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