#! /bin/ksh

# This script modifies 32-bit XCOFF variable o_maxdata (+4C).
# Non-zero o_maxdata uses the AIX "Large Address Space Model."
# See "AIX: General Programming Concepts, Writing and Debugging Pgms."

# To find the current maxdata setting for an executable
# run the command dump -ov executable  look for the maxDATA entry
# on the last line.

# exactly two parameters?
# 1st parm is name of executable
# 2nd parm is maxdata unit

# maxdata units are:
# 0 = 256mb
# 1 = 256mb
# 2 = 512mb
# 3 = 768mb
# 4 = 1024mb-1gb 
# 5 = 1280mb
# 6 = 1536mb
# 7 = 1792mb
# 8 = 2048mb-2gb-max size for 32bit software/hardware
#
if [[ $# -ne 2 ]] 
then
  print 'usage: "maxdata XCOFF [0-8]"' ; 
  print '\tThe second parameter (maxdata size) specifies units of 256M.' ;
  print '\te.g.:  "maxdata /bin/xldb  4" sets /bin/xldb maxdata to 1G.' ;
  exit ;
fi

# first parm a 32-bit xcoff?
file $1 | grep -q 'executable (RISC System/6000) or object module' ;
if [[ $? -ne 0 ]] 
then 
  print "$1 isn't a readable 32-bit XCOFF file." ;
  exit ;
fi

# ... and writable?
if [[ ! -w $1 ]] 
then
  print "$1 isn't a writable and executable file." ;
  exit ;
fi

# second parm equals 0,1,2,...,8 ?
case ${2:-4} in 
[0-8] ) typeset -i8  d=${2:-4}*16  ;
        typeset -i10 m=${2:-4}*256 ;;
    * ) print 'The second parameter has to be an integer [0-8].' ;
        exit 1 ;; 
esac

# Do it:
print -n "$1 o_maxdata before: " ; od -HAx -N4 -j76 $1 | head -1 ;

eval "print -n '\\0'${d#*#}'\\0\\0\\0' | 
      dd of=$1 bs=4 count=1 seek=19 conv=notrunc 2>/dev/null" ;

print -n "$1 o_maxdata after:  " ; od -HAx -N4 -j76 $1 | head -1 ;

print "Maxdata in $1 now set to ${m}M." ;