From cec12a5c30cf6dbb96733f5f01cd9cbbc8fbe249 Mon Sep 17 00:00:00 2001 From: Jim Laskey Date: Tue, 14 Mar 2006 18:08:46 +0000 Subject: Bring debugging information up to date. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26759 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/SourceLevelDebugging.html | 1802 ++++++++++++++++++++++++++-------------- 1 file changed, 1166 insertions(+), 636 deletions(-) (limited to 'docs/SourceLevelDebugging.html') diff --git a/docs/SourceLevelDebugging.html b/docs/SourceLevelDebugging.html index c735e4e781..6a3d675080 100644 --- a/docs/SourceLevelDebugging.html +++ b/docs/SourceLevelDebugging.html @@ -17,46 +17,41 @@
  1. Philosophy behind LLVM debugging information
  2. Debugging optimized code
    3. -
  3. Future work
-
  • Using the llvm-db tool -
      -
    1. Limitations of llvm-db
      2. -
    2. A sample llvm-db session
      3. -
    3. Starting the debugger
      4. -
    4. Commands recognized by the debugger
      5. -
    • - -
  • Architecture of the LLVM debugger -
      -
    1. The Debugger and InferiorProcess classes
      2. -
    2. The RuntimeInfo, ProgramInfo, and SourceLanguage classes
      3. -
    3. The llvm-db tool
      4. -
    4. Short-term TODO list
      5. -
    • -
  • Debugging information format
      -
    1. Anchors for global objects
      2. -
    2. Representing stopping points in the source program
      3. -
    3. Object lifetimes and scoping
      4. -
    4. Object descriptor formats +
    5. Debug information descriptors
      6. +
    6. Debugger intrinsic functions +
      7. -
    7. Debugger intrinsic functions
      8. -
    8. Values for debugger tags
      9. +
    9. Representing stopping points in the + source program
  • C/C++ front-end specific debug information
      -
    1. Program Scope Entries -
      2. -
    2. Data objects (program variables)
      3. +
    3. C/C++ source file information
      4. +
    4. C/C++ global variable information
      5. +
    5. C/C++ function information
      6. +
    6. C/C++ basic types
      7. +
    7. C/C++ derived types
      8. +
    8. C/C++ struct/union types
      9. +
    9. C/C++ enumeration types
    • @@ -67,7 +62,8 @@ height="369">
    -

    Written by Chris Lattner

    +

    Written by Chris Lattner + and Jim Laskey

    @@ -78,15 +74,10 @@ height="369">

    This document is the central repository for all information pertaining to -debug information in LLVM. It describes the user -interface for the llvm-db tool, which provides a -powerful source-level debugger -to users of LLVM-based compilers. It then describes the various components that make up the debugger and the -libraries which future clients may use. Finally, it describes the actual format that the LLVM debug information takes, -which is useful for those interested in creating front-ends or dealing directly -with the information.

    +debug information in LLVM. It describes the actual format +that the LLVM debug information 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++.

    @@ -133,15 +124,13 @@ href="#ccxx_frontend">implementation-defined format (the C/C++ front-end currently uses working draft 7 of the Dwarf 3 standard).

    -

    When a program is debugged, the debugger interacts with the user and turns -the stored debug information into source-language specific information. As -such, the debugger must be aware of the source-language, and is thus tied to a -specific language of family of languages. The LLVM -debugger is designed to be modular in its support for source-languages.

    +

    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, the debugger must be aware of the source-language, and is thus tied to +a specific language of family of languages.

    -
    Debugging optimized code @@ -195,508 +184,531 @@ completely.

    - -
    - Future work + +
    + Debugging information format
    +
    -

    There are several important extensions that could be eventually added to the -LLVM debugger. The most important extension would be to upgrade the LLVM code -generators to support debugging information. This would also allow, for -example, the X86 code generator to emit native objects that contain debugging -information consumable by traditional source-level debuggers like GDB or -DBX.

    -

    Additionally, LLVM optimizations can be upgraded to incrementally update the -debugging information, new commands can be added to the -debugger, and thread support could be added to the debugger.

    +

    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 +linkonce functions.

    -

    The "SourceLanguage" modules provided by llvm-db could be -substantially improved to provide good support for C++ language features like -namespaces and scoping rules.

    +

    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 +-globaldce pass), the extraneous debug information will automatically +become dead and be removed by the optimizer.

    + +

    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 "llvm.metadata" +section. All values declared in this section are stripped away after target +debug information is constructed and before the program object is emitted.

    -

    After working with the debugger for a while, perhaps the nicest improvement -would be to add some sort of line editor, such as GNU readline (but one that is -compatible with the LLVM license).

    +

    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 source files, and program objects. These abstract objects are +used by the debugger to form stack traces, show information about local +variables, etc.

    -

    For someone so inclined, it should be straight-forward to write different -front-ends for the LLVM debugger, as the LLVM debugging engine is cleanly -separated from the llvm-db front-end. A new LLVM GUI debugger or IDE -would be nice.

    +

    This section of the documentation first describes the representation aspects +common to any source-language. The next section +describes the data layout conventions used by the C and C++ front-ends.

    - -
    - Using the llvm-db tool + +
    + Debug information descriptors
    -
    +

    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.

    + +

    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.

    + +

    The fields of debug descriptors used internally by LLVM (MachineDebugInfo) +are restricted to only the simple data types int, uint, +bool, float, double, sbyte* and { }* +. References to arbitrary values are handled using a { }* and a +cast to { }* expression; typically references to other field +descriptors, arrays of descriptors or global variables.

    + +
    +  %llvm.dbg.object.type = type {
+    uint,   ;; A tag
+    ...
+  }
+
    -

    The llvm-db tool provides a GDB-like interface for source-level -debugging of programs. This tool provides many standard commands for inspecting -and modifying the program as it executes, loading new programs, single stepping, -placing breakpoints, etc. This section describes how to use the debugger.

    +

    The first field of a descriptor is always an uint 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.

