aboutsummaryrefslogtreecommitdiffstats
path: root/docs/buildroot.html
blob: a79cd4ad42c0faca318e64dfcb8801735d09bbcd (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title>Buildroot - Usage and documentation</title>
  <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
  <link rel="stylesheet" type="text/css" href="stylesheet.css" />
</head>

<body>
  <div class="main">
    <div class="titre">
      <h1>Buildroot</h1>
    </div>

    <p><a href="http://buildroot.net/">Buildroot</a>
    usage and documentation by Thomas Petazzoni. Contributions from
    Karsten Kruse, Ned Ludd, Martin Herren and others. </p>

    <p><small>$LastChangedDate$</small></p>

    <ul>

      <li><a href="#about">About Buildroot</a></li>
      <li><a href="#download">Obtaining Buildroot</a></li>
      <li><a href="#using">Using Buildroot</a></li>
      <li><a href="#custom_targetfs">Customizing the target filesystem</a></li>
      <li><a href="#custom_busybox">Customizing the Busybox
      configuration</a></li>
      <li><a href="#custom_uclibc">Customizing the uClibc
      configuration</a></li>
      <li><a href="#buildroot_innards">How Buildroot works</a></li>
      <li><a href="#multi_project">Building several projects in the
      same buildroot source tree</a></li>
      <li><a href="#using_toolchain">Using the uClibc toolchain
      outside Buildroot</a></li>
      <li><a href="#external_toolchain">Use an external toolchain</a></li>
      <li><a href="#downloaded_packages">Location of downloaded packages</a>
      </li>
      <li><a href="#add_software">Extending Buildroot with more
      Software</a></li>
      <li><a href="#links">Resources</a></li>
    </ul>

    <h2><a name="about" id="about"></a>About Buildroot</h2>

    <p>Buildroot is a set of Makefiles and patches that allow to easily
    generate both a cross-compilation toolchain and a root filesystem for your
    target. The cross-compilation toolchain uses uClibc (<a href=
    "http://www.uclibc.org/">http://www.uclibc.org/</a>), a tiny C standard
    library. </p>

    <p>Buildroot is useful mainly for people working with embedded systems.
    Embedded systems often use processors that are not the regular x86
    processors everyone is used to have on his PC. It can be PowerPC
    processors, MIPS processors, ARM processors, etc. </p>

    <p>A compilation toolchain is the set of tools that allows to
    compile code for your system. It consists of a compiler (in our
    case, <code>gcc</code>), binary utils like assembler and linker
    (in our case, <code>binutils</code>) and a C standard library (for
    example <a href="http://www.gnu.org/software/libc/libc.html">GNU
    Libc</a>, <a href="http://www.uclibc.org/">uClibc</a> or <a
    href="http://www.fefe.de/dietlibc/">dietlibc</a>). The system
    installed on your development station certainly already has a
    compilation toolchain that you can use to compile application that
    runs on your system. If you're using a PC, your compilation
    toolchain runs on an x86 processor and generates code for a x86
    processor. Under most Linux systems, the compilation toolchain
    uses the GNU libc as C standard library.  This compilation
    toolchain is called the &quot;host compilation toolchain&quot;, and more
    generally, the machine on which it is running, and on which you're
    working is called the &quot;host system&quot;. The compilation toolchain
    is provided by your distribution, and Buildroot has nothing to do
    with it. </p>

    <p>As said above, the compilation toolchain that comes with your system
    runs and generates code for the processor of your host system. As your
    embedded system has a different processor, you need a cross-compilation
    toolchain: it's a compilation toolchain that runs on your host system but
    that generates code for your target system (and target processor). For
    example, if your host system uses x86 and your target system uses ARM, the
    regular compilation toolchain of your host runs on x86 and generates code
    for x86, while the cross-compilation toolchain runs on x86 and generates
    code for ARM. </p>

    <p>Even if your embedded system uses a x86 processor, you might interested
    in Buildroot, for two reasons:</p>

    <ul>
      <li>The compilation toolchain of your host certainly uses the GNU Libc
      which is a complete but huge C standard library. Instead of using GNU
      Libc on your target system, you can use uClibc which is a tiny C standard
      library. If you want to use this C library, then you need a compilation
      toolchain to generate binaries linked with it. Buildroot can do it for
      you. </li>

      <li>Buildroot automates the building of a root filesystem with all needed
      tools like busybox. It makes it much easier than doing it by hand. </li>
    </ul>

    <p>You might wonder why such a tool is needed when you can compile
    <code>gcc</code>, <code>binutils</code>, uClibc and all the tools by hand.
    Of course, doing so is possible. But dealing with all configure options,
    with all problems of every <code>gcc</code> or <code>binutils</code>
    version it very time-consuming and uninteresting. Buildroot automates this
    process through the use of Makefiles, and has a collection of patches for
    each <code>gcc</code> and <code>binutils</code> version to make them work
    on most architectures. </p>

    <p>Moreover, Buildroot provides an infrastructure for reproducing
    the build process of your embedded root filesystem. Being able to
    reproduce the build process will be useful when a component needs
    to be patched or updated, or when another person is supposed to
    take over the project.</p>

    <h2><a name="download" id="download"></a>Obtaining Buildroot</h2>

    <p>Buildroot releases are made approximately every 3
    months. Direct Git access and daily snapshots are also
    available if you want more bleeding edge.</p>

    <p>Releases are available at <a
    href="http://buildroot.net/downloads/">http://buildroot.net/downloads/</a>.</p>

    <p>The latest snapshot is always available at <a
    href="http://buildroot.net/downloads/snapshots/buildroot-snapshot.tar.bz2">http://buildroot.net/downloads/snapshots/buildroot-snapshot.tar.bz2</a>,
    and previous snapshots are also available at <a
    href="http://buildroot.net/downloads/snapshots/">http://buildroot.net/downloads/snapshots/</a>. </p>

    <p>To download Buildroot using Git, you can simply follow
    the rules described on the &quot;Accessing Git&quot;-page (<a href=
    "http://buildroot.net/git.html">http://buildroot.net/git.html</a>)
    of the Buildroot website (<a href=
    "http://buildroot.net">http://buildroot.net</a>), and download
    <code>buildroot</code> from Git. For the impatient, here's a quick
    recipe:</p>

