basic DWARF reading.

R=r
DELTA=949  (949 added, 0 deleted, 0 changed)
OCL=34676
CL=34678

src/pkg/Make.deps

@@ -18,6 +18,7 @@ crypto/md5.install: hash.install os.install
 crypto/sha1.install: hash.install os.install
 datafmt.install: bytes.install container/vector.install fmt.install go/scanner.install go/token.install io.install os.install reflect.install runtime.install strconv.install strings.install
 debug/binary.install: io.install math.install os.install reflect.install
+debug/dwarf.install: debug/binary.install fmt.install os.install strconv.install
 debug/elf.install: debug/binary.install fmt.install io.install os.install strconv.install
 debug/gosym.install: debug/binary.install fmt.install io.install os.install strconv.install strings.install
 debug/proc.install: container/vector.install fmt.install io.install os.install runtime.install strconv.install strings.install sync.install syscall.install

src/pkg/Makefile

@@ -32,6 +32,7 @@ DIRS=\
 	crypto/sha1\
 	datafmt\
 	debug/binary\
+	debug/dwarf\
 	debug/elf\
 	debug/gosym\
 	debug/proc\
@@ -81,6 +82,7 @@ DIRS=\
 	utf8\
 
 NOTEST=\
+	debug/dwarf\
 	debug/proc\
 	go/ast\
 	go/doc\

src/pkg/debug/dwarf/Makefile

+# Copyright 2009 The Go Authors.  All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include $(GOROOT)/src/Make.$(GOARCH)
+
+TARG=debug/dwarf
+GOFILES=\
+	buf.go\
+	const.go\
+	entry.go\
+	open.go\
+	unit.go\
+
+include $(GOROOT)/src/Make.pkg

src/pkg/debug/dwarf/buf.go

+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Buffered reading and decoding of DWARF data streams.
+
+package dwarf
+
+import (
+	"debug/binary";
+	"os";
+	"strconv";
+)
+
+// Data buffer being decoded.
+type buf struct {
+	dwarf *Data;
+	order binary.ByteOrder;
+	name string;
+	off Offset;
+	data []byte;
+	addrsize int;
+	err os.Error;
+}
+
+func makeBuf(d *Data, name string, off Offset, data []byte, addrsize int) buf {
+	return buf{d, d.order, name, off, data, addrsize, nil}
+}
+
+func (b *buf) uint8() uint8 {
+	if len(b.data) < 1 {
+		b.error("underflow");
+		return 0;
+	}
+	val := b.data[0];
+	b.data = b.data[1:len(b.data)];
+	b.off++;
+	return val;
+}
+
+func (b *buf) bytes(n int) []byte {
+	if len(b.data) < n {
+		b.error("underflow");
+		return nil;
+	}
+	data := b.data[0:n];
+	b.data = b.data[n:len(b.data)];
+	b.off += Offset(n);
+	return data;
+}
+
+func (b *buf) skip(n int) {
+	b.bytes(n);
+}
+
+func (b *buf) string() string {
+	for i := 0; i < len(b.data); i++ {
+		if b.data[i] == 0 {
+			s := string(b.data[0:i]);
+			b.data = b.data[i+1:len(b.data)];
+			b.off += Offset(i+1);
+			return s;
+		}
+	}
+	b.error("underflow");
+	return "";
+}
+
+func (b *buf) uint16() uint16{
+	a := b.bytes(2);
+	if a == nil {
+		return 0;
+	}
+	return b.order.Uint16(a);
+}
+
+func (b *buf) uint32() uint32 {
+	a := b.bytes(4);
+	if a == nil {
+		return 0;
+	}
+	return b.order.Uint32(a);
+}
+
+func (b *buf) uint64() uint64 {
+	a := b.bytes(8);
+	if a == nil {
+		return 0;
+	}
+	return b.order.Uint64(a);
+}
+
+// Read a varint, which is 7 bits per byte, little endian.
+// the 0x80 bit means read another byte.
+func (b *buf) varint() (c uint64, bits uint) {
+	for i := 0; i < len(b.data); i++ {
+		byte := b.data[i];
+		c |= uint64(byte&0x7F) << bits;
+		bits += 7;
+		if byte&0x80 == 0 {
+			b.off += Offset(i+1);
+			b.data = b.data[i+1:len(b.data)];
+			return c, bits;
+		}
+	}
+	return 0, 0;
+}
+
+// Unsigned int is just a varint.
+func (b *buf) uint() uint64 {
+	x, _ := b.varint();
+	return x;
+}
+
+// Signed int is a sign-extended varint.
+func (b *buf) int() int64 {
+	ux, bits := b.varint();
+	x := int64(ux);
+	if x & (1<<(bits-1)) != 0 {
+		x |= -1<<bits;
+	}
+	return x;
+}
+
+// Address-sized uint.
+func (b *buf) addr() uint64 {
+	switch b.addrsize {
+	case 1:
+		return uint64(b.uint8());
+	case 2:
+		return uint64(b.uint16());
+	case 4:
+		return uint64(b.uint32());
+	case 8:
+		return uint64(b.uint64());
+	}
+	b.error("unknown address size");
+	return 0;
+}
+
+func (b *buf) error(s string) {
+	if b.err == nil {
+		b.data = nil;
+		b.err = DecodeError{b.name, b.off, s}
+	}
+}
+
+type DecodeError struct {
+	Name string;
+	Offset Offset;
+	Error string;
+}
+
+func (e DecodeError) String() string {
+	return "decoding dwarf section " + e.Name + " at offset " + strconv.Itoa64(int64(e.Offset)) + ": " + e.Error;
+}
+

