Xcode Debugger - how to single step at level of CPU instructions

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+1 Q:

Xcode Debugger - how to single step at level of CPU instructions

This is definitely obsessive, but I am fascinated by how cleverly the compiler translates C code into machine instructions. Since I am a little fuzzy on some instructions, it would be helpful if I could watch the operation of a compiled program at the level of individual machine instructions - "below" the level of a C statement (which might generate several CPU instructions). In other words, can I watch the registers/memory change after a single machine instruction?

I'm sure it's possible with some other debuggers, but I am only using Xcode.

+1 A:

In the Debugger window, enable assembly: Run/Debugger display/Source and disassembly. Wait till you hit a breakpoint. Then use Run/Step into(over) instruction to step in assembly.

Seva Alekseyev 2010-01-05 20:56:37

Thanks - I had the 'Step Into', but overlooked the OPTION key for machine level steps

gary 2010-01-05 21:18:06

Ooops, didn't check closely enough - Step Into w/Option (Cmd-Opt-Shft-I = ⌘⌥⇧I)

gary 2010-01-05 21:15:10

+1 A:

si is "Step Instruction", and ni is "Next Instruction". They have the same semantics as "step" and "next" do for lines of code, just on the instruction level.

Dave DeLong 2010-01-05 21:18:22

That sounds like gdb - can I do that from XCode?

gary 2010-01-05 21:21:47

shift-cmd-R brings up the console window, where (once you break) you get a standard GDB prompt. Also, it looks like the Run menu has a "Step Into Instruction" item (opt-shift-cmd-I) and a "Step Over Instruction" item (opt-shift-cmd-O).

Dave DeLong 2010-01-05 21:26:37

that's a capital "I" (as in "Indigo"), not a lower-case "L".

Dave DeLong 2010-01-05 21:27:20

ansaurus

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Xcode Debugger - how to single step at level of CPU instructions

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