.TL
Regenerating System Software
.AU
Charles B. Haley
.AU
Dennis. M. Ritchie
.MH
.SH
Introduction
.PP
This document discusses how to
assemble or compile various parts of the
.UX
system software.
This may be necessary because
a command or library is accidentally
deleted or otherwise
destroyed;
also, it may be desirable to install a modified
version of some command or library routine.
A few commands depend
to some degree on the current configuration
of the system;
thus in any new system modifications to some commands
are advisable.
Most of the likely modifications
relate to the standard disk devices contained
in the system.
For example, the df(1) (`disk free')
command has built into it the names of
the standardly present disk storage drives
(e.g. `/dev/rf0', `/dev/rp0').
Df(1) takes an argument to indicate which
disk to examine, but it is convenient
if its default argument is adjusted to
reflect the ordinarily present devices.
The companion document `Setting up UNIX'
discusses which commands are likely to require
changes.
.SH
Where Commands and Subroutines Live
.PP
The
source files for commands and subroutines reside
in several subdirectories
of the directory /usr/src.
These subdirectories, and a general
description of their contents, are
.IP cmd 12
Source files for commands.
.IP libc/stdio 12
Source files making up the `standard i/o package'.
.IP libc/sys 12
Source files for the C system call interfaces.
.IP libc/gen 12
Source files for most of the remaining routines described
in section 3 of the manual.
.IP libc/crt 12
Source files making up the C runtime support package, as
in call save-return and long arithmetic.
.IP libc/csu 12
Source for the C startup routines.
.IP games 12
Source for (some of) the games.
No great care has been taken to try to make it obvious how
to compile these; treat it as a game.
.IP libF77 12
Source for the Fortran 77 runtime library, exclusive of IO.
.IP libI77 12
Source for the Fortran 77 IO runtime routines.
.IP libdbm 12
Source for the `data-base manager' package
.I dbm
(3).
.IP libfpsim 12
Source for the floating-point simulator routine.
.IP libm 12
Source for the mathematical library.
.IP libplot 12
Source for plotting routines.
.SH
Commands
.PP
The regeneration of most commands
is straightforward.
The `cmd' directory will contain either a source file
for the command or a subdirectory containing the set
of files that make up the command.
If it is a single file the command
.DS
cd /usr/src/cmd
cmake cmd_name
.DE
suffices. (Cmd_name is the name of the command you
are playing with.)
The result of the cmake command will be an executable version.
If you type
.DS
cmake \-cp cmd_name
.DE
the result
will be copied to /bin
(or perhaps /etc or other places if appropriate).
.PP
If the source files are in a subdirectory there will be a `makefile'
(see make(1)) to control the regeneration.
After changing to the proper directory (cd(1)) you type one of the following:
.IP "make all" 12
The program is compiled and loaded; the executable is
left in the current directory.
.IP "make cp" 12
The program is compiled and loaded, and the executable is
installed.
Everything is cleaned up afterwards;
for example .o files are deleted.
.IP "make cmp" 12
The program is compiled and loaded, and the executable is compared
against the one in /bin.
.PP
Some of the makefiles have other options. Print (cat(1)) the ones you
are interested in to find out.
.SH
The Assembler
.PP
The assembler consists of two executable files:
/bin/as and /lib/as2.
The first is the 0-th pass:
it reads the source program, converts it to
an intermediate form in a temporary file `/tmp/atm0?',
and estimates the final locations
of symbols.
It also makes two or three other temporary
files which contain the ordinary symbol table,
a table of temporary symbols (like 1:)
and possibly an overflow intermediate file.
The program /lib/as2
acts as an ordinary multiple pass assembler
with input taken from the files produced by /bin/as.
.PP
The source files for /bin/as
are named `/usr/src/cmd/as/as1?.s'
(there are 9 of them);
/lib/as2 is produced
from the source files
`/usr/src/cmd/as/as2?.s';
they likewise are 9 in number.
