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Updated information related to local variables and scopes.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26982 91177308-0d34-0410-b5e6-96231b3b80d8
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Jim Laskey
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@ -16,6 +16,7 @@
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<li><a href="#introduction">Introduction</a>
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<ol>
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<li><a href="#phil">Philosophy behind LLVM debugging information</a></li>
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<li><a href="#consumers">Debug information consumers</a></li>
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<li><a href="#debugopt">Debugging optimized code</a></li>
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</ol></li>
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<li><a href="#format">Debugging information format</a>
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@ -32,6 +33,7 @@
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<li><a href="#format_composite_type">Composite type descriptors</a></li>
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<li><a href="#format_subrange">Subrange descriptors</a></li>
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<li><a href="#format_enumeration">Enumerator descriptors</a></li>
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<li><a href="#format_variables">Local variables</a></li>
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</ul></li>
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<li><a href="#format_common_intrinsics">Debugger intrinsic functions</a>
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<ul>
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@ -132,6 +134,29 @@ a specific language of family of languages.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="consumers">Debug information consumers</a>
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</div>
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<div class="doc_text">
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<p>The role of debug information is to provide meta information normally
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stripped away during the compilation process. This meta information provides an
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llvm user a relationship between generated code and the original program source
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code.</p>
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<p>Currently, debug information is consumed by the DwarfWriter to produce dwarf
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information used by the gdb debugger. Other targets could use the same
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information to produce stabs or other debug forms.</p>
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<p>It would also be reasonable to use debug information to feed profiling tools
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for analysis of generated code, or, tools for reconstructing the original source
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from generated code.</p>
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<p>TODO - expound a bit more.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="debugopt">Debugging optimized code</a>
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@ -248,12 +273,13 @@ debug descriptors.</p>
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<p>Consumers of LLVM debug information expect the descriptors for program
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objects to start in a canonical format, but the descriptors can include
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additional information appended at the end that is source-language specific.
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All LLVM debugging information is versioned, allowing backwards compatibility in
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the case that the core structures need to change in some way. Also, all
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debugging information objects start with a tag to indicate what type of object
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it is. The source-language is allowed to define its own objects, by using
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unreserved tag numbers.</p>
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additional information appended at the end that is source-language specific. All
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LLVM debugging information is versioned, allowing backwards compatibility in the
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case that the core structures need to change in some way. Also, all debugging
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information objects start with a tag to indicate what type of object it is. The
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source-language is allowed to define its own objects, by using unreserved tag
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numbers. We recommend using with tags in the range 0x1000 thru 0x2000 (there is
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a defined enum DW_TAG_user_base = 0x1000.)</p>
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<p>The fields of debug descriptors used internally by LLVM (MachineDebugInfo)
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are restricted to only the simple data types <tt>int</tt>, <tt>uint</tt>,
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@ -328,7 +354,7 @@ deleted.</p>
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%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = type {
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uint, ;; Tag = 17 (DW_TAG_compile_unit)
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{ }*, ;; Compile unit anchor = cast = (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_units</a> to { }*)
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uint, ;; LLVM debug version number = 2
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uint, ;; LLVM debug version number = 3
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uint, ;; Dwarf language identifier (ex. DW_LANG_C89)
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sbyte*, ;; Source file name
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sbyte*, ;; Source file directory (includes trailing slash)
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@ -337,7 +363,7 @@ deleted.</p>
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</pre>
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<p>These descriptors contain the version number for the debug info (currently
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2), a source language ID for the file (we use the Dwarf 3.0 ID numbers, such as
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3), a source language ID for the file (we use the Dwarf 3.0 ID numbers, such as
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<tt>DW_LANG_C89</tt>, <tt>DW_LANG_C_plus_plus</tt>, <tt>DW_LANG_Cobol74</tt>,
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etc), three strings describing the filename, working directory of the compiler,
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and an identifier string for the compiler that produced it.</p>
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@ -363,7 +389,7 @@ line correspondence.</p>
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{ }*, ;; Reference to context descriptor
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sbyte*, ;; Name
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{ }*, ;; Reference to compile unit where defined
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int, ;; Line number where defined
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uint, ;; Line number where defined
