gtsocial-umbx

dwarf.go (43976B)

---

 // 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 (
 	"bytes"
 	"github.com/twitchyliquid64/golang-asm/objabi"
 	"errors"
 	"fmt"
 	"os/exec"
 	"sort"
 	"strconv"
 	"strings"
 )
 
 // InfoPrefix is the prefix for all the symbols containing DWARF info entries.
 const InfoPrefix = "go.info."
 
 // 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 {
 	Length(dwarfContext interface{}) int64
 }
 
 // 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
 	// This package can't use the ssa package, so it can't mention ssa.FuncDebug,
 	// so indirect through a closure.
 	PutLocationList func(listSym, startPC Sym)
 	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
 	UseBASEntries bool
 }
 
 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
 }
 
 // AppendRange adds r to s, if r is non-empty.
 // If possible, it extends the last Range in s.Ranges; if not, it creates a new one.
 func (s *Scope) AppendRange(r Range) {
 	if r.End <= r.Start {
 		return
 	}
 	i := len(s.Ranges)
 	if i > 0 && s.Ranges[i-1].End == r.Start {
 		s.Ranges[i-1].End = r.End
 		return
 	}
 	s.Ranges = append(s.Ranges, r)
 }
 
 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)
 	AddDWARFAddrSectionOffset(s Sym, 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 on a per-platform basis (that is,
  * each platform will see a fixed abbrev table for all objects); the number
  * of abbrev entries is fairly small (compared to C++ objects).  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_go_runtime_type   = 0x2904
 
 	DW_AT_go_package_name = 0x2905 // Attribute for DW_TAG_compile_unit
 
 	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_COMPUNIT_TEXTLESS
 	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 abbrevsFinalized bool
 
 // expandPseudoForm takes an input DW_FORM_xxx value and translates it
 // into a platform-appropriate concrete form. Existing concrete/real
 // DW_FORM values are left untouched. For the moment the only
 // pseudo-form is DW_FORM_udata_pseudo, which gets expanded to
 // DW_FORM_data4 on Darwin and DW_FORM_udata everywhere else. See
 // issue #31459 for more context.
 func expandPseudoForm(form uint8) uint8 {
 	// Is this a pseudo-form?
 	if form != DW_FORM_udata_pseudo {
 		return form
 	}
 	expandedForm := DW_FORM_udata
 	if objabi.GOOS == "darwin" {
 		expandedForm = DW_FORM_data4
 	}
 	return uint8(expandedForm)
 }
 
 // Abbrevs() returns the finalized abbrev array for the platform,
 // expanding any DW_FORM pseudo-ops to real values.
 func Abbrevs() []dwAbbrev {
 	if abbrevsFinalized {
 		return abbrevs[:]
 	}
 	for i := 1; i < DW_NABRV; i++ {
 		for j := 0; j < len(abbrevs[i].attr); j++ {
 			abbrevs[i].attr[j].form = expandPseudoForm(abbrevs[i].attr[j].form)
 		}
 	}
 	abbrevsFinalized = true
 	return abbrevs[:]
 }
 
 // abbrevs is a raw table of abbrev entries; it needs to be post-processed
 // by the Abbrevs() function above prior to being consumed, to expand
 // the 'pseudo-form' entries below to real DWARF form values.
 
 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},
 			{DW_AT_go_package_name, DW_FORM_string},
 		},
 	},
 
 	/* COMPUNIT_TEXTLESS */
 	{
 		DW_TAG_compile_unit,
 		DW_CHILDREN_yes,
 		[]dwAttrForm{
 			{DW_AT_name, DW_FORM_string},
 			{DW_AT_language, DW_FORM_data1},
 			{DW_AT_comp_dir, DW_FORM_string},
 			{DW_AT_producer, DW_FORM_string},
 			{DW_AT_go_package_name, 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_pseudo}, // pseudo-form
 		},
 	},
 
 	/* 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_pseudo}, // pseudo-form
 		},
 	},
 
 	/* 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},
 			{DW_AT_go_runtime_type, DW_FORM_addr},
 		},
 	},
 
 	/* 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},
 			{DW_AT_go_runtime_type, DW_FORM_addr},
 		},
 	},
 
 	/* 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_runtime_type, DW_FORM_addr},
 			{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_go_kind, DW_FORM_data1},
 			{DW_AT_go_runtime_type, DW_FORM_addr},
 		},
 	},
 
 	/* 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},
 			{DW_AT_go_runtime_type, DW_FORM_addr},
 		},
 	},
 
 	/* 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_runtime_type, DW_FORM_addr},
 			{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},
 			{DW_AT_go_runtime_type, DW_FORM_addr},
 		},
 	},
 
 	/* 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_runtime_type, DW_FORM_addr},
 			{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},
 			{DW_AT_go_runtime_type, DW_FORM_addr},
 		},
 	},
 
 	/* 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},
 			{DW_AT_go_runtime_type, DW_FORM_addr},
 		},
 	},
 
