Understanding Large Codebases

From 360iDev 2019

Find the sample “project” (GitHawk fork) here.

Slides are available here.

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Some tips for starting out on a new project

Xcode

• Use the Symbol Navigator to navigate through a project
• Use the Call Hierarchy to understand flow through project
• Use ⌃⌘J to jump to a definition in a project

LLDB

• Add breakpoint sounds to quickly identify issues
  • Debugging with “sound”
  • Custom Sounds
• Import LLDB commands/breakpoints from a file (put this in ~/.lldbinit)

command source ~/.lldb-scripts/sounds/breakpoints.txt

• Auto-continuing sound breakpoints tagged with a name (contents of breakpoints.txt above)

breakpoint set -n "-[UIViewController dealloc]" -C "platform shell afplay /System/Library/Sounds/Submarine.aiff" --auto-continue true -d -N audio

• Use common scripts across projects

• Facebook’s Chisel commands and helpers

• apropos command to search commands and help text
• log enable -f /tmp/log.txt lldb all enable logging to a file
• value.GetError().GetCString() retrieve string from error in SBValue (using LLDB’s Python APIs)

Instruments

• Use system os_log messages for debugging
• Create Custom Instruments for system APIs: CommonInstruments repo

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What can you do to make the onboarding process easier for new developers?

Xcode

• Documentation mini map
• Hold ⌘ to show symbols

LLDB

• Add a file to contain breakpoints and other LLDB setup
• Create application specific commands: see the GitHawk commands
• Use named breakpoints to quickly enable and disable breakpoints

breakpoint set -n malloc -N memory
breakpoint set -n free -N memory
breakpoint disable memory

To re-enable:

breakpoint enable memory

Instruments

• Add Logs, Signposts and Points of Interest to construct a big picture of your app
• Create custom instruments that focus on parts, whether large and small, so issues can be debugged visually
  • Instruments packages can be distributed throughout the team and packaged into a single Xcode project for easy development

CLIPS

• LISP variant that describes expert systems
• General language + functions manual - this is not specific to Instruments but presents some basic primitives that can be used with CLIPS expressions.

Debugging

• Make sure message format matches
• Refer to Instruments documentation online. (Help > Instruments Developer Help)

• Use the “Instrument Inspector” and its “Schemas” tab to discover provided columns

• Can add CI step to verify Instruments traces
  • Risky since the file format is closed source
  • TraceUtility tool uses the libraries bundled in the app

Questions

• Is there a way to avoid the absolute paths?
  • I’m still trying to figure out a good way to do this. I’ll update the docs and 360 Slack if I find one. In the meantime, you could add a symbolic link to point to a main imported file.
• A way to not import each time:
  • target stop-hook add run code each time debugger stops. Add imports there and you can avoid having to import each time.