src/pkg/debug/dwarf/const.go

+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Constants
+
+package dwarf
+
+import "strconv"
+
+// An Attr identifies the attribute type in a DWARF Entry's Field.
+type Attr uint32
+
+const (
+	AttrSibling Attr = 0x01;
+	AttrLocation Attr = 0x02;
+	AttrName Attr = 0x03;
+	AttrOrdering Attr = 0x09;
+	AttrByteSize Attr = 0x0B;
+	AttrBitOffset Attr = 0x0C;
+	AttrBitSize Attr = 0x0D;
+	AttrStmtList Attr = 0x10;
+	AttrLowpc Attr = 0x11;
+	AttrHighpc Attr = 0x12;
+	AttrLanguage Attr = 0x13;
+	AttrDiscr Attr = 0x15;
+	AttrDiscrValue Attr = 0x16;
+	AttrVisibility Attr = 0x17;
+	AttrImport Attr = 0x18;
+	AttrStringLength Attr = 0x19;
+	AttrCommonRef Attr = 0x1A;
+	AttrCompDir Attr = 0x1B;
+	AttrConstValue Attr = 0x1C;
+	AttrContainingType Attr = 0x1D;
+	AttrDefaultValue Attr = 0x1E;
+	AttrInline Attr = 0x20;
+	AttrIsOptional Attr = 0x21;
+	AttrLowerBound Attr = 0x22;
+	AttrProducer Attr = 0x25;
+	AttrPrototyped Attr = 0x27;
+	AttrReturnAddr Attr = 0x2A;
+	AttrStartScope Attr = 0x2C;
+	AttrStrideSize Attr = 0x2E;
+	AttrUpperBound Attr = 0x2F;
+	AttrAbstractOrigin Attr = 0x31;
+	AttrAccessibility Attr = 0x32;
+	AttrAddrClass Attr = 0x33;
+	AttrArtificial Attr = 0x34;
+	AttrBaseTypes Attr = 0x35;
+	AttrCalling Attr = 0x36;
+	AttrCount Attr = 0x37;
+	AttrDataMemberLoc Attr = 0x38;
+	AttrDeclColumn Attr = 0x39;
+	AttrDeclFile Attr = 0x3A;
+	AttrDeclLine Attr = 0x3B;
+	AttrDeclaration Attr = 0x3C;
+	AttrDiscrList Attr = 0x3D;
+	AttrEncoding Attr = 0x3E;
+	AttrExternal Attr = 0x3F;
+	AttrFrameBase Attr = 0x40;
+	AttrFriend Attr = 0x41;
+	AttrIdentifierCase Attr = 0x42;
+	AttrMacroInfo Attr = 0x43;
+	AttrNamelistItem Attr = 0x44;
+	AttrPriority Attr = 0x45;
+	AttrSegment Attr = 0x46;
+	AttrSpecification Attr = 0x47;
+	AttrStaticLink Attr = 0x48;
+	AttrType Attr = 0x49;
+	AttrUseLocation Attr = 0x4A;
+	AttrVarParam Attr = 0x4B;
+	AttrVirtuality Attr = 0x4C;
+	AttrVtableElemLoc Attr = 0x4D;
+	AttrAllocated Attr = 0x4E;
+	AttrAssociated Attr = 0x4F;
+	AttrDataLocation Attr = 0x50;
+	AttrStride Attr = 0x51;
+	AttrEntrypc Attr = 0x52;
+	AttrUseUTF8 Attr = 0x53;
+	AttrExtension Attr = 0x54;
+	AttrRanges Attr = 0x55;
+	AttrTrampoline Attr = 0x56;
+	AttrCallColumn Attr = 0x57;
+	AttrCallFile Attr = 0x58;
+	AttrCallLine Attr = 0x59;
+	AttrDescription Attr = 0x5A;
+)
+
+var attrNames = [...]string {
+	AttrSibling: "Sibling",
+	AttrLocation: "Location",
