所謂的 Crash Report 是在實體機器上，執行程式時發生 crash 時，此時 iOS 會幫忙將程式出錯的相關資訊存起來，這時候用 Xcode 的 Organizer - Devices 時，可以去點選設備，並且可以查看有哪些 report 在上頭，這時候就可以稍作觀看，但是上頭記錄的資訊是有稍微類似做過保護的，只會看到類似(這是網路上收集的資訊，但我嘗試做出的 log 好像已經轉好了？)：
Thread 0 Crashed: 0 libSystem.B.dylib 0x35de3ad0 0x######## + ## 1 libSystem.B.dylib 0x35de3abe 0x######## + ## 2 libSystem.B.dylib 0x35de3ab2 0x######## + ## 3 libSystem.B.dylib 0x35dfad5e 0x######## + ## 4 libSystem.B.dylib 0x35de967e 0x######## + ## 5 libSystem.B.dylib 0x35de974c 0x######## + ## 6 libSystem.B.dylib 0x35d5c8e0 0x######## + ## 7 libSystem.B.dylib 0x35d5c798 0x######## + ## 8 CoreFoundation 0x3750022c 0x######## + ## 9 CoreFoundation 0x374fc206 0x######## + ## 10 CoreFoundation 0x37504564 0x######## + ## 11 CoreFoundation 0x37504406 0x######## + ## 12 Foundation 0x351530f0 0x######## + ## 13 CrashTesting 0x00002712 0x######## + ## 14 UIKit 0x35924fd0 0x######## + ## 15 UIKit 0x3591ea70 0x######## + ## 16 UIKit 0x358d82dc 0x######## + ## 17 UIKit 0x358d7b14 0x######## + ## 18 UIKit 0x358d73ac 0x######## + ## 19 GraphicsServices 0x33e77c80 0x######## + ## 20 CoreFoundation 0x3752f5c4 0x######## + ## 21 CoreFoundation 0x3752f582 0x######## + ## 22 CoreFoundation 0x3752182e 0x######## + ## 23 CoreFoundation 0x37521504 0x######## + ## 24 CoreFoundation 0x37521412 0x######## + ## 25 UIKit 0x3591d54c 0x######## + ## 26 UIKit 0x3591a550 0x######## + ## 27 CrashTesting 0x0000266e 0x######## + ## 28 CrashTesting 0x00002620 0x######## + ##
這時候需要使用原先編譯 app 時，在同一目錄中會產生對應的 dSYM 檔案，搭配 dwarfdump 使用才可以查詢到真正的片段程式(例如想看 line 13 的意思)：
$ dwarfdump --lookup 0x00002712 -arch armv6 CrashTesting.app.dSYM/
----------------------------------------------------------------------
File: CrashTesting.app.dSYM/Contents/Resources/DWARF/CrashTesting (armv6)
----------------------------------------------------------------------
Looking up address: 0x0000000000002712 in .debug_info... found!
0x00000132: Compile Unit: length = 0x000049b0 version = 0x0002 abbr_offset = 0x00000000 addr_size = 0x04 (next CU at 0x00004ae6)
0x0000013d: TAG_compile_unit [1] *
AT_producer( "4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2373.6)" )
AT_language( DW_LANG_ObjC )
AT_name( "CrashTestingAppDelegate.m" )
AT_entry_pc( 0x000026b4 )
AT_stmt_list( 0x0000006b )
AT_comp_dir( "/Volumes/Data/iPhoneDev/trunk/CrashTesting/CrashTesting" )
AT_APPLE_major_runtime_vers( 0x02 )
0x00000166: TAG_subprogram [16] *
AT_sibling( {0x000001d2} )
AT_name( "-[CrashTestingAppDelegate application:didFinishLaunchingWithOptions:]" )
AT_decl_file( "/Volumes/Data/iPhoneDev/trunk/CrashTesting/CrashTesting/CrashTestingAppDelegate.m" )
AT_decl_line( 17 )
AT_prototyped( 0x01 )
AT_type( {0x0000015b} ( BOOL ) )
AT_APPLE_isa( 0x01 )
AT_low_pc( 0x000026b4 )
AT_high_pc( 0x00002780 )
AT_frame_base( r7 )
0x000001b9: TAG_lexical_block [5] *
AT_low_pc( 0x000026c4 )
AT_high_pc( 0x00002780 )
Line table file: 'CrashTestingAppDelegate.m' line 20, column 0 with start address 0x000000000000270e
Looking up address: 0x0000000000002712 in .debug_frame... found!