 	/* 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 {
 	abbrevs := Abbrevs()
 	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, 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
 		// Allow nil addresses for DW_AT_go_runtime_type.
 		if data == nil && value == 0 {
 			ctxt.AddInt(s, ctxt.PtrSize(), 0)
 			break
 		}
 		if cls == DW_CLS_GO_TYPEREF {
 			ctxt.AddSectionOffset(s, ctxt.PtrSize(), data, value)
 			break
 		}
 		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.AddDWARFAddrSectionOffset(s, 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.AddDWARFAddrSectionOffset(s, 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) {
 	abbrevs := Abbrevs()
 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 reports whether 'die' uses an abbrev that supports children.
 func HasChildren(die *DWDie) bool {
 	abbrevs := Abbrevs()
 	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)
 }
 
 // PutBasedRanges writes a range table to sym. All addresses in ranges are
 // relative to some base address, which must be arranged by the caller
 // (e.g., with a DW_AT_low_pc attribute, or in a BASE-prefixed range).
 func PutBasedRanges(ctxt Context, sym Sym, ranges []Range) {
 	ps := ctxt.PtrSize()
 	// Write ranges.
 	for _, r := range ranges {
 		ctxt.AddInt(sym, ps, r.Start)
 		ctxt.AddInt(sym, ps, r.End)
 	}
 	// Write trailer.
 	ctxt.AddInt(sym, ps, 0)
 	ctxt.AddInt(sym, ps, 0)
 }
 
 // PutRanges writes a range table to s.Ranges.
 // All addresses in ranges are relative to s.base.
 func (s *FnState) PutRanges(ctxt Context, ranges []Range) {
 	ps := ctxt.PtrSize()
 	sym, base := s.Ranges, s.StartPC
 
 	if s.UseBASEntries {
 		// Using a Base Address Selection Entry reduces the number of relocations, but
 		// this is not done on macOS because it is not supported by dsymutil/dwarfdump/lldb
 		ctxt.AddInt(sym, ps, -1)
 		ctxt.AddAddress(sym, base, 0)
 		PutBasedRanges(ctxt, sym, ranges)
 		return
 	}
 
 	// Write ranges full of relocations
 	for _, r := range ranges {
 		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 = objabi.PathToPrefix(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.Length(ctxt), s.Ranges)
 		s.PutRanges(ctxt, 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)
 	form := int(expandPseudoForm(DW_FORM_udata_pseudo))
 	putattr(ctxt, s.Info, abbrev, form, 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))
 
 	// Expand '"".' to import path.
 	name := s.Name
 	if s.Importpath != "" {
 		name = strings.Replace(name, "\"\".", objabi.PathToPrefix(s.Importpath)+".", -1)
 	}
 
 	putattr(ctxt, s.Info, DW_ABRV_FUNCTION, DW_FORM_string, DW_CLS_STRING, int64(len(name)), 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(scopes[curscope].Vars) == 0 {
 			curscope = putscope(ctxt, s, scopes, curscope, fnabbrev, encbuf)
 			continue
 		}
 
 		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.Length(ctxt), s.Ranges)
 
 			s.PutRanges(ctxt, 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 && v.PutLocationList == nil:
 		missing = true
 		abbrev = DW_ABRV_AUTO
 	case abbrev == DW_ABRV_PARAM_LOCLIST && v.PutLocationList == nil:
 		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, s.Loc.Length(ctxt), s.Loc)
 		v.PutLocationList(s.Loc, s.StartPC)
 	} 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
 }
 
 // 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] }
 
 // IsDWARFEnabledOnAIX returns true if DWARF is possible on the
 // current extld.
 // AIX ld doesn't support DWARF with -bnoobjreorder with version
 // prior to 7.2.2.
 func IsDWARFEnabledOnAIXLd(extld string) (bool, error) {
 	out, err := exec.Command(extld, "-Wl,-V").CombinedOutput()
 	if err != nil {
 		// The normal output should display ld version and
 		// then fails because ".main" is not defined:
 		// ld: 0711-317 ERROR: Undefined symbol: .main
 		if !bytes.Contains(out, []byte("0711-317")) {
 			return false, fmt.Errorf("%s -Wl,-V failed: %v\n%s", extld, err, out)
 		}
 	}
 	// gcc -Wl,-V output should be:
 	//   /usr/bin/ld: LD X.X.X(date)
 	//   ...
 	out = bytes.TrimPrefix(out, []byte("/usr/bin/ld: LD "))
 	vers := string(bytes.Split(out, []byte("("))[0])
 	subvers := strings.Split(vers, ".")
 	if len(subvers) != 3 {
 		return false, fmt.Errorf("cannot parse %s -Wl,-V (%s): %v\n", extld, out, err)
 	}
 	if v, err := strconv.Atoi(subvers[0]); err != nil || v < 7 {
 		return false, nil
 	} else if v > 7 {
 		return true, nil
 	}
 	if v, err := strconv.Atoi(subvers[1]); err != nil || v < 2 {
 		return false, nil
 	} else if v > 2 {
 		return true, nil
 	}
 	if v, err := strconv.Atoi(subvers[2]); err != nil || v < 2 {
 		return false, nil
 	}
 	return true, nil
 }