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 forests. 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 ### Boot JDK and Build JDK
888
889 When cross-compiling, make sure you use a boot JDK that runs on the *build*
890 system, and not on the *target* system.
891
892 To be able to build, we need a "Build JDK", which is a JDK built from the
893 current sources (that is, the same as the end result of the entire build
894 process), but able to run on the *build* system, and not the *target* system.
895 (In contrast, the Boot JDK should be from an older release, e.g. JDK 8 when
896 building JDK 9.)
897
898 The build process will create a minimal Build JDK for you, as part of building.
899 To speed up the build, you can use `--with-build-jdk` to `configure` to point
900 to a pre-built Build JDK. Please note that the build result is unpredictable,
901 and can possibly break in subtle ways, if the Build JDK does not **exactly**
902 match the current sources.
903
904 ### Specifying the Target Platform
905
906 You *must* specify the target platform when cross-compiling. Doing so will also
907 automatically turn the build into a cross-compiling mode. The simplest way to
908 do this is to use the `--openjdk-target` argument, e.g.
909 `--openjdk-target=arm-linux-gnueabihf`. or `--openjdk-target=aarch64-oe-linux`.
910 This will automatically set the `--build`, `--host` and `--target` options for
911 autoconf, which can otherwise be confusing. (In autoconf terminology, the
912 "target" is known as "host", and "target" is used for building a Canadian
913 cross-compiler.)
914
915 ### Toolchain Considerations
916
917 You will need two copies of your toolchain, one which generates output that can
918 run on the target system (the normal, or *target*, toolchain), and one that
919 generates output that can run on the build system (the *build* toolchain). Note
920 that cross-compiling is only supported for gcc at the time being. The gcc
921 standard is to prefix cross-compiling toolchains with the target denominator.
922 If you follow this standard, `configure` is likely to pick up the toolchain
923 correctly.
924
925 The *build* toolchain will be autodetected just the same way the normal
926 *build*/*target* toolchain will be autodetected when not cross-compiling. If
927 this is not what you want, or if the autodetection fails, you can specify a
928 devkit containing the *build* toolchain using `--with-build-devkit` to
929 `configure`, or by giving `BUILD_CC` and `BUILD_CXX` arguments.
930
931 It is often helpful to locate the cross-compilation tools, headers and
932 libraries in a separate directory, outside the normal path, and point out that
933 directory to `configure`. Do this by setting the sysroot (`--with-sysroot`) and
934 appending the directory when searching for cross-compilations tools
935 (`--with-toolchain-path`). As a compact form, you can also use `--with-devkit`
936 to point to a single directory, if it is correctly setup. (See `basics.m4` for
937 details.)
938
939 If you are unsure what toolchain and versions to use, these have been proved
940 working at the time of writing:
941
942 * [aarch64](
943 https://releases.linaro.org/archive/13.11/components/toolchain/binaries/gcc-linaro-aarch64-linux-gnu-4.8-2013.11_linux.tar.xz)
944 * [arm 32-bit hardware floating point](
945 https://launchpad.net/linaro-toolchain-unsupported/trunk/2012.09/+download/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux.tar.bz2)
946
947 ### Native Libraries
948
949 You will need copies of external native libraries for the *target* system,
950 present on the *build* machine while building.
951
952 Take care not to replace the *build* system's version of these libraries by
953 mistake, since that can render the *build* machine unusable.
954
955 Make sure that the libraries you point to (ALSA, X11, etc) are for the
956 *target*, not the *build*, platform.
957
958 #### ALSA
959
960 You will need alsa libraries suitable for your *target* system. For most cases,
961 using Debian's pre-built libraries work fine.
962
963 Note that alsa is needed even if you only want to build a headless JDK.
964
965 * Go to [Debian Package Search](https://www.debian.org/distrib/packages) and
966 search for the `libasound2` and `libasound2-dev` packages for your *target*
967 system. Download them to /tmp.
968
969 * Install the libraries into the cross-compilation toolchain. For instance:
970 ```
971 cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc
972 dpkg-deb -x /tmp/libasound2_1.0.25-4_armhf.deb .
973 dpkg-deb -x /tmp/libasound2-dev_1.0.25-4_armhf.deb .
974 ```
975
976 * If alsa is not properly detected by `configure`, you can point it out by
977 `--with-alsa`.
978
979 #### X11
980
981 You will need X11 libraries suitable for your *target* system. For most cases,
982 using Debian's pre-built libraries work fine.
983
984 Note that X11 is needed even if you only want to build a headless JDK.
985
986 * Go to [Debian Package Search](https://www.debian.org/distrib/packages),
987 search for the following packages for your *target* system, and download them
988 to /tmp/target-x11:
989 * libxi
990 * libxi-dev
991 * x11proto-core-dev
992 * x11proto-input-dev
993 * x11proto-kb-dev
994 * x11proto-render-dev
995 * x11proto-xext-dev
996 * libice-dev
997 * libxrender
998 * libxrender-dev
999 * libsm-dev
1000 * libxt-dev
1001 * libx11
1002 * libx11-dev
1003 * libxtst
1004 * libxtst-dev
1005 * libxext
1006 * libxext-dev
1007
1008 * Install the libraries into the cross-compilation toolchain. For instance:
1009 ```
1010 cd /tools/gcc-linaro-arm-linux-gnueabihf-raspbian-2012.09-20120921_linux/arm-linux-gnueabihf/libc/usr
1011 mkdir X11R6
1012 cd X11R6
1013 for deb in /tmp/target-x11/*.deb ; do dpkg-deb -x $deb . ; done
1014 mv usr/* .