    -

    llvm-db has been designed to be as similar to GDB in its user -interface as possible. This should make it extremely easy to learn -llvm-db if you already know GDB. In general, llvm-db -provides the subset of GDB commands that are applicable to LLVM debugging users. -If there is a command missing that make a reasonable amount of sense within the -limitations of llvm-db, please report it as -a bug or, better yet, submit a patch to add it.

    +

    The details of the various descriptors follow.

    -
    - Limitations of llvm-db +
    + Anchor descriptors
    -

    llvm-db is designed to be modular and easy to extend. This -extensibility was key to getting the debugger up-and-running quickly, because we -can start with simple-but-unsophisicated implementations of various components. -Because of this, it is currently missing many features, though they should be -easy to add over time (patches welcomed!). The biggest inherent limitations of -llvm-db are currently due to extremely simple debugger backend (implemented in -"lib/Debugger/UnixLocalInferiorProcess.cpp") which is designed to work without -any cooperation from the code generators. Because it is so simple, it suffers -from the following inherent limitations:

    +
    +  %llvm.dbg.anchor.type = type {
+    uint,   ;; Tag = 0
+    uint    ;; Tag of descriptors grouped by the anchor
+  }
+
    -
      +

      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 +the debugger to use def-use chains to find all global objects of that type.

      -
    • Running a program in llvm-db is a bit slower than running it with -lli (i.e., in the JIT).
      • +

      The following names are recognized as anchors by LLVM:

      -
    • Inspection of the target hardware is not supported. This means that you -cannot, for example, print the contents of X86 registers.
      • +
      +  %llvm.dbg.compile_units       = linkonce constant %llvm.dbg.anchor.type  { uint 0, uint 17 } ;; DW_TAG_compile_unit
+  %llvm.dbg.global_variables    = linkonce constant %llvm.dbg.anchor.type  { uint 0, uint 52 } ;; DW_TAG_variable
+  %llvm.dbg.subprograms         = linkonce constant %llvm.dbg.anchor.type  { uint 0, uint 46 } ;; DW_TAG_subprogram
+
      -
    • Inspection of LLVM code is not supported. This means that you cannot print -the contents of arbitrary LLVM values, or use commands such as stepi. -This also means that you cannot debug code without debug information.
      • +

      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.

      -
    • Portions of the debugger run in the same address space as the program being -debugged. This means that memory corruption by the program could trample on -portions of the debugger.
      • +
    -
  • Attaching to existing processes and core files is not currently -supported.
    • + +
    + Compile unit descriptors +
    - +
    -

    That said, the debugger is still quite useful, and all of these limitations -can be eliminated by integrating support for the debugger into the code -generators, and writing a new InferiorProcess -subclass to use it. See the future work section for ideas -of how to extend the LLVM debugger despite these limitations.

    +
    +  %llvm.dbg.compile_unit.type = type {
+    uint,   ;; Tag = 17 (DW_TAG_compile_unit)
+    {  }*,  ;; Compile unit anchor = cast = (%llvm.dbg.anchor.type* %llvm.dbg.compile_units to {  }*)
+    uint,   ;; LLVM debug version number = 1
+    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)")
+  }
+
    -
    +

    These descriptors contain the version number for the debug info (currently +1), a source language ID for the file (we use the Dwarf 3.0 ID numbers, such as +DW_LANG_C89, DW_LANG_C_plus_plus, DW_LANG_Cobol74, +etc), three strings describing the filename, working directory of the compiler, +and an identifier string for the compiler that produced it.

    +

    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.

    + +
    -
    - A sample llvm-db session +
    + Global variable descriptors
    -

    TODO: this is obviously lame, when more is implemented, this can be much -better.

    - 
    -$ llvm-db funccall
-llvm-db: The LLVM source-level debugger
-Loading program... successfully loaded 'funccall.bc'!
-(llvm-db) create
-Starting program: funccall.bc
-main at funccall.c:9:2
-9 ->            q = 0;
-(llvm-db) list main
-4       void foo() {
-5               int t = q;
-6               q = t + 1;
-7       }
-8       int main() {
-9 ->            q = 0;
-10              foo();
-11              q = q - 1;
-12
-13              return q;
-(llvm-db) list
-14      }
-(llvm-db) step
-10 ->           foo();
-(llvm-db) s
-foo at funccall.c:5:2
-5 ->            int t = q;
-(llvm-db) bt
-#0 ->   0x85ffba0 in foo at funccall.c:5:2
-#1      0x85ffd98 in main at funccall.c:10:2
-(llvm-db) finish
-main at funccall.c:11:2
-11 ->           q = q - 1;
-(llvm-db) s
-13 ->           return q;
-(llvm-db) s
-The program stopped with exit code 0
-(llvm-db) quit
-$
+  %llvm.dbg.global_variable.type = type {
+    uint,   ;; Tag = 52 (DW_TAG_variable)
+    {  }*,  ;; Global variable anchor = cast (%llvm.dbg.anchor.type* %llvm.dbg.global_variables to {  }*),  
+    {  }*,  ;; Reference to compile unit
+    sbyte*, ;; Name
+    {  }*,  ;; 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
+    uint    ;; Line number in compile unit where variable is defined
+  }
    +

    These descriptors provide debug information about globals variables. The +provide details such as name, type and where the variable is defined.

    + +
    + + +
    + Subprogram descriptors
    +
    + +
    +  %llvm.dbg.subprogram.type = type {
+    uint,   ;; Tag = 46 (DW_TAG_subprogram)
+    {  }*,  ;; Subprogram anchor = cast (%llvm.dbg.anchor.type* %llvm.dbg.subprograms to {  }*),  
+    {  }*,  ;; Reference to compile unit
+    sbyte*, ;; Name
+    {  }*,  ;; 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)
+    TODO - MORE TO COME
+  }
+
+
    + +

    These descriptors provide debug information about functions, methods and +subprograms. The provide details such as name, return and argument types and +where the subprogram is defined.

