1// Copyright 2009 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package runtime
6
7import (
8	"runtime/internal/math"
9	"runtime/internal/sys"
10	"unsafe"
11)
12
13type slice struct {
14	array unsafe.Pointer
15	len   int
16	cap   int
17}
18
19// A notInHeapSlice is a slice backed by go:notinheap memory.
20type notInHeapSlice struct {
21	array *notInHeap
22	len   int
23	cap   int
24}
25
26func panicmakeslicelen() {
27	panic(errorString("makeslice: len out of range"))
28}
29
30func panicmakeslicecap() {
31	panic(errorString("makeslice: cap out of range"))
32}
33
34func makeslice(et *_type, len, cap int) unsafe.Pointer {
35	mem, overflow := math.MulUintptr(et.size, uintptr(cap))
36	if overflow || mem > maxAlloc || len < 0 || len > cap {
37		// NOTE: Produce a 'len out of range' error instead of a
38		// 'cap out of range' error when someone does make([]T, bignumber).
39		// 'cap out of range' is true too, but since the cap is only being
40		// supplied implicitly, saying len is clearer.
41		// See golang.org/issue/4085.
42		mem, overflow := math.MulUintptr(et.size, uintptr(len))
43		if overflow || mem > maxAlloc || len < 0 {
44			panicmakeslicelen()
45		}
46		panicmakeslicecap()
47	}
48
49	return mallocgc(mem, et, true)
50}
51
52func makeslice64(et *_type, len64, cap64 int64) unsafe.Pointer {
53	len := int(len64)
54	if int64(len) != len64 {
55		panicmakeslicelen()
56	}
57
58	cap := int(cap64)
59	if int64(cap) != cap64 {
60		panicmakeslicecap()
61	}
62
63	return makeslice(et, len, cap)
64}
65
66// growslice handles slice growth during append.
67// It is passed the slice element type, the old slice, and the desired new minimum capacity,
68// and it returns a new slice with at least that capacity, with the old data
69// copied into it.
70// The new slice's length is set to the old slice's length,
71// NOT to the new requested capacity.
72// This is for codegen convenience. The old slice's length is used immediately
73// to calculate where to write new values during an append.
74// TODO: When the old backend is gone, reconsider this decision.
75// The SSA backend might prefer the new length or to return only ptr/cap and save stack space.
76func growslice(et *_type, old slice, cap int) slice {
77	if raceenabled {
78		callerpc := getcallerpc()
79		racereadrangepc(old.array, uintptr(old.len*int(et.size)), callerpc, funcPC(growslice))
80	}
81	if msanenabled {
82		msanread(old.array, uintptr(old.len*int(et.size)))
83	}
84
85	if cap < old.cap {
86		panic(errorString("growslice: cap out of range"))
87	}
88
89	if et.size == 0 {
90		// append should not create a slice with nil pointer but non-zero len.
91		// We assume that append doesn't need to preserve old.array in this case.
92		return slice{unsafe.Pointer(&zerobase), old.len, cap}
93	}
94
95	newcap := old.cap
96	doublecap := newcap + newcap
97	if cap > doublecap {
98		newcap = cap
99	} else {
100		if old.len < 1024 {
101			newcap = doublecap
102		} else {
103			// Check 0 < newcap to detect overflow
104			// and prevent an infinite loop.
105			for 0 < newcap && newcap < cap {
106				newcap += newcap / 4
107			}
108			// Set newcap to the requested cap when
109			// the newcap calculation overflowed.
110			if newcap <= 0 {
111				newcap = cap
112			}
113		}
114	}
115
116	var overflow bool
117	var lenmem, newlenmem, capmem uintptr
118	// Specialize for common values of et.size.
119	// For 1 we don't need any division/multiplication.
120	// For sys.PtrSize, compiler will optimize division/multiplication into a shift by a constant.
121	// For powers of 2, use a variable shift.
122	switch {
123	case et.size == 1:
124		lenmem = uintptr(old.len)
125		newlenmem = uintptr(cap)
126		capmem = roundupsize(uintptr(newcap))
127		overflow = uintptr(newcap) > maxAlloc
128		newcap = int(capmem)
129	case et.size == sys.PtrSize:
130		lenmem = uintptr(old.len) * sys.PtrSize
131		newlenmem = uintptr(cap) * sys.PtrSize
132		capmem = roundupsize(uintptr(newcap) * sys.PtrSize)
133		overflow = uintptr(newcap) > maxAlloc/sys.PtrSize
134		newcap = int(capmem / sys.PtrSize)
135	case isPowerOfTwo(et.size):
136		var shift uintptr
137		if sys.PtrSize == 8 {
138			// Mask shift for better code generation.
