Old doc/building.md

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.
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 aarch64
118
119 At a minimum, a machine with 8 cores is advisable, as well as 8 GB of RAM.
120 (The more cores to use, the more memory you need.) At least 6 GB of free disk
121 space is required.
122
123 If you do not have access to sufficiently powerful hardware, it is also
124 possible to use [cross-compiling](#cross-compiling).
125
126 ### Building on 32-bit arm
127
128 This is not recommended. Instead, see the section on [Cross-compiling](
129 #cross-compiling).
130
131 ## Operating System Requirements
132
133 The mainline JDK project supports Linux, macOS, AIX and Windows.
134 Support for other operating system, e.g. BSD, exists in separate "port"
135 projects.
136
137 In general, the JDK can be built on a wide range of versions of these operating
138 systems, but the further you deviate from what is tested on a daily basis, the
139 more likely you are to run into problems.
140
141 This table lists the OS versions used by Oracle when building the JDK. Such
142 information is always subject to change, but this table is up to date at the
143 time of writing.
144
145 Operating system Vendor/version used
146 ----------------- -------------------------------------------------------
147 Linux Oracle Enterprise Linux 6.4 / 7.6
148 macOS Mac OS X 10.13 (High Sierra)
149 Windows Windows Server 2012 R2
150
151 The double version numbers for Linux are due to the hybrid model
152 used at Oracle, where header files and external libraries from an older version
153 are used when building on a more modern version of the OS.
154
155 The Build Group has a wiki page with [Supported Build Platforms](
156 https://wiki.openjdk.java.net/display/Build/Supported+Build+Platforms). From
157 time to time, this is updated by contributors to list successes or failures of
158 building on different platforms.
159
160 ### Windows
161
162 Windows XP is not a supported platform, but all newer Windows should be able to
163 build the JDK.
164
165 On Windows, it is important that you pay attention to the instructions in the
166 [Special Considerations](#special-considerations).
167
168 Windows is the only non-POSIX OS supported by the JDK, and as such, requires
169 some extra care. A POSIX support layer is required to build on Windows.
170 Currently, the only supported such layers are Cygwin and Windows Subsystem for
171 Linux (WSL). (Msys is no longer supported due to a too old bash; msys2 would
172 likely be possible to support in a future version but that would require effort
173 to implement.)
174
175 Internally in the build system, all paths are represented as Unix-style paths,
176 e.g. `/cygdrive/c/hg/jdk9/Makefile` rather than `C:\hg\jdk9\Makefile`. This
177 rule also applies to input to the build system, e.g. in arguments to
178 `configure`. So, use `--with-msvcr-dll=/cygdrive/c/msvcr100.dll` rather than
179 `--with-msvcr-dll=c:\msvcr100.dll`. For details on this conversion, see the section
180 on [Fixpath](#fixpath).
181
182 #### Cygwin
183
184 A functioning [Cygwin](http://www.cygwin.com/) environment is required for
185 building the JDK on Windows. If you have a 64-bit OS, we strongly recommend
186 using the 64-bit version of Cygwin.
187
188 **Note:** Cygwin has a model of continuously updating all packages without any
189 easy way to install or revert to a specific version of a package. This means
190 that whenever you add or update a package in Cygwin, you might (inadvertently)
191 update tools that are used by the JDK build process, and that can cause
192 unexpected build problems.
193
194 The JDK requires GNU Make 4.0 or greater in Cygwin. This is usually not a
195 problem, since Cygwin currently only distributes GNU Make at a version above
196 4.0.
197
198 Apart from the basic Cygwin installation, the following packages must also be
199 installed:
200
201 * `autoconf`
202 * `make`
203 * `zip`
204 * `unzip`
205
206 Often, you can install these packages using the following command line:
207 ```
208 <path to Cygwin setup>/setup-x86_64 -q -P autoconf -P make -P unzip -P zip
209 ```
210
211 Unfortunately, Cygwin can be unreliable in certain circumstances. If you
212 experience build tool crashes or strange issues when building on Windows,
213 please check the Cygwin FAQ on the ["BLODA" list](
214 https://cygwin.com/faq/faq.html#faq.using.bloda) and the section on [fork()
215 failures](https://cygwin.com/faq/faq.html#faq.using.fixing-fork-failures).
216
217 #### Windows Subsystem for Linux (WSL)
218
219 Windows 10 1809 or newer is supported due to a dependency on the wslpath utility
220 and support for environment variable sharing through WSLENV. Version 1803 can
221 work but intermittent build failures have been observed.
222
223 It's possible to build both Windows and Linux binaries from WSL. To build
224 Windows binaries, you must use a Windows boot JDK (located in a
225 Windows-accessible directory). To build Linux binaries, you must use a Linux
226 boot JDK. The default behavior is to build for Windows. To build for Linux, pass
227 `--build=x86_64-unknown-linux-gnu --host=x86_64-unknown-linux-gnu` to
228 `configure`.
229
230 If building Windows binaries, the source code must be located in a Windows-
231 accessible directory. This is because Windows executables (such as Visual Studio
232 and the boot JDK) must be able to access the source code. Also, the drive where
233 the source is stored must be mounted as case-insensitive by changing either
234 /etc/fstab or /etc/wsl.conf in WSL. Individual directories may be corrected
235 using the fsutil tool in case the source was cloned before changing the mount
236 options.
237
238 Note that while it's possible to build on WSL, testing is still not fully
239 supported.
240
241 ### macOS
242
243 Apple is using a quite aggressive scheme of pushing OS updates, and coupling
244 these updates with required updates of Xcode. Unfortunately, this makes it
245 difficult for a project such as the JDK to keep pace with a continuously updated
246 machine running macOS. See the section on [Apple Xcode](#apple-xcode) on some
247 strategies to deal with this.
248
249 It is recommended that you use at least Mac OS X 10.13 (High Sierra). At the time
250 of writing, the JDK has been successfully compiled on macOS 10.12 (Sierra).
251
252 The standard macOS environment contains the basic tooling needed to build, but
253 for external libraries a package manager is recommended. The JDK uses
254 [homebrew](https://brew.sh/) in the examples, but feel free to use whatever
255 manager you want (or none).
256
257 ### Linux
258
259 It is often not much problem to build the JDK on Linux. The only general advice
260 is to try to use the compilers, external libraries and header files as provided
261 by your distribution.
262
263 The basic tooling is provided as part of the core operating system, but you
264 will most likely need to install developer packages.
265
266 For apt-based distributions (Debian, Ubuntu, etc), try this:
267 ```
268 sudo apt-get install build-essential
269 ```
270
271 For rpm-based distributions (Fedora, Red Hat, etc), try this:
272 ```
273 sudo yum groupinstall "Development Tools"
274 ```
275
276 ### AIX
277
278 Please consult the AIX section of the [Supported Build Platforms](
279 https://wiki.openjdk.java.net/display/Build/Supported+Build+Platforms) OpenJDK
280 Build Wiki page for details about which versions of AIX are supported.
281
282 ## Native Compiler (Toolchain) Requirements
283
284 Large portions of the JDK consists of native code, that needs to be compiled to
285 be able to run on the target platform. In theory, toolchain and operating
286 system should be independent factors, but in practice there's more or less a
287 one-to-one correlation between target operating system and toolchain.
288
289 Operating system Supported toolchain
290 ------------------ -------------------------
291 Linux gcc, clang
292 macOS Apple Xcode (using clang)
293 AIX IBM XL C/C++
294 Windows Microsoft Visual Studio
295
296 Please see the individual sections on the toolchains for version
297 recommendations. As a reference, these versions of the toolchains are used, at
298 the time of writing, by Oracle for the daily builds of the JDK. It should be
299 possible to compile the JDK with both older and newer versions, but the closer
300 you stay to this list, the more likely you are to compile successfully without
301 issues.
302
303 Operating system Toolchain version
304 ------------------ -------------------------------------------------------
305 Linux gcc 9.2.0
306 macOS Apple Xcode 10.1 (using clang 10.0.0)
307 Windows Microsoft Visual Studio 2019 update 16.5.3
308
309 All compilers are expected to be able to compile to the C99 language standard,
310 as some C99 features are used in the source code. Microsoft Visual Studio
311 doesn't fully support C99 so in practice shared code is limited to using C99
312 features that it does support.
313
314 ### gcc
315
316 The minimum accepted version of gcc is 5.0. Older versions will generate a warning
317 by `configure` and are unlikely to work.
318
319 The JDK is currently known to be able to compile with at least version 9.2 of
320 gcc.
321
322 In general, any version between these two should be usable.
323
324 ### clang
325
326 The minimum accepted version of clang is 3.5. Older versions will not be
327 accepted by `configure`.
328
329 To use clang instead of gcc on Linux, use `--with-toolchain-type=clang`.
330
331 ### Apple Xcode
332
333 The oldest supported version of Xcode is 8.
334
335 You will need the Xcode command lines developers tools to be able to build
336 the JDK. (Actually, *only* the command lines tools are needed, not the IDE.)
