X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=docs%2FSourceLevelDebugging.html;h=2bbe18118e122bd8825b7b558beeedb58b6c70b2;hb=4de8ba8940171f442d09e84cd597bf8bd45a8701;hp=fab63046a484414672b10315527ce3707ef08d74;hpb=8ad2f9873939b1815bd4f788969ca210df42a8d4;p=oota-llvm.git diff --git a/docs/SourceLevelDebugging.html b/docs/SourceLevelDebugging.html index fab63046a48..2bbe18118e1 100644 --- a/docs/SourceLevelDebugging.html +++ b/docs/SourceLevelDebugging.html @@ -25,6 +25,7 @@
The approach used by the LLVM implementation is to use a small set of intrinsic functions to define a mapping between LLVM program objects and the source-level objects. The - description of the source-level program is maintained in LLVM global - variables in an implementation-defined format + description of the source-level program is maintained in LLVM metadata + in an implementation-defined format (the C/C++ front-end currently uses working draft 7 of the DWARF 3 standard).
@@ -147,7 +144,7 @@ height="369"> an LLVM user a relationship between generated code and the original program source code. -Currently, debug information is consumed by the DwarfWriter to produce dwarf +
Currently, debug information is consumed by DwarfDebug to produce dwarf information used by the gdb debugger. Other targets could use the same information to produce stabs or other debug forms.
@@ -240,36 +237,26 @@ height="369">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.
+ particular, the use of metadata avoids duplicated debugging information from + the beginning, and the global dead code elimination pass automatically + deletes debugging information for a function if it decides to delete the + function.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.
+ front-end in the form of LLVM metadata.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.
+ generic 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.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, + exist are source files, and program objects. These abstract objects are used by a debugger to form stack traces, show information about local variables, etc.
@@ -288,9 +275,7 @@ height="369">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.
+ provides a specification for well formed debug descriptors.Consumers of LLVM debug information expect the descriptors for program objects to start in a canonical format, but the descriptors can include @@ -300,34 +285,30 @@ height="369"> way. Also, all debugging information objects start with a tag to indicate what type of object it is. The source-language is allowed to define its own objects, by using unreserved tag numbers. We recommend using with tags in - the range 0x1000 thru 0x2000 (there is a defined enum DW_TAG_user_base = + the range 0x1000 through 0x2000 (there is a defined enum DW_TAG_user_base = 0x1000.)
-The fields of debug descriptors used internally by LLVM (MachineModuleInfo) - are restricted to only the simple data types int, uint, - bool, float, double, i8* 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.
+The fields of debug descriptors used internally by LLVM + are restricted to only the simple data types i32, i1, + float, double, mdstring and mdnode.
-%llvm.dbg.object.type = type { - uint, ;; A tag +!1 = metadata !{ + i32, ;; A tag ... }
The details of the various descriptors follow.
@@ -342,17 +323,18 @@ height="369">-%llvm.dbg.compile_unit.type = type { - i32, ;; Tag = 17 + LLVMDebugVersion (DW_TAG_compile_unit) - { }*, ;; Compile unit anchor = cast = (%llvm.dbg.anchor.type* %llvm.dbg.compile_units to { }*) - i32, ;; DWARF language identifier (ex. DW_LANG_C89) - i8*, ;; Source file name - i8*, ;; Source file directory (includes trailing slash) - i8* ;; Producer (ex. "4.0.1 LLVM (LLVM research group)") - i1, ;; True if this is a main compile unit. - i1, ;; True if this is optimized. - i8*, ;; Flags - i32 ;; Runtime version +!0 = metadata !{ + i32, ;; Tag = 17 + LLVMDebugVersion + ;; (DW_TAG_compile_unit) + i32, ;; Unused field. + i32, ;; DWARF language identifier (ex. DW_LANG_C89) + metadata, ;; Source file name + metadata, ;; Source file directory (includes trailing slash) + metadata ;; Producer (ex. "4.0.1 LLVM (LLVM research group)") + i1, ;; True if this is a main compile unit. + i1, ;; True if this is optimized. + metadata, ;; Flags + i32 ;; Runtime version }
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.
