1// Copyright (c) 2010 Google Inc.
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3//
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29
30#ifndef CLIENT_LINUX_HANDLER_EXCEPTION_HANDLER_H_
31#define CLIENT_LINUX_HANDLER_EXCEPTION_HANDLER_H_
32
33#include <signal.h>
34#include <stdint.h>
35#include <stdio.h>
36#include <sys/ucontext.h>
37
38#include <string>
39
40#include "client/linux/crash_generation/crash_generation_client.h"
41#include "client/linux/handler/minidump_descriptor.h"
42#include "client/linux/minidump_writer/minidump_writer.h"
43#include "common/scoped_ptr.h"
44#include "common/using_std_string.h"
45#include "google_breakpad/common/minidump_format.h"
46
47namespace google_breakpad {
48
49// ExceptionHandler
50//
51// ExceptionHandler can write a minidump file when an exception occurs,
52// or when WriteMinidump() is called explicitly by your program.
53//
54// To have the exception handler write minidumps when an uncaught exception
55// (crash) occurs, you should create an instance early in the execution
56// of your program, and keep it around for the entire time you want to
57// have crash handling active (typically, until shutdown).
58// (NOTE): There should be only be one this kind of exception handler
59// object per process.
60//
61// If you want to write minidumps without installing the exception handler,
62// you can create an ExceptionHandler with install_handler set to false,
63// then call WriteMinidump. You can also use this technique if you want to
64// use different minidump callbacks for different call sites.
65//
66// In either case, a callback function is called when a minidump is written,
67// which receives the full path or file descriptor of the minidump. The
68// caller can collect and write additional application state to that minidump,
69// and launch an external crash-reporting application.
70//
71// Caller should try to make the callbacks as crash-friendly as possible,
72// it should avoid use heap memory allocation as much as possible.
73
74class ExceptionHandler {
75 public:
76 // A callback function to run before Breakpad performs any substantial
77 // processing of an exception. A FilterCallback is called before writing
78 // a minidump. |context| is the parameter supplied by the user as
79 // callback_context when the handler was created.
80 //
81 // If a FilterCallback returns true, Breakpad will continue processing,
82 // attempting to write a minidump. If a FilterCallback returns false,
83 // Breakpad will immediately report the exception as unhandled without
84 // writing a minidump, allowing another handler the opportunity to handle it.
85 typedef bool (*FilterCallback)(void* context);
86
87 // A callback function to run after the minidump has been written.
88 // |descriptor| contains the file descriptor or file path containing the
89 // minidump. |context| is the parameter supplied by the user as
90 // callback_context when the handler was created. |succeeded| indicates
91 // whether a minidump file was successfully written.
92 //
93 // If an exception occurred and the callback returns true, Breakpad will
94 // treat the exception as fully-handled, suppressing any other handlers from
95 // being notified of the exception. If the callback returns false, Breakpad
96 // will treat the exception as unhandled, and allow another handler to handle
97 // it. If there are no other handlers, Breakpad will report the exception to
98 // the system as unhandled, allowing a debugger or native crash dialog the
99 // opportunity to handle the exception. Most callback implementations
100 // should normally return the value of |succeeded|, or when they wish to
101 // not report an exception of handled, false. Callbacks will rarely want to
102 // return true directly (unless |succeeded| is true).
103 typedef bool (*MinidumpCallback)(const MinidumpDescriptor& descriptor,
104 void* context,
105 bool succeeded);
106
107 // In certain cases, a user may wish to handle the generation of the minidump
108 // themselves. In this case, they can install a handler callback which is
109 // called when a crash has occurred. If this function returns true, no other
110 // processing of occurs and the process will shortly be crashed. If this
111 // returns false, the normal processing continues.
112 typedef bool (*HandlerCallback)(const void* crash_context,
113 size_t crash_context_size,
114 void* context);
115
116 // Creates a new ExceptionHandler instance to handle writing minidumps.
117 // Before writing a minidump, the optional |filter| callback will be called.
118 // Its return value determines whether or not Breakpad should write a
119 // minidump. The minidump content will be written to the file path or file
120 // descriptor from |descriptor|, and the optional |callback| is called after
121 // writing the dump file, as described above.
122 // If install_handler is true, then a minidump will be written whenever
123 // an unhandled exception occurs. If it is false, minidumps will only
124 // be written when WriteMinidump is called.
125 // If |server_fd| is valid, the minidump is generated out-of-process. If it
126 // is -1, in-process generation will always be used.
127 ExceptionHandler(const MinidumpDescriptor& descriptor,
128 FilterCallback filter,
129 MinidumpCallback callback,
130 void* callback_context,
131 bool install_handler,
132 const int server_fd);
133 ~ExceptionHandler();
134
135 const MinidumpDescriptor& minidump_descriptor() const {
136 return minidump_descriptor_;
137 }
138
139 void set_minidump_descriptor(const MinidumpDescriptor& descriptor) {
140 minidump_descriptor_ = descriptor;
141 }
142
143 void set_crash_handler(HandlerCallback callback) {
144 crash_handler_ = callback;
145 }
146
147 void set_crash_generation_client(CrashGenerationClient* client) {
148 crash_generation_client_.reset(client);
149 }
150
151 // Writes a minidump immediately. This can be used to capture the execution
152 // state independently of a crash.