337 The simplest way to install these is to run:
338 ```
339 xcode-select --install
340 ```
341
342 It is advisable to keep an older version of Xcode for building the JDK when
343 updating Xcode. This [blog page](
344 http://iosdevelopertips.com/xcode/install-multiple-versions-of-xcode.html) has
345 good suggestions on managing multiple Xcode versions. To use a specific version
346 of Xcode, use `xcode-select -s` before running `configure`, or use
347 `--with-toolchain-path` to point to the version of Xcode to use, e.g.
348 `configure --with-toolchain-path=/Applications/Xcode8.app/Contents/Developer/usr/bin`
349
350 If you have recently (inadvertently) updated your OS and/or Xcode version, and
351 the JDK can no longer be built, please see the section on [Problems with the
352 Build Environment](#problems-with-the-build-environment), and [Getting
353 Help](#getting-help) to find out if there are any recent, non-merged patches
354 available for this update.
355
356 ### Microsoft Visual Studio
357
358 The minimum accepted version of Visual Studio is 2017. Older versions will not
359 be accepted by `configure` and will not work. The maximum accepted
360 version of Visual Studio is 2019.
361
362 If you have multiple versions of Visual Studio installed, `configure` will by
363 default pick the latest. You can request a specific version to be used by
364 setting `--with-toolchain-version`, e.g. `--with-toolchain-version=2017`.
365
366 ### IBM XL C/C++
367
368 Please consult the AIX section of the [Supported Build Platforms](
369 https://wiki.openjdk.java.net/display/Build/Supported+Build+Platforms) OpenJDK
370 Build Wiki page for details about which versions of XLC are supported.
371
372
373 ## Boot JDK Requirements
374
375 Paradoxically, building the JDK requires a pre-existing JDK. This is called the
376 "boot JDK". The boot JDK does not, however, have to be a JDK built directly from
377 the source code available in the OpenJDK Community. If you are porting the JDK
378 to a new platform, chances are that there already exists another JDK for that
379 platform that is usable as boot JDK.
380
381 The rule of thumb is that the boot JDK for building JDK major version *N*
382 should be a JDK of major version *N-1*, so for building JDK 9 a JDK 8 would be
383 suitable as boot JDK. However, the JDK should be able to "build itself", so an
384 up-to-date build of the current JDK source is an acceptable alternative. If
385 you are following the *N-1* rule, make sure you've got the latest update
386 version, since JDK 8 GA might not be able to build JDK 9 on all platforms.
387
388 Early in the release cycle, version *N-1* may not yet have been released. In
389 that case, the preferred boot JDK will be version *N-2* until version *N-1*
390 is available.
391
392 If the boot JDK is not automatically detected, or the wrong JDK is picked, use
393 `--with-boot-jdk` to point to the JDK to use.
394
395 ### Getting JDK binaries
396
397 JDK binaries for Linux, Windows and macOS can be downloaded from
398 [jdk.java.net](http://jdk.java.net). An alternative is to download the
399 [Oracle JDK](http://www.oracle.com/technetwork/java/javase/downloads). Another
400 is the [Adopt OpenJDK Project](https://adoptopenjdk.net/), which publishes
401 experimental prebuilt binaries for various platforms.
402
403 On Linux you can also get a JDK from the Linux distribution. On apt-based
404 distros (like Debian and Ubuntu), `sudo apt-get install openjdk-<VERSION>-jdk`
405 is typically enough to install a JDK \<VERSION\>. On rpm-based distros (like
406 Fedora and Red Hat), try `sudo yum install java-<VERSION>-openjdk-devel`.
407
408 ## External Library Requirements
409
410 Different platforms require different external libraries. In general, libraries
411 are not optional - that is, they are either required or not used.
412
413 If a required library is not detected by `configure`, you need to provide the
414 path to it. There are two forms of the `configure` arguments to point to an
415 external library: `--with-<LIB>=<path>` or `--with-<LIB>-include=<path to
416 include> --with-<LIB>-lib=<path to lib>`. The first variant is more concise,
417 but require the include files and library files to reside in a default
418 hierarchy under this directory. In most cases, it works fine.
419
420 As a fallback, the second version allows you to point to the include directory
421 and the lib directory separately.
422
423 ### FreeType
424
425 FreeType2 from [The FreeType Project](http://www.freetype.org/) is not required
426 on any platform. The exception is on Unix-based platforms when configuring such
427 that the build artifacts will reference a system installed library,
428 rather than bundling the JDK's own copy.
429
430 * To install on an apt-based Linux, try running `sudo apt-get install
431 libfreetype6-dev`.
432 * To install on an rpm-based Linux, try running `sudo yum install
433 freetype-devel`.
434
435 Use `--with-freetype-include=<path>` and `--with-freetype-lib=<path>`
436 if `configure` does not automatically locate the platform FreeType files.
437
438 ### CUPS
439
440 CUPS, [Common UNIX Printing System](http://www.cups.org) header files are
441 required on all platforms, except Windows. Often these files are provided by
442 your operating system.
443
444 * To install on an apt-based Linux, try running `sudo apt-get install
445 libcups2-dev`.
446 * To install on an rpm-based Linux, try running `sudo yum install
447 cups-devel`.
448
449 Use `--with-cups=<path>` if `configure` does not properly locate your CUPS
450 files.
451
452 ### X11
453
454 Certain [X11](http://www.x.org/) libraries and include files are required on
455 Linux.
456
457 * To install on an apt-based Linux, try running `sudo apt-get install
458 libx11-dev libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev`.
459 * To install on an rpm-based Linux, try running `sudo yum install
460 libXtst-devel libXt-devel libXrender-devel libXrandr-devel libXi-devel`.
461
462 Use `--with-x=<path>` if `configure` does not properly locate your X11 files.
463
464 ### ALSA
465
466 ALSA, [Advanced Linux Sound Architecture](https://www.alsa-project.org/) is
467 required on Linux. At least version 0.9.1 of ALSA is required.
468
469 * To install on an apt-based Linux, try running `sudo apt-get install
470 libasound2-dev`.
471 * To install on an rpm-based Linux, try running `sudo yum install
472 alsa-lib-devel`.
473
474 Use `--with-alsa=<path>` if `configure` does not properly locate your ALSA
475 files.
476
477 ### libffi
478
479 libffi, the [Portable Foreign Function Interface Library](
480 http://sourceware.org/libffi) is required when building the Zero version of
481 Hotspot.
482
483 * To install on an apt-based Linux, try running `sudo apt-get install
484 libffi-dev`.
485 * To install on an rpm-based Linux, try running `sudo yum install
486 libffi-devel`.
487
488 Use `--with-libffi=<path>` if `configure` does not properly locate your libffi
489 files.
490
491 ## Build Tools Requirements
492
493 ### Autoconf
494
495 The JDK requires [Autoconf](http://www.gnu.org/software/autoconf) on all
496 platforms. At least version 2.69 is required.
497
498 * To install on an apt-based Linux, try running `sudo apt-get install
499 autoconf`.
500 * To install on an rpm-based Linux, try running `sudo yum install
501 autoconf`.
502 * To install on macOS, try running `brew install autoconf`.
503 * To install on Windows, try running `<path to Cygwin setup>/setup-x86_64 -q
504 -P autoconf`.
505
506 If `configure` has problems locating your installation of autoconf, you can
507 specify it using the `AUTOCONF` environment variable, like this:
508
509 ```
510 AUTOCONF=<path to autoconf> configure ...
511 ```
512
513 ### GNU Make
514
515 The JDK requires [GNU Make](http://www.gnu.org/software/make). No other flavors
516 of make are supported.
517
518 At least version 3.81 of GNU Make must be used. For distributions supporting
519 GNU Make 4.0 or above, we strongly recommend it. GNU Make 4.0 contains useful
520 functionality to handle parallel building (supported by `--with-output-sync`)
521 and speed and stability improvements.
522
523 Note that `configure` locates and verifies a properly functioning version of
524 `make` and stores the path to this `make` binary in the configuration. If you
525 start a build using `make` on the command line, you will be using the version
526 of make found first in your `PATH`, and not necessarily the one stored in the
527 configuration. This initial make will be used as "bootstrap make", and in a
528 second stage, the make located by `configure` will be called. Normally, this
529 will present no issues, but if you have a very old `make`, or a non-GNU Make
530 `make` in your path, this might cause issues.
531
532 If you want to override the default make found by `configure`, use the `MAKE`
533 configure variable, e.g. `configure MAKE=/opt/gnu/make`.
534
535 ### GNU Bash
536
537 The JDK requires [GNU Bash](http://www.gnu.org/software/bash). No other shells
538 are supported.
539
540 At least version 3.2 of GNU Bash must be used.
541
542 ## Running Configure
543
544 To build the JDK, you need a "configuration", which consists of a directory
545 where to store the build output, coupled with information about the platform,
546 the specific build machine, and choices that affect how the JDK is built.
547
548 The configuration is created by the `configure` script. The basic invocation of
549 the `configure` script looks like this:
550
551 ```
552 bash configure [options]
553 ```
554
555 This will create an output directory containing the configuration and setup an
556 area for the build result. This directory typically looks like
557 `build/linux-x64-server-release`, but the actual name depends on your specific
558 configuration. (It can also be set directly, see [Using Multiple
559 Configurations](#using-multiple-configurations)). This directory is referred to
560 as `$BUILD` in this documentation.