1015 cd lib
1016 cp arm-linux-gnueabihf/* .
1017 ```
1018
1019 You can ignore the following messages. These libraries are not needed to
1020 successfully complete a full JDK build.
1021 ```
1022 cp: cannot stat `arm-linux-gnueabihf/libICE.so': No such file or directory
1023 cp: cannot stat `arm-linux-gnueabihf/libSM.so': No such file or directory
1024 cp: cannot stat `arm-linux-gnueabihf/libXt.so': No such file or directory
1025 ```
1026
1027 * If the X11 libraries are not properly detected by `configure`, you can
1028 point them out by `--with-x`.
1029
1030 ### Creating And Using Sysroots With qemu-deboostrap
1031
1032 Fortunately, you can create sysroots for foreign architectures with tools
1033 provided by your OS. On Debian/Ubuntu systems, one could use `qemu-deboostrap` to
1034 create the *target* system chroot, which would have the native libraries and headers
1035 specific to that *target* system. After that, we can use the cross-compiler on the *build*
1036 system, pointing into chroot to get the build dependencies right. This allows building
1037 for foreign architectures with native compilation speed.
1038
1039 For example, cross-compiling to AArch64 from x86_64 could be done like this:
1040
1041 * Install cross-compiler on the *build* system:
1042 ```
1043 apt install g++-aarch64-linux-gnu gcc-aarch64-linux-gnu
1044 ```
1045
1046 * Create chroot on the *build* system, configuring it for *target* system:
1047 ```
1048 sudo qemu-debootstrap --arch=arm64 --verbose \
1049 --include=fakeroot,build-essential,libx11-dev,libxext-dev,libxrender-dev,libxtst-dev,libxt-dev,libcups2-dev,libfontconfig1-dev,libasound2-dev,libfreetype6-dev,libpng12-dev \
1050 --resolve-deps jessie /chroots/arm64 http://httpredir.debian.org/debian/
1051 ```
1052
1053 * Configure and build with newly created chroot as sysroot/toolchain-path:
1054 ```
1055 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/
1056 make images
1057 ls build/linux-aarch64-normal-server-release/
1058 ```
1059
1060 The build does not create new files in that chroot, so it can be reused for multiple builds
1061 without additional cleanup.
1062
1063 Architectures that are known to successfully cross-compile like this are:
1064
1065 Target `CC` `CXX` `--arch=...` `--openjdk-target=...`
1066 ------------ ------------------------- --------------------------- ------------ ----------------------
1067 x86 default default i386 i386-linux-gnu
1068 armhf gcc-arm-linux-gnueabihf g++-arm-linux-gnueabihf armhf arm-linux-gnueabihf
1069 aarch64 gcc-aarch64-linux-gnu g++-aarch64-linux-gnu arm64 aarch64-linux-gnu
1070 ppc64el gcc-powerpc64le-linux-gnu g++-powerpc64le-linux-gnu ppc64el powerpc64le-linux-gnu
1071 s390x gcc-s390x-linux-gnu g++-s390x-linux-gnu s390x s390x-linux-gnu
1072
1073 Additional architectures might be supported by Debian/Ubuntu Ports.
1074
1075 ### Building for ARM/aarch64
1076
1077 A common cross-compilation target is the ARM CPU. When building for ARM, it is
1078 useful to set the ABI profile. A number of pre-defined ABI profiles are
1079 available using `--with-abi-profile`: arm-vfp-sflt, arm-vfp-hflt, arm-sflt,
1080 armv5-vfp-sflt, armv6-vfp-hflt. Note that soft-float ABIs are no longer
1081 properly supported by the JDK.
1082
1083 The JDK contains two different ports for the aarch64 platform, one is the
1084 original aarch64 port from the [AArch64 Port Project](
1085 http://openjdk.java.net/projects/aarch64-port) and one is a 64-bit version of
1086 the Oracle contributed ARM port. When targeting aarch64, by the default the
1087 original aarch64 port is used. To select the Oracle ARM 64 port, use
1088 `--with-cpu-port=arm64`. Also set the corresponding value (`aarch64` or
1089 `arm64`) to --with-abi-profile, to ensure a consistent build.
1090
1091 ### Verifying the Build
1092
1093 The build will end up in a directory named like
1094 `build/linux-arm-normal-server-release`.
1095
1096 Inside this build output directory, the `images/jdk` will contain the newly
1097 built JDK, for your *target* system.
1098
1099 Copy these folders to your *target* system. Then you can run e.g.
1100 `images/jdk/bin/java -version`.
