summaryrefslogtreecommitdiffstats
path: root/src/reflect/abi.go
blob: 2b5f40538057a727bdede3083da61b882c7f1db5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
// Copyright 2021 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 reflect

import (
	"internal/abi"
	"internal/goarch"
	"unsafe"
)

// These variables are used by the register assignment
// algorithm in this file.
//
// They should be modified with care (no other reflect code
// may be executing) and are generally only modified
// when testing this package.
//
// They should never be set higher than their internal/abi
// constant counterparts, because the system relies on a
// structure that is at least large enough to hold the
// registers the system supports.
//
// Currently they're set to zero because using the actual
// constants will break every part of the toolchain that
// uses reflect to call functions (e.g. go test, or anything
// that uses text/template). The values that are currently
// commented out there should be the actual values once
// we're ready to use the register ABI everywhere.
var (
	intArgRegs   = abi.IntArgRegs
	floatArgRegs = abi.FloatArgRegs
	floatRegSize = uintptr(abi.EffectiveFloatRegSize)
)

// abiStep represents an ABI "instruction." Each instruction
// describes one part of how to translate between a Go value
// in memory and a call frame.
type abiStep struct {
	kind abiStepKind

	// offset and size together describe a part of a Go value
	// in memory.
	offset uintptr
	size   uintptr // size in bytes of the part

	// These fields describe the ABI side of the translation.
	stkOff uintptr // stack offset, used if kind == abiStepStack
	ireg   int     // integer register index, used if kind == abiStepIntReg or kind == abiStepPointer
	freg   int     // FP register index, used if kind == abiStepFloatReg
}

// abiStepKind is the "op-code" for an abiStep instruction.
type abiStepKind int

const (
	abiStepBad      abiStepKind = iota
	abiStepStack                // copy to/from stack
	abiStepIntReg               // copy to/from integer register
	abiStepPointer              // copy pointer to/from integer register
	abiStepFloatReg             // copy to/from FP register
)

// abiSeq represents a sequence of ABI instructions for copying
// from a series of reflect.Values to a call frame (for call arguments)
// or vice-versa (for call results).
//
// An abiSeq should be populated by calling its addArg method.
type abiSeq struct {
	// steps is the set of instructions.
	//
	// The instructions are grouped together by whole arguments,
	// with the starting index for the instructions
	// of the i'th Go value available in valueStart.
	//
	// For instance, if this abiSeq represents 3 arguments
	// passed to a function, then the 2nd argument's steps
	// begin at steps[valueStart[1]].
	//
	// Because reflect accepts Go arguments in distinct
	// Values and each Value is stored separately, each abiStep
	// that begins a new argument will have its offset
	// field == 0.
	steps      []abiStep
	valueStart []int

	stackBytes   uintptr // stack space used
	iregs, fregs int     // registers used
}

func (a *abiSeq) dump() {
	for i, p := range a.steps {
		println("part", i, p.kind, p.offset, p.size, p.stkOff, p.ireg, p.freg)
	}
	print("values ")
	for _, i := range a.valueStart {
		print(i, " ")
	}
	println()
	println("stack", a.stackBytes)
	println("iregs", a.iregs)
	println("fregs", a.fregs)
}

// stepsForValue returns the ABI instructions for translating
// the i'th Go argument or return value represented by this
// abiSeq to the Go ABI.
func (a *abiSeq) stepsForValue(i int) []abiStep {
	s := a.valueStart[i]
	var e int
	if i == len(a.valueStart)-1 {
		e = len(a.steps)
	} else {
		e = a.valueStart[i+1]
	}
	return a.steps[s:e]
}

