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><HEAD
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><TITLE
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>Determining Program Behavior</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
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"/><LINK
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REL="HOME"
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HREF="t1.htm"/><LINK
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TITLE="Gathering Info"
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HREF="x47.htm"/><LINK
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TITLE="Determining Interesting Functions"
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HREF="x125.htm"/></HEAD
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>Prev</A
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>Next</A
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WIDTH="100%"/></DIV
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><DIV
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CLASS="sect1"
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><H1
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CLASS="sect1"
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><A
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NAME="AEN79"/>4. Determining Program Behavior</H1
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><P
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> There are a couple of tools that allow us to look into program
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behavior at a more closer level. Lets look at some of these:
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</P
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><DIV
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CLASS="sect2"
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><H2
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CLASS="sect2"
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><A
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NAME="AEN82"/>4.1. strace/truss(Solaris)</H2
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><P
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> These programs trace system calls a program makes as it makes them.
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</P
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><P
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>Useful options:
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<P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>-f (follow fork)</P
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></LI
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><LI
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><P
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>-ffo filename (output trace to filename.pid for
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forking)</P
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></LI
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><LI
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><P
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>-i (Print instruction pointer for each system
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call)</P
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></LI
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></OL
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>
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</P
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></DIV
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><DIV
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CLASS="sect2"
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><H2
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CLASS="sect2"
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><A
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NAME="AEN93"/>4.2. ltrace</H2
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><P
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> This utility is extremely useful. It traces ALL library calls made by a
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program.
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</P
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><P
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>Useful options:
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<P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>-S (display syscalls too)</P
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></LI
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><LI
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><P
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>-f (follow fork)</P
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></LI
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><LI
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><P
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>-o filename (output trace to filename)</P
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></LI
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><LI
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><P
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>-C (demangle C++ function call names)</P
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></LI
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><LI
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><P
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>-n 2 (indent each nested call 2 spaces)</P
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></LI
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><LI
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><P
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>-i (prints instruction pointer of caller)</P
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></LI
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><LI
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><P
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>-p pid (attaches to specified pid)</P
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></LI
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></OL
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>
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</P
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></DIV
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><DIV
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CLASS="sect2"
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><H2
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CLASS="sect2"
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><A
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NAME="AEN112"/>4.3. LD_PRELOAD</H2
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><P
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> This is an environment variable that allows us to add a library to the
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execution of a particular program. Any functions in this library
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automatically override standard library functions. Sorry, you can't use
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this with suid programs.
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</P
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><P
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>Example:</P
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><P
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>% gcc -o preload.so -shared <A
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HREF="code/preload.c"
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TARGET="_top"
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>preload.c</A
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> -ldl</P
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><P
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>% LD_PRELOAD=preload.so ssh students.uiuc.edu</P
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></DIV
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><DIV
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CLASS="sect2"
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><H2
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CLASS="sect2"
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><A
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NAME="AEN119"/>4.4. gdb</H2
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><P
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> gdb is the GNU debugger. It is very intimidating to most people, but
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there really is no reason for it to be. It is very well done for a
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command line debugger. There is a nice GUI front end to it known as
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<A
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HREF="http://www.gnu.org/software/ddd/"
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TARGET="_top"
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>DDD</A
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>,
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but our purposes will require a closer relationship with the command
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line.
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</P
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><P
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> gdb has a nice built-in help system organized by topic. typing help will
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show you the catagories. The main commands we will be interested in are
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run, break, cont, stepi, finish, disassemble, bt, info [registers/frame], and x.
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Every command in gdb can be followed by a number N, which means repeat N
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times. For example, stepi 1000 will step over 1000 assembly instructions.
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</P
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><P
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> -> Example using gdb to set breakpoints in functions with and without
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debugging symbols.
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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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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="x47.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="t1.htm"
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ACCESSKEY="H"
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>Home</A
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WIDTH="33%"
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VALIGN="top"
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HREF="x125.htm"
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ACCESSKEY="N"
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>Next</A
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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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>Gathering Info</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
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Determining Interesting Functions</TD
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></TR
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></TABLE
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