Xcode的使用中總是離不開(kāi)調(diào)試這個(gè)環(huán)境，在一年多的iOS開(kāi)發(fā)時(shí)間中，我更多地依賴于XCode本身提供的GUI工具來(lái)進(jìn)行調(diào)試，而對(duì)LLDB敬而遠(yuǎn)之，這段時(shí)間好好學(xué)習(xí)了LLDB的使用，發(fā)覺(jué)我錯(cuò)過(guò)了太多東西了……因此做一個(gè)比較完備的總結(jié)，也希望在寫(xiě)這篇文章的過(guò)程中進(jìn)一步學(xué)習(xí)LLDB調(diào)試的各種實(shí)踐方法。
LLDB闡述
LLDB 是一個(gè)有著 REPL 的特性和 C++ ,Python 插件的開(kāi)源調(diào)試器。LLDB 綁定在 Xcode 內(nèi)部，存在于主窗口底部的控制臺(tái)中。調(diào)試器允許你在程序運(yùn)行的特定時(shí)暫停它，你可以查看變量的值，執(zhí)行自定的指令，并且按照你所認(rèn)為合適的步驟來(lái)操作程序的進(jìn)展。
lldb下，相信大家用的較多的是po，或者使用條件斷點(diǎn)。但是面對(duì)復(fù)雜的問(wèn)題時(shí)，比如.a靜態(tài)庫(kù)，就需要其他調(diào)試方法了。
breakpoint
給某個(gè)文件的某一行下斷點(diǎn)?？梢允褂萌缦聝煞N方法，比如我想給Person.m文件的10行下一個(gè)斷點(diǎn)。可以使用如下的方法。
(lldb) breakpoint set --file Person.m --line 10
如果出現(xiàn)如下提示則說(shuō)明設(shè)置斷點(diǎn)成功
Breakpoint 2: where = BreakPointDemo`-[Person foo] + 23 at Foo.m:10, address = 0x000000010b22e687
也可以使用簡(jiǎn)寫(xiě)的形式如下。
(lldb) breakpoint set -f Foo.m -l 10
給一個(gè)函數(shù)下斷點(diǎn)
(lldb) breakpoint set --name foo
(lldb) breakpoint set -n foo
一次性給多個(gè)函數(shù)下斷點(diǎn)
(lldb) breakpoint set --name foo --name bar
OC的方法，可以使用以下兩種方式打斷點(diǎn)，第二種S需要大寫(xiě)
(lldb) breakpoint set --selector foo
(lldb) breakpoint set -S foo
使用 正則匹配 你要打斷點(diǎn)的函數(shù)。這個(gè)不限語(yǔ)言
(lldb) breakpoint set -r cFoo
(lldb) breakpoint set -r foo
也可以指定加載的動(dòng)態(tài)庫(kù)
(lldb) breakpoint set --shlib foo.dylib --name foo
(lldb) breakpoint set -s foo.dylib -n foo
我們同樣可以對(duì)命令進(jìn)行簡(jiǎn)寫(xiě)。下面兩個(gè)命令的效果是一樣的
(lldb) breakpoint set -n "-[Foo foo]"
(lldb) br s -n "-[Foo foo]"
查看有多少斷點(diǎn)可以使用
(lldb) breakpoint list
打印結(jié)果如下:
Current breakpoints:
1: file = '/Users/jianquan/Xcode/BreakPointDemo/BreakPointDemo/ViewCo ntroller.m', line = 20, exact_match = 0, locations = 0 (pending)
2: file = '/Users/jianquan/Xcode/BreakPointDemo/BreakPointDemo/ViewController.mm', line = 33, exact_match = 0, locations = 1, resolved = 1, hit count = 0
2.1: where = BreakPointDemo`::-[ViewController viewDidLoad]() + 186 at ViewController.mm:34, address = 0x0000000105f8362a, resolved, hit count = 0
......
我們可以對(duì)斷點(diǎn)進(jìn)行相關(guān)的操作，比如在執(zhí)行到2.1斷點(diǎn)的時(shí)候打印追蹤軌跡。bt是
(lldb) breakpoint command add 2.1
Enter your debugger command(s). Type 'DONE' to end.
