iOS exception capture

Article Directory

I. System crash

Two. Handling signal

• Here are some signal descriptions

• Key points Note

Three. Actual combat

Four. Crash callstack analysis – one step into the analysis

Five. Demo Address

Six. References

Objective

Today in the iOS Advanced group, a friend asked about iOS's exception capture problem, which has not been studied before, taking this opportunity to study. and wrote a demo, if necessary, can be downloaded at the bottom of the article.

Before reading the article, it is recommended that you read this article after reading a ramble about iOS crash Collection framework, to understand the principle.

Developing iOS apps, solving crash problems is always a challenge. Crash is divided into two types, one of which is caused by exc_bad_access, because it accesses memory addresses that are not part of the process, it is possible to access memory that has been freed, and the other is an uncaught objective-c exception (nsexception). Causes the program to send itself a SIGABRT signal and crashes. In fact, for the uncaught objective-c exception, we have a way to record it down, if the log is properly recorded, can solve most of the crash problem. Here, the UI thread and the background thread are explained separately

I. System crash

For the system crash, the program exception exits can be captured by the Uncaughtexceptionhandler mechanism, that is, the content outside the catch in the program is captured by the system's own error handling. All we have to do is replace the Exceptionhandler with a custom function.

Two. Handling signal

Exception handling using OBJECTIVE-C can not get signal, if we want to deal with it, we also use the UNIX standard signal mechanism, register SIGABRT, Sigbus, SIGSEGV and other signals occur when the processing function. In this function we can output the stack information, the version information and so on everything else we want.

Here are some signal descriptions

1) SIGHUP

This signal is issued at the end of the user terminal connection (normal or abnormal), usually at the end of the control process of the terminal to notify the same session of the various jobs, when they are no longer associated with the control terminal.

When you log in to Linux, the system is assigned to a terminal (Session) of the logged-on user. All programs running at this terminal, including the foreground process group and the background process group, usually belong to this Session. When the user exits the Linux login, the foreground process group and the background will receive a sighup signal to the terminal output process. The default action for this signal is to terminate the process, so the foreground process group and the process that has terminal output in the background will be aborted. However, this signal can be captured, such as wget can capture the sighup signal, and ignore it, so even if you quit the Linux login, wget can continue to download.

In addition, for daemons with terminal disengagement, this signal is used to notify it to reread the configuration file.

2) SIGINT

A program termination (interrupt) signal, issued when the user types the intr character (usually ctrl-c), to inform the foreground process group that the process is terminated.

3) Sigquit

Similar to SIGINT, but controlled by the quit character (usually ctrl). The process generates a core file when it receives a sigquit exit, similar to a program error signal in this sense.

4) Sigill

An illegal instruction was executed. This is usually due to an error in the executable file itself or an attempt to execute a data segment. This signal can also be generated when a stack overflows.

5) SIGTRAP

Generated by a breakpoint instruction or other trap instruction. Used by debugger.

6) SIGABRT

Invokes the signal generated by the abort function.

7) Sigbus

Illegal address, including memory address alignment (alignment) error. For example, a four-word integer is accessed, but its address is not a multiple of 4. It differs from SIGSEGV in that the latter is triggered by illegal access to a legitimate storage address (such as Access does not belong to its own storage space or read-only storage space).

8) SIGFPE

Emitted when a fatal arithmetic operation error occurs. This includes not only floating-point arithmetic errors, but also all other arithmetic errors such as overflow and divisor 0.

9) SIGKILL

Used to immediately end the run of the program. This signal cannot be blocked, processed, or ignored. If an administrator discovers that a process is not terminating, try sending this signal.

) SIGUSR1

Leave it to the user

One) SIGSEGV

An attempt was made to access memory that is not assigned to itself or to write data to a memory address that does not have write permissions.

SIGUSR2)

Leave it to the user

Sigpipe)

Pipe rupture. This signal is usually generated between interprocess communication, such as two processes with FIFO (pipeline) communication, the read pipeline is not opened or terminated unexpectedly to the pipeline to write, the writing process will receive sigpipe signal. In addition, two processes with the socket communication, the write process when the socket is written, the read process has been terminated.

SIGALRM)

A clock timing signal that calculates the actual time or clock time. The alarm function uses this signal.

SIGTERM)

The end of program (terminate) signal, unlike Sigkill, is that the signal can be blocked and processed. Typically used to require the program to exit gracefully, the shell command kill generates this signal by default. If the process does not stop, we will try to Sigkill.

SIGCHLD)

The parent process receives this signal at the end of the child process.

If the parent process does not process the signal and does not wait for the (wait) child process, although the child process terminates, it also occupies the table entry in the kernel process table, when the child process is called a zombie process. In this case we should avoid (the parent process either ignores the sigchild signal, or catches it, or wait for its derived child process, or the parent process terminates first, and the termination of the child process is automatically taken over by the Init process).

) Sigcont

Let a stop (stopped) process continue execution. This signal cannot be blocked. You can use a handler to get the program to do certain work when the stopped state changes to continue. For example, to re-display the prompt

SIGSTOP)

Stop (stopped) the execution of the process. Notice the difference between it and terminate and interrupt: The process is not over yet, just pause execution. This signal cannot be blocked, processed or ignored.

SIGTSTP)

Stops the process from running, but the signal can be processed and ignored. This signal is emitted when the user types Susp characters (usually ctrl-z)

) Sigttin

When a background job wants to read data from the user terminal, all processes in the job receive a sigttin signal. By default, these processes stop executing.

Sigttou)

Similar to Sigttin, but received when writing a terminal (or modifying terminal mode).

Sigurg)

When there is "emergency" data or Out-of-band data arrives at the socket.

