When you debug the code, very oftern you need to deal with memory and registers. It would be beneficial to understand the eight general-purpose registers in the x86 processor family. Each register has a unique purpose and has special instructions and opcodes which make fulfilling this purpose more convenient or efficient. The registers and their uses are shown briefly below:
- EAX - Accumulator register.
- EDX - The data register is the an extension to the accumulator. It is most useful for storing data related to the accumulator’s current calculation.
- ECX - The count register.
- EDI - Every loop must store its result somewhere, and the destination index points to that place. With a single-byte STOS instruction to write data out of the accumulator, this register makes data operations much more size-efficient.
- ESI - In loops that process data, the source index holds the location of the input data stream. Like the destination index, ESI had a convenient one-byte instruction for loading data out of memory into the accumulator.
- ESP - ESP is the stack pointer. Its value is required by PUSH, POP, CALL, and RET instructions.
- EBP - In functions that store parameters or variables on the stack, the base pointer holds the location of the current stack frame. In other situations, however, EBP is a free data-storage register.
- EBX - In 16-bit mode, the base register was useful as a pointer. Now it is completely free for extra storage space.