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// Derived from Inferno utils/6l/l.h and related files.
// Copyright © 1994-1999 Lucent Technologies Inc. All rights reserved.
// Portions Copyright © 1995-1997 C H Forsyth (
// Portions Copyright © 1997-1999 Vita Nuova Limited
// Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (
// Portions Copyright © 2004,2006 Bruce Ellis
// Portions Copyright © 2005-2007 C H Forsyth (
// Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
// Portions Copyright © 2009 The Go Authors. All rights reserved.
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
package obj
import (
// An Addr is an argument to an instruction.
// The general forms and their encodings are:
// sym±offset(symkind)(reg)(index*scale)
// Memory reference at address &sym(symkind) + offset + reg + index*scale.
// Any of sym(symkind), ±offset, (reg), (index*scale), and *scale can be omitted.
// If (reg) and *scale are both omitted, the resulting expression (index) is parsed as (reg).
// To force a parsing as index*scale, write (index*1).
// Encoding:
// type = TYPE_MEM
// name = symkind (NAME_AUTO, ...) or 0 (NAME_NONE)
// sym = sym
// offset = ±offset
// reg = reg (REG_*)
// index = index (REG_*)
// scale = scale (1, 2, 4, 8)
// $<mem>
// Effective address of memory reference <mem>, defined above.
// Encoding: same as memory reference, but type = TYPE_ADDR.
// $<±integer value>
// This is a special case of $<mem>, in which only ±offset is present.
// It has a separate type for easy recognition.
// Encoding:
// type = TYPE_CONST
// offset = ±integer value
// *<mem>
// Indirect reference through memory reference <mem>, defined above.
// Only used on x86 for CALL/JMP *sym(SB), which calls/jumps to a function
// pointer stored in the data word sym(SB), not a function named sym(SB).
// Encoding: same as above, but type = TYPE_INDIR.
// $*$<mem>
// No longer used.
// On machines with actual SB registers, $*$<mem> forced the
// instruction encoding to use a full 32-bit constant, never a
// reference relative to SB.
// $<floating point literal>
// Floating point constant value.
// Encoding:
// type = TYPE_FCONST
// val = floating point value
// $<string literal, up to 8 chars>
// String literal value (raw bytes used for DATA instruction).
// Encoding:
// type = TYPE_SCONST
// val = string
// <register name>
// Any register: integer, floating point, control, segment, and so on.
// If looking for specific register kind, must check type and reg value range.
// Encoding:
// type = TYPE_REG
// reg = reg (REG_*)
// x(PC)
// Encoding:
// type = TYPE_BRANCH
// val = Prog* reference OR ELSE offset = target pc (branch takes priority)
// $±x-±y
// Final argument to TEXT, specifying local frame size x and argument size y.
// In this form, x and y are integer literals only, not arbitrary expressions.
// This avoids parsing ambiguities due to the use of - as a separator.
// The ± are optional.
// If the final argument to TEXT omits the -±y, the encoding should still
// use TYPE_TEXTSIZE (not TYPE_CONST), with u.argsize = ArgsSizeUnknown.
// Encoding:
// offset = x
// val = int32(y)
// reg<<shift, reg>>shift, reg->shift, reg@>shift
// Shifted register value, for ARM and ARM64.
// In this form, reg must be a register and shift can be a register or an integer constant.
// Encoding:
// type = TYPE_SHIFT
// On ARM:
// offset = (reg&15) | shifttype<<5 | count
// shifttype = 0, 1, 2, 3 for <<, >>, ->, @>
// count = (reg&15)<<8 | 1<<4 for a register shift count, (n&31)<<7 for an integer constant.
// On ARM64:
// offset = (reg&31)<<16 | shifttype<<22 | (count&63)<<10
// shifttype = 0, 1, 2 for <<, >>, ->
// (reg, reg)
// A destination register pair. When used as the last argument of an instruction,
// this form makes clear that both registers are destinations.
// Encoding:
// type = TYPE_REGREG
// reg = first register
// offset = second register
// [reg, reg, reg-reg]
// Register list for ARM, ARM64, 386/AMD64.
// Encoding:
// type = TYPE_REGLIST
// On ARM:
// offset = bit mask of registers in list; R0 is low bit.