    +
    -
    - Starting the debugger +
    + Basic type descriptors
    -

    There are three ways to start up the llvm-db debugger:

    +
    +  %llvm.dbg.basictype.type = type {
+    uint,   ;; Tag = 36 (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)
+    int,    ;; Line number where defined (may be 0)
+    uint,   ;; Size in bits
+    uint,   ;; Alignment in bits
+    uint,   ;; Offset in bits
+    uint    ;; Dwarf type encoding
+  }
+
    -

    When run with no options, just llvm-db, the debugger starts up -without a program loaded at all. You must use the file command to load a program, and the set args or run -commands to specify the arguments for the program.

    +

    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 composite type +(example to keep float doubles on 64 bit boundaries.) The offset is the bit +offset if embedded in a composite +type.

    -

    If you start the debugger with one argument, as llvm-db -<program>, the debugger will start up and load in the specified -program. You can then optionally specify arguments to the program with the set args or run -commands.

    +

    The type encoding provides the details of the type. The values are typically +one of the following;

    -

    The third way to start the program is with the --args option. This -option allows you to specify the program to load and the arguments to start out -with. Example use: llvm-db --args ls /home

    +
    +  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
+
    -
    - Commands recognized by the debugger +
    + Derived type descriptors
    -

    FIXME: this needs work obviously. See the GDB documentation for -information about what these do, or try 'help [command]' within -llvm-db to get information.

    +
    +  %llvm.dbg.derivedtype.type = type {
+    uint,   ;; Tag (see below)
+    {  }*,  ;; Reference to context
+    sbyte*, ;; Name (may be "" for anonymous types)
+    {  }*,  ;; Reference to compile unit where defined (may be NULL)
+    int,    ;; Line number where defined (may be 0)
+    uint,   ;; Size in bits
+    uint,   ;; Alignment in bits
+    uint,   ;; Offset in bits
+    {  }*   ;; Reference to type derived from
+  }
+
    -

    -

    General usage:

    -
      -
    • help [command]
      • -
    • quit
      • -
    • file [program]
      • -
    +

    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;

    -

    Program inspection and interaction:

    -
      -
    • create (start the program, stopping it ASAP in main)
      • -
    • kill
      • -
    • run [args]
      • -
    • step [num]
      • -
    • next [num]
      • -
    • cont
      • -
    • finish
      • - -
    • list [start[, end]]
      • -
    • info source
      • -
    • info sources
      • -
    • info functions
      • -
    +
    +  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
+
    -

    Call stack inspection:

    -
      -
    • backtrace
      • -
    • up [n]
      • -
    • down [n]
      • -
    • frame [n]
      • -
    +

    DW_TAG_member is used to define a member of a composite type. The type of the member is the +derived type.

    +

    DW_TAG_typedef is used to +provide a name for the derived type.

    -

    Debugger inspection and interaction:

    -
      -
    • info target
      • -
    • show prompt
      • -
    • set prompt
      • -
    • show listsize
      • -
    • set listsize
      • -
    • show language
      • -
    • set language
      • -
    • show args
      • -
    • set args [args]
      • -
    +

    DW_TAG_pointer_type, +DW_TAG_reference_type, DW_TAG_const_type, +DW_TAG_volatile_type and DW_TAG_restrict_type are used to +qualify the derived type.

    -

    TODO:

    -
      -
    • info frame
      • -
    • break
      • -
    • print
      • -
    • ptype
      • - -
    • info types
      • -
    • info variables
      • -
    • info program
      • - -
    • info args
      • -
    • info locals
      • -
    • info catch
      • -
    • ... many others
      • -
    +

    Derived type 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 composite type +(example to keep float doubles on 64 bit boundaries.) The offset is the bit +offset if embedded in a composite +type.

    + +

    Note that the void * type is expressed as a +llvm.dbg.derivedtype.type with tag of DW_TAG_pointer_type and +NULL derived type.

    - -
    - Architecture of the LLVM debugger + +
    + Composite type descriptors
    -
    -

    The LLVM debugger is built out of three distinct layers of software. These -layers provide clients with different interface options depending on what pieces -of they want to implement themselves, and it also promotes code modularity and -good design. The three layers are the Debugger -interface, the "info" interfaces, and the llvm-db tool itself.

    + +
    +  %llvm.dbg.compositetype.type = type {
+    uint,   ;; Tag (see below)
+    {  }*,  ;; Reference to context
+    sbyte*, ;; Name (may be "" for anonymous types)
+    {  }*,  ;; Reference to compile unit where defined (may be NULL)
+    int,    ;; 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
+  }
+
    + +

    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;

    + +
    +  DW_TAG_array_type = 1
+  DW_TAG_enumeration_type = 4
+  DW_TAG_structure_type = 19
+  DW_TAG_union_type = 23
+
    + +

    The members of array types (tag = DW_TAG_array_type) are subrange descriptors, each representing the range of +subscripts at that level of indexing.

    + +

    The members of enumeration types (tag = DW_TAG_enumeration_type) are +enumerator descriptors, each representing the +definition of enumeration value +for the set.

    + +

    The members of structure (tag = DW_TAG_structure_type) or union (tag += DW_TAG_union_type) types are any one of the basic, derived +or composite type descriptors, each +representing a field member of the structure or union.

    + +

    Composite type 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 composite +type (as an example, to keep float doubles on 64 bit boundaries.) The offset +is the bit offset if embedded in a composite +type.

    +
    -
    - The Debugger and InferiorProcess classes +
    + Subrange descriptors
    -

    The Debugger class (defined in the include/llvm/Debugger/ directory) -is a low-level class which is used to maintain information about the loaded -program, as well as start and stop the program running as necessary. This class -does not provide any high-level analysis or control over the program, only -exposing simple interfaces like load/unloadProgram, -create/killProgram, step/next/finish/contProgram, and -low-level methods for installing breakpoints.