561
562 `configure` will try to figure out what system you are running on and where all
563 necessary build components are. If you have all prerequisites for building
564 installed, it should find everything. If it fails to detect any component
565 automatically, it will exit and inform you about the problem.
566
567 Some command line examples:
568
569 * Create a 32-bit build for Windows with FreeType2 in `C:\freetype-i586`:
570 ```
571 bash configure --with-freetype=/cygdrive/c/freetype-i586 --with-target-bits=32
572 ```
573
574 * Create a debug build with the `server` JVM and DTrace enabled:
575 ```
576 bash configure --enable-debug --with-jvm-variants=server --enable-dtrace
577 ```
578
579 ### Common Configure Arguments
580
581 Here follows some of the most common and important `configure` argument.
582
583 To get up-to-date information on *all* available `configure` argument, please
584 run:
585 ```
586 bash configure --help
587 ```
588
589 (Note that this help text also include general autoconf options, like
590 `--dvidir`, that is not relevant to the JDK. To list only JDK-specific
591 features, use `bash configure --help=short` instead.)
592
593 #### Configure Arguments for Tailoring the Build
594
595 * `--enable-debug` - Set the debug level to `fastdebug` (this is a shorthand
596 for `--with-debug-level=fastdebug`)
597 * `--with-debug-level=<level>` - Set the debug level, which can be `release`,
598 `fastdebug`, `slowdebug` or `optimized`. Default is `release`. `optimized`
599 is variant of `release` with additional Hotspot debug code.
600 * `--with-native-debug-symbols=<method>` - Specify if and how native debug
601 symbols should be built. Available methods are `none`, `internal`,
602 `external`, `zipped`. Default behavior depends on platform. See [Native
603 Debug Symbols](#native-debug-symbols) for more details.
604 * `--with-version-string=<string>` - Specify the version string this build
605 will be identified with.
606 * `--with-version-<part>=<value>` - A group of options, where `<part>` can be
607 any of `pre`, `opt`, `build`, `major`, `minor`, `security` or `patch`. Use
608 these options to modify just the corresponding part of the version string
609 from the default, or the value provided by `--with-version-string`.
610 * `--with-jvm-variants=<variant>[,<variant>...]` - Build the specified variant
611 (or variants) of Hotspot. Valid variants are: `server`, `client`,
612 `minimal`, `core`, `zero`, `custom`. Note that not all
613 variants are possible to combine in a single build.
614 * `--enable-jvm-feature-<feature>` or `--disable-jvm-feature-<feature>` -
615 Include (or exclude) `<feature>` as a JVM feature in Hotspot. You can also
616 specify a list of features to be enabled, separated by space or comma, as
617 `--with-jvm-features=<feature>[,<feature>...]`. If you prefix `<feature>`
618 with a `-`, it will be disabled. These options will modify the default list
619 of features for the JVM variant(s) you are building. For the `custom` JVM
620 variant, the default list is empty. A complete list of valid JVM features
621 can be found using `bash configure --help`.
622 * `--with-target-bits=<bits>` - Create a target binary suitable for running
623 on a `<bits>` platform. Use this to create 32-bit output on a 64-bit build
624 platform, instead of doing a full cross-compile. (This is known as a
625 *reduced* build.)
626
627 On Linux, BSD and AIX, it is possible to override where Java by default
628 searches for runtime/JNI libraries. This can be useful in situations where
629 there is a special shared directory for system JNI libraries. This setting
630 can in turn be overriden at runtime by setting the `java.library.path` property.
631
632 * `--with-jni-libpath=<path>` - Use the specified path as a default
633 when searching for runtime libraries.
634
635 #### Configure Arguments for Native Compilation
636
637 * `--with-devkit=<path>` - Use this devkit for compilers, tools and resources
638 * `--with-sysroot=<path>` - Use this directory as sysroot
639 * `--with-extra-path=<path>[;<path>]` - Prepend these directories to the
640 default path when searching for all kinds of binaries
641 * `--with-toolchain-path=<path>[;<path>]` - Prepend these directories when
642 searching for toolchain binaries (compilers etc)
643 * `--with-extra-cflags=<flags>` - Append these flags when compiling JDK C
644 files
645 * `--with-extra-cxxflags=<flags>` - Append these flags when compiling JDK C++
646 files
647 * `--with-extra-ldflags=<flags>` - Append these flags when linking JDK
648 libraries
649
650 #### Configure Arguments for External Dependencies
651
652 * `--with-boot-jdk=<path>` - Set the path to the [Boot JDK](
653 #boot-jdk-requirements)
654 * `--with-freetype=<path>` - Set the path to [FreeType](#freetype)
655 * `--with-cups=<path>` - Set the path to [CUPS](#cups)
656 * `--with-x=<path>` - Set the path to [X11](#x11)
657 * `--with-alsa=<path>` - Set the path to [ALSA](#alsa)
658 * `--with-libffi=<path>` - Set the path to [libffi](#libffi)
659 * `--with-jtreg=<path>` - Set the path to JTReg. See [Running Tests](
660 #running-tests)
661
662 Certain third-party libraries used by the JDK (libjpeg, giflib, libpng, lcms
663 and zlib) are included in the JDK repository. The default behavior of the
664 JDK build is to use the included ("bundled") versions of libjpeg, giflib,
665 libpng and lcms.
666 For zlib, the system lib (if present) is used except on Windows and AIX.
667 However the bundled libraries may be replaced by an external version.
668 To do so, specify `system` as the `<source>` option in these arguments.
669 (The default is `bundled`).
670
671 * `--with-libjpeg=<source>` - Use the specified source for libjpeg
672 * `--with-giflib=<source>` - Use the specified source for giflib
673 * `--with-libpng=<source>` - Use the specified source for libpng
674 * `--with-lcms=<source>` - Use the specified source for lcms
675 * `--with-zlib=<source>` - Use the specified source for zlib
676
677 On Linux, it is possible to select either static or dynamic linking of the C++
678 runtime. The default is static linking, with dynamic linking as fallback if the
679 static library is not found.
680
681 * `--with-stdc++lib=<method>` - Use the specified method (`static`, `dynamic`
682 or `default`) for linking the C++ runtime.
683
684 ### Configure Control Variables
685
686 It is possible to control certain aspects of `configure` by overriding the
687 value of `configure` variables, either on the command line or in the
688 environment.
689
690 Normally, this is **not recommended**. If used improperly, it can lead to a
691 broken configuration. Unless you're well versed in the build system, this is
692 hard to use properly. Therefore, `configure` will print a warning if this is
693 detected.
694
695 However, there are a few `configure` variables, known as *control variables*
696 that are supposed to be overriden on the command line. These are variables that
697 describe the location of tools needed by the build, like `MAKE` or `GREP`. If
698 any such variable is specified, `configure` will use that value instead of
699 trying to autodetect the tool. For instance, `bash configure
700 MAKE=/opt/gnumake4.0/bin/make`.
701
702 If a configure argument exists, use that instead, e.g. use `--with-jtreg`
703 instead of setting `JTREGEXE`.
704
705 Also note that, despite what autoconf claims, setting `CFLAGS` will not
706 accomplish anything. Instead use `--with-extra-cflags` (and similar for
707 `cxxflags` and `ldflags`).
708
709 ## Running Make
710
711 When you have a proper configuration, all you need to do to build the JDK is to
712 run `make`. (But see the warning at [GNU Make](#gnu-make) about running the
713 correct version of make.)
714
715 When running `make` without any arguments, the default target is used, which is
716 the same as running `make default` or `make jdk`. This will build a minimal (or
717 roughly minimal) set of compiled output (known as an "exploded image") needed
718 for a developer to actually execute the newly built JDK. The idea is that in an
719 incremental development fashion, when doing a normal make, you should only
720 spend time recompiling what's changed (making it purely incremental) and only
721 do the work that's needed to actually run and test your code.
722
723 The output of the exploded image resides in `$BUILD/jdk`. You can test the
724 newly built JDK like this: `$BUILD/jdk/bin/java -version`.
725
726 ### Common Make Targets
727
728 Apart from the default target, here are some common make targets:
729
730 * `hotspot` - Build all of hotspot (but only hotspot)
731 * `hotspot-<variant>` - Build just the specified jvm variant
732 * `images` or `product-images` - Build the JDK image
733 * `docs` or `docs-image` - Build the documentation image
734 * `test-image` - Build the test image
735 * `all` or `all-images` - Build all images (product, docs and test)
736 * `bootcycle-images` - Build images twice, second time with newly built JDK
737 (good for testing)
738 * `clean` - Remove all files generated by make, but not those generated by
739 configure
740 * `dist-clean` - Remove all files, including configuration
741
742 Run `make help` to get an up-to-date list of important make targets and make
743 control variables.
744
745 It is possible to build just a single module, a single phase, or a single phase
746 of a single module, by creating make targets according to these followin
747 patterns. A phase can be either of `gensrc`, `gendata`, `copy`, `java`,
748 `launchers`, or `libs`. See [Using Fine-Grained Make Targets](
749 #using-fine-grained-make-targets) for more details about this functionality.
