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How to play with
LLDB in iOS runtime?
@stinge
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• slide url
https://ppt.cc/fhdtqx
• QR Code
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Background
stinge
• Mercari iOS Engineer
• twitter: @StingeSu
• hobby: traveling & cooking
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Outline
• Why LLDB(Low Level Debugger)?
• How LLDB works?
• LLDB OSS
• Custom LLDB command
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Why LLDB?
• high-performance debugger
• Clang expression parser & LLVM disassembler
• Default debugger in Xcode
• Run Swift REPL & python supported
• Save your time
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Clang v.s GCC(GNU Compiler Collection)
Clang
• Apple official compiler
• Frontend for LLVM
• High performance
• BSD license
• ……
GCC
• Linux based
• Support more languages
• GPL license
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Clang (Xcode 10.2.1)
GCC (Darwin Kernel on Raspberry Pi)
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• How Apple deprecated GCC
Front-end Back-end
Xcode 3 GCC GCC
Xcode 4 GCC LLVM
Xcode 5 Clang LLVM
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• gcc hello.c
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Is it good for iOS?
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Is it good for iOS?
NO
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build process
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Clang-Swift
• The compiler process of swift
cmd+B
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Clang-Swift
• The compiler process of swift
Clang AST Reference
https://ppt.cc/fnA4Qx
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Clang-Swift
• The compiler process of swift
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How LLDB works?
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How LLDB works?
command action option argument
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• p(print) → expr --
expr -- foo
• po(print object) → expr -O --
expr -O -- foo
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p v.s po
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• Changes the value of variables
• Creates temporary variables
• Validates the values
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• DEMO
• Tasks
1. Changes UIButton title into red
2. Moves UIView up
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• Can we use a efficient way to finish these commands?
- YES
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LLDB Python API
https://lldb.llvm.org/python_reference/index.html
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LLDB OSS
• Facebook/chisel
• DEMO
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Customized command
• nudge(swift)
• DEMO
https://gist.github.com/sTinGe/059dc4c15347b7fef4ee537efdcc6e53