mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2024-12-23 12:08:25 +00:00
562 lines
22 KiB
HTML
562 lines
22 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
|
|
"http://www.w3.org/TR/html4/strict.dtd">
|
|
<html>
|
|
<head>
|
|
<title>Exception Handling in LLVM</title>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<meta name="description"
|
|
content="Exception Handling in LLVM.">
|
|
<link rel="stylesheet" href="llvm.css" type="text/css">
|
|
</head>
|
|
|
|
<body>
|
|
|
|
<h1>Exception Handling in LLVM</h1>
|
|
|
|
<table class="layout" style="width:100%">
|
|
<tr class="layout">
|
|
<td class="left">
|
|
<ul>
|
|
<li><a href="#introduction">Introduction</a>
|
|
<ol>
|
|
<li><a href="#itanium">Itanium ABI Zero-cost Exception Handling</a></li>
|
|
<li><a href="#sjlj">Setjmp/Longjmp Exception Handling</a></li>
|
|
<li><a href="#overview">Overview</a></li>
|
|
</ol></li>
|
|
<li><a href="#codegen">LLVM Code Generation</a>
|
|
<ol>
|
|
<li><a href="#throw">Throw</a></li>
|
|
<li><a href="#try_catch">Try/Catch</a></li>
|
|
<li><a href="#cleanups">Cleanups</a></li>
|
|
<li><a href="#throw_filters">Throw Filters</a></li>
|
|
<li><a href="#restrictions">Restrictions</a></li>
|
|
</ol></li>
|
|
<li><a href="#format_common_intrinsics">Exception Handling Intrinsics</a>
|
|
<ol>
|
|
<li><a href="#llvm_eh_typeid_for"><tt>llvm.eh.typeid.for</tt></a></li>
|
|
<li><a href="#llvm_eh_sjlj_setjmp"><tt>llvm.eh.sjlj.setjmp</tt></a></li>
|
|
<li><a href="#llvm_eh_sjlj_longjmp"><tt>llvm.eh.sjlj.longjmp</tt></a></li>
|
|
<li><a href="#llvm_eh_sjlj_lsda"><tt>llvm.eh.sjlj.lsda</tt></a></li>
|
|
<li><a href="#llvm_eh_sjlj_callsite"><tt>llvm.eh.sjlj.callsite</tt></a></li>
|
|
</ol></li>
|
|
<li><a href="#asm">Asm Table Formats</a>
|
|
<ol>
|
|
<li><a href="#unwind_tables">Exception Handling Frame</a></li>
|
|
<li><a href="#exception_tables">Exception Tables</a></li>
|
|
</ol></li>
|
|
</ul>
|
|
</td>
|
|
</tr></table>
|
|
|
|
<div class="doc_author">
|
|
<p>Written by the <a href="http://llvm.org/">LLVM Team</a></p>
|
|
</div>
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2><a name="introduction">Introduction</a></h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<p>This document is the central repository for all information pertaining to
|
|
exception handling in LLVM. It describes the format that LLVM exception
|
|
handling information takes, which is useful for those interested in creating
|
|
front-ends or dealing directly with the information. Further, this document
|
|
provides specific examples of what exception handling information is used for
|
|
in C and C++.</p>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="itanium">Itanium ABI Zero-cost Exception Handling</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>Exception handling for most programming languages is designed to recover from
|
|
conditions that rarely occur during general use of an application. To that
|
|
end, exception handling should not interfere with the main flow of an
|
|
application's algorithm by performing checkpointing tasks, such as saving the
|
|
current pc or register state.</p>
|
|
|
|
<p>The Itanium ABI Exception Handling Specification defines a methodology for
|
|
providing outlying data in the form of exception tables without inlining
|
|
speculative exception handling code in the flow of an application's main
|
|
algorithm. Thus, the specification is said to add "zero-cost" to the normal
|
|
execution of an application.</p>
|
|
|
|
<p>A more complete description of the Itanium ABI exception handling runtime
|
|
support of can be found at
|
|
<a href="http://www.codesourcery.com/cxx-abi/abi-eh.html">Itanium C++ ABI:
|
|
Exception Handling</a>. A description of the exception frame format can be
|
|
found at
|
|
<a href="http://refspecs.freestandards.org/LSB_3.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html">Exception
|
|
Frames</a>, with details of the DWARF 4 specification at
|
|
<a href="http://dwarfstd.org/Dwarf4Std.php">DWARF 4 Standard</a>.
