Add gops agentv0.10.2-dev

1 files changed, 974 insertions, 0 deletions

diff --git a/vendor/github.com/google/gops/internal/obj/link.go b/vendor/github.com/google/gops/internal/obj/link.go
new file mode 100644
index 00000000..e2530615
--- /dev/null
+++ b/vendor/github.com/google/gops/internal/obj/link.go
@@ -0,0 +1,974 @@
+// Derived from Inferno utils/6l/l.h and related files.
+// https://bitbucket.org/inferno-os/inferno-os/src/default/utils/6l/l.h
+//
+//	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
+//	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
+//	Portions Copyright © 1997-1999 Vita Nuova Limited
+//	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
+//	Portions Copyright © 2004,2006 Bruce Ellis
+//	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
+//	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.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package obj
+
+import (
+	"bufio"
+	"fmt"
+
+	"github.com/google/gops/internal/sys"
+)
+
+// 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:
+//			type = TYPE_TEXTSIZE
+//			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.
+//		Encoding:
+//			type = TYPE_REGLIST
+//			offset = bit mask of registers in list; R0 is low bit.
+//
+//	reg, reg
+//		Register pair for ARM.
+//		TYPE_REGREG2
+//
+//	(reg+reg)
+//		Register pair for PPC64.
+//		Encoding:
+//			type = TYPE_MEM
+//			reg = first register
+//			index = second register
+//			scale = 1
+//
+type Addr struct {
+	Reg    int16
+	Index  int16
+	Scale  int16 // Sometimes holds a register.
+	Type   AddrType
+	Name   int8
+	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{}
+
+	Node interface{} // for use by compiler
+}
+
+type AddrType uint8
+
+const (
+	NAME_NONE = 0 + iota
+	NAME_EXTERN
+	NAME_STATIC
+	NAME_AUTO
+	NAME_PARAM
+	// A reference to name@GOT(SB) is a reference to the entry in the global offset
+	// table for 'name'.
+	NAME_GOTREF
+)
+
+const (
+	TYPE_NONE AddrType = 0
+
+	TYPE_BRANCH AddrType = 5 + iota
+	TYPE_TEXTSIZE
+	TYPE_MEM
+	TYPE_CONST
+	TYPE_FCONST
+	TYPE_SCONST
+	TYPE_REG
+	TYPE_ADDR
+	TYPE_SHIFT
+	TYPE_REGREG
+	TYPE_REGREG2
+	TYPE_INDIR
+	TYPE_REGLIST
+)
+
+// Prog describes a single machine instruction.
+//
+// The general instruction form is:
+//
+//	As.Scond From, Reg, From3, To, RegTo2
+//
+// where As is an opcode and the others are arguments:
+// From, Reg, From3 are sources, and To, RegTo2 are 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.
+//
+// Jump instructions use the Pcond field to point to the target instruction,
+// 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 Lineno, an index into the line history (see LineHist).
+// Every Prog has a Ctxt field that defines various context, including the current LineHist.
+// Progs should be allocated using ctxt.NewProg(), not 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
+	From3  *Addr       // third source operand (second is Reg below)
+	To     Addr        // destination operand (second is RegTo2 below)
+	Pcond  *Prog       // target of conditional jump
+	Opt    interface{} // available to optimization passes to hold per-Prog state
+	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
+	Lineno int32       // line number 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       // condition bits for conditional instruction (e.g., on ARM)
+	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
+	Mode   int8        // for x86 back end: 32- or 64-bit mode
+}
+
+// From3Type returns From3.Type, or TYPE_NONE when From3 is nil.
+func (p *Prog) From3Type() AddrType {
+	if p.From3 == nil {
+		return TYPE_NONE
+	}
+	return p.From3.Type
+}
+
+// From3Offset returns From3.Offset, or 0 when From3 is nil.
+func (p *Prog) From3Offset() int64 {
+	if p.From3 == nil {
+		return 0
+	}
+	return p.From3.Offset
+}
+
+// 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
+	ACALL
+	ADUFFCOPY
+	ADUFFZERO
+	AEND
+	AFUNCDATA
+	AJMP
+	ANOP
+	APCDATA
+	ARET
+	ATEXT
+	ATYPE
+	AUNDEF
+	AUSEFIELD
+	AVARDEF
+	AVARKILL
+	AVARLIVE
+	A_ARCHSPECIFIC
+)
+
+// 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) << 10
+	ABaseARM
+	ABaseAMD64
+	ABasePPC64
+	ABaseARM64
+	ABaseMIPS64
+	ABaseS390X
+
+	AllowedOpCodes = 1 << 10            // 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.
