README

            [THIS REPOSITORY IS ARCHIVED FOR HISTORICAL PURPOSES]


			Mach 4 distribution
			    Bryan Ford
	  University of Utah Computer Systems Laboratory


NOTE: This README is out-of-date.  Instead of this, you should read the
installation instructions in our public WWW pages at:
http://www.cs.utah.edu/projects/flexmach/mach4-proj.html


INTRODUCTION
~~~~~~~~~~~~

This is a distribution of Mach with a totally new build environment
and a new microkernel boot system.  (And soon, the new migrating threads-based
IPC system CSL developed on our PA-RISC version of Mach...)  This i386 release
is based on Remy Card's version of CMU's MK83, with modifications to the
server bootstrap code to load servers from a Linux ext2fs.  The microkernel
now boots directly from LILO as a Linux-like boot image, initializes itself,
and runs the bootstrap code and Remy's test server.


Requirements
------------

You will need the following programs installed and available in order
to compile this version of Mach:

	* GNU make.  You can name it whatever you want
	  (e.g. you can install it as `gmake' if you already
	  have another version of make that you want to keep).
	* GNU awk, or another version of awk that has `toupper()'.
	  If you call it `gawk', it will be used instead of `awk'.

Quick Start
-----------

The new build environment pretty much follows the standard GNU guidelines.
To configure the system, unpack the machine-independent and machine-dependent
source trees (e.g. "mach4" and "mach4-i386") somewhere, create a separate
object directory to build into, and run the configure script in the
machine-dependent source tree from within the object directory.  (Currently
the object directories MUST be SEPARATE FROM the source directories.)  You'll
have to specify the location of the machine-independent source tree on the
configure command line with a "--with-mach4=DIR" option.  Finally, type
`make -r' or `make -r install' to build the kernel and optionally install it.
(You don't actually have to use `-r', but GNU make runs faster if you do.)
For example:

tar xvzf /tmp/mach4.tar.gz
tar xvzf /tmp/mach4-i386.tar.gz
mkdir obj
cd obj
../mach4-i386/configure --with-mach4=../mach4
make -r install

All installed files will go into directories named relative to the
prefix you specify on the configure command line, or `/usr/local'
by default, as per normal GNU conventions.

The sectons below describe in more detail exactly what you get, but to try
the new kernel and bootstrap code quickly, go into the directory
$(prefix)/lib/mach-boot, and type `mkbootimage *.bmod'.  (Make sure the
$(prefix)/bin directory is in your path, if you didn't install Mach into
/usr/local or /usr or another "standard" place.)  This command should create
a file called `boot' in the same directory.  This file is an ordinary LILO
boot image which you can add to your lilo.conf file with an entry that looks
something like this:

image = <appropriate path>/lib/mach-boot/boot
	label = mach

You can then run `lilo' to update the boot map, reboot, and try running Mach.
Of course, if you want to load a server, you'll have to create a /mach_servers
directory and put a server into it.


Cross Compilation
-----------------

With this build environment you can easly cross compile Mach from a different
architecture and/or OS.  To cross compile from a different (non-Mach) OS but
on the same processor architecture, you normally shouldn't have to do anything
special; the "normal" procedure above is known to work on Linux anyway.
If you have any problems, try the cross compilation procedure described below.

To cross compile from a different architecture, you will have to have all the
standard cross-development tools built.  In particular, Mach requires cross
development versions of gcc, gas, ld, ar, and ranlib.  You can get all these
from prep.ai.mit.edu:/pub/{gcc-*,gas-*,binutils-*}.  Just build and install
them as the INSTALL files say to, using the `--target=' option to specify
the target architecture and OS (e.g. `--target=i386-gnu').  It will probably
be easiest if you install them in the same place your ordinary compiler is
located: for example, use `--prefix=/usr' if gcc et al is in /usr/bin.  As
long as the new tools are configured for cross development, they will not
overwrite the native tools that are already there, because they are given
names prefixed with the target specification, e.g. `i386-gnu-gcc'.

Be sure to build and install gas and binutils _before_ GCC.  Even then, GCC may
fail to compile completely because of missing header files (probably stdio.h).
If it fails while trying to build libgcc2.a, then you've gotten far enough for
the purposes of Mach - the compiler has already been built, and you can just
`make install' at that point and go back to Mach.

To cross compile Mach itself, the only additional thing you need to do is tell
the Mach build environment where to find the cross compilation tools.  The
normal GNU way to do this, I understand, is to specify the tools as variable
overrides on the `make' command line; e.g. `make CC=i386-gnu-gcc LD=...'
You can do it this way if you want; if you do, you'll need to set the variables
CC, LD, AR, and RANLIB.

However, with this Mach distribution, there's an easier way.  If you specify
a --target option on the command line when running Mach's configure script,
(e.g. `--target=i386-gnu'), then the makefiles will automatically be set up
with the default names of the development tools it uses prefixed with the
target name (e.g. `i386-gnu-gcc' etc.).  You can still override those defaults
on the `make' command line, but it should not be necessary to if your tools
are named according to the standard conventions and are in your path.

Note that the LILO boot configuration requires an as86 and ld86 to
assemble. These are available on linux, but I do noy know of any cross
versions of these programs. (I haven't yet tried to compile them
anywhere other then linux.) Therefore, if you want your kernel to be
bootable with LILO, you must find a way to get bootsetup (in mach4-i386/boot)
assembled and linked. A cross build that does not have the x86 tools
available will simply fail to make LILO-compatible boot images for you;
the resulting boot images will still boot from NetBSD or Mach boot blocks
however.


BUILD ENVIRONMENT
~~~~~~~~~~~~~~~~~