1101
1102 ## Build Performance
1103
1104 Building the JDK requires a lot of horsepower. Some of the build tools can be
1105 adjusted to utilize more or less of resources such as parallel threads and
1106 memory. The `configure` script analyzes your system and selects reasonable
1107 values for such options based on your hardware. If you encounter resource
1108 problems, such as out of memory conditions, you can modify the detected values
1109 with:
1110
1111 * `--with-num-cores` -- number of cores in the build system, e.g.
1112 `--with-num-cores=8`.
1113
1114 * `--with-memory-size` -- memory (in MB) available in the build system, e.g.
1115 `--with-memory-size=1024`
1116
1117 You can also specify directly the number of build jobs to use with
1118 `--with-jobs=N` to `configure`, or `JOBS=N` to `make`. Do not use the `-j` flag
1119 to `make`. In most cases it will be ignored by the makefiles, but it can cause
1120 problems for some make targets.
1121
1122 It might also be necessary to specify the JVM arguments passed to the Boot JDK,
1123 using e.g. `--with-boot-jdk-jvmargs="-Xmx8G"`. Doing so will override the
1124 default JVM arguments passed to the Boot JDK.
1125
1126 At the end of a successful execution of `configure`, you will get a performance
1127 summary, indicating how well the build will perform. Here you will also get
1128 performance hints. If you want to build fast, pay attention to those!
1129
1130 If you want to tweak build performance, run with `make LOG=info` to get a build
1131 time summary at the end of the build process.
1132
1133 ### Disk Speed
1134
1135 If you are using network shares, e.g. via NFS, for your source code, make sure
1136 the build directory is situated on local disk (e.g. by `ln -s
1137 /localdisk/jdk-build $JDK-SHARE/build`). The performance penalty is extremely
1138 high for building on a network share; close to unusable.
1139
1140 Also, make sure that your build tools (including Boot JDK and toolchain) is
1141 located on a local disk and not a network share.
1142
1143 As has been stressed elsewhere, do use SSD for source code and build directory,
1144 as well as (if possible) the build tools.
1145
1146 ### Virus Checking
1147
1148 The use of virus checking software, especially on Windows, can *significantly*
1149 slow down building of the JDK. If possible, turn off such software, or exclude
1150 the directory containing the JDK source code from on-the-fly checking.
1151
1152 ### Ccache
1153
1154 The JDK build supports building with ccache when using gcc or clang. Using
1155 ccache can radically speed up compilation of native code if you often rebuild
1156 the same sources. Your milage may vary however, so we recommend evaluating it
1157 for yourself. To enable it, make sure it's on the path and configure with
1158 `--enable-ccache`.
1159
1160 ### Precompiled Headers
1161
1162 By default, the Hotspot build uses preccompiled headers (PCH) on the toolchains
1163 were it is properly supported (clang, gcc, and Visual Studio). Normally, this
1164 speeds up the build process, but in some circumstances, it can actually slow
1165 things down.
1166
1167 You can experiment by disabling precompiled headers using
1168 `--disable-precompiled-headers`.
1169
1170 ### Icecc / icecream
1171
1172 [icecc/icecream](http://github.com/icecc/icecream) is a simple way to setup a
1173 distributed compiler network. If you have multiple machines available for
1174 building the JDK, you can drastically cut individual build times by utilizing
1175 it.
1176
1177 To use, setup an icecc network, and install icecc on the build machine. Then
1178 run `configure` using `--enable-icecc`.
1179
1180 ### Using sjavac
1181
1182 To speed up Java compilation, especially incremental compilations, you can try
1183 the experimental sjavac compiler by using `--enable-sjavac`.
1184
1185 ### Building the Right Target
1186
1187 Selecting the proper target to build can have dramatic impact on build time.
1188 For normal usage, `jdk` or the default target is just fine. You only need to
1189 build `images` for shipping, or if your tests require it.
1190
1191 See also [Using Fine-Grained Make Targets](#using-fine-grained-make-targets) on
1192 how to build an even smaller subset of the product.
1193
1194 ## Troubleshooting
1195
1196 If your build fails, it can sometimes be difficult to pinpoint the problem or
1197 find a proper solution.
1198
1199 ### Locating the Source of the Error
1200
1201 When a build fails, it can be hard to pinpoint the actual cause of the error.
1202 In a typical build process, different parts of the product build in parallel,
1203 with the output interlaced.
1204
1205 #### Build Failure Summary
1206
1207 To help you, the build system will print a failure summary at the end. It looks
1208 like this:
1209
1210 ```
1211 ERROR: Build failed for target 'hotspot' in configuration 'linux-x64' (exit code 2)
1212
1213 === Output from failing command(s) repeated here ===
1214 * For target hotspot_variant-server_libjvm_objs_psMemoryPool.o:
1215 /localhome/hg/jdk9-sandbox/hotspot/src/share/vm/services/psMemoryPool.cpp:1:1: error: 'failhere' does not name a type
1216 ... (rest of output omitted)
1217
1218 * All command lines available in /localhome/hg/jdk9-sandbox/build/linux-x64/make-support/failure-logs.