153 // Returns true on success.
154 // If the ExceptionHandler has been created with a path, a new file is
155 // generated for each minidump. The file path can be retrieved in the
156 // MinidumpDescriptor passed to the MinidumpCallback or by accessing the
157 // MinidumpDescriptor directly from the ExceptionHandler (with
158 // minidump_descriptor()).
159 // If the ExceptionHandler has been created with a file descriptor, the file
160 // descriptor is repositioned to its beginning and the previous generated
161 // minidump is overwritten.
162 // Note that this method is not supposed to be called from a compromised
163 // context as it uses the heap.
164 bool WriteMinidump();
165
166 // Convenience form of WriteMinidump which does not require an
167 // ExceptionHandler instance.
168 static bool WriteMinidump(const string& dump_path,
169 MinidumpCallback callback,
170 void* callback_context);
171
172 // Write a minidump of |child| immediately. This can be used to
173 // capture the execution state of |child| independently of a crash.
174 // Pass a meaningful |child_blamed_thread| to make that thread in
175 // the child process the one from which a crash signature is
176 // extracted.
177 //
178 // WARNING: the return of this function *must* happen before
179 // the code that will eventually reap |child| executes.
180 // Otherwise there's a pernicious race condition in which |child|
181 // exits, is reaped, another process created with its pid, then that
182 // new process dumped.
183 static bool WriteMinidumpForChild(pid_t child,
184 pid_t child_blamed_thread,
185 const string& dump_path,
186 MinidumpCallback callback,
187 void* callback_context);
188
189 // This structure is passed to minidump_writer.h:WriteMinidump via an opaque
190 // blob. It shouldn't be needed in any user code.
191 struct CrashContext {
192 siginfo_t siginfo;
193 pid_t tid; // the crashing thread.
194 ucontext_t context;
195#if !defined(__ARM_EABI__) && !defined(__mips__)
196 // #ifdef this out because FP state is not part of user ABI for Linux ARM.
197 // In case of MIPS Linux FP state is already part of ucontext_t so
198 // 'float_state' is not required.
199 fpstate_t float_state;
200#endif
201 };
202
203 // Returns whether out-of-process dump generation is used or not.
204 bool IsOutOfProcess() const {
205 return crash_generation_client_.get() != NULL;
206 }
207
208 // Add information about a memory mapping. This can be used if
209 // a custom library loader is used that maps things in a way
210 // that the linux dumper can't handle by reading the maps file.
211 void AddMappingInfo(const string& name,
212 const uint8_t identifier[sizeof(MDGUID)],
213 uintptr_t start_address,
214 size_t mapping_size,
215 size_t file_offset);
216
217 // Register a block of memory of length bytes starting at address ptr
218 // to be copied to the minidump when a crash happens.
219 void RegisterAppMemory(void* ptr, size_t length);
220
221 // Unregister a block of memory that was registered with RegisterAppMemory.
222 void UnregisterAppMemory(void* ptr);
223
224 // Force signal handling for the specified signal.
225 bool SimulateSignalDelivery(int sig);
226
227 // Report a crash signal from an SA_SIGINFO signal handler.
228 bool HandleSignal(int sig, siginfo_t* info, void* uc);
229
230 private:
231 // Save the old signal handlers and install new ones.
232 static bool InstallHandlersLocked();
233 // Restore the old signal handlers.
234 static void RestoreHandlersLocked();
235
236 void PreresolveSymbols();
237 bool GenerateDump(CrashContext* context);
238 void SendContinueSignalToChild();
239 void WaitForContinueSignal();
240
241 static void SignalHandler(int sig, siginfo_t* info, void* uc);
242 static int ThreadEntry(void* arg);
243 bool DoDump(pid_t crashing_process, const void* context,
244 size_t context_size);
245
246 const FilterCallback filter_;
247 const MinidumpCallback callback_;
248 void* const callback_context_;
249
250 scoped_ptr<CrashGenerationClient> crash_generation_client_;
251
252 MinidumpDescriptor minidump_descriptor_;
253
254 // Must be volatile. The compiler is unaware of the code which runs in
255 // the signal handler which reads this variable. Without volatile the
256 // compiler is free to optimise away writes to this variable which it
257 // believes are never read.
258 volatile HandlerCallback crash_handler_;
259
260 // We need to explicitly enable ptrace of parent processes on some
261 // kernels, but we need to know the PID of the cloned process before we
262 // can do this. We create a pipe which we can use to block the
263 // cloned process after creating it, until we have explicitly enabled
264 // ptrace. This is used to store the file descriptors for the pipe
265 int fdes[2] = {-1, -1};
266
267 // Callers can add extra info about mappings for cases where the
268 // dumper code cannot extract enough information from /proc/<pid>/maps.
269 MappingList mapping_list_;
270
271 // Callers can request additional memory regions to be included in
272 // the dump.
273 AppMemoryList app_memory_list_;
274};
275
276typedef bool (*FirstChanceHandler)(int, siginfo_t*, void*);
277void SetFirstChanceExceptionHandler(FirstChanceHandler callback);
278
279} // namespace google_breakpad
280
281#endif // CLIENT_LINUX_HANDLER_EXCEPTION_HANDLER_H_
282