mirror of
https://github.com/serge1/ELFIO.git
synced 2024-10-06 23:10:06 +00:00
265 lines
5.7 KiB
HTML
Executable File
265 lines
5.7 KiB
HTML
Executable File
<HTML
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><HEAD
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><TITLE
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> IELFO - ELF File Producer Interface
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</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.74b"><LINK
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REL="HOME"
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TITLE="ELFIO"
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HREF="index.php"><LINK
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REL="PREVIOUS"
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TITLE="ELFDump Utility"
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HREF="c63.htm"></HEAD
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><BODY
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CLASS="CHAPTER"
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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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>ELFIO: Tutorial</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="c63.htm"
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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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></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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> </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="CHAPTER"
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><H1
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><A
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NAME="ielfo"
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>Chapter 3. <FONT
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COLOR="RED"
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>IELFO</FONT
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> - ELF File Producer Interface
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</A
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></H1
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>
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<P
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> The ELFIO library can help you build a very short ELF executable file.
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This chapter shows how to build an executable file that will run on
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x86 Linux machines and print "Hello World!" on your console.
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</P
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>
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<P
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> Just as with the reader, the first step is to get
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a pointer onto the ELF File Writer (Producer):
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<PRE
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CLASS="PROGRAMLISTING"
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> IELFO* pELFO;
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ELFIO::GetInstance()->CreateELFO( &pELFO );</PRE
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>
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</P
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>
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<P
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> Before continuing, the library must be informed about the main
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attributes of the executable file to be built. To do this, declare
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that the executable ELF file will run on a 32 bit x86 machine; has little
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endian encoding and uses the current version of the ELF file format:
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<PRE
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CLASS="PROGRAMLISTING"
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> // You can't proceed without this function call!
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pELFO->SetAttr( ELFCLASS32, ELFDATA2LSB, EV_CURRENT,
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ET_EXEC, EM_386, EV_CURRENT, 0 );</PRE
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>
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</P
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>
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<P
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> Some sections of an ELF executable file should reside in the program
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segments. To create this loadable segment call the
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<TT
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CLASS="METHODNAME"
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>AddSegment()</TT
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> function.
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<PRE
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CLASS="PROGRAMLISTING"
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> // Create a loadable segment
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IELFOSegment* pSegment = pELFO->AddSegment( PT_LOAD,
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0x08040000,
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0x08040000,
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PF_X | PF_R,
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0x1000 );</PRE
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>
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</P
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>
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<P
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> The following segment serves as a placeholder for our code section. To create
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this code section call the AddSection() function:
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<PRE
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CLASS="PROGRAMLISTING"
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> // Create code section
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IELFOSection* pTextSec = pELFO->AddSection( ".text",
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SHT_PROGBITS,
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SHF_ALLOC | SHF_EXECINSTR,
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0,
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0x10,
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0 );</PRE
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>
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</P
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>
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<P
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> Then, add the executable code for the section:
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<PRE
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CLASS="PROGRAMLISTING"
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> char text[] =
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{ '\xB8', '\x04', '\x00', '\x00', '\x00', // mov eax, 4
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'\xBB', '\x01', '\x00', '\x00', '\x00', // mov ebx, 1
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'\xB9', '\xFD', '\x00', '\x04', '\x08', // mov ecx, msg
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'\xBA', '\x0E', '\x00', '\x00', '\x00', // mov edx, 14
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'\xCD', '\x80', // int 0x80
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'\xB8', '\x01', '\x00', '\x00', '\x00', // mov eax, 1
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'\xCD', '\x80', // int 0x80
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'\x48', '\x65', '\x6C', '\x6C', '\x6F', // db 'Hello'
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'\x2C', '\x20', '\x57', '\x6F', '\x72', // db ', Wor'
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'\x6C', '\x64', '\x21', '\x0A' // db 'ld!', 10
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};
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pTextSec->SetData( text, sizeof( text ) );</PRE
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>
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</P
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>
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<P
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> Next, this code section is put into the loadable segment:
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<PRE
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CLASS="PROGRAMLISTING"
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> // Add code section into program segment
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pSegment->AddSection( pTextSec );
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pTextSec->Release();
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pSegment->Release();</PRE
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>
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</P
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>
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<P
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> Finally, define the start address of the program
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and create the result file:
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<PRE
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CLASS="PROGRAMLISTING"
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> // Set program entry point
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pELFO->SetEntry( 0x08040000 );
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// Create ELF file
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pELFO->Save( "test.elf" );
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pELFO->Release();</PRE
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>
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</P
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>
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<P
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> Please note: Call the <TT
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CLASS="METHODNAME"
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>Release()</TT
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> functions
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for each interface you have used.
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This will free all resources the ELFIO library has created.
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</P
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>
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<P
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> Now compile the program and run it. The result is a new ELF file
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called "test.elf". The size of this working executable file is only
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267 bytes! Run it on your Linux machine with the following commands:
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<PRE
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CLASS="PROGRAMLISTING"
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> [Writer]$ ./Writer
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[Writer]$ chmod +x test.elf
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[Writer]$ ./test.elf
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Hello, World!</PRE
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>
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</P
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>
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<P
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> The full text for this program can be found in the "Writer" directory.
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Also, in the "Examples" directory, two other programs "WriteObj"
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and "WriteObj2" demonstrate the creation of ELF object files.
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</P
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>
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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="c63.htm"
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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.php"
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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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> </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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>ELFDump Utility</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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> </TD
|
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><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
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VALIGN="top"
|
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> </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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>
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