1219 === End of repeated output ===
1220
1221 === Make failed targets repeated here ===
1222 lib/CompileJvm.gmk:207: recipe for target '/localhome/hg/jdk9-sandbox/build/linux-x64/hotspot/variant-server/libjvm/objs/psMemoryPool.o' failed
1223 make/Main.gmk:263: recipe for target 'hotspot-server-libs' failed
1224 === End of repeated output ===
1225
1226 Hint: Try searching the build log for the name of the first failed target.
1227 Hint: If caused by a warning, try configure --disable-warnings-as-errors.
1228 ```
1229
1230 Let's break it down! First, the selected configuration, and the top-level
1231 target you entered on the command line that caused the failure is printed.
1232
1233 Then, between the `Output from failing command(s) repeated here` and `End of
1234 repeated output` the first lines of output (stdout and stderr) from the actual
1235 failing command is repeated. In most cases, this is the error message that
1236 caused the build to fail. If multiple commands were failing (this can happen in
1237 a parallel build), output from all failed commands will be printed here.
1238
1239 The path to the `failure-logs` directory is printed. In this file you will find
1240 a `<target>.log` file that contains the output from this command in its
1241 entirety, and also a `<target>.cmd`, which contain the complete command line
1242 used for running this command. You can re-run the failing command by executing
1243 `. <path to failure-logs>/<target>.cmd` in your shell.
1244
1245 Another way to trace the failure is to follow the chain of make targets, from
1246 top-level targets to individual file targets. Between `Make failed targets
1247 repeated here` and `End of repeated output` the output from make showing this
1248 chain is repeated. The first failed recipe will typically contain the full path
1249 to the file in question that failed to compile. Following lines will show a
1250 trace of make targets why we ended up trying to compile that file.
1251
1252 Finally, some hints are given on how to locate the error in the complete log.
1253 In this example, we would try searching the log file for "`psMemoryPool.o`".
1254 Another way to quickly locate make errors in the log is to search for "`]
1255 Error`" or "`***`".
1256
1257 Note that the build failure summary will only help you if the issue was a
1258 compilation failure or similar. If the problem is more esoteric, or is due to
1259 errors in the build machinery, you will likely get empty output logs, and `No
1260 indication of failed target found` instead of the make target chain.
1261
1262 #### Checking the Build Log File
1263
1264 The output (stdout and stderr) from the latest build is always stored in
1265 `$BUILD/build.log`. The previous build log is stored as `build.log.old`. This
1266 means that it is not necessary to redirect the build output yourself if you
1267 want to process it.
1268
1269 You can increase the verbosity of the log file, by the `LOG` control variable
1270 to `make`. If you want to see the command lines used in compilations, use
1271 `LOG=cmdlines`. To increase the general verbosity, use `LOG=info`, `LOG=debug`
1272 or `LOG=trace`. Both of these can be combined with `cmdlines`, e.g.
1273 `LOG=info,cmdlines`. The `debug` log level will show most shell commands
1274 executed by make, and `trace` will show all. Beware that both these log levels
1275 will produce a massive build log!
1276
1277 ### Fixing Unexpected Build Failures
1278
1279 Most of the time, the build will fail due to incorrect changes in the source
1280 code.
1281
1282 Sometimes the build can fail with no apparent changes that have caused the
1283 failure. If this is the first time you are building the JDK on this particular
1284 computer, and the build fails, the problem is likely with your build
1285 environment. But even if you have previously built the JDK with success, and it
1286 now fails, your build environment might have changed (perhaps due to OS
1287 upgrades or similar). But most likely, such failures are due to problems with
1288 the incremental rebuild.
1289
1290 #### Problems with the Build Environment
1291
1292 Make sure your configuration is correct. Re-run `configure`, and look for any
1293 warnings. Warnings that appear in the middle of the `configure` output is also
1294 repeated at the end, after the summary. The entire log is stored in
1295 `$BUILD/configure.log`.
1296
1297 Verify that the summary at the end looks correct. Are you indeed using the Boot
1298 JDK and native toolchain that you expect?
1299
1300 By default, the JDK has a strict approach where warnings from the compiler is
1301 considered errors which fail the build. For very new or very old compiler
1302 versions, this can trigger new classes of warnings, which thus fails the build.
1303 Run `configure` with `--disable-warnings-as-errors` to turn of this behavior.
1304 (The warnings will still show, but not make the build fail.)
1305
1306 #### Problems with Incremental Rebuilds
1307
1308 Incremental rebuilds mean that when you modify part of the product, only the
1309 affected parts get rebuilt. While this works great in most cases, and
1310 significantly speed up the development process, from time to time complex
1311 interdependencies will result in an incorrect build result. This is the most
1312 common cause for unexpected build problems, together with inconsistencies
1313 between the different Mercurial repositories in the forest.
1314
1315 Here are a suggested list of things to try if you are having unexpected build
1316 problems. Each step requires more time than the one before, so try them in
1317 order. Most issues will be solved at step 1 or 2.
1318
1319 1. Make sure your forest is up-to-date
1320
1321 Run `bash get_source.sh` to make sure you have the latest version of all
1322 repositories.