+type LSym struct {
+	Name    string
+	Type    SymKind
+	Version int16
+	Attribute
+
+	RefIdx int // Index of this symbol in the symbol reference list.
+	Args   int32
+	Locals int32
+	Size   int64
+	Gotype *LSym
+	Autom  *Auto
+	Text   *Prog
+	Pcln   *Pcln
+	P      []byte
+	R      []Reloc
+}
+
+// Attribute is a set of symbol attributes.
+type Attribute int16
+
+const (
+	AttrDuplicateOK Attribute = 1 << iota
+	AttrCFunc
+	AttrNoSplit
+	AttrLeaf
+	AttrSeenGlobl
+	AttrOnList
+
+	// MakeTypelink means that the type should have an entry in the typelink table.
+	AttrMakeTypelink
+
+	// 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.
+	AttrReflectMethod
+
+	// 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).
+	AttrLocal
+)
+
+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) SeenGlobl() bool     { return a&AttrSeenGlobl != 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) Set(flag Attribute, value bool) {
+	if value {
+		*a |= flag
+	} else {
+		*a &^= flag
+	}
+}
+
+// The compiler needs LSym to satisfy fmt.Stringer, because it stores
+// an LSym in ssa.ExternSymbol.
+func (s *LSym) String() string {
+	return s.Name
+}
+
+type Pcln struct {
+	Pcsp        Pcdata
+	Pcfile      Pcdata
+	Pcline      Pcdata
+	Pcdata      []Pcdata
+	Funcdata    []*LSym
+	Funcdataoff []int64
+	File        []*LSym
+	Lastfile    *LSym
+	Lastindex   int
+}
+
+// A SymKind describes the kind of memory represented by a symbol.
+type SymKind int16
+
+// Defined SymKind values.
+//
+// TODO(rsc): Give idiomatic Go names.
+// TODO(rsc): Reduce the number of symbol types in the object files.
+//go:generate stringer -type=SymKind
+const (
+	Sxxx SymKind = iota
+	STEXT
+	SELFRXSECT
+
+	// Read-only sections.
+	STYPE
+	SSTRING
+	SGOSTRING
+	SGOFUNC
+	SGCBITS
+	SRODATA
+	SFUNCTAB
+
+	SELFROSECT
+	SMACHOPLT
+
+	// Read-only sections with relocations.
+	//
+	// Types STYPE-SFUNCTAB above are written to the .rodata section by default.
+	// When linking a shared object, some conceptually "read only" types need to
+	// be written to by relocations and putting them in a section called
+	// ".rodata" interacts poorly with the system linkers. The GNU linkers
+	// support this situation by arranging for sections of the name
+	// ".data.rel.ro.XXX" to be mprotected read only by the dynamic linker after
+	// relocations have applied, so when the Go linker is creating a shared
+	// object it checks all objects of the above types and bumps any object that
+	// has a relocation to it to the corresponding type below, which are then
+	// written to sections with appropriate magic names.
+	STYPERELRO
+	SSTRINGRELRO
+	SGOSTRINGRELRO
+	SGOFUNCRELRO
+	SGCBITSRELRO
+	SRODATARELRO
+	SFUNCTABRELRO
+
+	// Part of .data.rel.ro if it exists, otherwise part of .rodata.
+	STYPELINK
+	SITABLINK
+	SSYMTAB
+	SPCLNTAB
+
+	// Writable sections.
+	SELFSECT
+	SMACHO
+	SMACHOGOT
+	SWINDOWS
+	SELFGOT
+	SNOPTRDATA
+	SINITARR
+	SDATA
+	SBSS
+	SNOPTRBSS
+	STLSBSS
+	SXREF
+	SMACHOSYMSTR
+	SMACHOSYMTAB
+	SMACHOINDIRECTPLT
+	SMACHOINDIRECTGOT
+	SFILE
+	SFILEPATH
+	SCONST
+	SDYNIMPORT
+	SHOSTOBJ
+	SDWARFSECT
+	SDWARFINFO
+	SSUB       = SymKind(1 << 8)
+	SMASK      = SymKind(SSUB - 1)
+	SHIDDEN    = SymKind(1 << 9)
+	SCONTAINER = SymKind(1 << 10) // has a sub-symbol
+)
+
+// ReadOnly are the symbol kinds that form read-only sections. In some
+// cases, if they will require relocations, they are transformed into
+// rel-ro sections using RelROMap.
