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// Copyright 2018 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 aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || (solaris && go1.20)
package base
import (
"internal/unsafeheader"
"os"
"runtime"
"syscall"
"unsafe"
)
// TODO(mdempsky): Is there a higher-level abstraction that still
// works well for iimport?
// MapFile returns length bytes from the file starting at the
// specified offset as a string.
func MapFile(f *os.File, offset, length int64) (string, error) {
// POSIX mmap: "The implementation may require that off is a
// multiple of the page size."
x := offset & int64(os.Getpagesize()-1)
offset -= x
length += x
buf, err := syscall.Mmap(int(f.Fd()), offset, int(length), syscall.PROT_READ, syscall.MAP_SHARED)
runtime.KeepAlive(f)
if err != nil {
return "", err
}
buf = buf[x:]
pSlice := (*unsafeheader.Slice)(unsafe.Pointer(&buf))
var res string
pString := (*unsafeheader.String)(unsafe.Pointer(&res))
pString.Data = pSlice.Data
pString.Len = pSlice.Len
return res, nil
}
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