1323
1324 2. Clean build results
1325
1326 The simplest way to fix incremental rebuild issues is to run `make clean`.
1327 This will remove all build results, but not the configuration or any build
1328 system support artifacts. In most cases, this will solve build errors
1329 resulting from incremental build mismatches.
1330
1331 3. Completely clean the build directory.
1332
1333 If this does not work, the next step is to run `make dist-clean`, or
1334 removing the build output directory (`$BUILD`). This will clean all
1335 generated output, including your configuration. You will need to re-run
1336 `configure` after this step. A good idea is to run `make
1337 print-configuration` before running `make dist-clean`, as this will print
1338 your current `configure` command line. Here's a way to do this:
1339
1340 ```
1341 make print-configuration > current-configuration
1342 make dist-clean
1343 bash configure $(cat current-configuration)
1344 make
1345 ```
1346
1347 4. Re-clone the Mercurial forest
1348
1349 Sometimes the Mercurial repositories themselves gets in a state that causes
1350 the product to be un-buildable. In such a case, the simplest solution is
1351 often the "sledgehammer approach": delete the entire forest, and re-clone
1352 it. If you have local changes, save them first to a different location
1353 using `hg export`.
1354
1355 ### Specific Build Issues
1356
1357 #### Clock Skew
1358
1359 If you get an error message like this:
1360 ```
1361 File 'xxx' has modification time in the future.
1362 Clock skew detected. Your build may be incomplete.
1363 ```
1364 then the clock on your build machine is out of sync with the timestamps on the
1365 source files. Other errors, apparently unrelated but in fact caused by the
1366 clock skew, can occur along with the clock skew warnings. These secondary
1367 errors may tend to obscure the fact that the true root cause of the problem is
1368 an out-of-sync clock.
1369
1370 If you see these warnings, reset the clock on the build machine, run `make
1371 clean` and restart the build.
1372
1373 #### Out of Memory Errors
1374
1375 On Solaris, you might get an error message like this:
1376 ```
1377 Trouble writing out table to disk
1378 ```
1379 To solve this, increase the amount of swap space on your build machine.
1380
1381 On Windows, you might get error messages like this:
1382 ```
1383 fatal error - couldn't allocate heap
1384 cannot create ... Permission denied
1385 spawn failed
1386 ```
1387 This can be a sign of a Cygwin problem. See the information about solving
1388 problems in the [Cygwin](#cygwin) section. Rebooting the computer might help
1389 temporarily.
1390
1391 ### Getting Help
1392
1393 If none of the suggestions in this document helps you, or if you find what you
1394 believe is a bug in the build system, please contact the Build Group by sending
1395 a mail to [build-dev@openjdk.java.net](mailto:build-dev@openjdk.java.net).
1396 Please include the relevant parts of the configure and/or build log.
1397
1398 If you need general help or advice about developing for the JDK, you can also
1399 contact the Adoption Group. See the section on [Contributing to OpenJDK](
1400 #contributing-to-openjdk) for more information.
1401
1402 ## Hints and Suggestions for Advanced Users
1403
1404 ### Setting Up a Forest for Pushing Changes (defpath)
1405
1406 To help you prepare a proper push path for a Mercurial repository, there exists
1407 a useful tool known as [defpath](
1408 http://openjdk.java.net/projects/code-tools/defpath). It will help you setup a
1409 proper push path for pushing changes to the JDK.
1410
1411 Install the extension by cloning
1412 `http://hg.openjdk.java.net/code-tools/defpath` and updating your `.hgrc` file.
1413 Here's one way to do this:
1414
1415 ```
1416 cd ~
1417 mkdir hg-ext
1418 cd hg-ext
1419 hg clone http://hg.openjdk.java.net/code-tools/defpath
1420 cat << EOT >> ~/.hgrc
1421 [extensions]
1422 defpath=~/hg-ext/defpath/defpath.py
1423 EOT
1424 ```
1425
1426 You can now setup a proper push path using:
1427 ```
1428 hg defpath -d -u <your OpenJDK username>
1429 ```
1430
1431 If you also have the `trees` extension installed in Mercurial, you will
1432 automatically get a `tdefpath` command, which is even more useful. By running
1433 `hg tdefpath -du <username>` in the top repository of your forest, all repos
1434 will get setup automatically. This is the recommended usage.
1435
1436 ### Bash Completion
1437
1438 The `configure` and `make` commands tries to play nice with bash command-line
1439 completion (using `<tab>` or `<tab><tab>`). To use this functionality, make
1440 sure you enable completion in your `~/.bashrc` (see instructions for bash in
1441 your operating system).