    - -

    -The Debugger class is itself a wrapper around the lowest-level InferiorProcess -class. This class is used to represent an instance of the program running under -debugger control. The InferiorProcess class can be implemented in different -ways for different targets and execution scenarios (e.g., remote debugging). -The InferiorProcess class exposes a small and simple collection of interfaces -which are useful for inspecting the current state of the program (such as -collecting stack trace information, reading the memory image of the process, -etc). The interfaces in this class are designed to be as low-level and simple -as possible, to make it easy to create new instances of the class. -

    - -

    -The Debugger class exposes the currently active instance of InferiorProcess -through the Debugger::getRunningProcess method, which returns a -const reference to the class. This means that clients of the Debugger -class can only inspect the running instance of the program directly. To -change the executing process in some way, they must use the interces exposed by -the Debugger class. -

    + +
    +  %llvm.dbg.subrange.type = type {
+    uint,   ;; Tag = 33 (DW_TAG_subrange_type)
+    uint,   ;; Low value
+    uint    ;; High value
+  }
+
    + +

    These descriptors are used to define ranges of array subscripts for an array +composite type. 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.

    +
    -
    - The RuntimeInfo, ProgramInfo, and SourceLanguage classes +
    + Enumerator descriptors
    -

    -The next-highest level of debugger abstraction is provided through the -ProgramInfo, RuntimeInfo, SourceLanguage and related classes (also defined in -the include/llvm/Debugger/ directory). These classes efficiently -decode the debugging information and low-level interfaces exposed by -InferiorProcess into a higher-level representation, suitable for analysis by the -debugger. -

    - -

    -The ProgramInfo class exposes a variety of different kinds of information about -the program objects in the source-level-language. The SourceFileInfo class -represents a source-file in the program (e.g. a .cpp or .h file). The -SourceFileInfo class captures information such as which SourceLanguage was used -to compile the file, where the debugger can get access to the actual file text -(which is lazily loaded on demand), etc. The SourceFunctionInfo class -represents a... FIXME: finish. The ProgramInfo class provides interfaces -to lazily find and decode the information needed to create the Source*Info -classes requested by the debugger. -

    - -

    -The RuntimeInfo class exposes information about the currently executed program, -by decoding information from the InferiorProcess and ProgramInfo classes. It -provides a StackFrame class which provides an easy-to-use interface for -inspecting the current and suspended stack frames in the program. -

    - -

    -The SourceLanguage class is an abstract interface used by the debugger to -perform all source-language-specific tasks. For example, this interface is used -by the ProgramInfo class to decode language-specific types and functions and by -the debugger front-end (such as llvm-db to -evaluate source-langauge expressions typed into the debugger. This class uses -the RuntimeInfo & ProgramInfo classes to get information about the current -execution context and the loaded program, respectively. -

    + +
    +  %llvm.dbg.enumerator.type = type {
+    uint,   ;; Tag = 40 (DW_TAG_enumerator)
+    sbyte*, ;; Name
+    uint    ;; Value
+  }
+
    + +

    These descriptors are used to define members of an enumeration composite type, it associates the name to the +value.

    - The llvm-db tool + Debugger intrinsic functions
    -

    -The llvm-db is designed to be a debugger providing an interface as similar to GDB as reasonable, but no more so than that. -Because the Debugger and info classes implement all of the heavy lifting and -analysis, llvm-db (which lives in llvm/tools/llvm-db) consists -mainly of of code to interact with the user and parse commands. The CLIDebugger -constructor registers all of the builtin commands for the debugger, and each -command is implemented as a CLIDebugger::[name]Command method. -

    -
    +

    LLVM uses several intrinsic functions (name prefixed with "llvm.dbg") to +provide debug information at various points in generated code.

    + +
    -
    - Short-term TODO list +
    + llvm.dbg.stoppoint
    +
    +  void %llvm.dbg.stoppoint( uint, uint, %llvm.dbg.compile_unit* )
+
    -

    -FIXME: this section will eventually go away. These are notes to myself of -things that should be implemented, but haven't yet. -

    - -

    -Breakpoints: Support is already implemented in the 'InferiorProcess' -class, though it hasn't been tested yet. To finish breakpoint support, we need -to implement breakCommand (which should reuse the linespec parser from the list -command), and handle the fact that 'break foo' or 'break file.c:53' may insert -multiple breakpoints. Also, if you say 'break file.c:53' and there is no -stoppoint on line 53, the breakpoint should go on the next available line. My -idea was to have the Debugger class provide a "Breakpoint" class which -encapsulated this messiness, giving the debugger front-end a simple interface. -The debugger front-end would have to map the really complex semantics of -temporary breakpoints and 'conditional' breakpoints onto this intermediate -level. Also, breakpoints should survive as much as possible across program -reloads. -

    - -

    -UnixLocalInferiorProcess.cpp speedup: There is no reason for the debugged -process to code gen the globals corresponding to debug information. The -IntrinsicLowering object could instead change descriptors into constant expr -casts of the constant address of the LLVM objects for the descriptors. This -would also allow us to eliminate the mapping back and forth between physical -addresses that must be done.

    - -

    -Process deaths: The InferiorProcessDead exception should be extended to -know "how" a process died, i.e., it was killed by a signal. This is easy to -collect in the UnixLocalInferiorProcess, we just need to represent it.

    +

    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 si the column number (0 if unknown) and the third argument the source +compile unit. 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 lvm.dbg.stoppoint.

    - -
    - Debugging information format + +
    + llvm.dbg.func.start
    -
    +
    +  void %llvm.dbg.func.start( %llvm.dbg.subprogram.type* )
+
    -

    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 -linkonce functions.

    +

    This intrinsic is used to link the debug information in %llvm.dbg.subprogram 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.

    -

    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 --globaldce pass), the extraneous debug information will automatically -become dead and be removed by the optimizer.

    +
    -

    The debugger is designed to be agnostic about the contents of most of the -debugging information. It uses a source-language-specific -module 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 -debugger to interpret the information.

    + +
    + llvm.dbg.region.start +
    -

    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 source files, and program objects. These abstract objects are -used by the debugger to form stack traces, show information about local -variables, etc.

    +
    +
    +  void %llvm.dbg.region.start()
+
    -

    This section of the documentation first describes the representation aspects -common to any source-language. The next section -describes the data layout conventions used by the C and C++ front-ends.

    +

    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 +%llvm.dbg.region.end.

    -
    - Anchors for global objects +
    + llvm.dbg.region.end
    -

    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" globals of -type "{}", with designated names. These anchor objects obviously do -not contain any content or meaning by themselves, but all of the global objects -of a particular type (e.g., source file descriptors) contain a pointer to the -anchor. This pointer allows the debugger to use def-use chains to find all -global objects of that type.

