(libc.info)Porting to Unix


Porting the GNU C Library to Unix Systems
-----------------------------------------

   Most Unix systems are fundamentally very similar.  There are
variations between different machines, and variations in what
facilities are provided by the kernel.  But the interface to the
operating system facilities is, for the most part, pretty uniform and
simple.

   The code for Unix systems is in the directory `unix', at the top
level of the `sysdeps' hierarchy.  This directory contains
subdirectories (and subdirectory trees) for various Unix variants.

   The functions which are system calls in most Unix systems are
implemented in assembly code, which is generated automatically from
specifications in files named `syscalls.list'.  There are several such
files, one in `sysdeps/unix' and others in its subdirectories.  Some
special system calls are implemented in files that are named with a
suffix of `.S'; for example, `_exit.S'.  Files ending in `.S' are run
through the C preprocessor before being fed to the assembler.

   These files all use a set of macros that should be defined in
`sysdep.h'.  The `sysdep.h' file in `sysdeps/unix' partially defines
them; a `sysdep.h' file in another directory must finish defining them
for the particular machine and operating system variant.  See
`sysdeps/unix/sysdep.h' and the machine-specific `sysdep.h'
implementations to see what these macros are and what they should do.

   The system-specific makefile for the `unix' directory
(`sysdeps/unix/Makefile') gives rules to generate several files from
the Unix system you are building the library on (which is assumed to be
the target system you are building the library _for_).  All the
generated files are put in the directory where the object files are
kept; they should not affect the source tree itself.  The files
generated are `ioctls.h', `errnos.h', `sys/param.h', and `errlist.c'
(for the `stdio' section of the library).


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