> bt
> DONE
刪除所有斷點(diǎn)
(lldb) breakpoint delete
watchpoint
觀察變量值的具體變化
比如我需要觀察某個(gè)變量a的值變化,我可以使用如下命令
(lldb) watchpoint set variable a
bt命令用來(lái)追蹤程序的運(yùn)行過(guò)程
(lldb) bt
* thread #1: tid = 0x5c52c2, 0x000000010ff465fe BreakPointDemo`::-[ViewController viewDidLoad](self=0x00007f932cc07c50, _cmd="viewDidLoad") + 158 at ViewController.mm:36, queue = 'com.apple.main-thread', stop reason = watchpoint 1
* frame #0: 0x000000010ff465fe BreakPointDemo`::-[ViewController viewDidLoad](self=0x00007f932cc07c50, _cmd="viewDidLoad") + 158 at ViewController.mm:36
frame #1: 0x000000011112ba3d UIKit`-[UIViewController loadViewIfRequired] + 1258
......
我們可以使用frame命令查看變量a的具體值。
(lldb) frame variable a
(int) a = 100
補(bǔ)充一點(diǎn)watchpoint list的東西。這個(gè)命令包括了三個(gè)可選參數(shù)，我們可以使用help命令查看具體的值
(lldb) help watchpoint list
-b ( --brief )
Give a brief description of the watchpoint (no location info).
-f ( --full )
Give a full description of the watchpoint and its locations.
-v ( --verbose )
Explain everything we know about the watchpoint (for debugging
debugger bugs).
-b是比較簡(jiǎn)略的信息，-f是比較全面的信息，-v是完整的信息。經(jīng)過(guò)我的實(shí)驗(yàn)，如果使用watchpoint list,默認(rèn)的是 watchpoint list -f。
process
使用process命令也可以做很多有趣的操作。具體能做什么，我們也可使用help命令查看
(lldb) process help
attach -- Attach to a process.
connect -- Connect to a remote debug service.
continue -- Continue execution of all threads in the current process.
detach -- Detach from the current target process.
handle -- Manage LLDB handling of OS signals for the current target
......
查看更詳細(xì)的命令使用help <command> <subcommand>。比如
(lldb) help process attach
thread
其實(shí)這個(gè)功能主要就是斷點(diǎn)調(diào)試?yán)锩娴娜缦逻@個(gè)功能。
我們可以使用thread命令來(lái)做一些斷點(diǎn)的操作，具體有那些命令我們可以使用thread help進(jìn)行查看
(lldb) thread help
......
select -- Change the currently selected thread.
step-in -- Source level single step, stepping into calls.
Defaults to current thread unless specified.
step-inst -- Instruction level single step, stepping into calls.
Defaults to current thread unless specified.
step-inst-over -- Instruction level single step, stepping over calls.
Defaults to current thread unless specified.
step-out -- Finish executing the current stack frame and stop after
returning. Defaults to current thread unless
specified.
step-over -- Source level single step, stepping over calls.
Defaults to current thread unless specified.
step-scripted -- Step as instructed by the script class passed in the -C
option.
until -- Continue until a line number or address is reached by
the current or specified thread. Stops when returning
from the current function as a safety measure.
用得比較多的應(yīng)該是 step-開(kāi)頭的這幾個(gè)命令，使用起來(lái)很容易。我個(gè)人感覺(jué)比用鼠標(biāo)點(diǎn)擊斷點(diǎn)好用多了~
檢查當(dāng)前進(jìn)程的狀態(tài)，可以使用如下命令
lldb) thread list
Process 22323 stopped
* thread #1: tid = 0x62d0d7, 0x00000001082185fe BreakPointDemo`::-[ViewController viewDidLoad](self=0x00007ff81b60ab20, _cmd="viewDidLoad") + 158 at ViewController.mm:36, queue = 'com.apple.main-thread', stop reason = step until
......
