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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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<HTML
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><HEAD
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><TITLE
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>Building eCos</TITLE
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><meta name="MSSmartTagsPreventParsing" content="TRUE">
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<META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
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"><LINK
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REL="HOME"
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TITLE="The eCos Component Writer's Guide"
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HREF="cdl-guide.html"><LINK
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REL="UP"
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TITLE="The Build Process"
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HREF="build.html"><LINK
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REL="PREVIOUS"
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TITLE="Configuration Header File Generation"
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HREF="build.headers.html"><LINK
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REL="NEXT"
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TITLE="Building Test Cases"
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HREF="build.tests.html"></HEAD
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><BODY
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CLASS="SECT1"
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#840084"
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ALINK="#0000FF"
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><DIV
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CLASS="NAVHEADER"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>The <SPAN
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CLASS="APPLICATION"
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>eCos</SPAN
52 
> Component Writer's Guide</TH
53 
></TR
54 
><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="build.headers.html"
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ACCESSKEY="P"
62 
>Prev</A
63 
></TD
64 
><TD
65 
WIDTH="80%"
66 
ALIGN="center"
67 
VALIGN="bottom"
68 
>Chapter 4. The Build Process</TD
69 
><TD
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WIDTH="10%"
71 
ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="build.tests.html"
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ACCESSKEY="N"
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>Next</A
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></TD
78 
></TR
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></TABLE
80 
><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
83 
><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
88 
NAME="BUILD.MAKE">Building eCos</H1
89 
><P
90 
>The primary goal of an eCos build is to produce the library
91 
<TT
92 
CLASS="FILENAME"
93 
>libtarget.a</TT
94 
>. A typical <SPAN
95 
CLASS="APPLICATION"
96 
>eCos</SPAN
97 
> build will also
98 
generate a number of other targets: <TT
99 
CLASS="FILENAME"
100 
>extras.o</TT
101 
>,
102 
startup code <TT
103 
CLASS="FILENAME"
104 
>vectors.o</TT
105 
>, and a linker script. Some
106 
packages may cause additional libraries or targets to be generated.
107 
The basic build process involves a number of different phases with
108 
corresponding priorities. There are a number of predefined priorities:</P
109 
><DIV
110 
CLASS="INFORMALTABLE"
111 
><A
112 
NAME="AEN2457"><P
113 
></P
114 
><TABLE
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BORDER="1"
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CLASS="CALSTABLE"
117 
><THEAD
118 
><TR
119 
><TH
120 
WIDTH="50%"
121 
ALIGN="RIGHT"
122 
VALIGN="TOP"
123 
>Priority</TH
124 
><TH
125 
WIDTH="50%"
126 
ALIGN="LEFT"
127 
VALIGN="TOP"
128 
>Action</TH
129 
></TR
130 
></THEAD
131 
><TBODY
132 
><TR
133 
><TD
134 
WIDTH="50%"
135 
ALIGN="RIGHT"
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VALIGN="TOP"
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>0</TD
138 
><TD
139 
WIDTH="50%"
140 
ALIGN="LEFT"
141 
VALIGN="TOP"
142 
>Export header files</TD
143 
></TR
144 
><TR
145 
><TD
146 
WIDTH="50%"
147 
ALIGN="RIGHT"
148 
VALIGN="TOP"
149 
>100</TD
150 
><TD
151 
WIDTH="50%"
152 
ALIGN="LEFT"
153 
VALIGN="TOP"
154 
>Process <SPAN
155 
CLASS="PROPERTY"
156 
>compile</SPAN
157 
> properties</TD
158 
></TR
159 
><TR
160 
><TD
161 
WIDTH="50%"
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ALIGN="RIGHT"
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VALIGN="TOP"
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>&nbsp;</TD
165 
><TD
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WIDTH="50%"
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ALIGN="LEFT"
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VALIGN="TOP"
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>and most <SPAN
170 
CLASS="PROPERTY"
171 
>make_object</SPAN
172 
> custom build steps</TD
173 
></TR
174 
><TR
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><TD
176 
WIDTH="50%"
177 
ALIGN="RIGHT"
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VALIGN="TOP"
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>200</TD
180 
><TD
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WIDTH="50%"
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ALIGN="LEFT"
183 
VALIGN="TOP"
184 
>Generate libraries</TD
185 
></TR
186 
><TR
187 
><TD
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WIDTH="50%"
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ALIGN="RIGHT"
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VALIGN="TOP"
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>300</TD
192 
><TD
193 
WIDTH="50%"
194 
ALIGN="LEFT"
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VALIGN="TOP"
196 
>Process <SPAN
197 
CLASS="PROPERTY"
198 
>make</SPAN
199 
> custom build steps</TD
200 
></TR
201 
></TBODY
202 
></TABLE
203 
><P
204 
></P
205 
></DIV
206 
><P
207 
>Generation of the <TT
208 
CLASS="FILENAME"
209 
>extras.o</TT
210 
> file, the startup code
211 
and the linker script actually happens via <SPAN
212 
CLASS="PROPERTY"
213 
>make</SPAN
214 
> custom build steps,
215 
typically defined in appropriate HAL packages. The component framework
216 
has no special knowledge of these targets.</P
217 
><P
218 
>By default custom build steps for a <SPAN
219 
CLASS="PROPERTY"
220 
>make_object</SPAN
221 
> property happen
222 
during the same phase as most compilations, but this can be changed
223 
using a <TT
224 
CLASS="LITERAL"
225 
>-priority</TT
226 
> option. Similarly custom build
227 
steps for a <SPAN
228 
CLASS="PROPERTY"
229 
>make</SPAN
230 
> property happen at the end of a build, but this can
231 
also be changed with a <TT
232 
CLASS="LITERAL"
233 
>-priority</TT
234 
> option. For
235 
example a priority of 50 can be used to run a custom build step
236 
between the header file export phase and the main compilation phase.
237 
Custom build steps are discussed in more detail below.</P
238 
><P
239 
>Some build systems may run several commands of the same priority in
240 
parallel. For example files listed in <SPAN
241 
CLASS="PROPERTY"
242 
>compile</SPAN
243 
> properties may get
244 
compiled in parallel, concurrently with <SPAN
245 
CLASS="PROPERTY"
246 
>make_object</SPAN
247 
> custom build
248 
steps with default priorities. Since most of the time for an <SPAN
249 
CLASS="APPLICATION"
250 
>eCos</SPAN
251 
>
252 
build involves processing <SPAN
253 
CLASS="PROPERTY"
254 
>compile</SPAN
255 
> properties, this allows builds to
256 
be speeded up on suitable host hardware. All build steps for a given
257 
phase will complete before the next phase is started.</P
258 
><DIV
259 
CLASS="SECT2"
260 
><H2
261 
CLASS="SECT2"
262 
><A
263 
NAME="BUILD.MAKE.UPDATE">Updating the Build Tree</H2
264 
><P
265 
>Some build systems may involve a phase before the header files get
266 
exported, to update the build and install trees automatically when
267 
there has been a change to the configuration savefile
268 
<TT
269 
CLASS="FILENAME"
270 
>ecos.ecc</TT
271 
>. This is useful mainly for application
272 
developers using the command line tools: it would allow users to
273 
create the build tree only once, and after any subsequent
274 
configuration changes the tree would be updated automatically by the
275 
build system. The facility would be analogous to the
276 
<TT
277 
CLASS="LITERAL"
278 
>--enable-maintainer-mode</TT
279 
> option provide by the
280 
<SPAN
281 
CLASS="APPLICATION"
282 
>autoconf</SPAN
283 
> and <SPAN
284 
CLASS="APPLICATION"
285 
>automake</SPAN
286 
> programs. At present no <SPAN
287 
CLASS="APPLICATION"
288 
>eCos</SPAN
289 
>
290 
build system implements this functionality, but it is likely to be
291 
added in a future release.</P
292 
></DIV
293 
><DIV
294 
CLASS="SECT2"
295 
><H2
296 
CLASS="SECT2"
297 
><A
298 
NAME="BUILD.MAKE.EXPORT">Exporting Public Header Files</H2
299 
><P
300 
>The first compulsory phase involves making sure that there is an up to
301 
date set of header files in the install tree. Each package can contain
302 
some number of header files defining the exported interface.
303 
Applications should only use exported functionality. A package can
304 
also contain some number of private header files which are only of
305 
interest to the implementation, and which should not be visible to
306 
application code. The various packages that go into a particular
307 
configuration can be spread all over the component repository. In
308 
theory it might be possible to make all the exported header files
309 
accessible by having a lengthy <TT
310 
CLASS="LITERAL"
311 
>-I</TT
312 
> header file
313 
search path, but this would be inconvenient both for building eCos and
314 
for building applications. Instead all the relevant header files are
315 
copied to a single location, the <TT
316 
CLASS="FILENAME"
317 
>include</TT
318 
> subdirectory of the install tree.
