linux/handler/exception_handler.h

// Copyright (c) 2010 Google Inc.
// All rights reserved.
//
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// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
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// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
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#ifndef CLIENT_LINUX_HANDLER_EXCEPTION_HANDLER_H_
#define CLIENT_LINUX_HANDLER_EXCEPTION_HANDLER_H_

#include <vector>
#include <string>

#include <signal.h>
#include <stdio.h>

#include "client/linux/crash_generation/crash_generation_client.h"
#include "processor/scoped_ptr.h"

struct sigaction;

namespace google_breakpad {

class ExceptionHandler;

// ExceptionHandler
//
// ExceptionHandler can write a minidump file when an exception occurs,
// or when WriteMinidump() is called explicitly by your program.
//
// To have the exception handler write minidumps when an uncaught exception
// (crash) occurs, you should create an instance early in the execution
// of your program, and keep it around for the entire time you want to
// have crash handling active (typically, until shutdown).
// (NOTE): There should be only be one this kind of exception handler
// object per process.
//
// If you want to write minidumps without installing the exception handler,
// you can create an ExceptionHandler with install_handler set to false,
// then call WriteMinidump.  You can also use this technique if you want to
// use different minidump callbacks for different call sites.
//
// In either case, a callback function is called when a minidump is written,
// which receives the unqiue id of the minidump.  The caller can use this
// id to collect and write additional application state, and to launch an
// external crash-reporting application.
//
// Caller should try to make the callbacks as crash-friendly as possible,
// it should avoid use heap memory allocation as much as possible.
class ExceptionHandler {
 public:
  // A callback function to run before Breakpad performs any substantial
  // processing of an exception.  A FilterCallback is called before writing
  // a minidump.  context is the parameter supplied by the user as
  // callback_context when the handler was created.
  //
  // If a FilterCallback returns true, Breakpad will continue processing,
  // attempting to write a minidump.  If a FilterCallback returns false,
  // Breakpad  will immediately report the exception as unhandled without
  // writing a minidump, allowing another handler the opportunity to handle it.
  typedef bool (*FilterCallback)(void *context);

  // A callback function to run after the minidump has been written.
  // minidump_id is a unique id for the dump, so the minidump
  // file is <dump_path>\<minidump_id>.dmp.  context is the parameter supplied
  // by the user as callback_context when the handler was created.  succeeded
  // indicates whether a minidump file was successfully written.
  //
  // If an exception occurred and the callback returns true, Breakpad will
  // treat the exception as fully-handled, suppressing any other handlers from
  // being notified of the exception.  If the callback returns false, Breakpad
  // will treat the exception as unhandled, and allow another handler to handle
  // it. If there are no other handlers, Breakpad will report the exception to
  // the system as unhandled, allowing a debugger or native crash dialog the
  // opportunity to handle the exception.  Most callback implementations
  // should normally return the value of |succeeded|, or when they wish to
  // not report an exception of handled, false.  Callbacks will rarely want to
  // return true directly (unless |succeeded| is true).
  typedef bool (*MinidumpCallback)(const char *dump_path,
                                   const char *minidump_id,
                                   void *context,
                                   bool succeeded);

  // In certain cases, a user may wish to handle the generation of the minidump
  // themselves. In this case, they can install a handler callback which is
  // called when a crash has occured. If this function returns true, no other
  // processing of occurs and the process will shortly be crashed. If this
  // returns false, the normal processing continues.
  typedef bool (*HandlerCallback)(const void* crash_context,
                                  size_t crash_context_size,
                                  void* context);

  // Creates a new ExceptionHandler instance to handle writing minidumps.
  // Before writing a minidump, the optional filter callback will be called.
  // Its return value determines whether or not Breakpad should write a
  // minidump.  Minidump files will be written to dump_path, and the optional
  // callback is called after writing the dump file, as described above.
  // If install_handler is true, then a minidump will be written whenever
  // an unhandled exception occurs.  If it is false, minidumps will only
  // be written when WriteMinidump is called.
  ExceptionHandler(const std::string &dump_path,
                   FilterCallback filter, MinidumpCallback callback,
                   void *callback_context,
                   bool install_handler);

