Where is it? Is there any other tool available from Xcode?
Thank you.
Now that the NDA no longer applies for xcode 4.2, here are the screenshots with the required steps.
This should make it quicker for people still looking for Guard Malloc.
As per my comment, it's not currently possible to comment on Xcode 4.2 in public.
However, if this is your first step into Xcode 4 from 3.2 then you may be having difficulty finding Guard Malloc in any event. As of 4.0 it's considered a diagnostic attribute of your scheme. So to enable it you should click the left part of pull down for your current scheme (the thing in the top bar to the right of the stop button), select 'edit scheme...', choose 'Run .app' in the left pane, then the 'Diagnostics' tab in the dialogue that appears on the right. You can enable or disable Guard Malloc in there.
That's true for 4.0 and 4.1. Hopefully it'll help you find your way in 4.2.
来源：https://stackoverflow.com/questions/7381210/guard-malloc-in-xcode-4-2-where-is-it