Home | History | Annotate | Download | only in docs
      1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
      2                       "http://www.w3.org/TR/html4/strict.dtd">
      3 <html>
      4 <head>
      5   <title>Exception Handling in LLVM</title>
      6   <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
      7   <meta name="description"
      8         content="Exception Handling in LLVM.">
      9   <link rel="stylesheet" href="llvm.css" type="text/css">
     10 </head>
     11 
     12 <body>
     13 
     14 <h1>Exception Handling in LLVM</h1>
     15 
     16 <table class="layout" style="width:100%">
     17   <tr class="layout">
     18     <td class="left">
     19 <ul>
     20   <li><a href="#introduction">Introduction</a>
     21   <ol>
     22     <li><a href="#itanium">Itanium ABI Zero-cost Exception Handling</a></li>
     23     <li><a href="#sjlj">Setjmp/Longjmp Exception Handling</a></li>
     24     <li><a href="#overview">Overview</a></li>
     25   </ol></li>
     26   <li><a href="#codegen">LLVM Code Generation</a>
     27   <ol>
     28     <li><a href="#throw">Throw</a></li>
     29     <li><a href="#try_catch">Try/Catch</a></li>
     30     <li><a href="#cleanups">Cleanups</a></li>
     31     <li><a href="#throw_filters">Throw Filters</a></li>
     32     <li><a href="#restrictions">Restrictions</a></li>
     33   </ol></li>
     34   <li><a href="#format_common_intrinsics">Exception Handling Intrinsics</a>
     35   <ol>
     36   	<li><a href="#llvm_eh_typeid_for"><tt>llvm.eh.typeid.for</tt></a></li>
     37   	<li><a href="#llvm_eh_sjlj_setjmp"><tt>llvm.eh.sjlj.setjmp</tt></a></li>
     38   	<li><a href="#llvm_eh_sjlj_longjmp"><tt>llvm.eh.sjlj.longjmp</tt></a></li>
     39   	<li><a href="#llvm_eh_sjlj_lsda"><tt>llvm.eh.sjlj.lsda</tt></a></li>
     40   	<li><a href="#llvm_eh_sjlj_callsite"><tt>llvm.eh.sjlj.callsite</tt></a></li>
     41   	<li><a href="#llvm_eh_sjlj_dispatchsetup"><tt>llvm.eh.sjlj.dispatchsetup</tt></a></li>
     42   </ol></li>
     43   <li><a href="#asm">Asm Table Formats</a>
     44   <ol>
     45     <li><a href="#unwind_tables">Exception Handling Frame</a></li>
     46     <li><a href="#exception_tables">Exception Tables</a></li>
     47   </ol></li>
     48 </ul>
     49 </td>
     50 </tr></table>
     51 
     52 <div class="doc_author">
     53   <p>Written by <a href="mailto:jlaskey (a] mac.com">Jim Laskey</a></p>
     54 </div>
     55 
     56 
     57 <!-- *********************************************************************** -->
     58 <h2><a name="introduction">Introduction</a></h2>
     59 <!-- *********************************************************************** -->
     60 
     61 <div>
     62 
     63 <p>This document is the central repository for all information pertaining to
     64    exception handling in LLVM.  It describes the format that LLVM exception
     65    handling information takes, which is useful for those interested in creating
     66    front-ends or dealing directly with the information.  Further, this document
     67    provides specific examples of what exception handling information is used for
     68    in C and C++.</p>
     69 
     70 <!-- ======================================================================= -->
     71 <h3>
     72   <a name="itanium">Itanium ABI Zero-cost Exception Handling</a>
     73 </h3>
     74 
     75 <div>
     76 
     77 <p>Exception handling for most programming languages is designed to recover from
     78    conditions that rarely occur during general use of an application.  To that
     79    end, exception handling should not interfere with the main flow of an
     80    application's algorithm by performing checkpointing tasks, such as saving the
     81    current pc or register state.</p>
     82 
     83 <p>The Itanium ABI Exception Handling Specification defines a methodology for
     84    providing outlying data in the form of exception tables without inlining
     85    speculative exception handling code in the flow of an application's main
     86    algorithm.  Thus, the specification is said to add "zero-cost" to the normal
     87    execution of an application.</p>
     88 
     89 <p>A more complete description of the Itanium ABI exception handling runtime
     90    support of can be found at
     91    <a href="http://www.codesourcery.com/cxx-abi/abi-eh.html">Itanium C++ ABI:
     92    Exception Handling</a>. A description of the exception frame format can be
     93    found at
     94    <a href="http://refspecs.freestandards.org/LSB_3.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html">Exception
     95    Frames</a>, with details of the DWARF 4 specification at
     96    <a href="http://dwarfstd.org/Dwarf4Std.php">DWARF 4 Standard</a>.
