gcc/4.7: add patch to warn about unsafe header paths

This commit adds a patch to gcc borrowed from CodeSourcery/Yocto that
warns about unsafe include paths (i.e /usr/include,
/usr/local/include, etc.). The patch was adapted to gcc 4.7.4, and
modified to support the BR_COMPILER_PARANOID_UNSAFE_PATH environment
variable to error out instead of just warn when unsafe paths are
used. Even though erroring out can be chosen by passing
-Werror=poison-system-directories, we are not sure this option in
CFLAGS will always be passed, so having an environment variable
guarantees it will always be passed, and also allows to have an
identical behavior to the external toolchain wrapper.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Romain Naour <romain.naour@openwide.fr>

package/gcc/4.7.4/910-gcc-poison-system-directories.patch

@@ -0,0 +1,207 @@
+From 160397ef3c3331099af028f1b8d3e085b07d88ad Mon Sep 17 00:00:00 2001
+From: Khem Raj <raj.khem@gmail.com>
+Date: Fri, 29 Mar 2013 08:59:00 +0400
+Subject: [PATCH 16/35] gcc: poison-system-directories
+
+Adapted to Buildroot and gcc 4.7.4 by Thomas Petazzoni, especially the
+addition of the BR_COMPILER_PARANOID_UNSAFE_PATH environment variable.
+
+Signed-off-by: Khem Raj <raj.khem@gmail.com>
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+
+Upstream-Status: Inappropriate [distribution: codesourcery]
+---
+ gcc/Makefile.in     |    2 +-
+ gcc/common.opt      |    4 ++++
+ gcc/config.in       |    6 ++++++
+ gcc/configure       |   20 ++++++++++++++++++--
+ gcc/configure.ac    |   10 ++++++++++
+ gcc/doc/invoke.texi |    9 +++++++++
+ gcc/gcc.c           |    2 ++
+ gcc/incpath.c       |   19 +++++++++++++++++++
+ 8 files changed, 69 insertions(+), 3 deletions(-)
+
+Index: b/gcc/common.opt
+===================================================================
+--- a/gcc/common.opt
++++ b/gcc/common.opt
+@@ -585,6 +585,10 @@
+ Common Var(warn_padded) Warning
+ Warn when padding is required to align structure members
+ 
++Wpoison-system-directories
++Common Var(flag_poison_system_directories) Init(1) Warning
++Warn for -I and -L options using system directories if cross compiling
++
+ Wshadow
+ Common Var(warn_shadow) Warning
+ Warn when one local variable shadows another
+Index: b/gcc/config.in
+===================================================================
+--- a/gcc/config.in
++++ b/gcc/config.in
+@@ -144,6 +144,12 @@
+ #endif
+ 
+ 
++/* Define to warn for use of native system header directories */
++#ifndef USED_FOR_TARGET
++#undef ENABLE_POISON_SYSTEM_DIRECTORIES
++#endif
++
++
+ /* Define if you want all operations on RTL (the basic data structure of the
+    optimizer and back end) to be checked for dynamic type safety at runtime.
+    This is quite expensive. */
+Index: b/gcc/configure
+===================================================================
+--- a/gcc/configure
++++ b/gcc/configure
+@@ -918,6 +918,7 @@
+ with_system_zlib
+ enable_maintainer_mode
+ enable_version_specific_runtime_libs
++enable_poison_system_directories
+ enable_plugin
+ enable_libquadmath_support
+ with_linker_hash_style
+@@ -1632,6 +1633,8 @@
+   --enable-version-specific-runtime-libs
+                           specify that runtime libraries should be installed
+                           in a compiler-specific directory
++  --enable-poison-system-directories
++                          warn for use of native system header directories
+   --enable-plugin         enable plugin support
+   --disable-libquadmath-support
+                           disable libquadmath support for Fortran
+@@ -27186,6 +27189,19 @@
+ fi
+ 
+ 
++# Check whether --enable-poison-system-directories was given.
++if test "${enable_poison_system_directories+set}" = set; then :
++  enableval=$enable_poison_system_directories;
++else
++  enable_poison_system_directories=no
++fi
++
++if test "x${enable_poison_system_directories}" = "xyes"; then
++
++$as_echo "#define ENABLE_POISON_SYSTEM_DIRECTORIES 1" >>confdefs.h
++
++fi
++
+ # Substitute configuration variables
+ 
+ 
+Index: b/gcc/configure.ac
+===================================================================
