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// Derived from Inferno utils/6l/l.h and related files.
// http://code.google.com/p/inferno-os/source/browse/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"
"cmd/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.
// In this form, reg must be a register and shift can be a register or an integer constant.
// Encoding:
// type = TYPE_SHIFT
// 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.
//
// (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
Etype uint8
Offset int64
Width int64
Sym *LSym
Gotype *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
)
// TODO(rsc): Describe prog.
// TODO(rsc): Describe TEXT/GLOBL flag in from3
type Prog struct {
Ctxt *Link
Link *Prog
From Addr
From3 *Addr // optional
To Addr
Opt interface{}
Forwd *Prog
Pcond *Prog
Rel *Prog // Source of forward jumps on x86; pcrel on arm
Pc int64
Lineno int32
Spadj int32
As As // Assembler opcode.
Reg int16
RegTo2 int16 // 2nd register output operand
Mark uint16 // bitmask of arch-specific items
Optab uint16
Scond uint8
Back uint8
Ft uint8
Tt uint8
Isize uint8 // size of the instruction in bytes (x86 only)
Mode int8
Info ProgInfo
}
// 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
}
// ProgInfo holds information about the instruction for use
// by clients such as the compiler. The exact meaning of this
// data is up to the client and is not interpreted by the cmd/internal/obj/... packages.
type ProgInfo struct {
_ struct{} // to prevent unkeyed literals. Trailing zero-sized field will take space.
Flags uint32 // flag bits
Reguse uint64 // registers implicitly used by this instruction
Regset uint64 // registers implicitly set by this instruction
Regindex uint64 // registers used by addressing mode
}
// 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
ACHECKNIL
ADUFFCOPY
ADUFFZERO
AEND
AFUNCDATA
AGLOBL
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) << 12
ABaseARM
ABaseAMD64
ABasePPC64
ABaseARM64
ABaseMIPS64
ABaseS390X
AMask = 1<<12 - 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 int16
Version int16
Dupok bool
Cfunc bool
Nosplit bool
Leaf bool
Seenglobl bool
Onlist bool
// 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.
ReflectMethod bool
// 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).
Local bool
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
}
// 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
}
// LSym.type
const (
Sxxx = iota
STEXT
SELFRXSECT
STYPE
SSTRING
SGOSTRING
SGOSTRINGHDR
SGOFUNC
SGCBITS
SRODATA
SFUNCTAB
// 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
SGOSTRINGHDRRELRO
SGOFUNCRELRO
SGCBITSRELRO
SRODATARELRO
SFUNCTABRELRO
STYPELINK
SITABLINK
SSYMTAB
SPCLNTAB
SELFROSECT
SMACHOPLT
SELFSECT
SMACHO
SMACHOGOT
SWINDOWS
SELFGOT
SNOPTRDATA
SINITARR
SDATA
SBSS
SNOPTRBSS
STLSBSS
SXREF
SMACHOSYMSTR
SMACHOSYMTAB
SMACHOINDIRECTPLT
SMACHOINDIRECTGOT
SFILE
SFILEPATH
SCONST
SDYNIMPORT
SHOSTOBJ
SDWARFSECT
SDWARFINFO
SSUB = 1 << 8
SMASK = SSUB - 1
SHIDDEN = 1 << 9
SCONTAINER = 1 << 10 // has a sub-symbol
)
type Reloc struct {
Off int32
Siz uint8
Type int32
Add int64
Sym *LSym
}
// Reloc.type
const (
R_ADDR = 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
)
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 {
Goarm int32
Headtype int
Arch *LinkArch
Debugasm int32
Debugvlog int32
Debugdivmod int32
Debugpcln int32
Flag_shared bool
Flag_dynlink bool
Flag_optimize bool
Bso *bufio.Writer
Pathname string
Goroot string
Goroot_final string
Hash map[SymVer]*LSym
LineHist LineHist
Imports []string
Plist *Plist
Plast *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
Textp *LSym
Etextp *LSym
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...)
}
// 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.
}
/* executable header types */
const (
Hunknown = 0 + iota
Hdarwin
Hdragonfly
Hfreebsd
Hlinux
Hnacl
Hnetbsd
Hopenbsd
Hplan9
Hsolaris
Hwindows
)
// 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] }