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| author | Bill Wendling <isanbard@gmail.com> | 2009-08-15 08:56:09 +0000 |
|---|---|---|
| committer | Bill Wendling <isanbard@gmail.com> | 2009-08-15 08:56:09 +0000 |
| commit | c4f661e3dec2e574a59d32bef8679af832349fd2 (patch) | |
| tree | 73199e0f8766a40591d9108d55f149cec6bcfccd /docs | |
| parent | e96507c73111d88743a15db6d6329f4fbdde7dec (diff) | |
| download | llvm-c4f661e3dec2e574a59d32bef8679af832349fd2.tar.gz llvm-c4f661e3dec2e574a59d32bef8679af832349fd2.tar.bz2 llvm-c4f661e3dec2e574a59d32bef8679af832349fd2.tar.xz | |
Reformatting and some cleanup.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79088 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/ExceptionHandling.html | 470 |
1 files changed, 247 insertions, 223 deletions
diff --git a/docs/ExceptionHandling.html b/docs/ExceptionHandling.html index 851ed1238b..166fe4cf11 100644 --- a/docs/ExceptionHandling.html +++ b/docs/ExceptionHandling.html @@ -3,8 +3,12 @@ <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> <div class="doc_title">Exception Handling in LLVM</div> @@ -58,11 +62,11 @@ <div class="doc_text"> <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 -C/C++.</p> + 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/C++.</p> </div> @@ -74,27 +78,28 @@ C/C++.</p> <div class="doc_text"> <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> + 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> + 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 -specification at <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">Dwarf 3 -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> + 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 3 specification at + <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3 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> @@ -105,41 +110,44 @@ Tables.</a></p> <div class="doc_text"> -<p>When an exception is thrown in llvm code, the runtime does a best effort to -find a handler suited to process the circumstance.</p> +<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 (ex. -C++) supports exception handling, the exception frame contains a reference to an -exception table describing how to process the exception. If the language (ex. -C) does not support exception handling 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>Since 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> (ex. for C++ <tt>__gxx_personality_v0</tt>) 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> + the function where the exception was thrown. If the programming language + (e.g. C++) supports exception handling, the exception frame contains a + reference to an exception table describing how to process the exception. If + the language (e.g. C) does not support exception handling, 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> + 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 to the code found in the catch portion of a -try/catch sequence. When execution resumes at a landing pad, it receives the -exception structure and a selector corresponding to the <i>type</i> of exception -thrown. The selector is then used to determine which catch should actually -process the exception.</p> +<p>A landing pad corresponds to the code found in the <i>catch</i> portion of + a <i>try</i>/<i>catch</i> sequence. When execution resumes at a landing + pad, it receives the exception structure and a selector 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> @@ -151,12 +159,12 @@ process the exception.</p> <div class="doc_text"> <p>At the time of this writing, only C++ exception handling support is available -in LLVM. So the remainder of this document will be somewhat C++-centric.</p> + in LLVM. So the remainder of this document will be somewhat C++-centric.</p> <p>From the C++ developers perspective, exceptions are defined in terms of the -<tt>throw</tt> and <tt>try/catch</tt> statements. In this section we will -describe the implementation of llvm exception handling in terms of C++ -examples.</p> + <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> </div> @@ -168,17 +176,17 @@ examples.</p> <div class="doc_text"> <p>Languages that support exception handling typically provide a <tt>throw</tt> -operation to initiate the exception process. Internally, a throw operation -breaks down into two steps. First, 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. Second, a call is made to the runtime to raise the -exception, passing the exception structure as an argument.</p> + operation to initiate the exception process. Internally, a throw operation + breaks down into two steps. First, 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. Second, a call is made to the runtime to raise the + exception, passing the exception structure as an argument.</p> -<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 type info structure.</p> +<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> @@ -189,67 +197,77 @@ a C++ RTTI type info structure.</p> <div class="doc_text"> -<p>A call within the scope of a try 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 invoke has two potential -continuation points; where to continue when the call succeeds as per normal, and -where to continue if the call raises an exception, either by a throw or the -unwinding of a throw.</p> - -<p>The term used to define a the place where an invoke continues after an -exception is called a <i>landing pad</i>. LLVM landing pads are conceptually -alternative function entry points where a 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>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: where to continue when the call succeeds + as per normal; and where to continue if the call raises an exception, either + by a throw or the unwinding of a throw.