     97    A description for the C++ exception table formats can be found at
     98    <a href="http://www.codesourcery.com/cxx-abi/exceptions.pdf">Exception Handling
     99    Tables</a>.</p>
    100 
    101 </div>
    102 
    103 <!-- ======================================================================= -->
    104 <h3>
    105   <a name="sjlj">Setjmp/Longjmp Exception Handling</a>
    106 </h3>
    107 
    108 <div>
    109 
    110 <p>Setjmp/Longjmp (SJLJ) based exception handling uses LLVM intrinsics
    111    <a href="#llvm_eh_sjlj_setjmp"><tt>llvm.eh.sjlj.setjmp</tt></a> and
    112    <a href="#llvm_eh_sjlj_longjmp"><tt>llvm.eh.sjlj.longjmp</tt></a> to
    113    handle control flow for exception handling.</p>
    114 
    115 <p>For each function which does exception processing &mdash; be
    116    it <tt>try</tt>/<tt>catch</tt> blocks or cleanups &mdash; that function
    117    registers itself on a global frame list. When exceptions are unwinding, the
    118    runtime uses this list to identify which functions need processing.<p>
    119 
    120 <p>Landing pad selection is encoded in the call site entry of the function
    121    context. The runtime returns to the function via
    122    <a href="#llvm_eh_sjlj_longjmp"><tt>llvm.eh.sjlj.longjmp</tt></a>, where
    123    a switch table transfers control to the appropriate landing pad based on
    124    the index stored in the function context.</p>
    125 
    126 <p>In contrast to DWARF exception handling, which encodes exception regions
    127    and frame information in out-of-line tables, SJLJ exception handling
    128    builds and removes the unwind frame context at runtime. This results in
    129    faster exception handling at the expense of slower execution when no
    130    exceptions are thrown. As exceptions are, by their nature, intended for
    131    uncommon code paths, DWARF exception handling is generally preferred to
    132    SJLJ.</p>
    133 
    134 </div>
    135 
    136 <!-- ======================================================================= -->
    137 <h3>
    138   <a name="overview">Overview</a>
    139 </h3>
    140 
    141 <div>
    142 
    143 <p>When an exception is thrown in LLVM code, the runtime does its best to find a
    144    handler suited to processing the circumstance.</p>
    145 
    146 <p>The runtime first attempts to find an <i>exception frame</i> corresponding to
    147    the function where the exception was thrown.  If the programming language
    148    supports exception handling (e.g. C++), the exception frame contains a
    149    reference to an exception table describing how to process the exception.  If
    150    the language does not support exception handling (e.g. C), or if the
    151    exception needs to be forwarded to a prior activation, the exception frame
    152    contains information about how to unwind the current activation and restore
    153    the state of the prior activation.  This process is repeated until the
    154    exception is handled. If the exception is not handled and no activations
    155    remain, then the application is terminated with an appropriate error
    156    message.</p>
    157 
    158 <p>Because different programming languages have different behaviors when
    159    handling exceptions, the exception handling ABI provides a mechanism for
    160    supplying <i>personalities</i>. An exception handling personality is defined
    161    by way of a <i>personality function</i> (e.g. <tt>__gxx_personality_v0</tt>
    162    in C++), which receives the context of the exception, an <i>exception
    163    structure</i> containing the exception object type and value, and a reference
    164    to the exception table for the current function.  The personality function
    165    for the current compile unit is specified in a <i>common exception
    166    frame</i>.</p>
    167 
    168 <p>The organization of an exception table is language dependent. For C++, an
    169    exception table is organized as a series of code ranges defining what to do
    170    if an exception occurs in that range. Typically, the information associated
    171    with a range defines which types of exception objects (using C++ <i>type
    172    info</i>) that are handled in that range, and an associated action that
    173    should take place. Actions typically pass control to a <i>landing
    174    pad</i>.</p>
    175 
    176 <p>A landing pad corresponds roughly to the code found in the <tt>catch</tt>
    177    portion of a <tt>try</tt>/<tt>catch</tt> sequence. When execution resumes at
    178    a landing pad, it receives an <i>exception structure</i> and a
    179    <i>selector value</i> corresponding to the <i>type</i> of exception
    180    thrown. The selector is then used to determine which <i>catch</i> should
    181    actually process the exception.</p>
    182 
    183 </div>
    184 
    185 </div>
    186 
    187 <!-- ======================================================================= -->
