1// Copyright (c) 2013 The Chromium Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style license that can be 3// found in the LICENSE file. 4 5#ifndef BASE_DEBUG_PROC_MAPS_LINUX_H_ 6#define BASE_DEBUG_PROC_MAPS_LINUX_H_ 7 8#include <string> 9#include <vector> 10 11#include "base/base_export.h" 12#include "base/basictypes.h" 13 14namespace base { 15namespace debug { 16 17// Describes a region of mapped memory and the path of the file mapped. 18struct MappedMemoryRegion { 19 enum Permission { 20 READ = 1 << 0, 21 WRITE = 1 << 1, 22 EXECUTE = 1 << 2, 23 PRIVATE = 1 << 3, // If set, region is private, otherwise it is shared. 24 }; 25 26 // The address range [start,end) of mapped memory. 27 uintptr_t start; 28 uintptr_t end; 29 30 // Byte offset into |path| of the range mapped into memory. 31 unsigned long long offset; 32 33 // Bitmask of read/write/execute/private/shared permissions. 34 uint8 permissions; 35 36 // Name of the file mapped into memory. 37 // 38 // NOTE: path names aren't guaranteed to point at valid files. For example, 39 // "[heap]" and "[stack]" are used to represent the location of the process' 40 // heap and stack, respectively. 41 std::string path; 42}; 43 44// Reads the data from /proc/self/maps and stores the result in |proc_maps|. 45// Returns true if successful, false otherwise. 46// 47// There is *NO* guarantee that the resulting contents will be free of 48// duplicates or even contain valid entries by time the method returns. 49// 50// 51// THE GORY DETAILS 52// 53// Did you know it's next-to-impossible to atomically read the whole contents 54// of /proc/<pid>/maps? You would think that if we passed in a large-enough 55// buffer to read() that It Should Just Work(tm), but sadly that's not the case. 56// 57// Linux's procfs uses seq_file [1] for handling iteration, text formatting, 58// and dealing with resulting data that is larger than the size of a page. That 59// last bit is especially important because it means that seq_file will never 60// return more than the size of a page in a single call to read(). 61// 62// Unfortunately for a program like Chrome the size of /proc/self/maps is 63// larger than the size of page so we're forced to call read() multiple times. 64// If the virtual memory table changed in any way between calls to read() (e.g., 65// a different thread calling mprotect()), it can make seq_file generate 66// duplicate entries or skip entries. 67// 68// Even if seq_file was changed to keep flushing the contents of its page-sized 69// buffer to the usermode buffer inside a single call to read(), it has to 70// release its lock on the virtual memory table to handle page faults while 71// copying data to usermode. This puts us in the same situation where the table 72// can change while we're copying data. 73// 74// Alternatives such as fork()-and-suspend-the-parent-while-child-reads were 75// attempted, but they present more subtle problems than it's worth. Depending 76// on your use case your best bet may be to read /proc/<pid>/maps prior to 77// starting other threads. 78// 79// [1] http://kernelnewbies.org/Documents/SeqFileHowTo 80BASE_EXPORT bool ReadProcMaps(std::string* proc_maps); 81 82// Parses /proc/<pid>/maps input data and stores in |regions|. Returns true 83// and updates |regions| if and only if all of |input| was successfully parsed. 84BASE_EXPORT bool ParseProcMaps(const std::string& input, 85 std::vector<MappedMemoryRegion>* regions); 86 87} // namespace debug 88} // namespace base 89 90#endif // BASE_DEBUG_PROC_MAPS_LINUX_H_ 91