Repo created

TMessagesProj/jni/voip/webrtc/base/debug/proc_maps_linux.h

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+// 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 <stdint.h>
+
+#include <string>
+#include <vector>
+
+#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/<pid>/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/<pid>/maps prior to
+// starting other threads.
+//
+// [1] http://kernelnewbies.org/Documents/SeqFileHowTo
+BASE_EXPORT bool ReadProcMaps(std::string* proc_maps);
+
+// Parses /proc/<pid>/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<MappedMemoryRegion>* regions);
+
+}  // namespace debug
+}  // namespace base
+
+#endif  // BASE_DEBUG_PROC_MAPS_LINUX_H_