319 
The process involves the following:</P
320 
><P
321 
></P
322 
><OL
323 
TYPE="1"
324 
><LI
325 
><P
326 
>The install tree, for example <TT
327 
CLASS="FILENAME"
328 
>/usr/local/ecos/install</TT
329 
>, and its <TT
330 
CLASS="FILENAME"
331 
>include</TT
332 
> subdirectory <TT
333 
CLASS="FILENAME"
334 
>/usr/local/ecos/install/include</TT
335 
> will typically be
336 
created when the build tree is generated or updated. At the same time
337 
configuration header files will be written to the <TT
338 
CLASS="FILENAME"
339 
>pkgconf</TT
340 
> subdirectory, for example
341 
<TT
342 
CLASS="FILENAME"
343 
>/usr/local/ecos/include/pkgconf</TT
344 
>, so that
345 
the configuration data is visible to all the packages and to
346 
application code that may wish to examine some of the configuration
347 
options.</P
348 
></LI
349 
><LI
350 
><P
351 
>Each package in the configuration is examined for exported header
352 
files. The exact order in which the packages are processed is not
353 
defined, but should not matter.</P
354 
><P
355 
></P
356 
><OL
357 
TYPE="a"
358 
><LI
359 
><P
360 
>If the package has an <A
361 
HREF="ref.include-files.html"
362 
><SPAN
363 
CLASS="PROPERTY"
364 
>include_files</SPAN
365 
></A
366 
> property then this
367 
lists all the exported header files:</P
368 
><TABLE
369 
BORDER="5"
370 
BGCOLOR="#E0E0F0"
371 
WIDTH="70%"
372 
><TR
373 
><TD
374 
><PRE
375 
CLASS="PROGRAMLISTING"
376 
>cdl_package &lt;some_package&gt; {
377 
    &#8230;
378 
    include_files header1.h header2.h
379 
}    </PRE
380 
></TD
381 
></TR
382 
></TABLE
383 
><P
384 
>If no arguments are given then the package does not export any header
385 
files.</P
386 
><TABLE
387 
BORDER="5"
388 
BGCOLOR="#E0E0F0"
389 
WIDTH="70%"
390 
><TR
391 
><TD
392 
><PRE
393 
CLASS="PROGRAMLISTING"
394 
>cdl_package &lt;some_package&gt; {
395 
    &#8230;
396 
    include_files
397 
}    </PRE
398 
></TD
399 
></TR
400 
></TABLE
401 
><P
402 
>The listed files may be in an <TT
403 
CLASS="FILENAME"
404 
>include</TT
405 
> subdirectory within the package's
406 
hierarchy, or they may be relative to the package's toplevel
407 
directory. The <SPAN
408 
CLASS="PROPERTY"
409 
>include_files</SPAN
410 
> property is intended mainly for very
411 
simple packages. It can also be useful when converting existing code
412 
to an <SPAN
413 
CLASS="APPLICATION"
414 
>eCos</SPAN
415 
> package, to avoid rearranging the sources.</P
416 
></LI
417 
><LI
418 
><P
419 
>If there is no <SPAN
420 
CLASS="PROPERTY"
421 
>include_files</SPAN
422 
> property then the component framework
423 
will look for an <TT
424 
CLASS="FILENAME"
425 
>include</TT
426 
>
427 
subdirectory in the package, as per the layout conventions. All files,
428 
including those in subdirectories, will be treated as exported header
429 
files. For example, the math library package contains files <TT
430 
CLASS="FILENAME"
431 
>include/math.h</TT
432 
> and <TT
433 
CLASS="FILENAME"
434 
>include/sys/ieeefp.h</TT
435 
>, both of which will
436 
be exported to the install tree.</P
437 
></LI
438 
><LI
439 
><P
440 
>As a last resort, if there is neither an <SPAN
441 
CLASS="PROPERTY"
442 
>include_files</SPAN
443 
> property nor
444 
an <TT
445 
CLASS="FILENAME"
446 
>include</TT
447 
> subdirectory, the
448 
component framework will search the package's toplevel directory and
449 
all of its subdirectories for files with one of the following
450 
suffixes: <TT
451 
CLASS="LITERAL"
452 
>.h</TT
453 
>, <TT
454 
CLASS="LITERAL"
455 
>.hxx</TT
456 
>,
457 
<TT
458 
CLASS="LITERAL"
459 
>.inl</TT
460 
> or <TT
461 
CLASS="LITERAL"
462 
>.inc</TT
463 
>. All such files
464 
will be interpreted as exported header files.</P
465 
><P
466 
>This last resort rule could cause confusion for packages which have no
467 
exported header files but which do contain one or more private header
468 
files. For example a typical device driver simply implements an
469 
existing interface rather than define a new one, so it does not need
470 
to export a header file. However it may still have one or more private
471 
header files. Such packages should use an <SPAN
472 
CLASS="PROPERTY"
473 
>include_files</SPAN
474 
> property
475 
with no arguments.</P
476 
></LI
477 
></OL
478 
></LI
479 
><LI
480 
><P
481 
>If the package has one or more exported header files, the next step is
482 
to determine where the files should end up. By default all exported
483 
header files will just end up relative to the install tree's <TT
484 
CLASS="FILENAME"
485 
>include</TT
486 
> subdirectory. For example the
487 
math library's <TT
488 
CLASS="FILENAME"
489 
>math.h</TT
490 
> header
491 
would end up as <TT
492 
CLASS="FILENAME"
493 
>/usr/local/ecos/include/math.h</TT
494 
>,
495 
and the <TT
496 
CLASS="FILENAME"
497 
>sys/ieeefp.h</TT
498 
> header
499 
would end up as
500 
<TT
501 
CLASS="FILENAME"
502 
>/usr/local/ecos/include/sys/ieeefp.h</TT
503 
>. This
504 
behaviour is correct for packages like the C library where the
505 
interface is defined by appropriate standards. For other packages this
506 
behaviour can lead to file name clashes, and the <A
507 
HREF="ref.include-dir.html"
508 
><SPAN
509 
CLASS="PROPERTY"
510 
>include_dir</SPAN
511 
></A
512 
> property should be used
513 
to avoid this:</P
514 
><TABLE
515 
BORDER="5"
516 
BGCOLOR="#E0E0F0"
517 
WIDTH="70%"
518 
><TR
519 
><TD
520 
><PRE
521 
CLASS="PROGRAMLISTING"
522 
>cdl_package CYGPKG_KERNEL {
523 
    include_dir cyg/kernel
524 
}</PRE
525 
></TD
526 
></TR
527 
></TABLE
528 
><P
529 
>This means that the kernel's exported header file
530 
<TT
531 
CLASS="FILENAME"
532 
>include/kapi.h</TT
533 
> should be copied to
534 
<TT
535 
CLASS="FILENAME"
536 
>/usr/local/ecos/include/cyg/kernel/kapi.h</TT
537 
>, where
538 
it is very unlikely to clash with a header file from some other
539 
package.</P
540 
></LI
541 
><LI
542 
><P
543 
>For typical application developers there will be little or no need for
544 
the installed header files to change after the first build. Changes
545 
will be necessary only if packages are added to or removed from the
546 
configuration. For component writers, the build system should detect
547 
changes to the master copy of the header file source code and update
548 
the installed copies automatically during the next build. The build
549 
system is expected to perform a header file dependency analysis, so
550 
any source files affected should get rebuilt as well.</P
551 
></LI
552 
><LI
553 
><P
554 
>Some build systems may provide additional support for application
555 
developers who want to make minor changes to a package, especially for
556 
debugging purposes. A header file could be copied from the
557 
component repository (which for application developers is assumed to
558 
be a read-only resource) into the build tree and edited there. The
559 
build system would detect a more recent version of such a header file
560 
in the build tree and install it. Care would have to be taken to
561 
recover properly if the modified copy in the build tree is
562 
subsequently removed, in order to revert to the original behaviour.</P
563 
></LI
564 
><LI
565 
><P
566 
>When updating the install tree's <TT
567 
CLASS="FILENAME"
568 
>include</TT
569 
> subdirectory, the build tree may
570 
also perform a clean-up operation. Specifically, it may check for any
571 
files which do not correspond to known exported header files and
572 
delete them.</P
573 
></LI
574 
></OL
575 
><DIV
576 
CLASS="NOTE"
577 
><BLOCKQUOTE
578 
CLASS="NOTE"
579 
><P
580 
><B
581 
>Note: </B
582 
>At present there is no defined support in the build system for
583 
defining custom build steps that generate exported header files. Any
584 
attempt to use the existing custom build step support may fall foul of
585 
unexpected header files being deleted automatically by the build
586 
system. This limitation will be addressed in a future release of the
587 
component framework, and may require changing the priority for
588 
exporting header files so that a custom build step can happen first.</P
589 
></BLOCKQUOTE
590 
></DIV
591 
></DIV
592 
><DIV
593 
CLASS="SECT2"
594 
><H2
595 
CLASS="SECT2"
596 
><A
597 
NAME="BUILD.MAKE.COMPILES">Compiling</H2
598 
><P
599 
>Once there are up to date copies of all the exported header files in
600 
the build tree, the main build can proceed. Most of this involves
601 
compiling source files listed in <SPAN
602 
CLASS="PROPERTY"
603 
>compile</SPAN
604 
> properties in the <SPAN
605 
CLASS="APPLICATION"
606 
>CDL</SPAN
607 
>
608 
scripts for the various packages, for example:</P
609 
><TABLE
610 
BORDER="5"
611 
BGCOLOR="#E0E0F0"
612 
WIDTH="70%"
613 
><TR
614 
><TD
615 
><PRE
616 
CLASS="PROGRAMLISTING"
617 
>cdl_package CYGPKG_ERROR {
618 
    display       "Common error code support"
619 
    compile       strerror.cxx
620 
    &#8230;
621 
}</PRE
622 
></TD
623 
></TR
624 
></TABLE
625 
><P
626 
><SPAN
627 
CLASS="PROPERTY"
628 
>compile</SPAN
629 
> properties may appear in the body of a <TT
630 
CLASS="LITERAL"
631 
>cdl_package</TT
632 
>,
633 
<TT
634 
CLASS="LITERAL"
635 
>cdl_component</TT
636 
>, <TT
637 
CLASS="LITERAL"
638 
>cdl_option</TT
639 
> or <TT
640 
CLASS="LITERAL"
641 
>cdl_interface</TT
642 
>. If the option or
643 
other <SPAN
644 
CLASS="APPLICATION"
645 
>CDL</SPAN
646 
> entity is active and enabled, the property takes effect.