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{ }*, ;; Reference to type descriptor
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bool, ;; True if the global is local to compile unit (static)
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bool, ;; True if the global is defined in the compile unit (not extern)
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@ -390,20 +416,16 @@ provide details such as name, type and where the variable is defined.</p>
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{ }*, ;; Reference to context descriptor
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sbyte*, ;; Name
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{ }*, ;; Reference to compile unit where defined
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int, ;; Line number where defined
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uint, ;; Line number where defined
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{ }*, ;; Reference to type descriptor
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bool, ;; True if the global is local to compile unit (static)
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bool, ;; True if the global is defined in the compile unit (not extern)
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{ }* ;; Reference to array of member descriptors
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bool ;; True if the global is defined in the compile unit (not extern)
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}
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</pre>
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<p>These descriptors provide debug information about functions, methods and
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subprograms. The provide details such as name, return and argument types and
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where the subprogram is defined.</p>
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<p>The array of member descriptors is used to define arguments local variables
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and nested blocks.</p>
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subprograms. They provide details such as name, return types and the source
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location where the subprogram is defined.</p>
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</div>
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<!-- ======================================================================= -->
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@ -416,7 +438,7 @@ and nested blocks.</p>
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<pre>
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%<a href="#format_blocks">llvm.dbg.block</a> = type {
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uint, ;; Tag = 13 (DW_TAG_lexical_block)
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{ }* ;; Reference to array of member descriptors
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{ }* ;; Reference to context descriptor
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}
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</pre>
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@ -439,7 +461,7 @@ and deeper nested blocks.</p>
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{ }*, ;; Reference to context (typically a compile unit)
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sbyte*, ;; Name (may be "" for anonymous types)
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{ }*, ;; Reference to compile unit where defined (may be NULL)
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int, ;; Line number where defined (may be 0)
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uint, ;; Line number where defined (may be 0)
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uint, ;; Size in bits
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uint, ;; Alignment in bits
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uint, ;; Offset in bits
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@ -485,7 +507,7 @@ one of the following;</p>
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{ }*, ;; Reference to context
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sbyte*, ;; Name (may be "" for anonymous types)
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{ }*, ;; Reference to compile unit where defined (may be NULL)
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int, ;; Line number where defined (may be 0)
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uint, ;; Line number where defined (may be 0)
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uint, ;; Size in bits
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uint, ;; Alignment in bits
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uint, ;; Offset in bits
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@ -549,7 +571,7 @@ NULL derived type.</p>
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{ }*, ;; Reference to context
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sbyte*, ;; Name (may be "" for anonymous types)
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{ }*, ;; Reference to compile unit where defined (may be NULL)
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int, ;; Line number where defined (may be 0)
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uint, ;; Line number where defined (may be 0)
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uint, ;; Size in bits
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uint, ;; Alignment in bits
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uint, ;; Offset in bits
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@ -637,6 +659,44 @@ value.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsubsection">
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<a name="format_variables">Local variables</a>
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</div>
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<div class="doc_text">
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<pre>
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%<a href="#format_variables">llvm.dbg.variable.type</a> = type {
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uint, ;; Tag (see below)
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{ }*, ;; Context
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sbyte*, ;; Name
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{ }*, ;; Reference to compile unit where defined
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uint, ;; Line number where defined
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{ }* ;; Type descriptor
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}
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</pre>
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<p>These descriptors are used to define variables local to a sub program. The
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value of the tag depends on the usage of the variable;</p>
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<pre>
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DW_TAG_auto_variable = 256
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DW_TAG_arg_variable = 257
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DW_TAG_return_variable = 258
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</pre>
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<p>An auto variable is any variable declared in the body of the function. An
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argument variable is any variable that appears as a formal argument to the
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function. A return variable is used to track the result of a function and has
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no source correspondent.</p>
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<p>The context is eitehr the subprogram or block where the variable is defined.