Design Philosophy
-----------------

In the original Mach source code environment, the general orientation of the
entire system was toward the machine-independent code being "master" and the
machine-dependent code being the "slave".  The "main" machine-independent parts
would generally include or invoke the machine-dependent parts to implement
machine-dependent aspects of the system.  However, this structure assumes
that the machine-independent code can always "know" what is really machine-
dependent and what isn't, which is generally not possible without horrible
kludging.  Different subsets of the available machine-independent functionality
often apply to different variants of the microkernel, and this is difficult to
express if the machine-independent code is trying to make all the decisions.

Therefore, in the new build environment, the roles of the components are
reversed: the more-specific component is always the "master", and it determines
which pieces of less-specific functionality to incorporate, and in what way.
The machine-independent code takes the role of "slave", merely a source code
repository to pick and choose from, much like a library.  This way, specific
variants of the system can have complete control over the finished product.

Good microkernels tend to contain a fairly high percentage of machine-dependent
code, because most of the generic, high-level, machine-independent functionality
has been moved out to user-level servers.  This percentage is already pretty
high in Mach, and is probably going to go up even more as the kernel becomes
more "micro".  For this reason, instead of including the source code for every
different supported architecture in one big source tree, I'm splitting up the
Mach sources into smaller "packages".  There is one generic, machine-independent
package ("mach4"), and at least one machine-specific package for each supported
architecture ("mach4-i386", "mach4-parisc", etc.).

In keeping with the idea of more-specific code being "master", the actual
configure scripts and bottom-level makefiles come from the architecture-specific
source tree; they can use scripts and makefiles from the machine-independent
source tree as appropriate.  A third, even-more-specific source package "layer"
could even be used, say for a specific vendor or machine type.  For example,
if support for the Sequent Symmetry gets added back in, it could be a
third-level package based on both the mach4 and the mach4-i386 packages.


Gory Details
------------

The configure script is generated from configure.in by autoconf.  It requires
two new autoconf macros, AC_DIR and AC_SRCDIR, which I've just submitted to
bug-gnu-utils as a patch to autoconf-1.11.  Hopefully the addition will be
incorporated by the next release of autoconf.  In the meantime, you can either
use the configure script I generated, or ask me and I'll send you the patches.

There are two types of makefiles in the source directories: "Makerules" files
and "Makefile.in" files.  The former are used primarily in generic, machine-
independent directories, and are meant to be included by other makefiles.
The latter are templates for "real" makefiles, which will be translated and
copied into corresponding object directories by the configure script.

The configure script generates one Makefile in the top-level object directory,
and a Makefile in the object subdirectories for each major system component.
The top-level Makefile simply runs make recursively on each of the
subdirectories in the correct order; it does not actually create anything.
All the other makefiles are independent of each other (there are no other
recursive make invocations), and do all the real work.