647 
If the option is inactive or disabled the property is ignored. It is
648 
possible for a <SPAN
649 
CLASS="PROPERTY"
650 
>compile</SPAN
651 
> property to list multiple source files, and
652 
it is also possible for a given <SPAN
653 
CLASS="APPLICATION"
654 
>CDL</SPAN
655 
> entity to contain multiple
656 
<SPAN
657 
CLASS="PROPERTY"
658 
>compile</SPAN
659 
> properties. The following three examples are equivalent:</P
660 
><TABLE
661 
BORDER="5"
662 
BGCOLOR="#E0E0F0"
663 
WIDTH="70%"
664 
><TR
665 
><TD
666 
><PRE
667 
CLASS="PROGRAMLISTING"
668 
>cdl_option &lt;some_option&gt; {
669 
    &#8230;
670 
    compile file1.c file2.c file3.c
671 
}
672 
 
673 
cdl_option &lt;some_option&gt; {
674 
    &#8230;
675 
    compile file1.c
676 
    compile file2.c
677 
    compile file3.c
678 
}
679 
 
680 
cdl_option &lt;some_option&gt; {
681 
    &#8230;
682 
    compile file1.c file2.c
683 
    compile file3.c
684 
}</PRE
685 
></TD
686 
></TR
687 
></TABLE
688 
><P
689 
>Packages that follow the directory layout conventions should have a
690 
subdirectory <TT
691 
CLASS="FILENAME"
692 
>src</TT
693 
>, and the
694 
component framework will first look for the specified files there.
695 
Failing that it will look for the specified files relative to the
696 
package's root directory. For example if a package contains a source
697 
file <TT
698 
CLASS="FILENAME"
699 
>strerror.cxx</TT
700 
> then the following two lines
701 
are equivalent:</P
702 
><TABLE
703 
BORDER="5"
704 
BGCOLOR="#E0E0F0"
705 
WIDTH="70%"
706 
><TR
707 
><TD
708 
><PRE
709 
CLASS="PROGRAMLISTING"
710 
>    compile strerror.cxx
711 
    compile src/strerror.cxx</PRE
712 
></TD
713 
></TR
714 
></TABLE
715 
><P
716 
>In the first case the component framework will find the file
717 
immediately in the packages <TT
718 
CLASS="FILENAME"
719 
>src</TT
720 
>
721 
subdirectory. In the second case the framework will first look for a
722 
file <TT
723 
CLASS="FILENAME"
724 
>src/src/strerror.cxx</TT
725 
>, and then for
726 
<TT
727 
CLASS="FILENAME"
728 
>str/strerror.cxx</TT
729 
> relative to the package's root
730 
directory. The result is the same.</P
731 
><P
732 
>The file names may be relative paths, allowing the source code to be
733 
split over multiple directories. For example if a package contains a
734 
file <TT
735 
CLASS="FILENAME"
736 
>src/sync/mutex.cxx</TT
737 
> then the corresponding
738 
<SPAN
739 
CLASS="APPLICATION"
740 
>CDL</SPAN
741 
> entry would be:</P
742 
><TABLE
743 
BORDER="5"
744 
BGCOLOR="#E0E0F0"
745 
WIDTH="70%"
746 
><TR
747 
><TD
748 
><PRE
749 
CLASS="PROGRAMLISTING"
750 
>    compile sync/mutex.cxx</PRE
751 
></TD
752 
></TR
753 
></TABLE
754 
><P
755 
>All the source files relevant to the current configuration will be
756 
identified when the build tree is generated or updated, and added to
757 
the appropriate makefile (or its equivalent for other build systems).
758 
The actual build will involve a rule of the form:</P
759 
><TABLE
760 
BORDER="5"
761 
BGCOLOR="#E0E0F0"
762 
WIDTH="70%"
763 
><TR
764 
><TD
765 
><PRE
766 
CLASS="PROGRAMLISTING"
767 
>&lt;object file&gt; : &lt;source file&gt;
768 
        $(CC) -c $(INCLUDE_PATH) $(CFLAGS) -o $@ $&#60;</PRE
769 
></TD
770 
></TR
771 
></TABLE
772 
><P
773 
>The component framework has built-in knowledge for processing source
774 
files written in C, C++ or assembler. These should have a
775 
<TT
776 
CLASS="LITERAL"
777 
>.c</TT
778 
>, <TT
779 
CLASS="LITERAL"
780 
>.cxx</TT
781 
> and
782 
<TT
783 
CLASS="LITERAL"
784 
>.S</TT
785 
> suffix respectively. The current implementation
786 
has no simple mechanism for extending this with support for other
787 
languages or for alternative suffixes, but this should be addressed in
788 
a future release.</P
789 
><P
790 
>The compiler command that will be used is something like
791 
<TT
792 
CLASS="LITERAL"
793 
>arm-elf-gcc</TT
794 
>. This consists of a command prefix, in
795 
this case <TT
796 
CLASS="LITERAL"
797 
>arm-elf</TT
798 
>, and a specific command such as
799 
<TT
800 
CLASS="LITERAL"
801 
>gcc</TT
802 
>. The command prefix will depend on the target
803 
architecture and is controlled by a configuration option in the
804 
appropriate HAL package. It will have a sensible default value for the
805 
current architecture, but users can modify this option when necessary.
806 
The command prefix cannot be changed on a per-package basis, since
807 
it is usually essential that all packages are built with a consistent
808 
set of tools.</P
809 
><P
810 
>The <TT
811 
CLASS="LITERAL"
812 
>$(INCLUDE_PATH)</TT
813 
> header file search path
814 
consists of at least the following:</P
815 
><P
816 
></P
817 
><OL
818 
TYPE="1"
819 
><LI
820 
><P
821 
>The <TT
822 
CLASS="FILENAME"
823 
>include</TT
824 
> directory in the
825 
install tree. This allows source files to access the various header
826 
files exported by all the packages in the configuration, and also the
827 
configuration header files.</P
828 
></LI
829 
><LI
830 
><P
831 
>The current package's root directory. This ensures that all files in
832 
the package are accessible at build time.</P
833 
></LI
834 
><LI
835 
><P
836 
>The current package's <TT
837 
CLASS="FILENAME"
838 
>src</TT
839 
>
840 
subdirectory, if it is present. Generally all files to be compiled are
841 
located in or below this directory. Typically this is used to access
842 
private header files containing implementation details only.</P
843 
></LI
844 
></OL
845 
><P
846 
>The compiler flags <TT
847 
CLASS="LITERAL"
848 
>$(CFLAGS)</TT
849 
> are determined in two
850 
steps. First the appropriate HAL package will provide a configuration
851 
option defining the global flags. Typically this includes flags that
852 
are needed for the target processor, for example
853 
<TT
854 
CLASS="LITERAL"
855 
>-mcpu=arm9</TT
856 
>, various flags related to warnings,
857 
debugging and optimization, and flags such as
858 
<TT
859 
CLASS="LITERAL"
860 
>-finit-priority</TT
861 
> which are needed by <SPAN
862 
CLASS="APPLICATION"
863 
>eCos</SPAN
864 
> itself.
865 
Users can modify the global flags option as required. In addition it
866 
is possible for existing flags to be removed from and new flags to be
867 
added to the current set on a per-package basis, again by means of
868 
user-modifiable configuration options. More details are given below.</P
869 
><P
870 
>Component writers can assume that the build system will perform full
871 
header file dependency analysis, including dependencies on
872 
configuration headers, but the exact means by which this happens is
873 
implementation-defined. Typical application developers are unlikely to
874 
modify exported or private header files, but configuration headers are
875 
likely to change as the configuration is changed to better meet the
876 
needs of the application. Full header file dependency analysis also
877 
makes things easier for the component writers themselves.</P
878 
><P
879 
>The current directory used during a compilation is an implementation
880 
detail of the build system. However it can be assumed that each
881 
package will have its own directory somewhere in the build tree, to
882 
prevent file name clashes, that this will be the current directory,
883 
and that intermediate object files will end up here.</P
884 
></DIV
885 
><DIV
886 
CLASS="SECT2"
887 
><H2
888 
CLASS="SECT2"
889 
><A
890 
NAME="BUILD.MAKE.LIBRARIES">Generating the Libraries</H2
891 
><P
892 
>Once all the <SPAN
893 
CLASS="PROPERTY"
894 
>compile</SPAN
895 
> and <SPAN
896 
CLASS="PROPERTY"
897 
>make_object</SPAN
898 
> properties have been
899 
processed and the required object files have been built or rebuilt,
900 
these can be collected together in one or more libraries. The archiver
901 
will be the <SPAN
902 
CLASS="APPLICATION"
903 
>ar</SPAN
904 
> command
905 
corresponding to the current architecture, for example <SPAN
906 
CLASS="APPLICATION"
907 
>powerpc-eabi-ar</SPAN
908 
>. By default al of the
909 
object files will end up in a single library
910 
<TT
911 
CLASS="FILENAME"
912 
>libtarget.a</TT
913 
>. This can be changed on a per-package
914 
basis using the <A
915 
HREF="ref.library.html"
916 
><SPAN
917 
CLASS="PROPERTY"
918 
>library</SPAN
919 
></A
920 
> property
921 
in the body of the corresponding <TT
922 
CLASS="LITERAL"
923 
>cdl_package</TT
924 
> command, for example:</P
925 
><TABLE
926 
BORDER="5"
927 
BGCOLOR="#E0E0F0"
928 
WIDTH="70%"
929 
><TR
930 
><TD
931 
><PRE
932 
CLASS="PROGRAMLISTING"
933 
>cdl_package &lt;SOME_PACKAGE&gt; {
934 
    &#8230;
935 
    library  libSomePackage.a
936 
}</PRE
937 
></TD
938 
></TR
939 
></TABLE
940 
><P
941 
>However using different libraries for each package should be avoided.