    +
    +  void %llvm.dbg.region.end()
+
    -

    So far, the following names are recognized as anchors by the LLVM -debugger:

    +

    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 %llvm.dbg.region.start or %llvm.dbg.func.start.

    +
    + + +
    + llvm.dbg.declare +
    + +
    -  %llvm.dbg.translation_units = linkonce global {} {}
-  %llvm.dbg.globals         = linkonce global {} {}
+  void %llvm.dbg.declare( {} *, ... )
    -

    Using anchors in this way (where the source file descriptor points to the -anchors, as opposed to having a list of source file 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.

    +

    This intrinsic provides information about a local element (ex. variable.) +TODO - details.

    - + Representing stopping points in the source program
    @@ -706,13 +718,14 @@ deleted.

    LLVM debugger "stop points" are a key part of the debugging representation that allows the LLVM to maintain simple semantics for debugging optimized code. The basic idea is that the -front-end inserts calls to the %llvm.dbg.stoppoint intrinsic function -at every point in the program where the debugger should be able to inspect the -program (these correspond to places the debugger stops when you "step" -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.

    +front-end inserts calls to the %llvm.dbg.stoppoint intrinsic +function at every point in the program where the debugger should be able to +inspect the program (these correspond to places the debugger stops when you +"step" 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.

    Using calls to this intrinsic function to demark legal points for the debugger to inspect the program automatically disables any optimizations that @@ -724,12 +737,6 @@ such as code motion of non-trapping instructions, nor does it impact optimization of subexpressions, code duplication transformations, or basic-block reordering transformations.

    -

    An important aspect of the calls to the %llvm.dbg.stoppoint -intrinsic is that the function-local debugging information is woven together -with use-def chains. This makes it easy for the debugger to, for example, -locate the 'next' stop point. For a concrete example of stop points, see the -example in the next section.

    -
    @@ -764,54 +771,67 @@ lifetime expires. Consider the following C fragment, for example:

    9. } -

    Compiled to LLVM, this function would be represented like this (FIXME: CHECK -AND UPDATE THIS):

    +

    Compiled to LLVM, this function would be represented like this:

     void %foo() {
+entry:
     %X = alloca int
     %Y = alloca int
     %Z = alloca int
-    %D1 = call {}* %llvm.dbg.func.start(%lldb.global* %d.foo)
-    %D2 = call {}* %llvm.dbg.stoppoint({}* %D1, uint 2, uint 2, %lldb.compile_unit* %file)
-
-    %D3 = call {}* %llvm.dbg.DEFINEVARIABLE({}* %D2, ...)
+    
+    ...
+    
+    call void %llvm.dbg.func.start( %llvm.dbg.subprogram.type* %llvm.dbg.subprogram )
+    
+    call void %llvm.dbg.stoppoint( uint 2, uint 2, %llvm.dbg.compile_unit* %llvm.dbg.compile_unit )
+    
+    call void %llvm.dbg.declare({}* %X, ...)
+    call void %llvm.dbg.declare({}* %Y, ...)
+    
     ;; Evaluate expression on line 2, assigning to X.
-    %D4 = call {}* %llvm.dbg.stoppoint({}* %D3, uint 3, uint 2, %lldb.compile_unit* %file)
-
-    %D5 = call {}* %llvm.dbg.DEFINEVARIABLE({}* %D4, ...)
+    
+    call void %llvm.dbg.stoppoint( uint 3, uint 2, %llvm.dbg.compile_unit* %llvm.dbg.compile_unit )
+    
     ;; Evaluate expression on line 3, assigning to Y.
-    %D6 = call {}* %llvm.dbg.stoppoint({}* %D5, uint 5, uint 4, %lldb.compile_unit* %file)
-
-    %D7 = call {}* %llvm.region.start({}* %D6)
-    %D8 = call {}* %llvm.dbg.DEFINEVARIABLE({}* %D7, ...)
+    
+    call void %llvm.region.start()
+    call void %llvm.dbg.stoppoint( uint 5, uint 4, %llvm.dbg.compile_unit* %llvm.dbg.compile_unit )
+    call void %llvm.dbg.declare({}* %X, ...)
+    
     ;; Evaluate expression on line 5, assigning to Z.
-    %D9 = call {}* %llvm.dbg.stoppoint({}* %D8, uint 6, uint 4, %lldb.compile_unit* %file)
-
-    ;; Code for line 6.
-    %D10 = call {}* %llvm.region.end({}* %D9)
-    %D11 = call {}* %llvm.dbg.stoppoint({}* %D10, uint 8, uint 2, %lldb.compile_unit* %file)
-
-    ;; Code for line 8.
-    %D12 = call {}* %llvm.region.end({}* %D11)
+    
+    call void %llvm.dbg.stoppoint( uint 7, uint 2, %llvm.dbg.compile_unit* %llvm.dbg.compile_unit )
+    call void %llvm.region.end()
+    
+    call void %llvm.dbg.stoppoint( uint 9, uint 2, %llvm.dbg.compile_unit* %llvm.dbg.compile_unit )
+    
+    call void %llvm.region.end()
+    
     ret void
 }

    This example illustrates a few important details about the LLVM debugging -information. In particular, it shows how the various intrinsics used are woven -together with def-use and use-def chains, similar to how anchors are used with globals. This allows -the debugger to analyze the relationship between statements, variable -definitions, and the code used to implement the function.

    - -

    In this example, two explicit regions are defined, one with the definition of the %D1 variable and one with the -definition of %D7. In the case of -%D1, the debug information indicates that the function whose descriptor is specified as an argument to the -intrinsic. This defines a new stack frame whose lifetime ends when the region -is ended by the %D12 call.

    +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.

    + +

    The first intrinsic %llvm.dbg.func.start provides +a link with the subprogram descriptor +containing the details of this function. This call also defines the beginning +of the function region, bounded by the %llvm.region.end 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.