|
|
A description for the C++ exception table formats can be found at
|
|
<a href="http://www.codesourcery.com/cxx-abi/exceptions.pdf">Exception Handling
|
|
Tables</a>.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="sjlj">Setjmp/Longjmp Exception Handling</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>Setjmp/Longjmp (SJLJ) based exception handling uses LLVM intrinsics
|
|
<a href="#llvm_eh_sjlj_setjmp"><tt>llvm.eh.sjlj.setjmp</tt></a> and
|
|
<a href="#llvm_eh_sjlj_longjmp"><tt>llvm.eh.sjlj.longjmp</tt></a> to
|
|
handle control flow for exception handling.</p>
|
|
|
|
<p>For each function which does exception processing — be
|
|
it <tt>try</tt>/<tt>catch</tt> blocks or cleanups — that function
|
|
registers itself on a global frame list. When exceptions are unwinding, the
|
|
runtime uses this list to identify which functions need processing.<p>
|
|
|
|
<p>Landing pad selection is encoded in the call site entry of the function
|
|
context. The runtime returns to the function via
|
|
<a href="#llvm_eh_sjlj_longjmp"><tt>llvm.eh.sjlj.longjmp</tt></a>, where
|
|
a switch table transfers control to the appropriate landing pad based on
|
|
the index stored in the function context.</p>
|
|
|
|
<p>In contrast to DWARF exception handling, which encodes exception regions
|
|
and frame information in out-of-line tables, SJLJ exception handling
|
|
builds and removes the unwind frame context at runtime. This results in
|
|
faster exception handling at the expense of slower execution when no
|
|
exceptions are thrown. As exceptions are, by their nature, intended for
|
|
uncommon code paths, DWARF exception handling is generally preferred to
|
|
SJLJ.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="overview">Overview</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>When an exception is thrown in LLVM code, the runtime does its best to find a
|
|
handler suited to processing the circumstance.</p>
|
|
|
|
<p>The runtime first attempts to find an <i>exception frame</i> corresponding to
|
|
the function where the exception was thrown. If the programming language
|
|
supports exception handling (e.g. C++), the exception frame contains a
|
|
reference to an exception table describing how to process the exception. If
|
|
the language does not support exception handling (e.g. C), or if the
|
|
exception needs to be forwarded to a prior activation, the exception frame
|
|
contains information about how to unwind the current activation and restore
|
|
the state of the prior activation. This process is repeated until the
|
|
exception is handled. If the exception is not handled and no activations
|
|
remain, then the application is terminated with an appropriate error
|
|
message.</p>
|
|
|
|
<p>Because different programming languages have different behaviors when
|
|
handling exceptions, the exception handling ABI provides a mechanism for
|
|
supplying <i>personalities</i>. An exception handling personality is defined
|
|
by way of a <i>personality function</i> (e.g. <tt>__gxx_personality_v0</tt>
|
|
in C++), which receives the context of the exception, an <i>exception
|
|
structure</i> containing the exception object type and value, and a reference
|
|
to the exception table for the current function. The personality function
|
|
for the current compile unit is specified in a <i>common exception
|
|
frame</i>.</p>
|
|
|
|
<p>The organization of an exception table is language dependent. For C++, an
|
|
exception table is organized as a series of code ranges defining what to do
|
|
if an exception occurs in that range. Typically, the information associated
|
|
with a range defines which types of exception objects (using C++ <i>type
|
|
info</i>) that are handled in that range, and an associated action that
|
|
should take place. Actions typically pass control to a <i>landing
|
|
pad</i>.</p>
|
|
|
|
<p>A landing pad corresponds roughly to the code found in the <tt>catch</tt>
|
|
portion of a <tt>try</tt>/<tt>catch</tt> sequence. When execution resumes at
|
|
a landing pad, it receives an <i>exception structure</i> and a
|
|
<i>selector value</i> corresponding to the <i>type</i> of exception
|
|
thrown. The selector is then used to determine which <i>catch</i> should
|
|
actually process the exception.</p>
|
|
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h2>
|
|
<a name="codegen">LLVM Code Generation</a>
|
|
</h2>
|
|
|
|
<div>
|
|
|
|
<p>From a C++ developer's perspective, exceptions are defined in terms of the
|
|
<tt>throw</tt> and <tt>try</tt>/<tt>catch</tt> statements. In this section
|
|
we will describe the implementation of LLVM exception handling in terms of
|
|
C++ examples.</p>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="throw">Throw</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>Languages that support exception handling typically provide a <tt>throw</tt>
|
|
operation to initiate the exception process. Internally, a <tt>throw</tt>
|
|
operation breaks down into two steps.</p>
|
|
|
|
<ol>
|
|
<li>A request is made to allocate exception space for an exception structure.
