Your IP : 172.28.240.42
// Copyright 2018 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 wasm
import (
"cmd/compile/internal/base"
"cmd/compile/internal/ir"
"cmd/compile/internal/logopt"
"cmd/compile/internal/objw"
"cmd/compile/internal/ssa"
"cmd/compile/internal/ssagen"
"cmd/compile/internal/types"
"cmd/internal/obj"
"cmd/internal/obj/wasm"
"internal/buildcfg"
)
/*
Wasm implementation
-------------------
Wasm is a strange Go port because the machine isn't
a register-based machine, threads are different, code paths
are different, etc. We outline those differences here.
See the design doc for some additional info on this topic.
https://docs.google.com/document/d/131vjr4DH6JFnb-blm_uRdaC0_Nv3OUwjEY5qVCxCup4/edit#heading=h.mjo1bish3xni
PCs:
Wasm doesn't have PCs in the normal sense that you can jump
to or call to. Instead, we simulate these PCs using our own construct.
A PC in the Wasm implementation is the combination of a function
ID and a block ID within that function. The function ID is an index
into a function table which transfers control to the start of the
function in question, and the block ID is a sequential integer
indicating where in the function we are.
Every function starts with a branch table which transfers control
to the place in the function indicated by the block ID. The block
ID is provided to the function as the sole Wasm argument.
Block IDs do not encode every possible PC. They only encode places
in the function where it might be suspended. Typically these places
are call sites.
Sometimes we encode the function ID and block ID separately. When
recorded together as a single integer, we use the value F<<16+B.
Threads:
Wasm doesn't (yet) have threads. We have to simulate threads by
keeping goroutine stacks in linear memory and unwinding
the Wasm stack each time we want to switch goroutines.
To support unwinding a stack, each function call returns on the Wasm
stack a boolean that tells the function whether it should return
immediately or not. When returning immediately, a return address
is left on the top of the Go stack indicating where the goroutine
should be resumed.
Stack pointer:
There is a single global stack pointer which records the stack pointer
used by the currently active goroutine. This is just an address in
linear memory where the Go runtime is maintaining the stack for that
goroutine.
Functions cache the global stack pointer in a local variable for
faster access, but any changes must be spilled to the global variable
before any call and restored from the global variable after any call.
Calling convention:
All Go arguments and return values are passed on the Go stack, not
the wasm stack. In addition, return addresses are pushed on the
Go stack at every call point. Return addresses are not used during
normal execution, they are used only when resuming goroutines.
(So they are not really a "return address", they are a "resume address".)
All Go functions have the Wasm type (i32)->i32. The argument
is the block ID and the return value is the exit immediately flag.
Callsite:
- write arguments to the Go stack (starting at SP+0)
- push return address to Go stack (8 bytes)
- write local SP to global SP
- push 0 (type i32) to Wasm stack
- issue Call
- restore local SP from global SP
- pop int32 from top of Wasm stack. If nonzero, exit function immediately.
- use results from Go stack (starting at SP+sizeof(args))
- note that the callee will have popped the return address
Prologue:
- initialize local SP from global SP
- jump to the location indicated by the block ID argument
(which appears in local variable 0)
- at block 0
- check for Go stack overflow, call morestack if needed
- subtract frame size from SP
- note that arguments now start at SP+framesize+8
Normal epilogue:
- pop frame from Go stack
- pop return address from Go stack
- push 0 (type i32) on the Wasm stack
- return
Exit immediately epilogue:
- push 1 (type i32) on the Wasm stack
- return
- note that the return address and stack frame are left on the Go stack
The main loop that executes goroutines is wasm_pc_f_loop, in
runtime/rt0_js_wasm.s. It grabs the saved return address from
the top of the Go stack (actually SP-8?), splits it up into F
and B parts, then calls F with its Wasm argument set to B.
Note that when resuming a goroutine, only the most recent function
invocation of that goroutine appears on the Wasm stack. When that
Wasm function returns normally, the next most recent frame will
then be started up by wasm_pc_f_loop.
