK. Please note that the build result is unpredictable,
 959 and can possibly break in subtle ways, if the Build JDK does not **exactly**
 960 match the current sources.
 961 
 962 ### Specifying the Target Platform
 963 
 964 You *must* specify the target platform when cross-compiling. Doing so will also
 965 automatically turn the build into a cross-compiling mode. The simplest way to
 966 do this is to use the `--openjdk-target` argument, e.g.
 967 `--openjdk-target=arm-linux-gnueabihf`. or `--openjdk-target=aarch64-oe-linux`.
 968 This will automatically set the `--build`, `--host` and `--target` options for
 969 autoconf, which can otherwise be confusing. (In autoconf terminology, the
 970 "target" is known as "host", and "target" is used for building a Canadian
 971 cross-compiler.)
 972 
 973 ### Toolchain Considerations
 974 
 975 You will need two copies of your toolchain, one which generates output that can
 976 run on the target system (the normal, or *target*, toolchain), and one that
 977 generates output that can run on the build system (the *build* toolchain). Note
 978 that cross-compiling is only supported for gcc at the time being. The gcc
 979 standard is to prefix cross-compiling toolchains with the target denominator.
 980 If you follow this standard, `configure` is likely to pick up the toolchain
 981 correctly.
 982 
 983 The *build* toolchain will be autodetected just the same way the normal
 984 *build*/*target* toolchain will be autodetected when not cross-compiling. If
 985 this is not what you want, or if the autodetection fails, you can specify a
 986 devkit containing the *build* toolchain using `--with-build-devkit` to
 987 `configure`, or by giving `BUILD_CC` and `BUILD_CXX` arguments.
 988 
 989 It is often helpful to locate the cross-compilation tools, headers and
 990 libraries in a separate directory, outside the normal path, and point out that
 991 directory to `configure`. Do this by setting the sysroot (`--with-sysroot`) and
 992 appending the directory when searching for cross-compilations tools
 993 (`--with-toolchain-path`). As a compact form, you can also use `--with-devkit`
 994 to point to a single directory, if it is correctly setup. (See `basics.m4` for
 995 details.)
 996 
 997 If you are unsure what toolchain and versions to use, these have been proved
 998 working at the time of writing:
 999 
1000   * [aarch64](
1001 https://releases.linaro.org/archive/13.11/components/toolchain/binaries/gcc-linaro-aarch64-linux-gnu-4.8-2013.11_linux.tar.xz)
1002   * [arm 32-bit hardware floating  point](
1003 https://launchpad.net/linaro-toolchain-unsupported/trunk/2012.09/+download/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux.tar.bz2)
1004 
1005 ### Native Libraries
1006 
1007 You will need copies of external native libraries for the *target* system,
1008 present on the *build* machine while building.
1009 
1010 Take care not to replace the *build* system's version of these libraries by
1011 mistake, since that can render the *build* machine unusable.
1012 
1013 Make sure that the libraries you point to (ALSA, X11, etc) are for the
1014 *target*, not the *build*, platform.
1015 
1016 #### ALSA
1017 
1018 You will need alsa libraries suitable for your *target* system. For most cases,
1019 using Debian's pre-built libraries work fine.
1020 
1021 Note that alsa is needed even if you only want to build a headless JDK.
1022 
1023   * Go to [Debian Package Search](https://www.debian.org/distrib/packages) and
1024     search for the `libasound2` and `libasound2-dev` packages for your *target*
1025     system. Download them to /tmp.
1026 
1027   * Install the libraries into the cross-compilation toolchain. For instance:
1028 ```
1029 cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc
1030 dpkg-deb -x /tmp/libasound2_1.0.25-4_armhf.deb .
1031 dpkg-deb -x /tmp/libasound2-dev_1.0.25-4_armhf.deb .
1032 ```
1033 
1034   * If alsa is not properly detected by `configure`, you can point it out by
1035     `--with-alsa`.
1036 
1037 #### X11
1038 
1039 You will need X11 libraries suitable for your *target* system. For most cases,
1040 using Debian's pre-built libraries work fine.
1041 
1042 Note that X11 is needed even if you only want to build a headless JDK.
1043 
1044   * Go to [Debian Package Search](https://www.debian.org/distrib/packages),
1045     search for the following packages for your *target* system, and download them
1046     to /tmp/target-x11:
1047       * libxi
1048       * libxi-dev
1049       * x11proto-core-dev
1050       * x11proto-input-dev
1051       * x11proto-kb-dev
1052       * x11proto-render-dev
1053       * x11proto-xext-dev
1054       * libice-dev
1055       * libxrender
1056       * libxrender-dev
1057       * libsm-dev
1058       * libxt-dev
1059       * libx11
1060       * libx11-dev
1061       * libxtst
1062       * libxtst-dev
1063       * libxext
1064       * libxext-dev
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/usr
1069     mkdir X11R6
1070     cd X11R6
1071     for deb in /tmp/target-x11/*.deb ; do dpkg-deb -x $deb . ; done
1072     mv usr/* .