|
|
This structure needs to survive beyond the current activation. This
|
|
structure will contain the type and value of the object being thrown.</li>
|
|
|
|
<li>A call is made to the runtime to raise the exception, passing the
|
|
exception structure as an argument.</li>
|
|
</ol>
|
|
|
|
<p>In C++, the allocation of the exception structure is done by the
|
|
<tt>__cxa_allocate_exception</tt> runtime function. The exception raising is
|
|
handled by <tt>__cxa_throw</tt>. The type of the exception is represented
|
|
using a C++ RTTI structure.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="try_catch">Try/Catch</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>A call within the scope of a <i>try</i> statement can potentially raise an
|
|
exception. In those circumstances, the LLVM C++ front-end replaces the call
|
|
with an <tt>invoke</tt> instruction. Unlike a call, the <tt>invoke</tt> has
|
|
two potential continuation points:</p>
|
|
|
|
<ol>
|
|
<li>where to continue when the call succeeds as per normal, and</li>
|
|
|
|
<li>where to continue if the call raises an exception, either by a throw or
|
|
the unwinding of a throw</li>
|
|
</ol>
|
|
|
|
<p>The term used to define a the place where an <tt>invoke</tt> continues after
|
|
an exception is called a <i>landing pad</i>. LLVM landing pads are
|
|
conceptually alternative function entry points where an exception structure
|
|
reference and a type info index are passed in as arguments. The landing pad
|
|
saves the exception structure reference and then proceeds to select the catch
|
|
block that corresponds to the type info of the exception object.</p>
|
|
|
|
<p>The LLVM <a href="LangRef.html#i_landingpad"><tt>landingpad</tt>
|
|
instruction</a> is used to convey information about the landing pad to the
|
|
back end. For C++, the <tt>landingpad</tt> instruction returns a pointer and
|
|
integer pair corresponding to the pointer to the <i>exception structure</i>
|
|
and the <i>selector value</i> respectively.</p>
|
|
|
|
<p>The <tt>landingpad</tt> instruction takes a reference to the personality
|
|
function to be used for this <tt>try</tt>/<tt>catch</tt> sequence. The
|
|
remainder of the instruction is a list of <i>cleanup</i>, <i>catch</i>,
|
|
and <i>filter</i> clauses. The exception is tested against the clauses
|
|
sequentially from first to last. The selector value is a positive number if
|
|
the exception matched a type info, a negative number if it matched a filter,
|
|
and zero if it matched a cleanup. If nothing is matched, the behavior of
|
|
the program is <a href="#restrictions">undefined</a>. If a type info matched,
|
|
then the selector value is the index of the type info in the exception table,
|
|
which can be obtained using the
|
|
<a href="#llvm_eh_typeid_for"><tt>llvm.eh.typeid.for</tt></a> intrinsic.</p>
|
|
|
|
<p>Once the landing pad has the type info selector, the code branches to the
|
|
code for the first catch. The catch then checks the value of the type info
|
|
selector against the index of type info for that catch. Since the type info
|
|
index is not known until all the type infos have been gathered in the
|
|
backend, the catch code must call the
|
|
<a href="#llvm_eh_typeid_for"><tt>llvm.eh.typeid.for</tt></a> intrinsic to
|
|
determine the index for a given type info. If the catch fails to match the
|
|
selector then control is passed on to the next catch.</p>
|
|
|
|
<p>Finally, the entry and exit of catch code is bracketed with calls to
|
|
<tt>__cxa_begin_catch</tt> and <tt>__cxa_end_catch</tt>.</p>
|
|
|
|
<ul>
|
|
<li><tt>__cxa_begin_catch</tt> takes an exception structure reference as an
|
|
argument and returns the value of the exception object.</li>
|
|
|
|
<li><tt>__cxa_end_catch</tt> takes no arguments. This function:<br><br>
|
|
<ol>
|
|
<li>Locates the most recently caught exception and decrements its handler
|
|
count,</li>
|
|
<li>Removes the exception from the <i>caught</i> stack if the handler
|
|
count goes to zero, and</li>
|
|
<li>Destroys the exception if the handler count goes to zero and the
|
|
exception was not re-thrown by throw.</li>
|
|
</ol>
|
|
<p><b>Note:</b> a rethrow from within the catch may replace this call with
|
|
a <tt>__cxa_rethrow</tt>.</p></li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="cleanups">Cleanups</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>A cleanup is extra code which needs to be run as part of unwinding a scope.