 <pre>
 $ git clone git://git.buildroot.net/buildroot
</pre>

    <h2><a name="using" id="using"></a>Using Buildroot</h2>

    <p>Buildroot has a nice configuration tool similar to the one you can find
    in the Linux Kernel (<a href=
    "http://www.kernel.org/">http://www.kernel.org/</a>) or in Busybox
    (<a href="http://www.busybox.org/">http://www.busybox.org/</a>). Note that
    you can build everything as a normal user. There is no need to be root to
    configure and use Buildroot. The first step is to run the configuration
    assistant:</p>

<pre>
 $ make menuconfig
</pre>

    <p>For each entry of the configuration tool, you can find associated help
    that describes the purpose of the entry. </p>

    <p>One of the key configuration items is the <code>PROJECT</code> which
    determines where some board specific packages are built and where the
    results are stored. </p>

    <p>Once everything is configured, the configuration tool has generated a
    <code>.config</code> file that contains the description of your
    configuration. It will be used by the Makefiles to do what's needed. </p>


    <p>Let's go:</p>

<pre>
 $ make
</pre>

    <p>This command will download, configure and compile all the selected
    tools, and finally generate a target filesystem. The target filesystem will
    be named <code>root_fs_ARCH.EXT</code> where <code>ARCH</code> is your
    architecture and <code>EXT</code> depends on the type of target filesystem
    selected in the <code>Target options</code> section of the configuration
    tool.
    The file is stored in the "binaries/<code>$(PROJECT)</code>/" directory</p>

    <h3><a name="local_board_support" id="local_board_support"></a>
    Creating your own board support</h3>

    <p>Once a package has been unpacked, it is possible to manually update
    configuration files. Buildroot can automatically save the configuration
    of buildroot, linux, busybox, uclibc and u-boot in "local/$(PROJECT) by
    using the command:
    </p>

<pre>
 $ make saveconfig
</pre>

     <p>Once a buildroot configuration has been created by saveconfig,
     the default "$(TOPDIR)/.config" file can be overridden by</p>

<pre>
 $ make BOARD=&lt;project&gt;
</pre>

    <p>Buildroot will then use "local/&lt;project&gt;/&lt;project&gt;.config"
    instead of ".config". </p>

    <p>If you want to modify your board, you can copy the project configuration
     file to ".config" by using the command:</p>

<pre>
 $ make BOARD=&lt;project&gt; getconfig
</pre>

    <p>You can share your custom board support directory between several buildroot trees
    by setting the environment variable <code>BUILDROOT_LOCAL</code> to this directory,
    </p>


    <h3><a name="offline_builds" id="offline_builds"></a>
    Offline builds</h3>

    <p>If you intend to do an offline-build and just want to download all
    sources that you previously selected in &quot;make menuconfig&quot; then
    issue:</p>
<pre>
 $ make source
</pre>
    <p>You can now disconnect or copy the content of your <code>dl</code>
    directory to the build-host. </p>

    <h3><a name="building_out_of_tree" id="building_out_of_tree"></a>
    Building out-of-tree</h3>

    <p>Buildroot supports building out of tree with a syntax similar
    to the Linux kernel. To use it, add O=&lt;directory&gt; to the
    make command line, E.G.:</p>

<pre>
 $ make O=/tmp/build
</pre>

    <p>And all the output files will be located under
    <code>/tmp/build</code>.</p>

    <h3><a name="environment_variables" id="environment_variables"></a>
    Environment variables</h3>

    <p>Buildroot optionally honors some environment variables that are passed
    to <code>make</code> :</p>
    <ul>
    <li>HOSTCXX</li>
    <li>HOSTCC</li>
    <li>UCLIBC_CONFIG_FILE=&lt;path/to/.config&gt;</li>
    <li>BUSYBOX_CONFIG_FILE=&lt;path/to/.config&gt;</li>
    <li>BUILDROOT_COPYTO</li>
    <li>BUILDROOT_DL_DIR</li>
    <li>BUILDROOT_LOCAL</li>
    </ul>

    <p>An example that uses config files located in the toplevel directory and
    in your $HOME:</p>
<pre>
$ make UCLIBC_CONFIG_FILE=uClibc.config BUSYBOX_CONFIG_FILE=$HOME/bb.config
</pre>

    <p>If you want to use a compiler other than the default <code>gcc</code>
    or <code>g++</code> for building helper-binaries on your host, then do</p>
<pre>
$ make HOSTCXX=g++-4.3-HEAD HOSTCC=gcc-4.3-HEAD
</pre>

    <p>If you want the result of your build to be copied to another directory
    like /tftpboot for downloading to a board using tftp, then you
    can use BUILDROOT_COPYTO to specify your location</p>
    <p>Typically, this is set in your ~/.bashrc file

<pre>
$ export BUILDROOT_COPYTO=/tftpboot
</pre>


    <h3><a name="helper_completion" id="helper_completion"></a>
    Using auto-completion</h3>

    <p>If you are lazy enough that you don't want to type the entire <i>make
    menuconfig</i> command line, you can enable auto-completion in your shell.
    Here is how you can do that using <i>bash</i>:</p>
<pre>
$ complete -W menuconfig make
</pre>

    <p>Then just enter the beginning of the line, and ask <i>bash</i> to
    complete it for you by pressing the <i>TAB</i> key:</p>
<pre>
$ make me&lt;TAB&gt;
</pre>

    <p>will result in <i>bash</i> to append <i>nuconfig</i> for you!</p>

    <p>Alternatively, some distributions (of which Debian and Mandriva are but
    an example) have more powerful make completion. Depending on you
    distribution, you may have to install a package to enable completion. Under
    Mandriva, this is <i>bash-completion</i>, while Debian ships it as part of
    the <i>bash</i> package.</p>

    <p>Other shells, such as <i>zsh</i>, also have completion facilities. See
    the documentation for your shell.</p>

    <h2><a name="custom_targetfs" id="custom_targetfs"></a>Customizing the
    target filesystem</h2>

    <p>There are a few ways to customize the resulting target filesystem:</p>

    <ul>
      <li>Customize the target filesystem directly, and rebuild the image. The
      target filesystem is available under <code>project_build_ARCH/root/</code>
      where <code>ARCH</code> is the chosen target architecture.
      You can simply make your changes here, and run make afterwards, which will
      rebuild the target filesystem image. This method allows to do everything
      on the target filesystem, but if you decide to completely rebuild your
      toolchain and tools, these changes will be lost. </li>