+var ReadOnly = []SymKind{
+	STYPE,
+	SSTRING,
+	SGOSTRING,
+	SGOFUNC,
+	SGCBITS,
+	SRODATA,
+	SFUNCTAB,
+}
+
+// RelROMap describes the transformation of read-only symbols to rel-ro
+// symbols.
+var RelROMap = map[SymKind]SymKind{
+	STYPE:     STYPERELRO,
+	SSTRING:   SSTRINGRELRO,
+	SGOSTRING: SGOSTRINGRELRO,
+	SGOFUNC:   SGOFUNCRELRO,
+	SGCBITS:   SGCBITSRELRO,
+	SRODATA:   SRODATARELRO,
+	SFUNCTAB:  SFUNCTABRELRO,
+}
+
+type Reloc struct {
+	Off  int32
+	Siz  uint8
+	Type RelocType
+	Add  int64
+	Sym  *LSym
+}
+
+type RelocType int32
+
+//go:generate stringer -type=RelocType
+const (
+	R_ADDR RelocType = 1 + iota
+	// R_ADDRPOWER relocates a pair of "D-form" instructions (instructions with 16-bit
+	// immediates in the low half of the instruction word), usually addis followed by
+	// another add or a load, inserting the "high adjusted" 16 bits of the address of
+	// the referenced symbol into the immediate field of the first instruction and the
+	// low 16 bits into that of the second instruction.
+	R_ADDRPOWER
+	// R_ADDRARM64 relocates an adrp, add pair to compute the address of the
+	// referenced symbol.
+	R_ADDRARM64
+	// R_ADDRMIPS (only used on mips64) resolves to the low 16 bits of an external
+	// address, by encoding it into the instruction.
+	R_ADDRMIPS
+	// R_ADDROFF resolves to a 32-bit offset from the beginning of the section
+	// holding the data being relocated to the referenced symbol.
+	R_ADDROFF
+	R_SIZE
+	R_CALL
+	R_CALLARM
+	R_CALLARM64
+	R_CALLIND
+	R_CALLPOWER
+	// R_CALLMIPS (only used on mips64) resolves to non-PC-relative target address
+	// of a CALL (JAL) instruction, by encoding the address into the instruction.
+	R_CALLMIPS
+	R_CONST
+	R_PCREL
+	// R_TLS_LE, used on 386, amd64, and ARM, resolves to the offset of the
+	// thread-local symbol from the thread local base and is used to implement the
+	// "local exec" model for tls access (r.Sym is not set on intel platforms but is
+	// set to a TLS symbol -- runtime.tlsg -- in the linker when externally linking).
+	R_TLS_LE
+	// R_TLS_IE, used 386, amd64, and ARM resolves to the PC-relative offset to a GOT
+	// slot containing the offset from the thread-local symbol from the thread local
+	// base and is used to implemented the "initial exec" model for tls access (r.Sym
+	// is not set on intel platforms but is set to a TLS symbol -- runtime.tlsg -- in
+	// the linker when externally linking).
+	R_TLS_IE
+	R_GOTOFF
+	R_PLT0
+	R_PLT1
+	R_PLT2
+	R_USEFIELD
+	// R_USETYPE resolves to an *rtype, but no relocation is created. The
+	// linker uses this as a signal that the pointed-to type information
+	// should be linked into the final binary, even if there are no other
+	// direct references. (This is used for types reachable by reflection.)
+	R_USETYPE
+	// R_METHODOFF resolves to a 32-bit offset from the beginning of the section
+	// holding the data being relocated to the referenced symbol.
+	// It is a variant of R_ADDROFF used when linking from the uncommonType of a
+	// *rtype, and may be set to zero by the linker if it determines the method
+	// text is unreachable by the linked program.
+	R_METHODOFF
+	R_POWER_TOC
+	R_GOTPCREL
+	// R_JMPMIPS (only used on mips64) resolves to non-PC-relative target address
+	// of a JMP instruction, by encoding the address into the instruction.
+	// The stack nosplit check ignores this since it is not a function call.
+	R_JMPMIPS
+	// R_DWARFREF resolves to the offset of the symbol from its section.