|
|
C++ destructors are a typical example, but other languages and language
|
|
extensions provide a variety of different kinds of cleanups. In general, a
|
|
landing pad may need to run arbitrary amounts of cleanup code before actually
|
|
entering a catch block. To indicate the presence of cleanups, a
|
|
<a href="LangRef.html#i_landingpad"><tt>landingpad</tt> instruction</a>
|
|
should have a <i>cleanup</i> clause. Otherwise, the unwinder will not stop at
|
|
the landing pad if there are no catches or filters that require it to.</p>
|
|
|
|
<p><b>Note:</b> Do not allow a new exception to propagate out of the execution
|
|
of a cleanup. This can corrupt the internal state of the unwinder.
|
|
Different languages describe different high-level semantics for these
|
|
situations: for example, C++ requires that the process be terminated, whereas
|
|
Ada cancels both exceptions and throws a third.</p>
|
|
|
|
<p>When all cleanups are finished, if the exception is not handled by the
|
|
current function, resume unwinding by calling the
|
|
<a href="LangRef.html#i_resume"><tt>resume</tt> instruction</a>, passing in
|
|
the result of the <tt>landingpad</tt> instruction for the original landing
|
|
pad.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="throw_filters">Throw Filters</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>C++ allows the specification of which exception types may be thrown from a
|
|
function. To represent this, a top level landing pad may exist to filter out
|
|
invalid types. To express this in LLVM code the
|
|
<a href="LangRef.html#i_landingpad"><tt>landingpad</tt> instruction</a> will
|
|
have a filter clause. The clause consists of an array of type infos.
|
|
<tt>landingpad</tt> will return a negative value if the exception does not
|
|
match any of the type infos. If no match is found then a call
|
|
to <tt>__cxa_call_unexpected</tt> should be made, otherwise
|
|
<tt>_Unwind_Resume</tt>. Each of these functions requires a reference to the
|
|
exception structure. Note that the most general form of a
|
|
<a href="LangRef.html#i_landingpad"><tt>landingpad</tt> instruction</a> can
|
|
have any number of catch, cleanup, and filter clauses (though having more
|
|
than one cleanup is pointless). The LLVM C++ front-end can generate such
|
|
<a href="LangRef.html#i_landingpad"><tt>landingpad</tt> instructions</a> due
|
|
to inlining creating nested exception handling scopes.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="restrictions">Restrictions</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>The unwinder delegates the decision of whether to stop in a call frame to
|
|
that call frame's language-specific personality function. Not all unwinders
|
|
guarantee that they will stop to perform cleanups. For example, the GNU C++
|
|
unwinder doesn't do so unless the exception is actually caught somewhere
|
|
further up the stack.</p>
|
|
|
|
<p>In order for inlining to behave correctly, landing pads must be prepared to
|
|
handle selector results that they did not originally advertise. Suppose that
|
|
a function catches exceptions of type <tt>A</tt>, and it's inlined into a
|
|
function that catches exceptions of type <tt>B</tt>. The inliner will update
|
|
the <tt>landingpad</tt> instruction for the inlined landing pad to include
|
|
the fact that <tt>B</tt> is also caught. If that landing pad assumes that it
|
|
will only be entered to catch an <tt>A</tt>, it's in for a rude awakening.
|
|
Consequently, landing pads must test for the selector results they understand
|
|
and then resume exception propagation with the
|
|
<a href="LangRef.html#i_resume"><tt>resume</tt> instruction</a> if none of
|
|
the conditions match.</p>
|
|
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h2>
|
|
<a name="format_common_intrinsics">Exception Handling Intrinsics</a>
|
|
</h2>
|
|
|
|
<div>
|
|
|
|
<p>In addition to the
|
|
<a href="LangRef.html#i_landingpad"><tt>landingpad</tt></a> and
|
|
<a href="LangRef.html#i_resume"><tt>resume</tt></a> instructions, LLVM uses
|
|
several intrinsic functions (name prefixed with <i><tt>llvm.eh</tt></i>) to
|
|
provide exception handling information at various points in generated
|
|
code.</p>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h4>
|
|
<a name="llvm_eh_typeid_for">llvm.eh.typeid.for</a>
|
|
</h4>
|
|
|
|
<div>
|
|
|
|
<pre>
|
|
i32 @llvm.eh.typeid.for(i8* %type_info)
|
|
</pre>
|
|
|
|
<p>This intrinsic returns the type info index in the exception table of the
|
|
current function. This value can be used to compare against the result
|
|
of <a href="LangRef.html#i_landingpad"><tt>landingpad</tt> instruction</a>.
