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1<html>
2<head>
3<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
4<title>3.2. Cross-Development Toolchain Generation</title>
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12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="section" title="3.2. Cross-Development Toolchain Generation">
13<div class="titlepage"><div><div><h2 class="title" style="clear: both">
14<a name="cross-development-toolchain-generation"></a>3.2. Cross-Development Toolchain Generation</h2></div></div></div>
15<p>
16 The Yocto Project does most of the work for you when it comes to
17 creating
18 <a class="link" href="../ref-manual/cross-development-toolchain.html" target="_self">cross-development toolchains</a>.
19 This section provides some technical background on how
20 cross-development toolchains are created and used.
21 For more information on toolchains, you can also see the
22 <a class="link" href="../sdk-manual/index.html" target="_self">Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</a>
23 manual.
24 </p>
25<p>
26 In the Yocto Project development environment, cross-development
27 toolchains are used to build the image and applications that run
28 on the target hardware.
29 With just a few commands, the OpenEmbedded build system creates
30 these necessary toolchains for you.
31 </p>
32<p>
33 The following figure shows a high-level build environment regarding
34 toolchain construction and use.
35 </p>
36<p>
37 </p>
38<table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="720"><tr style="height: 540px"><td align="center"><img src="figures/cross-development-toolchains.png" align="middle" width="720"></td></tr></table>
39<p>
40 </p>
41<p>
42 Most of the work occurs on the Build Host.
43 This is the machine used to build images and generally work within the
44 the Yocto Project environment.
45 When you run BitBake to create an image, the OpenEmbedded build system
46 uses the host <code class="filename">gcc</code> compiler to bootstrap a
47 cross-compiler named <code class="filename">gcc-cross</code>.
48 The <code class="filename">gcc-cross</code> compiler is what BitBake uses to
49 compile source files when creating the target image.
50 You can think of <code class="filename">gcc-cross</code> simply as an
51 automatically generated cross-compiler that is used internally within
52 BitBake only.
53 </p>
54<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
55<h3 class="title">Note</h3>
56 The extensible SDK does not use
57 <code class="filename">gcc-cross-canadian</code> since this SDK
58 ships a copy of the OpenEmbedded build system and the sysroot
59 within it contains <code class="filename">gcc-cross</code>.
60 </div>
61<p>
62 </p>
63<p>
64 The chain of events that occurs when <code class="filename">gcc-cross</code> is
65 bootstrapped is as follows:
66 </p>
67<pre class="literallayout">
68 gcc -&gt; binutils-cross -&gt; gcc-cross-initial -&gt; linux-libc-headers -&gt; glibc-initial -&gt; glibc -&gt; gcc-cross -&gt; gcc-runtime
69 </pre>
70<p>
71 </p>
72<div class="itemizedlist"><ul class="itemizedlist" type="disc">
73<li class="listitem"><p>
74 <code class="filename">gcc</code>:
75 The build host's GNU Compiler Collection (GCC).
76 </p></li>
77<li class="listitem"><p>
78 <code class="filename">binutils-cross</code>:
79 The bare minimum binary utilities needed in order to run
80 the <code class="filename">gcc-cross-initial</code> phase of the
81 bootstrap operation.
82 </p></li>
83<li class="listitem"><p>
84 <code class="filename">gcc-cross-initial</code>:
85 An early stage of the bootstrap process for creating
86 the cross-compiler.
87 This stage builds enough of the <code class="filename">gcc-cross</code>,
88 the C library, and other pieces needed to finish building the
89 final cross-compiler in later stages.
90 This tool is a "native" package (i.e. it is designed to run on
91 the build host).
92 </p></li>
93<li class="listitem"><p>
94 <code class="filename">linux-libc-headers</code>:
95 Headers needed for the cross-compiler.
96 </p></li>
97<li class="listitem"><p>
98 <code class="filename">glibc-initial</code>:
99 An initial version of the Embedded GLIBC needed to bootstrap
100 <code class="filename">glibc</code>.
101 </p></li>
102<li class="listitem">
103<p>
104 <code class="filename">gcc-cross</code>:
105 The final stage of the bootstrap process for the
106 cross-compiler.
107 This stage results in the actual cross-compiler that
108 BitBake uses when it builds an image for a targeted
109 device.
110 </p>
111<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
112<h3 class="title">Note</h3>
113 If you are replacing this cross compiler toolchain
114 with a custom version, you must replace
115 <code class="filename">gcc-cross</code>.
116 </div>
117<p>
118 This tool is also a "native" package (i.e. it is
119 designed to run on the build host).
120 </p>
121</li>
122<li class="listitem"><p>
123 <code class="filename">gcc-runtime</code>:
124 Runtime libraries resulting from the toolchain bootstrapping
125 process.
126 This tool produces a binary that consists of the
127 runtime libraries need for the targeted device.