1073     cd lib
1074     cp arm-linux-gnueabihf/* .
1075     ```
1076 
1077     You can ignore the following messages. These libraries are not needed to
1078     successfully complete a full JDK build.
1079     ```
1080     cp: cannot stat `arm-linux-gnueabihf/libICE.so': No such file or directory
1081     cp: cannot stat `arm-linux-gnueabihf/libSM.so': No such file or directory
1082     cp: cannot stat `arm-linux-gnueabihf/libXt.so': No such file or directory
1083     ```
1084 
1085   * If the X11 libraries are not properly detected by `configure`, you can
1086     point them out by `--with-x`.
1087 
1088 ### Creating And Using Sysroots With qemu-deboostrap
1089 
1090 Fortunately, you can create sysroots for foreign architectures with tools
1091 provided by your OS. On Debian/Ubuntu systems, one could use `qemu-deboostrap` to
1092 create the *target* system chroot, which would have the native libraries and headers
1093 specific to that *target* system. After that, we can use the cross-compiler on the *build*
1094 system, pointing into chroot to get the build dependencies right. This allows building
1095 for foreign architectures with native compilation speed.
1096 
1097 For example, cross-compiling to AArch64 from x86_64 could be done like this:
1098 
1099   * Install cross-compiler on the *build* system:
1100 ```
1101 apt install g++-aarch64-linux-gnu gcc-aarch64-linux-gnu
1102 ```
1103 
1104   * Create chroot on the *build* system, configuring it for *target* system:
1105 ```
1106 sudo qemu-debootstrap --arch=arm64 --verbose \
1107        --include=fakeroot,build-essential,libx11-dev,libxext-dev,libxrender-dev,libxtst-dev,libxt-dev,libcups2-dev,libfontconfig1-dev,libasound2-dev,libfreetype6-dev,libpng12-dev \
1108        --resolve-deps jessie /chroots/arm64 http://httpredir.debian.org/debian/
1109 ```
1110 
1111   * Configure and build with newly created chroot as sysroot/toolchain-path:
1112 ```
1113 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/
1114 make images
1115 ls build/linux-aarch64-normal-server-release/
1116 ```
1117 
1118 The build does not create new files in that chroot, so it can be reused for multiple builds
1119 without additional cleanup.
1120 
1121 Architectures that are known to successfully cross-compile like this are:
1122 
1123   Target        `CC`                      `CXX`                       `--arch=...` `--openjdk-target=...`
1124   ------------  ------------------------- --------------------------- ------------ ----------------------
1125   x86           default                   default                     i386         i386-linux-gnu
1126   armhf         gcc-arm-linux-gnueabihf   g++-arm-linux-gnueabihf     armhf        arm-linux-gnueabihf
1127   aarch64       gcc-aarch64-linux-gnu     g++-aarch64-linux-gnu       arm64        aarch64-linux-gnu
1128   ppc64el       gcc-powerpc64le-linux-gnu g++-powerpc64le-linux-gnu   ppc64el      powerpc64le-linux-gnu
1129   s390x         gcc-s390x-linux-gnu       g++-s390x-linux-gnu         s390x        s390x-linux-gnu
1130 
1131 Additional architectures might be supported by Debian/Ubuntu Ports.
1132 
1133 ### Building for ARM/aarch64
1134 
1135 A common cross-compilation target is the ARM CPU. When building for ARM, it is
1136 useful to set the ABI profile. A number of pre-defined ABI profiles are
1137 available using `--with-abi-profile`: arm-vfp-sflt, arm-vfp-hflt, arm-sflt,
1138 armv5-vfp-sflt, armv6-vfp-hflt. Note that soft-float ABIs are no longer
1139 properly supported by the JDK.
1140 
1141 ### Verifying the Build
1142 
1143 The build will end up in a directory named like
1144 `build/linux-arm-normal-server-release`.
1145 
1146 Inside this build output directory, the `images/jdk` will contain the newly
1147 built JDK, for your *target* system.
1148 
1149 Copy these folders to your *target* system. Then you can run e.g.
1150 `images/jdk/bin/java -version`.
1151 
1152 ## Build Performance
1153 
1154 Building the JDK requires a lot of horsepower. Some of the build tools can be
1155 adjusted to utilize more or less of resources such as parallel threads and
1156 memory. The `configure` script analyzes your system and selects reasonable
1157 values for such options based on your hardware. If you encounter resource
1158 problems, such as out of memory conditions, you can modify the detected values
1159 with:
1160 
1161   * `--with-num-cores` -- number of cores in the build system, e.g.
1162     `--with-num-cores=8`.
1163 
1164   * `--with-memory-size` -- memory (in MB) available in the build system, e.g.
1165     `--with-memory-size=1024`
1166 
1167 You can also specify directly the number of build jobs to use with
1168 `--with-jobs=N` to `configure`, or `JOBS=N` to `make`. Do not use the `-j` flag
1169 to `make`. In most cases it will be ignored by the makefiles, but it can cause
1170 problems for some make targets.
