OS Course Assignments

1
OS Course Assignments

• Lecture foils are available on-line
  http//www.wright.edu/travis.doom/courses/CEG433
• WSUs CaTS UNIX system paladin.wright.edu
• Student information is available in the
  directory
• w001ted/pub
• lab assignments are available as
• w001ted/pub/ceg433/labs/labXX/labXX.worksheet.txt
  
• All lab assignments must
• be turned in complete and on-time (include all
  required files)
• labXX.makefile
• labXX.typescript (man script)
• labXX.readme
• compile without warning or error using your
  makefile on paladin.wright.edu (Solaris 2).
• The compiler must be invoked with the -Wall flag

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Grading Guidelines
To earn any points, your program must compile on
paladin (with -Wall flag and no warnings or
errors), with the makefile you submit (using
"make -f labXX.makefile") to the target
executable file "labXX" (where XX is the two
digit lab number). Implementation/Worksheet (4
points possible) Required a compiling
program / worksheet 4 All features implemented
perfectly / all answers correct. 2 Some
features implemented / some answers correct. 0
No features implemented / no answers
correct. Bugs (2 points possible)
Required most features implemented 2
No bugs found, complete error checking done. 1
A bug found documented in readme, demonstrated
in typescript. 0 An undocumented bug
found. Documentation (3 points possible)
Required a compiling program. 2
Extensive README Discussion of design and
implementation decisions,concepts learned,
bugs found and corrected, remaining bugs, etc.
Demonstrate mastery. 1 Code documentation
o File comment header - including your name and
email at least. o Descriptive comment blocks
in code file for program and all functions,
including purpose, arguments and flags,
return values, and errors handled. o In-code
comments (preferably comment blocks for code
blocks). Excellence (1 point possible)
Required No points deducted above.
Implementation is concise and elegant, code is
easy to read (descriptively named variables,
all lines less than 80 columns, etc.), extremely
well documented, all possible errors handled
and demonstrated in typescript. Generally
excellent work.
3
OS Programming in C/C

• C programs can easily access the services of the
  UNIX operating system
• System calls routines that make operating system
  services available to programmers
• creating/deleting files, allocating memory,
  sending signal to processes
• In C, system calls are used in the same way you
  use ordinary C program modules (functions)
• A variety of libraries have been developed to
  support programming in C
• libraries are collections of related functions
• many libraries functions access basic OS services
  through system calls
• default location is generally /usr/lib

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OS Programming in C/C

• Lines that begin with are pre-processor
  directives
• define used to define symbolic constants (a
  macro)
• provides mapping from symbolic name to
  replacement text (macro expansion). Improves
  readability and modification.
• Header files for a library contain function
  prototypes and macros.
• When several macro definitions are used in
  different modules they are typically collected
  together in a single file called a header (or
  include) file (these files use the .h extention
  by convention).
• A function prototype is a declaration that tells
  the compiler what type a function returns, how
  many argument a function expects, and what the
  types of the arguments are. This allows the
  compiler to detect and flag inconsistencies in
  the use of the function

ifndef ALLOC define ALLOC(type,num) ((type )
malloc(sizeof(type) (num))) endif
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OS Programming in C/C

• Include files are loaded by the preprocessor
  using the include directive.
• Angle brackets are used for include files located
  in the standard location (generally
  /usr/include)
• include ltstdio.hgt
• Double quotes are used for other locations
• include /user/doom/soft/include/doomC.h
• Another way to specify directories to be searched
  for header files is to use the -I option to the C
  compiler
• include doomC.h
• cc -I /user/doom/soft/include
• If you have difficulties with a system call,
  check the man page and/or the header file
• The technical details are available in the
  header files.

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OS Programming in C/C

• Each program must well organized into functional
  modules
• Main is the control module - execution begins and
  ends with the function main
• Functions are used to make both development and
  maintenance of the program more efficient
• Every function should have a clearly defined (and
  documented) purpose
• Necessary conditions (pre-conditions)
• side-effects (post-conditions)
• return values
• Generally speaking, a function should consist of
  5 to 40 lines of code

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Programming Tools man, vi, xemacs

