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Source file src/cmd/internal/dwarf/dwarf.go

Documentation: cmd/internal/dwarf

  // Copyright 2016 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 generates DWARF debugging information.
  // DWARF generation is split between the compiler and the linker,
  // this package contains the shared code.
  package dwarf
  
  import (
  	"errors"
  	"fmt"
  	"sort"
  	"strings"
  )
  
  // InfoPrefix is the prefix for all the symbols containing DWARF info entries.
  const InfoPrefix = "go.info."
  
  // RangePrefix is the prefix for all the symbols containing DWARF location lists.
  const LocPrefix = "go.loc."
  
  // RangePrefix is the prefix for all the symbols containing DWARF range lists.
  const RangePrefix = "go.range."
  
  // ConstInfoPrefix is the prefix for all symbols containing DWARF info
  // entries that contain constants.
  const ConstInfoPrefix = "go.constinfo."
  
  // CUInfoPrefix is the prefix for symbols containing information to
  // populate the DWARF compilation unit info entries.
  const CUInfoPrefix = "go.cuinfo."
  
  // Used to form the symbol name assigned to the DWARF 'abstract subprogram"
  // info entry for a function
  const AbstractFuncSuffix = "$abstract"
  
  // Controls logging/debugging for selected aspects of DWARF subprogram
  // generation (functions, scopes).
  var logDwarf bool
  
  // Sym represents a symbol.
  type Sym interface {
  	Len() int64
  }
  
  // A Location represents a variable's location at a particular PC range.
  // It becomes a location list entry in the DWARF.
  type Location struct {
  	StartPC, EndPC int64
  	Pieces         []Piece
  }
  
  // A Piece represents the location of a particular part of a variable.
  // It becomes part of a location list entry (a DW_OP_piece) in the DWARF.
  type Piece struct {
  	Length      int64
  	StackOffset int32
  	RegNum      int16
  	Missing     bool
  	OnStack     bool // if true, RegNum is unset.
  }
  
  // A Var represents a local variable or a function parameter.
  type Var struct {
  	Name          string
  	Abbrev        int // Either DW_ABRV_AUTO[_LOCLIST] or DW_ABRV_PARAM[_LOCLIST]
  	IsReturnValue bool
  	IsInlFormal   bool
  	StackOffset   int32
  	LocationList  []Location
  	Scope         int32
  	Type          Sym
  	DeclFile      string
  	DeclLine      uint
  	DeclCol       uint
  	InlIndex      int32 // subtract 1 to form real index into InlTree
  	ChildIndex    int32 // child DIE index in abstract function
  	IsInAbstract  bool  // variable exists in abstract function
  }
  
  // A Scope represents a lexical scope. All variables declared within a
  // scope will only be visible to instructions covered by the scope.
  // Lexical scopes are contiguous in source files but can end up being
  // compiled to discontiguous blocks of instructions in the executable.
  // The Ranges field lists all the blocks of instructions that belong
  // in this scope.
  type Scope struct {
  	Parent int32
  	Ranges []Range
  	Vars   []*Var
  }
  
  // A Range represents a half-open interval [Start, End).
  type Range struct {
  	Start, End int64
  }
  
  // This container is used by the PutFunc* variants below when
  // creating the DWARF subprogram DIE(s) for a function.
  type FnState struct {
  	Name       string
  	Importpath string
  	Info       Sym
  	Filesym    Sym
  	Loc        Sym
  	Ranges     Sym
  	Absfn      Sym
  	StartPC    Sym
  	Size       int64
  	External   bool
  	Scopes     []Scope
  	InlCalls   InlCalls
  }
  
  func EnableLogging(doit bool) {
  	logDwarf = doit
  }
  
  // UnifyRanges merges the list of ranges of c into the list of ranges of s
  func (s *Scope) UnifyRanges(c *Scope) {
  	out := make([]Range, 0, len(s.Ranges)+len(c.Ranges))
  
  	i, j := 0, 0
  	for {
  		var cur Range
  		if i < len(s.Ranges) && j < len(c.Ranges) {
  			if s.Ranges[i].Start < c.Ranges[j].Start {
  				cur = s.Ranges[i]
  				i++
  			} else {
  				cur = c.Ranges[j]
  				j++
  			}
  		} else if i < len(s.Ranges) {
  			cur = s.Ranges[i]
  			i++
  		} else if j < len(c.Ranges) {
  			cur = c.Ranges[j]
  			j++
  		} else {
  			break
  		}
  
  		if n := len(out); n > 0 && cur.Start <= out[n-1].End {
  			out[n-1].End = cur.End
  		} else {
  			out = append(out, cur)
  		}
  	}
  
  	s.Ranges = out
  }
  
  type InlCalls struct {
  	Calls []InlCall
  }
  
  type InlCall struct {
  	// index into ctx.InlTree describing the call inlined here
  	InlIndex int
  
  	// Symbol of file containing inlined call site (really *obj.LSym).
  	CallFile Sym
  
  	// Line number of inlined call site.
  	CallLine uint32
  
  	// Dwarf abstract subroutine symbol (really *obj.LSym).
  	AbsFunSym Sym
  
  	// Indices of child inlines within Calls array above.
  	Children []int
  
  	// entries in this list are PAUTO's created by the inliner to
  	// capture the promoted formals and locals of the inlined callee.
  	InlVars []*Var
  
  	// PC ranges for this inlined call.
  	Ranges []Range
  
  	// Root call (not a child of some other call).
  	Root bool
  }
  
  // A Context specifies how to add data to a Sym.
  type Context interface {
  	PtrSize() int
  	AddInt(s Sym, size int, i int64)
  	AddBytes(s Sym, b []byte)
  	AddAddress(s Sym, t interface{}, ofs int64)
  	AddCURelativeAddress(s Sym, t interface{}, ofs int64)
  	AddSectionOffset(s Sym, size int, t interface{}, ofs int64)
  	CurrentOffset(s Sym) int64
  	RecordDclReference(from Sym, to Sym, dclIdx int, inlIndex int)
  	RecordChildDieOffsets(s Sym, vars []*Var, offsets []int32)
  	AddString(s Sym, v string)
  	AddFileRef(s Sym, f interface{})
  	Logf(format string, args ...interface{})
  }
  
  // AppendUleb128 appends v to b using DWARF's unsigned LEB128 encoding.
  func AppendUleb128(b []byte, v uint64) []byte {
  	for {
  		c := uint8(v & 0x7f)
  		v >>= 7
  		if v != 0 {
  			c |= 0x80
  		}
  		b = append(b, c)
  		if c&0x80 == 0 {
  			break
  		}
  	}
  	return b
  }
  