// addArg extends the abiSeq with a new Go value of type t.
//
// If the value was stack-assigned, returns the single
// abiStep describing that translation, and nil otherwise.
func (a *abiSeq) addArg(t *abi.Type) *abiStep {
	// We'll always be adding a new value, so do that first.
	pStart := len(a.steps)
	a.valueStart = append(a.valueStart, pStart)
	if t.Size() == 0 {
		// If the size of the argument type is zero, then
		// in order to degrade gracefully into ABI0, we need
		// to stack-assign this type. The reason is that
		// although zero-sized types take up no space on the
		// stack, they do cause the next argument to be aligned.
		// So just do that here, but don't bother actually
		// generating a new ABI step for it (there's nothing to
		// actually copy).
		//
		// We cannot handle this in the recursive case of
		// regAssign because zero-sized *fields* of a
		// non-zero-sized struct do not cause it to be
		// stack-assigned. So we need a special case here
		// at the top.
		a.stackBytes = align(a.stackBytes, uintptr(t.Align()))
		return nil
	}
	// Hold a copy of "a" so that we can roll back if
	// register assignment fails.
	aOld := *a
	if !a.regAssign(t, 0) {
		// Register assignment failed. Roll back any changes
		// and stack-assign.
		*a = aOld
		a.stackAssign(t.Size(), uintptr(t.Align()))
		return &a.steps[len(a.steps)-1]
	}
	return nil
}

// addRcvr extends the abiSeq with a new method call
// receiver according to the interface calling convention.
//
// If the receiver was stack-assigned, returns the single
// abiStep describing that translation, and nil otherwise.
// Returns true if the receiver is a pointer.
func (a *abiSeq) addRcvr(rcvr *abi.Type) (*abiStep, bool) {
	// The receiver is always one word.
	a.valueStart = append(a.valueStart, len(a.steps))
	var ok, ptr bool
	if ifaceIndir(rcvr) || rcvr.Pointers() {
		ok = a.assignIntN(0, goarch.PtrSize, 1, 0b1)
		ptr = true
	} else {
		// TODO(mknyszek): Is this case even possible?
		// The interface data work never contains a non-pointer
		// value. This case was copied over from older code
		// in the reflect package which only conditionally added
		// a pointer bit to the reflect.(Value).Call stack frame's
		// GC bitmap.
		ok = a.assignIntN(0, goarch.PtrSize, 1, 0b0)
		ptr = false
	}
	if !ok {
		a.stackAssign(goarch.PtrSize, goarch.PtrSize)
		return &a.steps[len(a.steps)-1], ptr
	}
	return nil, ptr
}

// regAssign attempts to reserve argument registers for a value of
// type t, stored at some offset.
//
// It returns whether or not the assignment succeeded, but
// leaves any changes it made to a.steps behind, so the caller
// must undo that work by adjusting a.steps if it fails.
//
// This method along with the assign* methods represent the
// complete register-assignment algorithm for the Go ABI.
func (a *abiSeq) regAssign(t *abi.Type, offset uintptr) bool {
	switch Kind(t.Kind()) {
	case UnsafePointer, Pointer, Chan, Map, Func:
		return a.assignIntN(offset, t.Size(), 1, 0b1)
	case Bool, Int, Uint, Int8, Uint8, Int16, Uint16, Int32, Uint32, Uintptr:
		return a.assignIntN(offset, t.Size(), 1, 0b0)
	case Int64, Uint64:
		switch goarch.PtrSize {
		case 4:
			return a.assignIntN(offset, 4, 2, 0b0)
		case 8:
			return a.assignIntN(offset, 8, 1, 0b0)
		}
	case Float32, Float64:
		return a.assignFloatN(offset, t.Size(), 1)
	case Complex64:
		return a.assignFloatN(offset, 4, 2)
	case Complex128:
		return a.assignFloatN(offset, 8, 2)
	case String:
		return a.assignIntN(offset, goarch.PtrSize, 2, 0b01)
	case Interface:
		return a.assignIntN(offset, goarch.PtrSize, 2, 0b10)
	case Slice:
		return a.assignIntN(offset, goarch.PtrSize, 3, 0b001)
	case Array:
		tt := (*arrayType)(unsafe.Pointer(t))
		switch tt.Len {
		case 0:
			// There's nothing to assign, so don't modify
			// a.steps but succeed so the caller doesn't
			// try to stack-assign this value.
			return true
		case 1:
			return a.regAssign(tt.Elem, offset)
		default:
			return false
		}
	case Struct:
		st := (*structType)(unsafe.Pointer(t))
		for i := range st.Fields {
			f := &st.Fields[i]
			if !a.regAssign(f.Typ, offset+f.Offset) {
				return false
			}
		}
		return true
	default:
		print("t.Kind == ", t.Kind(), "\n")
		panic("unknown type kind")
	}
	panic("unhandled register assignment path")
}