Global 0 is SP (stack pointer)
Global 1 is CTXT (closure pointer)
Global 2 is GP (goroutine pointer)
*/
func Init(arch *ssagen.ArchInfo) {
arch.LinkArch = &wasm.Linkwasm
arch.REGSP = wasm.REG_SP
arch.MAXWIDTH = 1 << 50
arch.ZeroRange = zeroRange
arch.Ginsnop = ginsnop
arch.SSAMarkMoves = ssaMarkMoves
arch.SSAGenValue = ssaGenValue
arch.SSAGenBlock = ssaGenBlock
}
func zeroRange(pp *objw.Progs, p *obj.Prog, off, cnt int64, state *uint32) *obj.Prog {
if cnt == 0 {
return p
}
if cnt%8 != 0 {
base.Fatalf("zerorange count not a multiple of widthptr %d", cnt)
}
for i := int64(0); i < cnt; i += 8 {
p = pp.Append(p, wasm.AGet, obj.TYPE_REG, wasm.REG_SP, 0, 0, 0, 0)
p = pp.Append(p, wasm.AI64Const, obj.TYPE_CONST, 0, 0, 0, 0, 0)
p = pp.Append(p, wasm.AI64Store, 0, 0, 0, obj.TYPE_CONST, 0, off+i)
}
return p
}
func ginsnop(pp *objw.Progs) *obj.Prog {
return pp.Prog(wasm.ANop)
}
func ssaMarkMoves(s *ssagen.State, b *ssa.Block) {
}
func ssaGenBlock(s *ssagen.State, b, next *ssa.Block) {
switch b.Kind {
case ssa.BlockPlain:
if next != b.Succs[0].Block() {
s.Br(obj.AJMP, b.Succs[0].Block())
}
case ssa.BlockIf:
switch next {
case b.Succs[0].Block():
// if false, jump to b.Succs[1]
getValue32(s, b.Controls[0])
s.Prog(wasm.AI32Eqz)
s.Prog(wasm.AIf)
s.Br(obj.AJMP, b.Succs[1].Block())
s.Prog(wasm.AEnd)
case b.Succs[1].Block():
// if true, jump to b.Succs[0]
getValue32(s, b.Controls[0])
s.Prog(wasm.AIf)
s.Br(obj.AJMP, b.Succs[0].Block())
s.Prog(wasm.AEnd)
default:
// if true, jump to b.Succs[0], else jump to b.Succs[1]
getValue32(s, b.Controls[0])
s.Prog(wasm.AIf)
s.Br(obj.AJMP, b.Succs[0].Block())
s.Prog(wasm.AEnd)
s.Br(obj.AJMP, b.Succs[1].Block())
}
case ssa.BlockRet:
s.Prog(obj.ARET)
case ssa.BlockExit, ssa.BlockRetJmp:
case ssa.BlockDefer:
p := s.Prog(wasm.AGet)
p.From = obj.Addr{Type: obj.TYPE_REG, Reg: wasm.REG_RET0}
s.Prog(wasm.AI64Eqz)
s.Prog(wasm.AI32Eqz)
s.Prog(wasm.AIf)
s.Br(obj.AJMP, b.Succs[1].Block())
s.Prog(wasm.AEnd)
if next != b.Succs[0].Block() {
s.Br(obj.AJMP, b.Succs[0].Block())
}
default:
panic("unexpected block")
}
// Entry point for the next block. Used by the JMP in goToBlock.
s.Prog(wasm.ARESUMEPOINT)
if s.OnWasmStackSkipped != 0 {
panic("wasm: bad stack")
}
}
func ssaGenValue(s *ssagen.State, v *ssa.Value) {
switch v.Op {
case ssa.OpWasmLoweredStaticCall, ssa.OpWasmLoweredClosureCall, ssa.OpWasmLoweredInterCall, ssa.OpWasmLoweredTailCall:
s.PrepareCall(v)
if call, ok := v.Aux.(*ssa.AuxCall); ok && call.Fn == ir.Syms.Deferreturn {
// The runtime needs to inject jumps to
// deferreturn calls using the address in
// _func.deferreturn. Hence, the call to
// deferreturn must itself be a resumption
// point so it gets a target PC.
