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// 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)
}
}
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