    + +

    It is possible to define inner regions for short term variables by using the +%llvm.region.start and %llvm.region.end to bound a +region. The inner region in this example would be for the block containing the +declaration of Z.

    Using regions to represent the boundaries of source-level functions allow LLVM interprocedural optimizations to arbitrarily modify LLVM functions without @@ -824,280 +844,790 @@ its caller that it will not be possible for the user to manually invoke the inlined function from the debugger).

    Once the function has been defined, the stopping point corresponding to line #2 of -the function is encountered. At this point in the function, no local -variables are live. As lines 2 and 3 of the example are executed, their -variable definitions are automatically introduced into the program, without the +href="#format_common_stoppoint">stopping point corresponding to +line #2 (column #2) of the function is encountered. At this point in the +function, no local variables are live. As lines 2 and 3 of the example +are executed, their variable definitions are introduced into the program using +%llvm.dbg.declare, 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.

    In contrast, the Z variable goes out of scope at a different time, -on line 7. For this reason, it is defined within the -%D7 region, which kills the availability of Z 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).

    +on line 7. For this reason, it is defined within the inner region, which kills +the availability of Z 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).

    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 the llvm-db C++ -support routines could use this to change how name lookup is performed (though -this is not implemented yet).

    +C++ using declaration is controlled with this couldchange how name lookup is +performed.

    + +
    + + + + +
    + C/C++ front-end specific debug information +
    + + +
    + +

    The C and C++ front-ends represent information about the program in a format +that is effectively identical to Dwarf 3.0 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.

    + +

    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.

    + +

    The following sections provide examples of various C/C++ constructs and the +debug information that would best describe those constructs.

    - Object descriptor formats + C/C++ source file information
    -

    The LLVM debugger expects 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 allows to define its own objects, by -using unreserved tag numbers.

    -

    The lowest-level descriptor are those describing the files containing the program source -code, as most other descriptors (sometimes indirectly) refer to them. -

    +

    Given the source files "MySource.cpp" and "MyHeader.h" located in the +directory "/Users/mine/sources", the following code;

    + +
    +#include "MyHeader.h"
+
+int main(int argc, char *argv[]) {
+  return 0;
+}
+
    + +

    a C/C++ front-end would generate the following descriptors;

    + +
    +...
+;;
+;; Define types used.  In this case we need one for compile unit anchors and one
+;; for compile units.
+;;
+%llvm.dbg.anchor.type = type { uint, uint }
+%llvm.dbg.compile_unit.type = 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.)
+;;
+%llvm.dbg.compile_units = linkonce constant %llvm.dbg.anchor.type { uint 0, uint 17 }, section "llvm.metadata"
+
+;;
+;; Define the compile unit for the source file "/Users/mine/sources/MySource.cpp".
+;;
+%llvm.dbg.compile_unit1 = internal constant %llvm.dbg.compile_unit.type {
+    uint 17, 
+    {  }* cast (%llvm.dbg.anchor.type* %llvm.dbg.compile_units 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".
+;;
+%llvm.dbg.compile_unit2 = internal constant %llvm.dbg.compile_unit.type {
+    uint 17, 
+    {  }* cast (%llvm.dbg.anchor.type* %llvm.dbg.compile_units 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";
+...
+
    + +
    + + +
    + C/C++ global variable information
    +
    + +

    Given an integer global variable declared as follows;

    + +
    +int MyGlobal = 100;
+
    + +

    a C/C++ front-end would generate the following descriptors;

    + +
    +;;
+;; 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.
+;;
+%llvm.dbg.anchor.type = type { uint, uint }
+%llvm.dbg.global_variable.type = type { uint, {  }*, {  }*, sbyte*, {  }*, bool, bool, {  }*, uint }
+%llvm.dbg.basictype.type = type { uint, {  }*, sbyte*, {  }*, int, uint, uint, uint, uint }
+%llvm.dbg.compile_unit.type = ...
+...
+;;
+;; 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.)
+;;
+%llvm.dbg.global_variables = linkonce constant %llvm.dbg.anchor.type { 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.
+;;
+%llvm.dbg.global_variable = internal constant %llvm.dbg.global_variable.type {
+    uint 52, 
+    {  }* cast (%llvm.dbg.anchor.type* %llvm.dbg.global_variables to {  }*), 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    sbyte* getelementptr ([9 x sbyte]* %str1, int 0, int 0), 
+    {  }* cast (%llvm.dbg.basictype.type* %llvm.dbg.basictype to {  }*), 
+    bool false, 
+    bool true, 
+    {  }* cast (int* %MyGlobal to {  }*), 
+    uint 1 }, 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.
+;;    
+%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
+
+;;
+;; 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 [4 x sbyte] c"int\00", section "llvm.metadata"
+
    - +
    + C/C++ function information
    -

    -Source file descriptors are patterned after the Dwarf "compile_unit" object. -The descriptor currently is defined to have at least the following LLVM -type entries:

    + +

    Given a function declared as follows;

    -%lldb.compile_unit = type {
-       uint,                 ;; Tag: LLVM_COMPILE_UNIT
-       ushort,               ;; LLVM debug version number
-       ushort,               ;; Dwarf language identifier
-       sbyte*,               ;; Filename
-       sbyte*,               ;; Working directory when compiled
-       sbyte*                ;; Producer of the debug information
+int main(int argc, char *argv[]) {
+  return 0;
 }
    -

    -These descriptors contain the version number for the debug info, a source -language ID for the file (we use the Dwarf 3.0 ID numbers, such as -DW_LANG_C89, DW_LANG_C_plus_plus, DW_LANG_Cobol74, -etc), three strings describing the filename, working directory of the compiler, -and an identifier string for the compiler that produced it. Note that actual -compile_unit declarations must also include an anchor to llvm.dbg.translation_units, -but it is not specified where the anchor is to be located. Here is an example -descriptor: -