      <li>Customize the target filesystem skeleton, available under
      <code>target/generic/target_skeleton/</code>. You can customize
      configuration files or other stuff here. However, the full file hierarchy
      is not yet present, because it's created during the compilation process.
      So you can't do everything on this target filesystem skeleton, but
      changes to it remain even if you completely rebuild the cross-compilation
      toolchain and the tools. <br />
      You can also customize the <code>target/generic/device_table.txt</code>
      file which is used by the tools that generate the target filesystem image
      to properly set permissions and create device nodes. The
      <code>target/generic/skel.tar.gz</code> file contains the main
      directories of a root filesystem and there is no obvious reason for which
      it should be changed. These main directories are in an tarball inside of
      inside the skeleton because it contains symlinks that would be broken
      otherwise. <br />
      These customizations are deployed into
      <code>project_build_ARCH/root/</code> just before the actual image
      is made. So simply rebuilding the image by running
      make should propagate any new changes to the image. </li>

      <li>When configuring the build system, using <code>make menuconfig</code>,
      you can specify the contents of the /etc/hostname and /etc/issue
      (the welcome banner) in the <code>PROJECT</code> section</li>
    </ul>

    <h2><a name="custom_busybox" id="custom_busybox"></a>Customizing the
    Busybox configuration</h2>

    <p><a href="http://www.busybox.net/">Busybox</a> is very configurable, and
    you may want to customize it. You can
    follow these simple steps to do it. It's not an optimal way, but it's
    simple and it works. </p>

    <ol>
      <li>Make a first compilation of buildroot with busybox without trying to
      customize it. </li>

      <li>Invoke <code>make busybox-menuconfig</code>.
      The nice configuration tool appears and you can
      customize everything. </li>

      <li>Run the compilation of buildroot again. </li>
    </ol>

    <p>Otherwise, you can simply change the
    <code>package/busybox/busybox-&lt;version&gt;.config</code> file if you
    know the options you want to change without using the configuration tool.
    </p>
    <p>If you want to use an existing config file for busybox, then see
    section <a href="#environment_variables">environment variables</a>. </p>

    <h2><a name="custom_uclibc" id="custom_uclibc"></a>Customizing the uClibc
    configuration</h2>

    <p>Just like <a href="#custom_busybox">BusyBox</a>, <a
    href="http://www.uclibc.org/">uClibc</a> offers a lot of
    configuration options. They allow to select various
    functionalities, depending on your needs and limitations. </p>

    <p>The easiest way to modify the configuration of uClibc is to
    follow these steps :</p>

    <ol>

      <li>Make a first compilation of buildroot without trying to
      customize uClibc. </li>

      <li>Invoke <code>make uclibc-menuconfig</code>.
      The nice configuration assistant, similar to
      the one used in the Linux Kernel or in Buildroot appears. Make
      your configuration as appropriate. </li>

      <li>Copy the <code>.config</code> file to
      <code>toolchain/uClibc/uClibc.config</code> or
      <code>toolchain/uClibc/uClibc.config-locale</code>. The former
      is used if you haven't selected locale support in Buildroot
      configuration, and the latter is used if you have selected
      locale support. </li>

      <li>Run the compilation of Buildroot again</li>

    </ol>

    <p>Otherwise, you can simply change
    <code>toolchain/uClibc/uClibc.config</code> or
    <code>toolchain/uClibc/uClibc.config-locale</code> without running
    the configuration assistant. </p>

    <p>If you want to use an existing config file for uclibc, then see
    section <a href="#environment_variables">environment variables</a>. </p>

    <h2><a name="buildroot_innards" id="buildroot_innards"></a>How Buildroot
    works</h2>

    <p>As said above, Buildroot is basically a set of Makefiles that download,
    configure and compiles software with the correct options. It also includes
    some patches for various software, mainly the ones involved in the
    cross-compilation tool chain (<code>gcc</code>, <code>binutils</code> and
    uClibc). </p>

    <p>There is basically one Makefile per software, and they are named with
    the <code>.mk</code> extension. Makefiles are split into four
    sections:</p>

    <ul>
      <li><b>project</b> (in the <code>project/</code> directory) contains
      the Makefiles and associated files for all software related to the
      building several root file systems in the same buildroot tree. </li>

      <li><b>toolchain</b> (in the <code>toolchain/</code> directory) contains
      the Makefiles and associated files for all software related to the
      cross-compilation toolchain : <code>binutils</code>, <code>ccache</code>,
      <code>gcc</code>, <code>gdb</code>, <code>kernel-headers</code> and
      <code>uClibc</code>. </li>

      <li><b>package</b> (in the <code>package/</code> directory) contains the
      Makefiles and associated files for all user-space tools that Buildroot
      can compile and add to the target root filesystem. There is one
      sub-directory per tool. </li>

      <li><b>target</b> (in the <code>target</code> directory) contains the
      Makefiles and associated files for software related to the generation of
      the target root filesystem image. Four types of filesystems are supported
      : ext2, jffs2, cramfs and squashfs. For each of them, there's a
      sub-directory with the required files. There is also a
      <code>default/</code> directory that contains the target filesystem
      skeleton. </li>
    </ul>

    <p>Each directory contains at least 2 files :</p>

    <ul>
      <li><code>something.mk</code> is the Makefile that downloads, configures,
      compiles and installs the software <code>something</code>. </li>

      <li><code>Config.in</code> is a part of the configuration tool
      description file. It describes the option related to the current
      software. </li>

    </ul>

    <p>The main Makefile do the job through the following steps (once the
    configuration is done) :</p>

    <ol>
      <li>Create the download directory (<code>dl/</code> by default). This is
      where the tarballs will be downloaded. It is interesting to know that the
      tarballs are in this directory because it may be useful to save them
      somewhere to avoid further downloads. </li>

      <li>Create the shared build directory (<code>build_ARCH/</code> by
      default, where <code>ARCH</code> is your architecture). This is where all
      non configurable user-space tools will be compiled.When building two or
      more targets using the same architecture, the first build will go through
      the full download, configure, make process, but the second and later
      builds will only copy the result from the first build to its project
      specific target directory significantly speeding up the build process</li>

      <li>Create the project specific build directory
      (<code>project_build_ARCH/$(PROJECT)</code> by default, where
      <code>ARCH</code> is your architecture). This is where all configurable
      user-space tools will be compiled. The project specific build directory
      is neccessary, if two different targets needs to use a specific package,
      but the packages have different configuration for both targets. Some
      examples of packages built in this directory are busybox and linux.
      </li>

      <li>Create the project specific result directory
      (<code>binaries/$(PROJECT)</code> by default, where <code>ARCH</code>
      is your architecture). This is where the root filesystem images are
      stored, It is also used to store the linux kernel image and any
      utilities, boot-loaders etc. needed for a target.
      </li>