0x00000020: FDE
length: 0x0000000c
CIE_pointer: 0x00000000
start_addr: 0x000026b4 -[CrashTestingAppDelegate application:didFinishLaunchingWithOptions:]
range_size: 0x000000cc (end_addr = 0x00002780)
Instructions: 0x000026b4: CFA=4294967295+4294967295
----------------------------------------------------------------------
File: CrashTesting.app.dSYM/Contents/Resources/DWARF/CrashTesting (armv6)
----------------------------------------------------------------------
Looking up address: 0x0000000000002712 in .debug_info... found!
0x00000132: Compile Unit: length = 0x000049b0 version = 0x0002 abbr_offset = 0x00000000 addr_size = 0x04 (next CU at 0x00004ae6)
0x0000013d: TAG_compile_unit [1] *
AT_producer( "4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2373.6)" )
AT_language( DW_LANG_ObjC )
AT_name( "CrashTestingAppDelegate.m" )
AT_entry_pc( 0x000026b4 )
AT_stmt_list( 0x0000006b )
AT_comp_dir( "/Volumes/Data/iPhoneDev/trunk/CrashTesting/CrashTesting" )
AT_APPLE_major_runtime_vers( 0x02 )
0x00000166: TAG_subprogram [16] *
AT_sibling( {0x000001d2} )
AT_name( "-[CrashTestingAppDelegate application:didFinishLaunchingWithOptions:]" )
AT_decl_file( "/Volumes/Data/iPhoneDev/trunk/CrashTesting/CrashTesting/CrashTestingAppDelegate.m" )
AT_decl_line( 17 )
AT_prototyped( 0x01 )
AT_type( {0x0000015b} ( BOOL ) )
AT_APPLE_isa( 0x01 )
AT_low_pc( 0x000026b4 )
AT_high_pc( 0x00002780 )
AT_frame_base( r7 )
0x000001b9: TAG_lexical_block [5] *
AT_low_pc( 0x000026c4 )
AT_high_pc( 0x00002780 )
Line table file: 'CrashTestingAppDelegate.m' line 20, column 0 with start address 0x000000000000270e
Looking up address: 0x0000000000002712 in .debug_frame... found!
0x00000020: FDE
length: 0x0000000c
CIE_pointer: 0x00000000
start_addr: 0x000026b4 -[CrashTestingAppDelegate application:didFinishLaunchingWithOptions:]
range_size: 0x000000cc (end_addr = 0x00002780)
Instructions: 0x000026b4: CFA=4294967295+4294967295
因此就可以查看到 line 13 是指 CrashTestingAppDelegate.m' line 20，所以就可以去那邊追查看看。
以上的例子僅需建立一個 Project (此例名為 CrashTesting)，然後在 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 裡頭寫一段會 crash 的程式碼(此例為 double free)：
NSString *justCrash = [[NSString alloc] initWithFormat:@"CrashTesting"];
[justCrash release];
[justCrash release];
[justCrash release];
[justCrash release];
如此一來，在實機執行完並當機後，可以接上 Xcode 去 Organizer - Devices 查看：
而 dSYM 檔案，則是在 Xcode 編譯的地方：
點選後，就可以看到並且可以複製到習慣的工作目錄囉
參考資料：
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