+	AttrName: "Name",
+	AttrOrdering: "Ordering",
+	AttrByteSize: "ByteSize",
+	AttrBitOffset: "BitOffset",
+	AttrBitSize: "BitSize",
+	AttrStmtList: "StmtList",
+	AttrLowpc: "Lowpc",
+	AttrHighpc: "Highpc",
+	AttrLanguage: "Language",
+	AttrDiscr: "Discr",
+	AttrDiscrValue: "DiscrValue",
+	AttrVisibility: "Visibility",
+	AttrImport: "Import",
+	AttrStringLength: "StringLength",
+	AttrCommonRef: "CommonRef",
+	AttrCompDir: "CompDir",
+	AttrConstValue: "ConstValue",
+	AttrContainingType: "ContainingType",
+	AttrDefaultValue: "DefaultValue",
+	AttrInline: "Inline",
+	AttrIsOptional: "IsOptional",
+	AttrLowerBound: "LowerBound",
+	AttrProducer: "Producer",
+	AttrPrototyped: "Prototyped",
+	AttrReturnAddr: "ReturnAddr",
+	AttrStartScope: "StartScope",
+	AttrStrideSize: "StrideSize",
+	AttrUpperBound: "UpperBound",
+	AttrAbstractOrigin: "AbstractOrigin",
+	AttrAccessibility: "Accessibility",
+	AttrAddrClass: "AddrClass",
+	AttrArtificial: "Artificial",
+	AttrBaseTypes: "BaseTypes",
+	AttrCalling: "Calling",
+	AttrCount: "Count",
+	AttrDataMemberLoc: "DataMemberLoc",
+	AttrDeclColumn: "DeclColumn",
+	AttrDeclFile: "DeclFile",
+	AttrDeclLine: "DeclLine",
+	AttrDeclaration: "Declaration",
+	AttrDiscrList: "DiscrList",
+	AttrEncoding: "Encoding",
+	AttrExternal: "External",
+	AttrFrameBase: "FrameBase",
+	AttrFriend: "Friend",
+	AttrIdentifierCase: "IdentifierCase",
+	AttrMacroInfo: "MacroInfo",
+	AttrNamelistItem: "NamelistItem",
+	AttrPriority: "Priority",
+	AttrSegment: "Segment",
+	AttrSpecification: "Specification",
+	AttrStaticLink: "StaticLink",
+	AttrType: "Type",
+	AttrUseLocation: "UseLocation",
+	AttrVarParam: "VarParam",
+	AttrVirtuality: "Virtuality",
+	AttrVtableElemLoc: "VtableElemLoc",
+	AttrAllocated: "Allocated",
+	AttrAssociated: "Associated",
+	AttrDataLocation: "DataLocation",
+	AttrStride: "Stride",
+	AttrEntrypc: "Entrypc",
+	AttrUseUTF8: "UseUTF8",
+	AttrExtension: "Extension",
+	AttrRanges: "Ranges",
+	AttrTrampoline: "Trampoline",
+	AttrCallColumn: "CallColumn",
+	AttrCallFile: "CallFile",
+	AttrCallLine: "CallLine",
+	AttrDescription: "Description",
+}
+
+func (a Attr) String() string {
+	if int(a) < len(attrNames) {
+		s := attrNames[a];
+		if s != "" {
+			return s;
+		}
+	}
+	return strconv.Itoa(int(a));
+}
+
+func (a Attr) GoString() string {
+	if int(a) < len(attrNames) {
+		s := attrNames[a];
+		if s != "" {
+			return "dwarf.Attr" + s;
+		}