// On ARM64:
// offset = register count (Q:size) | arrangement (opcode) | first register
// On 386/AMD64:
// reg = range low register
// offset = 2 packed registers + kind tag (see x86.EncodeRegisterRange)
// reg, reg
// Register pair for ARM.
// (reg+reg)
// Register pair for PPC64.
// Encoding:
// type = TYPE_MEM
// reg = first register
// index = second register
// scale = 1
// reg.[US]XT[BHWX]
// Register extension for ARM64
// Encoding:
// type = TYPE_REG
// reg = REG_[US]XT[BHWX] + register + shift amount
// offset = ((reg&31) << 16) | (exttype << 13) | (amount<<10)
// reg.<T>
// Register arrangement for ARM64 SIMD register
// e.g.: V1.S4, V2.S2, V7.D2, V2.H4, V6.B16
// Encoding:
// type = TYPE_REG
// reg = REG_ARNG + register + arrangement
// reg.<T>[index]
// Register element for ARM64
// Encoding:
// type = TYPE_REG
// reg = REG_ELEM + register + arrangement
// index = element index
type Addr struct {
Reg int16
Index int16
Scale int16 // Sometimes holds a register.
Type AddrType
Name AddrName
Class int8
Offset int64
Sym *LSym
// argument value:
// for TYPE_SCONST, a string
// for TYPE_FCONST, a float64
// for TYPE_BRANCH, a *Prog (optional)
// for TYPE_TEXTSIZE, an int32 (optional)
Val interface{}
type AddrName int8
const (
NAME_NONE AddrName = iota
// A reference to name@GOT(SB) is a reference to the entry in the global offset
// table for 'name'.
// Indicates that this is a reference to a TOC anchor.
//go:generate stringer -type AddrType
type AddrType uint8
const (
TYPE_NONE AddrType = iota
func (a *Addr) Target() *Prog {
if a.Type == TYPE_BRANCH && a.Val != nil {
return a.Val.(*Prog)
return nil
func (a *Addr) SetTarget(t *Prog) {
if a.Type != TYPE_BRANCH {
panic("setting branch target when type is not TYPE_BRANCH")
a.Val = t
// Prog describes a single machine instruction.
// The general instruction form is:
// (1) As.Scond From [, ...RestArgs], To
// (2) As.Scond From, Reg [, ...RestArgs], To, RegTo2
// where As is an opcode and the others are arguments:
// From, Reg are sources, and To, RegTo2 are destinations.
// RestArgs can hold additional sources and destinations.
// Usually, not all arguments are present.
// For example, MOVL R1, R2 encodes using only As=MOVL, From=R1, To=R2.
// The Scond field holds additional condition bits for systems (like arm)
// that have generalized conditional execution.
// (2) form is present for compatibility with older code,
// to avoid too much changes in a single swing.
// (1) scheme is enough to express any kind of operand combination.
// Jump instructions use the To.Val field to point to the target *Prog,
// which must be in the same linked list as the jump instruction.
// The Progs for a given function are arranged in a list linked through the Link field.
// Each Prog is charged to a specific source line in the debug information,
// specified by Pos.Line().
// Every Prog has a Ctxt field that defines its context.
// For performance reasons, Progs usually are usually bulk allocated, cached, and reused;
// those bulk allocators should always be used, rather than new(Prog).
// The other fields not yet mentioned are for use by the back ends and should
// be left zeroed by creators of Prog lists.
type Prog struct {
Ctxt *Link // linker context
Link *Prog // next Prog in linked list
From Addr // first source operand
RestArgs []AddrPos // can pack any operands that not fit into {Prog.From, Prog.To}
To Addr // destination operand (second is RegTo2 below)
Pool *Prog // constant pool entry, for arm,arm64 back ends
Forwd *Prog // for x86 back end
Rel *Prog // for x86, arm back ends
Pc int64 // for back ends or assembler: virtual or actual program counter, depending on phase
Pos src.XPos // source position of this instruction
Spadj int32 // effect of instruction on stack pointer (increment or decrement amount)
As As // assembler opcode
Reg int16 // 2nd source operand
RegTo2 int16 // 2nd destination operand
Mark uint16 // bitmask of arch-specific items
Optab uint16 // arch-specific opcode index
Scond uint8 // bits that describe instruction suffixes (e.g. ARM conditions)
Back uint8 // for x86 back end: backwards branch state
Ft uint8 // for x86 back end: type index of Prog.From
Tt uint8 // for x86 back end: type index of Prog.To
Isize uint8 // for x86 back end: size of the instruction in bytes
// Pos indicates whether the oprand is the source or the destination.
type AddrPos struct {
Pos OperandPos
type OperandPos int8
const (
Source OperandPos = iota
// From3Type returns p.GetFrom3().Type, or TYPE_NONE when
// p.GetFrom3() returns nil.