The makefiles are very unlikely to work with anything but GNU make.
Also, you will probably want to use `make -r' instead of just `make', to
disable all the built-in implicit rules: it makes builds significantly faster.
I have `make' permanently aliased to `make -r', and I just use `\make' when
I'm building something that breaks when the built-in rules are missing.

To compile everything, just type `make' in the top-level object directory
that you executed the configure script from.  To build only a certain part,
such as the kernel, go into the appropriate object subdirectory (e.g. `kernel')
and run make from there.  You shouldn't have to set up any special shell
variables or anything.  You can say `make <objfile>' for some arbitrary object
file from within an object directory and get the expected results; `make -n'
works properly; and so on - in other words, no funny stuff.

Include file dependencies are kept track of automatically, much like in the
original Mach build environment, except that the work is done by a five-line
makefile rule (in mach4/Makerules) instead of a 1300-line C program.  Unlike
in the ODE build environment, the dependency file shouldn't get trashed if you
happen to ^C a build session at the wrong time.  It should not be significantly
slower this way either, maybe even faster.

Note that one problem with this automatic dependency tracking is that if you
rename or delete a header file, but the `depend' file in your object directory
still refers to it, make will die with an error message saying that it can't
find that header file and doesn't know how to build it.  The solution is to
edit the `depend' file and simply remove all references to the old header file.
(A more brute-force approach that also works is just to `make clean' and start
again from scratch.)

Ideas and suggestions on how to make the build environment better are welcome.
(For one thing, does anyone know of a way for a Makefile to disable the
default rules?)