  // AppendSleb128 appends v to b using DWARF's signed LEB128 encoding.
  func AppendSleb128(b []byte, v int64) []byte {
  	for {
  		c := uint8(v & 0x7f)
  		s := uint8(v & 0x40)
  		v >>= 7
  		if (v != -1 || s == 0) && (v != 0 || s != 0) {
  			c |= 0x80
  		}
  		b = append(b, c)
  		if c&0x80 == 0 {
  			break
  		}
  	}
  	return b
  }
  
  // sevenbits contains all unsigned seven bit numbers, indexed by their value.
  var sevenbits = [...]byte{
  	0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
  	0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
  	0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
  	0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
  	0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
  	0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f,
  	0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
  	0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
  }
  
  // sevenBitU returns the unsigned LEB128 encoding of v if v is seven bits and nil otherwise.
  // The contents of the returned slice must not be modified.
  func sevenBitU(v int64) []byte {
  	if uint64(v) < uint64(len(sevenbits)) {
  		return sevenbits[v : v+1]
  	}
  	return nil
  }
  
  // sevenBitS returns the signed LEB128 encoding of v if v is seven bits and nil otherwise.
  // The contents of the returned slice must not be modified.
  func sevenBitS(v int64) []byte {
  	if uint64(v) <= 63 {
  		return sevenbits[v : v+1]
  	}
  	if uint64(-v) <= 64 {
  		return sevenbits[128+v : 128+v+1]
  	}
  	return nil
  }
  
  // Uleb128put appends v to s using DWARF's unsigned LEB128 encoding.
  func Uleb128put(ctxt Context, s Sym, v int64) {
  	b := sevenBitU(v)
  	if b == nil {
  		var encbuf [20]byte
  		b = AppendUleb128(encbuf[:0], uint64(v))
  	}
  	ctxt.AddBytes(s, b)
  }
  
  // Sleb128put appends v to s using DWARF's signed LEB128 encoding.
  func Sleb128put(ctxt Context, s Sym, v int64) {
  	b := sevenBitS(v)
  	if b == nil {
  		var encbuf [20]byte
  		b = AppendSleb128(encbuf[:0], v)
  	}
  	ctxt.AddBytes(s, b)
  }
  
  /*
   * Defining Abbrevs.  This is hardcoded, and there will be
   * only a handful of them.  The DWARF spec places no restriction on
   * the ordering of attributes in the Abbrevs and DIEs, and we will
   * always write them out in the order of declaration in the abbrev.
   */
  type dwAttrForm struct {
  	attr uint16
  	form uint8
  }
  
  // Go-specific type attributes.
  const (
  	DW_AT_go_kind = 0x2900
  	DW_AT_go_key  = 0x2901
  	DW_AT_go_elem = 0x2902
  	// Attribute for DW_TAG_member of a struct type.
  	// Nonzero value indicates the struct field is an embedded field.
  	DW_AT_go_embedded_field = 0x2903
  
  	DW_AT_internal_location = 253 // params and locals; not emitted
  )
  
  // Index into the abbrevs table below.
  // Keep in sync with ispubname() and ispubtype() in ld/dwarf.go.
  // ispubtype considers >= NULLTYPE public
  const (
  	DW_ABRV_NULL = iota
  	DW_ABRV_COMPUNIT
  	DW_ABRV_FUNCTION
  	DW_ABRV_FUNCTION_ABSTRACT
  	DW_ABRV_FUNCTION_CONCRETE
  	DW_ABRV_INLINED_SUBROUTINE
  	DW_ABRV_INLINED_SUBROUTINE_RANGES
  	DW_ABRV_VARIABLE
  	DW_ABRV_INT_CONSTANT
  	DW_ABRV_AUTO
  	DW_ABRV_AUTO_LOCLIST
  	DW_ABRV_AUTO_ABSTRACT
  	DW_ABRV_AUTO_CONCRETE
  	DW_ABRV_AUTO_CONCRETE_LOCLIST
  	DW_ABRV_PARAM
  	DW_ABRV_PARAM_LOCLIST
  	DW_ABRV_PARAM_ABSTRACT
  	DW_ABRV_PARAM_CONCRETE
  	DW_ABRV_PARAM_CONCRETE_LOCLIST
  	DW_ABRV_LEXICAL_BLOCK_RANGES
  	DW_ABRV_LEXICAL_BLOCK_SIMPLE
  	DW_ABRV_STRUCTFIELD
  	DW_ABRV_FUNCTYPEPARAM
  	DW_ABRV_DOTDOTDOT
  	DW_ABRV_ARRAYRANGE
  	DW_ABRV_NULLTYPE
  	DW_ABRV_BASETYPE
  	DW_ABRV_ARRAYTYPE
  	DW_ABRV_CHANTYPE
  	DW_ABRV_FUNCTYPE
  	DW_ABRV_IFACETYPE
  	DW_ABRV_MAPTYPE
  	DW_ABRV_PTRTYPE
  	DW_ABRV_BARE_PTRTYPE // only for void*, no DW_AT_type attr to please gdb 6.
  	DW_ABRV_SLICETYPE
  	DW_ABRV_STRINGTYPE
  	DW_ABRV_STRUCTTYPE
  	DW_ABRV_TYPEDECL
  	DW_NABRV
  )
  
  type dwAbbrev struct {
  	tag      uint8
  	children uint8
  	attr     []dwAttrForm
  }
  
  var abbrevs = [DW_NABRV]dwAbbrev{
  	/* The mandatory DW_ABRV_NULL entry. */
  	{0, 0, []dwAttrForm{}},
  
  	/* COMPUNIT */
  	{
  		DW_TAG_compile_unit,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_language, DW_FORM_data1},
  			{DW_AT_stmt_list, DW_FORM_sec_offset},
  			{DW_AT_low_pc, DW_FORM_addr},
  			{DW_AT_ranges, DW_FORM_sec_offset},
  			{DW_AT_comp_dir, DW_FORM_string},
  			{DW_AT_producer, DW_FORM_string},
  		},
  	},
  
  	/* FUNCTION */
  	{
  		DW_TAG_subprogram,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_low_pc, DW_FORM_addr},
  			{DW_AT_high_pc, DW_FORM_addr},
  			{DW_AT_frame_base, DW_FORM_block1},
  			{DW_AT_decl_file, DW_FORM_data4},
  			{DW_AT_external, DW_FORM_flag},
  		},
  	},
  
  	/* FUNCTION_ABSTRACT */
  	{
  		DW_TAG_subprogram,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_inline, DW_FORM_data1},
  			{DW_AT_external, DW_FORM_flag},
  		},
  	},
  
