Debug Swift debugging with LLDB JJ Lin 

Issues: Cannot debug framework source code 

Issues: Cannot debug framework source code 

● When the compiler compiles a function, it generates machine code. 

● Debug info in object file: For the debugger to map the address in the executable to the source code and line number 

● For archiving distribution, debug info will be put into .dSYM bundles by dsymutil. 

DWARF & dSYM ● For debug at run-time ● Crash log symbolication 

DWARF ● Debugging With Attribute Record Formats ● A debugging file format used by many compilers and debuggers to support source-level debugging 

$ dwarfdump Framework1.framework.dSYM/Contents/Resources/DWARF/Framework1 

DWARF & dSYM ● DWARF ○ Keep debug symbols in the executable. ● DWARF with dSYM File ○ dSYM: debug SYMbol ○ Strips debug symbols from the executable, and places them into a separate dSYM file. ○ Reduce binary size, but slower 

Issues: Cannot debug framework source code ● So how to debug framework? ○ sample: TerminalInterface 

(lldb) image list ● `image` is an abbreviation for `target modules` ● List all the modules currently loaded ○ executable ○ dependent shared library ● Could help to verify that dSYM is actually found ● The UI framework is called TerminalInterface, and LLDB did find the framework and debug info. 

What if… dSYM is not loaded? ● (lldb) add-dsym {dSYM} 

(lldb) image lookup -va {memory-address} ● Look up information within executable and dependent shared library images. 

● The source file is pointed to build server, not local machine (lldb) image lookup -va {memory-address} 

(lldb) image lookup -r -n {symbol name} 

Redirect source map ● Since the source file is pointed to build server, not local machine ● We can redirect the source map ● (lldb) settings set target.source-map prefix new ● (lldb) settings show target.source-map ● Re-run the project, then the source code could be inspected ✅ 

Redirect source map - LLDB Init File ● Handy tips: Define per-project LLDB init file for commands 

Redirect source map - LLDB Init File ● Handy tips: Define per-project LLDB init file for commands 

● (lldb) po //failed Issues: Cannot debug framework source code 

(lldb) v ● but v works ● Xcode variable view ● = (lldb) frame variable ● = (lldb) v 

LLDB is debugger, and also a compiler 

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If you are interested… ● Type Metadata ○ The Swift runtime keeps a metadata record for every type used in a program, including every instantiation of generic types. ○ These metadata records can be used by reflection and debugger tools to discover information about types. ● Reflection ○ Reflection in Swift allows us to inspect and manipulate arbitrary values at runtime. ● https://github.com/apple/swift/blob/main/docs/ABI/TypeMetadata.rst 

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● Solution: Archive the framework again, with the missing module 

Some Tips 

What if… cannot find dSYM? ● Xcode Settings - Generate Debug Symbols ○ Default: Yes for both Debug and Release 

What if… symbol not found? ● Xcode Settings - Debug Information Level ○ Toggles the amount of debug information emitted when debug symbols are enabled. ○ Option - Compiler default ■ Generate source level debug information ○ Option - Generate line number tables only ■ Allows to obtain stack traces with function names, file names and line numbers ■ No other data (e.g. description of local variables, or function parameters). 

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Reference ● https://developer.apple.com/videos/play/wwdc2022/110370/ ● https://developer.apple.com/videos/play/wwdc2021/10211 ● https://developer.apple.com/documentation/xcode/build-settings-reference ● https://clang.llvm.org/docs/UsersManual.html#controlling-size-of-debug-information ● https://github.com/apple/swift/blob/main/docs/ABI/TypeMetadata.rst 

Thank you