• man
• Learn to use the man command it is the single
  best tool for solving any UNIX problem
• ex man -k fork
• ex man -s2 sleep
• man man to start
• Editors
• vi powerful and ubiquitous, steep learning curve
  (but worth it)
• emacs (xemacs) powerful yet cumbersome (probably
  worth it)
• pico weak, small learning curve
• X displays can be piped back to remote machines
  running an xserver
• (remote system) setenv DISPLAY
  remotesystemname0.0
• (host system) xhost remotesystemname

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Programming Tools

• GUI - Sun WorkShop
• workshop graphical environment for coding and
  debugging (licensed from Sun), used to be called
  SPARCworks in the SunOS5 days, includes
• cc C compiler
• sbrowser source browser
• analyzer performance tuner
• debugger or dbx debugger does a good job with
  forks (follow parent , child, or both)
• rsccs source code management
• dmake distributed make, similar to GNU make but
  allows concurrency exploitation
• etc.
• In my experience, workshop does not work well
  remotely.

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Programming Tools gcc

• C (C) compilers
• cc (CC) SunWorkShop Compiler
• gcc (g) GNU C Compiler, freeware,
  cross-platform, ubiquitous
• Compiler flags
• man gcc for details!
• -l specify library on command line (must come
  after all modules to which it applies)
• -L specify additional directories to by searched
  for library (default /usr/lib and /lib)
• -O invoke compiler optimizer
• -o specify executable name (default a.out)
• -W specify warning level (implicit, return-type,
  unused, comment, format, all, etc)
• ex gcc -o lab01 -Wall lab01.c

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Programming Tools gcc

• -c suppress linking phase (create object files
  (.o) without treating unresolved references as
  errors)
• ex gcc -c doomC.c lab01.c (creates doomC.o and
  lab01.o)
• ex gcc -o lab01 doomC.o lab01.o (creates
  executable lab01 by linking object files)
• -R specify location of run-time libraries
  (default /usr/lib) - Absolute pathnames only!
• UNIX systems use shared (dynamic) libraries - the
  library modules are not included in the
  executable, only the location of the .so file.
  Use ldd to find out what shared libraries and
  executable requires.
• Do not use the only style LD_LIBRARY_PATH and
  LD_RUN_PATH environment variables.
• The -fPIC flag to gcc can be used to generate
  position-independent code combined with the ld
  -G command, you can create your own shared
  libraries.

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Programming Tools Make

• Make Keep a set of programs current
• C programs depend on a number of files (system
  header files, user header files, C source files,
  object files, executable files, etc.)
• When a changed occurs to a file that others
  depend on, you MUST recompile all dependent
  files.
• The make program allows your to specify
  dependency relationships to automate this process
• Make looks at at dependency lines in the
  specified file
• default the files Makefile or makefile in the
  working directory
• explicit specified using the -f flag to make

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Programming Tools Make

• Each dependency lines specifies a target file
  that depends on one or more prerequisite files.
  If any of the files in the dependency list has
  been modified since the targets last
  modification date, then the specified commands
  are invoked (each line of the commands begins
  with a TAB)
• Syntax target prerequisite-list
  
  
  
  TAB construction-commands

lab01 doomC.o lab01.o cc -o lab01
doomC.o lab01.o lab01.o lab01.h cc
- c lab01.c doomC.o doomC.h cc -c
doomC.c clean rm -f core .o
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Programming Tools Make

• Implied dependencies If you do not include a
  dependency line for an object file, make assumes
  that it depends upon a compiler or assembler
  source code file with the same name. BEWARE
  using implied dependencies requires that you use
  MACROS to pass necessary flags
• If no dependency file is specified, only implied
  dependencies are used
• If no target is specified, the first dependency
  in the file is the default

CCgcc CFLAGS-Wall (SRC) doomC.c
lab01.c (OBJ)(SRC.c.o) lab01 (SRC)
(OBJ) (CC) -o lab01CFLAGS
(OBJECTS) (others are implicit)
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Programming Tools Debuggers

• Debuggers
• gdb (xgdb, xxgdb - grahical) powerful, freeware,
  ubiquitous
• use help command at gdb prompt for list, break,
  run, set args, print, display, up, down, cont
• lint checks programs for potential bugs and
  portability problems
• truss trace system calls and signals
• Other useful commands
• Standard file commands cp, mv, grep, diff, file,
  ls, mkdir, cd, rm, chmod, ln
• Know the uses for , , , , fg, bg, jobs
• Useful utilities script, tar, compress, gzip,
  which, whereis, apropos, who, w, talk, write,
  man, man, man