  	/* FUNCTION_CONCRETE */
  	{
  		DW_TAG_subprogram,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_abstract_origin, DW_FORM_ref_addr},
  			{DW_AT_low_pc, DW_FORM_addr},
  			{DW_AT_high_pc, DW_FORM_addr},
  			{DW_AT_frame_base, DW_FORM_block1},
  		},
  	},
  
  	/* INLINED_SUBROUTINE */
  	{
  		DW_TAG_inlined_subroutine,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_abstract_origin, DW_FORM_ref_addr},
  			{DW_AT_low_pc, DW_FORM_addr},
  			{DW_AT_high_pc, DW_FORM_addr},
  			{DW_AT_call_file, DW_FORM_data4},
  			{DW_AT_call_line, DW_FORM_udata},
  		},
  	},
  
  	/* INLINED_SUBROUTINE_RANGES */
  	{
  		DW_TAG_inlined_subroutine,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_abstract_origin, DW_FORM_ref_addr},
  			{DW_AT_ranges, DW_FORM_sec_offset},
  			{DW_AT_call_file, DW_FORM_data4},
  			{DW_AT_call_line, DW_FORM_udata},
  		},
  	},
  
  	/* VARIABLE */
  	{
  		DW_TAG_variable,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_location, DW_FORM_block1},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_external, DW_FORM_flag},
  		},
  	},
  
  	/* INT CONSTANT */
  	{
  		DW_TAG_constant,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_const_value, DW_FORM_sdata},
  		},
  	},
  
  	/* AUTO */
  	{
  		DW_TAG_variable,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_decl_line, DW_FORM_udata},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_location, DW_FORM_block1},
  		},
  	},
  
  	/* AUTO_LOCLIST */
  	{
  		DW_TAG_variable,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_decl_line, DW_FORM_udata},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_location, DW_FORM_sec_offset},
  		},
  	},
  
  	/* AUTO_ABSTRACT */
  	{
  		DW_TAG_variable,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_decl_line, DW_FORM_udata},
  			{DW_AT_type, DW_FORM_ref_addr},
  		},
  	},
  
  	/* AUTO_CONCRETE */
  	{
  		DW_TAG_variable,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_abstract_origin, DW_FORM_ref_addr},
  			{DW_AT_location, DW_FORM_block1},
  		},
  	},
  
  	/* AUTO_CONCRETE_LOCLIST */
  	{
  		DW_TAG_variable,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_abstract_origin, DW_FORM_ref_addr},
  			{DW_AT_location, DW_FORM_sec_offset},
  		},
  	},
  
  	/* PARAM */
  	{
  		DW_TAG_formal_parameter,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_variable_parameter, DW_FORM_flag},
  			{DW_AT_decl_line, DW_FORM_udata},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_location, DW_FORM_block1},
  		},
  	},
  
  	/* PARAM_LOCLIST */
  	{
  		DW_TAG_formal_parameter,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_variable_parameter, DW_FORM_flag},
  			{DW_AT_decl_line, DW_FORM_udata},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_location, DW_FORM_sec_offset},
  		},
  	},
  
  	/* PARAM_ABSTRACT */
  	{
  		DW_TAG_formal_parameter,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_variable_parameter, DW_FORM_flag},
  			{DW_AT_type, DW_FORM_ref_addr},
  		},
  	},
  
  	/* PARAM_CONCRETE */
  	{
  		DW_TAG_formal_parameter,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_abstract_origin, DW_FORM_ref_addr},
  			{DW_AT_location, DW_FORM_block1},
  		},
  	},
  
  	/* PARAM_CONCRETE_LOCLIST */
  	{
  		DW_TAG_formal_parameter,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_abstract_origin, DW_FORM_ref_addr},
  			{DW_AT_location, DW_FORM_sec_offset},
  		},
  	},
  
  	/* LEXICAL_BLOCK_RANGES */
  	{
  		DW_TAG_lexical_block,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_ranges, DW_FORM_sec_offset},
  		},
  	},
  
  	/* LEXICAL_BLOCK_SIMPLE */
  	{
  		DW_TAG_lexical_block,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_low_pc, DW_FORM_addr},
  			{DW_AT_high_pc, DW_FORM_addr},
  		},
  	},
  
  	/* STRUCTFIELD */
  	{
  		DW_TAG_member,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_data_member_location, DW_FORM_udata},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_go_embedded_field, DW_FORM_flag},
  		},
  	},
  
  	/* FUNCTYPEPARAM */
  	{
  		DW_TAG_formal_parameter,
  		DW_CHILDREN_no,
  
  		// No name!
  		[]dwAttrForm{
  			{DW_AT_type, DW_FORM_ref_addr},
  		},
  	},
  
  	/* DOTDOTDOT */
  	{
  		DW_TAG_unspecified_parameters,
  		DW_CHILDREN_no,
  		[]dwAttrForm{},
  	},
  
  	/* ARRAYRANGE */
  	{
  		DW_TAG_subrange_type,
  		DW_CHILDREN_no,
  
  		// No name!
  		[]dwAttrForm{
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_count, DW_FORM_udata},
  		},
  	},
  
  	// Below here are the types considered public by ispubtype
  	/* NULLTYPE */
  	{
  		DW_TAG_unspecified_type,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  		},
  	},
  
  	/* BASETYPE */
  	{
  		DW_TAG_base_type,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_encoding, DW_FORM_data1},
  			{DW_AT_byte_size, DW_FORM_data1},
  			{DW_AT_go_kind, DW_FORM_data1},
  		},
  	},
  
  	/* ARRAYTYPE */
  	// child is subrange with upper bound
  	{
  		DW_TAG_array_type,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_byte_size, DW_FORM_udata},
  			{DW_AT_go_kind, DW_FORM_data1},
  		},
  	},
  
  	/* CHANTYPE */
  	{
  		DW_TAG_typedef,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_go_kind, DW_FORM_data1},
  			{DW_AT_go_elem, DW_FORM_ref_addr},
  		},
  	},
  
  	/* FUNCTYPE */
  	{
  		DW_TAG_subroutine_type,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_byte_size, DW_FORM_udata},
  			// {DW_AT_type,	DW_FORM_ref_addr},
  			{DW_AT_go_kind, DW_FORM_data1},
  		},
  	},
  
  	/* IFACETYPE */
  	{
  		DW_TAG_typedef,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_go_kind, DW_FORM_data1},
  		},
  	},
  
  	/* MAPTYPE */
  	{
  		DW_TAG_typedef,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_go_kind, DW_FORM_data1},
  			{DW_AT_go_key, DW_FORM_ref_addr},
  			{DW_AT_go_elem, DW_FORM_ref_addr},
  		},
  	},
  