      <li>Create the toolchain build directory
      (<code>toolchain_build_ARCH/</code> by default, where <code>ARCH</code>
      is your architecture). This is where the cross compilation toolchain will
      be compiled. </li>

      <li>Setup the staging directory (<code>build_ARCH/staging_dir/</code> by
      default). This is where the cross-compilation toolchain will be
      installed. If you want to use the same cross-compilation toolchain for
      other purposes, such as compiling third-party applications, you can add
      <code>build_ARCH/staging_dir/usr/bin</code> to your PATH, and then use
      <code>arch-linux-gcc</code> to compile your application. In order to
      setup this staging directory, it first removes it, and then it creates
      various subdirectories and symlinks inside it. </li>

      <li>Create the target directory (<code>project_build_ARCH/root/</code> by
      default) and the target filesystem skeleton. This directory will contain
      the final root filesystem. To setup it up, it first deletes it, then it
      uncompress the <code>target/generic/skel.tar.gz</code> file to create the
      main subdirectories and symlinks, copies the skeleton available in
      <code>target/generic/target_skeleton</code> and then removes useless
      <code>.svn/CVS</code> directories. </li>

      <li>Add the <code>TARGETS</code> dependency. This should generally check
      if the configuration option for this package is enabled, and if so then
      &quot;subscribe&quot; this package to be compiled by adding it to the
      TARGETS global variable. </li>
    </ol>

    <h2><a name="multi_project" id="multi_project"></a>Building several
      projects in the same buildroot source tree</h2>

    <p><i>Note: the contents of this section are obsolete since this
    feature has been implemented.</i></p>

    <h3>Background</h3>

    <p>Buildroot has always supported building several projects in the same
    tree if each project was for a different architecture. </p>

    <p>The root file system has been created in the
    <code>&quot;build_&lt;ARCH&gt;/root&quot;</code>
    directory which is unique for each architecture.
    Toolchains have been built in
    <code>&quot;toolchain_build_&lt;ARCH&gt;&quot;</code>. </p>

    <p> It the user wanted to build several root file systems for the same
    architecture, a prefix or suffix could be added in the configuration file
    so the root file system would be built in
    <code>&quot;&lt;PREFIX&gt;_build_&lt;ARCH&gt;_&lt;SUFFIX&gt;/root&quot;</code>
    By supplying <u>unique</u> combinations of
    <code>&quot;&lt;PREFIX&gt;&quot;</code> and
    <code>&quot;&lt;SUFFIX&gt;&quot;</code>
    each project would get a <u>unique</u> root file system tree. </p>

    <p>The disadvantage of this approach is that a new toolchain was
    built for each project,  adding considerable time to the build
    process, even if it was two projects for the same chip. </p>

    <p>This drawback has been somewhat lessened with
    <code>gcc-4.x.y</code> which allows buildroot to use an external
    toolchain. Certain packages requires special
    features in the toolchain, and if an external toolchain is selected,
    this may lack the neccessary features to complete the build of the root
     file system.</p>

    <p>A bigger problem was that the
    <code>&quot;build_&lt;ARCH&gt;&quot;</code> tree
    was also duplicated, so each </code>package</code> would also
    be rebuilt once per project, resulting in even longer build times.</p>

    <h3>Project to share toolchain and package builds</h3>

    <p>Work has started on a project which will allow the user to build
    multiple root file systems for the same architecture in the same tree.
    The toolchain and the package build directory will be shared, but each
    project will have a dedicated directory tree for project specific
    builds. </p>

    <p>With this approach, most, if not all packages will be compiled
    when the first project is built.
    The process is almost identical to the original process.
    Packages are downloaded and extracted to the shared
    <code>&quot;build_&lt;ARCH&gt;/&lt;package&gt;&quot;</code>
    directory. They are configured and compiled. </p>

    <p>Package libraries and headers are installed in the shared $(STAGING_DIR),
    and then the project specific root file system &quot;$(TARGET_DIR)&quot;
    is populated. </p>

    <p>At the end of the build, the root file system will be used
    to generate the resulting root file system binaries. </p>

    <p>Once the first project has been built, building other projects will
    typically involve populating the new project's root file system directory
    from the existing binaries generated in the shared
    <code>&quot;build_&lt;ARCH&gt;/&lt;&gt;&quot;</code> directory. </p>

    <p>Only packages, not used by the first project, will have to go
    through the normal extract-configure-compile flow. </p>

    <h3>Implementation</h3>

    <p>The core of the solution is the introduction
    of two new directories: </p>

    <ul>
    <li><code>project_build_&lt;ARCH&gt;</code></li>

    <li><code>binaries;</code></li>
    </ul>

    <p>Each of the directories contain one subdirectory per project.
    The name of the subdirectory is configured by the user in the
    normal buildroot configuration, using the value of: </p>

    <p><code>Project Options ---> Project name</code></p>

    <p>The configuration defines the $(PROJECT) variable.</p>

    <p>The default project name is <code>&quot;uclibc&quot;</code>.</p>

    <p><code>&quot;package/Makefile.in&quot;</code> defines:
    <pre>
    <code>PROJECT_BUILD_DIR:=project_build_$(ARCH)/$(PROJECT)</code>
    <code>BINARIES_DIR:=binaries/$(PROJECT)</code>
    </pre>
    </p>

    <p>It also defines the location for the target root file system:
    <pre>
    <code>TARGET_DIR:=$(PROJECT_BUILD_DIR)/$(PROJECT)/root</code>
    </pre>
    </p>

    <p>I.E: If the user has choosen
    <code>&quot;myproject&quot;</code>
    as the $(PROJECT) name:

    <ul>
    <li><code>&quot;project_build_&lt;ARCH&gt;/myproject&quot;</code></li>
    <li><code>&quot;binaries/myproject&quot;</code></li>
    </ul>

    <p>will be created. </p>

    <p>Currently, the <u>root file system</u>, <u>busybox</u> and an Atmel
    customized version of
    <u><code>U-Boot</code></u>, as well as some Atmel specific
    bootloaders like <u>at91-bootstrap</u> and <u>dataflashboot.bin</u>
    are built in
    <code>&quot;$(PROJECT_BUILD_DIR)&quot;</code>

    <p>The resulting binaries for all architectures are stored in the
    <code>&quot;$(BINARIES_DIR)&quot;</code> directory. <p>