    - -

    -%arraytest_source_file = internal constant %lldb.compile_unit {
-    uint 17,                                                      ; Tag value
-    ushort 0,                                                     ; Version #0
-    ushort 1,                                                     ; DW_LANG_C89
-    sbyte* getelementptr ([12 x sbyte]* %.str_1, long 0, long 0), ; filename
-    sbyte* getelementptr ([12 x sbyte]* %.str_2, long 0, long 0), ; working dir
-    sbyte* getelementptr ([12 x sbyte]* %.str_3, long 0, long 0), ; producer
-    {}* %llvm.dbg.translation_units                               ; Anchor
+
    a C/C++ front-end would generate the following descriptors;
    
+
+
    +;;
+;; 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.
+;;
+%llvm.dbg.subprogram.type = type { uint, {  }*, {  }*, sbyte*, {  }*, bool, bool }
+%llvm.dbg.anchor.type = type { uint, uint }
+%llvm.dbg.compile_unit.type = ...
+	
+;;
+;; 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.)
+;;
+%llvm.dbg.subprograms = linkonce constant %llvm.dbg.anchor.type { uint 0, uint 46 }, section "llvm.metadata"
+
+;;
+;; Define the descriptor for the subprogram.  TODO - more details.
+;;
+%llvm.dbg.subprogram = internal constant %llvm.dbg.subprogram.type {
+    uint 46, 
+    {  }* cast (%llvm.dbg.anchor.type* %llvm.dbg.subprograms to {  }*), 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    sbyte* getelementptr ([5 x sbyte]* %str1, int 0, int 0), 
+    {  }* 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"
+
+;;
+;; Define the subprogram itself.
+;;
+int %main(int %argc, sbyte** %argv) {
+...
 }
-%.str_1 = internal constant [12 x sbyte] c"arraytest.c\00"
-%.str_2 = internal constant [12 x sbyte] c"/home/sabre\00"
-%.str_3 = internal constant [12 x sbyte] c"llvmgcc 3.4\00"
-
    
+
    -

    -Note that the LLVM constant merging pass should eliminate duplicate copies of -the strings that get emitted to each translation unit, such as the producer. -

    +
    + +
    + C/C++ basic types
    +
    + +

    The following are the basic type descriptors for C/C++ core types;

    + +
    - +
    - Representation of program objects + bool
    -

    -The LLVM debugger needs to know about some source-language program objects, in -order to build stack traces, print information about local variables, and other -related activities. The LLVM debugger differentiates between three different -types of program objects: subprograms (functions, messages, methods, etc), -variables (locals and globals), and others. Because source-languages have -widely varying forms of these objects, the LLVM debugger expects only a few -fields in the descriptor for each object: -

    -%lldb.object = type {
-       uint,                  ;; A tag
-       any*,                  ;; The context for the object
-       sbyte*                 ;; The object 'name'
-}
+%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
    -

    The first field contains a tag for the descriptor. The second field contains -either a pointer to the descriptor for the containing source file, or it contains a pointer to -another program object whose context pointer eventually reaches a source file. -Through this context pointer, the -LLVM debugger can establish the debug version number of the object.

    - -

    The third field contains a string that the debugger can use to identify the -object if it does not contain explicit support for the source-language in use -(ie, the 'unknown' source language handler uses this string). This should be -some sort of unmangled string that corresponds to the object, but it is a -quality of implementation issue what exactly it contains (it is legal, though -not useful, for all of these strings to be null).

    +
    -

    Note again that descriptors can be extended to include -source-language-specific information in addition to the fields required by the -LLVM debugger. See the section on the C/C++ -front-end for more information. Also remember that global objects -(functions, selectors, global variables, etc) must contain an anchor to the llvm.dbg.globals -variable.

    + +
    + char
    +
    + +
    +%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
+
    + +
    -
    - Program object contexts +
    + unsigned char
    + 
    -Allow source-language specific contexts, use to identify namespaces etc
-Must end up in a source file descriptor.
-Debugger core ignores all unknown context objects.
+%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
    +
    -
    - Debugger intrinsic functions +
    + short
    -
    -Define each intrinsics, as an extension of the language reference manual.
 
-llvm.dbg.stoppoint
-llvm.dbg.region.start
-llvm.dbg.region.end
-llvm.dbg.function.start
-llvm.dbg.declare
+
    +%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
 
    
+
    -
    - Values for debugger tags +
    + unsigned short
    -

    Happen to be the same value as the similarly named Dwarf-3 tags, this may -change in the future.

    - 
    -  LLVM_COMPILE_UNIT     : 17
-  LLVM_SUBPROGRAM       : 46
-  LLVM_VARIABLE         : 52
-
+%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
    +
    + +
    + int +
    +
    + +
    +%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
+
    - -
    - C/C++ front-end specific debug information
    - + + +
    + unsigned int +
    -

    The C and C++ front-ends represent information about the program in a format -that is effectively identical to Dwarf 3.0 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.

    +
    +%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
+
    -

    The basic debug information required by the debugger is (intentionally) -designed to be as minimal as possible. This basic information is so minimal -that it is unlikely that any source-language could be adequately -described by it. Because of this, the debugger format was designed for -extension to support source-language-specific information. The extended -descriptors are read and interpreted by the language-specific modules in the debugger if there is -support available, otherwise it is ignored.

    - -

    This section describes the extensions 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 extensions 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.

    +
    + + +
    + long long +
    + +
    + +
    +%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
+
    -
    - Program Scope Entries +
    + unsigned long long
    -

    TODO

    + +
    +%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
+
    +
    - +
    - Compilation unit entries + float
    -

    -Translation units do not add any information over the standard source file representation already -expected by the debugger. As such, it uses descriptors of the type specified, -with a trailing anchor. -

    + +
    +%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
+
    +
    - +
    - Module, namespace, and importing entries + double +
    + +
    + +
    +%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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"
+
    + +
    + + +
    + C/C++ derived types
    -

    TODO

    + +

    Given the following as an example of C/C++ derived type;

    + +
    +typedef const int *IntPtr;
+
    + +

    a C/C++ front-end would generate the following descriptors;