// Deprecated: for the same reasons as Prog.GetFrom3.
func (p *Prog) From3Type() AddrType {
if p.RestArgs == nil {
return TYPE_NONE
return p.RestArgs[0].Type
// GetFrom3 returns second source operand (the first is Prog.From).
// In combination with Prog.From and Prog.To it makes common 3 operand
// case easier to use.
// Should be used only when RestArgs is set with SetFrom3.
// Deprecated: better use RestArgs directly or define backend-specific getters.
// Introduced to simplify transition to []Addr.
// Usage of this is discouraged due to fragility and lack of guarantees.
func (p *Prog) GetFrom3() *Addr {
if p.RestArgs == nil {
return nil
return &p.RestArgs[0].Addr
// SetFrom3 assigns []Args{{a, 0}} to p.RestArgs.
// In pair with Prog.GetFrom3 it can help in emulation of Prog.From3.
// Deprecated: for the same reasons as Prog.GetFrom3.
func (p *Prog) SetFrom3(a Addr) {
p.RestArgs = []AddrPos{{a, Source}}
// SetTo2 assings []Args{{a, 1}} to p.RestArgs when the second destination
// operand does not fit into prog.RegTo2.
func (p *Prog) SetTo2(a Addr) {
p.RestArgs = []AddrPos{{a, Destination}}
// GetTo2 returns the second destination operand.
func (p *Prog) GetTo2() *Addr {
if p.RestArgs == nil {
return nil
return &p.RestArgs[0].Addr
// SetRestArgs assigns more than one source operands to p.RestArgs.
func (p *Prog) SetRestArgs(args []Addr) {
for i := range args {
p.RestArgs = append(p.RestArgs, AddrPos{args[i], Source})
// An As denotes an assembler opcode.
// There are some portable opcodes, declared here in package obj,
// that are common to all architectures.
// However, the majority of opcodes are arch-specific
// and are declared in their respective architecture's subpackage.
type As int16
// These are the portable opcodes.
const (
AXXX As = iota
// Each architecture is allotted a distinct subspace of opcode values
// for declaring its arch-specific opcodes.
// Within this subspace, the first arch-specific opcode should be
// at offset A_ARCHSPECIFIC.
// Subspaces are aligned to a power of two so opcodes can be masked
// with AMask and used as compact array indices.
const (
ABase386 = (1 + iota) << 11
AllowedOpCodes = 1 << 11 // The number of opcodes available for any given architecture.
AMask = AllowedOpCodes - 1 // AND with this to use the opcode as an array index.
// An LSym is the sort of symbol that is written to an object file.
// It represents Go symbols in a flat pkg+"."+name namespace.
type LSym struct {
Name string
Type objabi.SymKind
Size int64
Gotype *LSym
P []byte
R []Reloc
Extra *interface{} // *FuncInfo or *FileInfo, if present
Pkg string
PkgIdx int32
SymIdx int32
// A FuncInfo contains extra fields for STEXT symbols.
type FuncInfo struct {
Args int32
Locals int32
Align int32
FuncID objabi.FuncID
Text *Prog
Autot map[*LSym]struct{}
Pcln Pcln
InlMarks []InlMark
dwarfInfoSym *LSym
dwarfLocSym *LSym
dwarfRangesSym *LSym
dwarfAbsFnSym *LSym
dwarfDebugLinesSym *LSym
GCArgs *LSym
GCLocals *LSym
StackObjects *LSym
OpenCodedDeferInfo *LSym
FuncInfoSym *LSym
// NewFuncInfo allocates and returns a FuncInfo for LSym.
func (s *LSym) NewFuncInfo() *FuncInfo {
if s.Extra != nil {
panic(fmt.Sprintf("invalid use of LSym - NewFuncInfo with Extra of type %T", *s.Extra))
f := new(FuncInfo)
s.Extra = new(interface{})
*s.Extra = f
return f
// Func returns the *FuncInfo associated with s, or else nil.
func (s *LSym) Func() *FuncInfo {
if s.Extra == nil {
return nil
f, _ := (*s.Extra).(*FuncInfo)
return f
// A FileInfo contains extra fields for SDATA symbols backed by files.
