Debugging tips and tricks - coders on beers Santiago
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This document provides tips and tricks for debugging programs using lldb, a low-level debugger. It discusses basic lldb concepts like breakpoints, watchpoints, and expressions. It also demonstrates how to use lldb commands to print variables, set breakpoints and stop conditions, and evaluate expressions during debugging.
![lldb - mais expressões
(lldb) e let user.name = “John Doe”
(lldb) e let $count = 42
(lldb) po $count
42
(lldb) e let $dict: Dictionary<String, Int> = ["answer": 42]
(lldb) po $dict
▿ 1 element
▿ 0 : 2 elements
- key : "answer"
- value : 42](https://image.slidesharecdn.com/debuggingtipsandtricks-codersonbeerssantiago-190429211058/85/Debugging-tips-and-tricks-coders-on-beers-Santiago-18-320.jpg)
Debugging tips and tricks - coders on beers Santiago
- 2. Debugging tips and tricks
- 3. Everyone knows that debugging is twice as hard as writing a program in the first place. So if you're as clever as you can be when you write it, how will you ever debug it? Brian Kerninghan
- 4. Basic notions ○Breakpoint ○Watchpoint ○Continue to Here (gutter) ○Debug bar ○Show debug area (cmd + shift + y) ○variable view ○watch ○console ○Frame
- 5. Basic notions ○ Debug bar ○ (de)activate breakpoints ○ Continue execution ○ Step over ○ Execute current line and go to the next ○ Step in ○ “enter” the called method/function ○ Step out ○ “exit” the called method/function
- 6. Basic notions ○ Debug bar ○ Debug view hierarchy ○ Simulate location ○ Choose stack frame
- 7. Basic notions ○ watchpoint ○ Behaviors like a breakpoint ○ Stop at value change ○ Variable or memory address ○ Command line ○ Click ○ view memory ○ breakpoint navigator ○ edit ○ condition ○ action
- 8. lldb - low level debugger ○ Have you done that?: print("log just for debug: (self.object)") ○ Or that? let n = 0 // self.someMethodThatReturnInteger() ○ Or that? if true !|| self.someMethodThatReturnBool() { ○ Or that? func someMethodThatReturnBool() !-> Bool { return true !//TODO: implement }
- 9. lldb - breakpoints ○ Breakpoint stop execution of a instruction ○ Allow add command just for debug ○ May have stop condition ○ Via command breakpoint set —file ViewController.swift —line 7 ○ One shot - code execute just once, automatically removed breakpoint set —oneshot true —name MyType.myMethod() ○ Via Xcode - just click gutter
- 10. lldb - stop conditions
- 11. lldb - condições de parada ○ - NSManagedObject.setValue(Any?, forKey: String)
- 12. lldb - low level debugger ○ Exception Breakpoint ○ Symbolic Breakpoint UIKit symbols in Objective-C ○ Method signature ○ Symbols
- 13. lldb - exception breakpoint - stopping on crash - Exception Breakpoint
- 14. lldb - commands and expressions ○ Expression (expression) ○ Print - p / expression — : - lldb internal formatters ○ parray ○ Print Object - po / expression -O — - use implementation of debugDescription ○ poarray ○ Frame variable (only Xcode 10.2) - v Print variables of current stack frame. Can be way faster ○ Watchpoint (watchpoint)
- 16. Skipping line and returning value
- 17. Expressions ○ Evaluated as code ○ Result is shown and storage in convenience variable ($1, $2, etc) ○ Can do a lot ○ Arithmetic ○ function/method calling ○ type casting ○ Attributions ○ Variable declaration (let variable: Type = value)
- 18. lldb - mais expressões (lldb) e let user.name = “John Doe” (lldb) e let $count = 42 (lldb) po $count 42 (lldb) e let $dict: Dictionary<String, Int> = ["answer": 42] (lldb) po $dict ▿ 1 element ▿ 0 : 2 elements - key : "answer" - value : 42
- 19. lldb - low level debugger ○ Watchpoint ○ Monitor state/value of a variable ○ Variable inspector
- 20. lldb - low level debugger ○ Watchpoint ○ Monitor state/value of a variable ○ Since Xcode 10 shown in breakpoint navigator
- 21. lldb - low level debugger ○ Rule of Thumb - keep it fast ○ “Automatically continue after evaluating” ○ po $arg1 ○ Audible breakpoints ○ breakpoint with shell command ○ Command: say ○ Arguments: -v, Zarvox, “Your breakpoint %B has been hit %H times”
- 22. Referências ○ http://www.slideshare.net/talesp/debugging-fast-track ○ https://github.com/facebook/chisel ○ https://www.objc.io/issues/19-debugging/lldb-debugging/#let-s- dance ○ http://lldb.llvm.org/tutorial.html ○ https://www.bignerdranch.com/blog/xcode-breakpoint-wizardry/ ○ https://developer.apple.com/videos/play/wwdc2018/412/
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