source: http://patchwork.ozlabs.org/patch/129800/
Upstream-Status: Submitted

ChangeLog
        * Makefile.in (gcc_gxx_include_dir_add_sysroot): New.
          (PREPROCESSOR_DEFINES): Define GPLUSPLUS_INCLUDE_DIR_ADD_SYSROOT.

        * cppdefault.c (cpp_include_defaults): replace hard coded "1" with
          GPLUSPLUS_INCLUDE_DIR_ADD_SYSROOT for "add_sysroot" field.

        * configure.ac (AC_SUBST): Add gcc_gxx_include_dir_add_sysroot to
          control whether sysroot should be prepended to gxx include dir.

        * configure: Regenerate.

Hi, this is a follow up for issue "http://codereview.appspot.com/4641076".

The rationale for the patch copied from previous thread:
=======================================
The setup:

Configuring a toolchain targeting x86-64 GNU Linux (Ubuntu Lucid), as a
cross-compiler.  Using a sysroot to provide the Lucid headers+libraries,
with the sysroot path being within the GCC install tree.  Want to use the
Lucid system libstdc++ and headers, which means that I'm not
building/installing libstdc++-v3.

So, configuring with:
  --with-sysroot="$SYSROOT"
  --disable-libstdc++-v3 \
  --with-gxx-include-dir="$SYSROOT/usr/include/c++/4.4" \
(among other options).

Hoping to support two usage models with this configuration, w.r.t. use of
the sysroot:

(1) somebody installs the sysroot in the normal location relative to the
GCC install, and relocates the whole bundle (sysroot+GCC).  This works
great AFAICT, GCC finds its includes (including the C++ includes) thanks
to the add_standard_paths iprefix handling.

(2) somebody installs the sysroot in a non-standard location, and uses
--sysroot to try to access it.  This works fine for the C headers, but
doesn't work.

For the C headers, add_standard_paths prepends the sysroot location to
the /usr/include path (since that's what's specified in cppdefault.c for
that path).  It doesn't do the same for the C++ include path, though
(again, as specified in cppdefault.c).

add_standard_paths doesn't attempt to relocate built-in include paths that
start with the compiled-in sysroot location (e.g., the g++ include dir, in
this case).  This isn't surprising really: normally you either prepend the
sysroot location or you don't (as specified by cppdefault.c); none of the
built-in paths normally *start* with the sysroot location and need to be
relocated.  However, in this odd-ball case of trying to use the C++ headers
from the sysroot, one of the paths *does* need to be relocated in this way.
===========================
Index: gcc-4_6-branch/gcc/Makefile.in
===================================================================
--- gcc-4_6-branch.orig/gcc/Makefile.in	2011-12-13 22:52:15.000000000 -0800
+++ gcc-4_6-branch/gcc/Makefile.in	2011-12-13 22:52:21.933635767 -0800
@@ -587,6 +587,7 @@
 build_tooldir = $(exec_prefix)/$(target_noncanonical)
 # Directory in which the compiler finds target-independent g++ includes.
 gcc_gxx_include_dir = @gcc_gxx_include_dir@
+gcc_gxx_include_dir_add_sysroot = @gcc_gxx_include_dir_add_sysroot@
 # Directory to search for site-specific includes.
 local_includedir = $(local_prefix)/include
 includedir = $(prefix)/include
@@ -3964,6 +3965,7 @@
   -DGCC_INCLUDE_DIR=\"$(libsubdir)/include\" \
   -DFIXED_INCLUDE_DIR=\"$(libsubdir)/include-fixed\" \
   -DGPLUSPLUS_INCLUDE_DIR=\"$(gcc_gxx_include_dir)\" \
+  -DGPLUSPLUS_INCLUDE_DIR_ADD_SYSROOT=$(gcc_gxx_include_dir_add_sysroot) \
   -DGPLUSPLUS_TOOL_INCLUDE_DIR=\"$(gcc_gxx_include_dir)/$(target_noncanonical)\" \
   -DGPLUSPLUS_BACKWARD_INCLUDE_DIR=\"$(gcc_gxx_include_dir)/backward\" \
   -DLOCAL_INCLUDE_DIR=\"$(local_includedir)\" \
Index: gcc-4_6-branch/gcc/configure.ac
===================================================================
--- gcc-4_6-branch.orig/gcc/configure.ac	2011-12-13 22:52:15.000000000 -0800
+++ gcc-4_6-branch/gcc/configure.ac	2011-12-13 22:52:21.937635526 -0800
@@ -144,6 +144,15 @@
   fi
 fi
 