+ specific compilation unit. File descriptors are defined using this context. -Each input file is encoded as a separate compile unit in LLVM debugging - information output. However, many target specific tool chains prefer to - encode only one compile unit in an object file. In this situation, the LLVM - code generator will include debugging information entities in the compile - unit that is marked as main compile unit. The code generator accepts maximum - one main compile unit per module. If a module does not contain any main - compile unit then the code generator will emit multiple compile units in the - output object file.
++!0 = metadata !{ + i32, ;; Tag = 41 + LLVMDebugVersion + ;; (DW_TAG_file_type) + metadata, ;; Source file name + metadata, ;; Source file directory (includes trailing slash) + metadata ;; Reference to compile unit where defined +} ++
These descriptors contain information for a file. Global variables and top + level functions would be defined using this context.k File descriptors also + provide context for source line correspondence.
+ +Each input file is encoded as a separate file descriptor in LLVM debugging + information output. Each file descriptor would be defined using a + compile unit.
-%llvm.dbg.global_variable.type = type { - i32, ;; Tag = 52 + LLVMDebugVersion (DW_TAG_variable) - { }*, ;; Global variable anchor = cast (%llvm.dbg.anchor.type* %llvm.dbg.global_variables to { }*), - { }*, ;; Reference to context descriptor - i8*, ;; Name - i8*, ;; Display name (fully qualified C++ name) - i8*, ;; MIPS linkage name (for C++) - { }*, ;; Reference to compile unit where defined - i32, ;; Line number where defined - { }*, ;; Reference to type descriptor - i1, ;; True if the global is local to compile unit (static) - i1, ;; True if the global is defined in the compile unit (not extern) - { }* ;; Reference to the global variable +!1 = metadata !{ + i32, ;; Tag = 52 + LLVMDebugVersion + ;; (DW_TAG_variable) + i32, ;; Unused field. + metadata, ;; Reference to context descriptor + metadata, ;; Name + metadata, ;; Display name (fully qualified C++ name) + metadata, ;; MIPS linkage name (for C++) + metadata, ;; Reference to file where defined + i32, ;; Line number where defined + metadata, ;; Reference to type descriptor + i1, ;; True if the global is local to compile unit (static) + i1, ;; True if the global is defined in the compile unit (not extern) + {}* ;; Reference to the global variable }
-%llvm.dbg.subprogram.type = type { - i32, ;; Tag = 46 + LLVMDebugVersion (DW_TAG_subprogram) - { }*, ;; Subprogram anchor = cast (%llvm.dbg.anchor.type* %llvm.dbg.subprograms to { }*), - { }*, ;; Reference to context descriptor - i8*, ;; Name - i8*, ;; Display name (fully qualified C++ name) - i8*, ;; MIPS linkage name (for C++) - { }*, ;; Reference to compile unit where defined - i32, ;; Line number where defined - { }*, ;; Reference to type descriptor - i1, ;; True if the global is local to compile unit (static) - i1 ;; True if the global is defined in the compile unit (not extern) +!2 = metadata !{ + i32, ;; Tag = 46 + LLVMDebugVersion + ;; (DW_TAG_subprogram) + i32, ;; Unused field. + metadata, ;; Reference to context descriptor + metadata, ;; Name + metadata, ;; Display name (fully qualified C++ name) + metadata, ;; MIPS linkage name (for C++) + metadata, ;; Reference to file where defined + i32, ;; Line number where defined + metadata, ;; Reference to type descriptor + i1, ;; True if the global is local to compile unit (static) + i1 ;; True if the global is defined in the compile unit (not extern) + i32 ;; Virtuality, e.g. dwarf::DW_VIRTUALITY__virtual + i32 ;; Index into a virtual function + metadata, ;; indicates which base type contains the vtable pointer for the + ;; derived class + i1 ;; isArtificial + i1 ;; isOptimized + Function *;; Pointer to LLVM function }
-%llvm.dbg.block = type { - i32, ;; Tag = 13 + LLVMDebugVersion (DW_TAG_lexical_block) - { }* ;; Reference to context descriptor +!3 = metadata !{ + i32, ;; Tag = 13 + LLVMDebugVersion (DW_TAG_lexical_block) + metadata ;; Reference to context descriptor }