942 
It makes things more difficult for application developers since they
943 
now have to link the application code with more libraries, and
944 
possibly even change this set of libraries when packages are added to
945 
or removed from the configuration. The use of a single library
946 
<TT
947 
CLASS="FILENAME"
948 
>libtarget.a</TT
949 
> avoids any complications.</P
950 
><P
951 
>It is also possible to change the target library for individual files,
952 
using a <TT
953 
CLASS="LITERAL"
954 
>-library</TT
955 
> option with the corresponding
956 
<SPAN
957 
CLASS="PROPERTY"
958 
>compile</SPAN
959 
> or <SPAN
960 
CLASS="PROPERTY"
961 
>make_object</SPAN
962 
> property. For example:</P
963 
><TABLE
964 
BORDER="5"
965 
BGCOLOR="#E0E0F0"
966 
WIDTH="70%"
967 
><TR
968 
><TD
969 
><PRE
970 
CLASS="PROGRAMLISTING"
971 
>    compile -library=libSomePackage.a hello.c
972 
    make_object -library=libSomePackage.a {
973 
        &#8230;
974 
    }</PRE
975 
></TD
976 
></TR
977 
></TABLE
978 
><P
979 
>Again this should be avoided because it makes application development
980 
more difficult. There is one special library which can be used freely,
981 
<TT
982 
CLASS="FILENAME"
983 
>libextras.a</TT
984 
>, which is used to generate the
985 
<TT
986 
CLASS="FILENAME"
987 
>extras.o</TT
988 
> file as described below.</P
989 
><P
990 
>The order in which object files end up in a library is not defined.
991 
Typically each library will be created directly in the install tree,
992 
since there is little point in generating a file in the build tree and
993 
then immediately copying it to the install tree.</P
994 
></DIV
995 
><DIV
996 
CLASS="SECT2"
997 
><H2
998 
CLASS="SECT2"
999 
><A
1000 
NAME="BUILD.EXTRAS">The <TT
1001 
CLASS="FILENAME"
1002 
>extras.o</TT
1003 
> file</H2
1004 
><P
1005 
>Package sources files normally get compiled and then added to a
1006 
library, by default <TT
1007 
CLASS="FILENAME"
1008 
>libtarget.a</TT
1009 
>, which is then
1010 
linked with the application code. Because of the usual rules for
1011 
linking with libraries, augmented by the use of link-time garbage
1012 
collection, this means that code will only end up in the final
1013 
executable if there is a direct or indirect reference to it in the
1014 
application. Usually this is the desired behaviour: if the application
1015 
does not make any use of say kernel message boxes, directly or
1016 
indirectly, then that code should not end up in the final executable
1017 
taking up valuable memory space.</P
1018 
><P
1019 
>In a few cases it is desirable for package code to end up in the final
1020 
executable even if there are no direct or indirect references. For
1021 
example, device driver functions are often not called directly.
1022 
Instead the application will access the device via the string
1023 
<TT
1024 
CLASS="LITERAL"
1025 
>"/dev/xyzzy"</TT
1026 
> and call the device functions
1027 
indirectly. This will be impossible if the functions have been
1028 
removed at link-time.</P
1029 
><P
1030 
>Another example involves static C++ objects. It is possible to have a
1031 
static C++ object, preferably with a suitable constructor priority,
1032 
where all of the interesting work happens as a side effect of running
1033 
the constructor. For example a package might include a monitoring
1034 
thread or a garbage collection thread created from inside such a
1035 
constructor. Without a reference by the application to the static
1036 
object the latter will never get linked in, and the package will not
1037 
function as expected.</P
1038 
><P
1039 
>A third example would be copyright messages. A package vendor may want
1040 
to insist that all products shipped using that package include a
1041 
particular message in memory, even though many users of that package
1042 
will object to such a restriction.</P
1043 
><P
1044 
>To meet requirements such as these the build system provides support
1045 
for a file <TT
1046 
CLASS="FILENAME"
1047 
>extras.o</TT
1048 
>, which always gets linked
1049 
with the application code via the linker script. Because it is an
1050 
object file rather than a library everything in the file will be
1051 
linked in. The <TT
1052 
CLASS="FILENAME"
1053 
>extras.o</TT
1054 
> file is generated at the
1055 
end of a build from a library <TT
1056 
CLASS="FILENAME"
1057 
>libextras.a</TT
1058 
>, so
1059 
packages can put functions and variables in suitable source files and
1060 
add them to that library explicitly:</P
1061 
><TABLE
1062 
BORDER="5"
1063 
BGCOLOR="#E0E0F0"
1064 
WIDTH="70%"
1065 
><TR
1066 
><TD
1067 
><PRE
1068 
CLASS="PROGRAMLISTING"
1069 
>    compile -library=libextras.a xyzzy.c
1070 
    compile xyzzy_support.c</PRE
1071 
></TD
1072 
></TR
1073 
></TABLE
1074 
><P
1075 
>In this example <TT
1076 
CLASS="FILENAME"
1077 
>xyzzy.o</TT
1078 
> will end up in
1079 
<TT
1080 
CLASS="FILENAME"
1081 
>libextras.a</TT
1082 
>, and hence in
1083 
<TT
1084 
CLASS="FILENAME"
1085 
>extras.o</TT
1086 
> and in the final executable.
1087 
<TT
1088 
CLASS="FILENAME"
1089 
>xyzzy_support.o</TT
1090 
> will end up in
1091 
<TT
1092 
CLASS="FILENAME"
1093 
>libtarget.a</TT
1094 
> as usual, and is subject to linker
1095 
garbage collection.</P
1096 
></DIV
1097 
><DIV
1098 
CLASS="SECT2"
1099 
><H2
1100 
CLASS="SECT2"
1101 
><A
1102 
NAME="BUILD.FLAGS">Compilers and Flags</H2
1103 
><DIV
1104 
CLASS="CAUTION"
1105 
><P
1106 
></P
1107 
><TABLE
1108 
CLASS="CAUTION"
1109 
BORDER="1"
1110 
WIDTH="100%"
1111 
><TR
1112 
><TD
1113 
ALIGN="CENTER"
1114 
><B
1115 
>Caution</B
1116 
></TD
1117 
></TR
1118 
><TR
1119 
><TD
1120 
ALIGN="LEFT"
1121 
><P
1122 
>Some of the details of compiler selection and compiler flags described
1123 
below are subject to change in future revisions of the component
1124 
framework, although every reasonable attempt will be made to avoid
1125 
breaking backwards compatibility.</P
1126 
></TD
1127 
></TR
1128 
></TABLE
1129 
></DIV
1130 
><P
1131 
>The build system needs to know what compiler to use, what compiler
1132 
flags should be used for different stages of the build and so on. Much
1133 
of this information will vary from target to target, although users
1134 
should be able to override this when appropriate. There may also be a
1135 
need for some packages to modify the compiler flags. All platform HAL
1136 
packages should define a number of options with well-known names,
1137 
along the following lines (any existing platform HAL package can be
1138 
consulted for a complete example):</P
1139 
><TABLE
1140 
BORDER="5"
1141 
BGCOLOR="#E0E0F0"
1142 
WIDTH="70%"
1143 
><TR
1144 
><TD
1145 
><PRE
1146 
CLASS="PROGRAMLISTING"
1147 
>cdl_component CYGBLD_GLOBAL_OPTIONS {
1148 
    flavor  none
1149 
    parent  CYGPKG_NONE
1150 
    &#8230;
1151 
 
1152 
    cdl_option CYGBLD_GLOBAL_COMMAND_PREFIX {
1153 
        flavor  data
1154 
        default_value { "arm-elf" }
1155 
        &#8230;
1156 
    }
1157 
    cdl_option CYGBLD_GLOBAL_CFLAGS {
1158 
        flavor  data
1159 
        default_value "-Wall -g -O2 &#8230;"
1160 
        &#8230;
1161 
    }
1162 
 
1163 
    cdl_option CYGBLD_GLOBAL_LDFLAGS {
1164 
        flavor  data
1165 
        default_value "-g -nostdlib -Wl,--gc-sections &#8230;"
1166 
        &#8230;
1167 
    }
1168 
}</PRE
1169 
></TD
1170 
></TR
1171 
></TABLE
1172 
><P
1173 
>The <TT
1174 
CLASS="VARNAME"
1175 
>CYGBLD_GLOBAL_OPTIONS</TT
1176 
> component serves to
1177 
collect together all global build-related options. It has the flavor
1178 
<TT
1179 
CLASS="LITERAL"
1180 
>none</TT
1181 
> since disabling all of these options would
1182 
make it impossible to build anything and hence is not useful. It is
1183 
parented immediately below the root of the configuration hierarchy,
1184 
thus making sure that it is readily accessible in the graphical
1185 
configuration tool and, for command line users, in the
1186 
<TT
1187 
CLASS="FILENAME"
1188 
>ecos.ecc</TT
1189 
> save file.</P
1190 
><DIV
1191 
CLASS="NOTE"
1192 
><BLOCKQUOTE
1193 
CLASS="NOTE"
1194 
><P
1195 
><B
1196 
>Note: </B
1197 
>Currently the <SPAN
1198 
CLASS="PROPERTY"
1199 
>parent</SPAN
1200 
> property lists a parent of
1201 
<TT
1202 
CLASS="VARNAME"
1203 
>CYGPKG_NONE</TT
1204 
>, rather than an empty string. This
1205 
could be unfortunate if there was ever a package with that name. The
1206 
issue will be addressed in a future release of the component
1207 
framework.</P
1208 
></BLOCKQUOTE
1209 
></DIV
1210 
><P
1211 
>The option <TT
1212 
CLASS="VARNAME"
1213 
>CYGBLD_GLOBAL_COMMAND_PREFIX</TT
1214 
> defines
1215 
which tools should be used for the current target. Typically this is
1216 
determined by the processor on the target hardware. In some cases a
1217 
given target board may be able to support several different
1218 
processors, in which case the <SPAN
1219 
CLASS="PROPERTY"
1220 
>default_value</SPAN
1221 
> expression could select
1222 
a different toolchain depending on some other option that is used to
1223 
control which particular processor.