+gcc_gxx_include_dir_add_sysroot=0
+if test "${with_sysroot+set}" = set; then :
+  gcc_gxx_without_sysroot=`expr "${gcc_gxx_include_dir}" : "${with_sysroot}"'\(.*\)'`
+  if test "${gcc_gxx_without_sysroot}"; then :
+    gcc_gxx_include_dir="${gcc_gxx_without_sysroot}"
+    gcc_gxx_include_dir_add_sysroot=1
+  fi
+fi
+
 AC_ARG_WITH(cpp_install_dir,
 [  --with-cpp-install-dir=DIR
                           install the user visible C preprocessor in DIR
@@ -4737,6 +4746,7 @@
 AC_SUBST(float_h_file)
 AC_SUBST(gcc_config_arguments)
 AC_SUBST(gcc_gxx_include_dir)
+AC_SUBST(gcc_gxx_include_dir_add_sysroot)
 AC_SUBST(host_exeext)
 AC_SUBST(host_xm_file_list)
 AC_SUBST(host_xm_include_list)
Index: gcc-4_6-branch/gcc/cppdefault.c
===================================================================
--- gcc-4_6-branch.orig/gcc/cppdefault.c	2011-12-13 22:51:28.000000000 -0800
+++ gcc-4_6-branch/gcc/cppdefault.c	2011-12-13 22:52:21.937635526 -0800
@@ -48,15 +48,18 @@
 = {
 #ifdef GPLUSPLUS_INCLUDE_DIR
     /* Pick up GNU C++ generic include files.  */
-    { GPLUSPLUS_INCLUDE_DIR, "G++", 1, 1, 0, 0 },
+    { GPLUSPLUS_INCLUDE_DIR, "G++", 1, 1,
+      GPLUSPLUS_INCLUDE_DIR_ADD_SYSROOT, 0 },
 #endif
 #ifdef GPLUSPLUS_TOOL_INCLUDE_DIR
     /* Pick up GNU C++ target-dependent include files.  */
-    { GPLUSPLUS_TOOL_INCLUDE_DIR, "G++", 1, 1, 0, 1 },
+    { GPLUSPLUS_TOOL_INCLUDE_DIR, "G++", 1, 1,
+      GPLUSPLUS_INCLUDE_DIR_ADD_SYSROOT, 1 },
 #endif
 #ifdef GPLUSPLUS_BACKWARD_INCLUDE_DIR
     /* Pick up GNU C++ backward and deprecated include files.  */
-    { GPLUSPLUS_BACKWARD_INCLUDE_DIR, "G++", 1, 1, 0, 0 },
+    { GPLUSPLUS_BACKWARD_INCLUDE_DIR, "G++", 1, 1,
+      GPLUSPLUS_INCLUDE_DIR_ADD_SYSROOT, 0 },
 #endif
 #ifdef GCC_INCLUDE_DIR
     /* This is the dir for gcc's private headers.  */
Index: gcc-4_6-branch/gcc/configure
===================================================================
--- gcc-4_6-branch.orig/gcc/configure	2011-12-13 22:52:15.000000000 -0800
+++ gcc-4_6-branch/gcc/configure	2011-12-13 22:52:33.185690436 -0800
@@ -636,6 +636,7 @@
 host_xm_include_list
 host_xm_file_list
 host_exeext
+gcc_gxx_include_dir_add_sysroot
 gcc_gxx_include_dir
 gcc_config_arguments
 float_h_file
@@ -3313,6 +3314,15 @@
   fi
 fi
 
+gcc_gxx_include_dir_add_sysroot=0
+if test "${with_sysroot+set}" = set; then :
+  gcc_gxx_without_sysroot=`expr "${gcc_gxx_include_dir}" : "${with_sysroot}"'\(.*\)'`
+  if test "${gcc_gxx_without_sysroot}"; then :
+    gcc_gxx_include_dir="${gcc_gxx_without_sysroot}"
+    gcc_gxx_include_dir_add_sysroot=1
+  fi
+fi
+
 
 # Check whether --with-cpp_install_dir was given.
 if test "${with_cpp_install_dir+set}" = set; then :
@@ -17514,7 +17524,7 @@
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 17517 "configure"
+#line 17527 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -17620,7 +17630,7 @@
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 17623 "configure"
+#line 17633 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -26151,6 +26161,7 @@
 
 
 
+