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diff --git a/docs/SourceLevelDebugging.html b/docs/SourceLevelDebugging.html new file mode 100644 index 0000000..73a45cb --- /dev/null +++ b/docs/SourceLevelDebugging.html @@ -0,0 +1,1782 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> +<html> +<head> + <title>Source Level Debugging with LLVM</title> + <link rel="stylesheet" href="llvm.css" type="text/css"> +</head> +<body> + +<div class="doc_title">Source Level Debugging with LLVM</div> + +<table class="layout" style="width:100%"> + <tr class="layout"> + <td class="left"> +<ul> + <li><a href="#introduction">Introduction</a> + <ol> + <li><a href="#phil">Philosophy behind LLVM debugging information</a></li> + <li><a href="#consumers">Debug information consumers</a></li> + <li><a href="#debugopt">Debugging optimized code</a></li> + </ol></li> + <li><a href="#format">Debugging information format</a> + <ol> + <li><a href="#debug_info_descriptors">Debug information descriptors</a> + <ul> + <li><a href="#format_anchors">Anchor descriptors</a></li> + <li><a href="#format_compile_units">Compile unit descriptors</a></li> + <li><a href="#format_global_variables">Global variable descriptors</a></li> + <li><a href="#format_subprograms">Subprogram descriptors</a></li> + <li><a href="#format_blocks">Block descriptors</a></li> + <li><a href="#format_basic_type">Basic type descriptors</a></li> + <li><a href="#format_derived_type">Derived type descriptors</a></li> + <li><a href="#format_composite_type">Composite type descriptors</a></li> + <li><a href="#format_subrange">Subrange descriptors</a></li> + <li><a href="#format_enumeration">Enumerator descriptors</a></li> + <li><a href="#format_variables">Local variables</a></li> + </ul></li> + <li><a href="#format_common_intrinsics">Debugger intrinsic functions</a> + <ul> + <li><a href="#format_common_stoppoint">llvm.dbg.stoppoint</a></li> + <li><a href="#format_common_func_start">llvm.dbg.func.start</a></li> + <li><a href="#format_common_region_start">llvm.dbg.region.start</a></li> + <li><a href="#format_common_region_end">llvm.dbg.region.end</a></li> + <li><a href="#format_common_declare">llvm.dbg.declare</a></li> + </ul></li> + <li><a href="#format_common_stoppoints">Representing stopping points in the + source program</a></li> + </ol></li> + <li><a href="#ccxx_frontend">C/C++ front-end specific debug information</a> + <ol> + <li><a href="#ccxx_compile_units">C/C++ source file information</a></li> + <li><a href="#ccxx_global_variable">C/C++ global variable information</a></li> + <li><a href="#ccxx_subprogram">C/C++ function information</a></li> + <li><a href="#ccxx_basic_types">C/C++ basic types</a></li> + <li><a href="#ccxx_derived_types">C/C++ derived types</a></li> + <li><a href="#ccxx_composite_types">C/C++ struct/union types</a></li> + <li><a href="#ccxx_enumeration_types">C/C++ enumeration types</a></li> + </ol></li> +</ul> +</td> +<td class="right"> +<img src="img/venusflytrap.jpg" alt="A leafy and green bug eater" width="247" +height="369"> +</td> +</tr></table> + +<div class="doc_author"> + <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> + and <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p> +</div> + + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="introduction">Introduction</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>This document is the central repository for all information pertaining to +debug information in LLVM. It describes the <a href="#format">actual format +that the LLVM debug information</a> takes, which is useful for those interested +in creating front-ends or dealing directly with the information. Further, this +document provides specifc examples of what debug information for C/C++.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="phil">Philosophy behind LLVM debugging information</a> +</div> + +<div class="doc_text"> + +<p>The idea of the LLVM debugging information is to capture how the important +pieces of the source-language's Abstract Syntax Tree map onto LLVM code. +Several design aspects have shaped the solution that appears here. The +important ones are:</p> + +<ul> +<li>Debugging information should have very little impact on the rest of the +compiler. No transformations, analyses, or code generators should need to be +modified because of debugging information.</li> + +<li>LLVM optimizations should interact in <a href="#debugopt">well-defined and +easily described ways</a> with the debugging information.</li> + +<li>Because LLVM is designed to support arbitrary programming languages, +LLVM-to-LLVM tools should not need to know anything about the semantics of the +source-level-language.</li> + +<li>Source-level languages are often <b>widely</b> different from one another. +LLVM should not put any restrictions of the flavor of the source-language, and +the debugging information should work with any language.</li> + +<li>With code generator support, it should be possible to use an LLVM compiler +to compile a program to native machine code and standard debugging formats. +This allows compatibility with traditional machine-code level debuggers, like +GDB or DBX.</li> + +</ul> + +<p>The approach used by the LLVM implementation is to use a small set of <a +href="#format_common_intrinsics">intrinsic functions</a> to define a mapping +between LLVM program objects and the source-level objects. The description of +the source-level program is maintained in LLVM global variables in an <a +href="#ccxx_frontend">implementation-defined format</a> (the C/C++ front-end +currently uses working draft 7 of the <a +href="http://www.eagercon.com/dwarf/dwarf3std.htm">Dwarf 3 standard</a>).</p> + +<p>When a program is being debugged, a debugger interacts with the user and +turns the stored debug information into source-language specific information. +As such, a debugger must be aware of the source-language, and is thus tied to +a specific language of family of languages.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="consumers">Debug information consumers</a> +</div> + +<div class="doc_text"> +<p>The role of debug information is to provide meta information normally +stripped away during the compilation process. This meta information provides an +llvm user a relationship between generated code and the original program source +code.</p> + +<p>Currently, debug information is consumed by the DwarfWriter to produce dwarf +information used by the gdb debugger. Other targets could use the same +information to produce stabs or other debug forms.</p> + +<p>It would also be reasonable to use debug information to feed profiling tools +for analysis of generated code, or, tools for reconstructing the original source +from generated code.</p> + +<p>TODO - expound a bit more.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="debugopt">Debugging optimized code</a> +</div> + +<div class="doc_text"> + +<p>An extremely high priority of LLVM debugging information is to make it +interact well with optimizations and analysis. In particular, the LLVM debug +information provides the following guarantees:</p> + +<ul> + +<li>LLVM debug information <b>always provides information to accurately read the +source-level state of the program</b>, regardless of which LLVM optimizations +have been run, and without any modification to the optimizations themselves. +However, some optimizations may impact the ability to modify the current state +of the program with a debugger, such as setting program variables, or calling +function that have been deleted.</li> + +<li>LLVM optimizations gracefully interact with debugging information. If they +are not aware of debug information, they are automatically disabled as necessary +in the cases that would invalidate the debug info. This retains the LLVM +features making it easy to write new transformations.