// (If LSym.Extra is a *FileInfo, LSym.P == nil.)
type FileInfo struct {
Name string // name of file to read into object file
Size int64 // length of file
// NewFileInfo allocates and returns a FileInfo for LSym.
func (s *LSym) NewFileInfo() *FileInfo {
if s.Extra != nil {
panic(fmt.Sprintf("invalid use of LSym - NewFileInfo with Extra of type %T", *s.Extra))
f := new(FileInfo)
s.Extra = new(interface{})
*s.Extra = f
return f
// File returns the *FileInfo associated with s, or else nil.
func (s *LSym) File() *FileInfo {
if s.Extra == nil {
return nil
f, _ := (*s.Extra).(*FileInfo)
return f
type InlMark struct {
// When unwinding from an instruction in an inlined body, mark
// where we should unwind to.
// id records the global inlining id of the inlined body.
// p records the location of an instruction in the parent (inliner) frame.
p *Prog
id int32
// Mark p as the instruction to set as the pc when
// "unwinding" the inlining global frame id. Usually it should be
// instruction with a file:line at the callsite, and occur
// just before the body of the inlined function.
func (fi *FuncInfo) AddInlMark(p *Prog, id int32) {
fi.InlMarks = append(fi.InlMarks, InlMark{p: p, id: id})
// Record the type symbol for an auto variable so that the linker
// an emit DWARF type information for the type.
func (fi *FuncInfo) RecordAutoType(gotype *LSym) {
if fi.Autot == nil {
fi.Autot = make(map[*LSym]struct{})
fi.Autot[gotype] = struct{}{}
//go:generate stringer -type ABI
// ABI is the calling convention of a text symbol.
type ABI uint8
const (
// ABI0 is the stable stack-based ABI. It's important that the
// value of this is "0": we can't distinguish between
// references to data and ABI0 text symbols in assembly code,
// and hence this doesn't distinguish between symbols without
// an ABI and text symbols with ABI0.
ABI0 ABI = iota
// ABIInternal is the internal ABI that may change between Go
// versions. All Go functions use the internal ABI and the
// compiler generates wrappers for calls to and from other
// ABIs.
// ParseABI converts from a string representation in 'abistr' to the
// corresponding ABI value. Second return value is TRUE if the
// abi string is recognized, FALSE otherwise.
func ParseABI(abistr string) (ABI, bool) {
switch abistr {
return ABI0, false
case "ABI0":
return ABI0, true
case "ABIInternal":
return ABIInternal, true
// Attribute is a set of symbol attributes.
type Attribute uint32
const (
AttrDuplicateOK Attribute = 1 << iota
// MakeTypelink means that the type should have an entry in the typelink table.
// ReflectMethod means the function may call reflect.Type.Method or
// reflect.Type.MethodByName. Matching is imprecise (as reflect.Type
// can be used through a custom interface), so ReflectMethod may be
// set in some cases when the reflect package is not called.
// Used by the linker to determine what methods can be pruned.
// Local means make the symbol local even when compiling Go code to reference Go
// symbols in other shared libraries, as in this mode symbols are global by
// default. "local" here means in the sense of the dynamic linker, i.e. not
// visible outside of the module (shared library or executable) that contains its
// definition. (When not compiling to support Go shared libraries, all symbols are
// local in this sense unless there is a cgo_export_* directive).
// For function symbols; indicates that the specified function was the
// target of an inline during compilation
// TopFrame means that this function is an entry point and unwinders should not
// keep unwinding beyond this frame.
// Indexed indicates this symbol has been assigned with an index (when using the
// new object file format).
// Only applied on type descriptor symbols, UsedInIface indicates this type is
// converted to an interface.
