Call & JMP command

For JMP commands:

 

(1) JMP short label
Equivalent to (IP) = (IP) + 8-bit displacement jump range is [-128,127]
(2) JMP near PTR labels
Equivalent to (IP) = (IP) + 16-bit displacement jump range is [-32768,32767]
(3) JMP far PTR labels
Equivalent to (CS) = the segment address of the label, (IP) = the offset address of the label

The first two are intra-segment transfer, which is based on displacement. The first is short transfer, the second is near transfer, and the third is inter-segment transfer, directly modify CS and IP addresses for transfer.

There are also JMP commands in the memory for the transfer address, JMP word PTR memory unit address (intra-segment transfer), and jmp dword ptr memory unit address (Inter-segment transfer ).

 

 

For the call & RET command:

(1) call number
It is equivalent to push IP, and then (IP) = (IP) + 16-bit displacement
(2) Call far PTR label
Equivalent to push CS, push IP, (CS) = segment address of the label segment, (IP) = offset address of the label in the segment
(3) Call 16-bit register
Equivalent to push IP and then JMP 16-bit Reg
(4) Call word PTR memory unit address
Equivalent to push ip jmp word PTR memory unit address
For example, call word ptr ds: [0]
(5) Call dword ptr memory unit address
Equivalent to pushing CS push ip jmp dword ptr memory unit address

Call is often used with ret. RET is equivalent to pop IP. If it is inter-segment transfer, retf is used to return the function, which is equivalent to pop IP pop CS.

Call & JMP command