1171 
1172 It might also be necessary to specify the JVM arguments passed to the Boot JDK,
1173 using e.g. `--with-boot-jdk-jvmargs="-Xmx8G"`. Doing so will override the
1174 default JVM arguments passed to the Boot JDK.
1175 
1176 At the end of a successful execution of `configure`, you will get a performance
1177 summary, indicating how well the build will perform. Here you will also get
1178 performance hints. If you want to build fast, pay attention to those!
1179 
1180 If you want to tweak build performance, run with `make LOG=info` to get a build
1181 time summary at the end of the build process.
1182 
1183 ### Disk Speed
1184 
1185 If you are using network shares, e.g. via NFS, for your source code, make sure
1186 the build directory is situated on local disk (e.g. by `ln -s
1187 /localdisk/jdk-build $JDK-SHARE/build`). The performance penalty is extremely
1188 high for building on a network share; close to unusable.
1189 
1190 Also, make sure that your build tools (including Boot JDK and toolchain) is
1191 located on a local disk and not a network share.
1192 
1193 As has been stressed elsewhere, do use SSD for source code and build directory,
1194 as well as (if possible) the build tools.
1195 
1196 ### Virus Checking
1197 
1198 The use of virus checking software, especially on Windows, can *significantly*
1199 slow down building of the JDK. If possible, turn off such software, or exclude
1200 the directory containing the JDK source code from on-the-fly checking.
1201 
1202 ### Ccache
1203 
1204 The JDK build supports building with ccache when using gcc or clang. Using
1205 ccache can radically speed up compilation of native code if you often rebuild
1206 the same sources. Your milage may vary however, so we recommend evaluating it
1207 for yourself. To enable it, make sure it's on the path and configure with
1208 `--enable-ccache`.
1209 
1210 ### Precompiled Headers
1211 
1212 By default, the Hotspot build uses preccompiled headers (PCH) on the toolchains
1213 were it is properly supported (clang, gcc, and Visual Studio). Normally, this
1214 speeds up the build process, but in some circumstances, it can actually slow
1215 things down.
1216 
1217 You can experiment by disabling precompiled headers using
1218 `--disable-precompiled-headers`.
1219 
1220 ### Icecc / icecream
1221 
1222 [icecc/icecream](http://github.com/icecc/icecream) is a simple way to setup a
1223 distributed compiler network. If you have multiple machines available for
1224 building the JDK, you can drastically cut individual build times by utilizing
1225 it.
1226 
1227 To use, setup an icecc network, and install icecc on the build machine. Then
1228 run `configure` using `--enable-icecc`.
1229 
1230 ### Using sjavac
1231 
1232 To speed up Java compilation, especially incremental compilations, you can try
1233 the experimental sjavac compiler by using `--enable-sjavac`.
1234 
1235 ### Building the Right Target
1236 
1237 Selecting the proper target to build can have dramatic impact on build time.
1238 For normal usage, `jdk` or the default target is just fine. You only need to
1239 build `images` for shipping, or if your tests require it.
1240 
1241 See also [Using Fine-Grained Make Targets](#using-fine-grained-make-targets) on
1242 how to build an even smaller subset of the product.
1243 
1244 ## Troubleshooting
1245 
1246 If your build fails, it can sometimes be difficult to pinpoint the problem or
1247 find a proper solution.
1248 
1249 ### Locating the Source of the Error
1250 
1251 When a build fails, it can be hard to pinpoint the actual cause of the error.
1252 In a typical build process, different parts of the product build in parallel,
1253 with the output interlaced.
1254 
1255 #### Build Failure Summary
1256 
1257 To help you, the build system will print a failure summary at the end. It looks
1258 like this:
1259 
1260 ```
1261 ERROR: Build failed for target 'hotspot' in configuration 'linux-x64' (exit code 2)
1262 
1263 === Output from failing command(s) repeated here ===
1264 * For target hotspot_variant-server_libjvm_objs_psMemoryPool.o:
1265 /localhome/hg/jdk9-sandbox/hotspot/src/share/vm/services/psMemoryPool.cpp:1:1: error: 'failhere' does not name a type
1266    ... (rest of output omitted)
1267 
1268 * All command lines available in /localhome/hg/jdk9-sandbox/build/linux-x64/make-support/failure-logs.
1269 === End of repeated output ===
1270 
1271 === Make failed targets repeated here ===
1272 lib/CompileJvm.gmk:207: recipe for target '/localhome/hg/jdk9-sandbox/build/linux-x64/hotspot/variant-server/libjvm/objs/psMemoryPool.o' failed
1273 make/Main.gmk:263: recipe for target 'hotspot-server-libs' failed
1274 === End of repeated output ===
1275 
1276 Hint: Try searching the build log for the name of the first failed target.
1277 Hint: If caused by a warning, try configure --disable-warnings-as-errors.
1278 ```
1279 
1280 Let's break it down! First, the selected configuration, and the top-level
1281 target you entered on the command line that caused the failure is printed.