+--- a/gcc/configure.ac
++++ b/gcc/configure.ac
+@@ -5037,6 +5037,16 @@
+                 [specify that runtime libraries should be
+                  installed in a compiler-specific directory])])
+ 
++AC_ARG_ENABLE([poison-system-directories],
++             AS_HELP_STRING([--enable-poison-system-directories],
++                            [warn for use of native system header directories]),,
++             [enable_poison_system_directories=no])
++if test "x${enable_poison_system_directories}" = "xyes"; then
++  AC_DEFINE([ENABLE_POISON_SYSTEM_DIRECTORIES],
++           [1],
++           [Define to warn for use of native system header directories])
++fi
++
+ # Substitute configuration variables
+ AC_SUBST(subdirs)
+ AC_SUBST(srcdir)
+Index: b/gcc/doc/invoke.texi
+===================================================================
+--- a/gcc/doc/invoke.texi
++++ b/gcc/doc/invoke.texi
+@@ -260,6 +260,7 @@
+ -Woverlength-strings  -Wpacked  -Wpacked-bitfield-compat  -Wpadded @gol
+ -Wparentheses  -Wpedantic-ms-format -Wno-pedantic-ms-format @gol
+ -Wpointer-arith  -Wno-pointer-to-int-cast @gol
++-Wno-poison-system-directories @gol
+ -Wredundant-decls @gol
+ -Wreturn-type  -Wsequence-point  -Wshadow @gol
+ -Wsign-compare  -Wsign-conversion  -Wstack-protector @gol
+@@ -3880,6 +3881,14 @@
+  for most targets, it is made up of code and thus requires the stack
+  to be made executable in order for the program to work properly.
+ 
++@item -Wno-poison-system-directories
++@opindex Wno-poison-system-directories
++Do not warn for @option{-I} or @option{-L} options using system
++directories such as @file{/usr/include} when cross compiling.  This
++option is intended for use in chroot environments when such
++directories contain the correct headers and libraries for the target
++system rather than the host.
++
+ @item -Wfloat-equal
+ @opindex Wfloat-equal
+ @opindex Wno-float-equal
+Index: b/gcc/gcc.c
+===================================================================
+--- a/gcc/gcc.c
++++ b/gcc/gcc.c
+@@ -674,6 +674,8 @@
+     %{flto} %{flto=*} %l " LINK_PIE_SPEC \
+    "%X %{o*} %{e*} %{N} %{n} %{r}\
+     %{s} %{t} %{u*} %{z} %{Z} %{!nostdlib:%{!nostartfiles:%S}}\
++    %{Wno-poison-system-directories:--no-poison-system-directories}\
++    %{Werror=poison-system-directories:--error-poison-system-directories}\
+     %{static:} %{L*} %(mfwrap) %(link_libgcc) %o\
+     %{fopenmp|ftree-parallelize-loops=*:%:include(libgomp.spec)%(link_gomp)}\
+     %{fgnu-tm:%:include(libitm.spec)%(link_itm)}\
+@@ -3907,6 +3909,12 @@
+       gcc_assert (!compare_debug_opt);
+     }
+ 
++  temp = getenv("BR_COMPILER_PARANOID_UNSAFE_PATH");
++  if (temp && strlen(temp) > 0)
++    {
++      save_switch("-Werror=poison-system-directories", 0, NULL, false);
++    }
++
+   /* Set up the search paths.  We add directories that we expect to
+      contain GNU Toolchain components before directories specified by
+      the machine description so that we will find GNU components (like
+Index: b/gcc/incpath.c
+===================================================================
+--- a/gcc/incpath.c
++++ b/gcc/incpath.c
+@@ -30,6 +30,7 @@
+ #include "intl.h"
+ #include "incpath.h"
+ #include "cppdefault.h"
++#include "diagnostic-core.h"
+ 
+ /* Microsoft Windows does not natively support inodes.
+    VMS has non-numeric inodes.  */
+@@ -373,6 +374,24 @@
+ 	}
+       fprintf (stderr, _("End of search list.\n"));
+     }
++
++#ifdef ENABLE_POISON_SYSTEM_DIRECTORIES
++  if (flag_poison_system_directories)
++    {
++       struct cpp_dir *p;
++
++       for (p = heads[QUOTE]; p; p = p->next)
++         {
++          if ((!strncmp (p->name, "/usr/include", 12))
++              || (!strncmp (p->name, "/usr/local/include", 18))
++              || (!strncmp (p->name, "/usr/X11R6/include", 18)))
++            warning (OPT_Wpoison_system_directories,
++                     "include location \"%s\" is unsafe for "
++                     "cross-compilation",
++                     p->name);
++         }
++    }
++#endif
+ }
+ 
+ /* Use given -I paths for #include "..." but not #include <...>, and