) sigxcpu

CPU time resource limit exceeded. This restriction can be read/changed by Getrlimit/setrlimit.

SIGXFSZ)

When the process attempts to enlarge the file so that it exceeds the file size resource limit.

SIGVTALRM)

Virtual clock signal. is similar to SIGALRM, but calculates the CPU time that is consumed by the process.

SIGPROF)

Similar to SIGALRM/SIGVTALRM, but includes the CPU time used by the process and the time of the system call.

Sigwinch)

emitted when the window size changes.

) SIGIO

The file descriptor is ready to start the input/output operation.

SIGPWR)

Power failure

Sigsys)

An illegal system call.

Key points Note

• In the signals listed above, the program can not capture, block or ignore the signal is: sigkill,sigstop

• Signals that cannot be restored to the default action are: Sigill,sigtrap

• The default causes the process to abort the signal is: Sigabrt,sigbus,sigfpe,sigill,sigiot,sigquit,sigsegv,sigtrap,sigxcpu,sigxfsz

• The signal that causes the process to exit by default is:

• Sigalrm,sighup,sigint,sigkill,sigpipe,sigpoll,sigprof,sigsys,sigterm,sigusr1,sigusr2,sigvtalrm

• The signal that causes the process to stop by default is: Sigstop,sigtstp,sigttin,sigttou

• The default process ignores signals such as: Sigchld,sigpwr,sigurg,sigwinch

• In addition, Sigio in SVR4 is exited, is ignored in 4.3BSD, Sigcont is continued when the process hangs, otherwise it is ignored and cannot be blocked.

Three. Actual combat

In 1.APPDELEGATE.M

- (BOOL)application:(uiapplication *)application Didfinishlaunchingwithoptions:(nsdictionary *)launchoptions {

Override point for customization after application launch.

Installsignalhandler(); Semaphore truncation

Installuncaughtexceptionhandler(); System exception capture

return YES;

}

The realization of 2.SIGNALHANDLER.M

void Signalexceptionhandler(int signal)

{

nsmutablestring *mstr = [[nsmutablestring alloc] init];

[mstr appendString:@ "stack:\n"];

void* callstack[+];

int i, frames = backtrace(callstack, + );

Char* * strs = backtrace_symbols(callstack, frames);

for (i = 0; i

[mstr appendformat:@ "%s\n", strs[i]];

}

[signalhandler savecreash: Mstr];

}

void Installsignalhandler(void)

{

signal(SIGHUP, signalexceptionhandler);

signal(SIGINT, signalexceptionhandler);

signal(sigquit, signalexceptionhandler);

signal(sigabrt, signalexceptionhandler);

signal(sigill, signalexceptionhandler);

signal(SIGSEGV, signalexceptionhandler);

signal(SIGFPE, signalexceptionhandler);

signal(sigbus, signalexceptionhandler);

signal(sigpipe, signalexceptionhandler);

}

The error type can be seen in the above description, Signalexceptionhandler is the callback when the signal is wrong. This method can be recalled when there is a signal error.

The realization of 3.UNCAUGHTEXCEPTIONHANDLER.M

void handleexception(nsexception *exception)

{

//Exception stack information

nsarray *stackarray = [exception Callstacksymbols];

//Causes of anomalies

nsstring *reason = [exception reason];

//Exception name

nsstring *name = [exception name];

nsstring *exceptioninfo = [nsstring stringwithformat:@ "Exception reason:%@\ Nexception name:%@\nexception stack:%@ ",name, reason, stackarray];

NSLog(@ "%@", exceptioninfo);

[uncaughtexceptionhandler savecreash: Exceptioninfo];

}

void Installuncaughtexceptionhandler(void)

{

Nssetuncaughtexceptionhandler(&handleexception);

}

4. Test – The key to stepping on the pit

The most critical step here, Signalhandler do not test in the debug environment. Because the system debug will take precedence to intercept. After we have to run it once, turn off the debug state. You should click on our build app to run it directly on the simulator. While the Uncaughtexceptionhandler can be captured in the debug state

- (ibaction)buttonclick:(UIButton *)sender {

1. Signal Volume

Test *ptest = {1,2};

free(pTest); Cause SIGABRT error, because there is no space in memory, where free is the object in the stack

pTesta = 5;

}

- (ibaction)buttonocexception:(UIButton *)sender

{

//2.ios crashes

nsarray *array= @[@ "tom" @ "xxx" @ "ooo"];

[array objectatindex:5];

}

Four. Crash callstack analysis – one step into the analysis

Properties	Description
0x8badf00d	In the start-up, end-of-stop, or respond to system events spent a long time, meaning "ate bad food."
0xdeadfa11	The user is forced to quit, meaning "dead fall". (When the system is unresponsive, the user presses the power switch and home)
0xbaaaaaad	The user presses the home key and the volume key to get the current memory status, which does not represent a crash
0xbad22222	VoIP should be used because the recovery is too frequent cause crash
0xc00010ff	Because it was too hot to be killed, meaning "cool off"
0xdead10cc	Because in the background still occupy system resources (, such as Communication Records) was killed, meaning "dead lock"

Five. Demo Address

Ioscrashuncaught Download

Https://github.com/xcysuccess/iOSCrashUncaught

Six. References

1. Debugging skills after the program crash

2.iOS Development Socket Program is SIGPIPE signal terminate problem

3. Beauty, Miss.

4. How to locate obj-c field pointer random Crash (a): increase the crash rate of the wild hands first

5. How to locate obj-c field pointer random Crash (ii): Make the non-mandatory crash into a must

6. How to locate obj-c field pointer random Crash (iii): Add Black technology let crash tell

iOS exception capture