</li> + +<li>As desired, LLVM optimizations can be upgraded to be aware of the LLVM +debugging information, allowing them to update the debugging information as they +perform aggressive optimizations. This means that, with effort, the LLVM +optimizers could optimize debug code just as well as non-debug code.</li> + +<li>LLVM debug information does not prevent many important optimizations from +happening (for example inlining, basic block reordering/merging/cleanup, tail +duplication, etc), further reducing the amount of the compiler that eventually +is "aware" of debugging information.</li> + +<li>LLVM debug information is automatically optimized along with the rest of the +program, using existing facilities. For example, duplicate information is +automatically merged by the linker, and unused information is automatically +removed.</li> + +</ul> + +<p>Basically, the debug information allows you to compile a program with +"<tt>-O0 -g</tt>" and get full debug information, allowing you to arbitrarily +modify the program as it executes from a debugger. Compiling a program with +"<tt>-O3 -g</tt>" gives you full debug information that is always available and +accurate for reading (e.g., you get accurate stack traces despite tail call +elimination and inlining), but you might lose the ability to modify the program +and call functions where were optimized out of the program, or inlined away +completely.</p> + +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"> + <a name="format">Debugging information format</a> +</div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>LLVM debugging information has been carefully designed to make it possible +for the optimizer to optimize the program and debugging information without +necessarily having to know anything about debugging information. In particular, +the global constant merging pass automatically eliminates duplicated debugging +information (often caused by header files), the global dead code elimination +pass automatically deletes debugging information for a function if it decides to +delete the function, and the linker eliminates debug information when it merges +<tt>linkonce</tt> functions.</p> + +<p>To do this, most of the debugging information (descriptors for types, +variables, functions, source files, etc) is inserted by the language front-end +in the form of LLVM global variables. These LLVM global variables are no +different from any other global variables, except that they have a web of LLVM +intrinsic functions that point to them. If the last references to a particular +piece of debugging information are deleted (for example, by the +<tt>-globaldce</tt> pass), the extraneous debug information will automatically +become dead and be removed by the optimizer.</p> + +<p>Debug information is designed to be agnostic about the target debugger and +debugging information representation (e.g. DWARF/Stabs/etc). It uses a generic +machine debug information pass to decode the information that represents +variables, types, functions, namespaces, etc: this allows for arbitrary +source-language semantics and type-systems to be used, as long as there is a +module written for the target debugger to interpret the information. In +addition, debug global variables are declared in the <tt>"llvm.metadata"</tt> +section. All values declared in this section are stripped away after target +debug information is constructed and before the program object is emitted.</p> + +<p>To provide basic functionality, the LLVM debugger does have to make some +assumptions about the source-level language being debugged, though it keeps +these to a minimum. The only common features that the LLVM debugger assumes +exist are <a href="#format_compile_units">source files</a>, and <a +href="#format_global_variables">program objects</a>. These abstract objects are +used by a debugger to form stack traces, show information about local +variables, etc.</p> + +<p>This section of the documentation first describes the representation aspects +common to any source-language. The <a href="#ccxx_frontend">next section</a> +describes the data layout conventions used by the C and C++ front-ends.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="debug_info_descriptors">Debug information descriptors</a> +</div> + +<div class="doc_text"> +<p>In consideration of the complexity and volume of debug information, LLVM +provides a specification for well formed debug global variables. The constant +value of each of these globals is one of a limited set of structures, known as +debug descriptors.</p> + +<p>Consumers of LLVM debug information expect the descriptors for program +objects to start in a canonical format, but the descriptors can include +additional information appended at the end that is source-language specific. All +LLVM debugging information is versioned, allowing backwards compatibility in the +case that the core structures need to change in some way. Also, all debugging +information objects start with a tag to indicate what type of object it is. The +source-language is allowed to define its own objects, by using unreserved tag +numbers. We recommend using with tags in the range 0x1000 thru 0x2000 (there is +a defined enum DW_TAG_user_base = 0x1000.)</p> + +<p>The fields of debug descriptors used internally by LLVM (MachineModuleInfo) +are restricted to only the simple data types <tt>int</tt>, <tt>uint</tt>, +<tt>bool</tt>, <tt>float</tt>, <tt>double</tt>, <tt>sbyte*</tt> and <tt> { }* +</tt>. References to arbitrary values are handled using a <tt> { }* </tt> and a +cast to <tt> { }* </tt> expression; typically references to other field +descriptors, arrays of descriptors or global variables.</p> + +<pre> + %llvm.dbg.object.type = type { + uint, ;; A tag + ... + } +</pre> + +<p><a name="LLVMDebugVersion">The first field of a descriptor is always an +<tt>uint</tt> containing a tag value identifying the content of the descriptor. +The remaining fields are specific to the descriptor. The values of tags are +loosely bound to the tag values of Dwarf information entries. However, that +does not restrict the use of the information supplied to Dwarf targets. To +facilitate versioning of debug information, the tag is augmented with the +current debug version (LLVMDebugVersion = 4 << 16 or 0x40000 or 262144.)</a></p> + +<p>The details of the various descriptors follow.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_anchors">Anchor descriptors</a> +</div> + +<div class="doc_text"> + +<pre> + %<a href="#format_anchors">llvm.dbg.anchor.type</a> = type { + uint, ;; Tag = 0 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> + uint ;; Tag of descriptors grouped by the anchor + } +</pre> + +<p>One important aspect of the LLVM debug representation is that it allows the +LLVM debugger to efficiently index all of the global objects without having the +scan the program. To do this, all of the global objects use "anchor" +descriptors with designated names. All of the global objects of a particular +type (e.g., compile units) contain a pointer to the anchor. This pointer allows +a debugger to use def-use chains to find all global objects of that type.