Awesome-Xcode-Debugging

A list of Xcode launch arguments, environment variables and command line options that help with debugging tasks.

Launch arguments

Localization

• -NSDoubleLocalizedStrings YES: double the length of all localized strings to see how longer languages will affect UI/layout
• -NSShowNonLocalizedStrings YES: uppercase all nonlocaized strings
• -AppleLanguages (es): can either be the name of the language (“Spanish”), or its language code (es), but since localization files are keyed by their ISO 639 code, using the code is preferable to the actual name of the language

Core Data

• -com.apple.CoreData.SQLDebug 3: takes a value between 1 and 3, with increasing verbosity
• -com.apple.CoreData.SyntaxColoredLogging YES
• -com.apple.CoreData.MigrationDebug

Environment variables

Zombies

• NSZombieEnabled
• NSDeallocateZombies: actually free the memory of zombie objects, as opposed to secretly retaining them for reporting

Allocations

• MallocScribble
• MallocGuardEdges
• MallocStackLogging
• MallocStackLoggingNoCompact

Prior to Mac OS X 10.5 MallocStackLogging and MallocStackLoggingNoCompact could produce erroneous and misleading results in a multi-threaded program. source

I/O Buffering

• NSUnbufferedIO: don't buffer logging to stdout (sterr is unbuffered by default)

dyld

• DYLD_FRAMEWORK_PATH
• DYLD_FALLBACK_FRAMEWORK_PATH
• DYLD_VERSIONED_FRAMEWORK_PATH
• DYLD_LIBRARY_PATH
• DYLD_FALLBACK_LIBRARY_PATH
• DYLD_VERSIONED_LIBRARY_PATH
• DYLD_PRINT_TO_FILE
• DYLD_SHARED_REGION
• DYLD_INSERT_LIBRARIES
• DYLD_FORCE_FLAT_NAMESPACE
• DYLD_IMAGE_SUFFIX
• DYLD_PRINT_OPTS (macOS 10.4+)
• DYLD_PRINT_ENV (macOS 10.4+)
• DYLD_PRINT_LIBRARIES
• DYLD_BIND_AT_LAUNCH
• DYLD_DISABLE_DOFS
• DYLD_PRINT_APIS (macOS 10.4+)
• DYLD_PRINT_BINDINGS (macOS 10.4+)
• DYLD_PRINT_INITIALIZERS (macOS 10.4+)
• DYLD_PRINT_REBASINGS
• DYLD_PRINT_SEGMENTS (macOS 10.4+)
• DYLD_PRINT_STATISTICS (macOS 10.4+)
• DYLD_PRINT_DOFS
• DYLD_PRINT_RPATHS
• DYLD_SHARED_CACHE_DIR
• DYLD_SHARED_CACHE_DONT_VALIDATE
• DYLD_ROOT_PATH and DYLD_PATHS_ROOT appear to be synonyms and allow you to reset the "root" for searching for libraries/frameworks/etc. This is available on macOS/iPhoneSimulator but not iOS.
• DYLD_DISABLE_PREFETCH disables the pre-fetching of the content of __DATA and __LINKEDIT segments.
• DYLD_PRINT_LIBRARIES_POST_LAUNCH is the same as DYLD_PRINT_LIBRARIES but prints them right after launch has finished.
• DYLD_NEW_LOCAL_SHARED_REGIONS and DYLD_NO_FIX_PREBINDING are ignored and don't do anything anymore.
• DYLD_PREBIND_DEBUG prints out debug information on why prebinding was not used.
• DYLD_PRINT_TO_STDERR only applies to iOS and forces output to stderr (instead of stdout) to help it show up on console logs.
• DYLD_PRINT_WEAK_BINDINGS prints debug information on weak bindings.
• DYLD_PRINT_WARNINGS prints a bunch of warnings (mostly regards to closures and how they are being used).
• DYLD_PRINT_CS_NOTIFICATIONS prints information about the core symbolicator.
• DYLD_PRINT_INTERPOSING prints details about interposes that occur.
• DYLD_PRINT_CODE_SIGNATURES prints details about code signatures (specifically successes and failures).
• DYLD_USE_CLOSURES is a dyld3 feature, but doesn't appear to work for anybody non-internal (need CSR_ALLOW_APPLE_INTERNAL set).
• DYLD_IGNORE_PREBINDING has three values (all, app and nonsplit) with nonsplit being the default if a value is not supplied.
• DYLD_SKIP_MAIN is an apple only feature used for testing dyld (need CSR_ALLOW_APPLE_INTERNAL set).

xcodebuild -X options

• TODO

References

• https://nshipster.com/launch-arguments-and-environment-variables/
• https://stackoverflow.com/a/51504440/4789448 for some dyld environment variables
• https://developer.apple.com/library/archive/technotes/tn2239/_index.html
• https://developer.apple.com/library/archive/technotes/tn2124/_index.html
• man dyld, which can be read for those environment variables lacking descriptions