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<HTML><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><!-- Created on September, 12 2004 by texi2html 1.64 --><!-- Written by: Lionel Cons <Lionel.Cons@cern.ch> (original author) Karl Berry <karl@freefriends.org> Olaf Bachmann <obachman@mathematik.uni-kl.de> and many others.Maintained by: Olaf Bachmann <obachman@mathematik.uni-kl.de>Send bugs and suggestions to <texi2html@mathematik.uni-kl.de> --><HEAD><TITLE>Autoconf, Automake, and Libtool: Supporting Cross Compiler in Configure</TITLE><META NAME="description" CONTENT="Autoconf, Automake, and Libtool: Supporting Cross Compiler in Configure"><META NAME="keywords" CONTENT="Autoconf, Automake, and Libtool: Supporting Cross Compiler in Configure"><META NAME="resource-type" CONTENT="document"><META NAME="distribution" CONTENT="global"><META NAME="Generator" CONTENT="texi2html 1.64"><script language="Javascript"><!-- // Check the browser version. function checkVersion() { if (navigator.appVersion.charAt(0)>=3) return true; if (navigator.appVersion.charAt(0)>=4) return true; 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If the compiler isa cross compiler, which means that this is a Canadian Cross,<SAMP>`cross_compiling'</SAMP> will be <SAMP>`yes'</SAMP>. In a normal configuration,<SAMP>`cross_compiling'</SAMP> will be <SAMP>`no'</SAMP>.</P><P>You ordinarily do not need to know the type of the build system in a<TT>`configure'</TT> script. However, if you do need that information, youcan get it by using the macro <SAMP>`AC_CANONICAL_SYSTEM'</SAMP>, the same macrowhich is used to determine the target system. This macro will set thevariables <SAMP>`build'</SAMP>, <SAMP>`build_alias'</SAMP>, <SAMP>`build_cpu'</SAMP>,<SAMP>`build_vendor'</SAMP>, and <SAMP>`build_os'</SAMP>, which correspond to thesimilar <SAMP>`target'</SAMP> and <SAMP>`host'</SAMP> variables, except that theydescribe the build system. See section <A HREF="autobook_261.html#SEC261">26.3 Using the Target Type</A>.</P><P>When writing tests in <TT>`configure.in'</TT>, you must remember that youwant to test the host environment, not the build environment. Macroswhich use the compiler, such as like <SAMP>`AC_CHECK_FUNCS'</SAMP>, will testthe host environment. That is because the tests will be done by runningthe compiler, which is actually a build cross host compiler. If thecompiler can find the function, that means that the function is presentin the host environment.</P><P>Tests like <SAMP>`test -f /dev/ptyp0'</SAMP>, on the other hand, will test thebuild environment. Remember that the <TT>`configure'</TT> script is runningon the build system, not the host system. If your <TT>`configure'</TT>scripts examines files, those files will be on the build system.Whatever you determine based on those files may or may not be the caseon the host system.</P><P>Most Autoconf macros will work correctly when building with a crosscompiler. The main exception is <SAMP>`AC_TRY_RUN'</SAMP>. This macro tries tocompile and run a test program. This will fail when building with across compiler, because the program will be compiled for the hostsystem, which means that it will not run on the build system.</P><P>The <SAMP>`AC_TRY_RUN'</SAMP> macro provides an optional argument to tell the<TT>`configure'</TT> script what to do when building with a cross compiler.If that argument is not present, you will get a warning when you run<SAMP>`autoconf'</SAMP>:<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>warning: AC_TRY_RUN called without default to allow cross compiling</FONT></pre></td></tr></table>This tells you that the resulting <TT>`configure'</TT> script will not workwhen building with a cross compiler.</P><P>In some cases while it may better to perform a test at configure time,it is also possible to perform the test at run time (see section <A HREF="autobook_226.html#SEC226">23.3.2 Testing system features at application runtime</A>). In such a case you can usethe cross compiling argument to <SAMP>`AC_TRY_RUN'</SAMP> to tell your programthat the test could not be performed at configure time.</P><P>There are a few other autoconf macros which will not work correctly whenbuilding with a cross compiler: a partial list is<SAMP>`AC_FUNC_GETPGRP'</SAMP>, <SAMP>`AC_FUNC_SETPGRP'</SAMP>,<SAMP>`AC_FUNC_SETVBUF_REVERSED'</SAMP>, and <SAMP>`AC_SYS_RESTARTABLE_SYSCALLS'</SAMP>.The <SAMP>`AC_CHECK_SIZEOF'</SAMP> macro is generally not very useful whenbuilding with a cross compiler; it permits an optional argumentindicating the default size, but there is no way to know what thecorrect default should be.</P><P><A NAME="Supporting Cross Compiler in Make"></A></TR></TABLE><BR> <FONT SIZE="-1">This document was generatedby <I>Gary V. Vaughan</I> on <I>September, 12 2004</I>using <A HREF="http://www.mathematik.uni-kl.de/~obachman/Texi2html"><I>texi2html</I></A></BODY></HTML>⌨️ 快捷键说明
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