139			shift = uintptr(sys.Ctz64(uint64(et.size))) & 63
140		} else {
141			shift = uintptr(sys.Ctz32(uint32(et.size))) & 31
142		}
143		lenmem = uintptr(old.len) << shift
144		newlenmem = uintptr(cap) << shift
145		capmem = roundupsize(uintptr(newcap) << shift)
146		overflow = uintptr(newcap) > (maxAlloc >> shift)
147		newcap = int(capmem >> shift)
148	default:
149		lenmem = uintptr(old.len) * et.size
150		newlenmem = uintptr(cap) * et.size
151		capmem, overflow = math.MulUintptr(et.size, uintptr(newcap))
152		capmem = roundupsize(capmem)
153		newcap = int(capmem / et.size)
154	}
155
156	// The check of overflow in addition to capmem > maxAlloc is needed
157	// to prevent an overflow which can be used to trigger a segfault
158	// on 32bit architectures with this example program:
159	//
160	// type T [1<<27 + 1]int64
161	//
162	// var d T
163	// var s []T
164	//
165	// func main() {
166	//   s = append(s, d, d, d, d)
167	//   print(len(s), "\n")
168	// }
169	if overflow || capmem > maxAlloc {
170		panic(errorString("growslice: cap out of range"))
171	}
172
173	var p unsafe.Pointer
174	if et.ptrdata == 0 {
175		p = mallocgc(capmem, nil, false)
176		// The append() that calls growslice is going to overwrite from old.len to cap (which will be the new length).
177		// Only clear the part that will not be overwritten.
178		memclrNoHeapPointers(add(p, newlenmem), capmem-newlenmem)
179	} else {
180		// Note: can't use rawmem (which avoids zeroing of memory), because then GC can scan uninitialized memory.
181		p = mallocgc(capmem, et, true)
182		if lenmem > 0 && writeBarrier.enabled {
183			// Only shade the pointers in old.array since we know the destination slice p
184			// only contains nil pointers because it has been cleared during alloc.
185			bulkBarrierPreWriteSrcOnly(uintptr(p), uintptr(old.array), lenmem)
186		}
187	}
188	memmove(p, old.array, lenmem)
189
190	return slice{p, old.len, newcap}
191}
192
193func isPowerOfTwo(x uintptr) bool {
194	return x&(x-1) == 0
195}
196
197func slicecopy(to, fm slice, width uintptr) int {
198	if fm.len == 0 || to.len == 0 {
199		return 0
200	}
201
202	n := fm.len
203	if to.len < n {
204		n = to.len
205	}
206
207	if width == 0 {
208		return n
209	}
210
211	if raceenabled {
212		callerpc := getcallerpc()
213		pc := funcPC(slicecopy)
214		racewriterangepc(to.array, uintptr(n*int(width)), callerpc, pc)
215		racereadrangepc(fm.array, uintptr(n*int(width)), callerpc, pc)
216	}
217	if msanenabled {
218		msanwrite(to.array, uintptr(n*int(width)))
219		msanread(fm.array, uintptr(n*int(width)))
220	}
221
222	size := uintptr(n) * width
223	if size == 1 { // common case worth about 2x to do here
224		// TODO: is this still worth it with new memmove impl?
225		*(*byte)(to.array) = *(*byte)(fm.array) // known to be a byte pointer
226	} else {
227		memmove(to.array, fm.array, size)
228	}
229	return n
230}
231
232func slicestringcopy(to []byte, fm string) int {
233	if len(fm) == 0 || len(to) == 0 {
234		return 0
235	}
236
237	n := len(fm)
238	if len(to) < n {
239		n = len(to)
240	}
241
242	if raceenabled {
243		callerpc := getcallerpc()
244		pc := funcPC(slicestringcopy)
245		racewriterangepc(unsafe.Pointer(&to[0]), uintptr(n), callerpc, pc)
246	}
247	if msanenabled {
248		msanwrite(unsafe.Pointer(&to[0]), uintptr(n))
249	}
250
251	memmove(unsafe.Pointer(&to[0]), stringStructOf(&fm).str, uintptr(n))
252	return n
253}
254