+	}
+	return "dwarf.Attr(" + strconv.Itoa64(int64(a)) + ")";
+}
+
+// A format is a DWARF data encoding format.
+type format uint32
+
+const (
+	// value formats
+	formAddr format = 0x01;
+	formDwarfBlock2 format = 0x03;
+	formDwarfBlock4 format = 0x04;
+	formData2 format = 0x05;
+	formData4 format = 0x06;
+	formData8 format = 0x07;
+	formString format = 0x08;
+	formDwarfBlock format = 0x09;
+	formDwarfBlock1 format = 0x0A;
+	formData1 format = 0x0B;
+	formFlag format = 0x0C;
+	formSdata format = 0x0D;
+	formStrp format = 0x0E;
+	formUdata format = 0x0F;
+	formRefAddr format = 0x10;
+	formRef1 format = 0x11;
+	formRef2 format = 0x12;
+	formRef4 format = 0x13;
+	formRef8 format = 0x14;
+	formRefUdata format = 0x15;
+	formIndirect format = 0x16;
+)
+
+// A Tag is the classification (the type) of an Entry.
+type Tag uint32
+
+const (
+	TagArrayType Tag = 0x01;
+	TagClassType Tag = 0x02;
+	TagEntryPoint Tag = 0x03;
+	TagEnumerationType Tag = 0x04;
+	TagFormalParameter Tag = 0x05;
+	TagImportedDeclaration Tag = 0x08;
+	TagLabel Tag = 0x0A;
+	TagLexDwarfBlock Tag = 0x0B;
+	TagMember Tag = 0x0D;
+	TagPointerType Tag = 0x0F;
+	TagReferenceType Tag = 0x10;
+	TagCompileUnit Tag = 0x11;
+	TagStringType Tag = 0x12;
+	TagStructType Tag = 0x13;
+	TagSubroutineType Tag = 0x15;
+	TagTypedef Tag = 0x16;
+	TagUnionType Tag = 0x17;
+	TagUnspecifiedParameters Tag = 0x18;
+	TagVariant Tag = 0x19;
+	TagCommonDwarfBlock Tag = 0x1A;
+	TagCommonInclusion Tag = 0x1B;
+	TagInheritance Tag = 0x1C;
+	TagInlinedSubroutine Tag = 0x1D;
+	TagModule Tag = 0x1E;
+	TagPtrToMemberType Tag = 0x1F;
+	TagSetType Tag = 0x20;
+	TagSubrangeType Tag = 0x21;
+	TagWithStmt Tag = 0x22;
+	TagAccessDeclaration Tag = 0x23;
+	TagBaseType Tag = 0x24;
+	TagCatchDwarfBlock Tag = 0x25;
+	TagConstType Tag = 0x26;
+	TagConstant Tag = 0x27;
+	TagEnumerator Tag = 0x28;
+	TagFileType Tag = 0x29;
+	TagFriend Tag = 0x2A;
+	TagNamelist Tag = 0x2B;
+	TagNamelistItem Tag = 0x2C;
+	TagPackedType Tag = 0x2D;
+	TagSubprogram Tag = 0x2E;
+	TagTemplateTypeParameter Tag = 0x2F;
+	TagTemplateValueParameter Tag = 0x30;
+	TagThrownType Tag = 0x31;
+	TagTryDwarfBlock Tag = 0x32;
+	TagVariantPart Tag = 0x33;
+	TagVariable Tag = 0x34;
+	TagVolatileType Tag = 0x35;
+	TagDwarfProcedure Tag = 0x36;
+	TagRestrictType Tag = 0x37;
+	TagInterfaceType Tag = 0x38;
+	TagNamespace Tag = 0x39;
+	TagImportedModule Tag = 0x3A;
+	TagUnspecifiedType Tag = 0x3B;
