Finding Bugs Using Xcode Runtime Tools
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- Beverly Higgins
- 6 years ago
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1 Session Developer Tools #WWDC17 Finding Bugs Using Xcode Runtime Tools 406 Kuba Mracek, Program Analysis Engineer Vedant Kumar, Compiler Engineer 2017 Apple Inc. All rights reserved. Redistribution or public display not permitted without written permission from Apple.
2 Improvements in Runtime Checking
3 Improvements in Runtime Checking
4 Improvements in Runtime Checking
5 Improvements in Runtime Checking
6 Improvements in Runtime Checking
7 Improvements in Runtime Checking Runtime Issues
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18 Address Sanitizer Thread Sanitizer Undefined Behavior Sanitizer Main Thread Checker
19 Main Thread Checker Address Sanitizer Thread Sanitizer Undefined Behavior Sanitizer Using Runtime Tools Effectively
20 Main Thread Checker New Address Sanitizer Thread Sanitizer Undefined Behavior Sanitizer Using Runtime Tools Effectively
21 Main Thread Checker New Address Sanitizer Thread Sanitizer Undefined Behavior Sanitizer New Using Runtime Tools Effectively
22 NEW Main Thread Checker Detects misuses of common APIs
23 UI Updates and Threads Some APIs must only be used from the main thread
24 UI Updates and Threads Main Thread Background Thread
25 UI Updates and Threads Main Thread Background Thread AppKit.framework UIKit.framework
26 UI Updates and Threads Main Thread AppKit.framework UIKit.framework Background Thread
27 UI Updates and Threads Main Thread AppKit.framework UIKit.framework Background Thread File downloads Image processing
28 UI Updates and Threads Main Thread AppKit.framework UIKit.framework Background Thread File downloads Image processing
29 UI Updates and Threads Main Thread AppKit.framework UIKit.framework Background Thread File downloads Image processing UI update
30 UI Updates and Threads Main Thread AppKit.framework UIKit.framework! Background Thread File downloads Image processing UI update
31 UI Updates and Threads Main Thread AppKit.framework UIKit.framework Background Thread File downloads Image processing UI update Missed UI updates Visual defects Data corruptions Crashes
32 UI Updates and Threads Main Thread AppKit.framework UIKit.framework UI update Background Thread File downloads Image processing
33 Demo Main Thread Checker
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37 Common Places for Mistakes Networking callbacks Creating and destroying NSView and UIView objects Designing asynchronous APIs
38 Designing Asynchronous APIs Let API user specify callback queue
39 Designing Asynchronous APIs Let API user specify callback queue DeepThought.asyncComputeAnswer(to: thequestion) { reply in }
40 Designing Asynchronous APIs Let API user specify callback queue DeepThought.asyncComputeAnswer(to: thequestion, completionqueue: queue) { reply in }
41 Main Thread Checker NEW Detects violations of API threading rules AppKit, UIKit and WebKit APIs Swift and C languages No recompilation Enabled by default in the Xcode debugger
42 Address Sanitizer Detects memory issues
43 Finding Memory Issues Security critical bugs Use-after-free and buffer overflows Diagnoses hard-to-reproduce crashes Advanced Debugging and the Address Sanitizer WWDC 2015
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54 Address Sanitizer in Xcode 9 NEW Detects use-after-scope Detects use-after-return (opt-in) Compatible with Malloc Scribble
55 // Use of Stack Memory Out of Scope int *integer_pointer = NULL; if (is_some_condition_true()) { int value = calculate_value(); integer_pointer = &value; } *integer_pointer = 42;
56 // Use of Stack Memory Out of Scope int *integer_pointer = NULL; if (is_some_condition_true()) { int value = calculate_value(); integer_pointer = &value; } *integer_pointer = 42;
57 // Use of Stack Memory Out of Scope int *integer_pointer = NULL; if (is_some_condition_true()) { int value = calculate_value(); integer_pointer = &value; } *integer_pointer = 42;
58 // Use of Stack Memory Out of Scope int *integer_pointer = NULL; if (is_some_condition_true()) { int value = calculate_value(); integer_pointer = &value; } *integer_pointer = 42;
59 // Use of Stack Memory Out of Scope int *integer_pointer = NULL; if (is_some_condition_true()) { int value = calculate_value(); integer_pointer = &value; } *integer_pointer = 42; Use of out of scope stack memory