CHANGES TO MACH
~~~~~~~~~~~~~~~

(See mach4/ChangeLog and mach4-i386/ChangeLog for a brief list of changes.)


Potential Incompatibilities
---------------------------

Some of the changes I made to Mach are not completely transparent - a few can
potentially affect clients and servers.  For the most part these changes simply
help to get Mach "out of the way" of other software, and make it more
general and less Unix-specific (or, at least, less CMU-UX-single-server specific).

* Mach no longer has a global `sys' include directory.  The needed files
  in it have been moved to the `mach' directory or to private directories.
  The `sys' directory should be left available for higher-level OS software.
  (Already the Hurd was having to kludge around its presence;
  see below about how to compile it with this version of Mach.)

* Mach no longer exports a global `machine' or `i386' include directory
  (except for the `mach/machine' subdirectory).  Again, these are the domain
  of higher-level software and should not be touched by Mach.

* The exported directory `mach/machine' is now no longer a symlink; it's
  a real directory.  There is no longer an `i386' directory (or any other
  machine-specific subdirectory for that matter).  This makes things a
  little simpler and cleaner, and is easy since machine-dependent files
  are in separate source packages.

For the most part these changes shouldn't affect user-level software, since
they are all to files rarely or never accessed directly by Mach clients.

Another change that might cause incompatibilities is that MACH_IPC_COMPAT
is now _not_ defined by default.  If it breaks anything, you can turn it on
by saying `export DEFS=-DMACH_IPC_COMPAT' before running the configure script.
If this breaks a _lot_ of important old software (_what_ software? :-) ),
I may turn it back on by default.

I don't support the htg_vm_map kludge in libmach, which has no business
supporting special obscure presentations for higher-level software such as
the emulator (which is what this kludge is for).  Let the emulator create
its own client presentation of mach.defs with vm_map() renamed.
(I'll explain later what a presentation is. :-) )


Problems and Likely Changes
---------------------------

I'm not quite sure what to do with the kernel/chips directory.  The i386
port only uses chips/busses.c; for now I just put a copy of this file
into the i386 source tree and totally left the main chips directory out
of the build environment.  This will have to be fixed somehow, obviously.
Perhaps since this directory essentially contains a general-purpose
"implementation repository" for real device drivers to use, it should be
placed into some kind of link library used when linking the kernel.
Perhaps the scsi directory should be in that library as well.

There are also some little files duplicated because they are used by both
kernel and user code: for example, bcopy and setjmp/longjmp.  I'm not sure
what to do with these either.  Perhaps they should go into the library
mentioned above as well, and that library be used for both kernel and user
code.  Perhaps that library should simply be the existing libmach_sa.a.

Currently mach4-i386/libthreads/cthread_inline.awk is not used.  I need to turn
those routines into real GCC inline functions and get rid of the awk script.
However, until then this problem should only affect performance.

Currently, everywhere MIG is used to produce client stubs for a .defs file,
all the client stubs are placed in a single .c file, instead of one .c file
for each client stub.  This simplifies the build environment significantly,
but means that programs will get client stubs they don't need linked into them,
inflating program size.  However, this problem may not really need to be fixed.
For one thing, in a more mature Mach-based system down the road, libmach will
probably always be used as a shared library, so all the client stubs will have
to be present anyway.  Second, the GNU C library may make libmach obsolete,
because it contains essentially everything libmach does, and it already knows
how to deal with zillions of individual client stub files.  Third, in the
new IPC system "on its way", client stubs are way smaller, and many are inlined,
so size is no longer much of an issue.  Between these possible eventualities,
I'm hoping that at least one will come true and I'll be able to weasel out of
this job. :-)

Another thing about the current system that I'm not sure I like is that the
public cthreads and bootstrap header files are mixed in with the public kernel
header files.  For now this isn't too much of a problem, but it might be
desirable at some point to take all the optional user-level services such
as cthreads, libmach, the bootstrap program, and possibly other personality-
independent modules such as name servers and device drivers, and throw them
all into a separate package.  (Maybe call it the Flock - "Flock of Low-level
OS-independent Common Kludges". :-) )

In libmach, I didn't include the NO_TYPE_CHECK_SRCS kludge, which would turn off
type checking for messages that are "supposed" to come only from the kernel,
which is trusted.  This "feature" presumes that libmach knows what its clients are
using the Mach interfaces for, which totally violates the microkernel concept.
High-level software components can create their own presentations of the
standard interfaces with type checking disabled, if they want to.  This change
shouldn't cause any compatibility problems, only performance problems on
servers that use libmach's default presentations on the assumption that they
will be "optimized" in this way.


COMPILING THE HURD WITH MACH4
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Hurd itself shouldn't be affected by the changes to Mach and its build
environment, but the GNU C library depends on Mach's directory structure and
therefore was broken by these changes.  However, the fix is fairly simple.
First, in Michael Bushnell's Hurd README, where it talks about installing the
GNU C library, replace FOO with the Mach4 `include' directory instead of the
`kernel' directory.  Second, apply this small patch to the GNU C library,
on the file `glibc-<version>/mach/Makefile':

diff -u -r old/mach/Makefile ./mach/Makefile
--- old/mach/Makefile	Wed Jul  6 19:47:02 1994
+++ ./mach/Makefile	Wed Jul  6 20:10:12 1994
@@ -77,17 +77,10 @@
 
 # Install all .h and .defs files we find in some of the kernel's source
 # directories and their subdirectories (in MK82, max one level deep).
-mach-src-headers := $(wildcard $(foreach dir,mach device mach_debug \
-					     $(config-machine),\
-					 $(addprefix $(mach-srcdir)/$(dir)/,\
-						     *.defs *.h \
-						     */*.defs */*.h)))
-# Exclude mach/machine/*.  A symlink will be installed for mach/machine.
+mach-src-headers := $(wildcard $(addprefix $(mach-srcdir)/,*/*.* */*/*.*))
 # Exclude $(headers) for Mach files we have our own versions of.
-mach-headers = $(filter-out mach/machine/% $(headers),\
+mach-headers = $(filter-out $(headers),\
 			    $(mach-src-headers:$(mach-srcdir)/%=%))
-# Rename Mach's sys/version.h to mach/version.h.
-mach-headers := $(patsubst sys/version.h,mach/version.h,$(mach-headers))
 
 # Don't distribute the Mach headers; they are in the Mach distribution.
 dont_distribute = $(mach-headers)
@@ -96,16 +89,6 @@
 $(addprefix $(mach-srcdir)/,$(mach-headers)) : ;
 install-others += $(addprefix $(includedir)/,$(mach-headers))
 $(includedir)/%: $(mach-srcdir)/%; $(do-install)
-
-# Make symlinks for machine and mach/machine in the include directory.
-install-others += $(includedir)/mach/machine $(includedir)/machine
-$(includedir)/mach/machine $(includedir)/machine: $(common-objpfx)config.make
-	-rm -f $@
-	cd $(@D); ln -s $(config-machine) $(@F)
-
-# Install Mach's <sys/version.h> as <mach/version.h>.
-install-others += $(includedir)/mach/version.h
-$(includedir)/mach/version.h: $(mach-srcdir)/sys/version.h; $(do-install)
 
 # Define mach-syscalls and sysno-*.
 ifndef inhibit_mach_syscalls

This patch may not be enough, because I ran out of disk space before I managed
to build the entire GNU C library.  For one thing, it may be necessary to tell
glibc about the additional mach4-i386/include directory somehow...

I'm hoping to find a way to make all these shenanigans unnecessary,
so Mach and glibc can more cleanly.


COMPILING LITES WITH MACH4
~~~~~~~~~~~~~~~~~~~~~~~~~~

