Now that we've written a simple C program and seen its assembly and machine code, let's move on to something a little more challenging: a C program with inline assembly to access the contents of a CPU register.
Details on assembly-language programming are outside the scope of this book; refer to the Further reading section on the GitHub repository.
x86_64 has several registers; let's just go with the ordinary RCX register for this example. We do make use of an interesting trick: the x86 ABI calling convention states that the return value of a function will be the value placed in the accumulator, that is, RAX for the x86_64. Using this knowledge, we write a function that uses inline assembly ...