-%llvm.dbg.basictype.type = type { - i32, ;; Tag = 36 + LLVMDebugVersion (DW_TAG_base_type) - { }*, ;; Reference to context (typically a compile unit) - i8*, ;; Name (may be "" for anonymous types) - { }*, ;; Reference to compile unit where defined (may be NULL) - i32, ;; Line number where defined (may be 0) - i64, ;; Size in bits - i64, ;; Alignment in bits - i64, ;; Offset in bits - i32, ;; Flags - i32 ;; DWARF type encoding +!4 = metadata !{ + i32, ;; Tag = 36 + LLVMDebugVersion + ;; (DW_TAG_base_type) + metadata, ;; Reference to context (typically a compile unit) + metadata, ;; Name (may be "" for anonymous types) + metadata, ;; Reference to file where defined (may be NULL) + i32, ;; Line number where defined (may be 0) + i64, ;; Size in bits + i64, ;; Alignment in bits + i64, ;; Offset in bits + i32, ;; Flags + i32 ;; DWARF type encoding }
-%llvm.dbg.derivedtype.type = type { - i32, ;; Tag (see below) - { }*, ;; Reference to context - i8*, ;; Name (may be "" for anonymous types) - { }*, ;; Reference to compile unit where defined (may be NULL) - i32, ;; Line number where defined (may be 0) - i32, ;; Size in bits - i32, ;; Alignment in bits - i32, ;; Offset in bits - { }* ;; Reference to type derived from +!5 = metadata !{ + i32, ;; Tag (see below) + metadata, ;; Reference to context + metadata, ;; Name (may be "" for anonymous types) + metadata, ;; Reference to file where defined (may be NULL) + i32, ;; Line number where defined (may be 0) + i32, ;; Size in bits + i32, ;; Alignment in bits + i32, ;; Offset in bits + metadata ;; Reference to type derived from }
-%llvm.dbg.compositetype.type = type { - i32, ;; Tag (see below) - { }*, ;; Reference to context - i8*, ;; Name (may be "" for anonymous types) - { }*, ;; Reference to compile unit where defined (may be NULL) - i32, ;; Line number where defined (may be 0) - i64, ;; Size in bits - i64, ;; Alignment in bits - i64, ;; Offset in bits - i32, ;; Flags - { }*, ;; Reference to type derived from - { }*, ;; Reference to array of member descriptors - i32 ;; Runtime languages +!6 = metadata !{ + i32, ;; Tag (see below) + metadata, ;; Reference to context + metadata, ;; Name (may be "" for anonymous types) + metadata, ;; Reference to file where defined (may be NULL) + i32, ;; Line number where defined (may be 0) + i64, ;; Size in bits + i64, ;; Alignment in bits + i64, ;; Offset in bits + i32, ;; Flags + metadata, ;; Reference to type derived from + metadata, ;; Reference to array of member descriptors + i32 ;; Runtime languages }
-%llvm.dbg.enumerator.type = type { - i32, ;; Tag = 40 + LLVMDebugVersion (DW_TAG_enumerator) - i8*, ;; Name - i64 ;; Value +!6 = metadata !{ + i32, ;; Tag = 40 + LLVMDebugVersion + ;; (DW_TAG_enumerator) + metadata, ;; Name + i64 ;; Value }
-%llvm.dbg.variable.type = type { - i32, ;; Tag (see below) - { }*, ;; Context - i8*, ;; Name - { }*, ;; Reference to compile unit where defined - i32, ;; Line number where defined - { }* ;; Type descriptor +!7 = metadata !{ + i32, ;; Tag (see below) + metadata, ;; Context + metadata, ;; Name + metadata, ;; Reference to file where defined + i32, ;; Line number where defined + metadata ;; Type descriptor }
- void %llvm.dbg.stoppoint( uint, uint, { }* ) + void %llvm.dbg.declare({}*, metadata)-
This intrinsic is used to provide correspondence between the source file and - the generated code. The first argument is the line number (base 1), second - argument is the column number (0 if unknown) and the third argument the - source %llvm.dbg.compile_unit* - cast to a { }*. 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.
+This intrinsic provides information about a local element (ex. variable.) The + first argument is the alloca for the variable, cast to a {}*. The + second argument is + the %llvm.dbg.variable containing + the description of the variable.
- void %llvm.dbg.func.start( { }* ) + void %llvm.dbg.value(metadata, i64, metadata)-
This intrinsic is used to link the debug information - in %llvm.dbg.subprogram to the - function. It defines the beginning of the function's declarative region - (scope). It also implies a call to - %llvm.dbg.stoppoint which - defines a source line "stop point". The intrinsic should be called early in - the function after the all the alloca instructions. It should be paired off - with a closing - %llvm.dbg.region.end. - The function's single argument is - the %llvm.dbg.subprogram.type.
