On Tue, 2013-07-09 at 16:31 +0200, Roberto Nunnari wrote: > // configure gcc > # mkdir gcc-build && cd gcc-build > # ../gcc-4.8.1/gcc/configure --prefix=/opt/gcc481 > --enable-languages=c,fortran --with-gmp=/opt/gmp --with-isl=/opt/isl > --with-cloog=/opt/cloog > ... > configure: WARNING: unrecognized options: --with-gmp, --with-isl, > --with-cloog Your most immediate problem is that you're running gcc-4.8.1/gcc/configure when you should be running gcc-4.8.1/configure. ^^^ The configure script inside the gcc subdirectory ONLY configures the compiler itself, it doesn't know about all the other extra stuff. That's why it doesn't recognize those extra configure flags.