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215 lines
7.4 KiB
HTML
215 lines
7.4 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<h1>
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<center>
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LLVM: Frequently Asked Questions
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</center>
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</h1>
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<hr>
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<!--=====================================================================-->
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<h2>
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<a name="license">Licenses</a>
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</h2>
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<!--=====================================================================-->
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<dl compact>
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<dt> <b>Why are the LLVM source code and the front-end distributed
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under different licenses?</b>
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<dd>
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The C/C++ front-ends are based on GCC and must be distributed under
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the GPL. Our aim is to distribute LLVM source code under a <em>much
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less restrictive</em> license, in particular one that does not
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compel users who distribute tools based on modifying the source to
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redistribute the modified source code as well.
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<p>
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<dt><b>Does the Illinois Open Source License really qualify
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as an "open source" license?</b>
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<dd>The license is
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<a href="http://www.opensource.org/licenses/UoI-NCSA.php">certified</a>
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by the Open Source Initiative (OSI).
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<p>
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<dt> <b>Can I modify LLVM source code and redistribute the modified
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source?</b>
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<dd>
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Yes. The modified source distribution must retain the
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copyright notice and follow the three bulletted conditions listed in
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the <a href="http://llvm.cs.uiuc.edu/releases/1.0/LICENSE.TXT">LLVM license</a>.
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<p>
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<dt> <b>Can I modify LLVM source code and redistribute binaries or
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other tools based on it, without redistributing the source?</b>
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<dd>
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Yes, this is why we distribute LLVM under a less restrictive license
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than GPL, as explained in the first question above.
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<p>
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</dl>
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<hr>
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<!--=====================================================================-->
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<h2>
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<a name="source">Source Code</a>
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</h2>
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<!--=====================================================================-->
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<dl compact>
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<dt> <b>In what language is LLVM written?</b>
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<dd>
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All of the LLVM tools and libraries are written in C++ with extensive use
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of the STL.
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<p>
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<dt><b>How portable is the LLVM source code?</b>
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<dd>
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The LLVM source code should be portable to most modern UNIX-like operating
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systems. Most of the code is written in standard C++ with operating
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system services abstracted to a support library. The tools required to
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build and test LLVM have been ported to a plethora of platforms.
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<p>
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Some porting problems may exist in the following areas:
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<ul>
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<li>The GCC front end code is not as portable as the LLVM suite, so it
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may not compile as well on unsupported platforms.
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<p>
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<li>The Python test classes are more UNIX-centric than they should be,
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so porting to non-UNIX like platforms (i.e. Windows, MacOS 9) will
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require some effort.
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<p>
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<li>The LLVM build system relies heavily on UNIX shell tools, like the
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Bourne Shell and sed. Porting to systems without these tools (MacOS 9,
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Plan 9) will require more effort.
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</ul>
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</dl>
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<hr>
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<!--=====================================================================-->
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<h2>
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<a name="build">Build Problems</a>
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</h2>
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<!--=====================================================================-->
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<dl compact>
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<dt><b>When I run configure, it finds the wrong C compiler.</b>
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<dd>
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The <tt>configure</tt> script attempts to locate first <tt>gcc</tt> and
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then <tt>cc</tt>, unless it finds compiler paths set in <tt>CC</tt> and
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<tt>CXX</tt> for the C and C++ compiler, respectively.
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If <tt>configure</tt> finds the wrong compiler, either adjust your
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<tt>PATH</tt> environment variable or set <tt>CC</tt> and <tt>CXX</tt>
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explicitly.
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<p>
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<dt><b>I compile the code, and I get some error about /localhome</b>.
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<dd>
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There are several possible causes for this. The first is that you
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didn't set a pathname properly when using <tt>configure</tt>, and it
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defaulted to a pathname that we use on our research machines.
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<p>
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Another possibility is that we hardcoded a path in our Makefiles. If
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you see this, please email the LLVM bug mailing list with the name of
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the offending Makefile and a description of what is wrong with it.
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<dt><b>The <tt>configure</tt> script finds the right C compiler, but it
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uses the LLVM linker from a previous build. What do I do?</b>
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<dd>
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The <tt>configure</tt> script uses the <tt>PATH</tt> to find
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executables, so if it's grabbing the wrong linker/assembler/etc, there
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are two ways to fix it:
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<ol>
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<li>Adjust your <tt>PATH</tt> environment variable so that the
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correct program appears first in the <tt>PATH</tt>. This may work,
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but may not be convenient when you want them <i>first</i> in your
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path for other work.
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<p>
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<li>Run <tt>configure</tt> with an alternative <tt>PATH</tt> that
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is correct. In a Borne compatible shell, the syntax would be:
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<p>
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<tt>PATH=<the path without the bad program> ./configure ...</tt>
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<p>
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This is still somewhat inconvenient, but it allows
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<tt>configure</tt> to do its work without having to adjust your
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<tt>PATH</tt> permanently.
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</ol>
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<dt><b>When creating a dynamic library, I get a strange GLIBC error.</b>
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<dd>
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Under some operating systems (i.e. Linux), libtool does not work correctly
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if GCC was compiled with the --disable-shared option. To work around this,
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install your own version of GCC that has shared libraries enabled by
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default.
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<p>
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<dt><b>I've updated my source tree from CVS, and now my build is trying to
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use a file/directory that doesn't exist.</b>
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<dd>
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You need to re-run configure in your object directory. When new Makefiles
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are added to the source tree, they have to be copied over to the object
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tree in order to be used by the build.
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<p>
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<dt><b>I've modified a Makefile in my source tree, but my build tree keeps
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using the old version. What do I do?</b>
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<dd>
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If the Makefile already exists in your object tree, you can just run the
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following command in the top level directory of your object tree:
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<p>
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<tt>./config.status <relative path to Makefile></tt>
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<p>
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If the Makefile is new, you will have to modify the configure script to copy
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it over.
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<p>
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<dt><b>I've upgraded to a new version of LLVM, and I get strange build
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errors.</b>
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<dd>
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Sometimes changes to the LLVM source code alters how the build system
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works. Changes in libtool, autoconf, or header file dependencies are
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especially prone to this sort of problem.
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<p>
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The best thing to try is to remove the old files and re-build. In most
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cases, this takes care of the problem. To do this, just type <tt>make
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clean</tt> and then <tt>make</tt> in the directory that fails to build.
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<p>
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<dt><b>I've built LLVM and am testing it, but the tests freeze.</b>
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<dd>
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This is most likely occurring because you built a profile or release
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(optimized) build of LLVM and have not specified the same information on
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the <tt>gmake</tt> command line.
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<p>
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For example, if you built LLVM with the command:
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<p>
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<tt>gmake ENABLE_PROFILING=1</tt>
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<p>
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...then you must run the tests with the following commands:
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<p>
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<tt>cd llvm/test<br>gmake ENABLE_PROFILING=1</tt>
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<p>
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<dt><b>Why do test results differ when I perform different types of
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builds?</b>
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<dd>
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The LLVM test suite is dependent upon several features of the LLVM tools
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and libraries.
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<p>
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First, the debugging assertions in code are not enabled in optimized or
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profiling builds. Hence, tests that used to fail may pass.
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<p>
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Second, some tests may rely upon debugging options or behavior that is
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only available in the debug build. These tests will fail in an optimized
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or profile build.
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</dl>
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<hr>
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<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
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<br>
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</body>
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</html>
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