+This intrinsic provides information when a user source variable is set to a + new value. The first argument is the new value (wrapped as metadata). The + second argument is the offset in the user source variable where the new value + is written. The third argument is + the %llvm.dbg.variable containing + the description of the user source variable.
In many languages, the local variables in functions can have their lifetimes + or scopes limited to a subset of a function. In the C family of languages, + for example, variables are only live (readable and writable) within the + source block that they are defined in. In functional languages, values are + only readable after they have been defined. Though this is a very obvious + concept, it is non-trivial to model in LLVM, because it has no notion of + scoping in this sense, and does not want to be tied to a language's scoping + rules.
+ +In order to handle this, the LLVM debug format uses the metadata attached to + llvm instructions to encode line number and scoping information. Consider + the following C fragment, for example:
+ +- void %llvm.dbg.region.start( { }* ) +1. void foo() { +2. int X = 21; +3. int Y = 22; +4. { +5. int Z = 23; +6. Z = X; +7. } +8. X = Y; +9. }+
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. The - function's single argument is - the %llvm.dbg.block which is - starting.
+Compiled to LLVM, this function would be represented like this:
++define void @foo() nounwind ssp { +entry: + %X = alloca i32, align 4 ; <i32*> [#uses=4] + %Y = alloca i32, align 4 ; <i32*> [#uses=4] + %Z = alloca i32, align 4 ; <i32*> [#uses=3] + %0 = bitcast i32* %X to {}* ; <{}*> [#uses=1] + call void @llvm.dbg.declare({}* %0, metadata !0), !dbg !7 + store i32 21, i32* %X, !dbg !8 + %1 = bitcast i32* %Y to {}* ; <{}*> [#uses=1] + call void @llvm.dbg.declare({}* %1, metadata !9), !dbg !10 + store i32 22, i32* %Y, !dbg !11 + %2 = bitcast i32* %Z to {}* ; <{}*> [#uses=1] + call void @llvm.dbg.declare({}* %2, metadata !12), !dbg !14 + store i32 23, i32* %Z, !dbg !15 + %tmp = load i32* %X, !dbg !16 ; <i32> [#uses=1] + %tmp1 = load i32* %Y, !dbg !16 ; <i32> [#uses=1] + %add = add nsw i32 %tmp, %tmp1, !dbg !16 ; <i32> [#uses=1] + store i32 %add, i32* %Z, !dbg !16 + %tmp2 = load i32* %Y, !dbg !17 ; <i32> [#uses=1] + store i32 %tmp2, i32* %X, !dbg !17 + ret void, !dbg !18 +} +declare void @llvm.dbg.declare({}*, metadata) nounwind readnone + +!0 = metadata !{i32 459008, metadata !1, metadata !"X", + metadata !3, i32 2, metadata !6}; [ DW_TAG_auto_variable ] +!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ] +!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", metadata !"foo", + metadata !"foo", metadata !3, i32 1, metadata !4, + i1 false, i1 true}; [DW_TAG_subprogram ] +!3 = metadata !{i32 458769, i32 0, i32 12, metadata !"foo.c", + metadata !"/private/tmp", metadata !"clang 1.1", i1 true, + i1 false, metadata !"", i32 0}; [DW_TAG_compile_unit ] +!4 = metadata !{i32 458773, metadata !3, metadata !"", null, i32 0, i64 0, i64 0, + i64 0, i32 0, null, metadata !5, i32 0}; [DW_TAG_subroutine_type ] +!5 = metadata !{null} +!6 = metadata !{i32 458788, metadata !3, metadata !"int", metadata !3, i32 0, + i64 32, i64 32, i64 0, i32 0, i32 5}; [DW_TAG_base_type ] +!7 = metadata !{i32 2, i32 7, metadata !1, null} +!8 = metadata !{i32 2, i32 3, metadata !1, null} +!9 = metadata !{i32 459008, metadata !1, metadata !"Y", metadata !3, i32 3, + metadata !6}; [ DW_TAG_auto_variable ] +!10 = metadata !{i32 3, i32 7, metadata !1, null} +!11 = metadata !{i32 3, i32 3, metadata !1, null} +!12 = metadata !{i32 459008, metadata !13, metadata !"Z", metadata !3, i32 5, + metadata !6}; [ DW_TAG_auto_variable ] +!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ] +!14 = metadata !{i32 5, i32 9, metadata !13, null} +!15 = metadata !{i32 5, i32 5, metadata !13, null} +!16 = metadata !{i32 6, i32 5, metadata !13, null} +!17 = metadata !{i32 8, i32 3, metadata !1, null} +!18 = metadata !{i32 9, i32 1, metadata !2, null} +
This example illustrates a few important details about LLVM debugging + information. In particular, it shows how the llvm.dbg.declare + intrinsic and location information, which are attached to an instruction, + are applied together to allow a debugger to analyze the relationship between + statements, variable definitions, and the code used to implement the + function.