60 // Use of Stack Memory after Return int *returns_address_of_stack() { int a = 42; return &a; } int *integer_pointer = returns_address_of_stack(); *integer_pointer = 43;
61 // Use of Stack Memory after Return int *returns_address_of_stack() { int a = 42; return &a; } int *integer_pointer = returns_address_of_stack(); *integer_pointer = 43;
62 // Use of Stack Memory after Return int *returns_address_of_stack() { int a = 42; return &a; } int *integer_pointer = returns_address_of_stack(); *integer_pointer = 43;
63 // Use of Stack Memory after Return int *returns_address_of_stack() { int a = 42; return &a; } int *integer_pointer = returns_address_of_stack(); *integer_pointer = 43;
64 // Use of Stack Memory after Return int *returns_address_of_stack() { int a = 42; return &a; } int *integer_pointer = returns_address_of_stack(); *integer_pointer = 43; Use of stack memory after return
65 Address Sanitizer and Swift Swift is a much safer language Mixed projects Unsafe pointer types are not memory safe
66 // Use-after-free Bug Using UnsafePointer let string = "Hello, World!" var firstbytepointer: UnsafePointer<CChar> string.withcstring { pointertocstring in firstbytepointer = pointertocstring } let firstbyte = firstbytepointer.pointee print(firstbyte)
67 // Use-after-free Bug Using UnsafePointer let string = "Hello, World!" var firstbytepointer: UnsafePointer<CChar> string.withcstring { pointertocstring in firstbytepointer = pointertocstring } let firstbyte = firstbytepointer.pointee print(firstbyte)
68 // Use-after-free Bug Using UnsafePointer let string = "Hello, World!" var firstbytepointer: UnsafePointer<CChar> string.withcstring { pointertocstring in firstbytepointer = pointertocstring } let firstbyte = firstbytepointer.pointee print(firstbyte)
69 // Use-after-free Bug Using UnsafePointer let string = "Hello, World!" var firstbytepointer: UnsafePointer<CChar> string.withcstring { pointertocstring in firstbytepointer = pointertocstring } let firstbyte = firstbytepointer.pointee print(firstbyte)
70 // Use-after-free Bug Using UnsafePointer let string = "Hello, World!" var firstbytepointer: UnsafePointer<CChar> string.withcstring { pointertocstring in firstbytepointer = pointertocstring } let firstbyte = firstbytepointer.pointee print(firstbyte)
71 // Use-after-free Bug Using UnsafePointer let string = "Hello, World!" var firstbytepointer: UnsafePointer<CChar> string.withcstring { pointertocstring in firstbytepointer = pointertocstring } let firstbyte = firstbytepointer.pointee print(firstbyte)
72 // Use-after-free Bug Using UnsafePointer let string = "Hello, World!" var firstbytepointer: UnsafePointer<CChar> string.withcstring { pointertocstring in firstbytepointer = pointertocstring } let firstbyte = firstbytepointer.pointee print(firstbyte) Use of deallocated memory
73 // Use UnsafePointer Only Inside the Closure let string = "Hello, World!" var firstbytepointer: UnsafePointer<CChar> string.withcstring { pointertocstring in firstbytepointer = pointertocstring } let firstbyte = firstbytepointer.pointee print(firstbyte)
74 // Use UnsafePointer Only Inside the Closure let string = "Hello, World!" string.withcstring { pointertocstring in var firstbytepointer: UnsafePointer<CChar> firstbytepointer = pointertocstring let firstbyte = firstbytepointer.pointee print(firstbyte) }
75 // Use UnsafePointer Only Inside the Closure let string = "Hello, World!" string.withcstring { pointertocstring in var firstbytepointer: UnsafePointer<CChar> firstbytepointer = pointertocstring let firstbyte = firstbytepointer.pointee print(firstbyte) }
76 // Use UnsafePointer Only Inside the Closure let string = "Hello, World!" string.withcstring { pointertocstring in var firstbytepointer: UnsafePointer<CChar> firstbytepointer = pointertocstring let firstbyte = firstbytepointer.pointee print(firstbyte) }
77 // Use UnsafePointer Only Inside the Closure let string = "Hello, World!" string.withcstring { pointertocstring in let firstbyte = pointertocstring.pointee print(firstbyte) }
78 Better Debugging Experience Makes debugging easier Allocation and deallocation backtraces Shows valid and invalid bytes of memory
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90 memory history <expression>
91 memory history 0x cd0