1442
1443 Make completion will work out of the box, and will complete valid make targets.
1444 For instance, typing `make jdk-i<tab>` will complete to `make jdk-image`.
1445
1446 The `configure` script can get completion for options, but for this to work you
1447 need to help `bash` on the way. The standard way of running the script, `bash
1448 configure`, will not be understood by bash completion. You need `configure` to
1449 be the command to run. One way to achieve this is to add a simple helper script
1450 to your path:
1451
1452 ```
1453 cat << EOT > /tmp/configure
1454 #!/bin/bash
1455 if [ \$(pwd) = \$(cd \$(dirname \$0); pwd) ] ; then
1456 echo >&2 "Abort: Trying to call configure helper recursively"
1457 exit 1
1458 fi
1459
1460 bash \$PWD/configure "\$@"
1461 EOT
1462 chmod +x /tmp/configure
1463 sudo mv /tmp/configure /usr/local/bin
1464 ```
1465
1466 Now `configure --en<tab>-dt<tab>` will result in `configure --enable-dtrace`.
1467
1468 ### Using Multiple Configurations
1469
1470 You can have multiple configurations for a single source forest. When you
1471 create a new configuration, run `configure --with-conf-name=<name>` to create a
1472 configuration with the name `<name>`. Alternatively, you can create a directory
1473 under `build` and run `configure` from there, e.g. `mkdir build/<name> && cd
1474 build/<name> && bash ../../configure`.
1475
1476 Then you can build that configuration using `make CONF_NAME=<name>` or `make
1477 CONF=<pattern>`, where `<pattern>` is a substring matching one or several
1478 configurations, e.g. `CONF=debug`. The special empty pattern (`CONF=`) will
1479 match *all* available configuration, so `make CONF= hotspot` will build the
1480 `hotspot` target for all configurations. Alternatively, you can execute `make`
1481 in the configuration directory, e.g. `cd build/<name> && make`.
1482
1483 ### Handling Reconfigurations
1484
1485 If you update the forest and part of the configure script has changed, the
1486 build system will force you to re-run `configure`.
1487
1488 Most of the time, you will be fine by running `configure` again with the same
1489 arguments as the last time, which can easily be performed by `make
1490 reconfigure`. To simplify this, you can use the `CONF_CHECK` make control
1491 variable, either as `make CONF_CHECK=auto`, or by setting an environment
1492 variable. For instance, if you add `export CONF_CHECK=auto` to your `.bashrc`
1493 file, `make` will always run `reconfigure` automatically whenever the configure
1494 script has changed.
1495
1496 You can also use `CONF_CHECK=ignore` to skip the check for a needed configure
1497 update. This might speed up the build, but comes at the risk of an incorrect
1498 build result. This is only recommended if you know what you're doing.
1499
1500 From time to time, you will also need to modify the command line to `configure`
1501 due to changes. Use `make print-configure` to show the command line used for
1502 your current configuration.
1503
1504 ### Using Fine-Grained Make Targets
1505
1506 The default behavior for make is to create consistent and correct output, at
1507 the expense of build speed, if necessary.
1508
1509 If you are prepared to take some risk of an incorrect build, and know enough of
1510 the system to understand how things build and interact, you can speed up the
1511 build process considerably by instructing make to only build a portion of the
1512 product.
1513
1514 #### Building Individual Modules
1515
1516 The safe way to use fine-grained make targets is to use the module specific
1517 make targets. All source code in the JDK is organized so it belongs to a
1518 module, e.g. `java.base` or `jdk.jdwp.agent`. You can build only a specific
1519 module, by giving it as make target: `make jdk.jdwp.agent`. If the specified
1520 module depends on other modules (e.g. `java.base`), those modules will be built
1521 first.
1522
1523 You can also specify a set of modules, just as you can always specify a set of
1524 make targets: `make jdk.crypto.cryptoki jdk.crypto.ec jdk.crypto.mscapi
1525 jdk.crypto.ucrypto`
1526
1527 #### Building Individual Module Phases
1528
1529 The build process for each module is divided into separate phases. Not all
1530 modules need all phases. Which are needed depends on what kind of source code
1531 and other artifact the module consists of. The phases are:
1532
1533 * `gensrc` (Generate source code to compile)
1534 * `gendata` (Generate non-source code artifacts)
1535 * `copy` (Copy resource artifacts)
1536 * `java` (Compile Java code)
1537 * `launchers` (Compile native executables)
1538 * `libs` (Compile native libraries)
1539 * `rmic` (Run the `rmic` tool)
1540
1541 You can build only a single phase for a module by using the notation
1542 `$MODULE-$PHASE`. For instance, to build the `gensrc` phase for `java.base`,
1543 use `make java.base-gensrc`.
1544
1545 Note that some phases may depend on others, e.g. `java` depends on `gensrc` (if
1546 present). Make will build all needed prerequisites before building the
1547 requested phase.
1548
1549 #### Skipping the Dependency Check
1550
1551 When using an iterative development style with frequent quick rebuilds, the
1552 dependency check made by make can take up a significant portion of the time
1553 spent on the rebuild. In such cases, it can be useful to bypass the dependency
1554 check in make.
1555
1556 > **Note that if used incorrectly, this can lead to a broken build!**
1557
1558 To achieve this, append `-only` to the build target. For instance, `make
1559 jdk.jdwp.agent-java-only` will *only* build the `java` phase of the
1560 `jdk.jdwp.agent` module. If the required dependencies are not present, the
1561 build can fail. On the other hand, the execution time measures in milliseconds.
1562
1563 A useful pattern is to build the first time normally (e.g. `make
1564 jdk.jdwp.agent`) and then on subsequent builds, use the `-only` make target.
