Lecture 6 Software Development under Unix

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Lecture 6Software Development under Unix

CSCE 510 Systems Programming

• Topics
• Tsearch revisited
• Gcc
• Ar implementation
• make
• Time functions

September 6, 2005
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• Last Time
• File times
• Ar archive formats
• tsearch
• Ar implementation
• Today
• Overview of the Compilation Process
• Tsearch revisited
• Ar implementation headers
• make
• Time functions

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Unix Software Development Tools GCC

• NAME
• gcc - GNU project C and C compiler
• SYNOPSIS
• gcc -c-S-E -stdstandard
• -g -pg -Olevel
• -Wwarn... -pedantic
• -Idir... -Ldir...
• -Dmacrodefn... -Umacro
• -foption... -mmachine-option...
• -o outfile infile...
• Only the most useful options are listed
  here g accepts mostly the same options as gcc.
• DESCRIPTION
• When you invoke GCC, it normally does
  preprocessing, compilation,
• assembly and linking.

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Unix Tools GCC options

• -c-S-E ? stop process before linking
  assembly compiling
• -stdstandard ? C language options
• -g ? preserve symbol table - debugging
  information
• -Olevel ? optimizer
• -Wwarn... -pedantic
• -Idir...
• -Ldir...
• -Dmacrodefn... -Umacro
• -foption... -mmachine-option...
• -o outfile infile...

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Printf example

• thetisgt gcc -o printf printf.c
• /tmp/ccsvOtyD.o(.text0x41) In function main'
• undefined reference to atan'
• collect2 ld returned 1 exit status
• This strange looking message means the function
  atan is undefined
• thetisgt gcc -o printf printf.c -lm
• thetisgt

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Example catGetchar.c

• include ltstdio.hgt
• main() / copy input to output /
• char bufBUFSIZ
• int c
• while ((c getchar()) ! EOF)
• putchar(c)
• return 0
• Then try E (on Solaris), -S and examine the
  intermediate files

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Note on gcc E catGetchar.c

• On Solaris, Linux has getchar function
• / lots of whitespace and /
• while ((c (--( (__iob0) )-gt_cnt lt 0 ?
  __filbuf( (__iob0) ) (int)
• ( (__iob0) )-gt_ptr) ) ! (-1) )
• (--( (__iob1) )-gt_cnt lt 0 ?
  __flsbuf(( ( c ) ), ( (__iob1) ))
• (int)(( (__iob1) )-gt_ptr (unsigned
  char) ( ( c ) )))
• return 0

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Notes on gcc S catGetchar.c

• On Linux (so Intel assembly instead of Sparc)
• main
• pushl ebp
• movl esp, ebp
• subl 8216, esp
• andl -16, esp
• movl 0, eax
• subl eax, esp
• .L2
• call getchar / note getchar
  function /
• movl eax, -8204(ebp)
• cmpl -1, -8204(ebp)
• jne .L4
• jmp .L3
• .L4
• subl 12, esp
• pushl -8204(ebp)
• call putchar

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Optimizer
.L2 cmpl 99, -4(ebp) jle .L5
jmp .L3 .L5 movl -4(ebp), edx
movl edx, eax sall 3, eax
addl edx, eax addl eax,
eax addl edx, eax leal
-8(ebp), edx addl eax, (edx)
leal -4(ebp), eax incl (eax)
jmp .L2

• Several levels
• include ltstdio.hgt
• main()
• int i, sum
• for(i0,sum0 i lt 100 i)
• sum sum 19i
• printf("Sum is d\n", sum)

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AR - archive format revisited

• Ar Header
• struct ar_hdr
• char ar_name16
• char ar_date12
• char ar_uid6
• char ar_gid6
• char ar_mode8
• char ar_size10
• char ar_fmag2

Archive format !ltarchgt Header1 file1 Header2 file2
Note files of odd length are padded with a
blank (\b)
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TSEARCH(3) Revisited

• NAME
• tsearch, tfind, tdelete, twalk - manage a
  binary tree
• void tsearch(const void key, void
  rootp,
• int(compar)(const void ,
  const void ))

• Notes
• pointer to root pointer, so the function can
  change the root
• Compare function passed as argument

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Example tsearch.ex.c

• struct node
• char word
• int length
• int count
• struct node root NULL
• When we pass it as an argument we pass root

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Comparisons

• We need to supply a compare function to compare
  nodes for sorting
• Sorting (tree insertion) choices arument to
  compare
• define ASCEND 1
• define DESCEND 2
• define STRLEN 3
• int mode ASCEND / global variable /
  

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• printf("Enter words a single word to a line.
  terminated withControlD\n")
• while(gets(buffer) ! NULL)
• printf("Read s",buffer)
• if ((n (struct node
  )tfind(tmpnode,root,mycompare))
  NULL)
• printf("\tInserting s",buffer)
• new newnode()
• new -gt word strdup(buffer)
• new -gt length strlen(buffer)
• new -gt count 1
• info (struct node )
  (tsearch((void )new, (void )root,
  mycompare))
• printf("After insert s length
  d count d",
• info-gtword, info-gtlength,
  info-gtcount)
• else / just update node found /

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mycompare

• int
• mycompare(struct node new, struct node old)
• int val
• val strcmp(new-gtword, old-gtword)
• if(mode ASCEND) return(val)
• else if(mode DESCEND) return(-1val)
• else if(mode STRLEN)
• if (new-gtlength lt old-gtlength )
  return(-1)
• else if (new-gtlength gt
  old-gtlength) return(1)
• else return(0)
• / N.B. strings of same length
  are considered equal/
• else fatal("Mycompare undefined mode
  error")