+	R_DWARFREF
+
+	// Platform dependent relocations. Architectures with fixed width instructions
+	// have the inherent issue that a 32-bit (or 64-bit!) displacement cannot be
+	// stuffed into a 32-bit instruction, so an address needs to be spread across
+	// several instructions, and in turn this requires a sequence of relocations, each
+	// updating a part of an instruction. This leads to relocation codes that are
+	// inherently processor specific.
+
+	// Arm64.
+
+	// Set a MOV[NZ] immediate field to bits [15:0] of the offset from the thread
+	// local base to the thread local variable defined by the referenced (thread
+	// local) symbol. Error if the offset does not fit into 16 bits.
+	R_ARM64_TLS_LE
+
+	// Relocates an ADRP; LD64 instruction sequence to load the offset between
+	// the thread local base and the thread local variable defined by the
+	// referenced (thread local) symbol from the GOT.
+	R_ARM64_TLS_IE
+
+	// R_ARM64_GOTPCREL relocates an adrp, ld64 pair to compute the address of the GOT
+	// slot of the referenced symbol.
+	R_ARM64_GOTPCREL
+
+	// PPC64.
+
+	// R_POWER_TLS_LE is used to implement the "local exec" model for tls
+	// access. It resolves to the offset of the thread-local symbol from the
+	// thread pointer (R13) and inserts this value into the low 16 bits of an
+	// instruction word.
+	R_POWER_TLS_LE
+
+	// R_POWER_TLS_IE is used to implement the "initial exec" model for tls access. It
+	// relocates a D-form, DS-form instruction sequence like R_ADDRPOWER_DS. It
+	// inserts to the offset of GOT slot for the thread-local symbol from the TOC (the
+	// GOT slot is filled by the dynamic linker with the offset of the thread-local
+	// symbol from the thread pointer (R13)).
+	R_POWER_TLS_IE
+
+	// R_POWER_TLS marks an X-form instruction such as "MOVD 0(R13)(R31*1), g" as
+	// accessing a particular thread-local symbol. It does not affect code generation
+	// but is used by the system linker when relaxing "initial exec" model code to
+	// "local exec" model code.
+	R_POWER_TLS
+
+	// R_ADDRPOWER_DS is similar to R_ADDRPOWER above, but assumes the second
+	// instruction is a "DS-form" instruction, which has an immediate field occupying
+	// bits [15:2] of the instruction word. Bits [15:2] of the address of the
+	// relocated symbol are inserted into this field; it is an error if the last two
+	// bits of the address are not 0.
+	R_ADDRPOWER_DS
+
+	// R_ADDRPOWER_PCREL relocates a D-form, DS-form instruction sequence like
+	// R_ADDRPOWER_DS but inserts the offset of the GOT slot for the referenced symbol
+	// from the TOC rather than the symbol's address.
+	R_ADDRPOWER_GOT
+
+	// R_ADDRPOWER_PCREL relocates two D-form instructions like R_ADDRPOWER, but
+	// inserts the displacement from the place being relocated to the address of the
+	// the relocated symbol instead of just its address.
+	R_ADDRPOWER_PCREL
+
+	// R_ADDRPOWER_TOCREL relocates two D-form instructions like R_ADDRPOWER, but
+	// inserts the offset from the TOC to the address of the the relocated symbol
+	// rather than the symbol's address.
+	R_ADDRPOWER_TOCREL
+
+	// R_ADDRPOWER_TOCREL relocates a D-form, DS-form instruction sequence like
+	// R_ADDRPOWER_DS but inserts the offset from the TOC to the address of the the
+	// relocated symbol rather than the symbol's address.
+	R_ADDRPOWER_TOCREL_DS
+
+	// R_PCRELDBL relocates s390x 2-byte aligned PC-relative addresses.
+	// TODO(mundaym): remove once variants can be serialized - see issue 14218.
+	R_PCRELDBL
+
+	// R_ADDRMIPSU (only used on mips64) resolves to the sign-adjusted "upper" 16
+	// bits (bit 16-31) of an external address, by encoding it into the instruction.
+	R_ADDRMIPSU
+	// R_ADDRMIPSTLS (only used on mips64) resolves to the low 16 bits of a TLS
+	// address (offset from thread pointer), by encoding it into the instruction.
+	R_ADDRMIPSTLS
+)
+
+// IsDirectJump returns whether r is a relocation for a direct jump.