    <h3>Summary</h3>

    <p>The project will share directories which can be share without
    conflicts, but will use unique build directories, where the user
    can configure the build. </p>

    <h2><a name="Linux" id="Linux"></a>Linux</h2>

     <p>The user can select from three different Linux strategies:

     <ul>
     <li>Legacy: Only use version supported by the kernel headers</li>
     <li>Advanced: Allow any 2.6.X.Y combination.
	(Minimum 2.6.19)</li>
     <li>Power-User Strategy: Allow
     <code>&quot;-git&quot;</code>, or
     <code>&quot;-mm&quot;</code>, or user downloadable kernels</li>
     </ul>

     <p>The current kernel patches can be applied to the
     linux source tree even if the version differs from the
     kernel header version. </p>

     <p>Since the user can select any kernel-patch
     he/she will be able to select a non-working combination.
     If the patch fails, the user will have to generate a new
     proprietary kernel-patch or decide to not apply the kernel
     patches</p>

     <p>There is also support for <u>board specific</u> and
     <u>architecture specific</u> patches. </p>

     <p>There will also be a way for the user to supply absolute
     or relative paths to patches, possibly outside the main tree.
     This can be used to apply custom kernel-header-patches, if
     the versions available in buildroot cannot be applied to the
     specific linux version used</p>

     <p>Maybe, there will also be a possibility to supply an
     <code>&quot;URL&quot;</code> to a patch available on Internet. </p>

     <p>
	If there is no linux config file available,
	buildroot starts the linux configuration system, which
	defaults to "make menuconfig".
     </p>

    <h3>Todo</h3>
    <ol>

     <li>Configurable packages</li>
     <p>Many packages can, on top of the simple
     &quot;enable/disable build&quot;,
     be further configured using Kconfig.
     Currently these packages will be compiled using the
     configuration specified in the
     <code>&quot;.config&quot;</code> file of the <u>first</u>
     project demanding the build of the package.</p>

     <p>If <u>another</u> project uses the same packages, but with
     a different configuration,these packages will <u>not</u> be rebuilt,
     and the root file system for the new project will be populated
     with files from the build of the <u>first</u> project</p>

     <p>If multiple project are built, and a specific package
     needs two different configuration, then the user must
     delete the package from the
     <code>&quot;build_&lt;ARCH&gt;&quot;</code> directory
     before rebuilding the new project.<p>

     <p>A long term solution is to edit the package makefile and move
     the build of the configurable packages from
     <code>&quot;build_&lt;ARCH&gt;&quot;</code> to
     <code>&quot;project_build_&lt;ARCH&gt;/&lt;project name&gt;&quot;</code>
     and send a patch to the buildroot mailing list.

     <li>Naming conventions</li>

     <p>Names of resulting binaries should reflect the
     &quot;project name&quot;

     <li>Generating File System binaries</li>
     <p>
     Packages which needs to be installed with the &quot;root&quot;
     as owner, will generate a
     <code>&quot;.fakeroot.&lt;package&gt;&quot;</code> file
     which will be used for the final build of the root file system binary. </p>

     <p>This was previously located in the
     <code>&quot;$(STAGING_DIR)&quot;</code> directory, but was
     recently moved to the
     <code>&quot;$(PROJECT_BUILD_DIR)&quot;</code> directory. </p>

     <p>Currently only three packages:
     <code>&quot;at&quot;</code>,
     <code>&quot;ltp-testsuite&quot;</code> and
     <code>&quot;nfs-utils&quot;</code>
     requests fakeroot. <p>

     <p>The makefile fragments for each file system type like
     <code>&quot;ext2&quot;</code>,
     <code>&quot;jffs2&quot;</code> or
     <code>&quot;squashfs&quot;</code>
     will, when the file system binary is generated,
     collect all present
     <code>&quot;.fakeroot.&lt;package&gt;&quot;</code> files
     to a single <code>&quot;_fakeroot.&lt;file system&gt;&quot;</code>
     file and call fakeroot.</p>
     <code>&quot;.fakeroot.&lt;package&gt;&quot;</code>
     files are deleted as the last action of the Buildroot Makefile. </p>

     <p>It needs to be evaluated if any further action for the
     file system binary build is needed. </p>

     </ol>

    <h2><a name="using_toolchain" id="using_toolchain"></a>Using the
    uClibc toolchain outside Buildroot</h2>

    <p>You may want to compile your own programs or other software
    that are not packaged in Buildroot. In order to do this, you can
    use the toolchain that was generated by Buildroot. </p>

    <p>The toolchain generated by Buildroot by default is located in
    <code>build_ARCH/staging_dir/</code>. The simplest way to use it
    is to add <code>build_ARCH/staging_dir/usr/bin/</code> to your PATH
    environnement variable, and then to use
    <code>arch-linux-gcc</code>, <code>arch-linux-objdump</code>,
    <code>arch-linux-ld</code>, etc. </p>

    <p>For example, you may add the following to your
    <code>.bashrc</code> (considering you're building for the MIPS
    architecture and that Buildroot is located in
    <code>~/buildroot/</code>) :</p>

<pre>
export PATH=&quot;$PATH:~/buildroot/build_mips/staging_dir/usr/bin/&quot;
</pre>

    <p>Then you can simply do :</p>

<pre>
mips-linux-gcc -o foo foo.c
</pre>

     <p><b>Important</b> : do not try to move a gcc-3.x toolchain to an other
     directory, it won't work. There are some hardcoded paths in the
     <i>gcc</i> configuration. If you are using a current gcc-4.x, it
     is possible to relocate the toolchain, but then
     <code>--sysroot</code> must be passed every time the compiler is
     called to tell where the libraries and header files are, which
     might be cumbersome.</p>

     <p>It is also possible to generate the Buildroot toolchain in
     another directory than <code>build_ARCH/staging_dir</code> using
     the <code>Build options -&gt; Toolchain and header file
     location</code> option. This could be useful if the toolchain
     must be shared with other users.</p>

    <h2><a name="downloaded_packages"
    id="downloaded_packages"></a>Location of downloaded packages</h2>

    <p>It might be useful to know that the various tarballs that are
    downloaded by the <i>Makefiles</i> are all stored in the
    <code>DL_DIR</code> which by default is the <code>dl</code>
    directory. It's useful for example if you want to keep a complete
    version of Buildroot which is know to be working with the
    associated tarballs. This will allow you to regenerate the
    toolchain and the target filesystem with exactly the same
    versions. </p>

    <p>If you maintain several buildroot trees, it might be better to have
    a shared download location. This can be accessed by creating a symbolic link
    from the <code>dl</code> directory to the shared download location. </p>