92 memory history 0x cd0 thread..., name = 'Memory deallocated by Thread 1' frame #0: 0x1000fba26 wrap_free frame #1: 0x100001c04 deallocate(p=<unavailable>) at main.m:8 frame #2: 0x100001ce8 perform_heap_operations at main.m:15 frame #3: 0x100001d1a main(argc=<unavailable>, argv=<unavailable>) at main.m thread..., name = 'Memory allocated by Thread 1' frame #0: 0x1000fb85c wrap_malloc frame #1: 0x100001bdf allocate at main.m:4 frame #2: 0x100001c1c perform_heap_operations at main.m:12 frame #3: 0x100001d1a main(argc=<unavailable>, argv=<unavailable>) at main.m
93 When to Use Address Sanitizer C languages and Swift Memory corruptions and crashes General debugging
94 Thread Sanitizer Detects multithreading problems
95 What is Thread Sanitizer Multithreading issues Finds races even if they did not manifest 64-bit macos, 64-bit simulators Thread Sanitizer and Static Analysis WWDC 2016
96 Data Races Unsynchronized accesses to shared mutable variables Lead to data races Memory corruptions and crashes All of these problems apply to Swift!
97 // Swift Data Race Example class EventLog { private var lasteventsource: LogSource? } func log(source: LogSource, message: String) { print(message) lasteventsource = source }
98 // Swift Data Race Example class EventLog { private var lasteventsource: LogSource? } func log(source: LogSource, message: String) { print(message) lasteventsource = source }
99 // Swift Data Race Example class EventLog { private var lasteventsource: LogSource? } func log(source: LogSource, message: String) { print(message) lasteventsource = source }
100 // Swift Data Race Example class EventLog { private var lasteventsource: LogSource? } func log(source: LogSource, message: String) { print(message) lasteventsource = source }
101 // Swift Data Race Example class EventLog { private var lasteventsource: LogSource? } func log(source: LogSource, message: String) { print(message) lasteventsource = source }
102 // Swift Data Race Example class EventLog { private var lasteventsource: LogSource? } func log(source: LogSource, message: String) { print(message) lasteventsource = source } // Thread 1 eventlog.log(source: networkingsubsystem, message: "Download finished") // Thread 2 eventlog.log(source: databasesubsystem, message: "Query complete")
103 // Swift Data Race Example class EventLog { private var lasteventsource: LogSource? } func log(source: LogSource, message: String) { print(message) lasteventsource = source } // Thread 1 eventlog.log(source: networkingsubsystem, message: "Download finished") // Thread 2 eventlog.log(source: databasesubsystem, message: "Query complete")
104 // Swift Data Race Example class EventLog { private var lasteventsource: LogSource? } func log(source: LogSource, message: String) { print(message) lasteventsource = source } Thread 2: Data race in EventLog.log(source:message:) // Thread 1 eventlog.log(source: networkingsubsystem, message: "Download finished") // Thread 2 eventlog.log(source: databasesubsystem, message: "Query complete")
105 // Use DispatchQueue to Synchronize Access class EventLog { private var lasteventsource: LogSource? } func log(source: LogSource, message: String) { print(message) lasteventsource = source }
106 // Use DispatchQueue to Synchronize Access class EventLog { private var lasteventsource: LogSource? private var queue = DispatchQueue(label: "com.example.eventlog.queue") } func log(source: LogSource, message: String) { print(message) lasteventsource = source }
107 // Use DispatchQueue to Synchronize Access class EventLog { private var lasteventsource: LogSource? private var queue = DispatchQueue(label: "com.example.eventlog.queue") } func log(source: LogSource, message: String) { print(message) lasteventsource = source }
108 // Use DispatchQueue to Synchronize Access class EventLog { private var lasteventsource: LogSource? private var queue = DispatchQueue(label: "com.example.eventlog.queue") } func log(source: LogSource, message: String) { queue.async { print(message) lasteventsource = source } }
109 // Use DispatchQueue to Synchronize Access class EventLog { private var lasteventsource: LogSource? private var queue = DispatchQueue(label: "com.example.eventlog.queue") } func log(source: LogSource, message: String) { queue.async { print(message) lasteventsource = source } }
110 // Use DispatchQueue to Synchronize Access class EventLog { private var lasteventsource: LogSource? private var queue = DispatchQueue(label: "com.example.eventlog.queue") } func log(source: LogSource, message: String) { queue.async { print(message) lasteventsource = source } }
111 Dispatch Queues Grand Central Dispatch should be your first choice of synchronization Lightweight, convenient, simple Associate your data with serial dispatch queues Concurrent Programming With GCD in Swift 3 WWDC 2016