750
751 * `<phase>` - Build the specified phase and everything it depends on
752 * `<module>` - Build the specified module and everything it depends on
753 * `<module>-<phase>` - Compile the specified phase for the specified module
754 and everything it depends on
755
756 Similarly, it is possible to clean just a part of the build by creating make
757 targets according to these patterns:
758
759 * `clean-<outputdir>` - Remove the subdir in the output dir with the name
760 * `clean-<phase>` - Remove all build results related to a certain build
761 phase
762 * `clean-<module>` - Remove all build results related to a certain module
763 * `clean-<module>-<phase>` - Remove all build results related to a certain
764 module and phase
765
766 ### Make Control Variables
767
768 It is possible to control `make` behavior by overriding the value of `make`
769 variables, either on the command line or in the environment.
770
771 Normally, this is **not recommended**. If used improperly, it can lead to a
772 broken build. Unless you're well versed in the build system, this is hard to
773 use properly. Therefore, `make` will print a warning if this is detected.
774
775 However, there are a few `make` variables, known as *control variables* that
776 are supposed to be overriden on the command line. These make up the "make time"
777 configuration, as opposed to the "configure time" configuration.
778
779 #### General Make Control Variables
780
781 * `JOBS` - Specify the number of jobs to build with. See [Build
782 Performance](#build-performance).
783 * `LOG` - Specify the logging level and functionality. See [Checking the
784 Build Log File](#checking-the-build-log-file)
785 * `CONF` and `CONF_NAME` - Selecting the configuration(s) to use. See [Using
786 Multiple Configurations](#using-multiple-configurations)
787
788 #### Test Make Control Variables
789
790 These make control variables only make sense when running tests. Please see
791 [Testing the JDK](testing.html) for details.
792
793 * `TEST`
794 * `TEST_JOBS`
795 * `JTREG`
796 * `GTEST`
797
798 #### Advanced Make Control Variables
799
800 These advanced make control variables can be potentially unsafe. See [Hints and
801 Suggestions for Advanced Users](#hints-and-suggestions-for-advanced-users) and
802 [Understanding the Build System](#understanding-the-build-system) for details.
803
804 * `SPEC`
805 * `CONF_CHECK`
806 * `COMPARE_BUILD`
807 * `JDK_FILTER`
808 * `SPEC_FILTER`
809
810 ## Running Tests
811
812 Most of the JDK tests are using the [JTReg](http://openjdk.java.net/jtreg)
813 test framework. Make sure that your configuration knows where to find your
814 installation of JTReg. If this is not picked up automatically, use the
815 `--with-jtreg=<path to jtreg home>` option to point to the JTReg framework.
816 Note that this option should point to the JTReg home, i.e. the top directory,
817 containing `lib/jtreg.jar` etc.
818
819 The [Adoption Group](https://wiki.openjdk.java.net/display/Adoption) provides
820 recent builds of jtreg [here](
821 https://ci.adoptopenjdk.net/view/Dependencies/job/jtreg/lastSuccessfulBuild/artifact).
822 Download the latest `.tar.gz` file, unpack it, and point `--with-jtreg` to the
823 `jtreg` directory that you just unpacked.
824
825 Building of Hotspot Gtest suite requires the source code of Google Test framework.
826 The top directory, which contains both `googletest` and `googlemock`
827 directories, should be specified via `--with-gtest`.
828 The supported version of Google Test is 1.8.1, whose source code can be obtained:
829
830 * by downloading and unpacking the source bundle from [here](https://github.com/google/googletest/releases/tag/release-1.8.1)
831 * or by checking out `release-1.8.1` tag of `googletest` project: `git clone -b release-1.8.1 https://github.com/google/googletest`
832
833 To execute the most basic tests (tier 1), use:
834 ```
835 make run-test-tier1
836 ```
837
838 For more details on how to run tests, please see the [Testing
839 the JDK](testing.html) document.
840
841 ## Cross-compiling
842
843 Cross-compiling means using one platform (the *build* platform) to generate
844 output that can ran on another platform (the *target* platform).
845
846 The typical reason for cross-compiling is that the build is performed on a more
847 powerful desktop computer, but the resulting binaries will be able to run on a
848 different, typically low-performing system. Most of the complications that
849 arise when building for embedded is due to this separation of *build* and
850 *target* systems.
851
852 This requires a more complex setup and build procedure. This section assumes
853 you are familiar with cross-compiling in general, and will only deal with the
854 particularities of cross-compiling the JDK. If you are new to cross-compiling,
855 please see the [external links at Wikipedia](
856 https://en.wikipedia.org/wiki/Cross_compiler#External_links) for a good start
857 on reading materials.
858
859 Cross-compiling the JDK requires you to be able to build both for the build
860 platform and for the target platform. The reason for the former is that we need
861 to build and execute tools during the build process, both native tools and Java
862 tools.
863
864 If all you want to do is to compile a 32-bit version, for the same OS, on a
865 64-bit machine, consider using `--with-target-bits=32` instead of doing a
866 full-blown cross-compilation. (While this surely is possible, it's a lot more
867 work and will take much longer to build.)
868
869 ### Cross compiling the easy way with OpenJDK devkits
870
871 The OpenJDK build system provides out-of-the box support for creating and using
872 so called devkits. A `devkit` is basically a collection of a cross-compiling
873 toolchain and a sysroot environment which can easily be used together with the
874 `--with-devkit` configure option to cross compile the OpenJDK. On Linux/x86_64,
875 the following command:
876 ```
877 bash configure --with-devkit=<devkit-path> --openjdk-target=ppc64-linux-gnu && make
878 ```
879
880 will configure and build OpenJDK for Linux/ppc64 assuming that `<devkit-path>`
881 points to a Linux/x86_64 to Linux/ppc64 devkit.
882
883 Devkits can be created from the `make/devkit` directory by executing:
884 ```
885 make [ TARGETS="<TARGET_TRIPLET>+" ] [ BASE_OS=<OS> ] [ BASE_OS_VERSION=<VER> ]
886 ```
887
888 where `TARGETS` contains one or more `TARGET_TRIPLET`s of the form
889 described in [section 3.4 of the GNU Autobook](
890 https://sourceware.org/autobook/autobook/autobook_17.html). If no
891 targets are given, a native toolchain for the current platform will be
892 created. Currently, at least the following targets are known to work:
893
894 Supported devkit targets
895 -------------------------
896 x86_64-linux-gnu
897 aarch64-linux-gnu
898 arm-linux-gnueabihf
899 ppc64-linux-gnu
900 ppc64le-linux-gnu
901 s390x-linux-gnu
902
903 `BASE_OS` must be one of "OEL6" for Oracle Enterprise Linux 6 or
904 "Fedora" (if not specified "OEL6" will be the default). If the base OS
905 is "Fedora" the corresponding Fedora release can be specified with the
906 help of the `BASE_OS_VERSION` option (with "27" as default version).
907 If the build is successful, the new devkits can be found in the
908 `build/devkit/result` subdirectory:
909 ```
910 cd make/devkit
911 make TARGETS="ppc64le-linux-gnu aarch64-linux-gnu" BASE_OS=Fedora BASE_OS_VERSION=21
912 ls -1 ../../build/devkit/result/
913 x86_64-linux-gnu-to-aarch64-linux-gnu
914 x86_64-linux-gnu-to-ppc64le-linux-gnu
915 ```
916
917 Notice that devkits are not only useful for targeting different build
918 platforms. Because they contain the full build dependencies for a
919 system (i.e. compiler and root file system), they can easily be used
920 to build well-known, reliable and reproducible build environments. You
921 can for example create and use a devkit with GCC 7.3 and a Fedora 12
922 sysroot environment (with glibc 2.11) on Ubuntu 14.04 (which doesn't
923 have GCC 7.3 by default) to produce OpenJDK binaries which will run on
924 all Linux systems with runtime libraries newer than the ones from
925 Fedora 12 (e.g. Ubuntu 16.04, SLES 11 or RHEL 6).
926
927 ### Boot JDK and Build JDK
928
929 When cross-compiling, make sure you use a boot JDK that runs on the *build*
930 system, and not on the *target* system.
931
932 To be able to build, we need a "Build JDK", which is a JDK built from the
933 current sources (that is, the same as the end result of the entire build
934 process), but able to run on the *build* system, and not the *target* system.
935 (In contrast, the Boot JDK should be from an older release, e.g. JDK 8 when
936 building JDK 9.)
937
938 The build process will create a minimal Build JDK for you, as part of building.
939 To speed up the build, you can use `--with-build-jdk` to `configure` to point
940 to a pre-built Build JDK. Please note that the build result is unpredictable,
941 and can possibly break in subtle ways, if the Build JDK does not **exactly**
942 match the current sources.
943
944 ### Specifying the Target Platform
945
946 You *must* specify the target platform when cross-compiling. Doing so will also
947 automatically turn the build into a cross-compiling mode. The simplest way to
948 do this is to use the `--openjdk-target` argument, e.g.
949 `--openjdk-target=arm-linux-gnueabihf`. or `--openjdk-target=aarch64-oe-linux`.
950 This will automatically set the `--build`, `--host` and `--target` options for
951 autoconf, which can otherwise be confusing. (In autoconf terminology, the
952 "target" is known as "host", and "target" is used for building a Canadian
953 cross-compiler.)
