65 lines
1.8 KiB
Go
65 lines
1.8 KiB
Go
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// Copyright 2016 The Periph Authors. All rights reserved.
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// Use of this source code is governed under the Apache License, Version 2.0
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// that can be found in the LICENSE file.
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package pmem
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import (
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"encoding/binary"
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"errors"
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"fmt"
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"os"
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)
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// ReadPageMap reads a physical address mapping for a virtual page address from
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// /proc/self/pagemap.
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//
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// It returns the physical address that corresponds to the start of the virtual
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// page within which the virtual address virtAddr is located.
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//
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// The meaning of the return value is documented at
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// https://www.kernel.org/doc/Documentation/vm/pagemap.txt
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func ReadPageMap(virtAddr uintptr) (uint64, error) {
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if !isLinux {
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return 0, errors.New("pmem: pagemap is not supported on this platform")
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}
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return readPageMapLinux(virtAddr)
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}
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//
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var (
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pageMap fileIO
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pageMapErr error
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)
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func readPageMapLinux(virtAddr uintptr) (uint64, error) {
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var b [8]byte
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mu.Lock()
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defer mu.Unlock()
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if pageMap == nil && pageMapErr == nil {
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// Open /proc/self/pagemap.
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//
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// It is a uint64 array where the index represents the virtual 4Kb page
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// number and the value represents the physical page properties backing
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// this virtual page.
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pageMap, pageMapErr = openFile("/proc/self/pagemap", os.O_RDONLY|os.O_SYNC)
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}
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if pageMapErr != nil {
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return 0, pageMapErr
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}
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// Convert address to page number, then index in uint64 array.
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offset := int64(virtAddr / pageSize * 8)
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if _, err := pageMap.Seek(offset, os.SEEK_SET); err != nil {
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return 0, fmt.Errorf("pmem: failed to seek at 0x%x for 0x%x: %v", offset, virtAddr, err)
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}
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n, err := pageMap.Read(b[:])
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if err != nil {
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return 0, fmt.Errorf("pmem: failed to read at 0x%x for 0x%x: %v", offset, virtAddr, err)
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}
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if n != len(b) {
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return 0, fmt.Errorf("pmem: failed to read the amount of data %d", len(b))
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}
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return binary.LittleEndian.Uint64(b[:]), nil
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}
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