+	TagPartialUnit Tag = 0x3C;
+	TagImportedUnit Tag = 0x3D;
+	TagMutableType Tag = 0x3E;
+)
+
+var tagNames = [...]string {
+	TagArrayType: "ArrayType",
+	TagClassType: "ClassType",
+	TagEntryPoint: "EntryPoint",
+	TagEnumerationType: "EnumerationType",
+	TagFormalParameter: "FormalParameter",
+	TagImportedDeclaration: "ImportedDeclaration",
+	TagLabel: "Label",
+	TagLexDwarfBlock: "LexDwarfBlock",
+	TagMember: "Member",
+	TagPointerType: "PointerType",
+	TagReferenceType: "ReferenceType",
+	TagCompileUnit: "CompileUnit",
+	TagStringType: "StringType",
+	TagStructType: "StructType",
+	TagSubroutineType: "SubroutineType",
+	TagTypedef: "Typedef",
+	TagUnionType: "UnionType",
+	TagUnspecifiedParameters: "UnspecifiedParameters",
+	TagVariant: "Variant",
+	TagCommonDwarfBlock: "CommonDwarfBlock",
+	TagCommonInclusion: "CommonInclusion",
+	TagInheritance: "Inheritance",
+	TagInlinedSubroutine: "InlinedSubroutine",
+	TagModule: "Module",
+	TagPtrToMemberType: "PtrToMemberType",
+	TagSetType: "SetType",
+	TagSubrangeType: "SubrangeType",
+	TagWithStmt: "WithStmt",
+	TagAccessDeclaration: "AccessDeclaration",
+	TagBaseType: "BaseType",
+	TagCatchDwarfBlock: "CatchDwarfBlock",
+	TagConstType: "ConstType",
+	TagConstant: "Constant",
+	TagEnumerator: "Enumerator",
+	TagFileType: "FileType",
+	TagFriend: "Friend",
+	TagNamelist: "Namelist",
+	TagNamelistItem: "NamelistItem",
+	TagPackedType: "PackedType",
+	TagSubprogram: "Subprogram",
+	TagTemplateTypeParameter: "TemplateTypeParameter",
+	TagTemplateValueParameter: "TemplateValueParameter",
+	TagThrownType: "ThrownType",
+	TagTryDwarfBlock: "TryDwarfBlock",
+	TagVariantPart: "VariantPart",
+	TagVariable: "Variable",
+	TagVolatileType: "VolatileType",
+	TagDwarfProcedure: "DwarfProcedure",
+	TagRestrictType: "RestrictType",
+	TagInterfaceType: "InterfaceType",
+	TagNamespace: "Namespace",
+	TagImportedModule: "ImportedModule",
+	TagUnspecifiedType: "UnspecifiedType",
+	TagPartialUnit: "PartialUnit",
+	TagImportedUnit: "ImportedUnit",
+	TagMutableType: "MutableType",
+}
+
+func (t Tag) String() string {
+	if int(t) < len(tagNames) {
+		s := tagNames[t];
+		if s != "" {
+			return s;
+		}
+	}
+	return strconv.Itoa(int(t));
+}
+
+func (t Tag) GoString() string {
+	if int(t) < len(tagNames) {
+		s := tagNames[t];
+		if s != "" {
+			return "dwarf.Tag" + s;
+		}
+	}
+	return "dwarf.Tag(" + strconv.Itoa64(int64(t)) + ")";
+}
+