  	/* PTRTYPE */
  	{
  		DW_TAG_pointer_type,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_type, DW_FORM_ref_addr},
  			{DW_AT_go_kind, DW_FORM_data1},
  		},
  	},
  
  	/* BARE_PTRTYPE */
  	{
  		DW_TAG_pointer_type,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  		},
  	},
  
  	/* SLICETYPE */
  	{
  		DW_TAG_structure_type,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_byte_size, DW_FORM_udata},
  			{DW_AT_go_kind, DW_FORM_data1},
  			{DW_AT_go_elem, DW_FORM_ref_addr},
  		},
  	},
  
  	/* STRINGTYPE */
  	{
  		DW_TAG_structure_type,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_byte_size, DW_FORM_udata},
  			{DW_AT_go_kind, DW_FORM_data1},
  		},
  	},
  
  	/* STRUCTTYPE */
  	{
  		DW_TAG_structure_type,
  		DW_CHILDREN_yes,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_byte_size, DW_FORM_udata},
  			{DW_AT_go_kind, DW_FORM_data1},
  		},
  	},
  
  	/* TYPEDECL */
  	{
  		DW_TAG_typedef,
  		DW_CHILDREN_no,
  		[]dwAttrForm{
  			{DW_AT_name, DW_FORM_string},
  			{DW_AT_type, DW_FORM_ref_addr},
  		},
  	},
  }
  
  // GetAbbrev returns the contents of the .debug_abbrev section.
  func GetAbbrev() []byte {
  	var buf []byte
  	for i := 1; i < DW_NABRV; i++ {
  		// See section 7.5.3
  		buf = AppendUleb128(buf, uint64(i))
  		buf = AppendUleb128(buf, uint64(abbrevs[i].tag))
  		buf = append(buf, byte(abbrevs[i].children))
  		for _, f := range abbrevs[i].attr {
  			buf = AppendUleb128(buf, uint64(f.attr))
  			buf = AppendUleb128(buf, uint64(f.form))
  		}
  		buf = append(buf, 0, 0)
  	}
  	return append(buf, 0)
  }
  
  /*
   * Debugging Information Entries and their attributes.
   */
  
  // DWAttr represents an attribute of a DWDie.
  //
  // For DW_CLS_string and _block, value should contain the length, and
  // data the data, for _reference, value is 0 and data is a DWDie* to
  // the referenced instance, for all others, value is the whole thing
  // and data is null.
  type DWAttr struct {
  	Link  *DWAttr
  	Atr   uint16 // DW_AT_
  	Cls   uint8  // DW_CLS_
  	Value int64
  	Data  interface{}
  }
  
  // DWDie represents a DWARF debug info entry.
  type DWDie struct {
  	Abbrev int
  	Link   *DWDie
  	Child  *DWDie
  	Attr   *DWAttr
  	Sym    Sym
  }
  
  func putattr(ctxt Context, s Sym, abbrev int, form int, cls int, value int64, data interface{}) error {
  	switch form {
  	case DW_FORM_addr: // address
  		ctxt.AddAddress(s, data, value)
  
  	case DW_FORM_block1: // block
  		if cls == DW_CLS_ADDRESS {
  			ctxt.AddInt(s, 1, int64(1+ctxt.PtrSize()))
  			ctxt.AddInt(s, 1, DW_OP_addr)
  			ctxt.AddAddress(s, data, 0)
  			break
  		}
  
  		value &= 0xff
  		ctxt.AddInt(s, 1, value)
  		p := data.([]byte)[:value]
  		ctxt.AddBytes(s, p)
  
  	case DW_FORM_block2: // block
  		value &= 0xffff
  
  		ctxt.AddInt(s, 2, value)
  		p := data.([]byte)[:value]
  		ctxt.AddBytes(s, p)
  
  	case DW_FORM_block4: // block
  		value &= 0xffffffff
  
  		ctxt.AddInt(s, 4, value)
  		p := data.([]byte)[:value]
  		ctxt.AddBytes(s, p)
  
  	case DW_FORM_block: // block
  		Uleb128put(ctxt, s, value)
  
  		p := data.([]byte)[:value]
  		ctxt.AddBytes(s, p)
  
  	case DW_FORM_data1: // constant
  		ctxt.AddInt(s, 1, value)
  
  	case DW_FORM_data2: // constant
  		ctxt.AddInt(s, 2, value)
  
  	case DW_FORM_data4: // constant, {line,loclist,mac,rangelist}ptr
  		if cls == DW_CLS_PTR { // DW_AT_stmt_list and DW_AT_ranges
  			ctxt.AddSectionOffset(s, 4, data, value)
  			break
  		}
  		ctxt.AddInt(s, 4, value)
  
  	case DW_FORM_data8: // constant, {line,loclist,mac,rangelist}ptr
  		ctxt.AddInt(s, 8, value)
  
  	case DW_FORM_sdata: // constant
  		Sleb128put(ctxt, s, value)
  
  	case DW_FORM_udata: // constant
  		Uleb128put(ctxt, s, value)
  
  	case DW_FORM_string: // string
  		str := data.(string)
  		ctxt.AddString(s, str)
  		// TODO(ribrdb): verify padded strings are never used and remove this
  		for i := int64(len(str)); i < value; i++ {
  			ctxt.AddInt(s, 1, 0)
  		}
  
  	case DW_FORM_flag: // flag
  		if value != 0 {
  			ctxt.AddInt(s, 1, 1)
  		} else {
  			ctxt.AddInt(s, 1, 0)
  		}
  
  	// As of DWARF 3 the ref_addr is always 32 bits, unless emitting a large
  	// (> 4 GB of debug info aka "64-bit") unit, which we don't implement.
  	case DW_FORM_ref_addr: // reference to a DIE in the .info section
  		fallthrough
  	case DW_FORM_sec_offset: // offset into a DWARF section other than .info
  		if data == nil {
  			return fmt.Errorf("dwarf: null reference in %d", abbrev)
  		}
  		ctxt.AddSectionOffset(s, 4, data, value)
  
  	case DW_FORM_ref1, // reference within the compilation unit
  		DW_FORM_ref2,      // reference
  		DW_FORM_ref4,      // reference
  		DW_FORM_ref8,      // reference
  		DW_FORM_ref_udata, // reference
  
  		DW_FORM_strp,     // string
  		DW_FORM_indirect: // (see Section 7.5.3)
  		fallthrough
  	default:
  		return fmt.Errorf("dwarf: unsupported attribute form %d / class %d", form, cls)
  	}
  	return nil
  }
  