// assignIntN assigns n values to registers, each "size" bytes large,
// from the data at [offset, offset+n*size) in memory. Each value at
// [offset+i*size, offset+(i+1)*size) for i < n is assigned to the
// next n integer registers.
//
// Bit i in ptrMap indicates whether the i'th value is a pointer.
// n must be <= 8.
//
// Returns whether assignment succeeded.
func (a *abiSeq) assignIntN(offset, size uintptr, n int, ptrMap uint8) bool {
	if n > 8 || n < 0 {
		panic("invalid n")
	}
	if ptrMap != 0 && size != goarch.PtrSize {
		panic("non-empty pointer map passed for non-pointer-size values")
	}
	if a.iregs+n > intArgRegs {
		return false
	}
	for i := 0; i < n; i++ {
		kind := abiStepIntReg
		if ptrMap&(uint8(1)<<i) != 0 {
			kind = abiStepPointer
		}
		a.steps = append(a.steps, abiStep{
			kind:   kind,
			offset: offset + uintptr(i)*size,
			size:   size,
			ireg:   a.iregs,
		})
		a.iregs++
	}
	return true
}

// assignFloatN assigns n values to registers, each "size" bytes large,
// from the data at [offset, offset+n*size) in memory. Each value at
// [offset+i*size, offset+(i+1)*size) for i < n is assigned to the
// next n floating-point registers.
//
// Returns whether assignment succeeded.
func (a *abiSeq) assignFloatN(offset, size uintptr, n int) bool {
	if n < 0 {
		panic("invalid n")
	}
	if a.fregs+n > floatArgRegs || floatRegSize < size {
		return false
	}
	for i := 0; i < n; i++ {
		a.steps = append(a.steps, abiStep{
			kind:   abiStepFloatReg,
			offset: offset + uintptr(i)*size,
			size:   size,
			freg:   a.fregs,
		})
		a.fregs++
	}
	return true
}

// stackAssign reserves space for one value that is "size" bytes
// large with alignment "alignment" to the stack.
//
// Should not be called directly; use addArg instead.
func (a *abiSeq) stackAssign(size, alignment uintptr) {
	a.stackBytes = align(a.stackBytes, alignment)
	a.steps = append(a.steps, abiStep{
		kind:   abiStepStack,
		offset: 0, // Only used for whole arguments, so the memory offset is 0.
		size:   size,
		stkOff: a.stackBytes,
	})
	a.stackBytes += size
}

// abiDesc describes the ABI for a function or method.
type abiDesc struct {
	// call and ret represent the translation steps for
	// the call and return paths of a Go function.
	call, ret abiSeq

	// These fields describe the stack space allocated
	// for the call. stackCallArgsSize is the amount of space
	// reserved for arguments but not return values. retOffset
	// is the offset at which return values begin, and
	// spill is the size in bytes of additional space reserved
	// to spill argument registers into in case of preemption in
	// reflectcall's stack frame.
	stackCallArgsSize, retOffset, spill uintptr

	// stackPtrs is a bitmap that indicates whether
	// each word in the ABI stack space (stack-assigned
	// args + return values) is a pointer. Used
	// as the heap pointer bitmap for stack space
	// passed to reflectcall.
	stackPtrs *bitVector

	// inRegPtrs is a bitmap whose i'th bit indicates
	// whether the i'th integer argument register contains
	// a pointer. Used by makeFuncStub and methodValueCall
	// to make result pointers visible to the GC.
	//
	// outRegPtrs is the same, but for result values.
	// Used by reflectcall to make result pointers visible
	// to the GC.
	inRegPtrs, outRegPtrs abi.IntArgRegBitmap
}

func (a *abiDesc) dump() {
	println("ABI")
	println("call")
	a.call.dump()
	println("ret")
	a.ret.dump()
	println("stackCallArgsSize", a.stackCallArgsSize)
	println("retOffset", a.retOffset)
	println("spill", a.spill)
	print("inRegPtrs:")
	dumpPtrBitMap(a.inRegPtrs)
	println()
	print("outRegPtrs:")
	dumpPtrBitMap(a.outRegPtrs)
	println()
}

func dumpPtrBitMap(b abi.IntArgRegBitmap) {
	for i := 0; i < intArgRegs; i++ {
		x := 0
		if b.Get(i) {
			x = 1
		}
		print(" ", x)
	}
}

func newAbiDesc(t *funcType, rcvr *abi.Type) abiDesc {
	// We need to add space for this argument to
	// the frame so that it can spill args into it.
	//
	// The size of this space is just the sum of the sizes
	// of each register-allocated type.
	//
	// TODO(mknyszek): Remove this when we no longer have
	// caller reserved spill space.
	spill := uintptr(0)