1282 
1283 Then, between the `Output from failing command(s) repeated here` and `End of
1284 repeated output` the first lines of output (stdout and stderr) from the actual
1285 failing command is repeated. In most cases, this is the error message that
1286 caused the build to fail. If multiple commands were failing (this can happen in
1287 a parallel build), output from all failed commands will be printed here.
1288 
1289 The path to the `failure-logs` directory is printed. In this file you will find
1290 a `<target>.log` file that contains the output from this command in its
1291 entirety, and also a `<target>.cmd`, which contain the complete command line
1292 used for running this command. You can re-run the failing command by executing
1293 `. <path to failure-logs>/<target>.cmd` in your shell.
1294 
1295 Another way to trace the failure is to follow the chain of make targets, from
1296 top-level targets to individual file targets. Between `Make failed targets
1297 repeated here` and `End of repeated output` the output from make showing this
1298 chain is repeated. The first failed recipe will typically contain the full path
1299 to the file in question that failed to compile. Following lines will show a
1300 trace of make targets why we ended up trying to compile that file.
1301 
1302 Finally, some hints are given on how to locate the error in the complete log.
1303 In this example, we would try searching the log file for "`psMemoryPool.o`".
1304 Another way to quickly locate make errors in the log is to search for "`]
1305 Error`" or "`***`".
1306 
1307 Note that the build failure summary will only help you if the issue was a
1308 compilation failure or similar. If the problem is more esoteric, or is due to
1309 errors in the build machinery, you will likely get empty output logs, and `No
1310 indication of failed target found` instead of the make target chain.
1311 
1312 #### Checking the Build Log File
1313 
1314 The output (stdout and stderr) from the latest build is always stored in
1315 `$BUILD/build.log`. The previous build log is stored as `build.log.old`. This
1316 means that it is not necessary to redirect the build output yourself if you
1317 want to process it.
1318 
1319 You can increase the verbosity of the log file, by the `LOG` control variable
1320 to `make`. If you want to see the command lines used in compilations, use
1321 `LOG=cmdlines`. To increase the general verbosity, use `LOG=info`, `LOG=debug`
1322 or `LOG=trace`. Both of these can be combined with `cmdlines`, e.g.
1323 `LOG=info,cmdlines`. The `debug` log level will show most shell commands
1324 executed by make, and `trace` will show all. Beware that both these log levels
1325 will produce a massive build log!
1326 
1327 ### Fixing Unexpected Build Failures
1328 
1329 Most of the time, the build will fail due to incorrect changes in the source
1330 code.
1331 
1332 Sometimes the build can fail with no apparent changes that have caused the
1333 failure. If this is the first time you are building the JDK on this particular
1334 computer, and the build fails, the problem is likely with your build
1335 environment. But even if you have previously built the JDK with success, and it
1336 now fails, your build environment might have changed (perhaps due to OS
1337 upgrades or similar). But most likely, such failures are due to problems with
1338 the incremental rebuild.
1339 
1340 #### Problems with the Build Environment
1341 
1342 Make sure your configuration is correct. Re-run `configure`, and look for any
1343 warnings. Warnings that appear in the middle of the `configure` output is also
1344 repeated at the end, after the summary. The entire log is stored in
1345 `$BUILD/configure.log`.
1346 
1347 Verify that the summary at the end looks correct. Are you indeed using the Boot
1348 JDK and native toolchain that you expect?
1349 
1350 By default, the JDK has a strict approach where warnings from the compiler is
1351 considered errors which fail the build. For very new or very old compiler
1352 versions, this can trigger new classes of warnings, which thus fails the build.
1353 Run `configure` with `--disable-warnings-as-errors` to turn of this behavior.
1354 (The warnings will still show, but not make the build fail.)
1355 
1356 #### Problems with Incremental Rebuilds
1357 
1358 Incremental rebuilds mean that when you modify part of the product, only the
1359 affected parts get rebuilt. While this works great in most cases, and
1360 significantly speed up the development process, from time to time complex
1361 interdependencies will result in an incorrect build result. This is the most
1362 common cause for unexpected build problems.
1363 
1364 Here are a suggested list of things to try if you are having unexpected build
1365 problems. Each step requires more time than the one before, so try them in
1366 order. Most issues will be solved at step 1 or 2.
1367 
1368  1. Make sure your repository is up-to-date
1369 
1370     Run `hg pull -u` to make sure you have the latest changes.
1371 
1372  2. Clean build results
1373 
1374     The simplest way to fix incremental rebuild issues is to run `make clean`.
1375     This will remove all build results, but not the configuration or any build
1376     system support artifacts. In most cases, this will solve build errors
1377     resulting from incremental build mismatches.
1378 
1379  3. Completely clean the build directory.