1224 
<TT
1225 
CLASS="VARNAME"
1226 
>CYGBLD_GLOBAL_COMMAND_PREFIX</TT
1227 
> is modifiable rather
1228 
than calculated, so users can override this when necessary.</P
1229 
><P
1230 
>Given a command prefix such as <TT
1231 
CLASS="LITERAL"
1232 
>arm-elf</TT
1233 
>, all C
1234 
source files will be compiled with <TT
1235 
CLASS="LITERAL"
1236 
>arm-elf-gcc</TT
1237 
>, all
1238 
C++ sources will be built using <TT
1239 
CLASS="LITERAL"
1240 
>arm-elf-g++</TT
1241 
>,
1242 
and <TT
1243 
CLASS="LITERAL"
1244 
>arm-elf-ar</TT
1245 
> will be used to generate the
1246 
library. This is in accordance with the usual naming conventions for
1247 
GNU cross-compilers and similar tools. For the purposes of custom
1248 
build steps, tokens such as <TT
1249 
CLASS="LITERAL"
1250 
>$(CC)</TT
1251 
> will be set to
1252 
<TT
1253 
CLASS="LITERAL"
1254 
>arm-elf-gcc</TT
1255 
>.</P
1256 
><P
1257 
>The next option, <TT
1258 
CLASS="VARNAME"
1259 
>CYGBLD_GLOBAL_CFLAGS</TT
1260 
>, is used to
1261 
provide the initial value of <TT
1262 
CLASS="LITERAL"
1263 
>$(CFLAGS)</TT
1264 
>. Some
1265 
compiler flags such as <TT
1266 
CLASS="LITERAL"
1267 
>-Wall</TT
1268 
> and
1269 
<TT
1270 
CLASS="LITERAL"
1271 
>-g</TT
1272 
> are likely to be used on all targets. Other
1273 
flags such as <TT
1274 
CLASS="LITERAL"
1275 
>-mcpu=arm7tdmi</TT
1276 
> will be
1277 
target-specific. Again this is a modifiable option, so the user can
1278 
switch from say <TT
1279 
CLASS="LITERAL"
1280 
>-O2</TT
1281 
> to <TT
1282 
CLASS="LITERAL"
1283 
>-Os</TT
1284 
> if
1285 
desired. The option <TT
1286 
CLASS="VARNAME"
1287 
>CYGBLD_GLOBAL_LDFLAGS</TT
1288 
> serves
1289 
the same purpose for <TT
1290 
CLASS="LITERAL"
1291 
>$(LDFLAGS)</TT
1292 
> and linking. It is
1293 
used primarily when building test cases or possibly for some custom
1294 
build steps, since building eCos itself generally involves building
1295 
one or more libraries rather than executables.</P
1296 
><P
1297 
>Some packages may wish to add certain flags to the global set, or
1298 
possibly remove some flags. This can be achieved by having
1299 
appropriately named options in the package, for example:</P
1300 
><TABLE
1301 
BORDER="5"
1302 
BGCOLOR="#E0E0F0"
1303 
WIDTH="70%"
1304 
><TR
1305 
><TD
1306 
><PRE
1307 
CLASS="PROGRAMLISTING"
1308 
>cdl_component CYGPKG_KERNEL_OPTIONS {
1309 
    display "Kernel build options"
1310 
    flavor  none
1311 
    &#8230;
1312 
 
1313 
    cdl_option CYGPKG_KERNEL_CFLAGS_ADD {
1314 
        display "Additional compiler flags"
1315 
        flavor  data
1316 
        default_value { "" }
1317 
        &#8230;
1318 
    }
1319 
 
1320 
    cdl_option CYGPKG_KERNEL_CFLAGS_REMOVE {
1321 
        display "Suppressed compiler flags"
1322 
        flavor  data
1323 
        default_value { "" }
1324 
        &#8230;
1325 
    }
1326 
 
1327 
    cdl_option CYGPKG_KERNEL_LDFLAGS_ADD {
1328 
        display "Additional linker flags"
1329 
        flavor  data
1330 
        default_value { "" }
1331 
        &#8230;
1332 
    }
1333 
 
1334 
    cdl_option CYGPKG_KERNEL_LDFLAGS_REMOVE {
1335 
        display "Suppressed linker flags"
1336 
        flavor  data
1337 
        default_value { "" }
1338 
        &#8230;
1339 
    }
1340 
}</PRE
1341 
></TD
1342 
></TR
1343 
></TABLE
1344 
><P
1345 
>In this example the kernel does not modify the global compiler flags
1346 
by default, but it is possible for the users to modify the options if
1347 
desired. The value of <TT
1348 
CLASS="LITERAL"
1349 
>$(CFLAGS)</TT
1350 
> that is used for
1351 
the compilations and custom build steps in a given package is
1352 
determined as follows:</P
1353 
><P
1354 
></P
1355 
><OL
1356 
TYPE="1"
1357 
><LI
1358 
><P
1359 
>Start with the global settings from
1360 
<TT
1361 
CLASS="VARNAME"
1362 
>CYGBLD_GLOBAL_CFLAGS</TT
1363 
>, for example
1364 
<TT
1365 
CLASS="LITERAL"
1366 
>-g&nbsp;-O2</TT
1367 
>.</P
1368 
></LI
1369 
><LI
1370 
><P
1371 
>Remove any flags specified in the per-package
1372 
<TT
1373 
CLASS="LITERAL"
1374 
>CFLAGS_REMOVE</TT
1375 
> option, if any. For example
1376 
if <TT
1377 
CLASS="LITERAL"
1378 
>-O2</TT
1379 
> should be removed for this package then
1380 
<TT
1381 
CLASS="LITERAL"
1382 
>$(CFLAGS)</TT
1383 
> would now have a value of just
1384 
<TT
1385 
CLASS="LITERAL"
1386 
>-g</TT
1387 
>.</P
1388 
></LI
1389 
><LI
1390 
><P
1391 
>Then concatenate the flags specified by the per-package
1392 
<TT
1393 
CLASS="LITERAL"
1394 
>CFLAGS_ADD</TT
1395 
> option, if any. For example if
1396 
<TT
1397 
CLASS="LITERAL"
1398 
>-Os</TT
1399 
> should be added for the current package then
1400 
the final value of <TT
1401 
CLASS="LITERAL"
1402 
>$(CFLAGS)</TT
1403 
> will be
1404 
<TT
1405 
CLASS="LITERAL"
1406 
>-g&nbsp;-Os</TT
1407 
>.</P
1408 
></LI
1409 
></OL
1410 
><P
1411 
><TT
1412 
CLASS="LITERAL"
1413 
>$(LDFLAGS)</TT
1414 
> is determined in much the same way.</P
1415 
><DIV
1416 
CLASS="NOTE"
1417 
><BLOCKQUOTE
1418 
CLASS="NOTE"
1419 
><P
1420 
><B
1421 
>Note: </B
1422 
>The way compiler flags are handled at present has numerous limitations
1423 
that need to be addressed in a future release, although it should
1424 
suffice for nearly all cases. For the time being custom build steps
1425 
and in particular the <SPAN
1426 
CLASS="PROPERTY"
1427 
>make_object</SPAN
1428 
> property can be used to work
1429 
around the limitations.</P
1430 
><P
1431 
>Amongst the issues, there is a specific problem with package
1432 
encapsulation. For example the math library imposes some stringent
1433 
requirements on the compiler in order to guarantee exact IEEE
1434 
behavior, and may need special flags on a per-architecture basis. One
1435 
way of handling this is to have
1436 
<TT
1437 
CLASS="VARNAME"
1438 
>CYGPKG_LIBM_CFLAGS_ADD</TT
1439 
> and
1440 
<TT
1441 
CLASS="VARNAME"
1442 
>CYGPKG_LIBM_CFLAGS_REMOVE</TT
1443 
> <SPAN
1444 
CLASS="PROPERTY"
1445 
>default_value</SPAN
1446 
>
1447 
expressions which depend on the target architecture, but such
1448 
expressions may have to updated for each new architecture. An
1449 
alternative approach would allow the architectural HAL package to
1450 
modify the <SPAN
1451 
CLASS="PROPERTY"
1452 
>default_value</SPAN
1453 
> expressions for the math library, but this
1454 
breaks encapsulation. A third approach would allow some architectural
1455 
HAL packages to define one or more special options with well-known
1456 
names, and the math library could check if these options were defined
1457 
and adjust the default values appropriately. Other packages with
1458 
floating point requirements could do the same. This approach also has
1459 
scalability issues, in particular how many such categories of options
1460 
would be needed? It is not yet clear how best to resolve such issues.</P
1461 
></BLOCKQUOTE
1462 
></DIV
1463 
><DIV
1464 
CLASS="NOTE"
1465 
><BLOCKQUOTE
1466 
CLASS="NOTE"
1467 
><P
1468 
><B
1469 
>Note: </B
1470 
>When generating a build tree it would be desirable for the component
1471 
framework to output details of the tools and compiler flags in a
1472 
format that can be re-used for application builds, for example a
1473 
makefile fragment. This would make it easier for application
1474 