954
955 ### Toolchain Considerations
956
957 You will need two copies of your toolchain, one which generates output that can
958 run on the target system (the normal, or *target*, toolchain), and one that
959 generates output that can run on the build system (the *build* toolchain). Note
960 that cross-compiling is only supported for gcc at the time being. The gcc
961 standard is to prefix cross-compiling toolchains with the target denominator.
962 If you follow this standard, `configure` is likely to pick up the toolchain
963 correctly.
964
965 The *build* toolchain will be autodetected just the same way the normal
966 *build*/*target* toolchain will be autodetected when not cross-compiling. If
967 this is not what you want, or if the autodetection fails, you can specify a
968 devkit containing the *build* toolchain using `--with-build-devkit` to
969 `configure`, or by giving `BUILD_CC` and `BUILD_CXX` arguments.
970
971 It is often helpful to locate the cross-compilation tools, headers and
972 libraries in a separate directory, outside the normal path, and point out that
973 directory to `configure`. Do this by setting the sysroot (`--with-sysroot`) and
974 appending the directory when searching for cross-compilations tools
975 (`--with-toolchain-path`). As a compact form, you can also use `--with-devkit`
976 to point to a single directory, if it is correctly setup. (See `basics.m4` for
977 details.)
978
979 ### Native Libraries
980
981 You will need copies of external native libraries for the *target* system,
982 present on the *build* machine while building.
983
984 Take care not to replace the *build* system's version of these libraries by
985 mistake, since that can render the *build* machine unusable.
986
987 Make sure that the libraries you point to (ALSA, X11, etc) are for the
988 *target*, not the *build*, platform.
989
990 #### ALSA
991
992 You will need alsa libraries suitable for your *target* system. For most cases,
993 using Debian's pre-built libraries work fine.
994
995 Note that alsa is needed even if you only want to build a headless JDK.
996
997 * Go to [Debian Package Search](https://www.debian.org/distrib/packages) and
998 search for the `libasound2` and `libasound2-dev` packages for your *target*
999 system. Download them to /tmp.
1000
1001 * Install the libraries into the cross-compilation toolchain. For instance:
1002 ```
1003 cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc
1004 dpkg-deb -x /tmp/libasound2_1.0.25-4_armhf.deb .
1005 dpkg-deb -x /tmp/libasound2-dev_1.0.25-4_armhf.deb .
1006 ```
1007
1008 * If alsa is not properly detected by `configure`, you can point it out by
1009 `--with-alsa`.
1010
1011 #### X11
1012
1013 You will need X11 libraries suitable for your *target* system. For most cases,
1014 using Debian's pre-built libraries work fine.
1015
1016 Note that X11 is needed even if you only want to build a headless JDK.
1017
1018 * Go to [Debian Package Search](https://www.debian.org/distrib/packages),
1019 search for the following packages for your *target* system, and download them
1020 to /tmp/target-x11:
1021 * libxi
1022 * libxi-dev
1023 * x11proto-core-dev
1024 * x11proto-input-dev
1025 * x11proto-kb-dev
1026 * x11proto-render-dev
1027 * x11proto-xext-dev
1028 * libice-dev
1029 * libxrender
1030 * libxrender-dev
1031 * libxrandr-dev
1032 * libsm-dev
1033 * libxt-dev
1034 * libx11
1035 * libx11-dev
1036 * libxtst
1037 * libxtst-dev
1038 * libxext
1039 * libxext-dev
1040
1041 * Install the libraries into the cross-compilation toolchain. For instance:
1042 ```
1043 cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc/usr
1044 mkdir X11R6
1045 cd X11R6
1046 for deb in /tmp/target-x11/*.deb ; do dpkg-deb -x $deb . ; done
1047 mv usr/* .
1048 cd lib
1049 cp arm-linux-gnueabihf/* .
1050 ```
1051
1052 You can ignore the following messages. These libraries are not needed to
1053 successfully complete a full JDK build.
1054 ```
1055 cp: cannot stat `arm-linux-gnueabihf/libICE.so': No such file or directory
1056 cp: cannot stat `arm-linux-gnueabihf/libSM.so': No such file or directory
1057 cp: cannot stat `arm-linux-gnueabihf/libXt.so': No such file or directory
1058 ```
1059
1060 * If the X11 libraries are not properly detected by `configure`, you can
1061 point them out by `--with-x`.
1062
1063 ### Creating And Using Sysroots With qemu-deboostrap
1064
1065 Fortunately, you can create sysroots for foreign architectures with tools
1066 provided by your OS. On Debian/Ubuntu systems, one could use `qemu-deboostrap` to
1067 create the *target* system chroot, which would have the native libraries and headers
1068 specific to that *target* system. After that, we can use the cross-compiler on the *build*
1069 system, pointing into chroot to get the build dependencies right. This allows building
1070 for foreign architectures with native compilation speed.
1071
1072 For example, cross-compiling to AArch64 from x86_64 could be done like this:
1073
1074 * Install cross-compiler on the *build* system:
1075 ```
1076 apt install g++-aarch64-linux-gnu gcc-aarch64-linux-gnu
1077 ```
1078
1079 * Create chroot on the *build* system, configuring it for *target* system:
1080 ```
1081 sudo qemu-debootstrap --arch=arm64 --verbose \
1082 --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 \
1083 --resolve-deps jessie /chroots/arm64 http://httpredir.debian.org/debian/
1084 ```
1085
1086 * Configure and build with newly created chroot as sysroot/toolchain-path:
1087 ```
1088 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/
1089 make images
1090 ls build/linux-aarch64-normal-server-release/
1091 ```
1092
1093 The build does not create new files in that chroot, so it can be reused for multiple builds
1094 without additional cleanup.
1095
1096 Architectures that are known to successfully cross-compile like this are:
1097
1098 Target `CC` `CXX` `--arch=...` `--openjdk-target=...`
1099 ------------ ------------------------- --------------------------- ------------- -----------------------
1100 x86 default default i386 i386-linux-gnu
1101 armhf gcc-arm-linux-gnueabihf g++-arm-linux-gnueabihf armhf arm-linux-gnueabihf
1102 aarch64 gcc-aarch64-linux-gnu g++-aarch64-linux-gnu arm64 aarch64-linux-gnu
1103 ppc64el gcc-powerpc64le-linux-gnu g++-powerpc64le-linux-gnu ppc64el powerpc64le-linux-gnu
1104 s390x gcc-s390x-linux-gnu g++-s390x-linux-gnu s390x s390x-linux-gnu
1105
1106 Additional architectures might be supported by Debian/Ubuntu Ports.
1107
1108 ### Building for ARM/aarch64
1109
1110 A common cross-compilation target is the ARM CPU. When building for ARM, it is
1111 useful to set the ABI profile. A number of pre-defined ABI profiles are
1112 available using `--with-abi-profile`: arm-vfp-sflt, arm-vfp-hflt, arm-sflt,
1113 armv5-vfp-sflt, armv6-vfp-hflt. Note that soft-float ABIs are no longer
1114 properly supported by the JDK.
1115
1116 ### Verifying the Build
1117
1118 The build will end up in a directory named like
1119 `build/linux-arm-normal-server-release`.
1120
1121 Inside this build output directory, the `images/jdk` will contain the newly
1122 built JDK, for your *target* system.
1123
1124 Copy these folders to your *target* system. Then you can run e.g.
1125 `images/jdk/bin/java -version`.
1126
1127 ## Build Performance
1128
1129 Building the JDK requires a lot of horsepower. Some of the build tools can be
1130 adjusted to utilize more or less of resources such as parallel threads and
1131 memory. The `configure` script analyzes your system and selects reasonable
1132 values for such options based on your hardware. If you encounter resource
1133 problems, such as out of memory conditions, you can modify the detected values
1134 with:
1135
1136 * `--with-num-cores` -- number of cores in the build system, e.g.
1137 `--with-num-cores=8`.
1138
1139 * `--with-memory-size` -- memory (in MB) available in the build system, e.g.
1140 `--with-memory-size=1024`
1141
1142 You can also specify directly the number of build jobs to use with
1143 `--with-jobs=N` to `configure`, or `JOBS=N` to `make`. Do not use the `-j` flag
1144 to `make`. In most cases it will be ignored by the makefiles, but it can cause
1145 problems for some make targets.
1146
1147 It might also be necessary to specify the JVM arguments passed to the Boot JDK,
1148 using e.g. `--with-boot-jdk-jvmargs="-Xmx8G"`. Doing so will override the
1149 default JVM arguments passed to the Boot JDK.
1150
1151 At the end of a successful execution of `configure`, you will get a performance
1152 summary, indicating how well the build will perform. Here you will also get
1153 performance hints. If you want to build fast, pay attention to those!
1154
1155 If you want to tweak build performance, run with `make LOG=info` to get a build
1156 time summary at the end of the build process.
1157
1158 ### Disk Speed
1159
1160 If you are using network shares, e.g. via NFS, for your source code, make sure
1161 the build directory is situated on local disk (e.g. by `ln -s
1162 /localdisk/jdk-build $JDK-SHARE/build`). The performance penalty is extremely
1163 high for building on a network share; close to unusable.
1164
1165 Also, make sure that your build tools (including Boot JDK and toolchain) is
1166 located on a local disk and not a network share.
1167
1168 As has been stressed elsewhere, do use SSD for source code and build directory,
1169 as well as (if possible) the build tools.