1380 
1381     If this does not work, the next step is to run `make dist-clean`, or
1382     removing the build output directory (`$BUILD`). This will clean all
1383     generated output, including your configuration. You will need to re-run
1384     `configure` after this step. A good idea is to run `make
1385     print-configuration` before running `make dist-clean`, as this will print
1386     your current `configure` command line. Here's a way to do this:
1387 
1388     ```
1389     make print-configuration > current-configuration
1390     make dist-clean
1391     bash configure $(cat current-configuration)
1392     make
1393     ```
1394 
1395  4. Re-clone the Mercurial repository
1396 
1397     Sometimes the Mercurial repository gets in a state that causes the product
1398     to be un-buildable. In such a case, the simplest solution is often the
1399     "sledgehammer approach": delete the entire repository, and re-clone it.
1400     If you have local changes, save them first to a different location using
1401     `hg export`.
1402 
1403 ### Specific Build Issues
1404 
1405 #### Clock Skew
1406 
1407 If you get an error message like this:
1408 ```
1409 File 'xxx' has modification time in the future.
1410 Clock skew detected. Your build may be incomplete.
1411 ```
1412 then the clock on your build machine is out of sync with the timestamps on the
1413 source files. Other errors, apparently unrelated but in fact caused by the
1414 clock skew, can occur along with the clock skew warnings. These secondary
1415 errors may tend to obscure the fact that the true root cause of the problem is
1416 an out-of-sync clock.
1417 
1418 If you see these warnings, reset the clock on the build machine, run `make
1419 clean` and restart the build.
1420 
1421 #### Out of Memory Errors
1422 
1423 On Solaris, you might get an error message like this:
1424 ```
1425 Trouble writing out table to disk
1426 ```
1427 To solve this, increase the amount of swap space on your build machine.
1428 
1429 On Windows, you might get error messages like this:
1430 ```
1431 fatal error - couldn't allocate heap
1432 cannot create ... Permission denied
1433 spawn failed
1434 ```
1435 This can be a sign of a Cygwin problem. See the information about solving
1436 problems in the [Cygwin](#cygwin) section. Rebooting the computer might help
1437 temporarily.
1438 
1439 ### Getting Help
1440 
1441 If none of the suggestions in this document helps you, or if you find what you
1442 believe is a bug in the build system, please contact the Build Group by sending
1443 a mail to [build-dev@openjdk.java.net](mailto:build-dev@openjdk.java.net).
1444 Please include the relevant parts of the configure and/or build log.
1445 
1446 If you need general help or advice about developing for the JDK, you can also
1447 contact the Adoption Group. See the section on [Contributing to OpenJDK](
1448 #contributing-to-openjdk) for more information.
1449 
1450 ## Hints and Suggestions for Advanced Users
1451 
1452 ### Setting Up a Repository for Pushing Changes (defpath)
1453 
1454 To help you prepare a proper push path for a Mercurial repository, there exists
1455 a useful tool known as [defpath](
1456 http://openjdk.java.net/projects/code-tools/defpath). It will help you setup a
1457 proper push path for pushing changes to the JDK.
1458 
1459 Install the extension by cloning
1460 `http://hg.openjdk.java.net/code-tools/defpath` and updating your `.hgrc` file.
1461 Here's one way to do this:
1462 
1463 ```
1464 cd ~
1465 mkdir hg-ext
1466 cd hg-ext
1467 hg clone http://hg.openjdk.java.net/code-tools/defpath
1468 cat << EOT >> ~/.hgrc
1469 [extensions]
1470 defpath=~/hg-ext/defpath/defpath.py
1471 EOT
1472 ```
1473 
1474 You can now setup a proper push path using:
1475 ```
1476 hg defpath -d -u <your OpenJDK username>
1477 ```
1478 
1479 ### Bash Completion
1480 
1481 The `configure` and `make` commands tries to play nice with bash command-line
1482 completion (using `<tab>` or `<tab><tab>`). To use this functionality, make
1483 sure you enable completion in your `~/.bashrc` (see instructions for bash in
1484 your operating system).
1485 
1486 Make completion will work out of the box, and will complete valid make targets.
1487 For instance, typing `make jdk-i<tab>` will complete to `make jdk-image`.
1488 
1489 The `configure` script can get completion for options, but for this to work you
1490 need to help `bash` on the way. The standard way of running the script, `bash
1491 configure`, will not be understood by bash completion. You need `configure` to
1492 be the command to run. One way to achieve this is to add a simple helper script
1493 to your path:
1494 
1495 ```
1496 cat << EOT > /tmp/configure
1497 #!/bin/bash
1498 if [ \$(pwd) = \$(cd \$(dirname \$0); pwd) ] ; then
1499   echo >&2 "Abort: Trying to call configure helper recursively"
1500   exit 1
1501 fi
1502 
1503 bash \$PWD/configure "\$@"
1504 EOT
1505 chmod +x /tmp/configure
1506 sudo mv /tmp/configure /usr/local/bin
1507 ```
1508 
1509 Now `configure --en<tab>-dt<tab>` will result in `configure --enable-dtrace`.
1510 
1511 ### Using Multiple Configurations
1512 
1513 You can have multiple configurations for a single source repository. When you
1514 create a new configuration, run `configure --with-conf-name=<name>` to create a
1515 configuration with the name `<name>`. Alternatively, you can create a directory
1516 under `build` and run `configure` from there, e.g. `mkdir build/<name> && cd
1517 build/<name> && bash ../../configure`.
