-
Notifications
You must be signed in to change notification settings - Fork 1
/
MANUAL.html
1722 lines (1660 loc) · 54.4 KB
/
MANUAL.html
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
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta name="generator" content="AsciiDoc 8.5.2" />
<title>CCACHE(1)</title>
<style type="text/css">
/* Debug borders */
p, li, dt, dd, div, pre, h1, h2, h3, h4, h5, h6 {
/*
border: 1px solid red;
*/
}
body {
margin: 1em 5% 1em 5%;
}
a {
color: blue;
text-decoration: underline;
}
a:visited {
color: fuchsia;
}
em {
font-style: italic;
color: navy;
}
strong {
font-weight: bold;
color: #083194;
}
tt {
color: navy;
}
h1, h2, h3, h4, h5, h6 {
color: #527bbd;
font-family: sans-serif;
margin-top: 1.2em;
margin-bottom: 0.5em;
line-height: 1.3;
}
h1, h2, h3 {
border-bottom: 2px solid silver;
}
h2 {
padding-top: 0.5em;
}
h3 {
float: left;
}
h3 + * {
clear: left;
}
div.sectionbody {
font-family: serif;
margin-left: 0;
}
hr {
border: 1px solid silver;
}
p {
margin-top: 0.5em;
margin-bottom: 0.5em;
}
ul, ol, li > p {
margin-top: 0;
}
pre {
padding: 0;
margin: 0;
}
span#author {
color: #527bbd;
font-family: sans-serif;
font-weight: bold;
font-size: 1.1em;
}
span#email {
}
span#revnumber, span#revdate, span#revremark {
font-family: sans-serif;
}
div#footer {
font-family: sans-serif;
font-size: small;
border-top: 2px solid silver;
padding-top: 0.5em;
margin-top: 4.0em;
}
div#footer-text {
float: left;
padding-bottom: 0.5em;
}
div#footer-badges {
float: right;
padding-bottom: 0.5em;
}
div#preamble {
margin-top: 1.5em;
margin-bottom: 1.5em;
}
div.tableblock, div.imageblock, div.exampleblock, div.verseblock,
div.quoteblock, div.literalblock, div.listingblock, div.sidebarblock,
div.admonitionblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
div.admonitionblock {
margin-top: 2.0em;
margin-bottom: 2.0em;
margin-right: 10%;
color: #606060;
}
div.content { /* Block element content. */
padding: 0;
}
/* Block element titles. */
div.title, caption.title {
color: #527bbd;
font-family: sans-serif;
font-weight: bold;
text-align: left;
margin-top: 1.0em;
margin-bottom: 0.5em;
}
div.title + * {
margin-top: 0;
}
td div.title:first-child {
margin-top: 0.0em;
}
div.content div.title:first-child {
margin-top: 0.0em;
}
div.content + div.title {
margin-top: 0.0em;
}
div.sidebarblock > div.content {
background: #ffffee;
border: 1px solid silver;
padding: 0.5em;
}
div.listingblock > div.content {
border: 1px solid silver;
background: #f4f4f4;
padding: 0.5em;
}
div.quoteblock, div.verseblock {
padding-left: 1.0em;
margin-left: 1.0em;
margin-right: 10%;
border-left: 5px solid #dddddd;
color: #777777;
}
div.quoteblock > div.attribution {
padding-top: 0.5em;
text-align: right;
}
div.verseblock > div.content {
white-space: pre;
}
div.verseblock > div.attribution {
padding-top: 0.75em;
text-align: left;
}
/* DEPRECATED: Pre version 8.2.7 verse style literal block. */
div.verseblock + div.attribution {
text-align: left;
}
div.admonitionblock .icon {
vertical-align: top;
font-size: 1.1em;
font-weight: bold;
text-decoration: underline;
color: #527bbd;
padding-right: 0.5em;
}
div.admonitionblock td.content {
padding-left: 0.5em;
border-left: 3px solid #dddddd;
}
div.exampleblock > div.content {
border-left: 3px solid #dddddd;
padding-left: 0.5em;
}
div.imageblock div.content { padding-left: 0; }
