How do I override GCC's configuration for include searching? - c++

Question

Environment:
Ubuntu, GCC 4.6.3
Using Qt 4.8
By default, my include search order (as reported by gcc -v) is:
<clipped out my project specific includes>
/usr/include/c++/4.6
/usr/include/c++/4.6/x86_64-linux-gnu/.
/usr/include/c++/4.6/backward
/usr/lib/gcc/x86_64-linux-gnu/4.6/include
/usr/local/include
/usr/lib/gcc/x86_64-linux-gnu/4.6/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
I am trying to archive this build environment so that it doesn't build from the actual system folders, but only from a source tree that is checked-in and well-defined if my machine is recreated. I am running into issues overriding the system search paths for gcc.
Specifically, I first tried --sysroot=../../sysroot, but only the last two include folders changed:
/usr/include/c++/4.6
/usr/include/c++/4.6/x86_64-linux-gnu/.
/usr/include/c++/4.6/backward
/usr/lib/gcc/x86_64-linux-gnu/4.6/include
/usr/lib/gcc/x86_64-linux-gnu/4.6/include-fixed
../../sysroot/usr/include/x86_64-linux-gnu
../../sysroot/usr/include
GCC -v reports:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v
--with-pkgversion='Ubuntu/Linaro 4.6.3-1ubuntu5'
--with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.6
--enable-shared --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib
--enable-nls
--with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin
--enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)
So it appears that the /usr/lib/... and /usr/include... lines may be coming from the built-in GCC configuration. I'm a GCC/G++ noob, so I could be wrong here - please correct as appropriate.
At any rate, my question is how I change my configuration so that these folders:
/usr/include/c++/4.6
/usr/include/c++/4.6/x86_64-linux-gnu/.
/usr/include/c++/4.6/backward
/usr/lib/gcc/x86_64-linux-gnu/4.6/include
/usr/lib/gcc/x86_64-linux-gnu/4.6/include-fixed
are also relative to ../../sysroot?
(To be clear, I know about -I and these are not being specified on the command line, or in the make file.)
I can get almost the right result by using -nostdinc and specifying each folder directly (with -I), except the Qt Meta-Object-Compiler fails when it is fed some of these system include folders. Because I am using Qt, I want to change GCC's configured search paths instead of just listing every single system folder individually with -I.
Any advice would be greatly appreciated.
Thanks,
Brad

Answer 1

Just as one of possible solution directions, maybe too much for your case:
Actually as I understand what you are trying to achieve is close to cross-compilation against different system image. This task is very common in embedded development though it is not so easy. Most of idea is to build GCC so it 'thinks' system image is in place different from normal.
This link should at least help you to understand basic principles.
This is another and what's more it contains other useful links like cross-compiling FAQ.