    188 <h2>
    189   <a name="codegen">LLVM Code Generation</a>
    190 </h2>
    191 
    192 <div>
    193 
    194 <p>From a C++ developer's perspective, exceptions are defined in terms of the
    195    <tt>throw</tt> and <tt>try</tt>/<tt>catch</tt> statements. In this section
    196    we will describe the implementation of LLVM exception handling in terms of
    197    C++ examples.</p>
    198 
    199 <!-- ======================================================================= -->
    200 <h3>
    201   <a name="throw">Throw</a>
    202 </h3>
    203 
    204 <div>
    205 
    206 <p>Languages that support exception handling typically provide a <tt>throw</tt>
    207    operation to initiate the exception process. Internally, a <tt>throw</tt>
    208    operation breaks down into two steps.</p>
    209 
    210 <ol>
    211   <li>A request is made to allocate exception space for an exception structure.
    212       This structure needs to survive beyond the current activation. This
    213       structure will contain the type and value of the object being thrown.</li>
    214 
    215   <li>A call is made to the runtime to raise the exception, passing the
    216       exception structure as an argument.</li>
    217 </ol>
    218 
    219 <p>In C++, the allocation of the exception structure is done by the
    220    <tt>__cxa_allocate_exception</tt> runtime function. The exception raising is
    221    handled by <tt>__cxa_throw</tt>. The type of the exception is represented
    222    using a C++ RTTI structure.</p>
    223 
    224 </div>
    225 
    226 <!-- ======================================================================= -->
    227 <h3>
    228   <a name="try_catch">Try/Catch</a>
    229 </h3>
    230 
    231 <div>
    232 
    233 <p>A call within the scope of a <i>try</i> statement can potentially raise an
    234    exception. In those circumstances, the LLVM C++ front-end replaces the call
    235    with an <tt>invoke</tt> instruction. Unlike a call, the <tt>invoke</tt> has
    236    two potential continuation points:</p>
    237 
    238 <ol>
    239   <li>where to continue when the call succeeds as per normal, and</li>
    240 
    241   <li>where to continue if the call raises an exception, either by a throw or
    242       the unwinding of a throw</li>
    243 </ol>
    244 
    245 <p>The term used to define a the place where an <tt>invoke</tt> continues after
    246    an exception is called a <i>landing pad</i>. LLVM landing pads are
    247    conceptually alternative function entry points where an exception structure
    248    reference and a type info index are passed in as arguments. The landing pad
    249    saves the exception structure reference and then proceeds to select the catch
    250    block that corresponds to the type info of the exception object.</p>
    251 
    252 <p>The LLVM <a href="LangRef.html#i_landingpad"><tt>landingpad</tt>
    253    instruction</a> is used to convey information about the landing pad to the
    254    back end. For C++, the <tt>landingpad</tt> instruction returns a pointer and
    255    integer pair corresponding to the pointer to the <i>exception structure</i>
    256    and the <i>selector value</i> respectively.</p>
    257 
    258 <p>The <tt>landingpad</tt> instruction takes a reference to the personality
    259    function to be used for this <tt>try</tt>/<tt>catch</tt> sequence. The
    260    remainder of the instruction is a list of <i>cleanup</i>, <i>catch</i>,
    261    and <i>filter</i> clauses. The exception is tested against the clauses
    262    sequentially from first to last. The selector value is a positive number if
    263    the exception matched a type info, a negative number if it matched a filter,
    264    and zero if it matched a cleanup. If nothing is matched, the behavior of
    265    the program is <a href="#restrictions">undefined</a>. If a type info matched,
    266    then the selector value is the index of the type info in the exception table,
    267    which can be obtained using the
    268    <a href="#llvm_eh_typeid_for"><tt>llvm.eh.typeid.for</tt></a> intrinsic.</p>
    269 
    270 <p>Once the landing pad has the type info selector, the code branches to the
    271    code for the first catch. The catch then checks the value of the type info
    272    selector against the index of type info for that catch.  Since the type info
    273    index is not known until all the type infos have been gathered in the
    274    backend, the catch code must call the
    275    <a href="#llvm_eh_typeid_for"><tt>llvm.eh.typeid.for</tt></a> intrinsic to
    276    determine the index for a given type info. If the catch fails to match the
    277    selector then control is passed on to the next catch.</p>
    278 
    279 <p>Finally, the entry and exit of catch code is bracketed with calls to
    280    <tt>__cxa_begin_catch</tt> and <tt>__cxa_end_catch</tt>.</p>
    281 
    282 <ul>
    283   <li><tt>__cxa_begin_catch</tt> takes an exception structure reference as an