s.Prog(wasm.ARESUMEPOINT)
}
if v.Op == ssa.OpWasmLoweredClosureCall {
getValue64(s, v.Args[1])
setReg(s, wasm.REG_CTXT)
}
if call, ok := v.Aux.(*ssa.AuxCall); ok && call.Fn != nil {
sym := call.Fn
p := s.Prog(obj.ACALL)
p.To = obj.Addr{Type: obj.TYPE_MEM, Name: obj.NAME_EXTERN, Sym: sym}
p.Pos = v.Pos
if v.Op == ssa.OpWasmLoweredTailCall {
p.As = obj.ARET
}
} else {
getValue64(s, v.Args[0])
p := s.Prog(obj.ACALL)
p.To = obj.Addr{Type: obj.TYPE_NONE}
p.Pos = v.Pos
}
case ssa.OpWasmLoweredMove:
getValue32(s, v.Args[0])
getValue32(s, v.Args[1])
i32Const(s, int32(v.AuxInt))
s.Prog(wasm.AMemoryCopy)
case ssa.OpWasmLoweredZero:
getValue32(s, v.Args[0])
i32Const(s, 0)
i32Const(s, int32(v.AuxInt))
s.Prog(wasm.AMemoryFill)
case ssa.OpWasmLoweredNilCheck:
getValue64(s, v.Args[0])
s.Prog(wasm.AI64Eqz)
s.Prog(wasm.AIf)
p := s.Prog(wasm.ACALLNORESUME)
p.To = obj.Addr{Type: obj.TYPE_MEM, Name: obj.NAME_EXTERN, Sym: ir.Syms.SigPanic}
s.Prog(wasm.AEnd)
if logopt.Enabled() {
logopt.LogOpt(v.Pos, "nilcheck", "genssa", v.Block.Func.Name)
}
if base.Debug.Nil != 0 && v.Pos.Line() > 1 { // v.Pos.Line()==1 in generated wrappers
base.WarnfAt(v.Pos, "generated nil check")
}
case ssa.OpWasmLoweredWB:
p := s.Prog(wasm.ACall)
// AuxInt encodes how many buffer entries we need.
p.To = obj.Addr{Type: obj.TYPE_MEM, Name: obj.NAME_EXTERN, Sym: ir.Syms.GCWriteBarrier[v.AuxInt-1]}
setReg(s, v.Reg0()) // move result from wasm stack to register local
case ssa.OpWasmI64Store8, ssa.OpWasmI64Store16, ssa.OpWasmI64Store32, ssa.OpWasmI64Store, ssa.OpWasmF32Store, ssa.OpWasmF64Store:
getValue32(s, v.Args[0])
getValue64(s, v.Args[1])
p := s.Prog(v.Op.Asm())
p.To = obj.Addr{Type: obj.TYPE_CONST, Offset: v.AuxInt}
case ssa.OpStoreReg:
getReg(s, wasm.REG_SP)
getValue64(s, v.Args[0])
p := s.Prog(storeOp(v.Type))
ssagen.AddrAuto(&p.To, v)
case ssa.OpClobber, ssa.OpClobberReg:
// TODO: implement for clobberdead experiment. Nop is ok for now.
default:
if v.Type.IsMemory() {
return
}
if v.OnWasmStack {
s.OnWasmStackSkipped++
// If a Value is marked OnWasmStack, we don't generate the value and store it to a register now.
