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// Copyright 2023 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.
//go:build plan9 || wasm
package runtime
import "unsafe"
const isSbrkPlatform = true
const memDebug = false
// Memory management on sbrk systems (including the linear memory
// on Wasm).
// bloc is the runtime's sense of the break, which can go up or
// down. blocMax is the system's break, also the high water mark
// of bloc. The runtime uses memory up to bloc. The memory
// between bloc and blocMax is allocated by the OS but not used
// by the runtime.
//
// When the runtime needs to grow the heap address range, it
// increases bloc. When it needs to grow beyond blocMax, it calls
// the system sbrk to allocate more memory (and therefore
// increase blocMax).
//
// When the runtime frees memory at the end of the address space,
// it decreases bloc, but does not reduces the system break (as
// the OS doesn't support it). When the runtime frees memory in
// the middle of the address space, the memory goes to a free
// list.
var bloc uintptr // The runtime's sense of break. Can go up or down.
var blocMax uintptr // The break of the OS. Only increase.
var memlock mutex
type memHdr struct {
next memHdrPtr
size uintptr
}
var memFreelist memHdrPtr // sorted in ascending order
type memHdrPtr uintptr
func (p memHdrPtr) ptr() *memHdr { return (*memHdr)(unsafe.Pointer(p)) }
func (p *memHdrPtr) set(x *memHdr) { *p = memHdrPtr(unsafe.Pointer(x)) }
func memAlloc(n uintptr) unsafe.Pointer {
if p := memAllocNoGrow(n); p != nil {
return p
}
return sbrk(n)
}
func memAllocNoGrow(n uintptr) unsafe.Pointer {
n = memRound(n)
var prevp *memHdr
for p := memFreelist.ptr(); p != nil; p = p.next.ptr() {
if p.size >= n {
if p.size == n {
if prevp != nil {
prevp.next = p.next
} else {
memFreelist = p.next
}
} else {
p.size -= n
p = (*memHdr)(add(unsafe.Pointer(p), p.size))
}
*p = memHdr{}
return unsafe.Pointer(p)
}
prevp = p
}
return nil
}
func memFree(ap unsafe.Pointer, n uintptr) {
n = memRound(n)
memclrNoHeapPointers(ap, n)
bp := (*memHdr)(ap)
bp.size = n
bpn := uintptr(ap)
if memFreelist == 0 {
bp.next = 0
memFreelist.set(bp)
return
}
p := memFreelist.ptr()
if bpn < uintptr(unsafe.Pointer(p)) {
memFreelist.set(bp)
if bpn+bp.size == uintptr(unsafe.Pointer(p)) {
bp.size += p.size
bp.next = p.next
*p = memHdr{}
} else {
bp.next.set(p)
}
return
}
for ; p.next != 0; p = p.next.ptr() {
if bpn > uintptr(unsafe.Pointer(p)) && bpn < uintptr(unsafe.Pointer(p.next)) {
break
}
}
if bpn+bp.size == uintptr(unsafe.Pointer(p.next)) {
bp.size += p.next.ptr().size
bp.next = p.next.ptr().next
*p.next.ptr() = memHdr{}
} else {
bp.next = p.next
}
if uintptr(unsafe.Pointer(p))+p.size == bpn {
p.size += bp.size
p.next = bp.next
*bp = memHdr{}
} else {
p.next.set(bp)
}
}
func memCheck() {
if !memDebug {
return
}
for p := memFreelist.ptr(); p != nil && p.next != 0; p = p.next.ptr() {
if uintptr(unsafe.Pointer(p)) == uintptr(unsafe.Pointer(p.next)) {
print("runtime: ", unsafe.Pointer(p), " == ", unsafe.Pointer(p.next), "\n")
throw("mem: infinite loop")
}
if uintptr(unsafe.Pointer(p)) > uintptr(unsafe.Pointer(p.next)) {
print("runtime: ", unsafe.Pointer(p), " > ", unsafe.Pointer(p.next), "\n")
throw("mem: unordered list")
}
if uintptr(unsafe.Pointer(p))+p.size > uintptr(unsafe.Pointer(p.next)) {
print("runtime: ", unsafe.Pointer(p), "+", p.size, " > ", unsafe.Pointer(p.next), "\n")
throw("mem: overlapping blocks")
}
for b := add(unsafe.Pointer(p), unsafe.Sizeof(memHdr{})); uintptr(b) < uintptr(unsafe.Pointer(p))+p.size; b = add(b, 1) {
if *(*byte)(b) != 0 {
print("runtime: value at addr ", b, " with offset ", uintptr(b)-uintptr(unsafe.Pointer(p)), " in block ", p, " of size ", p.size, " is not zero\n")
throw("mem: uninitialised memory")
}
}
}
}
func memRound(p uintptr) uintptr {
return alignUp(p, physPageSize)
}
func initBloc() {
bloc = memRound(firstmoduledata.end)
blocMax = bloc
}
func sysAllocOS(n uintptr) unsafe.Pointer {
lock(&memlock)
p := memAlloc(n)
memCheck()
unlock(&memlock)
return p
}
func sysFreeOS(v unsafe.Pointer, n uintptr) {
lock(&memlock)
if uintptr(v)+n == bloc {
// Address range being freed is at the end of memory,
// so record a new lower value for end of memory.
// Can't actually shrink address space because segment is shared.
memclrNoHeapPointers(v, n)
bloc -= n
} else {
memFree(v, n)
memCheck()
}
unlock(&memlock)
}
func sysUnusedOS(v unsafe.Pointer, n uintptr) {
}
func sysUsedOS(v unsafe.Pointer, n uintptr) {
}
func sysHugePageOS(v unsafe.Pointer, n uintptr) {
}
func sysNoHugePageOS(v unsafe.Pointer, n uintptr) {
}
func sysHugePageCollapseOS(v unsafe.Pointer, n uintptr) {
}
func sysMapOS(v unsafe.Pointer, n uintptr) {
}
func sysFaultOS(v unsafe.Pointer, n uintptr) {
}
func sysReserveOS(v unsafe.Pointer, n uintptr) unsafe.Pointer {
lock(&memlock)
var p unsafe.Pointer
if uintptr(v) == bloc {
// Address hint is the current end of memory,
// so try to extend the address space.
p = sbrk(n)
}
if p == nil && v == nil {
p = memAlloc(n)
memCheck()
}
unlock(&memlock)
return p
}
func sysReserveAlignedSbrk(size, align uintptr) (unsafe.Pointer, uintptr) {
lock(&memlock)
if p := memAllocNoGrow(size + align); p != nil {
// We can satisfy the reservation from the free list.
// Trim off the unaligned parts.
pAligned := alignUp(uintptr(p), align)
if startLen := pAligned - uintptr(p); startLen > 0 {
memFree(p, startLen)
}
end := pAligned + size
if endLen := (uintptr(p) + size + align) - end; endLen > 0 {
memFree(unsafe.Pointer(end), endLen)
}
memCheck()
unlock(&memlock)
return unsafe.Pointer(pAligned), size
}
// Round up bloc to align, then allocate size.
p := alignUp(bloc, align)
r := sbrk(p + size - bloc)
if r == nil {
p, size = 0, 0
} else if l := p - uintptr(r); l > 0 {
// Free the area we skipped over for alignment.
memFree(r, l)
memCheck()
}
unlock(&memlock)
return unsafe.Pointer(p), size
}
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