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 14 namespace base { 15 namespace debug { 16 17 // Describes a region of mapped memory and the path of the file mapped. 18 struct 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 80 BASE_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. 84 BASE_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
