287 lines
5.2 KiB
HTML
287 lines
5.2 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>Hello, world!</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="Linux Assembly HOWTO"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Quick start"
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HREF="quickstart.html"><LINK
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REL="PREVIOUS"
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TITLE="Introduction"
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HREF="x832.html"><LINK
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REL="NEXT"
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TITLE="Building an executable"
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HREF="build.html"></HEAD
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><BODY
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CLASS="section"
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#840084"
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ALINK="#0000FF"
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><DIV
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CLASS="NAVHEADER"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>Linux Assembly HOWTO</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="x832.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 6. Quick start</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="build.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="section"
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><H1
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CLASS="section"
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><A
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NAME="AEN856"
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></A
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>6.2. Hello, world!</H1
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><DIV
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CLASS="section"
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><H2
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CLASS="section"
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><A
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NAME="AEN858"
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></A
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>6.2.1. Program layout</H2
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><P
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> Linux is 32-bit, runs in protected mode, has flat memory model, and uses the
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ELF format for binaries.
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</P
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><P
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> A program can be divided into sections: <TT
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CLASS="literal"
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>.text</TT
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> for your code
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(read-only), <TT
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CLASS="literal"
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>.data</TT
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> for your data (read-write),
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<TT
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CLASS="literal"
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>.bss</TT
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> for uninitialized data (read-write); there can actually
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be a few other standard sections, as well as some user-defined sections, but
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there's rare need to use them and they are out of our interest here. A program
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must have at least <TT
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CLASS="literal"
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>.text</TT
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> section.
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</P
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><P
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> Now we will write our first program. Here is sample code:
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</P
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></DIV
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><DIV
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CLASS="section"
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><H2
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CLASS="section"
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><A
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NAME="AEN867"
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></A
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>6.2.2. NASM (hello.asm)</H2
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><P
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> <TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="programlisting"
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> section .text ;section declaration
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;we must export the entry point to the ELF linker or
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global _start ;loader. They conventionally recognize _start as their
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;entry point. Use ld -e foo to override the default.
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_start:
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;write our string to stdout
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mov edx,len ;third argument: message length
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mov ecx,msg ;second argument: pointer to message to write
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mov ebx,1 ;first argument: file handle (stdout)
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mov eax,4 ;system call number (sys_write)
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int 0x80 ;call kernel
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;and exit
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mov ebx,0 ;first syscall argument: exit code
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mov eax,1 ;system call number (sys_exit)
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int 0x80 ;call kernel
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section .data ;section declaration
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msg db "Hello, world!",0xa ;our dear string
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len equ $ - msg ;length of our dear string
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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</P
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></DIV
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><DIV
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CLASS="section"
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><H2
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CLASS="section"
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><A
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NAME="AEN871"
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></A
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>6.2.3. GAS (hello.S)</H2
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><P
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> <TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="programlisting"
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> .text # section declaration
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# we must export the entry point to the ELF linker or
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.global _start # loader. They conventionally recognize _start as their
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# entry point. Use ld -e foo to override the default.
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_start:
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# write our string to stdout
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movl $len,%edx # third argument: message length
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movl $msg,%ecx # second argument: pointer to message to write
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movl $1,%ebx # first argument: file handle (stdout)
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movl $4,%eax # system call number (sys_write)
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int $0x80 # call kernel
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# and exit
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movl $0,%ebx # first argument: exit code
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movl $1,%eax # system call number (sys_exit)
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int $0x80 # call kernel
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.data # section declaration
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msg:
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.ascii "Hello, world!\n" # our dear string
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len = . - msg # length of our dear string
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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</P
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></DIV
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></DIV
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><DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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SUMMARY="Footer navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="x832.html"
|
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ACCESSKEY="P"
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>Prev</A
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></TD
|
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><TD
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WIDTH="34%"
|
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ALIGN="center"
|
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VALIGN="top"
|
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><A
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HREF="index.html"
|
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ACCESSKEY="H"
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>Home</A
|
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></TD
|
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><TD
|
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WIDTH="33%"
|
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ALIGN="right"
|
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VALIGN="top"
|
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><A
|
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HREF="build.html"
|
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ACCESSKEY="N"
|
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>Next</A
|
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></TD
|
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></TR
|
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><TR
|
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><TD
|
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WIDTH="33%"
|
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ALIGN="left"
|
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VALIGN="top"
|
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>Introduction</TD
|
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><TD
|
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WIDTH="34%"
|
|
ALIGN="center"
|
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VALIGN="top"
|
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><A
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HREF="quickstart.html"
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ACCESSKEY="U"
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>Up</A
|
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></TD
|
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><TD
|
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WIDTH="33%"
|
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ALIGN="right"
|
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VALIGN="top"
|
|
>Building an executable</TD
|
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></TR
|
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></TABLE
|
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></DIV
|
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></BODY
|
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></HTML
|
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> |