112 New in Thread Sanitizer in Xcode 9 NEW Races on collections Swift access races
113 Races on Collections Previously, only reported races on raw memory accesses Synchronization required for larger data structures
114 Races on Collections Previously, only reported races on raw memory accesses Synchronization required for larger data structures NSMutableDictionary *d = [NSMutableDictionary new]; // Thread 1 BOOL found = [d objectforkey:@"answer"]!= nil; // Thread 2 [d setobject:@42 forkey:@"answer"];
115 Races on Collections Previously, only reported races on raw memory accesses Synchronization required for larger data structures NSMutableDictionary *d = [NSMutableDictionary new]; // Thread 1 BOOL found = [d objectforkey:@"answer"]!= nil; // Thread 2 [d setobject:@42 forkey:@"answer"]; Thread 1: Previous access on NSMutableDictionary Thread 2: Race on NSMutableDictionary
116 Races on Collections NEW Races on collections in Objective-C and Swift NSMutableArray, NSMutableDictionary Swift Array and Dictionary
117 Demo Thread Sanitizer and race on NSMutableArray
118 // Race on Swift Array var usernames: [String] = ["alice", "bob"]
119 // Race on Swift Array var usernames: [String] = ["alice", "bob"] // Thread 1 found = usernames.contains("alice") if found { } // Thread 2 usernames.append("carol")
120 // Race on Swift Array var usernames: [String] = ["alice", "bob"] // Thread 1 found = usernames.contains("alice") if found { } Thread 1: Previous access // Thread 2 usernames.append("carol") Thread 2: Swift access race
121 // Use DispatchQueue to Synchronize Accesses var usernames: [String] = ["alice", "bob"] // Thread 1 found = usernames.contains("alice") if found { } // Thread 2 usernames.append("carol")
122 // Use DispatchQueue to Synchronize Accesses var usernames: [String] = ["alice", "bob"] var queue = DispatchQueue(label: "com.example.usernames.queue") // Thread 1 found = usernames.contains("alice") if found { } // Thread 2 usernames.append("carol")
123 // Use DispatchQueue to Synchronize Accesses var usernames: [String] = ["alice", "bob"] var queue = DispatchQueue(label: "com.example.usernames.queue") // Thread 1 found = usernames.contains("alice") if found { } // Thread 2 usernames.append("carol")
124 // Use DispatchQueue to Synchronize Accesses var usernames: [String] = ["alice", "bob"] var queue = DispatchQueue(label: "com.example.usernames.queue") // Thread 1 found = usernames.contains("alice") if found { } // Thread 2 usernames.append("carol")
125 // Use DispatchQueue to Synchronize Accesses var usernames: [String] = ["alice", "bob"] var queue = DispatchQueue(label: "com.example.usernames.queue") // Thread 1 queue.sync { found = usernames.contains("alice") } if found { } // Thread 2 queue.async { usernames.append("carol") }
126 // Use DispatchQueue to Synchronize Accesses var usernames: [String] = ["alice", "bob"] var queue = DispatchQueue(label: "com.example.usernames.queue") // Thread 1 queue.sync { found = usernames.contains("alice") } if found { } // Thread 2 queue.async { usernames.append("carol") }
127 Swift Access Races NEW Applies to all structs Mutating methods require exclusive access to the whole struct Methods on classes require exclusive access to stored properties they change What's New in Swift Tuesday 1:50PM
128 // Swift Access Race with Mutating Methods struct BluePoliceBoxLocation { private var x, y, z: Int private var time: Int }
129 // Swift Access Race with Mutating Methods struct BluePoliceBoxLocation { private var x, y, z: Int private var time: Int } mutating func teleport(toplanet: String) { } mutating func fly(tocity: String) { } mutating func traveltoendoftime() { }
130 // Swift Access Race with Mutating Methods struct BluePoliceBoxLocation { private var x, y, z: Int private var time: Int } mutating func teleport(toplanet: String) { } mutating func fly(tocity: String) { } mutating func traveltoendoftime() { }
131 // Swift Access Race with Mutating Methods struct BluePoliceBoxLocation { private var x, y, z: Int private var time: Int } mutating func teleport(toplanet: String) { } mutating func fly(tocity: String) { } mutating func traveltoendoftime() { } // Thread 1 location.teleport(toplanet: "Mars") // Thread 2 location.traveltoendoftime()
