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95 lines
3.5 KiB
C++
95 lines
3.5 KiB
C++
// Copyright (c) 2013 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_DEBUG_PROC_MAPS_LINUX_H_
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#define BASE_DEBUG_PROC_MAPS_LINUX_H_
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#include <stdint.h>
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#include <string>
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#include <vector>
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#include "base/base_export.h"
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namespace base {
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namespace debug {
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// Describes a region of mapped memory and the path of the file mapped.
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struct MappedMemoryRegion {
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enum Permission {
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READ = 1 << 0,
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WRITE = 1 << 1,
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EXECUTE = 1 << 2,
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PRIVATE = 1 << 3, // If set, region is private, otherwise it is shared.
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};
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// The address range [start,end) of mapped memory.
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uintptr_t start;
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uintptr_t end;
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// Byte offset into |path| of the range mapped into memory.
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unsigned long long offset;
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// Image base, if this mapping corresponds to an ELF image.
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uintptr_t base;
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// Bitmask of read/write/execute/private/shared permissions.
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uint8_t permissions;
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// Name of the file mapped into memory.
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//
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// NOTE: path names aren't guaranteed to point at valid files. For example,
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// "[heap]" and "[stack]" are used to represent the location of the process'
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// heap and stack, respectively.
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std::string path;
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};
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// Reads the data from /proc/self/maps and stores the result in |proc_maps|.
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// Returns true if successful, false otherwise.
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//
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// There is *NO* guarantee that the resulting contents will be free of
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// duplicates or even contain valid entries by time the method returns.
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//
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//
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// THE GORY DETAILS
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//
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// Did you know it's next-to-impossible to atomically read the whole contents
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// of /proc/<pid>/maps? You would think that if we passed in a large-enough
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// buffer to read() that It Should Just Work(tm), but sadly that's not the case.
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//
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// Linux's procfs uses seq_file [1] for handling iteration, text formatting,
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// and dealing with resulting data that is larger than the size of a page. That
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// last bit is especially important because it means that seq_file will never
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// return more than the size of a page in a single call to read().
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//
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// Unfortunately for a program like Chrome the size of /proc/self/maps is
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// larger than the size of page so we're forced to call read() multiple times.
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// If the virtual memory table changed in any way between calls to read() (e.g.,
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// a different thread calling mprotect()), it can make seq_file generate
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// duplicate entries or skip entries.
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//
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// Even if seq_file was changed to keep flushing the contents of its page-sized
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// buffer to the usermode buffer inside a single call to read(), it has to
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// release its lock on the virtual memory table to handle page faults while
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// copying data to usermode. This puts us in the same situation where the table
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// can change while we're copying data.
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//
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// Alternatives such as fork()-and-suspend-the-parent-while-child-reads were
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// attempted, but they present more subtle problems than it's worth. Depending
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// on your use case your best bet may be to read /proc/<pid>/maps prior to
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// starting other threads.
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//
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// [1] http://kernelnewbies.org/Documents/SeqFileHowTo
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BASE_EXPORT bool ReadProcMaps(std::string* proc_maps);
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// Parses /proc/<pid>/maps input data and stores in |regions|. Returns true
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// and updates |regions| if and only if all of |input| was successfully parsed.
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BASE_EXPORT bool ParseProcMaps(const std::string& input,
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std::vector<MappedMemoryRegion>* regions);
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} // namespace debug
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} // namespace base
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#endif // BASE_DEBUG_PROC_MAPS_LINUX_H_
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