-- void %llvm.dbg.region.end( { }* ) +call void @llvm.dbg.declare({}* %0, metadata !0), !dbg !7- -
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. - The function's single argument is either - the %llvm.dbg.block or - the %llvm.dbg.subprogram.type - which is ending.
-The first intrinsic + %llvm.dbg.declare + encodes debugging information for the variable X. The metadata + !dbg !7 attached to the intrinsic provides scope information for the + variable X.
-- void %llvm.dbg.declare( { } *, { }* ) +!7 = metadata !{i32 2, i32 7, metadata !1, null} +!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ] +!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", + metadata !"foo", metadata !"foo", metadata !3, i32 1, + metadata !4, i1 false, i1 true}; [DW_TAG_subprogram ]- -
This intrinsic provides information about a local element (ex. variable.) The - first argument is the alloca for the variable, cast to a { }*. The - second argument is - the %llvm.dbg.variable containing - the description of the variable, also cast to a { }*.
-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 a debugger should be - able to inspect the program (these correspond to places a 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 - could potentially confuse debugging information. To - non-debug-information-aware transformations, these calls simply look like - calls to an external function, which they must assume to do anything - (including reading or writing to any part of reachable memory). On the other - hand, it does not impact many optimizations, such as code motion of - non-trapping instructions, nor does it impact optimization of subexpressions, - code duplication transformations, or basic-block reordering - transformations.
+Here !7 is metadata providing location information. It has four + fields: line number, column number, scope, and original scope. The original + scope represents inline location if this instruction is inlined inside a + caller, and is null otherwise. In this example, scope is encoded by + !1. !1 represents a lexical block inside the scope + !2, where !2 is a + subprogram descriptor. This way the + location information attached to the intrinsics indicates that the + variable X is declared at line number 2 at a function level scope in + function foo.
-In many languages, the local variables in functions can have their lifetime - or scope limited to a subset of a function. In the C family of languages, - for example, variables are only live (readable and writable) within the - source block that they are defined in. In functional languages, values are - only readable after they have been defined. Though this is a very obvious - concept, it is also non-trivial to model in LLVM, because it has no notion of - scoping in this sense, and does not want to be tied to a language's scoping - rules.
- -In order to handle this, the LLVM debug format uses the notion of "regions" - of a function, delineated by calls to intrinsic functions. These intrinsic - functions define new regions of the program and indicate when the region - lifetime expires. Consider the following C fragment, for example:
+Now lets take another example.
-1. void foo() { -2. int X = ...; -3. int Y = ...; -4. { -5. int Z = ...; -6. ... -7. } -8. ... -9. } +call void @llvm.dbg.declare({}* %2, metadata !12), !dbg !14
Compiled to LLVM, this function would be represented like this:
+The second intrinsic + %llvm.dbg.declare + encodes debugging information for variable Z. The metadata + !dbg !14 attached to the intrinsic provides scope information for + the variable Z.
-void %foo() { -entry: - %X = alloca int - %Y = alloca int - %Z = alloca int - - ... - - 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. - - 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. - - 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. - - 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 -} +!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ] +!14 = metadata !{i32 5, i32 9, metadata !13, null}
This example illustrates a few important details about the LLVM debugging - information. In particular, it shows how the various intrinsics are applied - together to allow a debugger to analyze the relationship between statements, - variable definitions, and the code used to implement the function.