</p> + +<p>The following names are recognized as anchors by LLVM:</p> + +<pre> + %<a href="#format_compile_units">llvm.dbg.compile_units</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> { uint 0, uint 17 } ;; DW_TAG_compile_unit + %<a href="#format_global_variables">llvm.dbg.global_variables</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> { uint 0, uint 52 } ;; DW_TAG_variable + %<a href="#format_subprograms">llvm.dbg.subprograms</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> { uint 0, uint 46 } ;; DW_TAG_subprogram +</pre> + +<p>Using anchors in this way (where the compile unit descriptor points to the +anchors, as opposed to having a list of compile unit descriptors) allows for the +standard dead global elimination and merging passes to automatically remove +unused debugging information. If the globals were kept track of through lists, +there would always be an object pointing to the descriptors, thus would never be +deleted.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_compile_units">Compile unit descriptors</a> +</div> + +<div class="doc_text"> + +<pre> + %<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = type { + uint, ;; Tag = 17 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_compile_unit) + { }*, ;; Compile unit anchor = cast = (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_units</a> to { }*) + uint, ;; Dwarf language identifier (ex. DW_LANG_C89) + sbyte*, ;; Source file name + sbyte*, ;; Source file directory (includes trailing slash) + sbyte* ;; Producer (ex. "4.0.1 LLVM (LLVM research group)") + } +</pre> + +<p>These descriptors contain a source language ID for the file (we use the Dwarf +3.0 ID numbers, such as <tt>DW_LANG_C89</tt>, <tt>DW_LANG_C_plus_plus</tt>, +<tt>DW_LANG_Cobol74</tt>, etc), three strings describing the filename, working +directory of the compiler, and an identifier string for the compiler that +produced it.</p> + +<p> Compile unit descriptors provide the root context for objects declared in a +specific source file. Global variables and top level functions would be defined +using this context. Compile unit descriptors also provide context for source +line correspondence.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_global_variables">Global variable descriptors</a> +</div> + +<div class="doc_text"> + +<pre> + %<a href="#format_global_variables">llvm.dbg.global_variable.type</a> = type { + uint, ;; Tag = 52 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_variable) + { }*, ;; Global variable anchor = cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_global_variables">llvm.dbg.global_variables</a> to { }*), + { }*, ;; Reference to context descriptor + sbyte*, ;; Name + sbyte*, ;; Display name (fully qualified C++ name) + sbyte*, ;; MIPS linkage name (for C++) + { }*, ;; Reference to compile unit where defined + uint, ;; Line number where defined + { }*, ;; Reference to type descriptor + bool, ;; True if the global is local to compile unit (static) + bool, ;; True if the global is defined in the compile unit (not extern) + { }* ;; Reference to the global variable + } +</pre> + +<p>These descriptors provide debug information about globals variables. The +provide details such as name, type and where the variable is defined.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_subprograms">Subprogram descriptors</a> +</div> + +<div class="doc_text"> + +<pre> + %<a href="#format_subprograms">llvm.dbg.subprogram.type</a> = type { + uint, ;; Tag = 46 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_subprogram) + { }*, ;; Subprogram anchor = cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_subprograms">llvm.dbg.subprograms</a> to { }*), + { }*, ;; Reference to context descriptor + sbyte*, ;; Name + sbyte*, ;; Display name (fully qualified C++ name) + sbyte*, ;; MIPS linkage name (for C++) + { }*, ;; Reference to compile unit where defined + uint, ;; Line number where defined + { }*, ;; Reference to type descriptor + bool, ;; True if the global is local to compile unit (static) + bool ;; True if the global is defined in the compile unit (not extern) + } +</pre> + +<p>These descriptors provide debug information about functions, methods and +subprograms. They provide details such as name, return types and the source +location where the subprogram is defined.</p> + +</div> +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_blocks">Block descriptors</a> +</div> + +<div class="doc_text"> + +<pre> + %<a href="#format_blocks">llvm.dbg.block</a> = type { + uint, ;; Tag = 13 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block) + { }* ;; Reference to context descriptor + } +</pre> + +<p>These descriptors provide debug information about nested blocks within a +subprogram. The array of member descriptors is used to define local variables +and deeper nested blocks.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_basic_type">Basic type descriptors</a> +</div> + +<div class="doc_text"> + +<pre> + %<a href="#format_basic_type">llvm.dbg.basictype.type</a> = type { + uint, ;; Tag = 36 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_base_type) + { }*, ;; Reference to context (typically a compile unit) + sbyte*, ;; Name (may be "" for anonymous types) + { }*, ;; Reference to compile unit where defined (may be NULL) + uint, ;; Line number where defined (may be 0) + uint, ;; Size in bits + uint, ;; Alignment in bits + uint, ;; Offset in bits + uint ;; Dwarf type encoding + } +</pre> + +<p>These descriptors define primitive types used in the code. Example int, bool +and float. The context provides the scope of the type, which is usually the top +level. Since basic types are not usually user defined the compile unit and line +number can be left as NULL and 0. The size, alignment and offset are expressed +in bits and can be 64 bit values. The alignment is used to round the offset +when embedded in a <a href="#format_composite_type">composite type</a> +(example to keep float doubles on 64 bit boundaries.) The offset is the bit +offset if embedded in a <a href="#format_composite_type">composite +type</a>.</p> + +<p>The type encoding provides the details of the type. The values are typically +one of the following;</p> + +<pre> + DW_ATE_address = 1 + DW_ATE_boolean = 2 + DW_ATE_float = 4 + DW_ATE_signed = 5 + DW_ATE_signed_char = 6 + DW_ATE_unsigned = 7 + DW_ATE_unsigned_char = 8 +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_derived_type">Derived type descriptors</a> +</div> + +<div class="doc_text"> + +<pre> + %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> = type { + uint, ;; Tag (see below) + { }*, ;; Reference to context + sbyte*, ;; Name (may be "" for anonymous types) + { }*, ;; Reference to compile unit where defined (may be NULL) + uint, ;; Line number where defined (may be 0) + uint, ;; Size in bits + uint, ;; Alignment in bits + uint, ;; Offset in bits + { }* ;; Reference to type derived from + } +</pre> + +<p>These descriptors are used to define types derived from other types. The +value of the tag varies depending on the meaning. The following are possible +tag values;</p> + +<pre> + DW_TAG_formal_parameter = 5 + DW_TAG_member = 13 + DW_TAG_pointer_type = 15 + DW_TAG_reference_type = 16 + DW_TAG_typedef = 22 + DW_TAG_const_type = 38 + DW_TAG_volatile_type = 53 + DW_TAG_restrict_type = 55 +</pre> + +<p> <tt>DW_TAG_member</tt> is used to define a member of a <a +href="#format_composite_type">composite type</a> or <a +href="#format_subprograms">subprogram</a>. The type of the member is the <a +href="#format_derived_type">derived type</a>. <tt>DW_TAG_formal_parameter</tt> +is used to define a member which is a formal argument of a subprogram.</p> + +<p><tt>DW_TAG_typedef</tt> is used to +provide a name for the derived type.</p> + +<p><tt>DW_TAG_pointer_type</tt>, +<tt>DW_TAG_reference_type</tt>, <tt>DW_TAG_const_type</tt>, +<tt>DW_TAG_volatile_type</tt> and <tt>DW_TAG_restrict_type</tt> are used to +qualify the <a href="#format_derived_type">derived type</a>. </p> + +<p><a href="#format_derived_type">Derived type</a> location can be determined +from the compile unit and line number. The size, alignment and offset are +expressed in bits and can be 64 bit values. The alignment is used to round the +offset when embedded in a <a href="#format_composite_type">composite type</a> +(example to keep float doubles on 64 bit boundaries.) The offset is the bit +offset if embedded in a <a href="#format_composite_type">composite +type</a>.