    <p>I.E:</p>

<pre>
ln -s &lt;shared download location&gt; dl
</pre>

    <p>Another way of accessing a shared download location is to
    create the <code>BUILDROOT_DL_DIR</code> environment variable.
    If this is set, then the value of DL_DIR in the project is
    overridden. The following line should be added to
    <code>&quot;~/.bashrc&quot;</code>. <p>

<pre>
export BUILDROOT_DL_DIR &lt;shared download location&gt;
</pre>

    <h2><a name="external_toolchain" id="external_toolchain"></a>Using
    an external toolchain</h2>

<p>It might be useful not to use the toolchain generated by
Buildroot, for example if you already have a toolchain that is known
to work for your specific CPU, or if the toolchain generation feature
of Buildroot is not sufficiently flexible for you (for example if you
need to generate a system with <i>glibc</i> instead of
<i>uClibc</i>). Buildroot supports using an <i>external
toolchain</i>.</p>

<p>To enable the use of an external toolchain, go in the
<code>Toolchain</code> menu, and&nbsp;:</p>

<ul>
  <li>Select the <code>External binary toolchain</code> toolchain
  type</li>
  <li>Adjust the <code>External toolchain path</code>
  appropriately. It should be set to a path where a bin/ directory
  contains your cross-compiling tools</li>
  <li>Adjust the <code>External toolchain prefix</code>, so that the
  prefix, suffixed with <code>-gcc</code> or <code>-ld</code> will
  correspond to your cross-compiling tools</li>
</ul>

<p>If you are using an external toolchain based on <i>uClibc</i>, the
<code>Core C library from the external toolchain</code> and
<code>Libraries to copy from the external toolchain</code> options
should already have correct values. However, if your external
toolchain is based on <i>glibc</i>, you'll have to change these values
according to your cross-compiling toolchain.</p>

<p>To generate external toolchains, we recommend using <a
href="http://ymorin.is-a-geek.org/dokuwiki/projects/crosstool">Crosstool-NG</a>.
It allows to generate toolchains based on <i>uClibc</i>, <i>glibc</i>
and <i>eglibc</i> for a wide range of architectures, and has good
community support.</p>

    <h2><a name="add_software" id="add_software"></a>Extending Buildroot with
    more software</h2>

    <p>This section will only consider the case in which you want to
    add user-space software. </p>

    <h3>Package directory</h3>

    <p>First of all, create a directory under the <code>package</code>
    directory for your software, for example <code>foo</code>. </p>

    <h3><code>Config.in</code> file</h3>

    <p>Then, create a file named <code>Config.in</code>. This file
    will contain the portion of options description related to our
    <code>foo</code> software that will be used and displayed in the
    configuration tool. It should basically contain :</p>

<pre>
config BR2_PACKAGE_FOO
        bool "foo"
        help
	  This is a comment that explains what foo is.

	  http://foosoftware.org/foo/
</pre>

    <p>Of course, you can add other options to configure particular
    things in your software. </p>
    <p>Finally you have to add your new <code>foo/Config.in</code> to
    <code>package/Config.in</code>. The files included there are
    <em>sorted alphabetically</em> per category and are <em>NOT</em>
    supposed to contain anything but the <em>bare</em> name of the package.</p>
<pre>
if !BR2_PACKAGE_BUSYBOX_HIDE_OTHERS
source "package/procps/Config.in"
endif
</pre>
   <p><strong>Note:</strong><br>
   Generally all packages should live <em>directly</em> in the
   <code>package</code> directory to make it easier to find them.
   </p>
   <h3>The real <i>Makefile</i></h3>

   <p>Finally, here's the hardest part. Create a file named
   <code>foo.mk</code>. It will contain the <i>Makefile</i> rules that
   are in charge of downloading, configuring, compiling and installing
   the software.</p>

   <p>Two types of <i>Makefiles</i> can be written&nbsp;:</p>

   <ul>
    <li>Makefiles for autotools-based (autoconf, automake, etc.)
    softwares, are very easy to write thanks to the infrastructure
    available in <code>package/Makefile.autotools.in</code>.</li>
    <li>Makefiles for other types of packages are a little bit more
    complex to write.</li>
   </ul>

   <p>First, let's see how to write a <i>Makefile</i> for an
   autotools-based package, with an example&nbsp;:</p>

<pre>
     <a name="ex1line1" id="ex1line1">1</a>  #############################################################
     <a name="ex1line2" id="ex1line2">2</a>  #
     <a name="ex1line3" id="ex1line3">3</a>  # foo
     <a name="ex1line4" id="ex1line4">4</a>  #
     <a name="ex1line5" id="ex1line5">5</a>  #############################################################
     <a name="ex1line6" id="ex1line6">6</a>  FOO_VERSION:=1.0
     <a name="ex1line7" id="ex1line7">7</a>  FOO_SOURCE:=foo-$(FOO_VERSION).tar.gz
     <a name="ex1line8" id="ex1line8">8</a>  FOO_SITE:=http://www.foosoftware.org/downloads
     <a name="ex1line9" id="ex1line9">9</a>  FOO_INSTALL_STAGING = YES
     <a name="ex1line10" id="ex1line10">10</a>  FOO_INSTALL_TARGET = YES
     <a name="ex1line11" id="ex1line11">11</a>  FOO_CONF_OPT =  --enable-shared
     <a name="ex1line12" id="ex1line12">12</a>  FOO_DEPENDENCIES = libglib2 host-pkgconfig
     <a name="ex1line13" id="ex1line13">13</a>  $(eval $(call AUTOTARGETS,package,foo))
</pre>

    <p>On <a href="#ex1line6">line 6</a>, we declare the version of
    the package. On line <a href="#ex1line7">7</a> and <a
    href="#ex1line8">8</a>, we declare the name of the tarball and the
    location of the tarball on the Web. Buildroot will automatically
    download the tarball from this location.</p>

    <p>On <a href="#ex1line9">line 9</a>, we tell Buildroot to install
    the application to the staging directory. The staging directory,
    located in <code>build_ARCH/staging_dir/</code> is the directory
    where all the packages are installed, including their
    documentation, etc. By default, packages are installed in this
    location using the <code>make install</code> command.</p>

    <p>On <a href="#ex1line10">line 10</a>, we tell Buildroot to also
    install the application to the target directory. This directory
    contains what will become the root filesystem running on the
    target. Usually, we try not to install the documentation, and to
    install stripped versions of the binary. By default, packages are
    installed in this location using the <code>make
    install-strip</code> command.</p>