  // PutAttrs writes the attributes for a DIE to symbol 's'.
  //
  // Note that we can (and do) add arbitrary attributes to a DIE, but
  // only the ones actually listed in the Abbrev will be written out.
  func PutAttrs(ctxt Context, s Sym, abbrev int, attr *DWAttr) {
  Outer:
  	for _, f := range abbrevs[abbrev].attr {
  		for ap := attr; ap != nil; ap = ap.Link {
  			if ap.Atr == f.attr {
  				putattr(ctxt, s, abbrev, int(f.form), int(ap.Cls), ap.Value, ap.Data)
  				continue Outer
  			}
  		}
  
  		putattr(ctxt, s, abbrev, int(f.form), 0, 0, nil)
  	}
  }
  
  // HasChildren returns true if 'die' uses an abbrev that supports children.
  func HasChildren(die *DWDie) bool {
  	return abbrevs[die.Abbrev].children != 0
  }
  
  // PutIntConst writes a DIE for an integer constant
  func PutIntConst(ctxt Context, info, typ Sym, name string, val int64) {
  	Uleb128put(ctxt, info, DW_ABRV_INT_CONSTANT)
  	putattr(ctxt, info, DW_ABRV_INT_CONSTANT, DW_FORM_string, DW_CLS_STRING, int64(len(name)), name)
  	putattr(ctxt, info, DW_ABRV_INT_CONSTANT, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, typ)
  	putattr(ctxt, info, DW_ABRV_INT_CONSTANT, DW_FORM_sdata, DW_CLS_CONSTANT, val, nil)
  }
  
  // PutRanges writes a range table to sym. All addresses in ranges are
  // relative to some base address. If base is not nil, then they're
  // relative to the start of base. If base is nil, then the caller must
  // arrange a base address some other way (such as a DW_AT_low_pc
  // attribute).
  func PutRanges(ctxt Context, sym Sym, base Sym, ranges []Range) {
  	ps := ctxt.PtrSize()
  	// Write ranges.
  	// We do not emit base address entries here, even though they would reduce
  	// the number of relocations, because dsymutil (which is used on macOS when
  	// linking externally) does not support them.
  	for _, r := range ranges {
  		if base == nil {
  			ctxt.AddInt(sym, ps, r.Start)
  			ctxt.AddInt(sym, ps, r.End)
  		} else {
  			ctxt.AddCURelativeAddress(sym, base, r.Start)
  			ctxt.AddCURelativeAddress(sym, base, r.End)
  		}
  	}
  	// Write trailer.
  	ctxt.AddInt(sym, ps, 0)
  	ctxt.AddInt(sym, ps, 0)
  }
  
  // Return TRUE if the inlined call in the specified slot is empty,
  // meaning it has a zero-length range (no instructions), and all
  // of its children are empty.
  func isEmptyInlinedCall(slot int, calls *InlCalls) bool {
  	ic := &calls.Calls[slot]
  	if ic.InlIndex == -2 {
  		return true
  	}
  	live := false
  	for _, k := range ic.Children {
  		if !isEmptyInlinedCall(k, calls) {
  			live = true
  		}
  	}
  	if len(ic.Ranges) > 0 {
  		live = true
  	}
  	if !live {
  		ic.InlIndex = -2
  	}
  	return !live
  }
  
  // Slot -1:    return top-level inlines
  // Slot >= 0:  return children of that slot
  func inlChildren(slot int, calls *InlCalls) []int {
  	var kids []int
  	if slot != -1 {
  		for _, k := range calls.Calls[slot].Children {
  			if !isEmptyInlinedCall(k, calls) {
  				kids = append(kids, k)
  			}
  		}
  	} else {
  		for k := 0; k < len(calls.Calls); k += 1 {
  			if calls.Calls[k].Root && !isEmptyInlinedCall(k, calls) {
  				kids = append(kids, k)
  			}
  		}
  	}
  	return kids
  }
  
  func inlinedVarTable(inlcalls *InlCalls) map[*Var]bool {
  	vars := make(map[*Var]bool)
  	for _, ic := range inlcalls.Calls {
  		for _, v := range ic.InlVars {
  			vars[v] = true
  		}
  	}
  	return vars
  }
  
  // The s.Scopes slice contains variables were originally part of the
  // function being emitted, as well as variables that were imported
  // from various callee functions during the inlining process. This
  // function prunes out any variables from the latter category (since
  // they will be emitted as part of DWARF inlined_subroutine DIEs) and
  // then generates scopes for vars in the former category.
  func putPrunedScopes(ctxt Context, s *FnState, fnabbrev int) error {
  	if len(s.Scopes) == 0 {
  		return nil
  	}
  	scopes := make([]Scope, len(s.Scopes), len(s.Scopes))
  	pvars := inlinedVarTable(&s.InlCalls)
  	for k, s := range s.Scopes {
  		var pruned Scope = Scope{Parent: s.Parent, Ranges: s.Ranges}
  		for i := 0; i < len(s.Vars); i++ {
  			_, found := pvars[s.Vars[i]]
  			if !found {
  				pruned.Vars = append(pruned.Vars, s.Vars[i])
  			}
  		}
  		sort.Sort(byChildIndex(pruned.Vars))
  		scopes[k] = pruned
  	}
  	var encbuf [20]byte
  	if putscope(ctxt, s, scopes, 0, fnabbrev, encbuf[:0]) < int32(len(scopes)) {
  		return errors.New("multiple toplevel scopes")
  	}
  	return nil
  }
  
  // Emit DWARF attributes and child DIEs for an 'abstract' subprogram.
  // The abstract subprogram DIE for a function contains its
  // location-independent attributes (name, type, etc). Other instances
  // of the function (any inlined copy of it, or the single out-of-line
  // 'concrete' instance) will contain a pointer back to this abstract
  // DIE (as a space-saving measure, so that name/type etc doesn't have
  // to be repeated for each inlined copy).
  func PutAbstractFunc(ctxt Context, s *FnState) error {
  
  	if logDwarf {
  		ctxt.Logf("PutAbstractFunc(%v)\n", s.Absfn)
  	}
  
  	abbrev := DW_ABRV_FUNCTION_ABSTRACT
  	Uleb128put(ctxt, s.Absfn, int64(abbrev))
  
  	fullname := s.Name
  	if strings.HasPrefix(s.Name, "\"\".") {
  		// Generate a fully qualified name for the function in the
  		// abstract case. This is so as to avoid the need for the
  		// linker to process the DIE with patchDWARFName(); we can't
  		// allow the name attribute of an abstract subprogram DIE to
  		// be rewritten, since it would change the offsets of the
  		// child DIEs (which we're relying on in order for abstract
  		// origin references to work).
  		fullname = s.Importpath + "." + s.Name[3:]
  	}
  	putattr(ctxt, s.Absfn, abbrev, DW_FORM_string, DW_CLS_STRING, int64(len(fullname)), fullname)
  
