Quit Bugging Me: ABI

By Mike Deliman

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What's in an ABI?  An Application Binary Interface is a lot like a API – Applications Programming Interface, except instead of just telling you how to make a call, what parameters to provide, and what returns and errnos to expect, an ABI also tells you something about how the interfaces work.  Understanding an ABI for a CPU means you understand how the registers are used, what they're for, and what they mean under different contexts.

Among the things ABIs give you is how your CPU formats memory (the stack) when it makes a call to a routine. An easy way to take a look at an ABI is to set a break point on a routine, and look at what the stack contains.  This is on a PowerPC target.  First I'll spawn a task, then extract the current information about the task – stack pointer, stack base, etc, using target-side debug routines. 

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