span.image img { border-style: none; }
a.image:visited { color: white; }
dl {
margin-top: 0.8em;
margin-bottom: 0.8em;
}
dt {
margin-top: 0.5em;
margin-bottom: 0;
font-style: normal;
color: navy;
}
dd > *:first-child {
margin-top: 0.1em;
}
ul, ol {
list-style-position: outside;
}
ol.arabic {
list-style-type: decimal;
}
ol.loweralpha {
list-style-type: lower-alpha;
}
ol.upperalpha {
list-style-type: upper-alpha;
}
ol.lowerroman {
list-style-type: lower-roman;
}
ol.upperroman {
list-style-type: upper-roman;
}
div.compact ul, div.compact ol,
div.compact p, div.compact p,
div.compact div, div.compact div {
margin-top: 0.1em;
margin-bottom: 0.1em;
}
div.tableblock > table {
border: 3px solid #527bbd;
}
thead, p.table.header {
font-family: sans-serif;
font-weight: bold;
}
tfoot {
font-weight: bold;
}
td > div.verse {
white-space: pre;
}
p.table {
margin-top: 0;
}
/* Because the table frame attribute is overriden by CSS in most browsers. */
div.tableblock > table[frame="void"] {
border-style: none;
}
div.tableblock > table[frame="hsides"] {
border-left-style: none;
border-right-style: none;
}
div.tableblock > table[frame="vsides"] {
border-top-style: none;
border-bottom-style: none;
}
div.hdlist {
margin-top: 0.8em;
margin-bottom: 0.8em;
}
div.hdlist tr {
padding-bottom: 15px;
}
dt.hdlist1.strong, td.hdlist1.strong {
font-weight: bold;
}
td.hdlist1 {
vertical-align: top;
font-style: normal;
padding-right: 0.8em;
color: navy;
}
td.hdlist2 {
vertical-align: top;
}
div.hdlist.compact tr {
margin: 0;
padding-bottom: 0;
}
.comment {
background: yellow;
}
.footnote, .footnoteref {
font-size: 0.8em;
}
span.footnote, span.footnoteref {
vertical-align: super;
}
#footnotes {
margin: 20px 0 20px 0;
padding: 7px 0 0 0;
}
#footnotes div.footnote {
margin: 0 0 5px 0;
}
#footnotes hr {
border: none;
border-top: 1px solid silver;
height: 1px;
text-align: left;
margin-left: 0;
width: 20%;
min-width: 100px;
}
@media print {
div#footer-badges { display: none; }
}
div#toc {
margin-bottom: 2.5em;
}
div#toctitle {
color: #527bbd;
font-family: sans-serif;
font-size: 1.1em;
font-weight: bold;
margin-top: 1.0em;
margin-bottom: 0.1em;
}
div.toclevel1, div.toclevel2, div.toclevel3, div.toclevel4 {
margin-top: 0;
margin-bottom: 0;
}
div.toclevel2 {
margin-left: 2em;
font-size: 0.9em;
}
div.toclevel3 {
margin-left: 4em;
font-size: 0.9em;
}
div.toclevel4 {
margin-left: 6em;
font-size: 0.9em;
}
/* Workarounds for IE6's broken and incomplete CSS2. */
div.sidebar-content {
background: #ffffee;
border: 1px solid silver;
padding: 0.5em;
}
div.sidebar-title, div.image-title {
color: #527bbd;
font-family: sans-serif;
font-weight: bold;
margin-top: 0.0em;
margin-bottom: 0.5em;
}
div.listingblock div.content {
border: 1px solid silver;
background: #f4f4f4;
padding: 0.5em;
}
div.quoteblock-attribution {
padding-top: 0.5em;
text-align: right;
}
div.verseblock-content {
white-space: pre;
}
div.verseblock-attribution {
padding-top: 0.75em;
text-align: left;
}
div.exampleblock-content {
border-left: 3px solid #dddddd;
padding-left: 0.5em;
}
/* IE6 sets dynamically generated links as visited. */
div#toc a:visited { color: blue; }
</style>
<script type="text/javascript">
/*<+'])');
// Function that scans the DOM tree for header elements (the DOM2
// nodeIterator API would be a better technique but not supported by all
// browsers).
