diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index bf8f895ded6..bdc6b36c96c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,15 @@
+2006-11-20  Carlos O'Donell  <carlos@codesourcery.com>
+	    Mark Mitchell  <mark@codesourcery.com>
+
+	* cppdefault.c: Define cpp_PREFIX, cpp_PREFIX_len, and 
+	gcc_exec_prefix.
+	(cpp_relocated): New function.
+	* cppdefault.h: Declare cpp_PREFIX, cpp_PREFIX_len, gcc_exec_prefix 
+	and cpp_relocated. 
+	* Makefile.in (PREPROCESSOR_DEFINES): Add -DPREFIX option.
+	* c-incpath.c (add_standard_paths): Call cpp_relocated. If relocated,
+	replace configured prefix with gcc_exec_prefix. 
+
 2006-11-20  Bernd Schmidt  <bernd.schmidt@analog.com>
 
 	* config/bfin/bfin.h (LEGITIMATE_CONSTANT_P): Call
diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 8136290694e..c6334d70ec9 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -3071,6 +3071,7 @@ PREPROCESSOR_DEFINES = \
   -DLOCAL_INCLUDE_DIR=\"$(local_includedir)\" \
   -DCROSS_INCLUDE_DIR=\"$(CROSS_SYSTEM_HEADER_DIR)\" \
   -DTOOL_INCLUDE_DIR=\"$(gcc_tooldir)/include\" \
+  -DPREFIX=\"$(prefix)\" \
   @TARGET_SYSTEM_ROOT_DEFINE@
 
 cppdefault.o: cppdefault.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) \
diff --git a/gcc/c-incpath.c b/gcc/c-incpath.c
index 0e534dd2337..2c5ac6db89f 100644
--- a/gcc/c-incpath.c
+++ b/gcc/c-incpath.c
@@ -127,6 +127,7 @@ add_standard_paths (const char *sysroot, const char *iprefix,
 		    const char *imultilib, int cxx_stdinc)
 {
   const struct default_include *p;
+  int relocated = cpp_relocated();
   size_t len;
 
   if (iprefix && (len = cpp_GCC_INCLUDE_DIR_len) != 0)
@@ -163,6 +164,17 @@ add_standard_paths (const char *sysroot, const char *iprefix,
 	  /* Should this directory start with the sysroot?  */
 	  if (sysroot && p->add_sysroot)
 	    str = concat (sysroot, p->fname, NULL);
+	  else if (!p->add_sysroot && relocated)
+	    {
+	      /* If the compiler is relocated, and this is a configured 
+		 prefix relative path, then we use gcc_exec_prefix instead 
+		 of the configured prefix.  */
+	      gcc_assert (strncmp (p->fname, cpp_PREFIX,
+				     cpp_PREFIX_len) == 0);
+	      str = concat (gcc_exec_prefix, p->fname
+			      + cpp_PREFIX_len, NULL);
+	      str = update_path (str, p->component);
+	    }
 	  else
 	    str = update_path (p->fname, p->component);
 
diff --git a/gcc/cppdefault.c b/gcc/cppdefault.c
index d040558b54c..c72cb390aba 100644
--- a/gcc/cppdefault.c
+++ b/gcc/cppdefault.c
@@ -96,3 +96,31 @@ const size_t cpp_GCC_INCLUDE_DIR_len = sizeof GCC_INCLUDE_DIR - 8;
 const char cpp_GCC_INCLUDE_DIR[] = "";
 const size_t cpp_GCC_INCLUDE_DIR_len = 0;
 #endif
+
+/* The configured prefix.  */
+const char cpp_PREFIX[] = PREFIX;
+const size_t cpp_PREFIX_len = sizeof PREFIX - 1;
+
+/* This value is set by cpp_relocated at runtime */
+const char *gcc_exec_prefix;
+
+/* Return true if the toolchain is relocated.  */
+bool
+cpp_relocated (void)
+{
+  static int relocated = -1;
+
+  /* A relocated toolchain ignores standard include directories.  */
+  if (relocated == -1)
+    {
+      /* Check if the toolchain was relocated?  */
+      GET_ENVIRONMENT (gcc_exec_prefix, "GCC_EXEC_PREFIX");
+      if (gcc_exec_prefix)
+       relocated = 1;
+      else
+       relocated = 0;
+    }
+
+  return relocated;
+}
+
diff --git a/gcc/cppdefault.h b/gcc/cppdefault.h
index a3a24169554..2da6d05f564 100644
--- a/gcc/cppdefault.h
+++ b/gcc/cppdefault.h
@@ -52,4 +52,11 @@ extern const struct default_include cpp_include_defaults[];
 extern const char cpp_GCC_INCLUDE_DIR[];
 extern const size_t cpp_GCC_INCLUDE_DIR_len;
 
+extern const char cpp_PREFIX[];
+extern const size_t cpp_PREFIX_len;
+extern const char *gcc_exec_prefix;
+
+/* Return true if the toolchain is relocated.  */
+bool cpp_relocated (void);
+
 #endif /* ! GCC_CPPDEFAULT_H */