</p> -<p>Two llvm intrinsic functions are used convey information about the landing -pad to the back end.</p> +<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><a href="#llvm_eh_exception"><tt>llvm.eh.exception</tt></a> takes no -arguments and returns a pointer to the exception structure. This only returns a -sensible value if called after an invoke has branched to a landing pad. Due to -codegen limitations, it must currently be called in the landing pad itself.</p> +<p>Two LLVM intrinsic functions are used to convey information about the landing + pad to the back end.</p> -<p><a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> takes a minimum of -three arguments. The first argument is the reference to the exception -structure. The second argument is a reference to the personality function to be -used for this try catch sequence. Each of the remaining arguments is either a -reference to the type info for a catch statement, -a <a href="#throw_filters">filter</a> expression, -or the number zero representing a <a href="#cleanups">cleanup</a>. -The exception is tested against the arguments sequentially from first to last. -The result of the <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> 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 behaviour of -the program is <a href="#restrictions">undefined</a>. -This only returns a sensible value if called after an invoke has branched to a -landing pad. Due to codegen limitations, it must currently be called in the -landing pad itself. -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> +<ol> + <li><a href="#llvm_eh_exception"><tt>llvm.eh.exception</tt></a> takes no + arguments and returns a pointer to the exception structure. This only + returns a sensible value if called after an <tt>invoke</tt> has branched + to a landing pad. Due to code generation limitations, it must currently + be called in the landing pad itself.</li> + + <li><a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> takes a minimum + of three arguments. The first argument is the reference to the exception + structure. The second argument is a reference to the personality function + to be used for this <tt>try</tt>/<tt>catch</tt> sequence. Each of the + remaining arguments is either a reference to the type info for + a <tt>catch</tt> statement, a <a href="#throw_filters">filter</a> + expression, or the number zero (<tt>0</tt>) representing + a <a href="#cleanups">cleanup</a>. The exception is tested against the + arguments sequentially from first to last. The result of + the <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> 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 behaviour of the program + is <a href="#restrictions">undefined</a>. This only returns a sensible + value if called after an <tt>invoke</tt> has branched to a landing pad. + Due to codegen limitations, it must currently be called in the landing pad + itself. 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.</li> +</ol> <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 info have been gathered in the backend, -the catch code will 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. Note: Since the landing -pad will not be used if there is no match in the list of type info on the call -to <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a>, then neither the -last catch nor <i>catch all</i> need to perform the the check against the -selector.</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>. -<tt>__cxa_begin_catch</tt> takes a exception structure reference as an argument -and returns the value of the exception object. <tt>__cxa_end_catch</tt> -takes a exception structure reference as an argument. This function clears the -exception from the exception space. Note: a rethrow from within the catch may -replace this call with a <tt>__cxa_rethrow</tt>.</p> + 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 info have been gathered in the backend, + the catch code will 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. Note: Since the + landing pad will not be used if there is no match in the list of type info on + the call to <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a>, then + neither the last catch nor <i>catch all</i> need to perform the check + against the selector.</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 a exception structure reference as an + argument and returns the value of the exception object.</li> + + <li><tt>__cxa_end_catch</tt> takes a exception structure reference as an + argument. This function clears the exception from the exception space. + Note: a rethrow from within the catch may replace this call with + a <tt>__cxa_rethrow</tt>.</li> +</ul> </div> @@ -260,16 +278,15 @@ replace this call with a <tt>__cxa_rethrow</tt>.</p> <div class="doc_text"> -<p>To handle destructors and cleanups in try code, control may not run directly -from a landing pad to the first catch. Control may actually flow from the -landing pad to clean up code and then to the first catch. Since the required -clean up for each invoke in a try may be different (ex., intervening -constructor), there may be several landing pads for a given try. If cleanups -need to be run, the number zero should be passed as the last -<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> argument. -However for C++ a <tt>null i8*</tt> <a href="#restrictions">must</a> be passed -instead. -</p> +<p>To handle destructors and cleanups in <tt>try</tt> code, control may not run + directly from a landing pad to the first catch. Control may actually flow + from the landing pad to clean up code and then to the first catch. Since the + required clean up for each <tt>invoke</tt> in a <tt>try</tt> may be different + (e.g. intervening constructor), there may be several landing pads for a given + try. If cleanups need to be run, the number zero should be passed as the + last <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> argument. + However for C++ a <tt>null i8*</tt> <b><a href="#restrictions">must</a></b> + be passed instead.