    284       argument and returns the value of the exception object.</li>
    285 
    286   <li><tt>__cxa_end_catch</tt> takes no arguments. This function:<br><br>
    287     <ol>
    288       <li>Locates the most recently caught exception and decrements its handler
    289           count,</li>
    290       <li>Removes the exception from the <i>caught</i> stack if the handler
    291           count goes to zero, and</li>
    292       <li>Destroys the exception if the handler count goes to zero and the
    293           exception was not re-thrown by throw.</li>
    294     </ol>
    295     <p><b>Note:</b> a rethrow from within the catch may replace this call with
    296        a <tt>__cxa_rethrow</tt>.</p></li>
    297 </ul>
    298 
    299 </div>
    300 
    301 <!-- ======================================================================= -->
    302 <h3>
    303   <a name="cleanups">Cleanups</a>
    304 </h3>
    305 
    306 <div>
    307 
    308 <p>A cleanup is extra code which needs to be run as part of unwinding a scope.
    309    C++ destructors are a typical example, but other languages and language
    310    extensions provide a variety of different kinds of cleanups. In general, a
    311    landing pad may need to run arbitrary amounts of cleanup code before actually
    312    entering a catch block. To indicate the presence of cleanups, a
    313    <a href="LangRef.html#i_landingpad"><tt>landingpad</tt> instruction</a>
    314    should have a <i>cleanup</i> clause. Otherwise, the unwinder will not stop at
    315    the landing pad if there are no catches or filters that require it to.</p>
    316 
    317 <p><b>Note:</b> Do not allow a new exception to propagate out of the execution
    318    of a cleanup. This can corrupt the internal state of the unwinder.
    319    Different languages describe different high-level semantics for these
    320    situations: for example, C++ requires that the process be terminated, whereas
    321    Ada cancels both exceptions and throws a third.</p>
    322 
    323 <p>When all cleanups are finished, if the exception is not handled by the
    324    current function, resume unwinding by calling the
    325    <a href="LangRef.html#i_resume"><tt>resume</tt> instruction</a>, passing in
    326    the result of the <tt>landingpad</tt> instruction for the original landing
    327    pad.</p>
    328 
    329 </div>
    330 
    331 <!-- ======================================================================= -->
    332 <h3>
    333   <a name="throw_filters">Throw Filters</a>
    334 </h3>
    335 
    336 <div>
    337 
    338 <p>C++ allows the specification of which exception types may be thrown from a
    339    function. To represent this, a top level landing pad may exist to filter out
    340    invalid types. To express this in LLVM code the
    341    <a href="LangRef.html#i_landingpad"><tt>landingpad</tt> instruction</a> will
    342    have a filter clause. The clause consists of an array of type infos.
    343    <tt>landingpad</tt> will return a negative value if the exception does not
    344    match any of the type infos. If no match is found then a call
    345    to <tt>__cxa_call_unexpected</tt> should be made, otherwise
    346    <tt>_Unwind_Resume</tt>.  Each of these functions requires a reference to the
    347    exception structure.  Note that the most general form of a
    348    <a href="LangRef.html#i_landingpad"><tt>landingpad</tt> instruction</a> can
    349    have any number of catch, cleanup, and filter clauses (though having more
    350    than one cleanup is pointless). The LLVM C++ front-end can generate such
    351    <a href="LangRef.html#i_landingpad"><tt>landingpad</tt> instructions</a> due
    352    to inlining creating nested exception handling scopes.</p>
    353 
    354 </div>
    355 
    356 <!-- ======================================================================= -->
    357 <h3>
    358   <a name="restrictions">Restrictions</a>
    359 </h3>
    360 
    361 <div>
    362 
    363 <p>The unwinder delegates the decision of whether to stop in a call frame to
    364    that call frame's language-specific personality function. Not all unwinders
    365    guarantee that they will stop to perform cleanups. For example, the GNU C++
    366    unwinder doesn't do so unless the exception is actually caught somewhere
    367    further up the stack.</p>
    368 
    369 <p>In order for inlining to behave correctly, landing pads must be prepared to
    370    handle selector results that they did not originally advertise. Suppose that
    371    a function catches exceptions of type <tt>A</tt>, and it's inlined into a
    372    function that catches exceptions of type <tt>B</tt>. The inliner will update
    373    the <tt>landingpad</tt> instruction for the inlined landing pad to include
    374    the fact that <tt>B</tt> is also caught. If that landing pad assumes that it
    375    will only be entered to catch an <tt>A</tt>, it's in for a rude awakening.
