How can I figure out which general-purpose registers are modified by a function call. I am programming a Win32 Assembly program that calls IsDebuggerPresent(). According to MSDN, it will return a boolean value of nonzero is a debugger is present. How would I find out which register is modified without having to assemble and link the program to test it.


In general, this concept is referred to as register preservation or register volatility.

From http://en.wikipedia.org/wiki/X86_calling_conventions#Register_preservation --

According to the Intel ABI to which the vast majority of compilers conform, the EAX, EDX, and ECX are to be free for use within a procedure or function, and need not be preserved.

In other words, an API function such as IsDebuggerPresent() might modify EAX, EDX, and/or ECX, but it won't modify EBX, ESP, or EBP.

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