Fixed Header Files
==================

   GNU CC needs to install corrected versions of some system header
files.  This is because most target systems have some header files that
won't work with GNU CC unless they are changed.  Some have bugs, some
are incompatible with ANSI C, and some depend on special features of
other compilers.

   Installing GNU CC automatically creates and installs the fixed header
files, by running a program called `fixincludes' (or for certain
targets an alternative such as `fixinc.svr4').  Normally, you don't
need to pay attention to this.  But there are cases where it doesn't do
the right thing automatically.

   * If you update the system's header files, such as by installing a
     new system version, the fixed header files of GNU CC are not
     automatically updated.  The easiest way to update them is to
     reinstall GNU CC.  (If you want to be clever, look in the makefile
     and you can find a shortcut.)

   * On some systems, in particular SunOS 4, header file directories
     contain machine-specific symbolic links in certain places.  This
     makes it possible to share most of the header files among hosts
     running the same version of SunOS 4 on different machine models.

     The programs that fix the header files do not understand this
     special way of using symbolic links; therefore, the directory of
     fixed header files is good only for the machine model used to
     build it.

     In SunOS 4, only programs that look inside the kernel will notice
     the difference between machine models.  Therefore, for most
     purposes, you need not be concerned about this.

     It is possible to make separate sets of fixed header files for the
     different machine models, and arrange a structure of symbolic
     links so as to use the proper set, but you'll have to do this by
     hand.

   * On Lynxos, GNU CC by default does not fix the header files.  This
     is because bugs in the shell cause the `fixincludes' script to
     fail.

     This means you will encounter problems due to bugs in the system
     header files.  It may be no comfort that they aren't GNU CC's
     fault, but it does mean that there's nothing for us to do about
     them.