- -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 having to worry about breaking mapping information between the LLVM - code and the and source-level program. In particular, the inliner requires - no modification to support inlining with debugging information: there is no - explicit correlation drawn between LLVM functions and their source-level - counterparts (note however, that if the inliner inlines all instances of a - non-strong-linkage function into its caller that it will not be possible for - the user to manually invoke the inlined function from a debugger).
- -Once the function has been defined, - the 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 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 could change how name - lookup is performed.
+Here !14 indicates that Z is declared at line number 5 and + column number 9 inside of lexical scope !13. The lexical scope + itself resides inside of lexical scope !1 described above.
+ +The scope information attached with each instruction provides a + straightforward way to find instructions covered by a scope.
... ;; -;; Define types used. In this case we need one for compile unit anchors and one -;; for compile units. +;; Define the compile unit for the main source file "/Users/mine/sources/MySource.cpp". ;; -%llvm.dbg.anchor.type = type { uint, uint } -%llvm.dbg.compile_unit.type = type { uint, { }*, uint, uint, i8*, i8*, i8* } -... -;; -;; 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" +!2 = metadata !{ + i32 524305, ;; Tag + i32 0, ;; Unused + i32 4, ;; Language Id + metadata !"MySource.cpp", + metadata !"/Users/mine/sources", + metadata !"4.2.1 (Based on Apple Inc. build 5649) (LLVM build 00)", + i1 true, ;; Main Compile Unit + i1 false, ;; Optimized compile unit + metadata !"", ;; Compiler flags + i32 0} ;; Runtime version ;; -;; 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 add(uint 17, uint 262144), - { }* cast (%llvm.dbg.anchor.type* %llvm.dbg.compile_units to { }*), - uint 1, - uint 1, - i8* getelementptr ([13 x i8]* %str1, i32 0, i32 0), - i8* getelementptr ([21 x i8]* %str2, i32 0, i32 0), - i8* getelementptr ([33 x i8]* %str3, i32 0, i32 0) }, section "llvm.metadata" - -;; -;; Define the compile unit for the header file "/Users/mine/sources/MyHeader.h". +;; Define the file for the file "/Users/mine/sources/MySource.cpp". ;; -%llvm.dbg.compile_unit2 = internal constant %llvm.dbg.compile_unit.type { - uint add(uint 17, uint 262144), - { }* cast (%llvm.dbg.anchor.type* %llvm.dbg.compile_units to { }*), - uint 1, - uint 1, - i8* getelementptr ([11 x i8]* %str4, int 0, int 0), - i8* getelementptr ([21 x i8]* %str2, int 0, int 0), - i8* getelementptr ([33 x i8]* %str3, int 0, int 0) }, section "llvm.metadata" +!1 = metadata !{ + i32 524329, ;; Tag + metadata !"MySource.cpp", + metadata !"/Users/mine/sources", + metadata !3 ;; Compile unit +} ;; -;; Define each of the strings used in the compile units. +;; Define the file for the file "/Users/mine/sources/Myheader.h" ;; -%str1 = internal constant [13 x i8] c"MySource.cpp\00", section "llvm.metadata"; -%str2 = internal constant [21 x i8] c"/Users/mine/sources/\00", section "llvm.metadata"; -%str3 = internal constant [33 x i8] c"4.0.1 LLVM (LLVM research group)\00", section "llvm.metadata"; -%str4 = internal constant [11 x i8] c"MyHeader.h\00", section "llvm.metadata"; +!3 = metadata !{ + i32 524329, ;; Tag + metadata !"Myheader.h" + metadata !"/Users/mine/sources", + metadata !3 ;; Compile unit +} + ...