	// Compute gc program & stack bitmap for stack arguments
	stackPtrs := new(bitVector)

	// Compute the stack frame pointer bitmap and register
	// pointer bitmap for arguments.
	inRegPtrs := abi.IntArgRegBitmap{}

	// Compute abiSeq for input parameters.
	var in abiSeq
	if rcvr != nil {
		stkStep, isPtr := in.addRcvr(rcvr)
		if stkStep != nil {
			if isPtr {
				stackPtrs.append(1)
			} else {
				stackPtrs.append(0)
			}
		} else {
			spill += goarch.PtrSize
		}
	}
	for i, arg := range t.InSlice() {
		stkStep := in.addArg(arg)
		if stkStep != nil {
			addTypeBits(stackPtrs, stkStep.stkOff, arg)
		} else {
			spill = align(spill, uintptr(arg.Align()))
			spill += arg.Size()
			for _, st := range in.stepsForValue(i) {
				if st.kind == abiStepPointer {
					inRegPtrs.Set(st.ireg)
				}
			}
		}
	}
	spill = align(spill, goarch.PtrSize)

	// From the input parameters alone, we now know
	// the stackCallArgsSize and retOffset.
	stackCallArgsSize := in.stackBytes
	retOffset := align(in.stackBytes, goarch.PtrSize)

	// Compute the stack frame pointer bitmap and register
	// pointer bitmap for return values.
	outRegPtrs := abi.IntArgRegBitmap{}

	// Compute abiSeq for output parameters.
	var out abiSeq
	// Stack-assigned return values do not share
	// space with arguments like they do with registers,
	// so we need to inject a stack offset here.
	// Fake it by artificially extending stackBytes by
	// the return offset.
	out.stackBytes = retOffset
	for i, res := range t.OutSlice() {
		stkStep := out.addArg(res)
		if stkStep != nil {
			addTypeBits(stackPtrs, stkStep.stkOff, res)
		} else {
			for _, st := range out.stepsForValue(i) {
				if st.kind == abiStepPointer {
					outRegPtrs.Set(st.ireg)
				}
			}
		}
	}
	// Undo the faking from earlier so that stackBytes
	// is accurate.
	out.stackBytes -= retOffset
	return abiDesc{in, out, stackCallArgsSize, retOffset, spill, stackPtrs, inRegPtrs, outRegPtrs}
}

// intFromReg loads an argSize sized integer from reg and places it at to.
//
// argSize must be non-zero, fit in a register, and a power-of-two.
func intFromReg(r *abi.RegArgs, reg int, argSize uintptr, to unsafe.Pointer) {
	memmove(to, r.IntRegArgAddr(reg, argSize), argSize)
}

// intToReg loads an argSize sized integer and stores it into reg.
//
// argSize must be non-zero, fit in a register, and a power-of-two.
func intToReg(r *abi.RegArgs, reg int, argSize uintptr, from unsafe.Pointer) {
	memmove(r.IntRegArgAddr(reg, argSize), from, argSize)
}

// floatFromReg loads a float value from its register representation in r.
//
// argSize must be 4 or 8.
func floatFromReg(r *abi.RegArgs, reg int, argSize uintptr, to unsafe.Pointer) {
	switch argSize {
	case 4:
		*(*float32)(to) = archFloat32FromReg(r.Floats[reg])
	case 8:
		*(*float64)(to) = *(*float64)(unsafe.Pointer(&r.Floats[reg]))
	default:
		panic("bad argSize")
	}
}

// floatToReg stores a float value in its register representation in r.
//
// argSize must be either 4 or 8.
func floatToReg(r *abi.RegArgs, reg int, argSize uintptr, from unsafe.Pointer) {
	switch argSize {
	case 4:
		r.Floats[reg] = archFloat32ToReg(*(*float32)(from))
	case 8:
		r.Floats[reg] = *(*uint64)(from)
	default:
		panic("bad argSize")
	}
}