    + +
    +;;
+;; Define the typedef "IntPtr".
+;;
+%llvm.dbg.derivedtype1 = internal constant %llvm.dbg.derivedtype.type {
+    uint 22, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    sbyte* getelementptr ([7 x sbyte]* %str1, int 0, int 0), 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    int 1, 
+    uint 0, 
+    uint 0, 
+    uint 0, 
+    {  }* cast (%llvm.dbg.derivedtype.type* %llvm.dbg.derivedtype2 to {  }*) }, section "llvm.metadata"
+%str1 = internal constant [7 x sbyte] c"IntPtr\00", section "llvm.metadata"
+
+;;
+;; Define the pointer type.
+;;
+%llvm.dbg.derivedtype2 = internal constant %llvm.dbg.derivedtype.type {
+    uint 15, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    sbyte* getelementptr ([1 x sbyte]* %str2, int 0, int 0), 
+    {  }* null, 
+    int 0, 
+    uint 32, 
+    uint 32, 
+    uint 0, 
+    {  }* cast (%llvm.dbg.derivedtype.type* %llvm.dbg.derivedtype3 to {  }*) }, section "llvm.metadata"
+%str2 = internal constant [1 x sbyte] zeroinitializer, section "llvm.metadata"
+
+;;
+;; Define the const type.
+;;
+%llvm.dbg.derivedtype3 = internal constant %llvm.dbg.derivedtype.type {
+    uint 38, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    sbyte* getelementptr ([1 x sbyte]* %str2, int 0, int 0), 
+    {  }* null, 
+    int 0, 
+    uint 0, 
+    uint 0, 
+    uint 0, 
+    {  }* cast (%llvm.dbg.basictype.type* %llvm.dbg.basictype1 to {  }*) }, section "llvm.metadata"	
+
+;;
+;; Define the int type.
+;;
+%llvm.dbg.basictype1 = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    sbyte* getelementptr ([4 x sbyte]* %str4, int 0, int 0), 
+    {  }* null, 
+    int 0, 
+    uint 32, 
+    uint 32, 
+    uint 0, 
+    uint 5 }, section "llvm.metadata"
+%str4 = internal constant [4 x sbyte] c"int\00", section "llvm.metadata"
+
    +
    - Data objects (program variables) + C/C++ struct/union types
    -

    TODO

    + +

    Given the following as an example of C/C++ struct type;

    + +
    +struct Color {
+  unsigned Red;
+  unsigned Green;
+  unsigned Blue;
+};
+
    + +

    a C/C++ front-end would generate the following descriptors;

    + +
    +;;
+;; Define basic type for unsigned int.
+;;
+%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type {
+    uint 36, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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.
+;;
+%llvm.dbg.compositetype = internal constant %llvm.dbg.compositetype.type {
+    uint 19, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    sbyte* getelementptr ([6 x sbyte]* %str2, int 0, int 0), 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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.
+;;
+%llvm.dbg.derivedtype1 = internal constant %llvm.dbg.derivedtype.type {
+    uint 13, 
+    {  }* null, 
+    sbyte* getelementptr ([4 x sbyte]* %str3, int 0, int 0), 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    int 2, 
+    uint 32, 
+    uint 32, 
+    uint 0, 
+    {  }* cast (%llvm.dbg.basictype.type* %llvm.dbg.basictype to {  }*) }, section "llvm.metadata"
+%str3 = internal constant [4 x sbyte] c"Red\00", section "llvm.metadata"
+
+;;
+;; Define the Green field.
+;;
+%llvm.dbg.derivedtype2 = internal constant %llvm.dbg.derivedtype.type {
+    uint 13, 
+    {  }* null, 
+    sbyte* getelementptr ([6 x sbyte]* %str4, int 0, int 0), 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    int 3, 
+    uint 32, 
+    uint 32, 
+    uint 32, 
+    {  }* cast (%llvm.dbg.basictype.type* %llvm.dbg.basictype to {  }*) }, section "llvm.metadata"
+%str4 = internal constant [6 x sbyte] c"Green\00", section "llvm.metadata"
+
+;;
+;; Define the Blue field.
+;;
+%llvm.dbg.derivedtype3 = internal constant %llvm.dbg.derivedtype.type {
+    uint 13, 
+    {  }* null, 
+    sbyte* getelementptr ([5 x sbyte]* %str5, int 0, int 0), 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    int 4, 
+    uint 32, 
+    uint 32, 
+    uint 64, 
+    {  }* cast (%llvm.dbg.basictype.type* %llvm.dbg.basictype 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 (%llvm.dbg.derivedtype.type* %llvm.dbg.derivedtype1 to {  }*),
+      {  }* cast (%llvm.dbg.derivedtype.type* %llvm.dbg.derivedtype2 to {  }*),
+      {  }* cast (%llvm.dbg.derivedtype.type* %llvm.dbg.derivedtype3 to {  }*) ], section "llvm.metadata"
+
    + +
    + + +
    + C/C++ enumeration types
    +
    + +

    Given the following as an example of C/C++ enumeration type;

    + +
    +enum Trees {
+  Spruce = 100,
+  Oak = 200,
+  Maple = 300
+};
+
    + +

    a C/C++ front-end would generate the following descriptors;

    + +
    +;;
+;; Define composite type for enum Trees
+;;
+%llvm.dbg.compositetype = internal constant %llvm.dbg.compositetype.type {
+    uint 4, 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to {  }*), 
+    sbyte* getelementptr ([6 x sbyte]* %str1, int 0, int 0), 
+    {  }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit 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.
+;;
+%llvm.dbg.enumerator1 = internal constant %llvm.dbg.enumerator.type {
+    uint 40, 
+    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.
+;;
+%llvm.dbg.enumerator2 = internal constant %llvm.dbg.enumerator.type {
+    uint 40, 
+    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.
+;;
+%llvm.dbg.enumerator3 = internal constant %llvm.dbg.enumerator.type {
+    uint 40, 
+    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 (%llvm.dbg.enumerator.type* %llvm.dbg.enumerator1 to {  }*),
+  {  }* cast (%llvm.dbg.enumerator.type* %llvm.dbg.enumerator2 to {  }*),
+  {  }* cast (%llvm.dbg.enumerator.type* %llvm.dbg.enumerator3 to {  }*) ], section "llvm.metadata"
+
    + +
    -- cgit v1.2.3