    <p>On <a href="#ex1line11">line 11</a>, we tell Buildroot to pass
    a custom configure option, that will be passed to the
    <code>./configure</code> script before configuring and building
    the package.</p>

    <p>On <a href="#ex1line12">line 12</a>, we declare our
    dependencies, so that they are built before the build process of
    our package starts.</p>

    <p>Finally, on line <a href="#ex1line13">line 13</a>, we invoke
    the <code>package/Makefile.autotools.in</code> magic to get things
    working.</p>

    <p>For more details about the available variables and options, see
    the comment at the top of
    <code>package/Makefile.autotools.in</code> and the examples in all
    the available packages.</p>

    <p>The second solution, suitable for every type of package, looks
    like this&nbsp;:</p>


<pre>
     <a name="ex2line1" id="ex2line1">1</a>  #############################################################
     <a name="ex2line2" id="ex2line2">2</a>  #
     <a name="ex2line3" id="ex2line3">3</a>  # foo
     <a name="ex2line4" id="ex2line4">4</a>  #
     <a name="ex2line5" id="ex2line5">5</a>  #############################################################
     <a name="ex2line6" id="ex2line6">6</a>  FOO_VERSION:=1.0
     <a name="ex2line7" id="ex2line7">7</a>  FOO_SOURCE:=foo-$(FOO_VERSION).tar.gz
     <a name="ex2line8" id="ex2line8">8</a>  FOO_SITE:=http://www.foosoftware.org/downloads
     <a name="ex2line9" id="ex2line9">9</a>  FOO_DIR:=$(BUILD_DIR)/foo-$(FOO_VERSION)
    <a name="ex2line10" id="ex2line10">10</a>  FOO_BINARY:=foo
    <a name="ex2line11" id="ex2line11">11</a>  FOO_TARGET_BINARY:=usr/bin/foo
    <a name="ex2line12" id="ex2line12">12</a>
    <a name="ex2line13" id="ex2line13">13</a>  $(DL_DIR)/$(FOO_SOURCE):
    <a name="ex2line14" id="ex2line14">14</a>          $(call DOWNLOAD,$(FOO_SITE),$(FOO_SOURCE))
    <a name="ex2line15" id="ex2line15">15</a>
    <a name="ex2line16" id="ex2line16">16</a>  $(FOO_DIR)/.source: $(DL_DIR)/$(FOO_SOURCE)
    <a name="ex2line17" id="ex2line17">17</a>          $(ZCAT) $(DL_DIR)/$(FOO_SOURCE) | tar -C $(BUILD_DIR) $(TAR_OPTIONS) -
    <a name="ex2line18" id="ex2line18">18</a>          touch $@
    <a name="ex2line19" id="ex2line19">19</a>
    <a name="ex2line20" id="ex2line20">20</a>  $(FOO_DIR)/.configured: $(FOO_DIR)/.source
    <a name="ex2line21" id="ex2line21">21</a>          (cd $(FOO_DIR); rm -rf config.cache; \
    <a name="ex2line22" id="ex2line22">22</a>                  $(TARGET_CONFIGURE_OPTS) \
    <a name="ex2line23" id="ex2line23">23</a>                  $(TARGET_CONFIGURE_ARGS) \
    <a name="ex2line24" id="ex2line24">24</a>                  ./configure \
    <a name="ex2line25" id="ex2line25">25</a>                  --target=$(GNU_TARGET_NAME) \
    <a name="ex2line26" id="ex2line26">26</a>                  --host=$(GNU_TARGET_NAME) \
    <a name="ex2line27" id="ex2line27">27</a>                  --build=$(GNU_HOST_NAME) \
    <a name="ex2line28" id="ex2line28">28</a>                  --prefix=/usr \
    <a name="ex2line29" id="ex2line29">29</a>                  --sysconfdir=/etc \
    <a name="ex2line30" id="ex2line30">30</a>          )
    <a name="ex2line31" id="ex2line31">31</a>          touch $@
    <a name="ex2line32" id="ex2line32">32</a>
    <a name="ex2line33" id="ex2line33">33</a>  $(FOO_DIR)/$(FOO_BINARY): $(FOO_DIR)/.configured
    <a name="ex2line34" id="ex2line34">34</a>          $(MAKE) CC=$(TARGET_CC) -C $(FOO_DIR)
    <a name="ex2line35" id="ex2line35">35</a>
    <a name="ex2line36" id="ex2line36">36</a>  $(TARGET_DIR)/$(FOO_TARGET_BINARY): $(FOO_DIR)/$(FOO_BINARY)
    <a name="ex2line37" id="ex2line37">37</a>          $(MAKE) DESTDIR=$(TARGET_DIR) -C $(FOO_DIR) install-strip
    <a name="ex2line38" id="ex2line38">38</a>          rm -Rf $(TARGET_DIR)/usr/man
    <a name="ex2line39" id="ex2line39">39</a>
    <a name="ex2line40" id="ex2line40">40</a>  foo: uclibc ncurses $(TARGET_DIR)/$(FOO_TARGET_BINARY)
    <a name="ex2line41" id="ex2line41">41</a>
    <a name="ex2line42" id="ex2line42">42</a>  foo-source: $(DL_DIR)/$(FOO_SOURCE)
    <a name="ex2line43" id="ex2line43">43</a>
    <a name="ex2line44" id="ex2line44">44</a>  foo-clean:
    <a name="ex2line45" id="ex2line45">45</a>          $(MAKE) prefix=$(TARGET_DIR)/usr -C $(FOO_DIR) uninstall
    <a name="ex2line46" id="ex2line46">46</a>          -$(MAKE) -C $(FOO_DIR) clean
    <a name="ex2line47" id="ex2line47">47</a>
    <a name="ex2line48" id="ex2line48">48</a>  foo-dirclean:
    <a name="ex2line49" id="ex2line49">49</a>          rm -rf $(FOO_DIR)
    <a name="ex2line50" id="ex2line50">50</a>
    <a name="ex2line51" id="ex2line51">51</a> #############################################################
    <a name="ex2line52" id="ex2line52">52</a> #
    <a name="ex2line53" id="ex2line53">53</a> # Toplevel Makefile options
    <a name="ex2line54" id="ex2line54">54</a> #
    <a name="ex2line55" id="ex2line55">55</a> #############################################################
    <a name="ex2line56" id="ex2line56">56</a> ifeq ($(BR2_PACKAGE_FOO),y)
    <a name="ex2line57" id="ex2line57">57</a> TARGETS+=foo
    <a name="ex2line58" id="ex2line58">58</a> endif

