fix: Strip top bits from pointers before reading memory contents

In the new Xcode 10 build system, Swift object register values have the
top bit used as a flag. This change strips the flag while not losing
anything relevant to us in our quest to see error messages for assertion
failures.

This technique does not capture messages which are less than 16
characters, as short strings are stored as raw char arrays on the stack
rather than being allocated. (See WWDC 2018 #401 for more info on new
string optimizations)

While it is possible to check for char arrays as well as pointers when
searching for notable address values, sweeping up local variables has a
likely chance of capturing unintended data as well from the surrounding
code, some of which may be sensitive. It is also not guaranteed that the
value would still be on the stack after the message is logged, so it is
possible to get only unrelated string values as the message.

In the current Swift stdlib, the following messages passed to
fatalError, preconditionFailure, and precondition (and their internal
func counterparts) are less than 16 characters:

* empty string
* `unavailable`
* `not implemented`
* `abstract method`
* `unknown value`
* `invalid count` (where a dictionary contains < 0 items(?))
* `invalid index` (where a dictionary ceases to be a dictionary)
* `don't touch me` (from SpriteKit)
* `close() failed` (from the private Subprocess implementation)

The vast majority have more meaningful messages.

Reference:
* https://asciiwwdc.com/2018/sessions/401

Fixes #318

CHANGELOG.md

@@ -9,6 +9,11 @@ Changelog
   addresses
   [#319](https://github.com/bugsnag/bugsnag-cocoa/pull/319)
 
+* Add `fatalError` and other assertion failure messages in reports for
+  Swift 4.2 apps. Note that this only includes messages which are 16
+  characters or longer. See the linked pull request for more information.
+  [#320](https://github.com/bugsnag/bugsnag-cocoa/pull/320)
+
 ## 5.17.0 (2018-09-25)
 
 ### Enhancements

Source/KSCrash/Source/KSCrash/Recording/BSG_KSCrashReport.c

@@ -983,20 +983,30 @@ bool bsg_kscrw_i_isValidPointer(const uintptr_t address) {
     return true;
 }
 
+/**
+ * Strip higher order bits from addresses which aren't related to the actual
+ * location.
+ */
+#define BSG_ValidPointerMask  0x0000000fffffffff
+
 /** Write the contents of a memory location only if it contains notable data.
  * Also writes meta information about the data.
  *
  * @param writer The writer.
  *
  * @param key The object key, if needed.
  *
- * @param address The memory address.
+ * @param rawAddress The memory address.
  */
 void bsg_kscrw_i_writeMemoryContentsIfNotable(
     const BSG_KSCrashReportWriter *const writer, const char *const key,
-    const uintptr_t address) {
+    const uintptr_t rawAddress) {
+    uintptr_t address = rawAddress;
     if (!bsg_kscrw_i_isValidPointer(address)) {
-        return;
+        address &= BSG_ValidPointerMask;
+        if (!bsg_kscrw_i_isValidPointer(address)) {
+            return;
+        }
     }
 
     const void *object = (const void *)address;

features/crashprobe.feature

@@ -166,8 +166,15 @@ Scenario: Crash within Swift code
     And the exception "message" equals "Unexpectedly found nil while unwrapping an Optional value"
     And the exception "errorClass" equals "Fatal error"
 
-    And the "method" of stack frame 0 starts with "_T0s18_fatalErrorMessages5NeverOs12StaticStringV_A2E4fileSu4lines6UInt32V5"
-    And the "method" of stack frame 1 starts with "_T010iOSTestApp10SwiftCrashC3run"
+Scenario: Assertion failure in Swift code
+    When I set environment variable "BUGSNAG_API_KEY" to "a35a2a72bd230ac0aa0f52715bbdc6aa"
+    And I configure the app to run on "iPhone8-11.2"
+    And I crash the app using "SwiftAssertion"
+    And I relaunch the app
+    Then I should receive a request
+    And the request is a valid for the error reporting API
+    And the exception "errorClass" equals "Fatal error"
+    And the exception "message" equals "several unfortunate things just happened"
 
 Scenario: Dereference a null pointer
     When I set environment variable "BUGSNAG_API_KEY" to "a35a2a72bd230ac0aa0f52715bbdc6aa"

features/fixtures/ios-swift-cocoapods/Podfile.lock

@@ -1,16 +1,16 @@
 PODS:
-  - Bugsnag (5.15.6)
+  - Bugsnag (5.17.0)
 
 DEPENDENCIES:
   - Bugsnag (from `../../..`)
 
 EXTERNAL SOURCES:
   Bugsnag:
-    :path: ../../..
+    :path: "../../.."
 
