Jump (jmp, ljmp)

jmp	disp{8|16|32}
jmp	*r/m{16|32}
ljmp	immPtr
ljmp	*mem48
jcc	disp{8|32}

Operation

jump short or near; displacement relative to next instruction

jump far (intersegment; 4- or 6-byte immediate address

jump if condition is met; displacement relative to next instruction

Description

The jmp instruction transfers execution control to a different point in the instruction stream; records no return information.

Jumps with destinations of disp[8|16|32] or r/m[16|32] are near jumps and do not require changes to the segment register value.

jmp rel{16|32} adds a signed offset to the address of the instruction following the jmp instruction to determine the destination; that is, the displacement is relative to the next instruction. The displacement value is stored in the EIP register. For rel16, the upper 16 bits of EIP are cleared to zero resulting in an offset value not to exceed 16 bits.

ljmp ImmPtr or *mem48 use a four- or six-byte operand as a long pointer to the destination. In Real Address Mode or Virtual 8086 mode, the long pointer provides 16 bits for the CS register and 16 or 32 bits for the EIP register. In Protected mode, both long pointer forms consult the AR (Access Rights) byte of the descriptor indexed by the selector part of the long pointer. The jmp performs one of the following control transfers depending on the value of the AR byte:

• A jump to a code segment at the same privilege level

• A task switch

Example

Jump to the relative effective address (addressed by the EDI register plus an offset of 4):

jmp *4(%edi)

Long jump, use 0xfebc for the CS register and 0x12345678 for the EIP register:

ljmp $0xfebc, $0x12345678

Jump if not equal:

jne .+10