</pre>

    <p>First of all, this <i>Makefile</i> example works for a single
    binary software. For other software such as libraries or more
    complex stuff with multiple binaries, it should be adapted. Look at
    the other <code>*.mk</code> files in the <code>package</code>
    directory. </p>

    <p>At lines <a href="#ex2line6">6-11</a>, a couple of useful variables are
    defined :</p>

    <ul>

     <li><code>FOO_VERSION</code> : The version of <i>foo</i> that
     should be downloaded. </li>

     <li><code>FOO_SOURCE</code> : The name of the tarball of
     <i>foo</i> on the download website of FTP site. As you can see
     <code>FOO_VERSION</code> is used. </li>

     <li><code>FOO_SITE</code> : The HTTP or FTP site from which
     <i>foo</i> archive is downloaded. It must include the complete
     path to the directory where <code>FOO_SOURCE</code> can be
     found. </li>

     <li><code>FOO_DIR</code> : The directory into which the software
     will be configured and compiled. Basically, it's a subdirectory
     of <code>BUILD_DIR</code> which is created upon decompression of
     the tarball. </li>

     <li><code>FOO_BINARY</code> : Software binary name. As said
     previously, this is an example for a single binary software. </li>

     <li><code>FOO_TARGET_BINARY</code> : The full path of the binary
     inside the target filesystem. </li>

    </ul>

    <p>Lines <a href="#ex2line13">13-14</a> defines a target that downloads the
    tarball from the remote site to the download directory
    (<code>DL_DIR</code>). </p>

    <p>Lines <a href="#ex2line16">16-18</a> defines a target and associated rules
    that uncompress the downloaded tarball. As you can see, this target
    depends on the tarball file, so that the previous target (line
    <a href="#ex2line13">13-14</a>) is called before executing the rules of the
    current target. Uncompressing is followed by <i>touching</i> a hidden file
    to mark the software has having been uncompressed. This trick is
    used everywhere in Buildroot <i>Makefile</i> to split steps
    (download, uncompress, configure, compile, install) while still
    having correct dependencies. </p>

    <p>Lines <a href="#ex2line20">20-31</a> defines a target and associated rules
    that configures the software. It depends on the previous target (the
    hidden <code>.source</code> file) so that we are sure the software has
    been uncompressed. In order to configure it, it basically runs the
    well-known <code>./configure</code> script. As we may be doing
    cross-compilation, <code>target</code>, <code>host</code> and
    <code>build</code> arguments are given. The prefix is also set to
    <code>/usr</code>, not because the software will be installed in
    <code>/usr</code> on your host system, but in the target
    filesystem. Finally it creates a <code>.configured</code> file to
    mark the software as configured. </p>

    <p>Lines <a href="#ex2line33">33-34</a> defines a target and a rule that
    compiles the software. This target will create the binary file in the
    compilation directory, and depends on the software being already
    configured (hence the reference to the <code>.configured</code>
    file). It basically runs <code>make</code> inside the source
    directory. </p>

    <p>Lines <a href="#ex2line36">36-38</a> defines a target and associated rules
    that install the software inside the target filesystem. It depends on the
    binary file in the source directory, to make sure the software has
    been compiled. It uses the <code>install-strip</code> target of the
    software <code>Makefile</code> by passing a <code>DESTDIR</code>
    argument, so that the <code>Makefile</code> doesn't try to install
    the software inside host <code>/usr</code> but inside target
    <code>/usr</code>. After the installation, the
    <code>/usr/man</code> directory inside the target filesystem is
    removed to save space. </p>

    <p>Line <a href="#ex2line40">40</a> defines the main target of the software,
    the one that will be eventually be used by the top level
    <code>Makefile</code> to download, compile, and then install
    this package. This target should first of all depends on all
    needed dependecies of the software (in our example,
    <i>uclibc</i> and <i>ncurses</i>), and also depend on the
    final binary. This last dependency will call all previous
    dependencies in the correct order. </p>

    <p>Line <a href="#ex2line42">42</a> defines a simple target that only
    downloads the code source. This is not used during normal operation of
    Buildroot, but is needed if you intend to download all required sources at
    once for later offline build. Note that if you add a new package providing
    a <code>foo-source</code> target is <i>mandatory</i> to support
    users that wish to do offline-builds. Furthermore it eases checking
    if all package-sources are downloadable. </p>

    <p>Lines <a href="#ex2line44">44-46</a> define a simple target to clean the
    software build by calling the <i>Makefiles</i> with the appropriate option.
    The <code>-clean</code> target should run <code>make clean</code>
    on $(BUILD_DIR)/package-version and MUST uninstall all files of the
    package from $(STAGING_DIR) and from $(TARGET_DIR). </p>

    <p>Lines <a href="#ex2line48">48-49</a> define a simple target to completely
    remove the directory in which the software was uncompressed, configured and
    compiled. The <code>-dirclean</code> target MUST completely rm $(BUILD_DIR)/
    package-version. </p>

    <p>Lines <a href="#ex2line51">51-58</a> adds the target <code>foo</code> to
    the list of targets to be compiled by Buildroot by first checking if
    the configuration option for this package has been enabled
    using the configuration tool, and if so then &quot;subscribes&quot;
    this package to be compiled by adding it to the TARGETS
    global variable.  The name added to the TARGETS global
    variable is the name of this package's target, as defined on
    line <a href="#ex2line40">40</a>, which is used by Buildroot to download,
    compile, and then install this package. </p>


    <h3>Conclusion</h3>

    <p>As you can see, adding a software to buildroot is simply a
    matter of writing a <i>Makefile</i> using an already existing
    example and to modify it according to the compilation process of
    the software. </p>

    <p>If you package software that might be useful for other persons,
    don't forget to send a patch to Buildroot developers !</p>

     <h2><a name="links" id="links"></a>Resources</h2>

    <p>To learn more about Buildroot you can visit these
    websites:</p>

    <ul>
      <li><a href="http://www.uclibc.org/">http://www.uclibc.org/</a></li>
      <li><a href="http://www.busybox.net/">http://www.busybox.net/</a></li>
    </ul>
  </div>
<!--
       <a href="http://validator.w3.org/check?uri=referer"><img
       border="0" height="31" width="88"
       src="images/valid-html401.png"
       alt="Valid HTML"></img></a>
-->

</body>
</html>