Contents
What is ESI and EDI?
•ESI and EDI are general purpose registers. If a variable is to have register storage class, it is. often stored in either ESI or EDI. A few instructions use ESI and EDI as pointers to source and. destination addresses when copying a block of data.
What is ESI registration size?
The lower 32 bits, 16 bits, and 8 bits of each register are directly addressable in operands. This includes registers, like esi, whose lower 8 bits were not previously addressable. The following table specifies the assembly-language names for the lower portions of 64-bit registers.
What is the register %esi and %edi used for?
In addition to the registers being used for mass operations, they are useful for their property of being preserved through a function call (call-preserved) in 32-bit calling convention. The ESI, EDI, EBX, EBP, ESP are call-preserved whereas EAX, ECX and EDX are not call-preserved.
What is the purpose of the IP EIP register?
The EIP register (prior to transferring program control) contains the address of the instruction following the CALL instruction. When this address is pushed on the stack, it is referred to as the return instruction pointer or return address.
What is the difference between EAX and ax?
eax is the 32-bit, “int” size register. It was added in 1985 during the transition to 32-bit processors with the 80386 CPU. ax is the 16-bit, “short” size register. It was added in 1979 with the 8086 CPU, but is used in DOS or BIOS code to this day.
Which register holds a count for some instructions?
ECX
ECX: Count : Used to hold the count for some instructions, REP and LOOP.
Which are the four categories of registers?
Different Types of Registers
- MAR Register. The full form of MAR is the memory address register.
- MDR. The full form of MDR register is a memory data register.
- MBR. The full form of MBR is the memory buffer register.
- PC. The full form of PC is the program counter register.
- Accumulator.
- Index Register.
- Instruction Register.
What does the TEST instruction do?
In the x86 assembly language, the TEST instruction performs a bitwise AND on two operands. The flags SF , ZF , PF are modified while the result of the AND is discarded. The OF and CF flags are set to 0 , while AF flag is undefined.
Are Rax and EAX the same register?
rax is the 64-bit, “long” size register. It was added in 2003 during the transition to 64-bit processors. eax is the 32-bit, “int” size register. They’re pretty similar to the old 8-bit registers of the 8008 back in 1972.