developers to use the same set of flags as were used for building eCos
1475 
itself, thus avoiding some potential problems with incompatible
1476 
compiler flags.</P
1477 
></BLOCKQUOTE
1478 
></DIV
1479 
></DIV
1480 
><DIV
1481 
CLASS="SECT2"
1482 
><H2
1483 
CLASS="SECT2"
1484 
><A
1485 
NAME="BUILD.CUSTOM">Custom Build Steps</H2
1486 
><DIV
1487 
CLASS="CAUTION"
1488 
><P
1489 
></P
1490 
><TABLE
1491 
CLASS="CAUTION"
1492 
BORDER="1"
1493 
WIDTH="100%"
1494 
><TR
1495 
><TD
1496 
ALIGN="CENTER"
1497 
><B
1498 
>Caution</B
1499 
></TD
1500 
></TR
1501 
><TR
1502 
><TD
1503 
ALIGN="LEFT"
1504 
><P
1505 
>Some of the details of custom build steps as described below are
1506 
subject to change in future revisions of the component framework,
1507 
although every reasonable attempt will be made to avoid breaking
1508 
backwards compatibility.</P
1509 
></TD
1510 
></TR
1511 
></TABLE
1512 
></DIV
1513 
><P
1514 
>For most packages simply listing one or more source files in a
1515 
<SPAN
1516 
CLASS="PROPERTY"
1517 
>compile</SPAN
1518 
> property is sufficient. These files will get built using the
1519 
appropriate compiler and compiler flags and added to a library, which
1520 
then gets linked with application code. A package that can be built in
1521 
this way is likely to be more portable to different targets and build
1522 
environments, since it avoids build-time dependencies. However some
1523 
packages have special needs, and the component framework supports
1524 
custom build steps to allow for these needs. There are two properties
1525 
related to this, <SPAN
1526 
CLASS="PROPERTY"
1527 
>make</SPAN
1528 
> and <SPAN
1529 
CLASS="PROPERTY"
1530 
>make_object</SPAN
1531 
>, and both take the following
1532 
form:</P
1533 
><TABLE
1534 
BORDER="5"
1535 
BGCOLOR="#E0E0F0"
1536 
WIDTH="70%"
1537 
><TR
1538 
><TD
1539 
><PRE
1540 
CLASS="PROGRAMLISTING"
1541 
>    make {
1542 
        &lt;target_filepath&gt; : &lt;dependency_filepath&gt; &#8230;
1543 
            &lt;command&gt;
1544 
            ...
1545 
    }</PRE
1546 
></TD
1547 
></TR
1548 
></TABLE
1549 
><P
1550 
>Although this may look like makefile syntax, and although some build
1551 
environments will indeed involve generating makefiles and running
1552 
<SPAN
1553 
CLASS="APPLICATION"
1554 
>make</SPAN
1555 
>, this is not
1556 
guaranteed. It is possible for the component framework to be
1557 
integrated with some other build system, and custom build steps should
1558 
be written with that possibility in mind. Each custom build step
1559 
involves a target, some number of dependency files, and some number of
1560 
commands. If the target is not up to date with respect to one or more
1561 
of the dependencies then the commands need to be executed.</P
1562 
><P
1563 
></P
1564 
><OL
1565 
TYPE="a"
1566 
><LI
1567 
><P
1568 
>Only one target can be specified. For a <SPAN
1569 
CLASS="PROPERTY"
1570 
>make_object</SPAN
1571 
> property this
1572 
target must be an object file. For a <SPAN
1573 
CLASS="PROPERTY"
1574 
>make</SPAN
1575 
> property it can be any
1576 
file. In both cases it must refer to a physical file, the use of
1577 
phony targets is not supported. The target should not be an absolute
1578 
path name. If the generated file needs to end up in the install tree
1579 
then this can be achieved using a <TT
1580 
CLASS="LITERAL"
1581 
>&lt;PREFIX&gt;</TT
1582 
>
1583 
token, for example:</P
1584 
><TABLE
1585 
BORDER="5"
1586 
BGCOLOR="#E0E0F0"
1587 
WIDTH="70%"
1588 
><TR
1589 
><TD
1590 
><PRE
1591 
CLASS="PROGRAMLISTING"
1592 
>    make {
1593 
        &lt;PREFIX&gt;/lib/mytarget : &#8230;
1594 
            ...
1595 
    }</PRE
1596 
></TD
1597 
></TR
1598 
></TABLE
1599 
><P
1600 
>When the build tree is generated and the custom build step is added to
1601 
the makefile (or whatever build system is used)
1602 
<TT
1603 
CLASS="LITERAL"
1604 
>&lt;PREFIX&gt;</TT
1605 
> will be replaced with the absolute
1606 
path to the install tree. </P
1607 
></LI
1608 
><LI
1609 
><P
1610 
>All the dependencies must also refer to physical files, not to phony
1611 
targets. These files may be in the source tree. The
1612 
<TT
1613 
CLASS="LITERAL"
1614 
>&lt;PACKAGE&gt;</TT
1615 
> token can be used to indicate this:
1616 
when the build tree is generated this token will be replaced with the
1617 
absolute path to the package's root directory in the component
1618 
repository, for example:</P
1619 
><TABLE
1620 
BORDER="5"
1621 
BGCOLOR="#E0E0F0"
1622 
WIDTH="70%"
1623 
><TR
1624 
><TD
1625 
><PRE
1626 
CLASS="PROGRAMLISTING"
1627 
>    make_object {
1628 
        xyzzy.o : &lt;PACKAGE&gt;/src/xyzzy.c
1629 
            &#8230;</PRE
1630 
></TD
1631 
></TR
1632 
></TABLE
1633 
><P
1634 
>If the component repository was installed in <TT
1635 
CLASS="FILENAME"
1636 
>/usr/local/ecos</TT
1637 
> and this custom build
1638 
step existed in version 1_5 of the kernel,
1639 
<TT
1640 
CLASS="LITERAL"
1641 
>&lt;PACKAGE&gt;</TT
1642 
> would be replaced with
1643 
<TT
1644 
CLASS="FILENAME"
1645 
>/usr/local/ecos/packages/kernel/v1_5</TT
1646 
>.</P
1647 
><P
1648 
>Alternatively the dependencies may refer to files that are generated
1649 
during the build. These may be object files resulting from <SPAN
1650 
CLASS="PROPERTY"
1651 
>compile</SPAN
1652 
>
1653 
properties or other <SPAN
1654 
CLASS="PROPERTY"
1655 
>make_object</SPAN
1656 
> properties, or they may be other
1657 
files resulting from a <SPAN
1658 
CLASS="PROPERTY"
1659 
>make</SPAN
1660 
> property, for example:</P
1661 
><TABLE
1662 
BORDER="5"
1663 
BGCOLOR="#E0E0F0"
1664 
WIDTH="70%"
1665 
><TR
1666 
><TD
1667 
><PRE
1668 
CLASS="PROGRAMLISTING"
1669 
>    compile plugh.c
1670 
    make_object {
1671 
        xyzzy.o : plugh.o
1672 
            &#8230;
1673 
    }</PRE
1674 
></TD
1675 
></TR
1676 
></TABLE
1677 
></LI
1678 
><LI
1679 
><P
1680 
>No other token or makefile variables may be used in the target or
1681 
dependency file names. Also conditionals such as
1682 
<TT
1683 
CLASS="LITERAL"
1684 
>ifneq</TT
1685 
> and similar makefile functionality must not
1686 
be used.</P
1687 
></LI
1688 
><LI
1689 
><P
1690 
>
1691 
Similarly the list of commands must not use any makefile conditionals
1692 
or similar functionality. A number of tokens can be used to provide
1693 
access to target-specific or environmental data. Note that these
1694 
tokens look like makefile variables, unlike the
1695 
<TT
1696 
CLASS="LITERAL"
1697 
>&lt;PREFIX&gt;</TT
1698 
> and
1699 
<TT
1700 
CLASS="LITERAL"
1701 
>&lt;PACKAGE&gt;</TT
1702 
> tokens mentioned earlier:</P
1703 
><DIV
1704 
CLASS="INFORMALTABLE"
1705 
><A
1706 
NAME="AEN2778"><P
1707 
></P
1708 
><TABLE
1709 
BORDER="1"
1710 
CLASS="CALSTABLE"
1711 
><THEAD
1712 
><TR
1713 
><TH
1714 
ALIGN="LEFT"
1715 
VALIGN="TOP"
1716 
>Token</TH
1717 
><TH
1718 
ALIGN="LEFT"
1719 
VALIGN="TOP"
1720 
>Purpose</TH
1721 
><TH
1722 
ALIGN="LEFT"
1723 
VALIGN="TOP"
1724 
>Example value</TH
1725 
></TR
1726 
></THEAD
1727 
><TBODY
1728 
><TR
1729 
><TD
1730 
ALIGN="LEFT"
1731 
VALIGN="TOP"
1732 
><TT
1733 
CLASS="LITERAL"
1734 
>$(AR)</TT
1735 
></TD
1736 
><TD
1737 
ALIGN="LEFT"
1738 
VALIGN="TOP"
1739 
>the GNU archiver</TD
1740 
><TD
1741 
ALIGN="LEFT"
1742 
VALIGN="TOP"
1743 
><TT
1744 
CLASS="LITERAL"
1745 
>mips-tx39-elf-ar</TT