  // Creates a new ExceptionHandler instance that can attempt to
  // perform out-of-process dump generation if server_fd is valid. If
  // server_fd is invalid, in-process dump generation will be
  // used. See the above ctor for a description of the other
  // parameters.
  ExceptionHandler(const std::string& dump_path,
                   FilterCallback filter, MinidumpCallback callback,
                   void* callback_context,
                   bool install_handler,
                   const int server_fd);

  ~ExceptionHandler();

  // Get and set the minidump path.
  std::string dump_path() const { return dump_path_; }
  void set_dump_path(const std::string &dump_path) {
    dump_path_ = dump_path;
    dump_path_c_ = dump_path_.c_str();
    UpdateNextID();
  }

  void set_crash_handler(HandlerCallback callback) {
    crash_handler_ = callback;
  }

  // Writes a minidump immediately.  This can be used to capture the
  // execution state independently of a crash.  Returns true on success.
  bool WriteMinidump();

  // Convenience form of WriteMinidump which does not require an
  // ExceptionHandler instance.
  static bool WriteMinidump(const std::string &dump_path,
                            MinidumpCallback callback,
                            void *callback_context);

  // This structure is passed to minidump_writer.h:WriteMinidump via an opaque
  // blob. It shouldn't be needed in any user code.
  struct CrashContext {
    siginfo_t siginfo;
    pid_t tid;  // the crashing thread.
    struct ucontext context;
#if !defined(__ARM_EABI__)
    // #ifdef this out because FP state is not part of user ABI for Linux ARM.
    struct _libc_fpstate float_state;
#endif
  };

  // Returns whether out-of-process dump generation is used or not.
  bool IsOutOfProcess() const {
      return crash_generation_client_.get() != NULL;
  }

 private:
  void Init(const std::string &dump_path,
            const int server_fd);
  bool InstallHandlers();
  void UninstallHandlers();
  void PreresolveSymbols();
  bool GenerateDump(CrashContext *context);
  void SendContinueSignalToChild();
  void WaitForContinueSignal();

  void UpdateNextID();
  static void SignalHandler(int sig, siginfo_t* info, void* uc);
  bool HandleSignal(int sig, siginfo_t* info, void* uc);
  static int ThreadEntry(void* arg);
  bool DoDump(pid_t crashing_process, const void* context,
              size_t context_size);

  const FilterCallback filter_;
  const MinidumpCallback callback_;
  void* const callback_context_;

  scoped_ptr<CrashGenerationClient> crash_generation_client_;

  std::string dump_path_;
  std::string next_minidump_path_;
  std::string next_minidump_id_;

  // Pointers to C-string representations of the above. These are set
  // when the above are set so we can avoid calling c_str during
  // an exception.
  const char* dump_path_c_;
  const char* next_minidump_path_c_;
  const char* next_minidump_id_c_;

  const bool handler_installed_;
  void* signal_stack;  // the handler stack.
  HandlerCallback crash_handler_;

  // The global exception handler stack. This is need becuase there may exist
  // multiple ExceptionHandler instances in a process. Each will have itself
  // registered in this stack.
  static std::vector<ExceptionHandler*> *handler_stack_;
  // The index of the handler that should handle the next exception.
  static unsigned handler_stack_index_;
  static pthread_mutex_t handler_stack_mutex_;

  // A vector of the old signal handlers.
  std::vector<std::pair<int, struct sigaction *> > old_handlers_;

  // We need to explicitly enable ptrace of parent processes on some
  // kernels, but we need to know the PID of the cloned process before we
  // can do this. We create a pipe which we can use to block the
  // cloned process after creating it, until we have explicitly enabled
  // ptrace. This is used to store the file descriptors for the pipe
  int fdes[2];
};

}  // namespace google_breakpad

#endif  // CLIENT_LINUX_HANDLER_EXCEPTION_HANDLER_H_