Johannes will be releasing Lites under a new build environment soon,
designed to work well with this Mach distribution.


DIRECTORY STRUCTURE
~~~~~~~~~~~~~~~~~~~

mach4			Machine-independent source package
	bootstrap	User-level bootstrap code and default pager.
			I'm hoping to make this obsolete soon -
			just load the startup server(s) along with the kernel.
	include		Global include files to be copied into $(prefix)/include.
	kernel		Source files for the microkernel itself.
		bogus	Stub header files that `config' used to produce,
			which define various configuration symbols.
			This directory will be eliminated
			as soon as I implement a better way to handle
			this kind of configuration.
		chips	Repository for a bunch of semi-drivers; currently unused.
		ddb	Kernel debugger code.
		device	System-independent device code.
		kern	Miscellaneous kernel code.
		scsi	Host-adapter-independent SCSI device code.
		vm	Virtual memory management.
	libmach		Produces libmach.a, libmach_sa.a, and the default
			.h files for the public .defs files.
		standalone
		unixoid
			See discussion of libraries below.
	libthreads	C threads library.
	mig		Mach Interface Generator program, for compiling .defs
			files.  Incorporates the bugfixes in the GNU Hurd
			distribution of MiG.

mach4-i386		i386-specific source package
	boot		Necessary code and tools for smashing boot images together.
	bootstrap	i386 part of the traditional bootstrap code.
	include		i386 public includes to be copied to $(prefix)/include.
	kernel		i386 source files for the basic microkernel.
		aux	Contains genassym.c, which produces assym.s,
			a file describing structure offsets for assembly code.
		bogus	Same idea as system-independent bogus directory.
		chips	Contains a copy of mach4/kernel/chips/busses.c, big hack.
		i386	Code specific to the i386 processor architecture.
		i386at	Code specific to PCs (ISA bus, PC peripherals, etc.).
		intel	PMAP code, common to both i386 and i860 processors.
	libmach		i386 specific Mach library code.
	libthreads	i386 code for C threads.
	mig		Contains only a Makefile.in at the moment,
			since mig currently has no machine-specific files,
			but this may have to change to support cross-compilation.

Currently, this distribution produces two libraries, libmach.a and
libmach_sa.a, following CMU's model.  The libmach_sa.a library may be
used to link a Mach program without any other stuff that normally
comes with the higher-level OS.  It makes a completely "standalone",
personality-neutral Mach program and is used for programs like the
bootstrap server (and Remy Card's test server).  The libmach.a library
is used to link programs in a Unix-like envronment -- specifically,
the CMU UX server environment.  It is an unfortunate accident that it
has a "general purpose" name like "libmach.a", rather than a more
specific sounding name like "libmach_ux.a".  (As an aside, I tried
naming it libmach_ux.a in one of my releases, but I put it back to
libmach.a because it led to too much of a mess).

In CMU's build environment, all of the source files for both versions
of the library were packed into one big happy directory with an
enormous makefile to determine what went where.  In the Mach4
environment, all of the common source files are in libmach; the ones
specific to libmach_sa.a are in libmach/standalone; and the ones
specific to libmach.a are in libmach/unixoid, (with i386-specific
files in mach4-i386/libmach/... and generic files in mach4/libmach/...
as discussed above).  The makefiles that are installed in the object
directory are used to produce the two libraries and to install the
presentation header files that define the intefaces to the various
services provided by the kernel.  When libmach/Makefile is "made", it
generates all of the header, client, and server source files for the
common modules of the library.  When it is "make install"ed, it
installs the header files in their proper installation directories.
The makefiles in libmach/unixoid and libmach/standalone may be used to
compile and install libmach.a and libmach_sa.a respectively. 

The Hurd doesn't need and doesn't want libmach.a.  It really doesn't
belong in Mach at all; it's just there for historical reasons.  The
only reason I left it in the current distribution is because I think
that Johannes Helander's LITES distribution probably still needs it,
since it's based on CMU's UX server.  However, that is subject to
change in the future and hopefully, Mach will only have to create
libmach_sa.a.

INSTALLED FILES
~~~~~~~~~~~~~~~