132 // Swift Access Race with Mutating Methods struct BluePoliceBoxLocation { private var x, y, z: Int private var time: Int } mutating func teleport(toplanet: String) { } mutating func fly(tocity: String) { } mutating func traveltoendoftime() { } // Thread 1 location.teleport(toplanet: "Mars") Thread 1: Previous access // Thread 2 location.traveltoendoftime() Thread 2: Swift access race
133 // Swift Access Race with Mutating Methods struct BluePoliceBoxLocation { private var x, y, z: Int private var time: Int } mutating func teleport(toplanet: String) { } mutating func fly(tocity: String) { } mutating func traveltoendoftime() { } // Thread 1 location.teleport(toplanet: "Mars") Thread 1: Previous access // Thread 2 changes x, y, z location.traveltoendoftime() Thread 2: Swift access race changes time
134 // Swift Access Race with Mutating Methods struct BluePoliceBoxLocation { private var x, y, z: Int private var time: Int } mutating func teleport(toplanet: String) { } mutating func fly(tocity: String) { } mutating func traveltoendoftime() { } // Thread 1 location.teleport(toplanet: "Mars") Thread 1: Previous access // Thread 2 location.traveltoendoftime() Thread 2: Swift access race
135 // Incorrect Synchronization Inside a Struct struct BluePoliceBoxLocation { private var x, y, z: Int private var time: Int } mutating func teleport(toplanet: String) { } mutating func fly(tocity: String) { } mutating func traveltoendoftime() { }
136 // Incorrect Synchronization Inside a Struct struct BluePoliceBoxLocation { private var x, y, z: Int private var time: Int private var queue: DispatchQueue = } mutating func teleport(toplanet: String) { queue.sync { } } mutating func fly(tocity: String) { queue.sync { } } mutating func traveltoendoftime() { queue.sync { } }
137 // Incorrect Synchronization Inside a Struct struct BluePoliceBoxLocation { private var x, y, z: Int private var time: Int private var queue: DispatchQueue = } mutating func teleport(toplanet: String) { queue.sync { } } mutating func fly(tocity: String) { queue.sync { } } mutating func traveltoendoftime() { queue.sync { } }
138 // Incorrect Synchronization Inside a Struct struct BluePoliceBoxLocation { private var x, y, z: Int private var time: Int private var queue: DispatchQueue = } mutating func teleport(toplanet: String) { queue.sync { } } mutating func fly(tocity: String) { queue.sync { } } mutating func traveltoendoftime() { queue.sync { } }
139 // Synchronize Calls to Mutating Methods struct BluePoliceBoxLocation { }
140 // Synchronize Calls to Mutating Methods struct BluePoliceBoxLocation { } class BluePoliceBox { private var location: BluePoliceBoxLocation private var queue: DispatchQueue = }
141 // Synchronize Calls to Mutating Methods struct BluePoliceBoxLocation { } class BluePoliceBox { private var location: BluePoliceBoxLocation private var queue: DispatchQueue = func goonrescuemission() { queue.sync { location.teleport(toplanet: "Mars") } } func gotowrongplaceagain() { queue.sync { } } }
142 Find and Fix Your Races Use GCD to synchronize access to data Associate your shared data with a serial queue Thread Sanitizer is invaluable for finding races
143 NEW Undefined Behavior Sanitizer Vedant Kumar, Compiler Engineer
144 What is Undefined Behavior Sanitizer? Runtime bug finder Checks unsafe constructs in the C language family Compatible with other runtime tools Understanding Undefined Behavior Executive Ballroom Thursday 9:00AM
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146 C++ Dynamic Type Violation Invalid Float Cast Nonnull Return Value Violation Integer Overflow Invalid Shift Exponent Alignment Violation Invalid Boolean Invalid Variable-Length Array Invalid Enum Integer Division by Zero Invalid Integer Cast Reached Unreachable Code Invalid Shift Base Missing Return Value Invalid Object Size Null Dereference Nonnull Assignment Violation Nonnull Parameter Violation Out-of-Bounds Array Access
147 Integer Overflow Alignment Violation Nonnull Return Value Violation
148 Integer Overflow Arithmetic result too big Unsafe in indexing expressions (INT_MAX + 1) INT_MAX Opt-in check for unsigned overflow
149 Demo Undefined Behavior Sanitizer and integer overflow
150 Alignment Violation Unaligned load or store Causes crashes in Release builds Common in (de)serialization code
151 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; };
152 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender
153 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender
154 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender
155 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender H e y K u b a!