// Used by the linker to determine what methods can be pruned.
// ContentAddressable indicates this is a content-addressable symbol.
// attrABIBase is the value at which the ABI is encoded in
// Attribute. This must be last; all bits after this are
// assumed to be an ABI value.
// MUST BE LAST since all bits above this comprise the ABI.
func (a Attribute) DuplicateOK() bool { return a&AttrDuplicateOK != 0 }
func (a Attribute) MakeTypelink() bool { return a&AttrMakeTypelink != 0 }
func (a Attribute) CFunc() bool { return a&AttrCFunc != 0 }
func (a Attribute) NoSplit() bool { return a&AttrNoSplit != 0 }
func (a Attribute) Leaf() bool { return a&AttrLeaf != 0 }
func (a Attribute) OnList() bool { return a&AttrOnList != 0 }
func (a Attribute) ReflectMethod() bool { return a&AttrReflectMethod != 0 }
func (a Attribute) Local() bool { return a&AttrLocal != 0 }
func (a Attribute) Wrapper() bool { return a&AttrWrapper != 0 }
func (a Attribute) NeedCtxt() bool { return a&AttrNeedCtxt != 0 }
func (a Attribute) NoFrame() bool { return a&AttrNoFrame != 0 }
func (a Attribute) Static() bool { return a&AttrStatic != 0 }
func (a Attribute) WasInlined() bool { return a&AttrWasInlined != 0 }
func (a Attribute) TopFrame() bool { return a&AttrTopFrame != 0 }
func (a Attribute) Indexed() bool { return a&AttrIndexed != 0 }
func (a Attribute) UsedInIface() bool { return a&AttrUsedInIface != 0 }
func (a Attribute) ContentAddressable() bool { return a&AttrContentAddressable != 0 }
func (a *Attribute) Set(flag Attribute, value bool) {
if value {
*a |= flag
} else {
*a &^= flag
func (a Attribute) ABI() ABI { return ABI(a / attrABIBase) }
func (a *Attribute) SetABI(abi ABI) {
const mask = 1 // Only one ABI bit for now.
*a = (*a &^ (mask * attrABIBase)) | Attribute(abi)*attrABIBase
var textAttrStrings = [...]struct {
bit Attribute
s string
{bit: AttrDuplicateOK, s: "DUPOK"},
{bit: AttrMakeTypelink, s: ""},
{bit: AttrCFunc, s: "CFUNC"},
{bit: AttrNoSplit, s: "NOSPLIT"},
{bit: AttrLeaf, s: "LEAF"},
{bit: AttrOnList, s: ""},
{bit: AttrReflectMethod, s: "REFLECTMETHOD"},
{bit: AttrLocal, s: "LOCAL"},
{bit: AttrWrapper, s: "WRAPPER"},
{bit: AttrNeedCtxt, s: "NEEDCTXT"},
{bit: AttrNoFrame, s: "NOFRAME"},
{bit: AttrStatic, s: "STATIC"},
{bit: AttrWasInlined, s: ""},
{bit: AttrTopFrame, s: "TOPFRAME"},
{bit: AttrIndexed, s: ""},
{bit: AttrContentAddressable, s: ""},
// TextAttrString formats a for printing in as part of a TEXT prog.
func (a Attribute) TextAttrString() string {
var s string
for _, x := range textAttrStrings {
if a&x.bit != 0 {
if x.s != "" {
s += x.s + "|"
a &^= x.bit
switch a.ABI() {
case ABI0:
case ABIInternal:
s += "ABIInternal|"
a.SetABI(0) // Clear ABI so we don't print below.
if a != 0 {
s += fmt.Sprintf("UnknownAttribute(%d)|", a)
// Chop off trailing |, if present.
if len(s) > 0 {
s = s[:len(s)-1]
return s
func (s *LSym) String() string {
return s.Name
// The compiler needs *LSym to be assignable to cmd/compile/internal/ssa.Sym.