    376    Consequently, landing pads must test for the selector results they understand
    377    and then resume exception propagation with the
    378    <a href="LangRef.html#i_resume"><tt>resume</tt> instruction</a> if none of
    379    the conditions match.</p>
    380 
    381 </div>
    382 
    383 </div>
    384 
    385 <!-- ======================================================================= -->
    386 <h2>
    387   <a name="format_common_intrinsics">Exception Handling Intrinsics</a>
    388 </h2>
    389 
    390 <div>
    391 
    392 <p>In addition to the
    393    <a href="LangRef.html#i_landingpad"><tt>landingpad</tt></a> and
    394    <a href="LangRef.html#i_resume"><tt>resume</tt></a> instructions, LLVM uses
    395    several intrinsic functions (name prefixed with <i><tt>llvm.eh</tt></i>) to
    396    provide exception handling information at various points in generated
    397    code.</p>
    398 
    399 <!-- ======================================================================= -->
    400 <h4>
    401   <a name="llvm_eh_typeid_for">llvm.eh.typeid.for</a>
    402 </h4>
    403 
    404 <div>
    405 
    406 <pre>
    407   i32 @llvm.eh.typeid.for(i8* %type_info)
    408 </pre>
    409 
    410 <p>This intrinsic returns the type info index in the exception table of the
    411    current function.  This value can be used to compare against the result
    412    of <a href="LangRef.html#i_landingpad"><tt>landingpad</tt> instruction</a>.
    413    The single argument is a reference to a type info.</p>
    414 
    415 </div>
    416 
    417 <!-- ======================================================================= -->
    418 <h4>
    419   <a name="llvm_eh_sjlj_setjmp">llvm.eh.sjlj.setjmp</a>
    420 </h4>
    421 
    422 <div>
    423 
    424 <pre>
    425   i32 @llvm.eh.sjlj.setjmp(i8* %setjmp_buf)
    426 </pre>
    427 
    428 <p>For SJLJ based exception handling, this intrinsic forces register saving for
    429    the current function and stores the address of the following instruction for
    430    use as a destination address
    431    by <a href="#llvm_eh_sjlj_longjmp"><tt>llvm.eh.sjlj.longjmp</tt></a>. The
    432    buffer format and the overall functioning of this intrinsic is compatible
    433    with the GCC <tt>__builtin_setjmp</tt> implementation allowing code built
    434    with the clang and GCC to interoperate.</p>
    435 
    436 <p>The single parameter is a pointer to a five word buffer in which the calling
    437    context is saved. The front end places the frame pointer in the first word,
    438    and the target implementation of this intrinsic should place the destination
    439    address for a
    440    <a href="#llvm_eh_sjlj_longjmp"><tt>llvm.eh.sjlj.longjmp</tt></a> in the
    441    second word. The following three words are available for use in a
    442    target-specific manner.</p>
    443 
    444 </div>
    445 
    446 <!-- ======================================================================= -->
    447 <h4>
    448   <a name="llvm_eh_sjlj_longjmp">llvm.eh.sjlj.longjmp</a>
    449 </h4>
    450 
    451 <div>
    452 
    453 <pre>
    454   void @llvm.eh.sjlj.longjmp(i8* %setjmp_buf)
    455 </pre>
    456 
    457 <p>For SJLJ based exception handling, the <tt>llvm.eh.sjlj.longjmp</tt>
    458    intrinsic is used to implement <tt>__builtin_longjmp()</tt>. The single
    459    parameter is a pointer to a buffer populated
    460    by <a href="#llvm_eh_sjlj_setjmp"><tt>llvm.eh.sjlj.setjmp</tt></a>. The frame
    461    pointer and stack pointer are restored from the buffer, then control is
    462    transferred to the destination address.</p>
    463 
    464 </div>
    465 <!-- ======================================================================= -->
    466 <h4>
    467   <a name="llvm_eh_sjlj_lsda">llvm.eh.sjlj.lsda</a>
    468 </h4>
    469 
    470 <div>
    471 
    472 <pre>
    473   i8* @llvm.eh.sjlj.lsda()
    474 </pre>
    475 
    476 <p>For SJLJ based exception handling, the <tt>llvm.eh.sjlj.lsda</tt> intrinsic