1518 
1519 Then you can build that configuration using `make CONF_NAME=<name>` or `make
1520 CONF=<pattern>`, where `<pattern>` is a substring matching one or several
1521 configurations, e.g. `CONF=debug`. The special empty pattern (`CONF=`) will
1522 match *all* available configuration, so `make CONF= hotspot` will build the
1523 `hotspot` target for all configurations. Alternatively, you can execute `make`
1524 in the configuration directory, e.g. `cd build/<name> && make`.
1525 
1526 ### Handling Reconfigurations
1527 
1528 If you update the repository and part of the configure script has changed, the
1529 build system will force you to re-run `configure`.
1530 
1531 Most of the time, you will be fine by running `configure` again with the same
1532 arguments as the last time, which can easily be performed by `make
1533 reconfigure`. To simplify this, you can use the `CONF_CHECK` make control
1534 variable, either as `make CONF_CHECK=auto`, or by setting an environment
1535 variable. For instance, if you add `export CONF_CHECK=auto` to your `.bashrc`
1536 file, `make` will always run `reconfigure` automatically whenever the configure
1537 script has changed.
1538 
1539 You can also use `CONF_CHECK=ignore` to skip the check for a needed configure
1540 update. This might speed up the build, but comes at the risk of an incorrect
1541 build result. This is only recommended if you know what you're doing.
1542 
1543 From time to time, you will also need to modify the command line to `configure`
1544 due to changes. Use `make print-configure` to show the command line used for
1545 your current configuration.
1546 
1547 ### Using Fine-Grained Make Targets
1548 
1549 The default behavior for make is to create consistent and correct output, at
1550 the expense of build speed, if necessary.
1551 
1552 If you are prepared to take some risk of an incorrect build, and know enough of
1553 the system to understand how things build and interact, you can speed up the
1554 build process considerably by instructing make to only build a portion of the
1555 product.
1556 
1557 #### Building Individual Modules
1558 
1559 The safe way to use fine-grained make targets is to use the module specific
1560 make targets. All source code in the JDK is organized so it belongs to a
1561 module, e.g. `java.base` or `jdk.jdwp.agent`. You can build only a specific
1562 module, by giving it as make target: `make jdk.jdwp.agent`. If the specified
1563 module depends on other modules (e.g. `java.base`), those modules will be built
1564 first.
1565 
1566 You can also specify a set of modules, just as you can always specify a set of
1567 make targets: `make jdk.crypto.cryptoki jdk.crypto.ec jdk.crypto.mscapi
1568 jdk.crypto.ucrypto`
1569 
1570 #### Building Individual Module Phases
1571 
1572 The build process for each module is divided into separate phases. Not all
1573 modules need all phases. Which are needed depends on what kind of source code
1574 and other artifact the module consists of. The phases are:
1575 
1576   * `gensrc` (Generate source code to compile)
1577   * `gendata` (Generate non-source code artifacts)
1578   * `copy` (Copy resource artifacts)
1579   * `java` (Compile Java code)
1580   * `launchers` (Compile native executables)
1581   * `libs` (Compile native libraries)
1582   * `rmic` (Run the `rmic` tool)
1583 
1584 You can build only a single phase for a module by using the notation
1585 `$MODULE-$PHASE`. For instance, to build the `gensrc` phase for `java.base`,
1586 use `make java.base-gensrc`.
1587 
1588 Note that some phases may depend on others, e.g. `java` depends on `gensrc` (if
1589 present). Make will build all needed prerequisites before building the
1590 requested phase.
1591 
1592 #### Skipping the Dependency Check
1593 
1594 When using an iterative development style with frequent quick rebuilds, the
1595 dependency check made by make can take up a significant portion of the time
1596 spent on the rebuild. In such cases, it can be useful to bypass the dependency
1597 check in make.
1598 
1599 > **Note that if used incorrectly, this can lead to a broken build!**
1600 
1601 To achieve this, append `-only` to the build target. For instance, `make
1602 jdk.jdwp.agent-java-only` will *only* build the `java` phase of the
1603 `jdk.jdwp.agent` module. If the required dependencies are not present, the
1604 build can fail. On the other hand, the execution time measures in milliseconds.
1605 
1606 A useful pattern is to build the first time normally (e.g. `make
1607 jdk.jdwp.agent`) and then on subsequent builds, use the `-only` make target.
1608 
1609 #### Rebuilding Part of java.base (JDK\_FILTER)
1610 
1611 If you are modifying files in `java.base`, which is the by far largest module
1612 in the JDK, then you need to rebuild all those files whenever a single file has
1613 changed. (This inefficiency will hopefully be addressed in JDK 10.)