156 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender H e y K u b a! // Receiver // Read from stream Packet *P = (Packet *)bytestream; if (P->magic!= )
157 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender H e y K u b a! // Receiver // Read from stream Packet *P = (Packet *)bytestream; if (P->magic!= )
158 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender H e y K u b a!
159 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender H e y K u b a!
160 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender H e y K u b a!
161 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender H e y K u b a! H o w s i t g o i n g?
162 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender H e y K u b a! H o w s i t g o i n g? // Receiver // Read from stream Packet *P = (Packet *)(bytestream + 17); if (P->magic!= )
163 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender H e y K u b a! H o w s i t g o i n g? // Receiver // Read from stream Packet *P = (Packet *)(bytestream + 17); if (P->magic!= )
164 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender H e y K u b a! // Receiver // Read from stream Packet *P = (Packet *)(bytestream + 17); if (P->magic!= ) Load of misaligned address
165 // Serializing Packets for a Custom Network Protocol struct Packet { int magic; int payloadlength; char payload[]; }; // Sender H e y K u b a! // Receiver // Read from stream Packet *P = (Packet *)(bytestream + 17); if (P->magic!= ) Load of misaligned address
166 // Use Structure Packing to Decrease Expected Alignment struct Packet { int magic; int payloadlength; char payload[]; } attribute ((packed)); // Read from stream Packet *P = (Packet *)bytestream; if (P->magic!= )
167 // Use Structure Packing to Decrease Expected Alignment struct Packet { int magic; // Member alignment changes to 1 int payloadlength; char payload[]; } attribute ((packed)); // Read from stream Packet *P = (Packet *)bytestream; if (P->magic!= )
168 // Use Structure Packing to Decrease Expected Alignment struct Packet { int magic; // Member alignment changes to 1 int payloadlength; char payload[]; } attribute ((packed)); // Read from stream Packet *P = (Packet *)bytestream; if (P->magic!= ) // The load is aligned
169 // Use Structure Packing to Decrease Expected Alignment struct Packet { int magic; // Member alignment changes to 1 int payloadlength; char payload[]; } attribute ((packed)); // This can change structure layout and performance // Read from stream Packet *P = (Packet *)bytestream; if (P->magic!= ) // The load is aligned
170 // Use memcpy() to Perform Unaligned Accesses struct Packet { int magic; int payloadlength; char payload[]; }; // Read from stream int magic; memcpy(&magic, bytestream + offsetof(struct Packet, magic), sizeof(int)); if (magic!= )
171 // Use memcpy() to Perform Unaligned Accesses struct Packet { int magic; int payloadlength; char payload[]; }; // Read from stream int magic; memcpy(&magic, bytestream + offsetof(struct Packet, magic), sizeof(int)); if (magic!= )
172 Nonnull Return Value Violation Return value annotated nonnull Function returns nil anyway Can cause crashes in mixed C and Swift code Recommended to opt in to the check
173 // Nonnull Return Value SolarSystem + (nonnull NSDictionary *)planetmoons @"Styx"] }; } - (nonnull NSArray *)moonsofplanet:(nonnull NSString *)planet { return [[self class] planetmoons][planet];
174 // Nonnull Return Value SolarSystem + (nonnull NSDictionary *)planetmoons @"Styx"] }; } - (nonnull NSArray *)moonsofplanet:(nonnull NSString *)planet { return [[self class] planetmoons][planet];
175 // Nonnull Return Value SolarSystem + (nonnull NSDictionary *)planetmoons // }; } - (nonnull NSArray *)moonsofplanet:(nonnull NSString *)planet { return [[self class] planetmoons][planet];