All files installed by the build environment
are placed in directories based on the specified prefix
(/usr/local by default if you don't specify a prefix).
Here is a list of the files that get installed,
and where they go relative to the prefix:

/bin/mig		Mach Interface Generator (shell script front-end)
/include/*		Public Mach header files.
/lib/mach-boot/*	Boot modules and other booting-related files.
/lib/migcom		Executable invoked by the `mig' script.


BOOTSTRAP SYSTEM
~~~~~~~~~~~~~~~~

The new Mach boot mechanism introduces the concept of "boot modules".
Basically, any number of "boot modules" can be thrown together to create
a single boot image.  That boot image is what LILO or whatever loads,
and when the system starts up, all of the boot modules will be already
in memory and immediately available.  At least one of those modules is the
microkernel itself; others may be device drivers, other kernel modules,
user-level servers (e.g. the bootstrap code), etc.  Currently only the
kernel itself and the single server bootstrap program go into the boot
image, but that'll probably change soon.  I'd like to be able to get rid
of the server bootstrap code entirely, and simply embed the appropriate
server(s) directly into the boot image: for example, the LITES, or the
basic Hurd administration servers (exec, proc, etc.) and a file server
for the root filesystem.  Eventually it should be possible (though optional)
to throw an entire root filesystem snapshot into the boot image, so upon
startup you can get a Unix shell and a minimal set of utilities without
depending on the successful initialization of any devices other than
the console.

The exact structure of a boot module and a boot image is by nature somewhat
system-dependent.  On the i386, a boot module is a relocatable object file
created with the `mkbmod' script.  A boot module must contain no external
references (all externs must be resolved), and usually must have all
symbols stripped, leaving only relocations to be fixed up.  To facilitate
debugging of boot modules, _one_ boot module in a boot image may be left
unstripped; you can tell `mkbmod' to leave a boot module unstripped by giving
it the `-s' option.  (Note that `-s' on mkbmod has exactly the opposite effect
as `-s' on `gcc' or `ld'.)

The `mkbmod' program assumes when it creates boot modules that certain
entry points exist in the object. It links a bootmodule specific
runtime that calls the routine `mach_bmod_init' at boot
time. (Actually, the kernel calls this routine by following pointers
stored in the boot module header.) This init routine returns
information about the object file that `kernel/kern/bootstrap.c' uses
to execute the module in a thread.

The `mkubmod' command takes a more conventionally linked program (a
linked executable) and adds this `mach_bmod_init' routine. This allows
the kernel to load into an address space some linked executable.
Once your program is compiled and linked, use mkubmod to embed it
in a bmod object and you can add it to your larger boot image.

A boot image is simply a set of boot modules glued together with the
`mkbootimage' script, with some extra header/trailer code linked in with it
(see mach4-i386/boot/bootimage_*), with all relocations fixed, and with
a LILO-compatible boot sector and setup program tacked onto the front.

All boot modules created, along with the auxiliary stuff needed to create
boot images, gets thrown into the directory $(prefix)/lib/mach-boot.
The idea is that some or all of the boot modules in .../lib/mach-boot
will be glued together into a single boot image to be placed on the
root filesystem in `/' or `/boot' or whatever.  The boot modules and
other files used in constructing boot images don't themselves need
to be available immediately on bootup, so they can be located in the
"usual" places, even shared among multiple machines.  Eventually, the
mach-boot directory will probably contain a whole slew of boot modules
(e.g. both uniprocessor and SMP kernels, various device drivers, file system
servers for various file system formats, etc.).  You will then be able to
type something like `mkbootimage -o /boot/machboot /usr/lib/mach-boot/*.bmod'
and get a fully functional, generic boot image with "all" the possible
features and device drivers; or you might include only specific modules
to get a stripped-down image.


COMPILATION OPTIONS
~~~~~~~~~~~~~~~~~~~

