>>>gcc -c -g -I- -I. -Iada -I/cvs/gcc-svn/trunk/gcc/ada >>>/cvs/gcc-svn/trunk/gcc/ada/ada.ads -o ada/ada.o >>>ada.ads:16:01: language defined units may not be recompiled
So you need a -gnat<something> option, or compilation fails? Yes, because, as it says, the Ada standard does not permit recompilation of language-defined units. Obviously, we have to compile them as part of building the compiler and library, so -gnatg says to ignore that particular validity check.