问题
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.
回答1:
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.
回答2:
It's possible to use Xcode's step over, step in, and step out commands with the debugger. The trick is to hold the ctrl (Control) key while you mouse over the debugger step icons to change the context. Underneath each step icon, the line will change to a dot and you can then step at the instruction level.
See the attached screenshot highlighted with a red oval.
回答3:
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.
回答4:
Ooops, didn't check closely enough - Step Into w/Option (Cmd-Opt-Shft-I = ⌘⌥⇧I)
来源：https://stackoverflow.com/questions/2009009/xcode-debugger-how-to-single-step-at-level-of-cpu-instructions