    477    returns the address of the Language Specific Data Area (LSDA) for the current
    478    function. The SJLJ front-end code stores this address in the exception
    479    handling function context for use by the runtime.</p>
    480 
    481 </div>
    482 
    483 <!-- ======================================================================= -->
    484 <h4>
    485   <a name="llvm_eh_sjlj_callsite">llvm.eh.sjlj.callsite</a>
    486 </h4>
    487 
    488 <div>
    489 
    490 <pre>
    491   void @llvm.eh.sjlj.callsite(i32 %call_site_num)
    492 </pre>
    493 
    494 <p>For SJLJ based exception handling, the <tt>llvm.eh.sjlj.callsite</tt>
    495    intrinsic identifies the callsite value associated with the
    496    following <tt>invoke</tt> instruction. This is used to ensure that landing
    497    pad entries in the LSDA are generated in matching order.</p>
    498 
    499 </div>
    500 
    501 <!-- ======================================================================= -->
    502 <h4>
    503   <a name="llvm_eh_sjlj_dispatchsetup">llvm.eh.sjlj.dispatchsetup</a>
    504 </h4>
    505 
    506 <div>
    507 
    508 <pre>
    509   void @llvm.eh.sjlj.dispatchsetup(i32 %dispatch_value)
    510 </pre>
    511 
    512 <p>For SJLJ based exception handling, the <tt>llvm.eh.sjlj.dispatchsetup</tt>
    513    intrinsic is used by targets to do any unwind edge setup they need. By
    514    default, no action is taken.</p>
    515 
    516 </div>
    517 
    518 </div>
    519 
    520 <!-- ======================================================================= -->
    521 <h2>
    522   <a name="asm">Asm Table Formats</a>
    523 </h2>
    524 
    525 <div>
    526 
    527 <p>There are two tables that are used by the exception handling runtime to
    528    determine which actions should be taken when an exception is thrown.</p>
    529 
    530 <!-- ======================================================================= -->
    531 <h3>
    532   <a name="unwind_tables">Exception Handling Frame</a>
    533 </h3>
    534 
    535 <div>
    536 
    537 <p>An exception handling frame <tt>eh_frame</tt> is very similar to the unwind
    538    frame used by DWARF debug info. The frame contains all the information
    539    necessary to tear down the current frame and restore the state of the prior
    540    frame. There is an exception handling frame for each function in a compile
    541    unit, plus a common exception handling frame that defines information common
    542    to all functions in the unit.</p>
    543 
    544 <!-- Todo - Table details here. -->
    545 
    546 </div>
    547 
    548 <!-- ======================================================================= -->
    549 <h3>
    550   <a name="exception_tables">Exception Tables</a>
    551 </h3>
    552 
    553 <div>
    554 
    555 <p>An exception table contains information about what actions to take when an
    556    exception is thrown in a particular part of a function's code. There is one
    557    exception table per function, except leaf functions and functions that have
    558    calls only to non-throwing functions. They do not need an exception
    559    table.</p>
    560 
    561 <!-- Todo - Table details here. -->
    562 
    563 </div>
    564 
    565 </div>
    566 
    567 <!-- *********************************************************************** -->
    568 
    569 <hr>
    570 <address>
    571   <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
    572   src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
    573   <a href="http://validator.w3.org/check/referer"><img
    574   src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
    575 
    576   <a href="mailto:sabre (a] nondot.org">Chris Lattner</a><br>
    577   <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
    578   Last modified: $Date: 2011-09-27 16:16:57 -0400 (Tue, 27 Sep 2011) $
    579 </address>
    580 
    581 </body>
    582 </html>
    583