</p> + +<p>Note that the <tt>void *</tt> type is expressed as a +<tt>llvm.dbg.derivedtype.type</tt> with tag of <tt>DW_TAG_pointer_type</tt> and +NULL derived type.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_composite_type">Composite type descriptors</a> +</div> + +<div class="doc_text"> + +<pre> + %<a href="#format_composite_type">llvm.dbg.compositetype.type</a> = type { + uint, ;; Tag (see below) + { }*, ;; Reference to context + sbyte*, ;; Name (may be "" for anonymous types) + { }*, ;; Reference to compile unit where defined (may be NULL) + uint, ;; Line number where defined (may be 0) + uint, ;; Size in bits + uint, ;; Alignment in bits + uint, ;; Offset in bits + { }* ;; Reference to array of member descriptors + } +</pre> + +<p>These descriptors are used to define types that are composed of 0 or more +elements. The value of the tag varies depending on the meaning. The following +are possible tag values;</p> + +<pre> + DW_TAG_array_type = 1 + DW_TAG_enumeration_type = 4 + DW_TAG_structure_type = 19 + DW_TAG_union_type = 23 + DW_TAG_vector_type = 259 + DW_TAG_subroutine_type = 46 + DW_TAG_inheritance = 26 +</pre> + +<p>The vector flag indicates that an array type is a native packed vector.</p> + +<p>The members of array types (tag = <tt>DW_TAG_array_type</tt>) or vector types +(tag = <tt>DW_TAG_vector_type</tt>) are <a href="#format_subrange">subrange +descriptors</a>, each representing the range of subscripts at that level of +indexing.</p> + +<p>The members of enumeration types (tag = <tt>DW_TAG_enumeration_type</tt>) are +<a href="#format_enumeration">enumerator descriptors</a>, each representing the +definition of enumeration value +for the set.</p> + +<p>The members of structure (tag = <tt>DW_TAG_structure_type</tt>) or union (tag += <tt>DW_TAG_union_type</tt>) types are any one of the <a +href="#format_basic_type">basic</a>, <a href="#format_derived_type">derived</a> +or <a href="#format_composite_type">composite</a> type descriptors, each +representing a field member of the structure or union.</p> + +<p>For C++ classes (tag = <tt>DW_TAG_structure_type</tt>), member descriptors +provide information about base classes, static members and member functions. If +a member is a <a href="#format_derived_type">derived type descriptor</a> and has +a tag of <tt>DW_TAG_inheritance</tt>, then the type represents a base class. If +the member of is a <a href="#format_global_variables">global variable +descriptor</a> then it represents a static member. And, if the member is a <a +href="#format_subprograms">subprogram descriptor</a> then it represents a member +function. For static members and member functions, <tt>getName()</tt> returns +the members link or the C++ mangled name. <tt>getDisplayName()</tt> the +simplied version of the name.</p> + +<p>The first member of subroutine (tag = <tt>DW_TAG_subroutine_type</tt>) +type elements is the return type for the subroutine. The remaining +elements are the formal arguments to the subroutine.</p> + +<p><a href="#format_composite_type">Composite type</a> location can be +determined from the compile unit and line number. The size, alignment and +offset are expressed in bits and can be 64 bit values. The alignment is used to +round the offset when embedded in a <a href="#format_composite_type">composite +type</a> (as an example, to keep float doubles on 64 bit boundaries.) The offset +is the bit offset if embedded in a <a href="#format_composite_type">composite +type</a>.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_subrange">Subrange descriptors</a> +</div> + +<div class="doc_text"> + +<pre> + %<a href="#format_subrange">llvm.dbg.subrange.type</a> = type { + uint, ;; Tag = 33 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_subrange_type) + uint, ;; Low value + uint ;; High value + } +</pre> + +<p>These descriptors are used to define ranges of array subscripts for an array +<a href="#format_composite_type">composite type</a>. The low value defines the +lower bounds typically zero for C/C++. The high value is the upper bounds. +Values are 64 bit. High - low + 1 is the size of the array. If +low == high the array will be unbounded.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_enumeration">Enumerator descriptors</a> +</div> + +<div class="doc_text"> + +<pre> + %<a href="#format_enumeration">llvm.dbg.enumerator.type</a> = type { + uint, ;; Tag = 40 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_enumerator) + sbyte*, ;; Name + uint ;; Value + } +</pre> + +<p>These descriptors are used to define members of an enumeration <a +href="#format_composite_type">composite type</a>, it associates the name to the +value.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_variables">Local variables</a> +</div> + +<div class="doc_text"> +<pre> + %<a href="#format_variables">llvm.dbg.variable.type</a> = type { + uint, ;; Tag (see below) + { }*, ;; Context + sbyte*, ;; Name + { }*, ;; Reference to compile unit where defined + uint, ;; Line number where defined + { }* ;; Type descriptor + } +</pre> + +<p>These descriptors are used to define variables local to a sub program. The +value of the tag depends on the usage of the variable;</p> + +<pre> + DW_TAG_auto_variable = 256 + DW_TAG_arg_variable = 257 + DW_TAG_return_variable = 258 +</pre> + +<p>An auto variable is any variable declared in the body of the function. An +argument variable is any variable that appears as a formal argument to the +function. A return variable is used to track the result of a function and has +no source correspondent.</p> + +<p>The context is either the subprogram or block where the variable is defined. +Name the source variable name. Compile unit and line indicate where the +variable was defined. Type descriptor defines the declared type of the +variable.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="format_common_intrinsics">Debugger intrinsic functions</a> +</div> + +<div class="doc_text"> + +<p>LLVM uses several intrinsic functions (name prefixed with "llvm.dbg") to +provide debug information at various points in generated code.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_common_stoppoint">llvm.dbg.stoppoint</a> +</div> + +<div class="doc_text"> +<pre> + void %<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint, uint, { }* ) +</pre> + +<p>This intrinsic is used to provide correspondence between the source file and +the generated code. The first argument is the line number (base 1), second +argument is the column number (0 if unknown) and the third argument the source +<tt>%<a href="#format_compile_units">llvm.dbg.compile_unit</a>*</tt> cast to a +<tt>{ }*</tt>. Code following a call to this intrinsic will have been defined +in close proximity of the line, column and file. This information holds until +the next call to <tt>%<a +href="#format_common_stoppoint">lvm.dbg.stoppoint</a></tt>.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_common_func_start">llvm.dbg.func.start</a> +</div> + +<div class="doc_text"> +<pre> + void %<a href="#format_common_func_start">llvm.dbg.func.start</a>( { }* ) +</pre> + +<p>This intrinsic is used to link the debug information in <tt>%<a +href="#format_subprograms">llvm.dbg.subprogram</a></tt> to the function. It also +defines the beginning of the function's declarative region (scope.) The +intrinsic should be called early in the function after the all the alloca +instructions. It should be paired off with a closing <tt>%<a +href="#format_common_region_end">llvm.dbg.region.end</a></tt>. The function's +single argument is the <tt>%<a +href="#format_subprograms">llvm.dbg.subprogram.type</a></tt>.