+// A direct jump is a CALL or JMP instruction that takes the target address
+// as immediate. The address is embedded into the instruction, possibly
+// with limited width.
+// An indirect jump is a CALL or JMP instruction that takes the target address
+// in register or memory.
+func (r RelocType) IsDirectJump() bool {
+	switch r {
+	case R_CALL, R_CALLARM, R_CALLARM64, R_CALLPOWER, R_CALLMIPS, R_JMPMIPS:
+		return true
+	}
+	return false
+}
+
+type Auto struct {
+	Asym    *LSym
+	Link    *Auto
+	Aoffset int32
+	Name    int16
+	Gotype  *LSym
+}
+
+// Auto.name
+const (
+	A_AUTO = 1 + iota
+	A_PARAM
+)
+
+type Pcdata struct {
+	P []byte
+}
+
+// symbol version, incremented each time a file is loaded.
+// version==1 is reserved for savehist.
+const (
+	HistVersion = 1
+)
+
+// 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      HeadType
+	Arch          *LinkArch
+	Debugasm      int32
+	Debugvlog     int32
+	Debugdivmod   int32
+	Debugpcln     int32
+	Flag_shared   bool
+	Flag_dynlink  bool
+	Flag_optimize bool
+	Bso           *bufio.Writer
+	Pathname      string
+	Hash          map[SymVer]*LSym
+	LineHist      LineHist
+	Imports       []string
+	Plists        []*Plist
+	Sym_div       *LSym
+	Sym_divu      *LSym
+	Sym_mod       *LSym
+	Sym_modu      *LSym
+	Plan9privates *LSym
+	Curp          *Prog
+	Printp        *Prog
+	Blitrl        *Prog
+	Elitrl        *Prog
+	Rexflag       int
+	Vexflag       int
+	Rep           int
+	Repn          int
+	Lock          int
+	Asmode        int
+	AsmBuf        AsmBuf // instruction buffer for x86
+	Instoffset    int64
+	Autosize      int32
+	Armsize       int32
+	Pc            int64
+	DiagFunc      func(string, ...interface{})
+	Mode          int
+	Cursym        *LSym
+	Version       int
+	Errors        int
+
+	Framepointer_enabled bool
+
+	// state for writing objects
+	Text []*LSym
+	Data []*LSym
+
+	// Cache of Progs
+	allocIdx int
+	progs    [10000]Prog
+}
+
+func (ctxt *Link) Diag(format string, args ...interface{}) {
+	ctxt.Errors++
+	ctxt.DiagFunc(format, args...)
+}
+
+func (ctxt *Link) Logf(format string, args ...interface{}) {
+	fmt.Fprintf(ctxt.Bso, format, args...)
+	ctxt.Bso.Flush()
+}
+
+// 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:
+		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)
+	default:
+		return int64(ctxt.Arch.PtrSize)
+	}
+}
+
+type SymVer struct {
+	Name    string
+	Version int // TODO: make int16 to match LSym.Version?
+}
+
+// LinkArch is the definition of a single architecture.
+type LinkArch struct {
+	*sys.Arch
+	Preprocess func(*Link, *LSym)
+	Assemble   func(*Link, *LSym)
+	Follow     func(*Link, *LSym)
+	Progedit   func(*Link, *Prog)
+	UnaryDst   map[As]bool // Instruction takes one operand, a destination.
+}
+
+// HeadType is the executable header type.