src/pkg/debug/dwarf/entry.go

+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// DWARF debug information entry parser.
+// An entry is a sequence of data items of a given format.
+// The first word in the entry is an index into what DWARF
+// calls the ``abbreviation table.''  An abbreviation is really
+// just a type descriptor: it's an array of attribute tag/value format pairs.
+
+package dwarf
+
+import (
+	"os";
+	"strconv";
+)
+
+// a single entry's description: a sequence of attributes
+type abbrev struct {
+	tag Tag;
+	children bool;
+	field []afield;
+}
+
+type afield struct {
+	attr Attr;
+	fmt format;
+}
+
+// a map from entry format ids to their descriptions
+type abbrevTable map[uint32]abbrev
+
+// ParseAbbrev returns the abbreviation table that starts at byte off
+// in the .debug_abbrev section.
+func (d *Data) parseAbbrev(off uint32) (abbrevTable, os.Error) {
+	if m, ok := d.abbrevCache[off]; ok {
+		return m, nil;
+	}
+
+	data := d.abbrev;
+	if off > uint32(len(data)) {
+		data = nil;
+	} else {
+		data = data[off:len(data)];
+	}
+	b := makeBuf(d, "abbrev", 0, data, 0);
+
+	// Error handling is simplified by the buf getters
+	// returning an endless stream of 0s after an error.
+	m := make(abbrevTable);
+	for {
+		// Table ends with id == 0.
+		id := uint32(b.uint());
+		if id == 0 {
+			break;
+		}
+
+		// Walk over attributes, counting.
+		n := 0;
+		b1 := b;	// Read from copy of b.
+		b1.uint();
+		b1.uint8();
+		for {
+			tag := b1.uint();
+			fmt := b1.uint();
+			if tag == 0 && fmt == 0 {
+				break;
+			}
+			n++;
+		}
+		if b1.err != nil {
+			return nil, b1.err;
+		}
+
+		// Walk over attributes again, this time writing them down.
+		var a abbrev;
+		a.tag = Tag(b.uint());
+		a.children = b.uint8() != 0;
+		a.field = make([]afield, n);
+		for i := range a.field {
+			a.field[i].attr = Attr(b.uint());
+			a.field[i].fmt = format(b.uint());
+		}
+		b.uint();
+		b.uint();
+
+		m[id] = a;
+	}
+	if b.err != nil {
+		return nil, b.err;
+	}
+	d.abbrevCache[off] = m;
+	return m, nil;
+}
+
+// An entry is a sequence of attribute/value pairs.
+type Entry struct {
+	Offset Offset;	// offset of Entry in DWARF info
+	Tag Tag;	// tag (kind of Entry)
+	Children bool;	// whether Entry is followed by children
+	Field []Field;
+}
+
+// A Field is a single attribute/value pair in an Entry.
+type Field struct {
+	Attr Attr;
+	Val interface{};
+}
+
+// An Offset represents the location of an Entry within the DWARF info.
+// (See Reader.Seek.)
+type Offset uint32
+
+// Entry reads a single entry from buf, decoding
+// according to the given abbreviation table.
+func (b *buf) entry(atab abbrevTable, ubase Offset) *Entry {
+	off := b.off;
+	id := uint32(b.uint());
+	if id == 0 {
+		return &Entry{};
+	}
+	a, ok := atab[id];
+	if !ok {
+		b.error("unknown abbreviation table index");
+		return nil;
+	}
+	e := &Entry{
+		Offset: off,
+		Tag: a.tag,
+		Children: a.children,
+		Field: make([]Field, len(a.field))
+	};
+	for i := range e.Field {
+		e.Field[i].Attr = a.field[i].attr;
+		fmt := a.field[i].fmt;
+		if fmt == formIndirect {
+			fmt = format(b.uint());
+		}
+		var val interface{};
+		switch fmt {
+		default:
+			b.error("unknown entry attr format");
+
+		// address
+		case formAddr:
+			val = b.addr();
+
+		// block
+		case formDwarfBlock1:
+			val = b.bytes(int(b.uint8()));
+		case formDwarfBlock2:
+			val = b.bytes(int(b.uint16()));
+		case formDwarfBlock4:
+			val = b.bytes(int(b.uint32()));
+		case formDwarfBlock:
+			val = b.bytes(int(b.uint()));
+
+		// constant
+		case formData1:
+			val = uint64(b.uint8());
+		case formData2:
+			val = uint64(b.uint16());
+		case formData4:
+			val = uint64(b.uint32());
+		case formData8:
+			val = uint64(b.uint64());
+		case formSdata:
+			val = int64(b.int());
+		case formUdata:
+			val = uint64(b.uint());
+
+		// flag
+		case formFlag:
+			val = b.uint8() == 1;
+
+		// reference to other entry
+		case formRefAddr:
+			val = Offset(b.addr());
+		case formRef1:
+			val = Offset(b.uint8()) + ubase;
+		case formRef2:
+			val = Offset(b.uint16()) + ubase;
+		case formRef4:
+			val = Offset(b.uint32()) + ubase;
+		case formRef8:
+			val = Offset(b.uint64()) + ubase;
+		case formRefUdata:
+			val = Offset(b.uint()) + ubase;
+
+		// string
+		case formString:
+			val = b.string();
+		case formStrp:
+			off := b.uint32();	// offset into .debug_str
+			if b.err != nil {
+				return nil;
+			}
+			b1 := makeBuf(b.dwarf, "str", 0, b.dwarf.str, 0);
+			b1.skip(int(off));
+			val = b1.string();
+			if b1.err != nil {
+				b.err = b1.err;
+				return nil;
+			}
+		}
+		e.Field[i].Val = val;
+	}
+	if b.err != nil {
+		return nil;
+	}
+	return e;
+}
+
+// A Reader allows reading Entry structures from a DWARF ``info'' section.
+type Reader struct {
+	b buf;
+	d *Data;
+	err os.Error;
+	unit int;
+}
+
+// Reader returns a new Reader for Data.
+// The reader is positioned at byte offset 0 in the DWARF ``info'' section.
+func (d *Data) Reader() *Reader {
+	r := &Reader{d: d};
+	r.Seek(0);
+	return r;
+}
+
+// Seek positions the Reader at offset off in the encoded entry stream.
+// Offset 0 can be used to denote the first entry.
+func (r *Reader) Seek(off Offset) {
+	d := r.d;
+	r.err = nil;
+	if off == 0 {
+		if len(d.unit) == 0 {
+			return;
+		}
+		u := &d.unit[0];
+		r.unit = 0;
+		r.b = makeBuf(r.d, "info", u.off, u.data, u.addrsize);
+		return;
+	}
+
+	// TODO(rsc): binary search (maybe a new package)
+	var i int;
+	var u *unit;
+	for i = range d.unit {
+		u = &d.unit[i];
+		if u.off <= off && off < u.off+Offset(len(u.data)) {
+			r.unit = i;
+			r.b = makeBuf(r.d, "info", off, u.data[off-u.off:len(u.data)], u.addrsize);
+			return;
+		}
+	}
+	r.err = os.NewError("offset out of range");
+}
+
+// maybeNextUnit advances to the next unit if this one is finished.
+func (r *Reader) maybeNextUnit() {
+	for len(r.b.data) == 0 && r.unit < len(r.d.unit) {
+		r.unit++;
+		u := &r.d.unit[r.unit];
+		r.b = makeBuf(r.d, "info", u.off, u.data, u.addrsize);
+	}
+}
+
+// Next reads the next entry from the encoded entry stream.
+// It returns nil, nil when it reaches the end of the section.
+// It returns an error if the current offset is invalid or the data at the
+// offset cannot be decoded as a valid Entry.
+func (r *Reader) Next() (*Entry, os.Error) {
+	if r.err != nil {
+		return nil, r.err;
+	}
+	r.maybeNextUnit();
+	if len(r.b.data) == 0 {
+		return nil, nil;
+	}
+	u := &r.d.unit[r.unit];
+	e := r.b.entry(u.atable, u.base);
+	r.err = r.b.err;
+	return e, r.err;
+}

