257 lines
6.7 KiB
Go
257 lines
6.7 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package runtime
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import (
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"runtime/internal/math"
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"runtime/internal/sys"
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"unsafe"
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)
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// For gccgo, use go:linkname to export compiler-called functions.
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//
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//go:linkname makeslice
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//go:linkname makeslice64
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//go:linkname growslice
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//go:linkname slicecopy
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//go:linkname slicestringcopy
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type slice struct {
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array unsafe.Pointer
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len int
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cap int
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}
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// An notInHeapSlice is a slice backed by go:notinheap memory.
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type notInHeapSlice struct {
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array *notInHeap
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len int
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cap int
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}
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func panicmakeslicelen() {
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panic(errorString("makeslice: len out of range"))
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}
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func panicmakeslicecap() {
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panic(errorString("makeslice: cap out of range"))
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}
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func makeslice(et *_type, len, cap int) unsafe.Pointer {
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mem, overflow := math.MulUintptr(et.size, uintptr(cap))
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if overflow || mem > maxAlloc || len < 0 || len > cap {
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// NOTE: Produce a 'len out of range' error instead of a
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// 'cap out of range' error when someone does make([]T, bignumber).
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// 'cap out of range' is true too, but since the cap is only being
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// supplied implicitly, saying len is clearer.
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// See golang.org/issue/4085.
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mem, overflow := math.MulUintptr(et.size, uintptr(len))
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if overflow || mem > maxAlloc || len < 0 {
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panicmakeslicelen()
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}
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panicmakeslicecap()
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}
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return mallocgc(mem, et, true)
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}
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func makeslice64(et *_type, len64, cap64 int64) unsafe.Pointer {
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len := int(len64)
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if int64(len) != len64 {
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panicmakeslicelen()
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}
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cap := int(cap64)
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if int64(cap) != cap64 {
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panicmakeslicecap()
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}
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return makeslice(et, len, cap)
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}
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// growslice handles slice growth during append.
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// It is passed the slice element type, the old slice, and the desired new minimum capacity,
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// and it returns a new slice with at least that capacity, with the old data
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// copied into it.
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// The new slice's length is set to the requested capacity.
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func growslice(et *_type, oldarray unsafe.Pointer, oldlen, oldcap, cap int) slice {
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if raceenabled {
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callerpc := getcallerpc()
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racereadrangepc(oldarray, uintptr(oldlen*int(et.size)), callerpc, funcPC(growslice))
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}
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if msanenabled {
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msanread(oldarray, uintptr(oldlen*int(et.size)))
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}
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if cap < oldcap {
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panic(errorString("growslice: cap out of range"))
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}
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if et.size == 0 {
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// append should not create a slice with nil pointer but non-zero len.
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// We assume that append doesn't need to preserve oldarray in this case.
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return slice{unsafe.Pointer(&zerobase), cap, cap}
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}
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newcap := oldcap
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doublecap := newcap + newcap
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if cap > doublecap {
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newcap = cap
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} else {
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if oldlen < 1024 {
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newcap = doublecap
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} else {
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// Check 0 < newcap to detect overflow
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// and prevent an infinite loop.
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for 0 < newcap && newcap < cap {
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newcap += newcap / 4
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}
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// Set newcap to the requested cap when
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// the newcap calculation overflowed.
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if newcap <= 0 {
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newcap = cap
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}
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}
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}
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var overflow bool
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var lenmem, newlenmem, capmem uintptr
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// Specialize for common values of et.size.
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// For 1 we don't need any division/multiplication.
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// For sys.PtrSize, compiler will optimize division/multiplication into a shift by a constant.
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// For powers of 2, use a variable shift.
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switch {
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case et.size == 1:
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lenmem = uintptr(oldlen)
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newlenmem = uintptr(cap)
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capmem = roundupsize(uintptr(newcap))
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overflow = uintptr(newcap) > maxAlloc
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newcap = int(capmem)
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case et.size == sys.PtrSize:
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lenmem = uintptr(oldlen) * sys.PtrSize
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newlenmem = uintptr(cap) * sys.PtrSize
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capmem = roundupsize(uintptr(newcap) * sys.PtrSize)
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overflow = uintptr(newcap) > maxAlloc/sys.PtrSize
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newcap = int(capmem / sys.PtrSize)
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case isPowerOfTwo(et.size):
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var shift uintptr
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if sys.PtrSize == 8 {
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// Mask shift for better code generation.