+type HeadType uint8
+
+const (
+	Hunknown HeadType = iota
+	Hdarwin
+	Hdragonfly
+	Hfreebsd
+	Hlinux
+	Hnacl
+	Hnetbsd
+	Hopenbsd
+	Hplan9
+	Hsolaris
+	Hwindows
+	Hwindowsgui
+)
+
+func (h *HeadType) Set(s string) error {
+	switch s {
+	case "darwin":
+		*h = Hdarwin
+	case "dragonfly":
+		*h = Hdragonfly
+	case "freebsd":
+		*h = Hfreebsd
+	case "linux", "android":
+		*h = Hlinux
+	case "nacl":
+		*h = Hnacl
+	case "netbsd":
+		*h = Hnetbsd
+	case "openbsd":
+		*h = Hopenbsd
+	case "plan9":
+		*h = Hplan9
+	case "solaris":
+		*h = Hsolaris
+	case "windows":
+		*h = Hwindows
+	case "windowsgui":
+		*h = Hwindowsgui
+	default:
+		return fmt.Errorf("invalid headtype: %q", s)
+	}
+	return nil
+}
+
+func (h *HeadType) String() string {
+	switch *h {
+	case Hdarwin:
+		return "darwin"
+	case Hdragonfly:
+		return "dragonfly"
+	case Hfreebsd:
+		return "freebsd"
+	case Hlinux:
+		return "linux"
+	case Hnacl:
+		return "nacl"
+	case Hnetbsd:
+		return "netbsd"
+	case Hopenbsd:
+		return "openbsd"
+	case Hplan9:
+		return "plan9"
+	case Hsolaris:
+		return "solaris"
+	case Hwindows:
+		return "windows"
+	case Hwindowsgui:
+		return "windowsgui"
+	}
+	return fmt.Sprintf("HeadType(%d)", *h)
+}
+
+// AsmBuf is a simple buffer to assemble variable-length x86 instructions into.
+type AsmBuf struct {
+	buf [100]byte
+	off int
+}
+
+// Put1 appends one byte to the end of the buffer.
+func (a *AsmBuf) Put1(x byte) {
+	a.buf[a.off] = x
+	a.off++
+}
+
+// Put2 appends two bytes to the end of the buffer.
+func (a *AsmBuf) Put2(x, y byte) {
+	a.buf[a.off+0] = x
+	a.buf[a.off+1] = y
+	a.off += 2
+}
+
+// Put3 appends three bytes to the end of the buffer.
+func (a *AsmBuf) Put3(x, y, z byte) {
+	a.buf[a.off+0] = x
+	a.buf[a.off+1] = y
+	a.buf[a.off+2] = z
+	a.off += 3
+}
+
+// Put4 appends four bytes to the end of the buffer.
+func (a *AsmBuf) Put4(x, y, z, w byte) {
+	a.buf[a.off+0] = x
+	a.buf[a.off+1] = y
+	a.buf[a.off+2] = z
+	a.buf[a.off+3] = w
+	a.off += 4
+}
+
+// PutInt16 writes v into the buffer using little-endian encoding.
+func (a *AsmBuf) PutInt16(v int16) {
+	a.buf[a.off+0] = byte(v)
+	a.buf[a.off+1] = byte(v >> 8)
+	a.off += 2
+}
+
+// PutInt32 writes v into the buffer using little-endian encoding.
+func (a *AsmBuf) PutInt32(v int32) {
+	a.buf[a.off+0] = byte(v)
+	a.buf[a.off+1] = byte(v >> 8)
+	a.buf[a.off+2] = byte(v >> 16)
+	a.buf[a.off+3] = byte(v >> 24)
+	a.off += 4
+}
+
+// PutInt64 writes v into the buffer using little-endian encoding.
+func (a *AsmBuf) PutInt64(v int64) {
+	a.buf[a.off+0] = byte(v)
+	a.buf[a.off+1] = byte(v >> 8)
+	a.buf[a.off+2] = byte(v >> 16)
+	a.buf[a.off+3] = byte(v >> 24)
+	a.buf[a.off+4] = byte(v >> 32)
+	a.buf[a.off+5] = byte(v >> 40)
+	a.buf[a.off+6] = byte(v >> 48)
+	a.buf[a.off+7] = byte(v >> 56)
+	a.off += 8
+}
+
+// Put copies b into the buffer.
+func (a *AsmBuf) Put(b []byte) {
+	copy(a.buf[a.off:], b)
+	a.off += len(b)
+}
+
+// Insert inserts b at offset i.
+func (a *AsmBuf) Insert(i int, b byte) {
+	a.off++
+	copy(a.buf[i+1:a.off], a.buf[i:a.off-1])
+	a.buf[i] = b
+}
+
+// Last returns the byte at the end of the buffer.
+func (a *AsmBuf) Last() byte { return a.buf[a.off-1] }
+
+// Len returns the length of the buffer.
+func (a *AsmBuf) Len() int { return a.off }
+
+// Bytes returns the contents of the buffer.
+func (a *AsmBuf) Bytes() []byte { return a.buf[:a.off] }
+
+// Reset empties the buffer.
+func (a *AsmBuf) Reset() { a.off = 0 }
+
+// Peek returns the byte at offset i.
+func (a *AsmBuf) Peek(i int) byte { return a.buf[i] }