1746 
></TD
1747 
></TR
1748 
><TR
1749 
><TD
1750 
ALIGN="LEFT"
1751 
VALIGN="TOP"
1752 
><TT
1753 
CLASS="LITERAL"
1754 
>$(CC)</TT
1755 
></TD
1756 
><TD
1757 
ALIGN="LEFT"
1758 
VALIGN="TOP"
1759 
>the GNU compiler</TD
1760 
><TD
1761 
ALIGN="LEFT"
1762 
VALIGN="TOP"
1763 
><TT
1764 
CLASS="LITERAL"
1765 
>sh-elf-gcc</TT
1766 
></TD
1767 
></TR
1768 
><TR
1769 
><TD
1770 
ALIGN="LEFT"
1771 
VALIGN="TOP"
1772 
><TT
1773 
CLASS="LITERAL"
1774 
>$(CFLAGS)</TT
1775 
></TD
1776 
><TD
1777 
ALIGN="LEFT"
1778 
VALIGN="TOP"
1779 
>compiler flags</TD
1780 
><TD
1781 
ALIGN="LEFT"
1782 
VALIGN="TOP"
1783 
><TT
1784 
CLASS="LITERAL"
1785 
>-O2 -Wall</TT
1786 
></TD
1787 
></TR
1788 
><TR
1789 
><TD
1790 
ALIGN="LEFT"
1791 
VALIGN="TOP"
1792 
><TT
1793 
CLASS="LITERAL"
1794 
>$(COMMAND_PREFIX)</TT
1795 
></TD
1796 
><TD
1797 
ALIGN="LEFT"
1798 
VALIGN="TOP"
1799 
>the triplet prefix</TD
1800 
><TD
1801 
ALIGN="LEFT"
1802 
VALIGN="TOP"
1803 
><TT
1804 
CLASS="LITERAL"
1805 
>mn10300-elf-</TT
1806 
></TD
1807 
></TR
1808 
><TR
1809 
><TD
1810 
ALIGN="LEFT"
1811 
VALIGN="TOP"
1812 
><TT
1813 
CLASS="LITERAL"
1814 
>$(INCLUDE_PATH&#62;</TT
1815 
></TD
1816 
><TD
1817 
ALIGN="LEFT"
1818 
VALIGN="TOP"
1819 
>header file search path</TD
1820 
><TD
1821 
ALIGN="LEFT"
1822 
VALIGN="TOP"
1823 
><TT
1824 
CLASS="LITERAL"
1825 
>-I. -Isrc/misc</TT
1826 
></TD
1827 
></TR
1828 
><TR
1829 
><TD
1830 
ALIGN="LEFT"
1831 
VALIGN="TOP"
1832 
><TT
1833 
CLASS="LITERAL"
1834 
>$(LDFLAGS)</TT
1835 
></TD
1836 
><TD
1837 
ALIGN="LEFT"
1838 
VALIGN="TOP"
1839 
>linker flags</TD
1840 
><TD
1841 
ALIGN="LEFT"
1842 
VALIGN="TOP"
1843 
><TT
1844 
CLASS="LITERAL"
1845 
>-nostdlib -Wl,-static</TT
1846 
></TD
1847 
></TR
1848 
><TR
1849 
><TD
1850 
ALIGN="LEFT"
1851 
VALIGN="TOP"
1852 
><TT
1853 
CLASS="LITERAL"
1854 
>$(OBJCOPY)</TT
1855 
></TD
1856 
><TD
1857 
ALIGN="LEFT"
1858 
VALIGN="TOP"
1859 
>the objcopy utility</TD
1860 
><TD
1861 
ALIGN="LEFT"
1862 
VALIGN="TOP"
1863 
><TT
1864 
CLASS="LITERAL"
1865 
>arm-elf-objcopy</TT
1866 
></TD
1867 
></TR
1868 
><TR
1869 
><TD
1870 
ALIGN="LEFT"
1871 
VALIGN="TOP"
1872 
><TT
1873 
CLASS="LITERAL"
1874 
>$(PREFIX)</TT
1875 
></TD
1876 
><TD
1877 
ALIGN="LEFT"
1878 
VALIGN="TOP"
1879 
>location of the install tree</TD
1880 
><TD
1881 
ALIGN="LEFT"
1882 
VALIGN="TOP"
1883 
><TT
1884 
CLASS="FILENAME"
1885 
>/home/fred/ecos-install</TT
1886 
></TD
1887 
></TR
1888 
><TR
1889 
><TD
1890 
ALIGN="LEFT"
1891 
VALIGN="TOP"
1892 
><TT
1893 
CLASS="LITERAL"
1894 
>$(REPOSITORY)</TT
1895 
></TD
1896 
><TD
1897 
ALIGN="LEFT"
1898 
VALIGN="TOP"
1899 
>location of the component repository</TD
1900 
><TD
1901 
ALIGN="LEFT"
1902 
VALIGN="TOP"
1903 
><TT
1904 
CLASS="FILENAME"
1905 
>/home/fred/ecos/packages</TT
1906 
></TD
1907 
></TR
1908 
></TBODY
1909 
></TABLE
1910 
><P
1911 
></P
1912 
></DIV
1913 
><P
1914 
>In addition commands in a custom build step may refer to the target
1915 
and the dependencies using <TT
1916 
CLASS="LITERAL"
1917 
>$@</TT
1918 
>,
1919 
<TT
1920 
CLASS="LITERAL"
1921 
>$&#60;</TT
1922 
>, <TT
1923 
CLASS="LITERAL"
1924 
>$^</TT
1925 
> and
1926 
<TT
1927 
CLASS="LITERAL"
1928 
>$*</TT
1929 
>, all of which behave as per GNU make syntax. The
1930 
commands will execute in a suitable directory in the build tree.</P
1931 
></LI
1932 
><LI
1933 
><P
1934 
>The current directory used during a custom build step is an
1935 
implementation detail of the build system. However it can be assumed
1936 
that each package will have its own directory somewhere in the build
1937 
tree, to prevent file name clashes, and that this will be the current
1938 
directory. In addition any object files generated as a result of
1939 
<SPAN
1940 
CLASS="PROPERTY"
1941 
>compile</SPAN
1942 
> properties will be located here as well, which is useful for
1943 
custom build steps that depend on a <TT
1944 
CLASS="LITERAL"
1945 
>.o</TT
1946 
> file
1947 
previously generated.</P
1948 
><P
1949 
>Any temporary files created by a custom build step should be generated
1950 
in the build tree (in or under the current directory). Such files
1951 
should be given a <TT
1952 
CLASS="FILENAME"
1953 
>.tmp</TT
1954 
> file extension to ensure
1955 
that they are deleted during a <TT
1956 
CLASS="LITERAL"
1957 
>make&nbsp;clean</TT
1958 
> or
1959 
equivalent operation.</P
1960 
><P
1961 
>If a package contains multiple custom build steps with the same
1962 
priority, it is possible that these build steps will be run
1963 
concurrently. Therefore these custom build steps must not accidentally
1964 
use the same file names for intermediate files.</P
1965 
></LI
1966 
><LI
1967 
><P
1968 
>Care has to be taken to make sure that the commands in a custom build
1969 
step will run on all host platforms, including Windows NT as well as
1970 
Linux and other Unix systems. For example, all file paths should use
1971 
forward slashes as the directory separator. It can be assumed that
1972 
Windows users will have a full set of CygWin tools installed and
1973 
available on the path. The <A
1974 
HREF="http://www.gnu.org/prep/standards.html"
1975 
TARGET="_top"
1976 
>GNU coding
1977 
standards</A
1978 
> provide some useful guidelines for writing portable
1979 
build rules.</P
1980 
></LI
1981 
><LI
1982 
><P
1983 
>A custom build step must not make any assumptions concerning the
1984 
version of another package. This enforces package encapsulation,
1985 
preventing one package from accessing the internals of another.</P
1986 
></LI
1987 
><LI
1988 
><P
1989 
>No assumptions should be made about the target platform, unless the
1990 
package is inherently specific to that platform. Even then it is
1991 
better to use the various tokens whenever possible, rather than
1992 
hard-coding in details such as the compiler. For example, given a
1993 
custom build step such as:</P
1994 
><TABLE
1995 
BORDER="5"
1996 
BGCOLOR="#E0E0F0"
1997 
WIDTH="70%"
1998 
><TR
1999 
><TD
2000 
><PRE
2001 
CLASS="PROGRAMLISTING"
2002 
>    arm-elf-gcc -c -mcpu=arm7di -o $@ $&lt;</PRE
2003 
></TD
2004 
></TR
2005 
></TABLE
2006 
><P
2007 
>Even if this build step will only be invoked on ARM targets, it could
2008 
cause problems. For example the toolchain may have been installed
2009 
using a prefix other than <TT
2010 
CLASS="LITERAL"
2011 
>arm-elf</TT
2012 
>. Also, if the
2013 
user changes the compiler flags then this would not be reflected in
2014 
the build step. The correct way to write this rule would be:</P
2015 
><TABLE
2016 
BORDER="5"
2017 
BGCOLOR="#E0E0F0"
2018 
WIDTH="70%"
2019 
><TR
2020 
><TD
2021 
><PRE
2022 
CLASS="PROGRAMLISTING"
2023 
>    $(CC) -c $(CFLAGS) -o $@ $&lt;</PRE
2024 
></TD
2025 
></TR
2026 
></TABLE
2027 
><P
2028 
>Some commands such as the compiler, the archiver, and objcopy are
2029 
required sufficiently often to warrant their own tokens, for example
2030 
<TT
2031 
CLASS="LITERAL"
2032 
>$(CC)</TT
2033 
> and <TT
2034 
CLASS="LITERAL"
2035 
>$(OBJCOPY)</TT
2036 
>. Other
2037 
target-specific commands are needed only rarely and the
2038 
<TT
2039 
CLASS="LITERAL"
2040 
>$(COMMAND_PREFIX)</TT
2041 
> token can be used to construct
2042 
the appropriate command name, for example:</P
2043 
><TABLE
2044 
BORDER="5"
2045 
BGCOLOR="#E0E0F0"
2046 
WIDTH="70%"