1565
1566 #### Rebuilding Part of java.base (JDK\_FILTER)
1567
1568 If you are modifying files in `java.base`, which is the by far largest module
1569 in the JDK, then you need to rebuild all those files whenever a single file has
1570 changed. (This inefficiency will hopefully be addressed in JDK 10.)
1571
1572 As a hack, you can use the make control variable `JDK_FILTER` to specify a
1573 pattern that will be used to limit the set of files being recompiled. For
1574 instance, `make java.base JDK_FILTER=javax/crypto` (or, to combine methods,
1575 `make java.base-java-only JDK_FILTER=javax/crypto`) will limit the compilation
1576 to files in the `javax.crypto` package.
1577
1578 ### Learn About Mercurial
1579
1580 To become an efficient JDK developer, it is recommended that you invest in
1581 learning Mercurial properly. Here are some links that can get you started:
1582
1583 * [Mercurial for git users](http://www.mercurial-scm.org/wiki/GitConcepts)
1584 * [The official Mercurial tutorial](http://www.mercurial-scm.org/wiki/Tutorial)
1585 * [hg init](http://hginit.com/)
1586 * [Mercurial: The Definitive Guide](http://hgbook.red-bean.com/read/)
1587
1588 ## Understanding the Build System
1589
1590 This section will give you a more technical description on the details of the
1591 build system.
1592
1593 ### Configurations
1594
1595 The build system expects to find one or more configuration. These are
1596 technically defined by the `spec.gmk` in a subdirectory to the `build`
1597 subdirectory. The `spec.gmk` file is generated by `configure`, and contains in
1598 principle the configuration (directly or by files included by `spec.gmk`).
1599
1600 You can, in fact, select a configuration to build by pointing to the `spec.gmk`
1601 file with the `SPEC` make control variable, e.g. `make SPEC=$BUILD/spec.gmk`.
1602 While this is not the recommended way to call `make` as a user, it is what is
1603 used under the hood by the build system.
1604
1605 ### Build Output Structure
1606
1607 The build output for a configuration will end up in `build/<configuration
1608 name>`, which we refer to as `$BUILD` in this document. The `$BUILD` directory
1609 contains the following important directories:
1610
1611 ```
1612 buildtools/
1613 configure-support/
1614 hotspot/
1615 images/
1616 jdk/
1617 make-support/
1618 support/
1619 test-results/
1620 test-support/
1621 ```
1622
1623 This is what they are used for:
1624
1625 * `images`: This is the directory were the output of the `*-image` make
1626 targets end up. For instance, `make jdk-image` ends up in `images/jdk`.
1627
1628 * `jdk`: This is the "exploded image". After `make jdk`, you will be able to
1629 launch the newly built JDK by running `$BUILD/jdk/bin/java`.
1630
1631 * `test-results`: This directory contains the results from running tests.
1632
1633 * `support`: This is an area for intermediate files needed during the build,
1634 e.g. generated source code, object files and class files. Some noteworthy
1635 directories in `support` is `gensrc`, which contains the generated source
1636 code, and the `modules_*` directories, which contains the files in a
1637 per-module hierarchy that will later be collapsed into the `jdk` directory
1638 of the exploded image.
1639
1640 * `buildtools`: This is an area for tools compiled for the build platform
1641 that are used during the rest of the build.
1642
1643 * `hotspot`: This is an area for intermediate files needed when building
1644 hotspot.
1645
1646 * `configure-support`, `make-support` and `test-support`: These directories
1647 contain files that are needed by the build system for `configure`, `make`
1648 and for running tests.
1649
1650 ### Fixpath
1651
1652 Windows path typically look like `C:\User\foo`, while Unix paths look like
1653 `/home/foo`. Tools with roots from Unix often experience issues related to this
1654 mismatch when running on Windows.
1655
1656 In the JDK build, we always use Unix paths internally, and only just before
1657 calling a tool that does not understand Unix paths do we convert them to
1658 Windows paths.
1659
1660 This conversion is done by the `fixpath` tool, which is a small wrapper that
1661 modifies unix-style paths to Windows-style paths in command lines. Fixpath is
1662 compiled automatically by `configure`.
1663
1664 ### Native Debug Symbols
1665
1666 Native libraries and executables can have debug symbol (and other debug
1667 information) associated with them. How this works is very much platform
1668 dependent, but a common problem is that debug symbol information takes a lot of
1669 disk space, but is rarely needed by the end user.
1670
1671 The JDK supports different methods on how to handle debug symbols. The
1672 method used is selected by `--with-native-debug-symbols`, and available methods
1673 are `none`, `internal`, `external`, `zipped`.
1674
1675 * `none` means that no debug symbols will be generated during the build.
1676
1677 * `internal` means that debug symbols will be generated during the build, and
1678 they will be stored in the generated binary.
1679
1680 * `external` means that debug symbols will be generated during the build, and
1681 after the compilation, they will be moved into a separate `.debuginfo` file.
1682 (This was previously known as FDS, Full Debug Symbols).
1683
1684 * `zipped` is like `external`, but the .debuginfo file will also be zipped
1685 into a `.diz` file.