Considerable care should be exercised
in replacing either component of the
assembler.
Remember that if the assembler is lost,
the only recourse is to replace it from some backup storage;
a broken assembler cannot assemble itself.
.SH
The C Compiler
.PP
The C compiler consists of
seven routines:
`/bin/cc',
which calls the phases of the compiler proper,
the compiler control line expander `/lib/cpp',
the assembler (`as'), and the loader (`ld').
The phases of the C compiler are
`/lib/c0', which is the first phase of the compiler;
`/lib/c1', which is the second phase of the compiler;
and `/lib/c2', which is the optional
third phase optimizer.
The loss of the C compiler is as serious
as that of the assembler.
.PP
The source for /bin/cc
resides in `/usr/src/cmd/cc.c'.
Its loss alone (or that of c2) is not fatal.
If needed,
prog.c can be compiled by
.DS
/lib/cpp prog.c >temp0
/lib/c0 temp0 temp1 temp2
/lib/c1 temp1 temp2 temp3
as \- temp3
ld \-n /lib/crt0.o a.out \-lc
.DE
.PP
The source for the compiler proper is in the
directory /usr/src/cmd/c.
The first phase (/lib/c0)
is generated from the files c00.c, ..., c05.c,
which must be compiled by the C compiler.
There is also c0.h, a header file
.I included
by the C programs of the first phase.
To make a new /lib/c0 use
.DS
make c0
.DE
Before installing the new c0, it is prudent to save the old one someplace.
.PP
The second phase of C (/lib/c1)
is generated from the source files c10.c, ..., c13.c,
the include-file c1.h, and a set
of object-code tables combined into table.o.
To generate a new second phase use
.DS
make c1
.DE
It is likewise prudent to save c1 before
installing a new version.
In fact in general it is wise to save the
object files for the C compiler so that
if disaster strikes C can be reconstituted
without a working version of the compiler.
.PP
In a similar manner,
the third phase of the C compiler
(/lib/c2)
is made up from the files
c20.c and c21.c together with c2.h.
Its loss is not critical since it is completely optional.
.PP
The set of tables mentioned above
is generated from the file
table.s.
This `.s' file is not in fact assembler source;
it must be converted by use of the 
.I cvopt
program, whose source and object are
located in the C directory.
Normally this is taken care of by make(1). You
might want to look at the makefile to see what it does.
.SH
UNIX
.PP
The source and object programs for UNIX are kept in
four subdirectories of
.I /usr/sys.
In the subdirectory 
.I h
there are several files ending in `.h';
these are header files which are
picked up (via `#include ...')
as required by each system module.
The subdirectory
.I dev
consists mostly of the device drivers
together with a few other things.
The subdirectory
.I sys
is the rest of the system.
There are files of the form LIBx in the directories
sys and dev. These are archives (ar(1)) which contain the
object versions of the routines in the directory.
.PP
Subdirectory
.I conf
contains the files which control
device configuration of the system.
.I L.s
specifies the
contents of the interrupt vectors;
.I c.c
contains the tables which relate device numbers
to handler routines.
A third file,
.I mch.s ,
contains all the
machine-language code in the system.
A fourth file,
.I mch0.s ,
is generated by mkconf(1) and contains
flags indicating what sort of tape drive is available
for taking crash dumps.
.PP
There are two ways to recreate the system. Use
.DS
cd /usr/sys/conf
make unix
.DE
if the libraries /usr/sys/dev/LIB2 and /usr/sys/sys/LIB1,
and also c.o and l.o,
are correct.
Use
.DS
cd /usr/sys/conf
make all
.DE
to recompile everything
and recreate the libraries from scratch.
This is needed, for example, when a header included
in several source files is changed.
See `Setting Up UNIX' for other information about configuration
and such.
.PP
When the make is
done, the new system is present in the
current directory as `unix'.
It should be tested before destroying the currently
running `/unix', this is best done by doing something like
.DS
mv /unix /ounix
mv unix /unix
.DE
If the new system doesn't work, you can still boot `ounix'
and come up (see boot(8)).