var iterate = function (el) {
for (var i = el.firstChild; i != null; i = i.nextSibling) {
if (i.nodeType == 1 /* Node.ELEMENT_NODE */) {
var mo = re.exec(i.tagName);
if (mo && (i.getAttribute("class") || i.getAttribute("className")) != "float") {
result[result.length] = new TocEntry(i, getText(i), mo[1]-1);
}
iterate(i);
}
}
}
iterate(el);
return result;
}
var toc = document.getElementById("toc");
var entries = tocEntries(document.getElementById("content"), toclevels);
for (var i = 0; i < entries.length; ++i) {
var entry = entries[i];
if (entry.element.id == "")
entry.element.id = "_toc_" + i;
var a = document.createElement("a");
a.href = "#" + entry.element.id;
a.appendChild(document.createTextNode(entry.text));
var div = document.createElement("div");
div.appendChild(a);
div.className = "toclevel" + entry.toclevel;
toc.appendChild(div);
}
if (entries.length == 0)
toc.parentNode.removeChild(toc);
},
/////////////////////////////////////////////////////////////////////
// Footnotes generator
/////////////////////////////////////////////////////////////////////
/* Based on footnote generation code from:
* http://www.brandspankingnew.net/archive/2005/07/format_footnote.html
*/
footnotes: function () {
var cont = document.getElementById("content");
var noteholder = document.getElementById("footnotes");
var spans = cont.getElementsByTagName("span");
var refs = {};
var n = 0;
for (i=0; i<spans.length; i++) {
if (spans[i].className == "footnote") {
n++;
// Use [\s\S] in place of . so multi-line matches work.
// Because JavaScript has no s (dotall) regex flag.
note = spans[i].innerHTML.match(/\s*\[([\s\S]*)]\s*/)[1];
noteholder.innerHTML +=
"<div class='footnote' id='_footnote_" + n + "'>" +
"<a href='#_footnoteref_" + n + "' title='Return to text'>" +
n + "</a>. " + note + "</div>";
spans[i].innerHTML =
"[<a id='_footnoteref_" + n + "' href='#_footnote_" + n +
"' title='View footnote' class='footnote'>" + n + "</a>]";
var id =spans[i].getAttribute("id");
if (id != null) refs["#"+id] = n;
}
}
if (n == 0)
noteholder.parentNode.removeChild(noteholder);
else {
// Process footnoterefs.
for (i=0; i<spans.length; i++) {
if (spans[i].className == "footnoteref") {
var href = spans[i].getElementsByTagName("a")[0].getAttribute("href");
href = href.match(/#.*/)[0]; // Because IE return full URL.
n = refs[href];
spans[i].innerHTML =
"[<a href='#_footnote_" + n +
"' title='View footnote' class='footnote'>" + n + "</a>]";
}
}
}
}
}
/*]]>*/
</script>
</head>
<body>
<div id="header">
<h1>CCACHE(1)</h1>
<span id="revnumber">version 3.1</span>
<div id="toc">
<div id="toctitle">Table of Contents</div>
<noscript><p><b>JavaScript must be enabled in your browser to display the table of contents.</b></p></noscript>
</div>
</div>
<div id="content">
<h2 id="_name">Name</h2>
<div class="sectionbody">
<div class="paragraph"><p>ccache - a fast C/C++ compiler cache</p></div>
</div>
<h2 id="_synopsis">Synopsis</h2>
<div class="sectionbody">
<div class="verseblock">
<div class="verseblock-content"><strong>ccache</strong> [<em>options</em>]
<strong>ccache</strong> <em>compiler</em> [<em>compiler options</em>]
<em>compiler</em> [<em>compiler options</em>] (via symbolic link)</div>
<div class="verseblock-attribution">
</div></div>
</div>
<h2 id="_description">Description</h2>
<div class="sectionbody">
<div class="paragraph"><p>ccache is a compiler cache. It speeds up recompilation by caching the result of
previous compilations and detecting when the same compilation is being done
again. Supported languages are C, C++, Objective-C and Objective-C++.</p></div>
<div class="paragraph"><p>ccache has been carefully written to always produce exactly the same compiler
output that you would get without the cache. The only way you should be able to
tell that you are using ccache is the speed. Currently known exceptions to this
goal are listed under <a href="#_bugs">BUGS</a>. If you ever discover an undocumented case
where ccache changes the output of your compiler, please let us know.</p></div>
<h3 id="_features">Features</h3><div style="clear:left"></div>
<div class="ulist"><ul>
<li>
<p>
Keeps statistics on hits/misses.
</p>
</li>
<li>
<p>
Automatic cache size management.
</p>
</li>
<li>
<p>
Can cache compilations that generate warnings.
</p>
</li>
<li>
<p>
Easy installation.
</p>
</li>
<li>
<p>
Low overhead.
</p>
</li>
<li>
<p>
Optionally uses hard links where possible to avoid copies.
</p>
</li>
<li>
<p>
Optionally compresses files in the cache to reduce disk space.
