some question about gc

[zouq]

i am trying to port a front end to gcc,
and i am confused with the gc,
i see from the file gengtype.c, it can generate many files automaticlly,
but i don`t understand the rule to generate it, i can only understand
firstly use the yacc to analysize the gtfiles, then output something ,
and this is just what i don`t understand.

 can some one tell me about it, or tell me where i can get more
information about it.
thanks a lot.