  	// DW_AT_inlined value
  	putattr(ctxt, s.Absfn, abbrev, DW_FORM_data1, DW_CLS_CONSTANT, int64(DW_INL_inlined), nil)
  
  	var ev int64
  	if s.External {
  		ev = 1
  	}
  	putattr(ctxt, s.Absfn, abbrev, DW_FORM_flag, DW_CLS_FLAG, ev, 0)
  
  	// Child variables (may be empty)
  	var flattened []*Var
  
  	// This slice will hold the offset in bytes for each child var DIE
  	// with respect to the start of the parent subprogram DIE.
  	var offsets []int32
  
  	// Scopes/vars
  	if len(s.Scopes) > 0 {
  		// For abstract subprogram DIEs we want to flatten out scope info:
  		// lexical scope DIEs contain range and/or hi/lo PC attributes,
  		// which we explicitly don't want for the abstract subprogram DIE.
  		pvars := inlinedVarTable(&s.InlCalls)
  		for _, scope := range s.Scopes {
  			for i := 0; i < len(scope.Vars); i++ {
  				_, found := pvars[scope.Vars[i]]
  				if found || !scope.Vars[i].IsInAbstract {
  					continue
  				}
  				flattened = append(flattened, scope.Vars[i])
  			}
  		}
  		if len(flattened) > 0 {
  			sort.Sort(byChildIndex(flattened))
  
  			if logDwarf {
  				ctxt.Logf("putAbstractScope(%v): vars:", s.Info)
  				for i, v := range flattened {
  					ctxt.Logf(" %d:%s", i, v.Name)
  				}
  				ctxt.Logf("\n")
  			}
  
  			// This slice will hold the offset in bytes for each child
  			// variable DIE with respect to the start of the parent
  			// subprogram DIE.
  			for _, v := range flattened {
  				offsets = append(offsets, int32(ctxt.CurrentOffset(s.Absfn)))
  				putAbstractVar(ctxt, s.Absfn, v)
  			}
  		}
  	}
  	ctxt.RecordChildDieOffsets(s.Absfn, flattened, offsets)
  
  	Uleb128put(ctxt, s.Absfn, 0)
  	return nil
  }
  
  // Emit DWARF attributes and child DIEs for an inlined subroutine. The
  // first attribute of an inlined subroutine DIE is a reference back to
  // its corresponding 'abstract' DIE (containing location-independent
  // attributes such as name, type, etc). Inlined subroutine DIEs can
  // have other inlined subroutine DIEs as children.
  func PutInlinedFunc(ctxt Context, s *FnState, callersym Sym, callIdx int) error {
  	ic := s.InlCalls.Calls[callIdx]
  	callee := ic.AbsFunSym
  
  	abbrev := DW_ABRV_INLINED_SUBROUTINE_RANGES
  	if len(ic.Ranges) == 1 {
  		abbrev = DW_ABRV_INLINED_SUBROUTINE
  	}
  	Uleb128put(ctxt, s.Info, int64(abbrev))
  
  	if logDwarf {
  		ctxt.Logf("PutInlinedFunc(caller=%v,callee=%v,abbrev=%d)\n", callersym, callee, abbrev)
  	}
  
  	// Abstract origin.
  	putattr(ctxt, s.Info, abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, callee)
  
  	if abbrev == DW_ABRV_INLINED_SUBROUTINE_RANGES {
  		putattr(ctxt, s.Info, abbrev, DW_FORM_sec_offset, DW_CLS_PTR, s.Ranges.Len(), s.Ranges)
  		PutRanges(ctxt, s.Ranges, s.StartPC, ic.Ranges)
  	} else {
  		st := ic.Ranges[0].Start
  		en := ic.Ranges[0].End
  		putattr(ctxt, s.Info, abbrev, DW_FORM_addr, DW_CLS_ADDRESS, st, s.StartPC)
  		putattr(ctxt, s.Info, abbrev, DW_FORM_addr, DW_CLS_ADDRESS, en, s.StartPC)
  	}
  
  	// Emit call file, line attrs.
  	ctxt.AddFileRef(s.Info, ic.CallFile)
  	putattr(ctxt, s.Info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(ic.CallLine), nil)
  
  	// Variables associated with this inlined routine instance.
  	vars := ic.InlVars
  	sort.Sort(byChildIndex(vars))
  	inlIndex := ic.InlIndex
  	var encbuf [20]byte
  	for _, v := range vars {
  		if !v.IsInAbstract {
  			continue
  		}
  		putvar(ctxt, s, v, callee, abbrev, inlIndex, encbuf[:0])
  	}
  
  	// Children of this inline.
  	for _, sib := range inlChildren(callIdx, &s.InlCalls) {
  		absfn := s.InlCalls.Calls[sib].AbsFunSym
  		err := PutInlinedFunc(ctxt, s, absfn, sib)
  		if err != nil {
  			return err
  		}
  	}
  
  	Uleb128put(ctxt, s.Info, 0)
  	return nil
  }
  
  // Emit DWARF attributes and child DIEs for a 'concrete' subprogram,
  // meaning the out-of-line copy of a function that was inlined at some
  // point during the compilation of its containing package. The first
  // attribute for a concrete DIE is a reference to the 'abstract' DIE
  // for the function (which holds location-independent attributes such
  // as name, type), then the remainder of the attributes are specific
  // to this instance (location, frame base, etc).
  func PutConcreteFunc(ctxt Context, s *FnState) error {
  	if logDwarf {
  		ctxt.Logf("PutConcreteFunc(%v)\n", s.Info)
  	}
  	abbrev := DW_ABRV_FUNCTION_CONCRETE
  	Uleb128put(ctxt, s.Info, int64(abbrev))
  
  	// Abstract origin.
  	putattr(ctxt, s.Info, abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, s.Absfn)
  
  	// Start/end PC.
  	putattr(ctxt, s.Info, abbrev, DW_FORM_addr, DW_CLS_ADDRESS, 0, s.StartPC)
  	putattr(ctxt, s.Info, abbrev, DW_FORM_addr, DW_CLS_ADDRESS, s.Size, s.StartPC)
  
  	// cfa / frame base
  	putattr(ctxt, s.Info, abbrev, DW_FORM_block1, DW_CLS_BLOCK, 1, []byte{DW_OP_call_frame_cfa})
  
  	// Scopes
  	if err := putPrunedScopes(ctxt, s, abbrev); err != nil {
  		return err
  	}
  