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shift = uintptr(sys.Ctz64(uint64(et.size))) & 63
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} else {
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shift = uintptr(sys.Ctz32(uint32(et.size))) & 31
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}
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lenmem = uintptr(oldlen) << shift
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newlenmem = uintptr(cap) << shift
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capmem = roundupsize(uintptr(newcap) << shift)
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overflow = uintptr(newcap) > (maxAlloc >> shift)
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newcap = int(capmem >> shift)
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default:
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lenmem = uintptr(oldlen) * et.size
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newlenmem = uintptr(cap) * et.size
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capmem, overflow = math.MulUintptr(et.size, uintptr(newcap))
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capmem = roundupsize(capmem)
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newcap = int(capmem / et.size)
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}
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// The check of overflow in addition to capmem > maxAlloc is needed
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// to prevent an overflow which can be used to trigger a segfault
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// on 32bit architectures with this example program:
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//
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// type T [1<<27 + 1]int64
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//
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// var d T
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// var s []T
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//
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// func main() {
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// s = append(s, d, d, d, d)
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// print(len(s), "\n")
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// }
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if overflow || capmem > maxAlloc {
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panic(errorString("growslice: cap out of range"))
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}
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var p unsafe.Pointer
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if et.ptrdata == 0 {
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p = mallocgc(capmem, nil, false)
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// The append() that calls growslice is going to overwrite from oldlen to cap (which will be the new length).
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// Only clear the part that will not be overwritten.
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memclrNoHeapPointers(add(p, newlenmem), capmem-newlenmem)
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} else {
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// Note: can't use rawmem (which avoids zeroing of memory), because then GC can scan uninitialized memory.
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p = mallocgc(capmem, et, true)
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if lenmem > 0 && writeBarrier.enabled {
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// Only shade the pointers in old.array since we know the destination slice p
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// only contains nil pointers because it has been cleared during alloc.
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bulkBarrierPreWriteSrcOnly(uintptr(p), uintptr(oldarray), lenmem)
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}
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}
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memmove(p, oldarray, lenmem)
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return slice{p, cap, newcap}
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}
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func isPowerOfTwo(x uintptr) bool {
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return x&(x-1) == 0
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}
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func slicecopy(to, fm slice, width uintptr) int {
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if fm.len == 0 || to.len == 0 {
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return 0
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}
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n := fm.len
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if to.len < n {
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n = to.len
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}
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if width == 0 {
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return n
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}
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if raceenabled {
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callerpc := getcallerpc()
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pc := funcPC(slicecopy)
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racewriterangepc(to.array, uintptr(n*int(width)), callerpc, pc)
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racereadrangepc(fm.array, uintptr(n*int(width)), callerpc, pc)
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}
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if msanenabled {
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msanwrite(to.array, uintptr(n*int(width)))
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msanread(fm.array, uintptr(n*int(width)))
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}
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size := uintptr(n) * width
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if size == 1 { // common case worth about 2x to do here
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// TODO: is this still worth it with new memmove impl?
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*(*byte)(to.array) = *(*byte)(fm.array) // known to be a byte pointer
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} else {
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memmove(to.array, fm.array, size)
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}
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return n
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}
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func slicestringcopy(to []byte, fm string) int {
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if len(fm) == 0 || len(to) == 0 {
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return 0
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}
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n := len(fm)
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if len(to) < n {
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n = len(to)
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}
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if raceenabled {
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callerpc := getcallerpc()
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pc := funcPC(slicestringcopy)
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racewriterangepc(unsafe.Pointer(&to[0]), uintptr(n), callerpc, pc)
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}
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if msanenabled {
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msanwrite(unsafe.Pointer(&to[0]), uintptr(n))
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}
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memmove(unsafe.Pointer(&to[0]), stringStructOf(&fm).str, uintptr(n))
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return n
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}
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