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_common_region_start">llvm.dbg.region.start</a> +</div> + +<div class="doc_text"> +<pre> + void %<a href="#format_common_region_start">llvm.dbg.region.start</a>( { }* ) +</pre> + +<p>This intrinsic is used to define the beginning of a declarative scope (ex. +block) for local language elements. It should be paired off with a closing +<tt>%<a href="#format_common_region_end">llvm.dbg.region.end</a></tt>. The +function's single argument is the <tt>%<a +href="#format_blocks">llvm.dbg.block</a></tt> which is starting.</p> + + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_common_region_end">llvm.dbg.region.end</a> +</div> + +<div class="doc_text"> +<pre> + void %<a href="#format_common_region_end">llvm.dbg.region.end</a>( { }* ) +</pre> + +<p>This intrinsic is used to define the end of a declarative scope (ex. block) +for local language elements. It should be paired off with an opening <tt>%<a +href="#format_common_region_start">llvm.dbg.region.start</a></tt> or <tt>%<a +href="#format_common_func_start">llvm.dbg.func.start</a></tt>. The function's +single argument is either the <tt>%<a +href="#format_blocks">llvm.dbg.block</a></tt> or the <tt>%<a +href="#format_subprograms">llvm.dbg.subprogram.type</a></tt> which is +ending.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="format_common_declare">llvm.dbg.declare</a> +</div> + +<div class="doc_text"> +<pre> + void %<a href="#format_common_declare">llvm.dbg.declare</a>( { } *, { }* ) +</pre> + +<p>This intrinsic provides information about a local element (ex. variable.) The +first argument is the alloca for the variable, cast to a <tt>{ }*</tt>. The +second argument is the <tt>%<a +href="#format_variables">llvm.dbg.variable</a></tt> containing the description +of the variable, also cast to a <tt>{ }*</tt>.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="format_common_stoppoints"> + Representing stopping points in the source program + </a> +</div> + +<div class="doc_text"> + +<p>LLVM debugger "stop points" are a key part of the debugging representation +that allows the LLVM to maintain simple semantics for <a +href="#debugopt">debugging optimized code</a>. The basic idea is that the +front-end inserts calls to the <a +href="#format_common_stoppoint">%<tt>llvm.dbg.stoppoint</tt></a> intrinsic +function at every point in the program where a debugger should be able to +inspect the program (these correspond to places a debugger stops when you +"<tt>step</tt>" through it). The front-end can choose to place these as +fine-grained as it would like (for example, before every subexpression +evaluated), but it is recommended to only put them after every source statement +that includes executable code.</p> + +<p>Using calls to this intrinsic function to demark legal points for the +debugger to inspect the program automatically disables any optimizations that +could potentially confuse debugging information. To non-debug-information-aware +transformations, these calls simply look like calls to an external function, +which they must assume to do anything (including reading or writing to any part +of reachable memory). On the other hand, it does not impact many optimizations, +such as code motion of non-trapping instructions, nor does it impact +optimization of subexpressions, code duplication transformations, or basic-block +reordering transformations.</p> + +</div> + + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="format_common_lifetime">Object lifetimes and scoping</a> +</div> + +<div class="doc_text"> +<p>In many languages, the local variables in functions can have their lifetime +or scope limited to a subset of a function. In the C family of languages, for +example, variables are only live (readable and writable) within the source block +that they are defined in. In functional languages, values are only readable +after they have been defined. Though this is a very obvious concept, it is also +non-trivial to model in LLVM, because it has no notion of scoping in this sense, +and does not want to be tied to a language's scoping rules.</p> + +<p>In order to handle this, the LLVM debug format uses the notion of "regions" +of a function, delineated by calls to intrinsic functions. These intrinsic +functions define new regions of the program and indicate when the region +lifetime expires. Consider the following C fragment, for example:</p> + +<pre> +1. void foo() { +2. int X = ...; +3. int Y = ...; +4. { +5. int Z = ...; +6. ... +7. } +8. ... +9. } +</pre> + +<p>Compiled to LLVM, this function would be represented like this:</p> + +<pre> +void %foo() { +entry: + %X = alloca int + %Y = alloca int + %Z = alloca int + + ... + + call void %<a href="#format_common_func_start">llvm.dbg.func.start</a>( %<a href="#format_subprograms">llvm.dbg.subprogram.type</a>* %llvm.dbg.subprogram ) + + call void %<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint 2, uint 2, %<a href="#format_compile_units">llvm.dbg.compile_unit</a>* %llvm.dbg.compile_unit ) + + call void %<a href="#format_common_declare">llvm.dbg.declare</a>({}* %X, ...) + call void %<a href="#format_common_declare">llvm.dbg.declare</a>({}* %Y, ...) + + <i>;; Evaluate expression on line 2, assigning to X.</i> + + call void %<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint 3, uint 2, %<a href="#format_compile_units">llvm.dbg.compile_unit</a>* %llvm.dbg.compile_unit ) + + <i>;; Evaluate expression on line 3, assigning to Y.</i> + + call void %<a href="#format_common_stoppoint">llvm.region.start</a>() + call void %<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint 5, uint 4, %<a href="#format_compile_units">llvm.dbg.compile_unit</a>* %llvm.dbg.compile_unit ) + call void %<a href="#format_common_declare">llvm.dbg.declare</a>({}* %X, ...) + + <i>;; Evaluate expression on line 5, assigning to Z.</i> + + call void %<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint 7, uint 2, %<a href="#format_compile_units">llvm.dbg.compile_unit</a>* %llvm.dbg.compile_unit ) + call void %<a href="#format_common_region_end">llvm.region.end</a>() + + call void %<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint 9, uint 2, %<a href="#format_compile_units">llvm.dbg.compile_unit</a>* %llvm.dbg.compile_unit ) + + call void %<a href="#format_common_region_end">llvm.region.end</a>() + + ret void +} +</pre> + +<p>This example illustrates a few important details about the LLVM debugging +information. In particular, it shows how the various intrinsics are applied +together to allow a debugger to analyze the relationship between statements, +variable definitions, and the code used to implement the function.</p> + +<p>The first intrinsic <tt>%<a +href="#format_common_func_start">llvm.dbg.func.start</a></tt> provides +a link with the <a href="#format_subprograms">subprogram descriptor</a> +containing the details of this function. This call also defines the beginning +of the function region, bounded by the <tt>%<a +href="#format_common_region_end">llvm.region.end</a></tt> at the end of +the function. This region is used to bracket the lifetime of variables declared +within. For a function, this outer region defines a new stack frame whose +lifetime ends when the region is ended.</p> + +<p>It is possible to define inner regions for short term variables by using the +%<a href="#format_common_stoppoint"><tt>llvm.region.start</tt></a> and <a +href="#format_common_region_end"><tt>%llvm.region.end</tt></a> to bound a +region. The inner region in this example would be for the block containing the +declaration of Z.