llvm::Instruction provides easy access to metadata attached with an +instruction. One can extract line number information encoded in LLVM IR +using Instruction::getMetadata() and +DILocation::getLineNumber(). +
+ if (MDNode *N = I->getMetadata("dbg")) { // Here I is an LLVM instruction + DILocation Loc(N); // DILocation is in DebugInfo.h + unsigned Line = Loc.getLineNumber(); + StringRef File = Loc.getFilename(); + StringRef Dir = Loc.getDirectory(); + } +
;; -;; 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, { }*, { }*, i8*, { }*, uint, { }*, bool, bool, { }*, uint } -%llvm.dbg.basictype.type = type { uint, { }*, i8*, { }*, 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.) +;; List of debug info of globals ;; -%llvm.dbg.global_variables = linkonce constant %llvm.dbg.anchor.type { uint 0, uint 52 }, section "llvm.metadata" +!llvm.dbg.gv = !{!0} ;; ;; 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 add(uint 52, uint 262144), - { }* cast (%llvm.dbg.anchor.type* %llvm.dbg.global_variables to { }*), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([9 x i8]* %str1, int 0, int 0), - i8* getelementptr ([1 x i8]* %str2, int 0, int 0), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - uint 1, - { }* cast (%llvm.dbg.basictype.type* %llvm.dbg.basictype to { }*), - bool false, - bool true, - { }* cast (int* %MyGlobal to { }*) }, section "llvm.metadata" - +!0 = metadata !{ + i32 524340, ;; Tag + i32 0, ;; Unused + metadata !1, ;; Context + metadata !"MyGlobal", ;; Name + metadata !"MyGlobal", ;; Display Name + metadata !"MyGlobal", ;; Linkage Name + metadata !3, ;; Compile Unit + i32 1, ;; Line Number + metadata !4, ;; Type + i1 false, ;; Is a local variable + i1 true, ;; Is this a definition + i32* @MyGlobal ;; The global variable +} + ;; ;; 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 add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([4 x i8]* %str3, int 0, int 0), - { }* null, - int 0, - uint 32, - uint 32, - uint 0, - uint 5 }, section "llvm.metadata" +!4 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"int", ;; Name + metadata !1, ;; File + i32 0, ;; Line number + i64 32, ;; Size in Bits + i64 32, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 5 ;; Encoding +} -;; -;; Define the names of the global variable and basic type. -;; -%str1 = internal constant [9 x i8] c"MyGlobal\00", section "llvm.metadata" -%str2 = internal constant [1 x i8] c"\00", section "llvm.metadata" -%str3 = internal constant [4 x i8] c"int\00", section "llvm.metadata"
-;; -;; 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, { }*, { }*, i8*, { }*, 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 add(uint 46, uint 262144), - { }* cast (%llvm.dbg.anchor.type* %llvm.dbg.subprograms to { }*), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([5 x i8]* %str1, int 0, int 0), - i8* getelementptr ([1 x i8]* %str2, int 0, int 0), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - uint 1, - { }* null, - bool false, - bool true }, section "llvm.metadata" - -;; -;; Define the name of the subprogram. -;; -%str1 = internal constant [5 x i8] c"main\00", section "llvm.metadata" -%str2 = internal constant [1 x i8] c"\00", section "llvm.metadata" - +!6 = metadata !{ + i32 524334, ;; Tag + i32 0, ;; Unused + metadata !1, ;; Context + metadata !"main", ;; Name + metadata !"main", ;; Display name + metadata !"main", ;; Linkage name + metadata !1, ;; File + i32 1, ;; Line number + metadata !4, ;; Type + i1 false, ;; Is local + i1 true ;; Is definition +} ;; ;; Define the subprogram itself. ;; -int %main(int %argc, i8** %argv) { +define i32 @main(i32 %argc, i8** %argv) { ... }@@ -1320,17 +1229,18 @@ int %main(int %argc, i8** %argv) {
-%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type { - uint add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([5 x i8]* %str1, int 0, int 0), - { }* null, - int 0, - uint 32, - uint 32, - uint 0, - uint 2 }, section "llvm.metadata" -%str1 = internal constant [5 x i8] c"bool\00", section "llvm.metadata" +!2 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"bool", ;; Name + metadata !1, ;; File + i32 0, ;; Line number + i64 8, ;; Size in Bits + i64 8, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 2 ;; Encoding +}
-%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type { - uint add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([5 x i8]* %str1, int 0, int 0), - { }* null, - int 0, - uint 8, - uint 8, - uint 0, - uint 6 }, section "llvm.metadata" -%str1 = internal constant [5 x i8] c"char\00", section "llvm.metadata" +!2 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"char", ;; Name + metadata !1, ;; File + i32 0, ;; Line number + i64 8, ;; Size in Bits + i64 8, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 6 ;; Encoding +}