src/pkg/debug/dwarf/open.go

+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This package provides access to DWARF debugging information
+// loaded from executable files, as defined in the DWARF 2.0 Standard
+// at http://dwarfstd.org/dwarf-2.0.0.pdf.
+package dwarf
+
+import (
+	"debug/binary";
+	"fmt";
+	"os";
+)
+
+// Data represents the DWARF debugging information
+// loaded from an executable file (for example, an ELF or Mach-O executable).
+type Data struct {
+	// raw data
+	abbrev []byte;
+	aranges []byte;
+	frame []byte;
+	info []byte;
+	line []byte;
+	pubnames []byte;
+	ranges []byte;
+	str []byte;
+
+	// parsed data
+	abbrevCache map[uint32] abbrevTable;
+	addrsize int;
+	order binary.ByteOrder;
+	unit []unit;
+}
+
+// New returns a new Data object initialized from the given parameters.
+// Clients should typically use [TODO(rsc): method to be named later] instead of calling
+// New directly.
+//
+// The []byte arguments are the data from the corresponding debug section
+// in the object file; for example, for an ELF object, abbrev is the contents of
+// the ".debug_abbrev" section.
+func New(abbrev, aranges, frame, info, line, pubnames, ranges, str []byte) (*Data, os.Error) {
+	d := &Data{
+		abbrev: abbrev,
+		aranges: aranges,
+		frame: frame,
+		info: info,
+		line: line,
+		pubnames: pubnames,
+		ranges: ranges,
+		str: str,
+		abbrevCache: make(map[uint32]abbrevTable),
+	};
+
+	// Sniff .debug_info to figure out byte order.
+	// bytes 4:6 are the version, a tiny 16-bit number (1, 2, 3).
+	if len(d.info) < 6 {
+		return nil, DecodeError{"info", Offset(len(d.info)), "too short"};
+	}
+	x, y := d.info[4], d.info[5];
+	switch {
+	case x == 0 && y == 0:
+		return nil, DecodeError{"info", 4, "unsupported version 0"};
+	case x == 0:
+		d.order = binary.BigEndian;
+	case y == 0:
+		d.order = binary.LittleEndian;
+	default:
+		return nil, DecodeError{"info", 4, "cannot determine byte order"};
+	}
+
+	u, err := d.parseUnits();
+	if err != nil {
+		return nil, err;
+	}
+	d.unit = u;
+	return d, nil;
+}

src/pkg/debug/dwarf/unit.go

+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package dwarf
+
+import (
+	"os";
+	"strconv";
+)
+
+// DWARF debug info is split into a sequence of compilation units.
+// Each unit has its own abbreviation table and address size.
+
+type unit struct {
+	base Offset;	// byte offset of header within the aggregate info
+	off Offset;	// byte offset of data within the aggregate info
+	data []byte;
+	atable abbrevTable;
+	addrsize int;
+}
+
+func (d *Data) parseUnits() ([]unit, os.Error) {
+	// Count units.
+	nunit := 0;
+	b := makeBuf(d, "info", 0, d.info, 0);
+	for len(b.data) > 0 {
+		b.skip(int(b.uint32()));
+		nunit++;
+	}
+	if b.err != nil {
+		return nil, b.err;
+	}
+
+	// Again, this time writing them down.
+	b = makeBuf(d, "info", 0, d.info, 0);
+	units := make([]unit, nunit);
+	for i := range units {
+		u := &units[i];
+		u.base = b.off;
+		n := b.uint32();
+		if vers := b.uint16(); vers != 2 {
+			b.error("unsupported DWARF version " + strconv.Itoa(int(vers)));
+			break;
+		}
+		atable, err := d.parseAbbrev(b.uint32());
+		if err != nil {
+			if b.err == nil {
+				b.err = err;
+			}
+			break;
+		}
+		u.atable = atable;
+		u.addrsize = int(b.uint8());
+		u.off = b.off;
+		u.data = b.bytes(int(n - (2+4+1)));
+	}
+	if b.err != nil {
+		return nil, b.err;
+	}
+	return units, nil;
+}
+