1170
1171 ### Virus Checking
1172
1173 The use of virus checking software, especially on Windows, can *significantly*
1174 slow down building of the JDK. If possible, turn off such software, or exclude
1175 the directory containing the JDK source code from on-the-fly checking.
1176
1177 ### Ccache
1178
1179 The JDK build supports building with ccache when using gcc or clang. Using
1180 ccache can radically speed up compilation of native code if you often rebuild
1181 the same sources. Your milage may vary however, so we recommend evaluating it
1182 for yourself. To enable it, make sure it's on the path and configure with
1183 `--enable-ccache`.
1184
1185 ### Precompiled Headers
1186
1187 By default, the Hotspot build uses preccompiled headers (PCH) on the toolchains
1188 were it is properly supported (clang, gcc, and Visual Studio). Normally, this
1189 speeds up the build process, but in some circumstances, it can actually slow
1190 things down.
1191
1192 You can experiment by disabling precompiled headers using
1193 `--disable-precompiled-headers`.
1194
1195 ### Icecc / icecream
1196
1197 [icecc/icecream](http://github.com/icecc/icecream) is a simple way to setup a
1198 distributed compiler network. If you have multiple machines available for
1199 building the JDK, you can drastically cut individual build times by utilizing
1200 it.
1201
1202 To use, setup an icecc network, and install icecc on the build machine. Then
1203 run `configure` using `--enable-icecc`.
1204
1205 ### Using sjavac
1206
1207 To speed up Java compilation, especially incremental compilations, you can try
1208 the experimental sjavac compiler by using `--enable-sjavac`.
1209
1210 ### Building the Right Target
1211
1212 Selecting the proper target to build can have dramatic impact on build time.
1213 For normal usage, `jdk` or the default target is just fine. You only need to
1214 build `images` for shipping, or if your tests require it.
1215
1216 See also [Using Fine-Grained Make Targets](#using-fine-grained-make-targets) on
1217 how to build an even smaller subset of the product.
1218
1219 ## Troubleshooting
1220
1221 If your build fails, it can sometimes be difficult to pinpoint the problem or
1222 find a proper solution.
1223
1224 ### Locating the Source of the Error
1225
1226 When a build fails, it can be hard to pinpoint the actual cause of the error.
1227 In a typical build process, different parts of the product build in parallel,
1228 with the output interlaced.
1229
1230 #### Build Failure Summary
1231
1232 To help you, the build system will print a failure summary at the end. It looks
1233 like this:
1234
1235 ```
1236 ERROR: Build failed for target 'hotspot' in configuration 'linux-x64' (exit code 2)
1237
1238 === Output from failing command(s) repeated here ===
1239 * For target hotspot_variant-server_libjvm_objs_psMemoryPool.o:
1240 /localhome/hg/jdk9-sandbox/hotspot/src/share/vm/services/psMemoryPool.cpp:1:1: error: 'failhere' does not name a type
1241 ... (rest of output omitted)
1242
1243 * All command lines available in /localhome/hg/jdk9-sandbox/build/linux-x64/make-support/failure-logs.
1244 === End of repeated output ===
1245
1246 === Make failed targets repeated here ===
1247 lib/CompileJvm.gmk:207: recipe for target '/localhome/hg/jdk9-sandbox/build/linux-x64/hotspot/variant-server/libjvm/objs/psMemoryPool.o' failed
1248 make/Main.gmk:263: recipe for target 'hotspot-server-libs' failed
1249 === End of repeated output ===
1250
1251 Hint: Try searching the build log for the name of the first failed target.
1252 Hint: If caused by a warning, try configure --disable-warnings-as-errors.
1253 ```
1254
1255 Let's break it down! First, the selected configuration, and the top-level
1256 target you entered on the command line that caused the failure is printed.
1257
1258 Then, between the `Output from failing command(s) repeated here` and `End of
1259 repeated output` the first lines of output (stdout and stderr) from the actual
1260 failing command is repeated. In most cases, this is the error message that
1261 caused the build to fail. If multiple commands were failing (this can happen in
1262 a parallel build), output from all failed commands will be printed here.
1263
1264 The path to the `failure-logs` directory is printed. In this file you will find
1265 a `<target>.log` file that contains the output from this command in its
1266 entirety, and also a `<target>.cmd`, which contain the complete command line
1267 used for running this command. You can re-run the failing command by executing
1268 `. <path to failure-logs>/<target>.cmd` in your shell.
1269
1270 Another way to trace the failure is to follow the chain of make targets, from
1271 top-level targets to individual file targets. Between `Make failed targets
1272 repeated here` and `End of repeated output` the output from make showing this
1273 chain is repeated. The first failed recipe will typically contain the full path
1274 to the file in question that failed to compile. Following lines will show a
1275 trace of make targets why we ended up trying to compile that file.
1276
1277 Finally, some hints are given on how to locate the error in the complete log.
1278 In this example, we would try searching the log file for "`psMemoryPool.o`".
1279 Another way to quickly locate make errors in the log is to search for "`]
1280 Error`" or "`***`".
1281
1282 Note that the build failure summary will only help you if the issue was a
1283 compilation failure or similar. If the problem is more esoteric, or is due to
1284 errors in the build machinery, you will likely get empty output logs, and `No
1285 indication of failed target found` instead of the make target chain.
1286
1287 #### Checking the Build Log File
1288
1289 The output (stdout and stderr) from the latest build is always stored in
1290 `$BUILD/build.log`. The previous build log is stored as `build.log.old`. This
1291 means that it is not necessary to redirect the build output yourself if you
1292 want to process it.
1293
1294 You can increase the verbosity of the log file, by the `LOG` control variable
1295 to `make`. If you want to see the command lines used in compilations, use
1296 `LOG=cmdlines`. To increase the general verbosity, use `LOG=info`, `LOG=debug`
1297 or `LOG=trace`. Both of these can be combined with `cmdlines`, e.g.
1298 `LOG=info,cmdlines`. The `debug` log level will show most shell commands
1299 executed by make, and `trace` will show all. Beware that both these log levels
1300 will produce a massive build log!
1301
1302 ### Fixing Unexpected Build Failures
1303
1304 Most of the time, the build will fail due to incorrect changes in the source
1305 code.
1306
1307 Sometimes the build can fail with no apparent changes that have caused the
1308 failure. If this is the first time you are building the JDK on this particular
1309 computer, and the build fails, the problem is likely with your build
1310 environment. But even if you have previously built the JDK with success, and it
1311 now fails, your build environment might have changed (perhaps due to OS
1312 upgrades or similar). But most likely, such failures are due to problems with
1313 the incremental rebuild.
1314
1315 #### Problems with the Build Environment
1316
1317 Make sure your configuration is correct. Re-run `configure`, and look for any
1318 warnings. Warnings that appear in the middle of the `configure` output is also
1319 repeated at the end, after the summary. The entire log is stored in
1320 `$BUILD/configure.log`.
1321
1322 Verify that the summary at the end looks correct. Are you indeed using the Boot
1323 JDK and native toolchain that you expect?
1324
1325 By default, the JDK has a strict approach where warnings from the compiler is
1326 considered errors which fail the build. For very new or very old compiler
1327 versions, this can trigger new classes of warnings, which thus fails the build.
1328 Run `configure` with `--disable-warnings-as-errors` to turn of this behavior.
1329 (The warnings will still show, but not make the build fail.)
1330
1331 #### Problems with Incremental Rebuilds
1332
1333 Incremental rebuilds mean that when you modify part of the product, only the
1334 affected parts get rebuilt. While this works great in most cases, and
1335 significantly speed up the development process, from time to time complex
1336 interdependencies will result in an incorrect build result. This is the most
1337 common cause for unexpected build problems.
1338
1339 Here are a suggested list of things to try if you are having unexpected build
1340 problems. Each step requires more time than the one before, so try them in
1341 order. Most issues will be solved at step 1 or 2.
1342
1343 1. Make sure your repository is up-to-date
1344
1345 Run `hg pull -u` to make sure you have the latest changes.
1346
1347 2. Clean build results
1348
1349 The simplest way to fix incremental rebuild issues is to run `make clean`.
1350 This will remove all build results, but not the configuration or any build
1351 system support artifacts. In most cases, this will solve build errors
1352 resulting from incremental build mismatches.
1353
1354 3. Completely clean the build directory.
1355
1356 If this does not work, the next step is to run `make dist-clean`, or
1357 removing the build output directory (`$BUILD`). This will clean all
1358 generated output, including your configuration. You will need to re-run
1359 `configure` after this step. A good idea is to run `make
1360 print-configuration` before running `make dist-clean`, as this will print
1361 your current `configure` command line. Here's a way to do this:
1362
1363 ```
1364 make print-configuration > current-configuration
1365 make dist-clean
1366 bash configure $(cat current-configuration)
1367 make
1368 ```
1369
1370 4. Re-clone the Mercurial repository
1371
1372 Sometimes the Mercurial repository gets in a state that causes the product
1373 to be un-buildable. In such a case, the simplest solution is often the
1374 "sledgehammer approach": delete the entire repository, and re-clone it.
1375 If you have local changes, save them first to a different location using
1376 `hg export`.