// Instead, we delay the generation to when the value is used and then directly generate it on the WebAssembly stack.
return
}
ssaGenValueOnStack(s, v, true)
if s.OnWasmStackSkipped != 0 {
panic("wasm: bad stack")
}
setReg(s, v.Reg())
}
}
func ssaGenValueOnStack(s *ssagen.State, v *ssa.Value, extend bool) {
switch v.Op {
case ssa.OpWasmLoweredGetClosurePtr:
getReg(s, wasm.REG_CTXT)
case ssa.OpWasmLoweredGetCallerPC:
p := s.Prog(wasm.AI64Load)
// Caller PC is stored 8 bytes below first parameter.
p.From = obj.Addr{
Type: obj.TYPE_MEM,
Name: obj.NAME_PARAM,
Offset: -8,
}
case ssa.OpWasmLoweredGetCallerSP:
p := s.Prog(wasm.AGet)
// Caller SP is the address of the first parameter.
p.From = obj.Addr{
Type: obj.TYPE_ADDR,
Name: obj.NAME_PARAM,
Reg: wasm.REG_SP,
Offset: 0,
}
case ssa.OpWasmLoweredAddr:
if v.Aux == nil { // address of off(SP), no symbol
getValue64(s, v.Args[0])
i64Const(s, v.AuxInt)
s.Prog(wasm.AI64Add)
break
}
p := s.Prog(wasm.AGet)
p.From.Type = obj.TYPE_ADDR
switch v.Aux.(type) {
case *obj.LSym:
ssagen.AddAux(&p.From, v)
case *ir.Name:
p.From.Reg = v.Args[0].Reg()
ssagen.AddAux(&p.From, v)
default:
panic("wasm: bad LoweredAddr")
}
case ssa.OpWasmLoweredConvert:
getValue64(s, v.Args[0])
case ssa.OpWasmSelect:
getValue64(s, v.Args[0])
getValue64(s, v.Args[1])
getValue32(s, v.Args[2])
s.Prog(v.Op.Asm())
case ssa.OpWasmI64AddConst:
getValue64(s, v.Args[0])
i64Const(s, v.AuxInt)
s.Prog(v.Op.Asm())
case ssa.OpWasmI64Const:
i64Const(s, v.AuxInt)
case ssa.OpWasmF32Const:
f32Const(s, v.AuxFloat())
case ssa.OpWasmF64Const:
f64Const(s, v.AuxFloat())
case ssa.OpWasmI64Load8U, ssa.OpWasmI64Load8S, ssa.OpWasmI64Load16U, ssa.OpWasmI64Load16S, ssa.OpWasmI64Load32U, ssa.OpWasmI64Load32S, ssa.OpWasmI64Load, ssa.OpWasmF32Load, ssa.OpWasmF64Load:
getValue32(s, v.Args[0])
p := s.Prog(v.Op.Asm())
p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: v.AuxInt}
case ssa.OpWasmI64Eqz:
getValue64(s, v.Args[0])
s.Prog(v.Op.Asm())
if extend {
s.Prog(wasm.AI64ExtendI32U)
}
case ssa.OpWasmI64Eq, ssa.OpWasmI64Ne, ssa.OpWasmI64LtS, ssa.OpWasmI64LtU, ssa.OpWasmI64GtS, ssa.OpWasmI64GtU, ssa.OpWasmI64LeS, ssa.OpWasmI64LeU, ssa.OpWasmI64GeS, ssa.OpWasmI64GeU,
ssa.OpWasmF32Eq, ssa.OpWasmF32Ne, ssa.OpWasmF32Lt, ssa.OpWasmF32Gt, ssa.OpWasmF32Le, ssa.OpWasmF32Ge,
ssa.OpWasmF64Eq, ssa.OpWasmF64Ne, ssa.OpWasmF64Lt, ssa.OpWasmF64Gt, ssa.OpWasmF64Le, ssa.OpWasmF64Ge:
getValue64(s, v.Args[0])
getValue64(s, v.Args[1])
s.Prog(v.Op.Asm())
if extend {
s.Prog(wasm.AI64ExtendI32U)
}
case ssa.OpWasmI64Add, ssa.OpWasmI64Sub, ssa.OpWasmI64Mul, ssa.OpWasmI64DivU, ssa.OpWasmI64RemS, ssa.OpWasmI64RemU, ssa.OpWasmI64And, ssa.OpWasmI64Or, ssa.OpWasmI64Xor, ssa.OpWasmI64Shl, ssa.OpWasmI64ShrS, ssa.OpWasmI64ShrU, ssa.OpWasmI64Rotl,
ssa.OpWasmF32Add, ssa.OpWasmF32Sub, ssa.OpWasmF32Mul, ssa.OpWasmF32Div, ssa.OpWasmF32Copysign,
ssa.OpWasmF64Add, ssa.OpWasmF64Sub, ssa.OpWasmF64Mul, ssa.OpWasmF64Div, ssa.OpWasmF64Copysign:
getValue64(s, v.Args[0])
getValue64(s, v.Args[1])
s.Prog(v.Op.Asm())
case ssa.OpWasmI32Rotl:
getValue32(s, v.Args[0])
getValue32(s, v.Args[1])
s.Prog(wasm.AI32Rotl)
s.Prog(wasm.AI64ExtendI32U)
case ssa.OpWasmI64DivS:
getValue64(s, v.Args[0])
getValue64(s, v.Args[1])
if v.Type.Size() == 8 {
// Division of int64 needs helper function wasmDiv to handle the MinInt64 / -1 case.