*表明的就是當(dāng)前的線程，可以使用如下的命令得到線程的回溯，這個(gè)詞我也不確定怎么表達(dá)好，backtrace，也可以說(shuō)是追蹤。
(lldb) thread backtrace
* thread #1: tid = 0x354e72, 0x0000000103ce94bc RunTimeUse`-[ViewController viewDidLoad](self=0x00007ffea04050e0, _cmd="viewDidLoad") + 140 at ViewController.m:24, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
* frame #0: 0x0000000103ce94bc RunTimeUse`-[ViewController viewDidLoad](self=0x00007ffea04050e0, _cmd="viewDidLoad") + 140 at ViewController.m:24
frame #1: 0x0000000104e21c99 UIKit`-[UIViewController loadViewIfRequired] + 1258
frame #2: 0x0000000104e220cc UIKit`-[UIViewController view] + 27
frame #3: 0x0000000104cebc51 UIKit`-[UIWindow addRootViewControllerViewIfPossible] + 71
frame #4: 0x0000000104cec3a2 UIKit`-[UIWindow _setHidden:forced:] + 293
frame #5: 0x0000000104cffcb5 UIKit`-[UIWindow makeKeyAndVisible] + 42
frame #6: 0x0000000104c78c89 UIKit`-[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 4818
frame #7: 0x0000000104c7ede9 UIKit`-[UIApplication _runWithMainScene:transitionContext:completion:] + 1731
frame #8: 0x0000000104c7bf69 UIKit`-[UIApplication workspaceDidEndTransaction:] + 188
frame #9: 0x0000000107dd4723 FrontBoardServices`__FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 24
frame #10: 0x0000000107dd459c FrontBoardServices`-[FBSSerialQueue _performNext] + 189
frame #11: 0x0000000107dd4925 FrontBoardServices`-[FBSSerialQueue _performNextFromRunLoopSource] + 45
frame #12: 0x0000000104802311 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
frame #13: 0x00000001047e759c CoreFoundation`__CFRunLoopDoSources0 + 556
frame #14: 0x00000001047e6a86 CoreFoundation`__CFRunLoopRun + 918
frame #15: 0x00000001047e6494 CoreFoundation`CFRunLoopRunSpecific + 420
frame #16: 0x0000000104c7a7e6 UIKit`-[UIApplication _run] + 434
frame #17: 0x0000000104c80964 UIKit`UIApplicationMain + 159
frame #18: 0x0000000103ce9b1f RunTimeUse`main(argc=1, argv=0x00007fff5bf165e8) + 111 at main.m:14
frame #19: 0x000000010763d68d libdyld.dylib`start + 1
frame #20: 0x000000010763d68d libdyld.dylib`start + 1
當(dāng)然我們?nèi)绻肟此芯€程的backtrace，可以使用thread backtrace all命令。內(nèi)容太多，我這里就不演示log輸出了。
如果我們想單獨(dú)查看某個(gè)線程，我們可以先使用thread select 2跳到某個(gè)具體的線程，然后再進(jìn)行其他操作，比如thread backtrace
為了方便的觀測(cè)架構(gòu)參數(shù)和本地變量，我們可以使用 frame variable 命令
如果我什么參數(shù)也不加，將會(huì)把所有的參數(shù)和本地變量到打印出來(lái)。
(lldb) frame variable
(ViewController *) self = 0x00007ffea04050e0
(SEL) _cmd = "viewDidLoad"
(Person *) p = 0x0000610000001940
要打印某個(gè)變量需要在參數(shù)里面指定，這個(gè)命令我們?cè)谇懊嬉彩褂眠^(guò),比如要查看self
(lldb) frame variable self
(ViewController *) self = 0x00007ff81b60ab20
更進(jìn)一步，我們可以查看一些子元素
(lldb) frame variable self->isa
(Class) self->isa = ViewController
命令雖然不是完整的表達(dá)式解釋器，當(dāng)時(shí)可以識(shí)別一些基本的操作 比如 &, *, ->, []，不是重載運(yùn)算符，數(shù)組也可以使用，因?yàn)閿?shù)組本身也是指針。
(lldb) frame variable *self
(ViewController) *self = {
UIViewController = {
UIResponder = {
NSObject = {
isa = ViewController
}
......
