Question

(b) Determine whether the JMP instruction are SHORT, NEAR, or FAR jump. Explain your answer.

Answer 1

assuming your question pertains to the x86 architecture

A SHORT jump is a relative jump to a particular offset from the current instruction pointer address. A LONG jump uses a larger offset value, and so can jump further away from the current instruction pointer address. Both of these jump types are usually relative - that is, the operand is an offset from the current instruction pointer (though in assembly source, you normally provide the target label - the assembler or linker then computes the offset). Neither of them jump to a different code segment, so they are both 'near' jumps.

A FAR jump specifies both a segment and offset, which are both absolute in the sense that they specify the required code segment and instruction pointer, rather than an offset relative to the current code segment / instruction pointer.

(Note that it is also possible to perform an indirect absolute jump, where you specify an operand that holds the absolute address that you wish to jump to. In this case the jump can either be near or far - i.e. it can include or not include the required code segment).

If you don't specify the jump 'distance', it is up to the assembler whether you get a short, long or far jump. Most modern assemblers are "two-pass" and will use a short jump if possible, or a long or far jump otherwise - the latter only if required.