iOS uses Metrickit to collect crash logs

What is Metrickit

MetricKit is a tool introduced by Apple in iOS 13 that aggregates and analyzes reports on each device regarding exception and crash diagnostics as well as power and performance metrics.

Why use MetricKit to collect crash logs

Currently, some open source frameworks on the market, such as KSCrash and PLCrashReport, cannot capture some crashes. For example, PLCrashReport cannot capture stack overflow crashes, SIGKILL, SIGQUIT and other signal crashes. KSCrash can only capture part of SIGKILL crashes.

Metrickit flaws

Currently only supports crash log collection after iOS14
The crash log does not return the specific crash time and startup time, and the crash scene information does not contain any other information except the stack.
If segment migration compilation technology is used, the address and uuid of the main program macho cannot match.

The crash log of iOS14 will be called back once every 24 hours, which has low timeliness. After iOS15, the crash log will be returned after the next startup, but it has been verified that some will be called back immediately, while others will not, and the pattern is unpredictable.

Start access

1. Add MetricKit

2. Add MetricKit listeners

 if ( @ available ( iOS 14.0 , * )) {

 MXMetricManager * manager = [ MXMetricManager sharedManager ];

 if ( self && manager && [ manager respondsToSelector : @ selector ( addSubscriber :)]) {

 [ manager addSubscriber : self ];

 }

 }

3. The listener implements the MXMetricManagerSubscriber protocol method. The payloadDic contains the last crash log stack and information of this application.

 // If Apple has data, it will call back after registering the monitor

 - ( void ) didReceiveDiagnosticPayloads :( NSArray < MXDiagnosticPayload * > * _Nonnull ) payloads API_AVAILABLE ( ios ( 14.0 )) {

 if ( @ available ( iOS 14.0 , * )) {

 for ( MXDiagnosticPayload * payload in payloads ) {

 NSDictionary * payloadDic = [ payload dictionaryRepresentation ];



 });

 }

 }

 }

4. Log assembly key code examples

 NSArray * callStackRootFrames = [ dicFrame ArrayValueForKey : kMetrkitCallStackRootFramesKey ];

 if ( callStackRootFrames . count <= 0 ) {

 continue ;

 }

 NSDictionary * dicZero = [ callStackRootFrames ObjectAtIndex : 0 ];

 int rootIndex = 0 ;

 while ( dicZero && dicZero . count > 0 ) {

 NSString * binaryUUID = [ dicZero stringValueForKey : kMetrkitBinaryUUIDKey ];

 NSString * binaryName = [ dicZero stringValueForKey : kMetrkitBinaryNameKey ];

 long long baseAdd = [[ dicZero NumberValueForKey : kMetrkitOffsetIntoBinaryTextSegmentKey ] longLongValue ];

 long long address = [[ dicZero numberValueForKey : kMetrkitAddressKey ] longLongValue ];

 NSArray * subFrames = [ dicZero arrayValueForKey : kMetrkitSubFramesKey ];

 [ strStack appendFormat : @ "%d %@ 0x%llx 0x%llx + %lld\n" , rootIndex , binaryName , baseAdd , address , address - model . baseAddress ];

 rootIndex ++ ;

 if ( subFrames && subFrames . count >= 0 ) {

 dicZero = [ subFrames ObjectAtIndex : 0 ];

 } else {

 dicZero = nil ;

 }

MetricKit return fields meaning and details

JSON overall format

crashDiagnostics Details

Each crash is a dictionary with the following contents: