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From:	Brandon Chase <tapedispenser7 AT hotmail DOT com>
To:	<cygwin AT cygwin DOT com>
Subject:	Assembly language exit() syscall does not return correct value
Date:	Mon, 15 Mar 2010 16:23:39 +0000
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The following program is supposed to return a value of 222 when echo $?=20
run, but I get 127 every time, no matter what I change. I have looked=20
around but cannot seem to find out if this is an error or a=20
cygwin-specific value.

----------------------------------------------------------
#PURPOSE:
 This program finds the maximum number of a
# set of data items.
#
#VARIABLES:
 The registers have the following uses:
#
# %edi - Holds the index
 of the data item being examined
# %ebx - Largest data item found
#
 %eax - Current data item
#
# The following memory locations are=20
used:
#
# data_items - contains the item data. A 0 is used
# to
 terminate the data
#
.section .data

data_items: #These are
 the data items
.long 3,67,34,222,45,75,54,34,44,33,22,11,66,0

.section
 .text

.globl _start

_start:
movl $0,=20
%edi=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0 =A0 =A0 =A0 =A0=A0 # move 0 into the index register
movl
 data_items(,%edi,4), %eax=A0=A0=A0=A0=A0=A0=A0=A0 # load the first byte of=
 data
movl
 %eax, %ebx=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0 # since this is the first item,=20
%eax is
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 # the=20
biggest
start_loop:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 # start loop

cmpl
 $0, %eax=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0=A0=A0 # check to see if we=92ve hit the=20
end
je loop_exit
incl %edi=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 #=20
load next value
movl data_items(,%edi,4), %eax
cmpl %ebx,=20
%eax=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0 # compare values
jle=20
start_loop=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 # jump to loop beginning if=20
the new
# one isn=92t bigger
movl %eax,=20
%ebx=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0 # move the value as the largest
32

jmp
 start_loop=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0=A0=A0 # jump to loop beginning
loop_exit:

#
 %ebx is the status code for the exit system call
# and it already=20
has the maximum number

movl $1, %eax =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 #=
1 is the exit() syscall

-----------

$>
 as maximum.s -o maximum.o
$> ld maximum.o -o maximum
$>./maximum
$>echo
 $?
127











=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20

=20=09=09=20=09=20=20=20=09=09=20=20
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