When you have satisfied yourself that the new system works,
remove /ounix.
.PP
To install a new device driver,
compile it and
put it into its library.
The best way to put it into
the library is to use the command
.DS
ar uv LIB2 x.o
.DE
where x is the routine you just compiled.
(All the device drivers distributed with
the system are already in the library.)
.PP
Next, the device's interrupt vector must be entered in l.s.
This is probably already done by the routine mkconf(1), but if the
device is esoteric or nonstandard you will have to massage
l.s by hand.
This involves placing a pointer to a callout routine
and the device's priority level in the vector.
Use some other device (like the console) as a guide.
Notice that the entries in l.s must be in order
as the assembler does not permit moving the
location counter `.' backwards.
The assembler also does not permit assignation of
an absolute number to `.', which is the
reason for the `. = ZERO+100' subterfuge.
If a constant smaller than 16(10) is added to the
priority level,
this number will be available as the first argument of the interrupt routine.
This stratagem is used when
several similar devices share the same interrupt routine
(as in dl11's).
.PP
If you have to massage l.s, be sure to add the code
to actually transfer to the interrupt routine. Again use
the console as a guide. The apparent strangeness of this code
is due to running the kernel in separate I&D space.
The
.I call
routine
saves registers as required and prepares a C-style
call on the actual interrupt routine
named after the `jmp' instruction.
When the routine returns,
.I call
restores the registers and performs an
rti instruction.
As an aside, note that
external names in C programs have an
underscore (`_') prepended to them.
.PP
The second step which must be performed to add a 
device unknown to mkconf is
to add it to the configuration table
/usr/sys/conf/c.c.
This file contains two subtables,
one for block-type devices, and one for character-type devices.
Block devices include disks, DECtape, and magtape.
All other devices are character devices.
A line in each of these tables gives all the information
the system needs to know about the device handler;
the ordinal position of the line in the table implies
its major device number, starting at 0.
.PP
There are four subentries per line in the block device table,
which give its open routine, close routine, strategy routine, and
device table.
The open and close routines may be nonexistent,
in which case the name `nulldev' is given;
this routine merely returns.
The strategy routine is called to do any I/O,
and the device table contains status information for the device.
.PP
For character devices, each line in the table
specifies a routine for open,
close, read, and write, and one which sets and returns
device-specific status (used, for example, for stty and gtty
on typewriters).
If there is no open or close routine, `nulldev' may
be given; if there is no read, write, or status
routine, `nodev' may be given.
Nodev sets an error flag and returns.
.PP
The final step which must
be taken to install a device is to make a special file for it.
This is done by mknod(1), to which you must specify the
device class (block or character),
major device number (relative line in the configuration table)
and minor device number
(which is made available to the driver at appropriate times).
.PP
The documents
`Setting up Unix' and
`The Unix IO system'
may aid in comprehending these steps.
.SH
The Library libc.a
.PP
The library /lib/libc.a is where most of the subroutines
described in sections 2 and 3 of the manual are kept.
This library
can be remade using the following commands:
.DS
cd /usr/src/libc
sh compall
sh mklib
mv libc.a /lib/libc.a
.DE
If single routines need to be recompiled and replaced, use
.DS
cc \-c \-O x.c
ar vr /lib/libc.a x.o
rm x.o
.DE
The above can also be used to put new items into the library.
See ar(1), lorder(1), and tsort(1).
.PP
The routines in /usr/src/cmd/libc/csu (C start up) are not in
libc.a. These are separately assembled and put into
/lib. The commands to do this are
.DS
cd /usr/src/libc/csu
as \- x.s
mv a.out /lib/x
.DE
where x is the routine you want.
.SH
Other Libraries
.PP
Likewise,
the directories containing the source for the other libraries
have files compall (that recompiles everything)
and mklib (that recreates the library).