</p> </div> @@ -280,23 +297,23 @@ instead. <div class="doc_text"> -<p>C++ allows the specification of which exception types can 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 landing pad will call <a -href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a>. The arguments are a -reference to the exception structure, a reference to the personality function, -the length of the filter expression (the number of type infos plus one), -followed by the type infos themselves. -<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> 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 an -<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> call can contain -any number of type infos, filter expressions and cleanups (though having more -than one cleanup is pointless). The LLVM C++ front-end can generate such -<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> calls due to inlining -creating nested exception handling scopes.</p> +<p>C++ allows the specification of which exception types can 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 landing pad will + call <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a>. The + arguments are a reference to the exception structure, a reference to the + personality function, the length of the filter expression (the number of type + infos plus one), followed by the type infos themselves. + <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> 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 an + <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> call can contain + any number of type infos, filter expressions and cleanups (though having more + than one cleanup is pointless). The LLVM C++ front-end can generate such + <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> calls due to + inlining creating nested exception handling scopes.</p> </div> @@ -308,23 +325,21 @@ creating nested exception handling scopes.</p> <div class="doc_text"> <p>The semantics of the invoke instruction require that any exception that -unwinds through an invoke call should result in a branch to the invoke's unwind -label. However such a branch will only happen if the -<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> matches. -Thus in order to ensure correct operation, the front-end must only generate -<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> calls that are -guaranteed to always match whatever exception unwinds through the invoke. -For most languages it is enough to pass zero, indicating the presence of -a <a href="#cleanups">cleanup</a>, as the last -<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> argument. -However for C++ this is not sufficient, because the C++ personality function -will terminate the program if it detects that unwinding the exception only -results in matches with cleanups. For C++ a <tt>null i8*</tt> should -be passed as the last -<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> argument instead. -This is interpreted as a catch-all by the C++ personality function, and will -always match. -</p> + unwinds through an invoke call should result in a branch to the invoke's + unwind label. However such a branch will only happen if the + <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> matches. Thus in + order to ensure correct operation, the front-end must only generate + <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> calls that are + guaranteed to always match whatever exception unwinds through the invoke. + For most languages it is enough to pass zero, indicating the presence of + a <a href="#cleanups">cleanup</a>, as the + last <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> argument. + However for C++ this is not sufficient, because the C++ personality function + will terminate the program if it detects that unwinding the exception only + results in matches with cleanups. For C++ a <tt>null i8*</tt> should be + passed as the last <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> + argument instead. This is interpreted as a catch-all by the C++ personality + function, and will always match.</p> </div> @@ -336,7 +351,8 @@ always match. <div class="doc_text"> <p>LLVM uses several intrinsic functions (name prefixed with "llvm.eh") to -provide exception handling information at various points in generated code.</p> + provide exception handling information at various points in generated + code.</p> </div> @@ -347,8 +363,9 @@ provide exception handling information at various points in generated code.</p> <div class="doc_text"> <pre> - i8* %<a href="#llvm_eh_exception">llvm.eh.exception</a>( ) +i8* %<a href="#llvm_eh_exception">llvm.eh.exception</a>( ) </pre> +</div> <p>This intrinsic returns a pointer to the exception structure.</p> @@ -361,28 +378,29 @@ provide exception handling information at various points in generated code.</p> <div class="doc_text"> <pre> - i32 %<a href="#llvm_eh_selector">llvm.eh.selector.i32</a>(i8*, i8*, i8*, ...) - i64 %<a href="#llvm_eh_selector">llvm.eh.selector.i64</a>(i8*, i8*, i8*, ...) +i32 %<a href="#llvm_eh_selector">llvm.eh.selector.i32</a>(i8*, i8*, i8*, ...) +i64 %<a href="#llvm_eh_selector">llvm.eh.selector.i64</a>(i8*, i8*, i8*, ...) </pre> +</div> <p>This intrinsic is used to compare the exception with the given type infos, -filters and cleanups.