|
|
The single argument is a reference to a type info.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h4>
|
|
<a name="llvm_eh_sjlj_setjmp">llvm.eh.sjlj.setjmp</a>
|
|
</h4>
|
|
|
|
<div>
|
|
|
|
<pre>
|
|
i32 @llvm.eh.sjlj.setjmp(i8* %setjmp_buf)
|
|
</pre>
|
|
|
|
<p>For SJLJ based exception handling, this intrinsic forces register saving for
|
|
the current function and stores the address of the following instruction for
|
|
use as a destination address
|
|
by <a href="#llvm_eh_sjlj_longjmp"><tt>llvm.eh.sjlj.longjmp</tt></a>. The
|
|
buffer format and the overall functioning of this intrinsic is compatible
|
|
with the GCC <tt>__builtin_setjmp</tt> implementation allowing code built
|
|
with the clang and GCC to interoperate.</p>
|
|
|
|
<p>The single parameter is a pointer to a five word buffer in which the calling
|
|
context is saved. The front end places the frame pointer in the first word,
|
|
and the target implementation of this intrinsic should place the destination
|
|
address for a
|
|
<a href="#llvm_eh_sjlj_longjmp"><tt>llvm.eh.sjlj.longjmp</tt></a> in the
|
|
second word. The following three words are available for use in a
|
|
target-specific manner.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h4>
|
|
<a name="llvm_eh_sjlj_longjmp">llvm.eh.sjlj.longjmp</a>
|
|
</h4>
|
|
|
|
<div>
|
|
|
|
<pre>
|
|
void @llvm.eh.sjlj.longjmp(i8* %setjmp_buf)
|
|
</pre>
|
|
|
|
<p>For SJLJ based exception handling, the <tt>llvm.eh.sjlj.longjmp</tt>
|
|
intrinsic is used to implement <tt>__builtin_longjmp()</tt>. The single
|
|
parameter is a pointer to a buffer populated
|
|
by <a href="#llvm_eh_sjlj_setjmp"><tt>llvm.eh.sjlj.setjmp</tt></a>. The frame
|
|
pointer and stack pointer are restored from the buffer, then control is
|
|
transferred to the destination address.</p>
|
|
|
|
</div>
|
|
<!-- ======================================================================= -->
|
|
<h4>
|
|
<a name="llvm_eh_sjlj_lsda">llvm.eh.sjlj.lsda</a>
|
|
</h4>
|
|
|
|
<div>
|
|
|
|
<pre>
|
|
i8* @llvm.eh.sjlj.lsda()
|
|
</pre>
|
|
|
|
<p>For SJLJ based exception handling, the <tt>llvm.eh.sjlj.lsda</tt> intrinsic
|
|
returns the address of the Language Specific Data Area (LSDA) for the current
|
|
function. The SJLJ front-end code stores this address in the exception
|
|
handling function context for use by the runtime.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h4>
|
|
<a name="llvm_eh_sjlj_callsite">llvm.eh.sjlj.callsite</a>
|
|
</h4>
|
|
|
|
<div>
|
|
|
|
<pre>
|
|
void @llvm.eh.sjlj.callsite(i32 %call_site_num)
|
|
</pre>
|
|
|
|
<p>For SJLJ based exception handling, the <tt>llvm.eh.sjlj.callsite</tt>
|
|
intrinsic identifies the callsite value associated with the
|
|
following <tt>invoke</tt> instruction. This is used to ensure that landing
|
|
pad entries in the LSDA are generated in matching order.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h2>
|
|
<a name="asm">Asm Table Formats</a>
|
|
</h2>
|
|
|
|
<div>
|
|
|
|
<p>There are two tables that are used by the exception handling runtime to
|
|
determine which actions should be taken when an exception is thrown.</p>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="unwind_tables">Exception Handling Frame</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>An exception handling frame <tt>eh_frame</tt> is very similar to the unwind
|
|
frame used by DWARF debug info. The frame contains all the information
|
|
necessary to tear down the current frame and restore the state of the prior
|
|
frame. There is an exception handling frame for each function in a compile
|
|
unit, plus a common exception handling frame that defines information common
|
|
to all functions in the unit.</p>
|
|
|
|
<!-- Todo - Table details here. -->
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="exception_tables">Exception Tables</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>An exception table contains information about what actions to take when an
|
|
exception is thrown in a particular part of a function's code. There is one
|
|
exception table per function, except leaf functions and functions that have
|
|
calls only to non-throwing functions. They do not need an exception
|
|
table.</p>
|
|
|
|
<!-- Todo - Table details here. -->
|
|
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
<hr>
|
|
<address>
|
|
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
|
|
src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
|
|
<a href="http://validator.w3.org/check/referer"><img
|
|
src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
|
|
|
|
<a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
|
|
Last modified: $Date$
|
|
</address>
|
|
|
|
</body>
|
|
</html>
|