</p>
</li>
</ul></div>
<h3 id="_limitations">Limitations</h3><div style="clear:left"></div>
<div class="ulist"><ul>
<li>
<p>
Only knows how to cache the compilation of a single
C/C++/Objective-C/Objective-C++ file. Other types of compilations
(multi-file compilation, linking, etc) will silently fall back to running the
real compiler.
</p>
</li>
<li>
<p>
Only works with GCC and compilers that behave similar enough.
</p>
</li>
<li>
<p>
Some compiler flags are not supported. If such a flag is detected, ccache
will silently fall back to running the real compiler.
</p>
</li>
</ul></div>
</div>
<h2 id="_run_modes">Run modes</h2>
<div class="sectionbody">
<div class="paragraph"><p>There are two ways to use ccache. You can either prefix your compilation
commands with <strong>ccache</strong> or you can let ccache masquerade as the compiler by
creating a symbolic link (named as the compiler) to ccache. The first method is
most convenient if you just want to try out ccache or wish to use it for some
specific projects. The second method is most useful for when you wish to use
ccache for all your compilations.</p></div>
<div class="paragraph"><p>To use the first method, just make sure that <strong>ccache</strong> is in your <strong>PATH</strong>.</p></div>
<div class="paragraph"><p>To use the symlinks method, do something like this:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>cp ccache /usr/local/bin/
ln -s ccache /usr/local/bin/gcc
ln -s ccache /usr/local/bin/g++
ln -s ccache /usr/local/bin/cc
ln -s ccache /usr/local/bin/c++</tt></pre>
</div></div>
<div class="paragraph"><p>And so forth. This will work as long as the directory with symlinks comes
before the path to the compiler (which is usually in <tt>/usr/bin</tt>). After
installing you may wish to run “which gcc” to make sure that the correct link
is being used.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Warning</div>
</td>
<td class="content">The technique of letting ccache masquerade as the compiler works well,
but currently doesn’t interact well with other tools that do the same thing.
See <a href="#_using_ccache_with_other_compiler_wrappers">USING CCACHE WITH OTHER COMPILER WRAPPERS</a>.</td>
</tr></table>
</div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Warning</div>
</td>
<td class="content">Do not use a hard link, use a symbolic link. A hard link will cause
“interesting” problems.</td>
</tr></table>
</div>
</div>
<h2 id="_options">Options</h2>
<div class="sectionbody">
<div class="paragraph"><p>These options only apply when you invoke ccache as “ccache”. When invoked as
a compiler (via a symlink as described in the previous section), the normal
compiler options apply and you should refer to the compiler’s documentation.</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
<strong>-c, --cleanup</strong>
</dt>
<dd>
<p>
Clean up the cache by removing old cached files until the specified file
number and cache size limits are not exceeded. This also recalculates the
cache file count and size totals. Normally, it’s not needed to initiate
cleanup manually as ccache keeps the cache below the specified limits at
runtime and keeps statistics up to date on each compilation. Forcing a
cleanup is mostly useful if you manually modify the cache contents or
believe that the cache size statistics may be inaccurate.
</p>
</dd>
<dt class="hdlist1">
<strong>-C, --clear</strong>
</dt>
<dd>
<p>
Clear the entire cache, removing all cached files.
</p>
</dd>
<dt class="hdlist1">
<strong>-F, --max-files</strong>=<em>N</em>
</dt>
<dd>
<p>
Set the maximum number of files allowed in the cache. The value is stored
inside the cache directory and applies to all future compilations. Due to
the way the value is stored the actual value used is always rounded down to
the nearest multiple of 16.
</p>
</dd>
<dt class="hdlist1">
<strong>-h, --help</strong>
</dt>
<dd>
<p>
Print an options summary page.
</p>
</dd>
<dt class="hdlist1">
<strong>-M, --max-size</strong>=<em>SIZE</em>
</dt>
<dd>
<p>
Set the maximum size of the files stored in the cache. You can specify a
value in gigabytes, megabytes or kilobytes by appending a G, M or K to the
value. The default is gigabytes. The actual value stored is rounded down to
the nearest multiple of 16 kilobytes.
</p>
</dd>
<dt class="hdlist1">
<strong>-s, --show-stats</strong>
</dt>
<dd>
<p>
Print the current statistics summary for the cache.
</p>
</dd>
<dt class="hdlist1">
<strong>-V, --version</strong>
</dt>
<dd>
<p>
Print version and copyright information.