p := s.Prog(wasm.ACall)
p.To = obj.Addr{Type: obj.TYPE_MEM, Name: obj.NAME_EXTERN, Sym: ir.Syms.WasmDiv}
break
}
s.Prog(wasm.AI64DivS)
case ssa.OpWasmI64TruncSatF32S, ssa.OpWasmI64TruncSatF64S:
getValue64(s, v.Args[0])
if buildcfg.GOWASM.SatConv {
s.Prog(v.Op.Asm())
} else {
if v.Op == ssa.OpWasmI64TruncSatF32S {
s.Prog(wasm.AF64PromoteF32)
}
p := s.Prog(wasm.ACall)
p.To = obj.Addr{Type: obj.TYPE_MEM, Name: obj.NAME_EXTERN, Sym: ir.Syms.WasmTruncS}
}
case ssa.OpWasmI64TruncSatF32U, ssa.OpWasmI64TruncSatF64U:
getValue64(s, v.Args[0])
if buildcfg.GOWASM.SatConv {
s.Prog(v.Op.Asm())
} else {
if v.Op == ssa.OpWasmI64TruncSatF32U {
s.Prog(wasm.AF64PromoteF32)
}
p := s.Prog(wasm.ACall)
p.To = obj.Addr{Type: obj.TYPE_MEM, Name: obj.NAME_EXTERN, Sym: ir.Syms.WasmTruncU}
}
case ssa.OpWasmF32DemoteF64:
getValue64(s, v.Args[0])
s.Prog(v.Op.Asm())
case ssa.OpWasmF64PromoteF32:
getValue64(s, v.Args[0])
s.Prog(v.Op.Asm())
case ssa.OpWasmF32ConvertI64S, ssa.OpWasmF32ConvertI64U,
ssa.OpWasmF64ConvertI64S, ssa.OpWasmF64ConvertI64U,
ssa.OpWasmI64Extend8S, ssa.OpWasmI64Extend16S, ssa.OpWasmI64Extend32S,
ssa.OpWasmF32Neg, ssa.OpWasmF32Sqrt, ssa.OpWasmF32Trunc, ssa.OpWasmF32Ceil, ssa.OpWasmF32Floor, ssa.OpWasmF32Nearest, ssa.OpWasmF32Abs,
ssa.OpWasmF64Neg, ssa.OpWasmF64Sqrt, ssa.OpWasmF64Trunc, ssa.OpWasmF64Ceil, ssa.OpWasmF64Floor, ssa.OpWasmF64Nearest, ssa.OpWasmF64Abs,
ssa.OpWasmI64Ctz, ssa.OpWasmI64Clz, ssa.OpWasmI64Popcnt:
getValue64(s, v.Args[0])
s.Prog(v.Op.Asm())
case ssa.OpLoadReg:
p := s.Prog(loadOp(v.Type))
ssagen.AddrAuto(&p.From, v.Args[0])
case ssa.OpCopy:
getValue64(s, v.Args[0])
default:
v.Fatalf("unexpected op: %s", v.Op)
}
}
func isCmp(v *ssa.Value) bool {
switch v.Op {
case ssa.OpWasmI64Eqz, ssa.OpWasmI64Eq, ssa.OpWasmI64Ne, ssa.OpWasmI64LtS, ssa.OpWasmI64LtU, ssa.OpWasmI64GtS, ssa.OpWasmI64GtU, ssa.OpWasmI64LeS, ssa.OpWasmI64LeU, ssa.OpWasmI64GeS, ssa.OpWasmI64GeU,
ssa.OpWasmF32Eq, ssa.OpWasmF32Ne, ssa.OpWasmF32Lt, ssa.OpWasmF32Gt, ssa.OpWasmF32Le, ssa.OpWasmF32Ge,
ssa.OpWasmF64Eq, ssa.OpWasmF64Ne, ssa.OpWasmF64Lt, ssa.OpWasmF64Gt, ssa.OpWasmF64Le, ssa.OpWasmF64Ge:
