1 files changed, 119 insertions, 0 deletions
diff --git a/src/runtime/mem_windows.go b/src/runtime/mem_windows.go
new file mode 100644
index 000000000..a1dcad013
--- /dev/null
+++ b/src/runtime/mem_windows.go
@@ -0,0 +1,119 @@
+// Copyright 2010 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 runtime
+
+import (
+	"unsafe"
+)
+
+const (
+	_MEM_COMMIT   = 0x1000
+	_MEM_RESERVE  = 0x2000
+	_MEM_DECOMMIT = 0x4000
+	_MEM_RELEASE  = 0x8000
+
+	_PAGE_READWRITE = 0x0004
+	_PAGE_NOACCESS  = 0x0001
+)
+
+//go:cgo_import_dynamic runtime._VirtualAlloc VirtualAlloc "kernel32.dll"
+//go:cgo_import_dynamic runtime._VirtualFree VirtualFree "kernel32.dll"
+//go:cgo_import_dynamic runtime._VirtualProtect VirtualProtect "kernel32.dll"
+
+var (
+	_VirtualAlloc,
+	_VirtualFree,
+	_VirtualProtect stdFunction
+)
+
+//go:nosplit
+func sysAlloc(n uintptr, stat *uint64) unsafe.Pointer {
+	xadd64(stat, int64(n))
+	return unsafe.Pointer(stdcall4(_VirtualAlloc, 0, n, _MEM_COMMIT|_MEM_RESERVE, _PAGE_READWRITE))
+}
+
+func sysUnused(v unsafe.Pointer, n uintptr) {
+	r := stdcall3(_VirtualFree, uintptr(v), n, _MEM_DECOMMIT)
+	if r != 0 {
+		return
+	}
+
+	// Decommit failed. Usual reason is that we've merged memory from two different
+	// VirtualAlloc calls, and Windows will only let each VirtualFree handle pages from
+	// a single VirtualAlloc. It is okay to specify a subset of the pages from a single alloc,
+	// just not pages from multiple allocs. This is a rare case, arising only when we're
+	// trying to give memory back to the operating system, which happens on a time
+	// scale of minutes. It doesn't have to be terribly fast. Instead of extra bookkeeping
+	// on all our VirtualAlloc calls, try freeing successively smaller pieces until
+	// we manage to free something, and then repeat. This ends up being O(n log n)
+	// in the worst case, but that's fast enough.
+	for n > 0 {
+		small := n
+		for small >= 4096 && stdcall3(_VirtualFree, uintptr(v), small, _MEM_DECOMMIT) == 0 {
+			small /= 2
+			small &^= 4096 - 1
+		}
+		if small < 4096 {
+			gothrow("runtime: failed to decommit pages")
+		}
+		v = add(v, small)
+		n -= small
+	}
+}
+
+func sysUsed(v unsafe.Pointer, n uintptr) {
+	r := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE)
+	if r != uintptr(v) {
+		gothrow("runtime: failed to commit pages")
+	}
+
+	// Commit failed. See SysUnused.
+	for n > 0 {
+		small := n
+		for small >= 4096 && stdcall4(_VirtualAlloc, uintptr(v), small, _MEM_COMMIT, _PAGE_READWRITE) == 0 {
+			small /= 2
+			small &^= 4096 - 1
+		}
+		if small < 4096 {
+			gothrow("runtime: failed to decommit pages")
+		}
+		v = add(v, small)
+		n -= small
+	}
+}
+
+func sysFree(v unsafe.Pointer, n uintptr, stat *uint64) {
+	xadd64(stat, -int64(n))
+	r := stdcall3(_VirtualFree, uintptr(v), 0, _MEM_RELEASE)
+	if r == 0 {
+		gothrow("runtime: failed to release pages")
+	}
+}
+
+func sysFault(v unsafe.Pointer, n uintptr) {
+	// SysUnused makes the memory inaccessible and prevents its reuse
+	sysUnused(v, n)
+}
+
+func sysReserve(v unsafe.Pointer, n uintptr, reserved *bool) unsafe.Pointer {
+	*reserved = true
+	// v is just a hint.
+	// First try at v.
+	v = unsafe.Pointer(stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_RESERVE, _PAGE_READWRITE))
+	if v != nil {
+		return v
+	}
+
+	// Next let the kernel choose the address.
+	return unsafe.Pointer(stdcall4(_VirtualAlloc, 0, n, _MEM_RESERVE, _PAGE_READWRITE))
+}
+
+func sysMap(v unsafe.Pointer, n uintptr, reserved bool, stat *uint64) {
+	xadd64(stat, int64(n))
+	p := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE)
+	if p != uintptr(v) {
+		gothrow("runtime: cannot map pages in arena address space")
+	}
+}