LLDB Tips

Three tips that make debugging easier.

Step faster

Stepping over/into in the debugger can be really slow. Turns out that Debug navigator is the main culprit here. If it gets slow just hide navigator pane (⌘+0) or change to different navigator and enjoy full speed ¹.

Print bounds/frame like a normal person

Checking view’s bounds in LLDB by default produces this error:

(lldb) po self.view.bounds
error: property 'bounds' not found on object of type 'UIView *'
error: 1 errors parsing expression

There’s a bunch of workarounds for this. Most sane one was added in Xcode 6.3 with LLDB enchancements: expression parser can now import modules.

(lldb) e @import UIKit
(lldb) po self.view.bounds
(origin = (x = 0, y = 0), size = (width = 320, height = 548))
 (origin = (x = 0, y = 0), size = (width = 320, height = 548))

Entering import at the start of each debugging session gets tedious very quickly. To streamline this use Symbolic Breakpoint in a fashion similar to this Reveal tutorial. Go to Debuger pane and add Symbolic Breakpoint pointing to UIApplicationMain (it’s guaranteed to run only once), add e @import UIKit action and set it to automatically continue after evaluating. Using breakpoint’s context menu: Move Breakpoint To -> User, make it an user breakpoint and enjoy it in every project from now on ².

Breakpoint by regular expression on function name

Use case for this can be for example setting a breakpoint on all isEqual implementations:

(lldb) breakpoint set --func-regex isEqual

Shorthand:

(lldb) br s -r isEqual

To view all added locations:

(lldb) br list
...
5: regex = 'isEqual', locations = 428, resolved = 428, hit count = 0
  5.1: where = Foundation`-[NSKeyValueObservance isEqual:], address = 0x00148904, resolved, hit count = 0
  5.2: where = Foundation`-[NSString isEqual:], address = 0x0014f622, resolved, hit count = 0
  5.3: where = Foundation`-[NSString isEqualToString:], address = 0x0014f67e, resolved, hit count = 0
  5.4: where = Foundation`_isEqualCString, address = 0x0014fdae, resolved, hit count = 0
  5.5: where = Foundation`-[NSPathStore2 isEqualToString:], address = 0x0014feef, resolved, hit count = 0
  5.6: where = Foundation`-[NSURL(NSURL) isEqual:], address = 0x00170f37, resolved, hit count = 0

Disabling and deleting all locations for such breakpoint:

(lldb) br disable 5
(lldb) br delete 5