2047 
><TR
2048 
><TD
2049 
><PRE
2050 
CLASS="PROGRAMLISTING"
2051 
>&#13;    $(COMMAND_PREFIX)size $&lt; &gt; $@</PRE
2052 
></TD
2053 
></TR
2054 
></TABLE
2055 
></LI
2056 
><LI
2057 
><P
2058 
>Custom build steps should not be used to build host-side executables,
2059 
even if those executables are needed to build parts of the target side
2060 
code. Support for building host-side executables will be added in a
2061 
future version of the component framework, although it will not
2062 
necessarily involve these custom build steps.</P
2063 
></LI
2064 
></OL
2065 
><P
2066 
>By default custom build steps defined in a <SPAN
2067 
CLASS="PROPERTY"
2068 
>make_object</SPAN
2069 
> property
2070 
have a priority of 100, which means that they will be executed
2071 
in the same phase as compilations resulting from a <SPAN
2072 
CLASS="PROPERTY"
2073 
>compile</SPAN
2074 
> property.
2075 
It is possible to change the priority using a property option, for
2076 
example:</P
2077 
><TABLE
2078 
BORDER="5"
2079 
BGCOLOR="#E0E0F0"
2080 
WIDTH="70%"
2081 
><TR
2082 
><TD
2083 
><PRE
2084 
CLASS="PROGRAMLISTING"
2085 
>    make_object -priority 50 {
2086 
        &#8230;
2087 
    }</PRE
2088 
></TD
2089 
></TR
2090 
></TABLE
2091 
><P
2092 
>Specifying a priority smaller than a 100 means that the custom build
2093 
step happens before the normal compilations. Priorities between 100
2094 
and 200 happen after normal compilations but before the libraries are
2095 
archived together. <SPAN
2096 
CLASS="PROPERTY"
2097 
>make_object</SPAN
2098 
> properties should not specify a
2099 
priority of 200 or later. </P
2100 
><P
2101 
>Custom build steps defined in a <SPAN
2102 
CLASS="PROPERTY"
2103 
>make</SPAN
2104 
> property have a default
2105 
priority of 300, and so they will happen after the libraries have been
2106 
built. Again this can be changed using a <TT
2107 
CLASS="LITERAL"
2108 
>-priority</TT
2109 
>
2110 
property option.</P
2111 
></DIV
2112 
><DIV
2113 
CLASS="SECT2"
2114 
><H2
2115 
CLASS="SECT2"
2116 
><A
2117 
NAME="BUILD.STARTUP">Startup Code</H2
2118 
><P
2119 
>Linking an application requires the application code, a linker script,
2120 
the eCos library or libraries, the <TT
2121 
CLASS="LITERAL"
2122 
>extras.o</TT
2123 
> file,
2124 
and some startup code. Depending on the target hardware and how the
2125 
application gets booted, this startup code may do little more than
2126 
branching to <TT
2127 
CLASS="LITERAL"
2128 
>main()</TT
2129 
>, or it may have to perform a
2130 
considerable amount of hardware initialization. The startup code
2131 
generally lives in a file <TT
2132 
CLASS="LITERAL"
2133 
>vectors.o</TT
2134 
> which is
2135 
created by a custom build step in a HAL package. As far as application
2136 
developers are concered the existence of this file is largely
2137 
transparent, since the linker script ensures that the file is part of
2138 
the final executable.</P
2139 
><P
2140 
>This startup code is not generally of interest to component writers,
2141 
only to HAL developers who are referred to one of the existing HAL
2142 
packages for specific details. Other packages are not expected to
2143 
modify the startup in any way. If a package needs some work performed
2144 
early on during system initialization, before the application's main
2145 
entry point gets invoked, this can be achieved using a static object
2146 
with a suitable constructor priority.</P
2147 
><DIV
2148 
CLASS="NOTE"
2149 
><BLOCKQUOTE
2150 
CLASS="NOTE"
2151 
><P
2152 
><B
2153 
>Note: </B
2154 
>It is possible that the <TT
2155 
CLASS="LITERAL"
2156 
>extras.o</TT
2157 
> support, in
2158 
conjunction with appropriate linker script directives, could be used
2159 
to eliminate the need for a special startup file. The details are not
2160 
yet clear.</P
2161 
></BLOCKQUOTE
2162 
></DIV
2163 
></DIV
2164 
><DIV
2165 
CLASS="SECT2"
2166 
><H2
2167 
CLASS="SECT2"
2168 
><A
2169 
NAME="BUILD.LINKERSCRIPT">The Linker Script</H2
2170 
><DIV
2171 
CLASS="CAUTION"
2172 
><P
2173 
></P
2174 
><TABLE
2175 
CLASS="CAUTION"
2176 
BORDER="1"
2177 
WIDTH="100%"
2178 
><TR
2179 
><TD
2180 
ALIGN="CENTER"
2181 
><B
2182 
>Caution</B
2183 
></TD
2184 
></TR
2185 
><TR
2186 
><TD
2187 
ALIGN="LEFT"
2188 
><P
2189 
>This section is not finished, and the details are subject to change in
2190 
a future release. Arguably linker script issues should be documented
2191 
in the HAL documentation rather than in this guide.</P
2192 
></TD
2193 
></TR
2194 
></TABLE
2195 
></DIV
2196 
><P
2197 
>Generating the linker script is the responsibility of the various HAL
2198 
packages that are applicable to a given target. Developers of
2199 
components other than HAL packages need not be concerned about what is
2200 
involved. Developers of new HAL packages should use an existing HAL as
2201 
a template.</P
2202 
><DIV
2203 
CLASS="NOTE"
2204 
><BLOCKQUOTE
2205 
CLASS="NOTE"
2206 
><P
2207 
><B
2208 
>Note: </B
2209 
>It may be desirable for some packages to have some control over the
2210 
linker script, for example to add extra alignment details for a
2211 
particular section. This can be risky because it can result in subtle
2212 
portability problems, and the current component framework has no
2213 
support for any such operations. The issue may be addressed in a
2214 
future release.</P
2215 
></BLOCKQUOTE
2216 
></DIV
2217 
></DIV
2218 
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2219 
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2220 
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2221 
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2222 
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2230 
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2231 
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2232 
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2233 
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2234 
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2235 
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2236 
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2237 
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2238 
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2239 
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2240 
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2244 
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2245 
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2246 
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2248 
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2250 
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2258 
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2259 
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2260 
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2261 
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2262 
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2263 
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2264 
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2265 
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2268 
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2269 
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2274 
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