</p> + +<p>Using regions to represent the boundaries of source-level functions allow +LLVM interprocedural optimizations to arbitrarily modify LLVM functions without +having to worry about breaking mapping information between the LLVM code and the +and source-level program. In particular, the inliner requires no modification +to support inlining with debugging information: there is no explicit correlation +drawn between LLVM functions and their source-level counterparts (note however, +that if the inliner inlines all instances of a non-strong-linkage function into +its caller that it will not be possible for the user to manually invoke the +inlined function from a debugger).</p> + +<p>Once the function has been defined, the <a +href="#format_common_stoppoint"><tt>stopping point</tt></a> corresponding to +line #2 (column #2) of the function is encountered. At this point in the +function, <b>no</b> local variables are live. As lines 2 and 3 of the example +are executed, their variable definitions are introduced into the program using +%<a href="#format_common_declare"><tt>llvm.dbg.declare</tt></a>, without the +need to specify a new region. These variables do not require new regions to be +introduced because they go out of scope at the same point in the program: line +9.</p> + +<p>In contrast, the <tt>Z</tt> variable goes out of scope at a different time, +on line 7. For this reason, it is defined within the inner region, which kills +the availability of <tt>Z</tt> before the code for line 8 is executed. In this +way, regions can support arbitrary source-language scoping rules, as long as +they can only be nested (ie, one scope cannot partially overlap with a part of +another scope).</p> + +<p>It is worth noting that this scoping mechanism is used to control scoping of +all declarations, not just variable declarations. For example, the scope of a +C++ using declaration is controlled with this and could change how name lookup is +performed.</p> + +</div> + + + +<!-- *********************************************************************** --> +<div class="doc_section"> + <a name="ccxx_frontend">C/C++ front-end specific debug information</a> +</div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>The C and C++ front-ends represent information about the program in a format +that is effectively identical to <a +href="http://www.eagercon.com/dwarf/dwarf3std.htm">Dwarf 3.0</a> in terms of +information content. This allows code generators to trivially support native +debuggers by generating standard dwarf information, and contains enough +information for non-dwarf targets to translate it as needed.</p> + +<p>This section describes the forms used to represent C and C++ programs. Other +languages could pattern themselves after this (which itself is tuned to +representing programs in the same way that Dwarf 3 does), or they could choose +to provide completely different forms if they don't fit into the Dwarf model. +As support for debugging information gets added to the various LLVM +source-language front-ends, the information used should be documented here.</p> + +<p>The following sections provide examples of various C/C++ constructs and the +debug information that would best describe those constructs.</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="ccxx_compile_units">C/C++ source file information</a> +</div> + +<div class="doc_text"> + +<p>Given the source files "MySource.cpp" and "MyHeader.h" located in the +directory "/Users/mine/sources", the following code;</p> + +<pre> +#include "MyHeader.h" + +int main(int argc, char *argv[]) { + return 0; +} +</pre> + +<p>a C/C++ front-end would generate the following descriptors;</p> + +<pre> +... +;; +;; Define types used. In this case we need one for compile unit anchors and one +;; for compile units. +;; +%<a href="#format_anchors">llvm.dbg.anchor.type</a> = type { uint, uint } +%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = type { uint, { }*, uint, uint, sbyte*, sbyte*, sbyte* } +... +;; +;; Define the anchor for compile units. Note that the second field of the +;; anchor is 17, which is the same as the tag for compile units +;; (17 = DW_TAG_compile_unit.) +;; +%<a href="#format_compile_units">llvm.dbg.compile_units</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> { uint 0, uint 17 }, section "llvm.metadata" + +;; +;; Define the compile unit for the source file "/Users/mine/sources/MySource.cpp". +;; +%<a href="#format_compile_units">llvm.dbg.compile_unit1</a> = internal constant %<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> { + uint add(uint 17, uint 262144), + { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_units</a> to { }*), + uint 1, + uint 1, + sbyte* getelementptr ([13 x sbyte]* %str1, int 0, int 0), + sbyte* getelementptr ([21 x sbyte]* %str2, int 0, int 0), + sbyte* getelementptr ([33 x sbyte]* %str3, int 0, int 0) }, section "llvm.metadata" + +;; +;; Define the compile unit for the header file "/Users/mine/sources/MyHeader.h". +;; +%<a href="#format_compile_units">llvm.dbg.compile_unit2</a> = internal constant %<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> { + uint add(uint 17, uint 262144), + { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_units</a> to { }*), + uint 1, + uint 1, + sbyte* getelementptr ([11 x sbyte]* %str4, int 0, int 0), + sbyte* getelementptr ([21 x sbyte]* %str2, int 0, int 0), + sbyte* getelementptr ([33 x sbyte]* %str3, int 0, int 0) }, section "llvm.metadata" + +;; +;; Define each of the strings used in the compile units. +;; +%str1 = internal constant [13 x sbyte] c"MySource.cpp\00", section "llvm.metadata"; +%str2 = internal constant [21 x sbyte] c"/Users/mine/sources/\00", section "llvm.metadata"; +%str3 = internal constant [33 x sbyte] c"4.0.1 LLVM (LLVM research group)\00", section "llvm.metadata"; +%str4 = internal constant [11 x sbyte] c"MyHeader.h\00", section "llvm.metadata"; +... +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="ccxx_global_variable">C/C++ global variable information</a> +</div> + +<div class="doc_text"> + +<p>Given an integer global variable declared as follows;</p> + +<pre> +int MyGlobal = 100; +</pre> + +<p>a C/C++ front-end would generate the following descriptors;</p> + +<pre> +;; +;; Define types used. One for global variable anchors, one for the global +;; variable descriptor, one for the global's basic type and one for the global's +;; compile unit. +;; +%<a href="#format_anchors">llvm.dbg.anchor.type</a> = type { uint, uint } +%<a href="#format_global_variables">llvm.dbg.global_variable.type</a> = type { uint, { }*, { }*, sbyte*, { }*, uint, { }*, bool, bool, { }*, uint } +%<a href="#format_basic_type">llvm.dbg.basictype.type</a> = type { uint, { }*, sbyte*, { }*, int, uint, uint, uint, uint } +%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = ... +... +;; +;; Define the global itself. +;; +%MyGlobal = global int 100 +... +;; +;; Define the anchor for global variables. Note that the second field of the +;; anchor is 52, which is the same as the tag for global variables +;; (52 = DW_TAG_variable.) +;; +%<a href="#format_global_variables">llvm.dbg.global_variables</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> { uint 0, uint 52 }, section "llvm.metadata" + +;; +;; Define the global variable descriptor. Note the reference to the global +;; variable anchor and the global variable itself. +;; +%<a href="#format_global_variables">llvm.dbg.global_variable</a> = internal constant %<a href="#format_global_variables">llvm.dbg.global_variable.type</a> { + uint add(uint 52, uint 