</p> + filters and cleanups.</p> <p><a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> takes a minimum of -three arguments. The first argument is the reference to the exception -structure. The second argument is a reference to the personality function to be -used for this try catch sequence. Each of the remaining arguments is either a -reference to the type info for a catch statement, -a <a href="#throw_filters">filter</a> expression, -or the number zero representing a <a href="#cleanups">cleanup</a>. -The exception is tested against the arguments sequentially from first to last. -The result of the <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> 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 behaviour 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> + three arguments. The first argument is the reference to the exception + structure. The second argument is a reference to the personality function to + be used for this try catch sequence. Each of the remaining arguments is + either a reference to the type info for a catch statement, + a <a href="#throw_filters">filter</a> expression, or the number zero + representing a <a href="#cleanups">cleanup</a>. The exception is tested + against the arguments sequentially from first to last. The result of + the <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> 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 + behaviour 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> </div> @@ -393,14 +411,15 @@ the exception table, which can be obtained using the <div class="doc_text"> <pre> - i32 %<a href="#llvm_eh_typeid_for">llvm.eh.typeid.for.i32</a>(i8*) - i64 %<a href="#llvm_eh_typeid_for">llvm.eh.typeid.for.i64</a>(i8*) +i32 %<a href="#llvm_eh_typeid_for">llvm.eh.typeid.for.i32</a>(i8*) +i64 %<a href="#llvm_eh_typeid_for">llvm.eh.typeid.for.i64</a>(i8*) </pre> +</div> <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="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a>. The single argument is -a reference to a type info.</p> + current function. This value can be used to compare against the result + of <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a>. The single + argument is a reference to a type info.</p> </div> @@ -411,22 +430,25 @@ a reference to a type info.</p> <div class="doc_text"> <pre> - i32 %<a href="#llvm_eh_sjlj_setjmp">llvm.eh.sjlj.setjmp</a>(i8*) +i32 %<a href="#llvm_eh_sjlj_setjmp">llvm.eh.sjlj.setjmp</a>(i8*) </pre> +</div> -<p>The SJLJ exception handling uses this intrinsic to force register saving -for the current function and to store 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 two compilers to interoperate.</p> +<p>The SJLJ exception handling uses this intrinsic to force register saving for + the current function and to store 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 + two compilers 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> +<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> @@ -437,14 +459,15 @@ are available for use in a target-specific manner.</p> <div class="doc_text"> <pre> - i8* %<a href="#llvm_eh_sjlj_lsda">llvm.eh.sjlj.lsda</a>( ) +i8* %<a href="#llvm_eh_sjlj_lsda">llvm.eh.sjlj.lsda</a>( ) </pre> +</div> <p>Used for SJLJ based exception handling, the <a href="#llvm_eh_sjlj_lsda"> - <tt>llvm.eh.sjlj.lsda</tt></a> 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> + <tt>llvm.eh.sjlj.lsda</tt></a> 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> @@ -455,13 +478,14 @@ the runtime.</p> <div class="doc_text"> <pre> - void %<a href="#llvm_eh_sjlj_callsite">llvm.eh.sjlj.callsite</a>(i32) +void %<a href="#llvm_eh_sjlj_callsite">llvm.eh.sjlj.callsite</a>(i32) </pre> +</div> -<p>The SJLJ front-end allocates call site indices for invoke instrucitons. -These values are passed to the back-end via the -<a href="#llvm_eh_sjlj_callsite"><tt>llvm.eh.sjlj.callsite</tt></a> -intrinsic, where they are used to build the LSDA call-site table.</p> +<p>The SJLJ front-end allocates call site indices for invoke instrucitons. + These values are passed to the back-end via the + <a href="#llvm_eh_sjlj_callsite"><tt>llvm.eh.sjlj.callsite</tt></a> + intrinsic, where they are used to build the LSDA call-site table.</p> </div> @@ -473,7 +497,7 @@ intrinsic, where they are used to build the LSDA call-site table.</p> <div class="doc_text"> <p>There are two tables that are used by the exception handling runtime to -determine which actions should take place when an exception is thrown.</p> + determine which actions should take place when an exception is thrown.</p> </div> @@ -485,11 +509,11 @@ determine which actions should take place when an exception is thrown.</p> <div class="doc_text"> <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> + 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> <p>Todo - Table details here.</p> @@ -503,9 +527,9 @@ all functions in the unit.</p> <div class="doc_text"> <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 routines and functions that have -only calls to non-throwing functions will not need an exception table.</p> + exception is thrown in a particular part of a function's code. There is one + exception table per function except leaf routines and functions that have + only calls to non-throwing functions will not need an exception table.</p> <p>Todo - Table details here.</p> @@ -520,7 +544,7 @@ only calls to non-throwing functions will not need an exception table.</p> <ol> -<li><p>Testing/Testing/Testing.</p></li> + <li>Testing/Testing/Testing.</li> </ol> |