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| Next: <a href="Top-Level.html#Top-Level" accesskey="n" rel="next">Top Level</a>, Up: <a href="Source-Tree.html#Source-Tree" accesskey="u" rel="up">Source Tree</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Configure-Terms-and-History"></a> |
| <h3 class="section">6.1 Configure Terms and History</h3> |
| <a name="index-configure-terms"></a> |
| <a name="index-canadian"></a> |
| |
| <p>The configure and build process has a long and colorful history, and can |
| be confusing to anyone who doesn’t know why things are the way they are. |
| While there are other documents which describe the configuration process |
| in detail, here are a few things that everyone working on GCC should |
| know. |
| </p> |
| <p>There are three system names that the build knows about: the machine you |
| are building on (<em>build</em>), the machine that you are building for |
| (<em>host</em>), and the machine that GCC will produce code for |
| (<em>target</em>). When you configure GCC, you specify these with |
| <samp>--build=</samp>, <samp>--host=</samp>, and <samp>--target=</samp>. |
| </p> |
| <p>Specifying the host without specifying the build should be avoided, as |
| <code>configure</code> may (and once did) assume that the host you specify |
| is also the build, which may not be true. |
| </p> |
| <p>If build, host, and target are all the same, this is called a |
| <em>native</em>. If build and host are the same but target is different, |
| this is called a <em>cross</em>. If build, host, and target are all |
| different this is called a <em>canadian</em> (for obscure reasons dealing |
| with Canada’s political party and the background of the person working |
| on the build at that time). If host and target are the same, but build |
| is different, you are using a cross-compiler to build a native for a |
| different system. Some people call this a <em>host-x-host</em>, |
| <em>crossed native</em>, or <em>cross-built native</em>. If build and target |
| are the same, but host is different, you are using a cross compiler to |
| build a cross compiler that produces code for the machine you’re |
| building on. This is rare, so there is no common way of describing it. |
| There is a proposal to call this a <em>crossback</em>. |
| </p> |
| <p>If build and host are the same, the GCC you are building will also be |
| used to build the target libraries (like <code>libstdc++</code>). If build and host |
| are different, you must have already built and installed a cross |
| compiler that will be used to build the target libraries (if you |
| configured with <samp>--target=foo-bar</samp>, this compiler will be called |
| <code>foo-bar-gcc</code>). |
| </p> |
| <p>In the case of target libraries, the machine you’re building for is the |
| machine you specified with <samp>--target</samp>. So, build is the machine |
| you’re building on (no change there), host is the machine you’re |
| building for (the target libraries are built for the target, so host is |
| the target you specified), and target doesn’t apply (because you’re not |
| building a compiler, you’re building libraries). The configure/make |
| process will adjust these variables as needed. It also sets |
| <code>$with_cross_host</code> to the original <samp>--host</samp> value in case you |
| need it. |
| </p> |
| <p>The <code>libiberty</code> support library is built up to three times: once |
| for the host, once for the target (even if they are the same), and once |
| for the build if build and host are different. This allows it to be |
| used by all programs which are generated in the course of the build |
| process. |
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