--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2011-10-03  Bruno Haible  <bruno@clisp.org>
+
+	relocatable-lib[-lgpl]: Avoid expensive /proc access on Linux, Cygwin.
+	* lib/relocatable.c (ENABLE_COSTLY_RELOCATABLE): New macro.
+	(compute_curr_prefix, shared_library_fullname,
+	find_shared_library_fullname, get_shared_library_fullname, relocate):
+	Use it together with PIC && INSTALLDIR.
+	Reported by <jojelino@gmail.com>
+	via Charles Wilson <cygwin@cwilson.fastmail.fm>.
+
 2011-10-01  Jim Meyering  <meyering@redhat.com>
 
 	maint.mk: adjust a release-related rule not to require use of gzip

--- a/lib/relocatable.c
+++ b/lib/relocatable.c
@@ -85,6 +85,19 @@
 # define FILE_SYSTEM_PREFIX_LEN(P) 0
 #endif
 
+/* Whether to enable the more costly support for relocatable libraries.
+   It allows libraries to be have been installed with a different original
+   prefix than the program.  But it is quite costly, especially on Cygwin
+   platforms, see below.  Therefore we enable it by default only on native
+   Win32 platforms.  */
+#ifndef ENABLE_COSTLY_RELOCATABLE
+# if (defined _WIN32 || defined __WIN32__) && !defined __CYGWIN__
+#  define ENABLE_COSTLY_RELOCATABLE 1
+# else
+#  define ENABLE_COSTLY_RELOCATABLE 0
+# endif
+#endif
+
 /* Original installation prefix.  */
 static char *orig_prefix;
 static size_t orig_prefix_len;
@@ -154,7 +167,7 @@
 #endif
 }
 
-#if !defined IN_LIBRARY || (defined PIC && defined INSTALLDIR)
+#if !defined IN_LIBRARY || (defined PIC && defined INSTALLDIR && ENABLE_COSTLY_RELOCATABLE)
 
 /* Convenience function:
    Computes the current installation prefix, based on the original
@@ -284,7 +297,7 @@
 
 #endif /* !IN_LIBRARY || PIC */
 
-#if defined PIC && defined INSTALLDIR
+#if defined PIC && defined INSTALLDIR && ENABLE_COSTLY_RELOCATABLE
 
 /* Full pathname of shared library, or NULL.  */
 static char *shared_library_fullname;
@@ -330,7 +343,9 @@
 #if (defined __linux__ && (__GLIBC__ >= 2 || defined __UCLIBC__)) || defined __CYGWIN__
   /* Linux has /proc/self/maps. glibc 2 and uClibc have the getline()
      function.
-     Cygwin >= 1.5 has /proc/self/maps and the getline() function too.  */
+     Cygwin >= 1.5 has /proc/self/maps and the getline() function too.
+     But it is costly: ca. 0.3 ms on Linux, 3 ms on Cygwin 1.5, and 5 ms on
+     Cygwin 1.7.  */
   FILE *fp;
 
   /* Open the current process' maps file.  It describes one VMA per line.  */
@@ -403,7 +418,7 @@
 const char *
 relocate (const char *pathname)
 {
-#if defined PIC && defined INSTALLDIR
+#if defined PIC && defined INSTALLDIR && ENABLE_COSTLY_RELOCATABLE
   static int initialized;
 
   /* Initialization code for a shared library.  */