 SPEC CHECKSUMS:
-  Bugsnag: ff5f5e3059e6a9c9d27a899f3bf3774067553483
+  Bugsnag: 2d163d2f4c7acdb9bbcfc7a938c646f3aa39f566
 
 PODFILE CHECKSUM: 4d026fb83571f098c9fb4fa71c1564c72c55ab1a
 
-COCOAPODS: 1.4.0
+COCOAPODS: 1.5.3

features/fixtures/ios-swift-cocoapods/iOSTestApp.xcodeproj/project.pbxproj

@@ -7,6 +7,7 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		8A840FBA21AF5C450041DBFA /* SwiftAssertion.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8A840FB921AF5C450041DBFA /* SwiftAssertion.swift */; };
 		8A98400320FD11BF0023ECD1 /* AutoSessionCustomVersionScenario.m in Sources */ = {isa = PBXBuildFile; fileRef = 8A98400220FD11BF0023ECD1 /* AutoSessionCustomVersionScenario.m */; };
 		8AB8866420404DD30003E444 /* AppDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8AB8866320404DD30003E444 /* AppDelegate.swift */; };
 		8AB8866620404DD30003E444 /* ViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8AB8866520404DD30003E444 /* ViewController.swift */; };
@@ -54,6 +55,7 @@
 
 /* Begin PBXFileReference section */
 		4994F05E0421A0B037DD2CC5 /* Pods_iOSTestApp.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Pods_iOSTestApp.framework; sourceTree = BUILT_PRODUCTS_DIR; };
+		8A840FB921AF5C450041DBFA /* SwiftAssertion.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = SwiftAssertion.swift; sourceTree = "<group>"; };
 		8A98400120FD11BF0023ECD1 /* AutoSessionCustomVersionScenario.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = AutoSessionCustomVersionScenario.h; sourceTree = "<group>"; };
 		8A98400220FD11BF0023ECD1 /* AutoSessionCustomVersionScenario.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = AutoSessionCustomVersionScenario.m; sourceTree = "<group>"; };
 		8AB8866020404DD30003E444 /* iOSTestApp.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = iOSTestApp.app; sourceTree = BUILT_PRODUCTS_DIR; };
@@ -196,6 +198,7 @@
 		F42953DE2BB41023C0B07F41 /* scenarios */ = {
 			isa = PBXGroup;
 			children = (
+				8A840FB921AF5C450041DBFA /* SwiftAssertion.swift */,
 				F42957FA1A3724BFBDC22E14 /* NSExceptionScenario.swift */,
 				F4295F595986A279FA3BDEA7 /* UserEmailScenario.swift */,
 				F42954E2B3FF0C5C0474DA74 /* UserEnabledScenario.swift */,
@@ -277,7 +280,6 @@
 				8AB8865D20404DD30003E444 /* Frameworks */,
 				8AB8865E20404DD30003E444 /* Resources */,
 				4D2139E03F8B071F7DB7C7A6 /* [CP] Embed Pods Frameworks */,
-				F4E835AC090FCF28B6B12EC4 /* [CP] Copy Pods Resources */,
 			);
 			buildRules = (
 			);
@@ -373,21 +375,6 @@
 			shellScript = "\"${SRCROOT}/Pods/Target Support Files/Pods-iOSTestApp/Pods-iOSTestApp-frameworks.sh\"\n";
 			showEnvVarsInLog = 0;
 		};
-		F4E835AC090FCF28B6B12EC4 /* [CP] Copy Pods Resources */ = {
-			isa = PBXShellScriptBuildPhase;
-			buildActionMask = 2147483647;
-			files = (
-			);
-			inputPaths = (
-			);
-			name = "[CP] Copy Pods Resources";
-			outputPaths = (
-			);
-			runOnlyForDeploymentPostprocessing = 0;
-			shellPath = /bin/sh;
-			shellScript = "\"${SRCROOT}/Pods/Target Support Files/Pods-iOSTestApp/Pods-iOSTestApp-resources.sh\"\n";
-			showEnvVarsInLog = 0;
-		};
 /* End PBXShellScriptBuildPhase section */
 
 /* Begin PBXSourcesBuildPhase section */
@@ -415,6 +402,7 @@
 				F42955DB6D08642528917FAB /* CxxExceptionScenario.mm in Sources */,
 				F42954B7318A02824C65C514 /* ObjCMsgSendScenario.m in Sources */,
 				F42953498545B853CC0B635E /* NullPointerScenario.m in Sources */,
+				8A840FBA21AF5C450041DBFA /* SwiftAssertion.swift in Sources */,
 				F429538D8941382EC2C857CE /* AsyncSafeThreadScenario.m in Sources */,
 				F42955869D33EE0E510B9651 /* ReadGarbagePointerScenario.m in Sources */,
 				8AEFC73420F8D1BB00A78779 /* ManualSessionWithUserScenario.m in Sources */,

features/fixtures/ios-swift-cocoapods/iOSTestApp/scenarios/SwiftAssertion.swift

@@ -0,0 +1,12 @@
+import Foundation
+
+class SwiftAssertion: Scenario {
+    override func startBugsnag() {
+      self.config.shouldAutoCaptureSessions = false;
+      super.startBugsnag()
+    }
+
+    override func run() {
+        fatalError("several unfortunate things just happened")
+    }
+}