1614 
1615 As a hack, you can use the make control variable `JDK_FILTER` to specify a
1616 pattern that will be used to limit the set of files being recompiled. For
1617 instance, `make java.base JDK_FILTER=javax/crypto` (or, to combine methods,
1618 `make java.base-java-only JDK_FILTER=javax/crypto`) will limit the compilation
1619 to files in the `javax.crypto` package.
1620 
1621 ### Learn About Mercurial
1622 
1623 To become an efficient JDK developer, it is recommended that you invest in
1624 learning Mercurial properly. Here are some links that can get you started:
1625 
1626   * [Mercurial for git users](http://www.mercurial-scm.org/wiki/GitConcepts)
1627   * [The official Mercurial tutorial](http://www.mercurial-scm.org/wiki/Tutorial)
1628   * [hg init](http://hginit.com/)
1629   * [Mercurial: The Definitive Guide](http://hgbook.red-bean.com/read/)
1630 
1631 ## Understanding the Build System
1632 
1633 This section will give you a more technical description on the details of the
1634 build system.
1635 
1636 ### Configurations
1637 
1638 The build system expects to find one or more configuration. These are
1639 technically defined by the `spec.gmk` in a subdirectory to the `build`
1640 subdirectory. The `spec.gmk` file is generated by `configure`, and contains in
1641 principle the configuration (directly or by files included by `spec.gmk`).
1642 
1643 You can, in fact, select a configuration to build by pointing to the `spec.gmk`
1644 file with the `SPEC` make control variable, e.g. `make SPEC=$BUILD/spec.gmk`.
1645 While this is not the recommended way to call `make` as a user, it is what is
1646 used under the hood by the build system.
1647 
1648 ### Build Output Structure
1649 
1650 The build output for a configuration will end up in `build/<configuration
1651 name>`, which we refer to as `$BUILD` in this document. The `$BUILD` directory
1652 contains the following important directories:
1653 
1654 ```
1655 buildtools/
1656 configure-support/
1657 hotspot/
1658 images/
1659 jdk/
1660 make-support/
1661 support/
1662 test-results/
1663 test-support/
1664 ```
1665 
1666 This is what they are used for:
1667 
1668   * `images`: This is the directory were the output of the `*-image` make
1669     targets end up. For instance, `make jdk-image` ends up in `images/jdk`.
1670 
1671   * `jdk`: This is the "exploded image". After `make jdk`, you will be able to
1672     launch the newly built JDK by running `$BUILD/jdk/bin/java`.
1673 
1674   * `test-results`: This directory contains the results from running tests.
1675 
1676   * `support`: This is an area for intermediate files needed during the build,
1677     e.g. generated source code, object files and class files. Some noteworthy
1678     directories in `support` is `gensrc`, which contains the generated source
1679     code, and the `modules_*` directories, which contains the files in a
1680     per-module hierarchy that will later be collapsed into the `jdk` directory
1681     of the exploded image.
1682 
1683   * `buildtools`: This is an area for tools compiled for the build platform
1684     that are used during the rest of the build.
1685 
1686   * `hotspot`: This is an area for intermediate files needed when building
1687     hotspot.
1688 
1689   * `configure-support`, `make-support` and `test-support`: These directories
1690     contain files that are needed by the build system for `configure`, `make`
1691     and for running tests.
1692 
1693 ### Fixpath
1694 
1695 Windows path typically look like `C:\User\foo`, while Unix paths look like
1696 `/home/foo`. Tools with roots from Unix often experience issues related to this
1697 mismatch when running on Windows.
1698 
1699 In the JDK build, we always use Unix paths internally, and only just before
1700 calling a tool that does not understand Unix paths do we convert them to
1701 Windows paths.
1702 
1703 This conversion is done by the `fixpath` tool, which is a small wrapper that
1704 modifies unix-style paths to Windows-style paths in command lines. Fixpath is
1705 compiled automatically by `configure`.
1706 
1707 ### Native Debug Symbols
1708 
1709 Native libraries and executables can have debug symbol (and other debug
1710 information) associated with them. How this works is very much platform
1711 dependent, but a common problem is that debug symbol information takes a lot of
1712 disk space, but is rarely needed by the end user.
1713 
1714 The JDK supports different methods on how to handle debug symbols. The
1715 method used is selected by `--with-native-debug-symbols`, and available methods
1716 are `none`, `internal`, `external`, `zipped`.
1717 
1718   * `none` means that no debug symbols will be generated during the build.
1719 
1720   * `internal` means that debug symbols will be generated during the build, and
1721     they will be stored in the generated binary.
1722 
1723   * `external` means that debug symbols will be generated during the build, and
1724     after the compilation, they will be moved into a separate `.debuginfo` file.
1725     (This was previously known as FDS, Full Debug Symbols).
1726 
1727   * `zipped` is like `external`, but the .debuginfo file will also be zipped
1728     into a `.diz` file.
1729 
1730 When building for distribution, `zipped` is a good solution. Binaries built
1731 with `internal` is suitable for use by developers, since they facilitate
1732 debugging, but should be stripped before distributed to end users.
