swift在终端使用LLDB调试

Using the LLDB Debugger 使用LLDB调试器一步一步地运行Swift程序，通过设置断点调试运行状态。

创建一个名Factorial.swift，定义了一个factorial(n:)函数，并打印调用该函数的结果:

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func factorial(n: Int) -> Int {
    if n <= 1 { return n }
    return n * factorial(n: n - 1)
}

let number = 4
print("\(number)! is equal to \(factorial(n: number))")

swiftc命令运行swiftc命令-g选项生成swift调试信息,在目录中生存可执行的Factorial文件：

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$ swiftc -g Factorial.swift
$ ls
Factorial.dSYM
Factorial.swift
Factorial*

使用lldb启动Factorial文件通过LLDB调试器命令lldb运行:

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$ lldb Factorial
(lldb) target create "Factorial"
Current executable set to 'Factorial' (x86_64).

设置断点使用breakpoint set (b) 命令在factorial(n:)函数的第2行中设置一个断点，每次执行函数时中断进程:

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(lldb) b 2
Breakpoint 1: where = Factorial`Factorial.factorial (Swift.Int) -> Swift.Int + 12

运行调试使用run (r)命令运行进程。进程在factorial(n:)函数的调用位置停止。

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(lldb) r
Process 40246 resuming
Process 40246 stopped
* thread #1: tid = 0x14dfdf, 0x0000000100000e7c Factorial`Factorial.factorial (n=4) -> Swift.Int + 12 at Factorial.swift:2, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
frame #0: 0x0000000100000e7c Factorial`Factorial.factorial (n=4) -> Swift.Int + 12 at Factorial.swift:2
   1    func factorial(n: Int) -> Int {
-> 2        if n <= 1 { return n }
   3        return n * factorial(n: n - 1)
   4    }
   5
   6    let number = 4
   7    print("\(number)! is equal to \(factorial(n: number))")

Use the print (p) command to inspect the value of the n parameter.

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(lldb) p n
(Int) $R0 = 4

The print command can evaluate Swift expressions as well.

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(lldb) p n * n
(Int) $R1 = 16

Use the backtrace (bt) command to show the frames leading to factorial(n:) being called.

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(lldb) bt
* thread #1: tid = 0x14e393, 0x0000000100000e7c Factorial`Factorial.factorial (n=4) -> Swift.Int + 12 at Factorial.swift:2, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    * frame #0: 0x0000000100000e7c Factorial`Factorial.factorial (n=4) -> Swift.Int + 12 at Factorial.swift:2
    frame #1: 0x0000000100000daf Factorial`main + 287 at Factorial.swift:7
    frame #2: 0x00007fff890be5ad libdyld.dylib`start + 1
    frame #3: 0x00007fff890be5ad libdyld.dylib`start + 1

Use the continue (c) command to resume the process until the breakpoint is hit again.

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(lldb) c
Process 40246 resuming
Process 40246 stopped
* thread #1: tid = 0x14e393, 0x0000000100000e7c Factorial`Factorial.factorial (n=3) -> Swift.Int + 12 at Factorial.swift:2, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
frame #0: 0x0000000100000e7c Factorial`Factorial.factorial (n=3) -> Swift.Int + 12 at Factorial.swift:2
   1    func factorial(n: Int) -> Int {
-> 2        if n <= 1 { return n }
   3        return n * factorial(n: n - 1)
   4    }
   5
   6    let number = 4
   7    print("\(number)! is equal to \(factorial(n: number))")

Use the print (p) command again to inspect the value of the n parameter for the second call to factorial(n:).

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(lldb) p n
(Int) $R2 = 3

取消断点 Use the breakpoint disable (br di) command to disable all breakpoints and the continue (c) command to have the process run until it exits.

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(lldb) br di
All breakpoints disabled. (1 breakpoints)
(lldb) c
Process 40246 resuming
4! is equal to 24
Process 40246 exited with status = 0 (0x00000000)

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