}
和之前thread命令很類似，我可以使用frame select去選擇另外的一個(gè)frame
(lldb) frame select 9
如果想看更復(fù)雜的數(shù)據(jù)，我們可以使用expression命令
(lldb) expression self
(ViewController *) $0 = 0x00007fefa4705110
更復(fù)雜一些，我們可以用來(lái)輸出一個(gè)表達(dá)式
(lldb) expr (int) printf ("I have a pointer 0x%llx.\n", self)
I have a pointer 0x7fefa4705110.
(int) $1 = 33
call
其實(shí)這個(gè)命令完全可以使用po進(jìn)行替代，call一般可以用來(lái)調(diào)用不需要返回值的調(diào)試命令，比如更改View的背景顏色，以下兩個(gè)命令都可以達(dá)到相似的作用，更改當(dāng)前View的背景顏色值。
(lldb) po [self.view setBackgroundColor:[UIColor redColor]]
(lldb) call [self.view setBackgroundColor:[UIColor redColor]]
image
這個(gè)比較實(shí)用，可用于尋找棧地址對(duì)應(yīng)的代碼位置。
//測(cè)試image命令使用
NSArray *a = @[@"1"];
NSLog(@"%@",a[1]);
很顯然，數(shù)組越界了，以下顯示崩潰信息
RunTimeUse[46698:3510999] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSSingleObjectArrayI objectAtIndex:]: index 1 beyond bounds [0 .. 0]'
*** First throw call stack:
(
0 CoreFoundation 0x000000010934d34b __exceptionPreprocess + 171
1 libobjc.A.dylib 0x0000000108dae21e objc_exception_throw + 48
2 CoreFoundation 0x00000001093a5bdf -[__NSSingleObjectArrayI objectAtIndex:] + 111
3 RunTimeUse 0x00000001087d9480 -[ViewController viewDidLoad] + 320
4 UIKit 0x0000000109911c99 -[UIViewController loadViewIfRequired] + 1258
5 UIKit 0x00000001099120cc -[UIViewController view] + 27
6 UIKit 0x00000001097dbc51 -[UIWindow addRootViewControllerViewIfPossible] + 71
7 UIKit 0x00000001097dc3a2 -[UIWindow _setHidden:forced:] + 293
8 UIKit 0x00000001097efcb5 -[UIWindow makeKeyAndVisible] + 42
9 UIKit 0x0000000109768c89 -[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 4818
10 UIKit 0x000000010976ede9 -[UIApplication _runWithMainScene:transitionContext:completion:] + 1731
11 UIKit 0x000000010976bf69 -[UIApplication workspaceDidEndTransaction:] + 188
12 FrontBoardServices 0x000000010c8c4723 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 24
13 FrontBoardServices 0x000000010c8c459c -[FBSSerialQueue _performNext] + 189
14 FrontBoardServices 0x000000010c8c4925 -[FBSSerialQueue _performNextFromRunLoopSource] + 45
15 CoreFoundation 0x00000001092f2311 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
16 CoreFoundation 0x00000001092d759c __CFRunLoopDoSources0 + 556
17 CoreFoundation 0x00000001092d6a86 __CFRunLoopRun + 918
18 CoreFoundation 0x00000001092d6494 CFRunLoopRunSpecific + 420
19 UIKit 0x000000010976a7e6 -[UIApplication _run] + 434
20 UIKit 0x0000000109770964 UIApplicationMain + 159
21 RunTimeUse 0x00000001087d9acf main + 111
22 libdyld.dylib 0x000000010c12d68d start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)
程序奔潰在3，地址為：0x00000001087d9480，
因?yàn)槲业腄emo名字叫RunTimeUse。其他的名字很明顯是系統(tǒng)的庫(kù)。雖然log的21行也有RunTimeUse,但是經(jīng)過(guò)觀察應(yīng)該是main函數(shù)，不在考慮范圍之內(nèi)。
我們使用image的 lookup命令，可以很快的定位到具體的代碼行。
(lldb) image lookup --address 0x00000001087d9480
Address: RunTimeUse[0x0000000100001480] (RunTimeUse.__TEXT.__text + 320)
Summary: RunTimeUse`-[ViewController viewDidLoad] + 320 at ViewController.m:28
可以看出，奔潰在ViewController.m中的第28行。