262144), + { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_global_variables">llvm.dbg.global_variables</a> to { }*), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([9 x sbyte]* %str1, int 0, int 0), + sbyte* getelementptr ([1 x sbyte]* %str2, int 0, int 0), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + uint 1, + { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*), + bool false, + bool true, + { }* cast (int* %MyGlobal to { }*) }, section "llvm.metadata" + +;; +;; Define the basic type of 32 bit signed integer. Note that since int is an +;; intrinsic type the source file is NULL and line 0. +;; +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([4 x sbyte]* %str3, int 0, int 0), + { }* null, + int 0, + uint 32, + uint 32, + uint 0, + uint 5 }, section "llvm.metadata" + +;; +;; Define the names of the global variable and basic type. +;; +%str1 = internal constant [9 x sbyte] c"MyGlobal\00", section "llvm.metadata" +%str2 = internal constant [1 x sbyte] c"\00", section "llvm.metadata" +%str3 = internal constant [4 x sbyte] c"int\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="ccxx_subprogram">C/C++ function information</a> +</div> + +<div class="doc_text"> + +<p>Given a function declared as follows;</p> + +<pre> +int main(int argc, char *argv[]) { + return 0; +} +</pre> + +<p>a C/C++ front-end would generate the following descriptors;</p> + +<pre> +;; +;; Define types used. One for subprogram anchors, one for the subprogram +;; descriptor, one for the global's basic type and one for the subprogram's +;; compile unit. +;; +%<a href="#format_subprograms">llvm.dbg.subprogram.type</a> = type { uint, { }*, { }*, sbyte*, { }*, bool, bool } +%<a href="#format_anchors">llvm.dbg.anchor.type</a> = type { uint, uint } +%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = ... + +;; +;; Define the anchor for subprograms. Note that the second field of the +;; anchor is 46, which is the same as the tag for subprograms +;; (46 = DW_TAG_subprogram.) +;; +%<a href="#format_subprograms">llvm.dbg.subprograms</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> { uint 0, uint 46 }, section "llvm.metadata" + +;; +;; Define the descriptor for the subprogram. TODO - more details. +;; +%<a href="#format_subprograms">llvm.dbg.subprogram</a> = internal constant %<a href="#format_subprograms">llvm.dbg.subprogram.type</a> { + uint add(uint 46, uint 262144), + { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_subprograms">llvm.dbg.subprograms</a> to { }*), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([5 x sbyte]* %str1, int 0, int 0), + sbyte* getelementptr ([1 x sbyte]* %str2, int 0, int 0), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + uint 1, + { }* null, + bool false, + bool true }, section "llvm.metadata" + +;; +;; Define the name of the subprogram. +;; +%str1 = internal constant [5 x sbyte] c"main\00", section "llvm.metadata" +%str2 = internal constant [1 x sbyte] c"\00", section "llvm.metadata" + +;; +;; Define the subprogram itself. +;; +int %main(int %argc, sbyte** %argv) { +... +} +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="ccxx_basic_types">C/C++ basic types</a> +</div> + +<div class="doc_text"> + +<p>The following are the basic type descriptors for C/C++ core types;</p> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="ccxx_basic_type_bool">bool</a> +</div> + +<div class="doc_text"> + +<pre> +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([5 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 32, + uint 32, + uint 0, + uint 2 }, section "llvm.metadata" +%str1 = internal constant [5 x sbyte] c"bool\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="ccxx_basic_char">char</a> +</div> + +<div class="doc_text"> + +<pre> +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([5 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 8, + uint 8, + uint 0, + uint 6 }, section "llvm.metadata" +%str1 = internal constant [5 x sbyte] c"char\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="ccxx_basic_unsigned_char">unsigned char</a> +</div> + +<div class="doc_text"> + +<pre> +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([14 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 8, + uint 8, + uint 0, + uint 8 }, section "llvm.metadata" +%str1 = internal constant [14 x sbyte] c"unsigned char\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="ccxx_basic_short">short</a> +</div> + +<div class="doc_text"> + +<pre> +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([10 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 16, + uint 16, + uint 0, + uint 5 }, section "llvm.metadata" +%str1 = internal constant [10 x sbyte] c"short int\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="ccxx_basic_unsigned_short">unsigned short</a> +</div> + +<div class="doc_text"> + +<pre> +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([19 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 16, + uint 16, + uint 0, + uint 7 }, section "llvm.metadata" +%str1 = internal constant [19 x sbyte] c"short unsigned int\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="ccxx_basic_int">int</a> +</div> + +<div class="doc_text"> + +<pre> +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([4 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 32, + uint 32, + uint 0, + uint 5 }, section "llvm.metadata" +%str1 = internal constant [4 x sbyte] c"int\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="ccxx_basic_unsigned_int">unsigned int</a> +</div> + +<div class="doc_text"> + +<pre> +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([13 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 32, + uint 32, + uint 0, + uint 7 }, section "llvm.metadata" +%str1 = internal constant [13 x sbyte] c"unsigned int\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="ccxx_basic_long_long">long long</a> +</div> + +<div class="doc_text"> + +<pre> +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([14 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 64, + uint 64, + uint 0, + uint 5 }, section "llvm.metadata" +%str1 = internal constant [14 x sbyte] c"long long int\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="ccxx_basic_unsigned_long_long">unsigned long long</a> +</div> + +<div class="doc_text"> + +<pre> +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([23 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 64, + uint 64, + uint 0, + uint 7 }, section "llvm.metadata" +%str1 = internal constant [23 x sbyte] c"long long unsigned int\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="ccxx_basic_float">float</a> +</div> + +<div class="doc_text"> + +<pre> +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([6 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 32, + uint 32, + uint 0, + uint 4 }, section "llvm.metadata" +%str1 = internal constant [6 x sbyte] c"float\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsubsection"> + <a name="ccxx_basic_double">double</a> +</div> + +<div class="doc_text"> + +<pre> +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([7 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 64, + uint 64, + uint 0, + uint 4 }, section "llvm.metadata" +%str1 = internal constant [7 x sbyte] c"double\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="ccxx_derived_types">C/C++ derived types</a> +</div> + +<div class="doc_text"> + +<p>Given the following as an example of C/C++ derived type;</p> + +<pre> +typedef const int *IntPtr; +</pre> + +<p>a C/C++ front-end would generate the following descriptors;</p> + +<pre> +;; +;; Define the typedef "IntPtr". +;; +%<a href="#format_derived_type">llvm.dbg.derivedtype1</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> { + uint