outbuf_windows.go

Documentation: cmd/link/internal/ld

     1  // Copyright 2019 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package ld
     6  
     7  import (
     8  	"internal/unsafeheader"
     9  	"syscall"
    10  	"unsafe"
    11  )
    12  
    13  // Mmap maps the output file with the given size. It unmaps the old mapping
    14  // if it is already mapped. It also flushes any in-heap data to the new
    15  // mapping.
    16  func (out *OutBuf) Mmap(filesize uint64) error {
    17  	oldlen := len(out.buf)
    18  	if oldlen != 0 {
    19  		out.munmap()
    20  	}
    21  
    22  	err := out.f.Truncate(int64(filesize))
    23  	if err != nil {
    24  		Exitf("resize output file failed: %v", err)
    25  	}
    26  
    27  	low, high := uint32(filesize), uint32(filesize>>32)
    28  	fmap, err := syscall.CreateFileMapping(syscall.Handle(out.f.Fd()), nil, syscall.PAGE_READWRITE, high, low, nil)
    29  	if err != nil {
    30  		return err
    31  	}
    32  	defer syscall.CloseHandle(fmap)
    33  
    34  	ptr, err := syscall.MapViewOfFile(fmap, syscall.FILE_MAP_READ|syscall.FILE_MAP_WRITE, 0, 0, uintptr(filesize))
    35  	if err != nil {
    36  		return err
    37  	}
    38  	bufHdr := (*unsafeheader.Slice)(unsafe.Pointer(&out.buf))
    39  	bufHdr.Data = unsafe.Pointer(ptr)
    40  	bufHdr.Len = int(filesize)
    41  	bufHdr.Cap = int(filesize)
    42  
    43  	// copy heap to new mapping
    44  	if uint64(oldlen+len(out.heap)) > filesize {
    45  		panic("mmap size too small")
    46  	}
    47  	copy(out.buf[oldlen:], out.heap)
    48  	out.heap = out.heap[:0]
    49  	return nil
    50  }
    51  
    52  func (out *OutBuf) munmap() {
    53  	if out.buf == nil {
    54  		return
    55  	}
    56  	// Apparently unmapping without flush may cause ACCESS_DENIED error
    57  	// (see issue 38440).
    58  	err := syscall.FlushViewOfFile(uintptr(unsafe.Pointer(&out.buf[0])), 0)
    59  	if err != nil {
    60  		Exitf("FlushViewOfFile failed: %v", err)
    61  	}
    62  	// Issue 44817: apparently the call below may be needed (according
    63  	// to the Windows docs) in addition to the FlushViewOfFile call
    64  	// above, " ... to flush all the dirty pages plus the metadata for
    65  	// the file and ensure that they are physically written to disk".
    66  	// Windows DOC links:
    67  	//
    68  	// https://docs.microsoft.com/en-us/windows/win32/api/memoryapi/nf-memoryapi-flushviewoffile
    69  	// https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-flushfilebuffers
    70  	err = syscall.FlushFileBuffers(syscall.Handle(out.f.Fd()))
    71  	if err != nil {
    72  		Exitf("FlushFileBuffers failed: %v", err)
    73  	}
    74  	err = syscall.UnmapViewOfFile(uintptr(unsafe.Pointer(&out.buf[0])))
    75  	out.buf = nil
    76  	if err != nil {
    77  		Exitf("UnmapViewOfFile failed: %v", err)
    78  	}
    79  }
    80
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