return true
default:
return false
}
}
func getValue32(s *ssagen.State, v *ssa.Value) {
if v.OnWasmStack {
s.OnWasmStackSkipped--
ssaGenValueOnStack(s, v, false)
if !isCmp(v) {
s.Prog(wasm.AI32WrapI64)
}
return
}
reg := v.Reg()
getReg(s, reg)
if reg != wasm.REG_SP {
s.Prog(wasm.AI32WrapI64)
}
}
func getValue64(s *ssagen.State, v *ssa.Value) {
if v.OnWasmStack {
s.OnWasmStackSkipped--
ssaGenValueOnStack(s, v, true)
return
}
reg := v.Reg()
getReg(s, reg)
if reg == wasm.REG_SP {
s.Prog(wasm.AI64ExtendI32U)
}
}
func i32Const(s *ssagen.State, val int32) {
p := s.Prog(wasm.AI32Const)
p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: int64(val)}
}
func i64Const(s *ssagen.State, val int64) {
p := s.Prog(wasm.AI64Const)
p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: val}
}
func f32Const(s *ssagen.State, val float64) {
p := s.Prog(wasm.AF32Const)
p.From = obj.Addr{Type: obj.TYPE_FCONST, Val: val}
}
func f64Const(s *ssagen.State, val float64) {
p := s.Prog(wasm.AF64Const)
p.From = obj.Addr{Type: obj.TYPE_FCONST, Val: val}
}
func getReg(s *ssagen.State, reg int16) {
p := s.Prog(wasm.AGet)
p.From = obj.Addr{Type: obj.TYPE_REG, Reg: reg}
}
func setReg(s *ssagen.State, reg int16) {
p := s.Prog(wasm.ASet)
p.To = obj.Addr{Type: obj.TYPE_REG, Reg: reg}
}
func loadOp(t *types.Type) obj.As {
if t.IsFloat() {
switch t.Size() {
case 4:
return wasm.AF32Load
case 8:
return wasm.AF64Load
default:
panic("bad load type")
}
}
switch t.Size() {
case 1:
if t.IsSigned() {
return wasm.AI64Load8S
}
return wasm.AI64Load8U
case 2:
if t.IsSigned() {
return wasm.AI64Load16S
}
return wasm.AI64Load16U
case 4:
if t.IsSigned() {
return wasm.AI64Load32S
}
return wasm.AI64Load32U
case 8:
return wasm.AI64Load
default:
panic("bad load type")
}
}
func storeOp(t *types.Type) obj.As {
if t.IsFloat() {
switch t.Size() {
case 4:
return wasm.AF32Store
case 8:
return wasm.AF64Store
default:
panic("bad store type")
}
}
switch t.Size() {
case 1:
return wasm.AI64Store8
case 2:
return wasm.AI64Store16
case 4:
return wasm.AI64Store32
case 8:
return wasm.AI64Store
default:
panic("bad store type")
}
}