Print MMTk Object Information

MMTk provides a utility function to print object information for debugging, crate::mmtk::mmtk_debug_print_object. The function is marked as #[no_mangle], making it suitable to be used in a debugger.

The following example shows how to use the function to print MMTk's object metadata before and after a single GC in rr.

Set up break points before and after a GC.

(rr) b stop_all_mutators
Breakpoint 1 at 0x767cba8f74e8 (14 locations)
(rr) b resume_mutators
Breakpoint 2 at 0x767cba8f8908

When the program stops, call mmtk_debug_print_object. We might need to set the language context in the debugger to C when we stop in a Rust frame. Then call mmtk_debug_print_object with the interested object.

(rr) set language c
(rr) call mmtk_debug_print_object_info(0x200fffed9f0)
In immix:
marked = false
line marked = false
block state = Unmarked
forwarding bits = 0, forwarding pointer = None
vo bit = true