X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fdocs%2Fusers_guide%2Ffaq.sgml;h=0c274d79c86e7b78a11f2748782394bd416dc5de;hb=5affd8114e7ba87fa289eb72760a597456aea4cb;hp=8055d15db8ed8a76cce280fdae97740322cfae04;hpb=8c58d23464c76f52c6aad7e6653908eb99e64743;p=ghc-hetmet.git

diff --git a/ghc/docs/users_guide/faq.sgml b/ghc/docs/users_guide/faq.sgml
index 8055d15..0c274d7 100644
--- a/ghc/docs/users_guide/faq.sgml
+++ b/ghc/docs/users_guide/faq.sgml
@@ -45,6 +45,34 @@
     </varlistentry>
     
     <varlistentry>
+      <term>Do I have to recompile all my code if I upgrade
+      GHC?</term>
+      <listitem>
+	<para>Yes.  There are two reasons for this:</para>
+	<itemizedlist>
+	  <listitem>
+	    <para>GHC does a lot of cross-module optimisation, so
+	    compiled code will include parts of the libraries it was
+	    compiled against (including the Prelude), so will be
+	    deeply tied to the actual version of those libraries it
+	    was compiled against.  When you upgrade GHC, the libraries
+	    may change; even if the external interface of the
+	    libraries doesn't change, sometimes internal details may
+	    change because GHC optimised the code in the library
+	    differently.</para>
+	  </listitem>
+	  <listitem>
+	    <para>We sometimes change the ABI (application binary
+	    interface) between versions of GHC.  Code compiled with
+	    one version of GHC is not necessarily compatible with code
+	    compiled by a different version, even if you arrange to
+	    keep the same libraries.</para>
+	  </listitem>
+	</itemizedlist>
+      </listitem>
+    </varlistentry>
+
+    <varlistentry>
       <term>Why doesn't GHC use shared libraries?</term>
       <listitem>
 	<para>The subject of shared libraries has come up several
@@ -277,6 +305,24 @@ details.</para>
       </listitem>
     </varlistentry>
 
+    <varlistentry>
+      <term>Why does linking take so long?</term>
+      <listitem>
+	<para>Linking a small program should take no more than a few
+	seconds.  Larger programs can take longer, but even linking
+	GHC itself only takes 3-4 seconds on our development
+	machines.</para>
+	
+	<para>Long link times have been attributed to using Sun's
+	linker on Solaris, as compared to GNU <command>ld</command>
+	which appears to be much faster.  So if you're on a Sun box,
+	try switching to GNU <command>ld</command>.  <ulink
+	url="http://www.haskell.org/pipermail/glasgow-haskell-users/2002-November/004477.html">This
+	article</ulink> from the mailing list has more
+	information.</para>
+      </listitem>
+    </varlistentry>
+
   </variablelist>
 </chapter>