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Name the source variable name. Compile unit and line indicate where the
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variable was defined. Type descriptor defines the declared type of the
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variable.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="format_common_intrinsics">Debugger intrinsic functions</a>
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@ -664,7 +724,8 @@ the generated code. The first argument is the line number (base 1), second
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argument si the column number (0 if unknown) and the third argument the source
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compile unit. Code following a call to this intrinsic will have been defined in
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close proximity of the line, column and file. This information holds until the
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next call to <a href="#format_common_stoppoint">lvm.dbg.stoppoint</a>.</p>
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next call to <tt>%<a
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href="#format_common_stoppoint">lvm.dbg.stoppoint</a></tt>.</p>
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</div>
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@ -675,14 +736,17 @@ next call to <a href="#format_common_stoppoint">lvm.dbg.stoppoint</a>.</p>
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<div class="doc_text">
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<pre>
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void %<a href="#format_common_func_start">llvm.dbg.func.start</a>( %<a href="#format_subprograms">llvm.dbg.subprogram.type</a>* )
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void %<a href="#format_common_func_start">llvm.dbg.func.start</a>( { }* )
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</pre>
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<p>This intrinsic is used to link the debug information in <tt>%<a
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href="#format_subprograms">llvm.dbg.subprogram</a></tt> to the function. It also
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defines the beginning of the function's declarative region (scope.) The
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intrinsic should be called early in the function after the all the alloca
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instructions.</p>
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instructions. It should be paired off with a closing <tt>%<a
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href="#format_common_region_end">llvm.dbg.region.end</a></tt>. The function's
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single argument is the <tt>%<a
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href="#format_subprograms">llvm.dbg.subprogram.type</a></tt>.</p>
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</div>
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@ -693,12 +757,15 @@ instructions.</p>
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<div class="doc_text">
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<pre>
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void %<a href="#format_common_region_start">llvm.dbg.region.start</a>()
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void %<a href="#format_common_region_start">llvm.dbg.region.start</a>( { }* )
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</pre>
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<p>This intrinsic is used to define the beginning of a declarative scope (ex.
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block) for local language elements. It should be paired off with a closing
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<tt>%<a href="#format_common_region_end">llvm.dbg.region.end</a></tt>.</p>
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<tt>%<a href="#format_common_region_end">llvm.dbg.region.end</a></tt>. The
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function's single argument is the <tt>%<a
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href="#format_blocks">llvm.dbg.block</a></tt> which is starting.</p>
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</div>
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@ -709,13 +776,17 @@ block) for local language elements. It should be paired off with a closing
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<div class="doc_text">
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<pre>
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void %<a href="#format_common_region_end">llvm.dbg.region.end</a>()
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void %<a href="#format_common_region_end">llvm.dbg.region.end</a>( { }* )
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</pre>
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<p>This intrinsic is used to define the end of a declarative scope (ex. block)
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for local language elements. It should be paired off with an opening <tt>%<a
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href="#format_common_region_start">llvm.dbg.region.start</a></tt> or <tt>%<a
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href="#format_common_func_start">llvm.dbg.func.start</a></tt>.</p>
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href="#format_common_func_start">llvm.dbg.func.start</a></tt>. The function's
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single argument is either the <tt>%<a
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href="#format_blocks">llvm.dbg.block</a></tt> or the <tt>%<a
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href="#format_subprograms">llvm.dbg.subprogram.type</a></tt> which is
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ending.</p>
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</div>
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@ -726,11 +797,13 @@ href="#format_common_func_start">llvm.dbg.func.start</a></tt>.</p>
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<div class="doc_text">
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<pre>
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void %<a href="#format_common_declare">llvm.dbg.declare</a>( {} *, ... )
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void %<a href="#format_common_declare">llvm.dbg.declare</a>( { } *, { }* )
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</pre>
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<p>This intrinsic provides information about a local element (ex. variable.)
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TODO - details.</p>
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The first argument as a AllocA for the variable cast to a <tt>{ }*</tt>. The second
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argument is the <tt>%<a href="#format_variables">llvm.dbg.variable</a></tt>
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containing the description of the variable, also cast to a <tt>{ }*</tt>.</p>
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</div>
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@ -1097,7 +1170,7 @@ int main(int argc, char *argv[]) {
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;; descriptor, one for the global's basic type and one for the subprogram's
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;; compile unit.
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;;
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%<a href="#format_subprograms">llvm.dbg.subprogram.type</a> = type { uint, { }*, { }*, sbyte*, { }*, bool, bool, { }* }
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%<a href="#format_subprograms">llvm.dbg.subprogram.type</a> = type { uint, { }*, { }*, sbyte*, { }*, bool, bool }
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%<a href="#format_anchors">llvm.dbg.anchor.type</a> = type { uint, uint }
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%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = ...
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@ -1120,8 +1193,7 @@ int main(int argc, char *argv[]) {
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uint 1,
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{ }* null,
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bool false,
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bool true,
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null }, section "llvm.metadata"
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bool true }, section "llvm.metadata"
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;;
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;; Define the name of the subprogram.
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