  	// Inlined subroutines.
  	for _, sib := range inlChildren(-1, &s.InlCalls) {
  		absfn := s.InlCalls.Calls[sib].AbsFunSym
  		err := PutInlinedFunc(ctxt, s, absfn, sib)
  		if err != nil {
  			return err
  		}
  	}
  
  	Uleb128put(ctxt, s.Info, 0)
  	return nil
  }
  
  // Emit DWARF attributes and child DIEs for a subprogram. Here
  // 'default' implies that the function in question was not inlined
  // when its containing package was compiled (hence there is no need to
  // emit an abstract version for it to use as a base for inlined
  // routine records).
  func PutDefaultFunc(ctxt Context, s *FnState) error {
  	if logDwarf {
  		ctxt.Logf("PutDefaultFunc(%v)\n", s.Info)
  	}
  	abbrev := DW_ABRV_FUNCTION
  	Uleb128put(ctxt, s.Info, int64(abbrev))
  
  	putattr(ctxt, s.Info, DW_ABRV_FUNCTION, DW_FORM_string, DW_CLS_STRING, int64(len(s.Name)), s.Name)
  	putattr(ctxt, s.Info, abbrev, DW_FORM_addr, DW_CLS_ADDRESS, 0, s.StartPC)
  	putattr(ctxt, s.Info, abbrev, DW_FORM_addr, DW_CLS_ADDRESS, s.Size, s.StartPC)
  	putattr(ctxt, s.Info, abbrev, DW_FORM_block1, DW_CLS_BLOCK, 1, []byte{DW_OP_call_frame_cfa})
  	ctxt.AddFileRef(s.Info, s.Filesym)
  
  	var ev int64
  	if s.External {
  		ev = 1
  	}
  	putattr(ctxt, s.Info, abbrev, DW_FORM_flag, DW_CLS_FLAG, ev, 0)
  
  	// Scopes
  	if err := putPrunedScopes(ctxt, s, abbrev); err != nil {
  		return err
  	}
  
  	// Inlined subroutines.
  	for _, sib := range inlChildren(-1, &s.InlCalls) {
  		absfn := s.InlCalls.Calls[sib].AbsFunSym
  		err := PutInlinedFunc(ctxt, s, absfn, sib)
  		if err != nil {
  			return err
  		}
  	}
  
  	Uleb128put(ctxt, s.Info, 0)
  	return nil
  }
  
  func putscope(ctxt Context, s *FnState, scopes []Scope, curscope int32, fnabbrev int, encbuf []byte) int32 {
  
  	if logDwarf {
  		ctxt.Logf("putscope(%v,%d): vars:", s.Info, curscope)
  		for i, v := range scopes[curscope].Vars {
  			ctxt.Logf(" %d:%d:%s", i, v.ChildIndex, v.Name)
  		}
  		ctxt.Logf("\n")
  	}
  
  	for _, v := range scopes[curscope].Vars {
  		putvar(ctxt, s, v, s.Absfn, fnabbrev, -1, encbuf)
  	}
  	this := curscope
  	curscope++
  	for curscope < int32(len(scopes)) {
  		scope := scopes[curscope]
  		if scope.Parent != this {
  			return curscope
  		}
  
  		if len(scope.Ranges) == 1 {
  			Uleb128put(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_SIMPLE)
  			putattr(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_SIMPLE, DW_FORM_addr, DW_CLS_ADDRESS, scope.Ranges[0].Start, s.StartPC)
  			putattr(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_SIMPLE, DW_FORM_addr, DW_CLS_ADDRESS, scope.Ranges[0].End, s.StartPC)
  		} else {
  			Uleb128put(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_RANGES)
  			putattr(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_RANGES, DW_FORM_sec_offset, DW_CLS_PTR, s.Ranges.Len(), s.Ranges)
  
  			PutRanges(ctxt, s.Ranges, s.StartPC, scope.Ranges)
  		}
  
  		curscope = putscope(ctxt, s, scopes, curscope, fnabbrev, encbuf)
  		Uleb128put(ctxt, s.Info, 0)
  	}
  	return curscope
  }
  
  // Given a default var abbrev code, select corresponding concrete code.
  func concreteVarAbbrev(varAbbrev int) int {
  	switch varAbbrev {
  	case DW_ABRV_AUTO:
  		return DW_ABRV_AUTO_CONCRETE
  	case DW_ABRV_PARAM:
  		return DW_ABRV_PARAM_CONCRETE
  	case DW_ABRV_AUTO_LOCLIST:
  		return DW_ABRV_AUTO_CONCRETE_LOCLIST
  	case DW_ABRV_PARAM_LOCLIST:
  		return DW_ABRV_PARAM_CONCRETE_LOCLIST
  	default:
  		panic("should never happen")
  	}
  }
  
  // Pick the correct abbrev code for variable or parameter DIE.
  func determineVarAbbrev(v *Var, fnabbrev int) (int, bool, bool) {
  	abbrev := v.Abbrev
  
  	// If the variable was entirely optimized out, don't emit a location list;
  	// convert to an inline abbreviation and emit an empty location.
  	missing := false
  	switch {
  	case abbrev == DW_ABRV_AUTO_LOCLIST && len(v.LocationList) == 0:
  		missing = true
  		abbrev = DW_ABRV_AUTO
  	case abbrev == DW_ABRV_PARAM_LOCLIST && len(v.LocationList) == 0:
  		missing = true
  		abbrev = DW_ABRV_PARAM
  	}
  
  	// Determine whether to use a concrete variable or regular variable DIE.
  	concrete := true
  	switch fnabbrev {
  	case DW_ABRV_FUNCTION:
  		concrete = false
  		break
  	case DW_ABRV_FUNCTION_CONCRETE:
  		// If we're emitting a concrete subprogram DIE and the variable
  		// in question is not part of the corresponding abstract function DIE,
  		// then use the default (non-concrete) abbrev for this param.
  		if !v.IsInAbstract {
  			concrete = false
  		}
  	case DW_ABRV_INLINED_SUBROUTINE, DW_ABRV_INLINED_SUBROUTINE_RANGES:
  	default:
  		panic("should never happen")
  	}
  
  	// Select proper abbrev based on concrete/non-concrete
  	if concrete {
  		abbrev = concreteVarAbbrev(abbrev)
  	}
  
  	return abbrev, missing, concrete
  }
  
  func abbrevUsesLoclist(abbrev int) bool {
  	switch abbrev {
  	case DW_ABRV_AUTO_LOCLIST, DW_ABRV_AUTO_CONCRETE_LOCLIST,
  		DW_ABRV_PARAM_LOCLIST, DW_ABRV_PARAM_CONCRETE_LOCLIST:
  		return true
  	default:
  		return false
  	}
  }
  