128 </p></li>
129</ul></div>
130<p>
131 </p>
132<p>
133 You can use the OpenEmbedded build system to build an installer for
134 the relocatable SDK used to develop applications.
135 When you run the installer, it installs the toolchain, which contains
136 the development tools (e.g., the
137 <code class="filename">gcc-cross-canadian</code>),
138 <code class="filename">binutils-cross-canadian</code>, and other
139 <code class="filename">nativesdk-*</code> tools,
140 which are tools native to the SDK (i.e. native to
141 <a class="link" href="../ref-manual/var-SDK_ARCH.html" target="_self"><code class="filename">SDK_ARCH</code></a>),
142 you need to cross-compile and test your software.
143 The figure shows the commands you use to easily build out this
144 toolchain.
145 This cross-development toolchain is built to execute on the
146 <a class="link" href="../ref-manual/var-SDKMACHINE.html" target="_self"><code class="filename">SDKMACHINE</code></a>,
147 which might or might not be the same
148 machine as the Build Host.
149 </p>
150<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
151<h3 class="title">Note</h3>
152 If your target architecture is supported by the Yocto Project,
153 you can take advantage of pre-built images that ship with the
154 Yocto Project and already contain cross-development toolchain
155 installers.
156 </div>
157<p>
158 </p>
159<p>
160 Here is the bootstrap process for the relocatable toolchain:
161 </p>
162<pre class="literallayout">
163 gcc -&gt; binutils-crosssdk -&gt; gcc-crosssdk-initial -&gt; linux-libc-headers -&gt;
164 glibc-initial -&gt; nativesdk-glibc -&gt; gcc-crosssdk -&gt; gcc-cross-canadian
165 </pre>
166<p>
167 </p>
168<div class="itemizedlist"><ul class="itemizedlist" type="disc">
169<li class="listitem"><p>
170 <code class="filename">gcc</code>:
171 The build host's GNU Compiler Collection (GCC).
172 </p></li>
173<li class="listitem"><p>
174 <code class="filename">binutils-crosssdk</code>:
175 The bare minimum binary utilities needed in order to run
176 the <code class="filename">gcc-crosssdk-initial</code> phase of the
177 bootstrap operation.
178 </p></li>
179<li class="listitem"><p>
180 <code class="filename">gcc-crosssdk-initial</code>:
181 An early stage of the bootstrap process for creating
182 the cross-compiler.
183 This stage builds enough of the
184 <code class="filename">gcc-crosssdk</code> and supporting pieces so that
185 the final stage of the bootstrap process can produce the
186 finished cross-compiler.
187 This tool is a "native" binary that runs on the build host.
188 </p></li>
189<li class="listitem"><p>
190 <code class="filename">linux-libc-headers</code>:
191 Headers needed for the cross-compiler.
192 </p></li>
193<li class="listitem"><p>
194 <code class="filename">glibc-initial</code>:
195 An initial version of the Embedded GLIBC needed to bootstrap
196 <code class="filename">nativesdk-glibc</code>.
197 </p></li>
198<li class="listitem"><p>
199 <code class="filename">nativesdk-glibc</code>:
200 The Embedded GLIBC needed to bootstrap the
201 <code class="filename">gcc-crosssdk</code>.
202 </p></li>
203<li class="listitem"><p>
204 <code class="filename">gcc-crosssdk</code>:
205 The final stage of the bootstrap process for the
206 relocatable cross-compiler.
207 The <code class="filename">gcc-crosssdk</code> is a transitory compiler
208 and never leaves the build host.
209 Its purpose is to help in the bootstrap process to create the
210 eventual relocatable <code class="filename">gcc-cross-canadian</code>
211 compiler, which is relocatable.
212 This tool is also a "native" package (i.e. it is
213 designed to run on the build host).
214 </p></li>
215<li class="listitem"><p>
216 <code class="filename">gcc-cross-canadian</code>:
217 The final relocatable cross-compiler.
218 When run on the
219 <a class="link" href="../ref-manual/var-SDKMACHINE.html" target="_self"><code class="filename">SDKMACHINE</code></a>,
220 this tool
221 produces executable code that runs on the target device.
222 Only one cross-canadian compiler is produced per architecture
223 since they can be targeted at different processor optimizations
224 using configurations passed to the compiler through the
225 compile commands.
226 This circumvents the need for multiple compilers and thus
227 reduces the size of the toolchains.
228 </p></li>
229</ul></div>
230<p>
231 </p>
232<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
233<h3 class="title">Note</h3>
234 For information on advantages gained when building a
235 cross-development toolchain installer, see the
236 "<a class="link" href="../sdk-manual/sdk-building-an-sdk-installer.html" target="_self">Building an SDK Installer</a>"
237 section in the Yocto Project Application Development and the
238 Extensible Software Development Kit (eSDK) manual.
239 </div>
240</div></body>
241</html>
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