1377
1378 ### Specific Build Issues
1379
1380 #### Clock Skew
1381
1382 If you get an error message like this:
1383 ```
1384 File 'xxx' has modification time in the future.
1385 Clock skew detected. Your build may be incomplete.
1386 ```
1387 then the clock on your build machine is out of sync with the timestamps on the
1388 source files. Other errors, apparently unrelated but in fact caused by the
1389 clock skew, can occur along with the clock skew warnings. These secondary
1390 errors may tend to obscure the fact that the true root cause of the problem is
1391 an out-of-sync clock.
1392
1393 If you see these warnings, reset the clock on the build machine, run `make
1394 clean` and restart the build.
1395
1396 #### Out of Memory Errors
1397
1398 On Windows, you might get error messages like this:
1399 ```
1400 fatal error - couldn't allocate heap
1401 cannot create ... Permission denied
1402 spawn failed
1403 ```
1404 This can be a sign of a Cygwin problem. See the information about solving
1405 problems in the [Cygwin](#cygwin) section. Rebooting the computer might help
1406 temporarily.
1407
1408 ### Getting Help
1409
1410 If none of the suggestions in this document helps you, or if you find what you
1411 believe is a bug in the build system, please contact the Build Group by sending
1412 a mail to [build-dev@openjdk.java.net](mailto:build-dev@openjdk.java.net).
1413 Please include the relevant parts of the configure and/or build log.
1414
1415 If you need general help or advice about developing for the JDK, you can also
1416 contact the Adoption Group. See the section on [Contributing to OpenJDK](
1417 #contributing-to-openjdk) for more information.
1418
1419 ## Hints and Suggestions for Advanced Users
1420
1421 ### Setting Up a Repository for Pushing Changes (defpath)
1422
1423 To help you prepare a proper push path for a Mercurial repository, there exists
1424 a useful tool known as [defpath](
1425 http://openjdk.java.net/projects/code-tools/defpath). It will help you setup a
1426 proper push path for pushing changes to the JDK.
1427
1428 Install the extension by cloning
1429 `http://hg.openjdk.java.net/code-tools/defpath` and updating your `.hgrc` file.
1430 Here's one way to do this:
1431
1432 ```
1433 cd ~
1434 mkdir hg-ext
1435 cd hg-ext
1436 hg clone http://hg.openjdk.java.net/code-tools/defpath
1437 cat << EOT >> ~/.hgrc
1438 [extensions]
1439 defpath=~/hg-ext/defpath/defpath.py
1440 EOT
1441 ```
1442
1443 You can now setup a proper push path using:
1444 ```
1445 hg defpath -d -u <your OpenJDK username>
1446 ```
1447
1448 ### Bash Completion
1449
1450 The `configure` and `make` commands tries to play nice with bash command-line
1451 completion (using `<tab>` or `<tab><tab>`). To use this functionality, make
1452 sure you enable completion in your `~/.bashrc` (see instructions for bash in
1453 your operating system).
1454
1455 Make completion will work out of the box, and will complete valid make targets.
1456 For instance, typing `make jdk-i<tab>` will complete to `make jdk-image`.
1457
1458 The `configure` script can get completion for options, but for this to work you
1459 need to help `bash` on the way. The standard way of running the script, `bash
1460 configure`, will not be understood by bash completion. You need `configure` to
1461 be the command to run. One way to achieve this is to add a simple helper script
1462 to your path:
1463
1464 ```
1465 cat << EOT > /tmp/configure
1466 #!/bin/bash
1467 if [ \$(pwd) = \$(cd \$(dirname \$0); pwd) ] ; then
1468 echo >&2 "Abort: Trying to call configure helper recursively"
1469 exit 1
1470 fi
1471
1472 bash \$PWD/configure "\$@"
1473 EOT
1474 chmod +x /tmp/configure
1475 sudo mv /tmp/configure /usr/local/bin
1476 ```
1477
1478 Now `configure --en<tab>-dt<tab>` will result in `configure --enable-dtrace`.
1479
1480 ### Using Multiple Configurations
1481
1482 You can have multiple configurations for a single source repository. When you
1483 create a new configuration, run `configure --with-conf-name=<name>` to create a
1484 configuration with the name `<name>`. Alternatively, you can create a directory
1485 under `build` and run `configure` from there, e.g. `mkdir build/<name> && cd
1486 build/<name> && bash ../../configure`.
1487
1488 Then you can build that configuration using `make CONF_NAME=<name>` or `make
1489 CONF=<pattern>`, where `<pattern>` is a substring matching one or several
1490 configurations, e.g. `CONF=debug`. The special empty pattern (`CONF=`) will
1491 match *all* available configuration, so `make CONF= hotspot` will build the
1492 `hotspot` target for all configurations. Alternatively, you can execute `make`
1493 in the configuration directory, e.g. `cd build/<name> && make`.
1494
1495 ### Handling Reconfigurations
1496
1497 If you update the repository and part of the configure script has changed, the
1498 build system will force you to re-run `configure`.
1499
1500 Most of the time, you will be fine by running `configure` again with the same
1501 arguments as the last time, which can easily be performed by `make
1502 reconfigure`. To simplify this, you can use the `CONF_CHECK` make control
1503 variable, either as `make CONF_CHECK=auto`, or by setting an environment
1504 variable. For instance, if you add `export CONF_CHECK=auto` to your `.bashrc`
1505 file, `make` will always run `reconfigure` automatically whenever the configure
1506 script has changed.
1507
1508 You can also use `CONF_CHECK=ignore` to skip the check for a needed configure
1509 update. This might speed up the build, but comes at the risk of an incorrect
1510 build result. This is only recommended if you know what you're doing.
1511
1512 From time to time, you will also need to modify the command line to `configure`
1513 due to changes. Use `make print-configure` to show the command line used for
1514 your current configuration.
1515
1516 ### Using Fine-Grained Make Targets
1517
1518 The default behavior for make is to create consistent and correct output, at
1519 the expense of build speed, if necessary.
1520
1521 If you are prepared to take some risk of an incorrect build, and know enough of
1522 the system to understand how things build and interact, you can speed up the
1523 build process considerably by instructing make to only build a portion of the
1524 product.
1525
1526 #### Building Individual Modules
1527
1528 The safe way to use fine-grained make targets is to use the module specific
1529 make targets. All source code in the JDK is organized so it belongs to a
1530 module, e.g. `java.base` or `jdk.jdwp.agent`. You can build only a specific
1531 module, by giving it as make target: `make jdk.jdwp.agent`. If the specified
1532 module depends on other modules (e.g. `java.base`), those modules will be built
1533 first.
1534
1535 You can also specify a set of modules, just as you can always specify a set of
1536 make targets: `make jdk.crypto.cryptoki jdk.crypto.ec jdk.crypto.mscapi`
1537
1538 #### Building Individual Module Phases
1539
1540 The build process for each module is divided into separate phases. Not all
1541 modules need all phases. Which are needed depends on what kind of source code
1542 and other artifact the module consists of. The phases are:
1543
1544 * `gensrc` (Generate source code to compile)
1545 * `gendata` (Generate non-source code artifacts)
1546 * `copy` (Copy resource artifacts)
1547 * `java` (Compile Java code)
1548 * `launchers` (Compile native executables)
1549 * `libs` (Compile native libraries)
1550
1551 You can build only a single phase for a module by using the notation
1552 `$MODULE-$PHASE`. For instance, to build the `gensrc` phase for `java.base`,
1553 use `make java.base-gensrc`.
1554
1555 Note that some phases may depend on others, e.g. `java` depends on `gensrc` (if
1556 present). Make will build all needed prerequisites before building the
1557 requested phase.
1558
1559 #### Skipping the Dependency Check
1560
1561 When using an iterative development style with frequent quick rebuilds, the
1562 dependency check made by make can take up a significant portion of the time
1563 spent on the rebuild. In such cases, it can be useful to bypass the dependency
1564 check in make.
1565
1566 > **Note that if used incorrectly, this can lead to a broken build!**
1567
1568 To achieve this, append `-only` to the build target. For instance, `make
1569 jdk.jdwp.agent-java-only` will *only* build the `java` phase of the
1570 `jdk.jdwp.agent` module. If the required dependencies are not present, the
1571 build can fail. On the other hand, the execution time measures in milliseconds.
1572
1573 A useful pattern is to build the first time normally (e.g. `make
1574 jdk.jdwp.agent`) and then on subsequent builds, use the `-only` make target.
1575
1576 #### Rebuilding Part of java.base (JDK\_FILTER)
1577
1578 If you are modifying files in `java.base`, which is the by far largest module
1579 in the JDK, then you need to rebuild all those files whenever a single file has
1580 changed. (This inefficiency will hopefully be addressed in JDK 10.)
1581
1582 As a hack, you can use the make control variable `JDK_FILTER` to specify a
1583 pattern that will be used to limit the set of files being recompiled. For
1584 instance, `make java.base JDK_FILTER=javax/crypto` (or, to combine methods,
1585 `make java.base-java-only JDK_FILTER=javax/crypto`) will limit the compilation
1586 to files in the `javax.crypto` package.
