1 files changed, 67 insertions, 0 deletions
diff --git a/src/cmd/link/internal/ld/outbuf_windows.go b/src/cmd/link/internal/ld/outbuf_windows.go
new file mode 100644
index 0000000..915c72b
--- /dev/null
+++ b/src/cmd/link/internal/ld/outbuf_windows.go
@@ -0,0 +1,67 @@
+// Copyright 2019 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 ld
+
+import (
+	"reflect"
+	"syscall"
+	"unsafe"
+)
+
+// Mmap maps the output file with the given size. It unmaps the old mapping
+// if it is already mapped. It also flushes any in-heap data to the new
+// mapping.
+func (out *OutBuf) Mmap(filesize uint64) error {
+	oldlen := len(out.buf)
+	if oldlen != 0 {
+		out.munmap()
+	}
+
+	err := out.f.Truncate(int64(filesize))
+	if err != nil {
+		Exitf("resize output file failed: %v", err)
+	}
+
+	low, high := uint32(filesize), uint32(filesize>>32)
+	fmap, err := syscall.CreateFileMapping(syscall.Handle(out.f.Fd()), nil, syscall.PAGE_READWRITE, high, low, nil)
+	if err != nil {
+		return err
+	}
+	defer syscall.CloseHandle(fmap)
+
+	ptr, err := syscall.MapViewOfFile(fmap, syscall.FILE_MAP_READ|syscall.FILE_MAP_WRITE, 0, 0, uintptr(filesize))
+	if err != nil {
+		return err
+	}
+	bufHdr := (*reflect.SliceHeader)(unsafe.Pointer(&out.buf))
+	bufHdr.Data = ptr
+	bufHdr.Len = int(filesize)
+	bufHdr.Cap = int(filesize)
+
+	// copy heap to new mapping
+	if uint64(oldlen+len(out.heap)) > filesize {
+		panic("mmap size too small")
+	}
+	copy(out.buf[oldlen:], out.heap)
+	out.heap = out.heap[:0]
+	return nil
+}
+
+func (out *OutBuf) munmap() {
+	if out.buf == nil {
+		return
+	}
+	// Apparently unmapping without flush may cause ACCESS_DENIED error
+	// (see issue 38440).
+	err := syscall.FlushViewOfFile(uintptr(unsafe.Pointer(&out.buf[0])), 0)
+	if err != nil {
+		Exitf("FlushViewOfFile failed: %v", err)
+	}
+	err = syscall.UnmapViewOfFile(uintptr(unsafe.Pointer(&out.buf[0])))
+	out.buf = nil
+	if err != nil {
+		Exitf("UnmapViewOfFile failed: %v", err)
+	}
+}