+ <sect2 id="sec-platforms">
+ <title>Platform settings</title>
+ <indexterm><primary>Platform settings</primary>
+ </indexterm>
+
+ <para>There are three platforms of interest when building GHC:</para>
+
+ <variablelist>
+ <varlistentry>
+ <term>The <emphasis>build</emphasis> platform</term>
+ <listitem>
+ <para>The platform on which we are doing this build.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>The <emphasis>host</emphasis> platform</term>
+ <listitem>
+ <para>The platform on which these binaries will run.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>The <emphasis>target</emphasis> platform</term>
+ <listitem>
+ <para>The platform for which this compiler will generate code.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>These platforms are set when running the
+ <literal>configure</literal> script, using the
+ <option>--build</option>, <option>--host</option>, and
+ <option>--target</option> options. The <filename>mk/config.mk</filename>
+ file defines several symbols related to the platform settings (see
+ <filename>mk/config.mk</filename> for details).</para>
+
+ <para>We don't currently support build & host being different, because
+ the build process creates binaries that are both run during the build,
+ and also installed.</para>
+
+ <para>If host and target are different, then we are building a
+ cross-compiler. For GHC, this means a compiler
+ which will generate intermediate .hc files to port to the target
+ architecture for bootstrapping. The libraries and stage 2 compiler
+ will be built as HC files for the target system (see <xref
+ linkend="sec-porting-ghc" /> for details.</para>
+
+ <para>More details on when to use BUILD, HOST or TARGET can be found in
+ the comments in <filename>config.mk</filename>.</para>
+ </sect2>
+