1733 
1734 ### Autoconf Details
1735 
1736 The `configure` script is based on the autoconf framework, but in some details
1737 deviate from a normal autoconf `configure` script.
1738 
1739 The `configure` script in the top level directory of the JDK is just a thin
1740 wrapper that calls `make/autoconf/configure`. This in turn will run `autoconf`
1741 to create the runnable (generated) configure script, as
1742 `.build/generated-configure.sh`. Apart from being responsible for the
1743 generation of the runnable script, the `configure` script also provides
1744 functionality that is not easily expressed in the normal Autoconf framework. As
1745 part of this functionality, the generated script is called.
1746 
1747 The build system will detect if the Autoconf source files have changed, and
1748 will trigger a regeneration of the generated script if needed. You can also
1749 manually request such an update by `bash configure autogen`.
1750 
1751 In previous versions of the JDK, the generated script was checked in at
1752 `make/autoconf/generated-configure.sh`. This is no longer the case.
1753 
1754 ### Developing the Build System Itself
1755 
1756 This section contains a few remarks about how to develop for the build system
1757 itself. It is not relevant if you are only making changes in the product source
1758 code.
1759 
1760 While technically using `make`, the make source files of the JDK does not
1761 resemble most other Makefiles. Instead of listing specific targets and actions
1762 (perhaps using patterns), the basic modus operandi is to call a high-level
1763 function (or properly, macro) from the API in `make/common`. For instance, to
1764 compile all classes in the `jdk.internal.foo` package in the `jdk.foo` module,
1765 a call like this would be made:
1766 
1767 ```
1768 $(eval $(call SetupJavaCompilation, BUILD_FOO_CLASSES, \
1769     SETUP := GENERATE_OLDBYTECODE, \
1770     SRC := $(TOPDIR)/src/jkd.foo/share/classes, \
1771     INCLUDES := jdk/internal/foo, \
1772     BIN := $(SUPPORT_OUTPUTDIR)/foo_classes, \
1773 ))
1774 ```
1775 
1776 By encapsulating and expressing the high-level knowledge of *what* should be
1777 done, rather than *how* it should be done (as is normal in Makefiles), we can
1778 build a much more powerful and flexible build system.
1779 
1780 Correct dependency tracking is paramount. Sloppy dependency tracking will lead
1781 to improper parallelization, or worse, race conditions.
1782 
1783 To test for/debug race conditions, try running `make JOBS=1` and `make
1784 JOBS=100` and see if it makes any difference. (It shouldn't).
1785 
1786 To compare the output of two different builds and see if, and how, they differ,
1787 run `$BUILD1/compare.sh -o $BUILD2`, where `$BUILD1` and `$BUILD2` are the two
1788 builds you want to compare.
1789 
1790 To automatically build two consecutive versions and compare them, use
1791 `COMPARE_BUILD`. The value of `COMPARE_BUILD` is a set of variable=value
1792 assignments, like this:
1793 ```
1794 make COMPARE_BUILD=CONF=--enable-new-hotspot-feature:MAKE=hotspot
1795 ```
1796 See `make/InitSupport.gmk` for details on how to use `COMPARE_BUILD`.
1797 
1798 To analyze build performance, run with `LOG=trace` and check `$BUILD/build-trace-time.log`.
1799 Use `JOBS=1` to avoid parallelism.
1800 
1801 Please check that you adhere to the [Code Conventions for the Build System](
1802 http://openjdk.java.net/groups/build/doc/code-conventions.html) before
1803 submitting patches.
1804 
1805 ## Contributing to the JDK
1806 
1807 So, now you've built your JDK, and made your first patch, and want to
1808 contribute it back to the OpenJDK Community.
1809 
1810 First of all: Thank you! We gladly welcome your contribution.
1811 However, please bear in mind that the JDK is a massive project, and we must ask
1812 you to follow our rules and guidelines to be able to accept your contribution.
1813 
1814 The official place to start is the ['How to contribute' page](
1815 http://openjdk.java.net/contribute/). There is also an official (but somewhat
1816 outdated and skimpy on details) [Developer's Guide](
1817 http://openjdk.java.net/guide/).
1818 
1819 If this seems overwhelming to you, the Adoption Group is there to help you! A
1820 good place to start is their ['New Contributor' page](
1821 https://wiki.openjdk.java.net/display/Adoption/New+Contributor), or start
1822 reading the comprehensive [Getting Started Kit](
1823 https://adoptopenjdk.gitbooks.io/adoptopenjdk-getting-started-kit/en/). The
1824 Adoption Group will also happily answer any questions you have about
1825 contributing. Contact them by [mail](
1826 http://mail.openjdk.java.net/mailman/listinfo/adoption-discuss) or [IRC](
1827 http://openjdk.java.net/irc/).
1828 
1829 ---
1830 # Override styles from the base CSS file that are not ideal for this document.
1831 header-includes:
1832  - '<style type="text/css">pre, code, tt { color: #1d6ae5; }</style>'
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