add(uint 22, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([7 x sbyte]* %str1, int 0, int 0), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + int 1, + uint 0, + uint 0, + uint 0, + { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype2</a> to { }*) }, section "llvm.metadata" +%str1 = internal constant [7 x sbyte] c"IntPtr\00", section "llvm.metadata" + +;; +;; Define the pointer type. +;; +%<a href="#format_derived_type">llvm.dbg.derivedtype2</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> { + uint add(uint 15, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* null, + { }* null, + int 0, + uint 32, + uint 32, + uint 0, + { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype3</a> to { }*) }, section "llvm.metadata" + +;; +;; Define the const type. +;; +%<a href="#format_derived_type">llvm.dbg.derivedtype3</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> { + uint add(uint 38, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* null, + { }* null, + int 0, + uint 0, + uint 0, + uint 0, + { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype1</a> to { }*) }, section "llvm.metadata" + +;; +;; Define the int type. +;; +%<a href="#format_basic_type">llvm.dbg.basictype1</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([4 x sbyte]* %str2, int 0, int 0), + { }* null, + int 0, + uint 32, + uint 32, + uint 0, + uint 5 }, section "llvm.metadata" +%str2 = internal constant [4 x sbyte] c"int\00", section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="ccxx_composite_types">C/C++ struct/union types</a> +</div> + +<div class="doc_text"> + +<p>Given the following as an example of C/C++ struct type;</p> + +<pre> +struct Color { + unsigned Red; + unsigned Green; + unsigned Blue; +}; +</pre> + +<p>a C/C++ front-end would generate the following descriptors;</p> + +<pre> +;; +;; Define basic type for unsigned int. +;; +%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> { + uint add(uint 36, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([13 x sbyte]* %str1, int 0, int 0), + { }* null, + int 0, + uint 32, + uint 32, + uint 0, + uint 7 }, section "llvm.metadata" +%str1 = internal constant [13 x sbyte] c"unsigned int\00", section "llvm.metadata" + +;; +;; Define composite type for struct Color. +;; +%<a href="#format_composite_type">llvm.dbg.compositetype</a> = internal constant %<a href="#format_composite_type">llvm.dbg.compositetype.type</a> { + uint add(uint 19, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([6 x sbyte]* %str2, int 0, int 0), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + int 1, + uint 96, + uint 32, + uint 0, + { }* null, + { }* cast ([3 x { }*]* %llvm.dbg.array to { }*) }, section "llvm.metadata" +%str2 = internal constant [6 x sbyte] c"Color\00", section "llvm.metadata" + +;; +;; Define the Red field. +;; +%<a href="#format_derived_type">llvm.dbg.derivedtype1</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> { + uint add(uint 13, uint 262144), + { }* null, + sbyte* getelementptr ([4 x sbyte]* %str3, int 0, int 0), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + int 2, + uint 32, + uint 32, + uint 0, + { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*) }, section "llvm.metadata" +%str3 = internal constant [4 x sbyte] c"Red\00", section "llvm.metadata" + +;; +;; Define the Green field. +;; +%<a href="#format_derived_type">llvm.dbg.derivedtype2</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> { + uint add(uint 13, uint 262144), + { }* null, + sbyte* getelementptr ([6 x sbyte]* %str4, int 0, int 0), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + int 3, + uint 32, + uint 32, + uint 32, + { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*) }, section "llvm.metadata" +%str4 = internal constant [6 x sbyte] c"Green\00", section "llvm.metadata" + +;; +;; Define the Blue field. +;; +%<a href="#format_derived_type">llvm.dbg.derivedtype3</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> { + uint add(uint 13, uint 262144), + { }* null, + sbyte* getelementptr ([5 x sbyte]* %str5, int 0, int 0), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + int 4, + uint 32, + uint 32, + uint 64, + { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*) }, section "llvm.metadata" +%str5 = internal constant [5 x sbyte] c"Blue\00", section "llvm.metadata" + +;; +;; Define the array of fields used by the composite type Color. +;; +%llvm.dbg.array = internal constant [3 x { }*] [ + { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype1</a> to { }*), + { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype2</a> to { }*), + { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype3</a> to { }*) ], section "llvm.metadata" +</pre> + +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="ccxx_enumeration_types">C/C++ enumeration types</a> +</div> + +<div class="doc_text"> + +<p>Given the following as an example of C/C++ enumeration type;</p> + +<pre> +enum Trees { + Spruce = 100, + Oak = 200, + Maple = 300 +}; +</pre> + +<p>a C/C++ front-end would generate the following descriptors;</p> + +<pre> +;; +;; Define composite type for enum Trees +;; +%<a href="#format_composite_type">llvm.dbg.compositetype</a> = internal constant %<a href="#format_composite_type">llvm.dbg.compositetype.type</a> { + uint add(uint 4, uint 262144), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + sbyte* getelementptr ([6 x sbyte]* %str1, int 0, int 0), + { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*), + int 1, + uint 32, + uint 32, + uint 0, + { }* null, + { }* cast ([3 x { }*]* %llvm.dbg.array to { }*) }, section "llvm.metadata" +%str1 = internal constant [6 x sbyte] c"Trees\00", section "llvm.metadata" + +;; +;; Define Spruce enumerator. +;; +%<a href="#format_enumeration">llvm.dbg.enumerator1</a> = internal constant %<a href="#format_enumeration">llvm.dbg.enumerator.type</a> { + uint add(uint 40, uint 262144), + sbyte* getelementptr ([7 x sbyte]* %str2, int 0, int 0), + int 100 }, section "llvm.metadata" +%str2 = internal constant [7 x sbyte] c"Spruce\00", section "llvm.metadata" + +;; +;; Define Oak enumerator. +;; +%<a href="#format_enumeration">llvm.dbg.enumerator2</a> = internal constant %<a href="#format_enumeration">llvm.dbg.enumerator.type</a> { + uint add(uint 40, uint 262144), + sbyte* getelementptr ([4 x sbyte]* %str3, int 0, int 0), + int 200 }, section "llvm.metadata" +%str3 = internal constant [4 x sbyte] c"Oak\00", section "llvm.metadata" + +;; +;; Define Maple enumerator. +;; +%<a href="#format_enumeration">llvm.dbg.enumerator3</a> = internal constant %<a href="#format_enumeration">llvm.dbg.enumerator.type</a> { + uint add(uint 40, uint 262144), + sbyte* getelementptr ([6 x sbyte]* %str4, int 0, int 0), + int 300 }, section "llvm.metadata" +%str4 = internal constant [6 x sbyte] c"Maple\00", section "llvm.metadata" + +;; +;; Define the array of enumerators used by composite type Trees. +;; +%llvm.dbg.array = internal constant [3 x { }*] [ + { }* cast (%<a href="#format_enumeration">llvm.dbg.enumerator.type</a>* %<a href="#format_enumeration">llvm.dbg.enumerator1</a> to { }*), + { }* cast (%<a href="#format_enumeration">llvm.dbg.enumerator.type</a>* %<a href="#format_enumeration">llvm.dbg.enumerator2</a> to { }*), + { }* cast (%<a href="#format_enumeration">llvm.dbg.enumerator.type</a>* %<a href="#format_enumeration">llvm.dbg.enumerator3</a> to { }*) ], section "llvm.metadata" +</pre> + +</div> + +<!-- *********************************************************************** --> + +<hr> +<address> + <a href="http://jigsaw.w3.org/css-validator/check/referer"><img + src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a> + <a 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