1587
1588 ### Learn About Mercurial
1589
1590 To become an efficient JDK developer, it is recommended that you invest in
1591 learning Mercurial properly. Here are some links that can get you started:
1592
1593 * [Mercurial for git users](http://www.mercurial-scm.org/wiki/GitConcepts)
1594 * [The official Mercurial tutorial](http://www.mercurial-scm.org/wiki/Tutorial)
1595 * [hg init](http://hginit.com/)
1596 * [Mercurial: The Definitive Guide](http://hgbook.red-bean.com/read/)
1597
1598 ## Understanding the Build System
1599
1600 This section will give you a more technical description on the details of the
1601 build system.
1602
1603 ### Configurations
1604
1605 The build system expects to find one or more configuration. These are
1606 technically defined by the `spec.gmk` in a subdirectory to the `build`
1607 subdirectory. The `spec.gmk` file is generated by `configure`, and contains in
1608 principle the configuration (directly or by files included by `spec.gmk`).
1609
1610 You can, in fact, select a configuration to build by pointing to the `spec.gmk`
1611 file with the `SPEC` make control variable, e.g. `make SPEC=$BUILD/spec.gmk`.
1612 While this is not the recommended way to call `make` as a user, it is what is
1613 used under the hood by the build system.
1614
1615 ### Build Output Structure
1616
1617 The build output for a configuration will end up in `build/<configuration
1618 name>`, which we refer to as `$BUILD` in this document. The `$BUILD` directory
1619 contains the following important directories:
1620
1621 ```
1622 buildtools/
1623 configure-support/
1624 hotspot/
1625 images/
1626 jdk/
1627 make-support/
1628 support/
1629 test-results/
1630 test-support/
1631 ```
1632
1633 This is what they are used for:
1634
1635 * `images`: This is the directory were the output of the `*-image` make
1636 targets end up. For instance, `make jdk-image` ends up in `images/jdk`.
1637
1638 * `jdk`: This is the "exploded image". After `make jdk`, you will be able to
1639 launch the newly built JDK by running `$BUILD/jdk/bin/java`.
1640
1641 * `test-results`: This directory contains the results from running tests.
1642
1643 * `support`: This is an area for intermediate files needed during the build,
1644 e.g. generated source code, object files and class files. Some noteworthy
1645 directories in `support` is `gensrc`, which contains the generated source
1646 code, and the `modules_*` directories, which contains the files in a
1647 per-module hierarchy that will later be collapsed into the `jdk` directory
1648 of the exploded image.
1649
1650 * `buildtools`: This is an area for tools compiled for the build platform
1651 that are used during the rest of the build.
1652
1653 * `hotspot`: This is an area for intermediate files needed when building
1654 hotspot.
1655
1656 * `configure-support`, `make-support` and `test-support`: These directories
1657 contain files that are needed by the build system for `configure`, `make`
1658 and for running tests.
1659
1660 ### Fixpath
1661
1662 Windows path typically look like `C:\User\foo`, while Unix paths look like
1663 `/home/foo`. Tools with roots from Unix often experience issues related to this
1664 mismatch when running on Windows.
1665
1666 In the JDK build, we always use Unix paths internally, and only just before
1667 calling a tool that does not understand Unix paths do we convert them to
1668 Windows paths.
1669
1670 This conversion is done by the `fixpath` tool, which is a small wrapper that
1671 modifies unix-style paths to Windows-style paths in command lines. Fixpath is
1672 compiled automatically by `configure`.
1673
1674 ### Native Debug Symbols
1675
1676 Native libraries and executables can have debug symbol (and other debug
1677 information) associated with them. How this works is very much platform
1678 dependent, but a common problem is that debug symbol information takes a lot of
1679 disk space, but is rarely needed by the end user.
1680
1681 The JDK supports different methods on how to handle debug symbols. The
1682 method used is selected by `--with-native-debug-symbols`, and available methods
1683 are `none`, `internal`, `external`, `zipped`.
1684
1685 * `none` means that no debug symbols will be generated during the build.
1686
1687 * `internal` means that debug symbols will be generated during the build, and
1688 they will be stored in the generated binary.
1689
1690 * `external` means that debug symbols will be generated during the build, and
1691 after the compilation, they will be moved into a separate `.debuginfo` file.
1692 (This was previously known as FDS, Full Debug Symbols).
1693
1694 * `zipped` is like `external`, but the .debuginfo file will also be zipped
1695 into a `.diz` file.
1696
1697 When building for distribution, `zipped` is a good solution. Binaries built
1698 with `internal` is suitable for use by developers, since they facilitate
1699 debugging, but should be stripped before distributed to end users.
1700
1701 ### Autoconf Details
1702
1703 The `configure` script is based on the autoconf framework, but in some details
1704 deviate from a normal autoconf `configure` script.
1705
1706 The `configure` script in the top level directory of the JDK is just a thin
1707 wrapper that calls `make/autoconf/configure`. This in turn will run `autoconf`
1708 to create the runnable (generated) configure script, as
1709 `.build/generated-configure.sh`. Apart from being responsible for the
1710 generation of the runnable script, the `configure` script also provides
1711 functionality that is not easily expressed in the normal Autoconf framework. As
1712 part of this functionality, the generated script is called.
1713
1714 The build system will detect if the Autoconf source files have changed, and
1715 will trigger a regeneration of the generated script if needed. You can also
1716 manually request such an update by `bash configure autogen`.
1717
1718 In previous versions of the JDK, the generated script was checked in at
1719 `make/autoconf/generated-configure.sh`. This is no longer the case.
1720
1721 ### Developing the Build System Itself
1722
1723 This section contains a few remarks about how to develop for the build system
1724 itself. It is not relevant if you are only making changes in the product source
1725 code.
1726
1727 While technically using `make`, the make source files of the JDK does not
1728 resemble most other Makefiles. Instead of listing specific targets and actions
1729 (perhaps using patterns), the basic modus operandi is to call a high-level
1730 function (or properly, macro) from the API in `make/common`. For instance, to
1731 compile all classes in the `jdk.internal.foo` package in the `jdk.foo` module,
1732 a call like this would be made:
1733
1734 ```
1735 $(eval $(call SetupJavaCompilation, BUILD_FOO_CLASSES, \
1736 SETUP := GENERATE_OLDBYTECODE, \
1737 SRC := $(TOPDIR)/src/jkd.foo/share/classes, \
1738 INCLUDES := jdk/internal/foo, \
1739 BIN := $(SUPPORT_OUTPUTDIR)/foo_classes, \
1740 ))
1741 ```
1742
1743 By encapsulating and expressing the high-level knowledge of *what* should be
1744 done, rather than *how* it should be done (as is normal in Makefiles), we can
1745 build a much more powerful and flexible build system.
1746
1747 Correct dependency tracking is paramount. Sloppy dependency tracking will lead
1748 to improper parallelization, or worse, race conditions.
1749
1750 To test for/debug race conditions, try running `make JOBS=1` and `make
1751 JOBS=100` and see if it makes any difference. (It shouldn't).
1752
1753 To compare the output of two different builds and see if, and how, they differ,
1754 run `$BUILD1/compare.sh -o $BUILD2`, where `$BUILD1` and `$BUILD2` are the two
1755 builds you want to compare.
1756
1757 To automatically build two consecutive versions and compare them, use
1758 `COMPARE_BUILD`. The value of `COMPARE_BUILD` is a set of variable=value
1759 assignments, like this:
1760 ```
1761 make COMPARE_BUILD=CONF=--enable-new-hotspot-feature:MAKE=hotspot
1762 ```
1763 See `make/InitSupport.gmk` for details on how to use `COMPARE_BUILD`.
1764
1765 To analyze build performance, run with `LOG=trace` and check `$BUILD/build-trace-time.log`.
1766 Use `JOBS=1` to avoid parallelism.
1767
1768 Please check that you adhere to the [Code Conventions for the Build System](
1769 http://openjdk.java.net/groups/build/doc/code-conventions.html) before
1770 submitting patches.
1771
1772 ## Contributing to the JDK
1773
1774 So, now you've built your JDK, and made your first patch, and want to
1775 contribute it back to the OpenJDK Community.
1776
1777 First of all: Thank you! We gladly welcome your contribution.
1778 However, please bear in mind that the JDK is a massive project, and we must ask
1779 you to follow our rules and guidelines to be able to accept your contribution.
1780
1781 The official place to start is the ['How to contribute' page](
1782 http://openjdk.java.net/contribute/). There is also an official (but somewhat
1783 outdated and skimpy on details) [Developer's Guide](
1784 http://openjdk.java.net/guide/).
1785
1786 If this seems overwhelming to you, the Adoption Group is there to help you! A
1787 good place to start is their ['New Contributor' page](
1788 https://wiki.openjdk.java.net/display/Adoption/New+Contributor), or start
1789 reading the comprehensive [Getting Started Kit](
1790 https://adoptopenjdk.gitbooks.io/adoptopenjdk-getting-started-kit/en/). The
1791 Adoption Group will also happily answer any questions you have about
1792 contributing. Contact them by [mail](
1793 http://mail.openjdk.java.net/mailman/listinfo/adoption-discuss) or [IRC](
1794 http://openjdk.java.net/irc/).
1795
1796 ---
1797 # Override styles from the base CSS file that are not ideal for this document.
1798 header-includes:
1799 - '<style type="text/css">pre, code, tt { color: #1d6ae5; }</style>'
1800 ---