-%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type { - uint add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([14 x i8]* %str1, int 0, int 0), - { }* null, - int 0, - uint 8, - uint 8, - uint 0, - uint 8 }, section "llvm.metadata" -%str1 = internal constant [14 x i8] c"unsigned char\00", section "llvm.metadata" +!2 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"unsigned char", + metadata !1, ;; File + i32 0, ;; Line number + i64 8, ;; Size in Bits + i64 8, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 8 ;; Encoding +}
-%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type { - uint add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([10 x i8]* %str1, int 0, int 0), - { }* null, - int 0, - uint 16, - uint 16, - uint 0, - uint 5 }, section "llvm.metadata" -%str1 = internal constant [10 x i8] c"short int\00", section "llvm.metadata" +!2 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"short int", + metadata !1, ;; File + i32 0, ;; Line number + i64 16, ;; Size in Bits + i64 16, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 5 ;; Encoding +}
-%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type { - uint add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([19 x i8]* %str1, int 0, int 0), - { }* null, - int 0, - uint 16, - uint 16, - uint 0, - uint 7 }, section "llvm.metadata" -%str1 = internal constant [19 x i8] c"short unsigned int\00", section "llvm.metadata" +!2 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"short unsigned int", + metadata !1, ;; File + i32 0, ;; Line number + i64 16, ;; Size in Bits + i64 16, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 7 ;; Encoding +}
-%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type { - uint add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([4 x i8]* %str1, int 0, int 0), - { }* null, - int 0, - uint 32, - uint 32, - uint 0, - uint 5 }, section "llvm.metadata" -%str1 = internal constant [4 x i8] c"int\00", section "llvm.metadata" +!2 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"int", ;; Name + metadata !1, ;; File + i32 0, ;; Line number + i64 32, ;; Size in Bits + i64 32, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 5 ;; Encoding +}
-%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type { - uint add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([13 x i8]* %str1, int 0, int 0), - { }* null, - int 0, - uint 32, - uint 32, - uint 0, - uint 7 }, section "llvm.metadata" -%str1 = internal constant [13 x i8] c"unsigned int\00", section "llvm.metadata" +!2 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"unsigned int", + metadata !1, ;; File + i32 0, ;; Line number + i64 32, ;; Size in Bits + i64 32, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 7 ;; Encoding +}
-%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type { - uint add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([14 x i8]* %str1, int 0, int 0), - { }* null, - int 0, - uint 64, - uint 64, - uint 0, - uint 5 }, section "llvm.metadata" -%str1 = internal constant [14 x i8] c"long long int\00", section "llvm.metadata" +!2 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"long long int", + metadata !1, ;; File + i32 0, ;; Line number + i64 64, ;; Size in Bits + i64 64, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 5 ;; Encoding +}
-%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type { - uint add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([23 x i8]* %str1, int 0, int 0), - { }* null, - int 0, - uint 64, - uint 64, - uint 0, - uint 7 }, section "llvm.metadata" -%str1 = internal constant [23 x 8] c"long long unsigned int\00", section "llvm.metadata" +!2 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"long long unsigned int", + metadata !1, ;; File + i32 0, ;; Line number + i64 64, ;; Size in Bits + i64 64, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 7 ;; Encoding +}
-%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type { - uint add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - i8* getelementptr ([6 x i8]* %str1, int 0, int 0), - { }* null, - int 0, - uint 32, - uint 32, - uint 0, - uint 4 }, section "llvm.metadata" -%str1 = internal constant [6 x i8] c"float\00", section "llvm.metadata" +!2 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"float", + metadata !1, ;; File + i32 0, ;; Line number + i64 32, ;; Size in Bits + i64 32, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 4 ;; Encoding +}
-%llvm.dbg.basictype = internal constant %llvm.dbg.basictype.type { - uint add(uint 36, uint 262144), - { }* cast (%llvm.dbg.compile_unit.type* %llvm.dbg.compile_unit to { }*), - 8* getelementptr ([7 x 8]* %str1, int 0, int 0), - { }* null, - int 0, - uint 64, - uint 64, - uint 0, - uint 4 }, section "llvm.metadata" -%str1 = internal constant [7 x 8] c"double\00", section "llvm.metadata" +!2 = metadata !{ + i32 524324, ;; Tag + metadata !1, ;; Context + metadata !"double",;; Name + metadata !1, ;; File + i32 0, ;; Line number + i64 64, ;; Size in Bits + i64 64, ;; Align in Bits + i64 0, ;; Offset in Bits + i32 0, ;; Flags + i32 4 ;; Encoding +}