.SH
System Tuning
.PP
There are several tunable parameters in the system. These set
the size of various tables and limits. They are found in the
file /usr/sys/h/param.h as manifests (`#define's).
Their values are rather generous in the system as distributed.
Our typical maximum number of users is about 20, but there are
many daemon processes.
.PP
When any parameter is changed, it is prudent to recompile
the entire system, as discussed above.
A brief discussion of each follows:
.IP NBUF 12
This sets the size of the disk buffer cache. Each buffer is 512 bytes.
This number should be around 25 plus NMOUNT,
or as big as can be if the above number of
buffers cause the system to not fit in memory.
.IP NFILE 12
This sets the maximum number of open files. An entry is made in
this table every time a file is `opened' (see open(2), creat(2)).
Processes share these table entries across forks (fork(2)). This number
should be about the same size as NINODE below. (It can be a bit smaller.)
.IP NMOUNT 12
This indicates the maximum number of mounted file systems. Make it
big enough that you don't run out at inconvenient times.
.IP MAXMEM 12
This sets an administrative limit on the amount of memory
a process may have.
It is set automatically if the amount of physical memory is small,
and thus should not need to be changed.
.IP MAXUPRC 12
This sets the maximum number of processes that any one user can
be running at any one time. This should be set just large enough
that people can get work done but not so large that a user can
hog all the processes available (usually by accident!).
.IP NPROC 12
This sets the maximum number of processes that can be
active.
It depends on the demand pattern of the typical user;
we seem to need about 8 times the number
of terminals.
.DE
.IP NINODE 12
This sets the size of the inode table. There is one entry in the inode
table for every open device, current working directory,
sticky text segment,
open file, and mounted device.
Note that if two users have a file open there is still only one entry
in the inode table. A reasonable rule of thumb for the size of
this table is
.DS
NPROC + NMOUNT + (number of terminals)
.DE
.IP SSIZE 12
The initial size of a process stack. This may be made bigger
if commonly run processes have large data areas on the stack.
.IP SINCR 12
The size of the stack growth increment.
.IP NOFILE 12
This sets the maximum number of files that any one process can have
open.
20 is plenty.
.IP CANBSIZ 12
This is the size of the typewriter canonicalization buffer. It is
in this buffer that erase and kill processing is done. Thus this
is the maximum size of an input typewriter line. 256 is usually
plenty.
.IP CMAPSIZ 12
The number of fragments that memory can be broken into. This should
be big enough that it never runs out.
The theoretical maximum is twice the number of processes,
but this is a vast overestimate in practice.
50 seems enough.
.IP SMAPSIZ 12
Same as CMAPSIZ except for secondary (swap) memory.
.IP NCALL 12
This is the size of the callout table. Callouts are entered in this
table when some sort of internal system timing must be done, as in
carriage return delays for terminals. The number must be big enough
to handle all such requests.
.IP NTEXT 12
The maximum number of simultaneously executing pure programs. This
should be big enough so as to not run out of space under heavy load.
A reasonable rule of thumb is about
.DS
(number of terminals) + (number of sticky programs)
.DE
.IP NCLIST 12
The number of clist segments. A clist segment is 6 characters.
NCLIST should be big enough so that the list doesn't become exhausted
when the machine is busy. The characters that have arrived from a terminal
and are waiting to be given to a process live here. Thus enough space
should be left so that every terminal can have at least one average
line pending (about 30 or 40 characters).
.IP TIMEZONE 12
The number of minutes westward from Greenwich. See `Setting Up UNIX'.
.IP DSTFLAG 12
See `Setting Up UNIX' section on time conversion.
.IP MSGBUFS 12
The maximum number of characters of system error messages saved. This
is used as a circular buffer.
.IP NCARGS 12
The maximum number of characters in an exec(2) arglist. This
number controls how many arguments can be passed
into a process.
5120 is practically infinite.
.IP HZ 12
Set to the frequency of the system clock (e.g., 50 for
a 50 Hz. clock).