  // Emit DWARF attributes for a variable belonging to an 'abstract' subprogram.
  func putAbstractVar(ctxt Context, info Sym, v *Var) {
  	// Remap abbrev
  	abbrev := v.Abbrev
  	switch abbrev {
  	case DW_ABRV_AUTO, DW_ABRV_AUTO_LOCLIST:
  		abbrev = DW_ABRV_AUTO_ABSTRACT
  	case DW_ABRV_PARAM, DW_ABRV_PARAM_LOCLIST:
  		abbrev = DW_ABRV_PARAM_ABSTRACT
  	}
  
  	Uleb128put(ctxt, info, int64(abbrev))
  	putattr(ctxt, info, abbrev, DW_FORM_string, DW_CLS_STRING, int64(len(v.Name)), v.Name)
  
  	// Isreturn attribute if this is a param
  	if abbrev == DW_ABRV_PARAM_ABSTRACT {
  		var isReturn int64
  		if v.IsReturnValue {
  			isReturn = 1
  		}
  		putattr(ctxt, info, abbrev, DW_FORM_flag, DW_CLS_FLAG, isReturn, nil)
  	}
  
  	// Line
  	if abbrev != DW_ABRV_PARAM_ABSTRACT {
  		// See issue 23374 for more on why decl line is skipped for abs params.
  		putattr(ctxt, info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(v.DeclLine), nil)
  	}
  
  	// Type
  	putattr(ctxt, info, abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, v.Type)
  
  	// Var has no children => no terminator
  }
  
  func putvar(ctxt Context, s *FnState, v *Var, absfn Sym, fnabbrev, inlIndex int, encbuf []byte) {
  	// Remap abbrev according to parent DIE abbrev
  	abbrev, missing, concrete := determineVarAbbrev(v, fnabbrev)
  
  	Uleb128put(ctxt, s.Info, int64(abbrev))
  
  	// Abstract origin for concrete / inlined case
  	if concrete {
  		// Here we are making a reference to a child DIE of an abstract
  		// function subprogram DIE. The child DIE has no LSym, so instead
  		// after the call to 'putattr' below we make a call to register
  		// the child DIE reference.
  		putattr(ctxt, s.Info, abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, absfn)
  		ctxt.RecordDclReference(s.Info, absfn, int(v.ChildIndex), inlIndex)
  	} else {
  		// Var name, line for abstract and default cases
  		n := v.Name
  		putattr(ctxt, s.Info, abbrev, DW_FORM_string, DW_CLS_STRING, int64(len(n)), n)
  		if abbrev == DW_ABRV_PARAM || abbrev == DW_ABRV_PARAM_LOCLIST || abbrev == DW_ABRV_PARAM_ABSTRACT {
  			var isReturn int64
  			if v.IsReturnValue {
  				isReturn = 1
  			}
  			putattr(ctxt, s.Info, abbrev, DW_FORM_flag, DW_CLS_FLAG, isReturn, nil)
  		}
  		putattr(ctxt, s.Info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(v.DeclLine), nil)
  		putattr(ctxt, s.Info, abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, v.Type)
  	}
  
  	if abbrevUsesLoclist(abbrev) {
  		putattr(ctxt, s.Info, abbrev, DW_FORM_sec_offset, DW_CLS_PTR, int64(s.Loc.Len()), s.Loc)
  		addLocList(ctxt, s.Loc, s.StartPC, v, encbuf)
  	} else {
  		loc := encbuf[:0]
  		switch {
  		case missing:
  			break // no location
  		case v.StackOffset == 0:
  			loc = append(loc, DW_OP_call_frame_cfa)
  		default:
  			loc = append(loc, DW_OP_fbreg)
  			loc = AppendSleb128(loc, int64(v.StackOffset))
  		}
  		putattr(ctxt, s.Info, abbrev, DW_FORM_block1, DW_CLS_BLOCK, int64(len(loc)), loc)
  	}
  
  	// Var has no children => no terminator
  }
  
  func addLocList(ctxt Context, listSym, startPC Sym, v *Var, encbuf []byte) {
  	// Base address entry: max ptr followed by the base address.
  	ctxt.AddInt(listSym, ctxt.PtrSize(), ^0)
  	ctxt.AddAddress(listSym, startPC, 0)
  	for _, entry := range v.LocationList {
  		ctxt.AddInt(listSym, ctxt.PtrSize(), entry.StartPC)
  		ctxt.AddInt(listSym, ctxt.PtrSize(), entry.EndPC)
  		locBuf := encbuf[:0]
  		for _, piece := range entry.Pieces {
  			if !piece.Missing {
  				if piece.OnStack {
  					if piece.StackOffset == 0 {
  						locBuf = append(locBuf, DW_OP_call_frame_cfa)
  					} else {
  						locBuf = append(locBuf, DW_OP_fbreg)
  						locBuf = AppendSleb128(locBuf, int64(piece.StackOffset))
  					}
  				} else {
  					if piece.RegNum < 32 {
  						locBuf = append(locBuf, DW_OP_reg0+byte(piece.RegNum))
  					} else {
  						locBuf = append(locBuf, DW_OP_regx)
  						locBuf = AppendUleb128(locBuf, uint64(piece.RegNum))
  					}
  				}
  			}
  			if len(entry.Pieces) > 1 {
  				locBuf = append(locBuf, DW_OP_piece)
  				locBuf = AppendUleb128(locBuf, uint64(piece.Length))
  			}
  		}
  		ctxt.AddInt(listSym, 2, int64(len(locBuf)))
  		ctxt.AddBytes(listSym, locBuf)
  	}
  	// End list
  	ctxt.AddInt(listSym, ctxt.PtrSize(), 0)
  	ctxt.AddInt(listSym, ctxt.PtrSize(), 0)
  }
  
  // VarsByOffset attaches the methods of sort.Interface to []*Var,
  // sorting in increasing StackOffset.
  type VarsByOffset []*Var
  
  func (s VarsByOffset) Len() int           { return len(s) }
  func (s VarsByOffset) Less(i, j int) bool { return s[i].StackOffset < s[j].StackOffset }
  func (s VarsByOffset) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
  
  // byChildIndex implements sort.Interface for []*dwarf.Var by child index.
  type byChildIndex []*Var
  
  func (s byChildIndex) Len() int           { return len(s) }
  func (s byChildIndex) Less(i, j int) bool { return s[i].ChildIndex < s[j].ChildIndex }
  func (s byChildIndex) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
  

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