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Getopt References/Examples

• http//www.gnu.org/software/libc/manual/html_node/
  Getopt.html
• http//www.opengroup.org/onlinepubs/009695399/func
  tions/getopt.html

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Getopt variables

• int opterrIf the value of this variable is
  nonzero, then getopt prints an error message to
  the standard error stream if it encounters an
  unknown option character or an option with a
  missing required argument. This is the default
  behavior. If you set this variable to zero,
  getopt does not print any messages, but it still
  returns the character ? to indicate an error.
• int optoptWhen getopt encounters an unknown
  option character or an option with a missing
  required argument, it stores that option
  character in this variable. You can use this for
  providing your own diagnostic messages.
• int optindThis variable is set by getopt to the
  index of the next element of the argv array to be
  processed. Once getopt has found all of the
  option arguments, you can use this variable to
  determine where the remaining non-option
  arguments begin. The initial value of this
  variable is 1.
• char optargThis variable is set by getopt to
  point at the value of the option argument, for
  those options that accept arguments.
• int getopt (int argc, char argv, const char
  options)The getopt function gets the next
  option argument from the argument list specified
  by the argv and argc arguments.

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• while ((c getopt (argc, argv, "abc")) ! -1)
• switch (c)
• case 'a' aflag 1 break
• case 'b' bflag 1 break
• case 'c' cvalue optarg break
• default abort ()
• printf ("aflag d, bflag d, cvalue s\n",
  aflag, bflag, cvalue)

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Make

• Make - a system for maintaining programs that
  consist of multiple source files
• make specification files
• specification captures dependencies
• builds a tree
• performs minimal recompilation

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Make Advantages

• Make saves time - both typing and recompilation
• The Makefile documents the dependencies.
• For distribution of software one can make' and
  make install' a package with knowing anything
  about it.

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Make Specification Files

• Makefiles - Make Specification Files
• Definitions of the form namevalue
• Target Groups of the form
• target_1 dependencylist_1
• cmdlist_1
• target_2 dependencylist_2
• cmdlist_2
• ...

Nota Bene First character of command line must
be a TAB
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A Simple Makefile

• Makefile Example
• prog main.o routines.o
• cc -o prog main.o routines.o
• Each command line starts with a \tab
• main.o main.c defs.h
• cc -c main.c
• routines.o routines.c defs.h
• cc -c routines.c

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Make Tree (forest)
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Macros - Builtin Rules

• make p
• macros

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Another Makefile Example

• FILES Makefile defs.h main.c routines.c
• OBJS main.o routines.o
• LIBES -lm
• CFLAGS -g
• LP /fac/matthews/bin/p2c
• INSTALL_DIR /fac/matthews/bin
• prog main.o routines.o
• (CC) (CFLAGS) (OBJS) (LIBES) -o prog
• (OBJS) defs.h
• cleanup -rm .o -du
• install prog mv prog (INSTALL_DIR)
• print (FILES) pr ? gt /tmp/manton (LP)
  /tmp/manton -rm /tmp/manton touch print

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Make Implementation Algorithm

• Procedure newest(target)
• If target is not in the target tree then
• If file exists return(modification_time)
• Else return(FAIL)
• Else min modification_time of target
• Foreach child in the dependency list Do
• child_time newest(child)
• If child_time lt min Then min child_time
• End
• If min lt modification_time of target Then
• build(target)
• min now
• EndIf
• End
• End
• Begin Main
• Parse Specification File
• Build Dependency Tree
• newest(target)

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File Time Data Structures

• timeval, timezone and tm structures
• struct timeval
• long tv_sec / seconds since Jan. 1, 1970 /
• long tv_usec / and microseconds /
• struct timezone
• int tz_minuteswest / of Greenwich /
• int tz_dsttime / type of dst correction to
  apply /

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struct tm

• struct tm
• int tm_sec / seconds (0 - 59) /
• int tm_min / minutes (0 - 59) /
• int tm_hour / hours (0 - 23) /
• int tm_mday / day of month (1 - 31) /
• int tm_mon / month of year (0 - 11) /
• int tm_year / year - 1900 /
• int tm_wday / day of week (Sunday 0) /
• int tm_yday / day of year (0 - 365) /
• int tm_isdst / flag daylight savings time in
  effect /
• long tm_gmtoff / offset from GMT in seconds /
• char tm_zone / abbreviation of timezone name
  /

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File Time system calls and functions

• time_t time(time_t tloc) - return the current
  time
• char ctime(time_t clock) - convert time to
  character string for printing time_t now now
  time(NULL) printf("the current time is s\n",
  ctime(now))
• int gettimeofday(struct timeval tp, struct
  timezone tzp)
• char asctime(struct tm tm) convert struct tm
  pointer to character for printing
• struct tm localtime(time_t clock) - convert
  time_t to "broken down time"
• struct tm gmtime(time_t clock)- convert time_t
  to "broken down time"
• double difftime(time_t time1, time_t time0)
• time_t mktime(struct tm timeptr)
• int strftime (char s, size_t maxsize, char
  format, struct tm tm) - print time out using
  special conversion specifiers e.g. I -the hour
  on 12 hour clock, m the month, ...

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Figure 6.8 Time Function Relationships
string
gmtime
mktime
time
kernel
struct tm
time_t
mktime
formatted string
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Time.c

• include lttime.hgt
• include ltstdio.hgt
• main()
• time_t now
• struct tm bdtime, bdt_ptr
• char buf1024
• now time(NULL)
• printf("the number of seconds since the Epoch
  is ld\n", now)
• printf("the current time is s\n",
  ctime(now))
• bdt_ptr localtime(now)
• strftime(buf, 1024, "a b d H m j y u
  Z", bdt_ptr)
• printf("s\n", buf)