</p>
</dd>
<dt class="hdlist1">
<strong>-z, --zero-stats</strong>
</dt>
<dd>
<p>
Zero the cache statistics (but not the configured limits).
</p>
</dd>
</dl></div>
</div>
<h2 id="_extra_options">Extra options</h2>
<div class="sectionbody">
<div class="paragraph"><p>When run as a compiler, ccache usually just takes the same command line options
as the compiler you are using. The only exception to this is the option
<strong>--ccache-skip</strong>. That option can be used to tell ccache to avoid interpreting
the next option in any way and to pass it along to the compiler as-is.</p></div>
<div class="paragraph"><p>The reason this can be important is that ccache does need to parse the command
line and determine what is an input filename and what is a compiler option, as
it needs the input filename to determine the name of the resulting object file
(among other things). The heuristic ccache uses when parsing the command line
is that any argument that exists as a file is treated as an input file name. By
using <strong>--ccache-skip</strong> you can force an option to not be treated as an input
file name and instead be passed along to the compiler as a command line option.</p></div>
<div class="paragraph"><p>Another case where <strong>--ccache-skip</strong> can be useful is if ccache interprets an
option specially but shouldn’t, since the option has another meaning for your
compiler than what ccache thinks.</p></div>
</div>
<h2 id="_environment_variables">Environment variables</h2>
<div class="sectionbody">
<div class="paragraph"><p>ccache uses a number of environment variables to control operation. In most
cases you won’t need any of these as the defaults will be fine.</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
<strong>CCACHE_BASEDIR</strong>
</dt>
<dd>
<p>
If you set the environment variable <strong>CCACHE_BASEDIR</strong> to an absolute path to
a directory, ccache rewrites absolute paths into relative paths before
computing the hash that identifies the compilation, but only for paths
under the specified directory. See the discussion under
<a href="#_compiling_in_different_directories">COMPILING IN DIFFERENT DIRECTORIES</a>.
</p>
</dd>
<dt class="hdlist1">
<strong>CCACHE_CC</strong>
</dt>
<dd>
<p>
You can optionally set <strong>CCACHE_CC</strong> to force the name of the compiler to
use. If you don’t do this then ccache works it out from the command line.
</p>
</dd>
<dt class="hdlist1">
<strong>CCACHE_COMPRESS</strong>
</dt>
<dd>
<p>
If you set the environment variable <strong>CCACHE_COMPRESS</strong> then ccache will
compress object files and other compiler output it puts in the cache.
However, this setting has no effect on how files are retrieved from the
cache; compressed and uncompressed results will still be usable regardless
of this setting.
</p>
</dd>
<dt class="hdlist1">
<strong>CCACHE_COMPILERCHECK</strong>
</dt>
<dd>
<p>
By default, ccache includes the modification time (“mtime”) and size of
the compiler in the hash to ensure that results retrieved from the cache
are accurate. The <strong>CCACHE_COMPILERCHECK</strong> environment variable can be used
to select another strategy. Possible values are:
</p>
<div class="dlist"><dl>
<dt class="hdlist1">
<strong>content</strong>
</dt>
<dd>
<p>
Hash the content of the compiler binary. This makes ccache very slightly
slower compared to the <strong>mtime</strong> setting, but makes it cope better with
compiler upgrades during a build bootstrapping process.
</p>
</dd>
<dt class="hdlist1">
<strong>mtime</strong>
</dt>
<dd>
<p>
Hash the compiler’s mtime and size, which is fast. This is the default.
</p>
</dd>
<dt class="hdlist1">
<strong>none</strong>
</dt>
<dd>
<p>
Don’t hash anything. This may be good for situations where you can safely
use the cached results even though the compiler’s mtime or size has changed
(e.g. if the compiler is built as part of your build system and the
compiler’s source has not changed, or if the compiler only has changes that
don’t affect code generation). You should only use the <strong>none</strong> setting if
you know what you are doing.