func (s *LSym) CanBeAnSSASym() {
type Pcln struct {
// Aux symbols for pcln
Pcsp *LSym
Pcfile *LSym
Pcline *LSym
Pcinline *LSym
Pcdata []*LSym
Funcdata []*LSym
Funcdataoff []int64
UsedFiles map[goobj.CUFileIndex]struct{} // file indices used while generating pcfile
InlTree InlTree // per-function inlining tree extracted from the global tree
type Reloc struct {
Off int32
Siz uint8
Type objabi.RelocType
Add int64
Sym *LSym
type Auto struct {
Asym *LSym
Aoffset int32
Name AddrName
Gotype *LSym
// Link holds the context for writing object code from a compiler
// to be linker input or for reading that input into the linker.
type Link struct {
Headtype objabi.HeadType
Arch *LinkArch
Debugasm int
Debugvlog bool
Debugpcln string
Flag_shared bool
Flag_dynlink bool
Flag_linkshared bool
Flag_optimize bool
Flag_locationlists bool
Retpoline bool // emit use of retpoline stubs for indirect jmp/call
Bso *bufio.Writer
Pathname string
Pkgpath string // the current package's import path, "" if unknown
hashmu sync.Mutex // protects hash, funchash
hash map[string]*LSym // name -> sym mapping
funchash map[string]*LSym // name -> sym mapping for ABIInternal syms
statichash map[string]*LSym // name -> sym mapping for static syms
PosTable src.PosTable
InlTree InlTree // global inlining tree used by gc/inl.go
DwFixups *DwarfFixupTable
Imports []goobj.ImportedPkg
DiagFunc func(string, ...interface{})
DiagFlush func()
DebugInfo func(fn *LSym, info *LSym, curfn interface{}) ([]dwarf.Scope, dwarf.InlCalls) // if non-nil, curfn is a *gc.Node
GenAbstractFunc func(fn *LSym)
Errors int
InParallel bool // parallel backend phase in effect
UseBASEntries bool // use Base Address Selection Entries in location lists and PC ranges
IsAsm bool // is the source assembly language, which may contain surprising idioms (e.g., call tables)
// state for writing objects
Text []*LSym
Data []*LSym
// ABIAliases are text symbols that should be aliased to all
// ABIs. These symbols may only be referenced and not defined
// by this object, since the need for an alias may appear in a
// different object than the definition. Hence, this
// information can't be carried in the symbol definition.
// TODO(austin): Replace this with ABI wrappers once the ABIs
// actually diverge.
ABIAliases []*LSym
// Constant symbols (e.g. $i64.*) are data symbols created late
// in the concurrent phase. To ensure a deterministic order, we
// add them to a separate list, sort at the end, and append it
// to Data.
constSyms []*LSym
// pkgIdx maps package path to index. The index is used for
// symbol reference in the object file.
pkgIdx map[string]int32
defs []*LSym // list of defined symbols in the current package
hashed64defs []*LSym // list of defined short (64-bit or less) hashed (content-addressable) symbols
hasheddefs []*LSym // list of defined hashed (content-addressable) symbols
nonpkgdefs []*LSym // list of defined non-package symbols
nonpkgrefs []*LSym // list of referenced non-package symbols
Fingerprint goobj.FingerprintType // fingerprint of symbol indices, to catch index mismatch
func (ctxt *Link) Diag(format string, args ...interface{}) {
ctxt.DiagFunc(format, args...)
func (ctxt *Link) Logf(format string, args ...interface{}) {
fmt.Fprintf(ctxt.Bso, format, args...)
// The smallest possible offset from the hardware stack pointer to a local
// variable on the stack. Architectures that use a link register save its value
// on the stack in the function prologue and so always have a pointer between
// the hardware stack pointer and the local variable area.
func (ctxt *Link) FixedFrameSize() int64 {
switch ctxt.Arch.Family {
case sys.AMD64, sys.I386, sys.Wasm:
return 0
case sys.PPC64:
// PIC code on ppc64le requires 32 bytes of stack, and it's easier to
// just use that much stack always on ppc64x.
return int64(4 * ctxt.Arch.PtrSize)
return int64(ctxt.Arch.PtrSize)
// LinkArch is the definition of a single architecture.
type LinkArch struct {
Init func(*Link)
Preprocess func(*Link, *LSym, ProgAlloc)
Assemble func(*Link, *LSym, ProgAlloc)
Progedit func(*Link, *Prog, ProgAlloc)
UnaryDst map[As]bool // Instruction takes one operand, a destination.
DWARFRegisters map[int16]int16