Options settable through configure
----------------------------------

`--enable-mp' causes multiprocessor-safe kernel boot modules to be built.
They will only be used if they are included in a boot image and that boot
image is booted on a supported multiprocessor.
XX not working yet - waiting for imps implementation

`--enable-debug' defines the symbol DEBUG for compilation of everything.
If you want to enable debugging for only one module,
you can add the line `DEFINES += -DDEBUG' to the Makefile
in the appropriate object directory.


Options set when compiling certain modules
------------------------------------------
`MULTIPROCESSOR' is defined to 1 (by what?) when compiling a kernel.bmod
for a multiprocessor (e.g. kernel/imps).
XX not working yet - waiting for imps implementation


Other Options
-------------
`PROTECTION' is normally defined to 1 (by what?), but can be turned off if
the kernel is only going to need to support one protection domain (the
kernel's).  This is useful for embedded systems or systems that do not have
protected/virtual memory support.
XX not working yet - waiting for VM updates

`PAGING' is normally defined to 1 (by what?), but can be turned off
if only physical (wired) memory will be desu.  Potentially useful for the
same reasons as above.
XX not working yet - waiting for VM updates


CODING STYLE CHANGES
~~~~~~~~~~~~~~~~~~~~

While for the most part I'm remaining consistent with CMU's original Mach
coding style in order to keep the kernel code consistent and readable, there
are a few changes I'm making that you should probably know about.  Most of these
changes are currently "in progress", so far appearing only in a few places here
and there.  At some point I'll probably go through the whole kernel and finish
making the changes globally, but for now you should at least know what's
happening, and why.

* I'm using `#include ""' for local includes (e.g. "kern/thread.h"),
  and `#include <>' for global includes (e.g. <mach/message.h>).
  This will make the interface/implementation boundaries clearer,
  and once propagated throughout the system, will make the build
  environment slightly cleaner as well.

* When creating new private header files, I now include them _without_
  specifying the directory name - let make and GCC hunt them down.
  For example, say `#include "foo.h"' instead of `#include "kern/foo.h"'.
  This will allow more-specific header files to override less-specific files
  automatically, just like .c files already can.  Separate include file
  namespaces are pretty much useless in Mach anyway, because their
  corresponding object files all get thrown into one object directory
  and therefore have to have unique names.  Having separate .h
  namespaces but a single .c namespace is just an inconsistency without
  any real benefit.  In any case, namespace crowding should be less and less
  of a problem as the microkernel becomes more modular and more "micro".

* The web of cross-includes in the current Mach source is ridiculously huge,
  and is mostly due to the convention of using typedef'd names for
  pointers to structures (e.g. `ipc_port_t' instead of `struct ipc_port').
  I'm working on cutting down the web (and therefore make compiles go faster)
  by changing pointer references to the `struct' form instead of the `_t' form
  as needed within header files, so one file doesn't need to include another
  just because it uses a pointer to another structure.

* No more history lists embedded in each source file.  They just take a
  huge amount of space and don't provide any more information than a single
  GNU-style ChangeLog does.  Also they screw up diffs by making files
  appear to have changed when they really haven't.

* I'm trying to avoid putting any machine-dependent #ifdef's (e.g. #ifdef i386)
  in machine-independent code.  In the new build environment, where any
  machine-independent file can be modified or overridden by machine-dependent
  code, there is really no longer an excuse for machine-dependent #ifdef's.
  If you need to put machine-dependent #ifdef's in machine-independent code,
  then that code isn't really machine-independent, is it?


EPILOGUE
~~~~~~~~

Good luck!

				Bryan

Bryan Ford <baford@cs.utah.edu>