</p>
</dd>
<dt class="hdlist1">
<em>a command string</em>
</dt>
<dd>
<p>
Hash the standard output and standard error output of the specified
command. The string will be split on whitespace to find out the command and
arguments to run. No other interpretation of the command string will be
done, except that the special word “%compiler%” will be replaced with the
path to the compiler. Several commands can be specified with semicolon as
separator. Examples:
</p>
<div class="ulist"><ul>
<li>
<p>
<tt>%compiler% -v</tt>
</p>
</li>
<li>
<p>
<tt>%compiler% -dumpmachine; %compiler% -dumpversion</tt>
</p>
</li>
</ul></div>
<div class="paragraph"><p>You should make sure that the specified command is as fast as possible since it
will be run once for each ccache invocation.</p></div>
<div class="paragraph"><p>Identifying the compiler using a command is useful if you want to avoid cache
misses when the compiler has been rebuilt but not changed.</p></div>
<div class="paragraph"><p>Another case is when the compiler (as seen by ccache) actually isn’t the real
compiler but another compiler wrapper — in that case, the default <strong>mtime</strong>
method will hash the mtime and size of the other compiler wrapper, which means
that ccache won’t be able to detect a compiler upgrade. Using a suitable
command to identify the compiler is thus safer, but it’s also slower, so you
should consider continue using the <strong>mtime</strong> method in combination with
<strong>CCACHE_PREFIX</strong> if possible. See
<a href="#_using_ccache_with_other_compiler_wrappers">USING CCACHE WITH OTHER COMPILER WRAPPERS</a>.</p></div>
</dd>
</dl></div>
</dd>
<dt class="hdlist1">
<strong>CCACHE_CPP2</strong>
</dt>
<dd>
<p>
If you set the environment variable <strong>CCACHE_CPP2</strong> then ccache will not use
the optimisation of avoiding the second call to the preprocessor by
compiling the preprocessed output that was used for finding the hash in the
case of a cache miss. This is primarily a debugging option, although it is
possible that some unusual compilers will have problems with the
intermediate filename extensions used in this optimisation, in which case
this option could allow ccache to be used anyway.
</p>
</dd>
<dt class="hdlist1">
<strong>CCACHE_DETECT_SHEBANG</strong>
</dt>
<dd>
<p>
The <strong>CCACHE_DETECT_SHEBANG</strong> environment variable only has meaning on
Windows. It instructs ccache to open the executable file to detect the
<strong>#!/bin/sh</strong> string, in which case ccache will search for <strong>sh.exe</strong> in
<strong>PATH</strong> and use that to launch the executable.
</p>
</dd>
<dt class="hdlist1">
<strong>CCACHE_DIR</strong>
</dt>
<dd>
<p>
The <strong>CCACHE_DIR</strong> environment variable specifies where ccache will keep its
cached compiler output. The default is <strong>$HOME/.ccache</strong>.
</p>
</dd>
<dt class="hdlist1">
<strong>CCACHE_DISABLE</strong>
</dt>
<dd>
<p>
If you set the environment variable <strong>CCACHE_DISABLE</strong> then ccache will just
call the real compiler, bypassing the cache completely.
</p>
</dd>
<dt class="hdlist1">
<strong>CCACHE_EXTENSION</strong>
</dt>
<dd>
<p>
ccache tries to automatically determine the extension to use for
intermediate preprocessor files based on the type of file being compiled.
Unfortunately this sometimes doesn’t work, for example when using the
“aCC” compiler on HP-UX. On systems like this you can use the
<strong>CCACHE_EXTENSION</strong> option to override the default. On HP-UX set this
environment variable to <strong>i</strong> if you use the “aCC” compiler.
</p>
</dd>
<dt class="hdlist1">
<strong>CCACHE_EXTRAFILES</strong>
</dt>
<dd>
<p>
If you set the environment variable <strong>CCACHE_EXTRAFILES</strong> to a list of paths
then ccache will include the contents of those files when calculating the
hash sum. The list separator is semicolon in Windows systems and colon on
other systems.
</p>
</dd>
<dt class="hdlist1">
<strong>CCACHE_HARDLINK</strong>
</dt>
<dd>
<p>
If you set the environment variable <strong>CCACHE_HARDLINK</strong> then ccache will
attempt to use hard links from the cache directory when creating the
compiler output rather than using a file copy. Using hard links may be
slightly faster in some situations, but can confuse programs like “make”
that rely on modification times. Another thing to keep in mind is that if
the resulting object file is modified in any way, this corrupts the cached
object file as well. Hard links are never made for compressed cache files.
This means that you should not set the <strong>CCACHE_COMPRESS</strong> variable if you
want to use hard links.
</p>
</dd>
<dt class="hdlist1">
<strong>CCACHE_HASHDIR</strong>
</dt>
<dd>
<p>
This tells ccache to hash the current working directory when calculating
the hash that is used to distinguish two compilations. This prevents a
problem with the storage of the current working directory in the debug info
of a object file, which can lead ccache to give a cached object file that
has the working directory in the debug info set incorrectly. This option is