176 // Nonnull Return Value SolarSystem + (nonnull NSDictionary *)planetmoons // }; } - (nonnull NSArray *)moonsofplanet:(nonnull NSString *)planet { return [[self class] planetmoons][planet];
177 // Nonnull Return Value SolarSystem + (nonnull NSDictionary *)planetmoons // }; } - (nonnull NSArray *)moonsofplanet:(nonnull NSString *)planet { return [[self class] planetmoons][planet]; // Find the biggest moon for each planet NSMutableArray *biggestmoons = [NSMutableArray new]; [biggestmoons addobject:[solarsystem moonsofplanet:@"pluto"][0]];
178 // Nonnull Return Value SolarSystem + (nonnull NSDictionary *)planetmoons // }; } - (nonnull NSArray *)moonsofplanet:(nonnull NSString *)planet { return [[self class] planetmoons][planet]; Null pointer returned from function declared to never return null // Find the biggest moon for each planet NSMutableArray *biggestmoons = [NSMutableArray new]; [biggestmoons addobject:[solarsystem moonsofplanet:@"pluto"][0]];
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181 Using Runtime Tools Effectively
182 How to Use Runtime Tools Effectively Exercise more code Use the tools together
183 Exercise More Code Can only catch issues in code that is run Use runtime tools for daily development Use them before every release Avoid spreading bugs to users
184 Use Continuous Integration Simplifies testing with runtime tools Ensures that bugs are caught quickly Helps track code coverage Continuous Integration and Code Coverage in Xcode WWDC 2015
185 Use Runtime Tools Together Find more issues Most runtime tools can be used together Address Sanitizer and Thread Sanitizer are not compatible Product Scheme Edit Scheme Diagnostics
186 Runtime Tool Overhead Execution overhead Memory overhead Main Thread Checker 1.02x negligible Undefined Behavior Sanitizer 1.2x negligible Address Sanitizer 2 3x 2x Thread Sanitizer 5 10x 4x
187 Summary Xcode 9 enables you to catch critical issues Use runtime tools early and often Save time, keep users safe!
188 Summary Xcode 9 enables you to catch critical issues Use runtime tools early and often Save time, keep users safe!
189 More Information
190 Related Sessions What's New in Swift Debugging with Xcode 9 Modernizing Grand Central Dispatch Usage Tuesday 1:50PM Wednesday 10:00AM Wednesday 11:00AM Understanding Undefined Behavior Executive Ballroom Thursday 9:00AM What s New in Testing Hall 2 Thursday 3:10PM What's New in LLVM Hall 2 Thursday 4:10PM
191 Labs Performance Profiling and Runtime Analysis Tools Lab Technology Lab K Thu 1:00PM 4:10PM LLVM Compiler, Objective-C, and C++ Lab Technology Lab E Fri 9:00AM 11:00AM
192
Understanding Undefined Behavior
Session Developer Tools #WWDC17 Understanding Undefined Behavior 407 Fred Riss, Clang Team Ryan Govostes, Security Engineering and Architecture Team Anna Zaks, Program Analysis Team 2017 Apple Inc. All
Thread Sanitizer and Static Analysis
Developer Tools #WWDC16 Thread Sanitizer and Static Analysis Help with finding bugs in your code Session 412 Anna Zaks Manager, Program Analysis Team Devin Coughlin Engineer, Program Analysis Team 2016
Advanced Debugging and the Address Sanitizer
Developer Tools #WWDC15 Advanced Debugging and the Address Sanitizer Finding your undocumented features Session 413 Mike Swingler Xcode UI Infrastructure Anna Zaks LLVM Program Analysis 2015 Apple Inc.
Using and Extending the Xcode Source Editor
Developer Tools #WWDC16 Using and Extending the Xcode Source Editor Session 414 Mike Swingler Xcode Infrastructure and Editors Chris Hanson Xcode Infrastructure and Editors 2016 Apple Inc. All rights reserved.
What s New in LLDB. Debug your way to fame and glory #WWDC15. Developer Tools. Session 402
Developer Tools #WWDC15 What s New in LLDB Debug your way to fame and glory Session 402 Kate Stone Software Behavioralist Sean Callanan Master of Expressions Enrico Granata Data Wizard 2015 Apple Inc.
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