1686
1687 When building for distribution, `zipped` is a good solution. Binaries built
1688 with `internal` is suitable for use by developers, since they facilitate
1689 debugging, but should be stripped before distributed to end users.
1690
1691 ### Autoconf Details
1692
1693 The `configure` script is based on the autoconf framework, but in some details
1694 deviate from a normal autoconf `configure` script.
1695
1696 The `configure` script in the top level directory of the JDK is just a thin
1697 wrapper that calls `make/autoconf/configure`. This in turn will run `autoconf`
1698 to create the runnable (generated) configure script, as
1699 `.build/generated-configure.sh`. Apart from being responsible for the
1700 generation of the runnable script, the `configure` script also provides
1701 functionality that is not easily expressed in the normal Autoconf framework. As
1702 part of this functionality, the generated script is called.
1703
1704 The build system will detect if the Autoconf source files have changed, and
1705 will trigger a regeneration of the generated script if needed. You can also
1706 manually request such an update by `bash configure autogen`.
1707
1708 In previous versions of the JDK, the generated script was checked in at
1709 `make/autoconf/generated-configure.sh`. This is no longer the case.
1710
1711 ### Developing the Build System Itself
1712
1713 This section contains a few remarks about how to develop for the build system
1714 itself. It is not relevant if you are only making changes in the product source
1715 code.
1716
1717 While technically using `make`, the make source files of the JDK does not
1718 resemble most other Makefiles. Instead of listing specific targets and actions
1719 (perhaps using patterns), the basic modus operandi is to call a high-level
1720 function (or properly, macro) from the API in `make/common`. For instance, to
1721 compile all classes in the `jdk.internal.foo` package in the `jdk.foo` module,
1722 a call like this would be made:
1723
1724 ```
1725 $(eval $(call SetupJavaCompilation, BUILD_FOO_CLASSES, \
1726 SETUP := GENERATE_OLDBYTECODE, \
1727 SRC := $(TOPDIR)/src/jkd.foo/share/classes, \
1728 INCLUDES := jdk/internal/foo, \
1729 BIN := $(SUPPORT_OUTPUTDIR)/foo_classes, \
1730 ))
1731 ```
1732
1733 By encapsulating and expressing the high-level knowledge of *what* should be
1734 done, rather than *how* it should be done (as is normal in Makefiles), we can
1735 build a much more powerful and flexible build system.
1736
1737 Correct dependency tracking is paramount. Sloppy dependency tracking will lead
1738 to improper parallelization, or worse, race conditions.
1739
1740 To test for/debug race conditions, try running `make JOBS=1` and `make
1741 JOBS=100` and see if it makes any difference. (It shouldn't).
1742
1743 To compare the output of two different builds and see if, and how, they differ,
1744 run `$BUILD1/compare.sh -o $BUILD2`, where `$BUILD1` and `$BUILD2` are the two
1745 builds you want to compare.
1746
1747 To automatically build two consecutive versions and compare them, use
1748 `COMPARE_BUILD`. The value of `COMPARE_BUILD` is a set of variable=value
1749 assignments, like this:
1750 ```
1751 make COMPARE_BUILD=CONF=--enable-new-hotspot-feature:MAKE=hotspot
1752 ```
1753 See `make/InitSupport.gmk` for details on how to use `COMPARE_BUILD`.
1754
1755 To analyze build performance, run with `LOG=trace` and check `$BUILD/build-trace-time.log`.
1756 Use `JOBS=1` to avoid parallelism.
1757
1758 Please check that you adhere to the [Code Conventions for the Build System](
1759 http://openjdk.java.net/groups/build/doc/code-conventions.html) before
1760 submitting patches.
1761
1762 ## Contributing to the JDK
1763
1764 So, now you've built your JDK, and made your first patch, and want to
1765 contribute it back to the OpenJDK Community.
1766
1767 First of all: Thank you! We gladly welcome your contribution.
1768 However, please bear in mind that the JDK is a massive project, and we must ask
1769 you to follow our rules and guidelines to be able to accept your contribution.
1770
1771 The official place to start is the ['How to contribute' page](
1772 http://openjdk.java.net/contribute/). There is also an official (but somewhat
1773 outdated and skimpy on details) [Developer's Guide](
1774 http://openjdk.java.net/guide/).
1775
1776 If this seems overwhelming to you, the Adoption Group is there to help you! A
1777 good place to start is their ['New Contributor' page](
1778 https://wiki.openjdk.java.net/display/Adoption/New+Contributor), or start
1779 reading the comprehensive [Getting Started Kit](
1780 https://adoptopenjdk.gitbooks.io/adoptopenjdk-getting-started-kit/en/). The
1781 Adoption Group will also happily answer any questions you have about
1782 contributing. Contact them by [mail](
1783 http://mail.openjdk.java.net/mailman/listinfo/adoption-discuss) or [IRC](
1784 http://openjdk.java.net/irc/).
1785
1786 ---
1787 # Override styles from the base CSS file that are not ideal for this document.
1788 header-includes:
1789 - '<style type="text/css">pre, code, tt { color: #1d6ae5; }</style>'
1790 ---