Editing JMP (x86 instruction) (section)

{{Short description|Unconditional jump instruction in x86 assembly language}}
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{{Out of date|date=February 2017}}
{{Notability|date=September 2022}}
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In the [[x86 assembly language]], the '''<code>JMP</code>''' [[instruction (computer science)|instruction]] performs an unconditional jump. Such an instruction transfers the flow of [[execution (computers)|execution]] by changing the [[program counter]]. There are a number of different [[opcode]]s that perform a jump; depending on whether the processor is in [[real mode]] or [[protected mode]], and an override instruction is used, the instructions may take [[16-bit]], [[32-bit]], or segment:offset [[pointer (computer programming)|pointers]].<ref>{{cite web |url=http://download.intel.com/design/PentiumII/manuals/24319102.PDF| title=Intel Architecture Software Developer's Manual, Volume 2: Instruction Set Reference Manual (6.5MB)|accessdate=2009-11-03|archive-url=https://web.archive.org/web/20090219101735/http://download.intel.com/design/PentiumII/manuals/24319102.PDF|archive-date=2009-02-19|url-status=dead}}</ref> {{Wiktionary|relative|absolute}}

There are many different forms of jumps: relative, [[conditional jump|conditional]], absolute and [[indirect branch|register-indirect jumps]].

The following examples illustrate:
# a relative jump with a 16-bit pointer;
# a long jump (inter-segment), a relative jump with a 32-bit pointer;
# and a register-indirect absolute jump using the [[EAX register]].
(Note that although the first and second jumps are relative, commonly the destination address is shown instead of the relative offset as encoded in the opcode.)

Example one: Load IP with the new value <code>0x89AB</code>, then load [[CS register|CS]] with <code>0xACDC</code> and IP with <code>0x5578</code>.
<syntaxhighlight lang="asm">
JMP 0x89AB
JMP 0xACDC:0x5578
</syntaxhighlight>

Example two: Load EIP with the value <code>0x56789AB1</code>, only in [[protected mode]] or [[unreal mode]].
<syntaxhighlight lang="asm">
JMP 0x56789AB1
</syntaxhighlight>

Example three: Jump to the value stored in the EAX register, only in protected mode.
<syntaxhighlight lang="asm">
JMP EAX
</syntaxhighlight>





The <code>JMP</code> (Jump) instruction transfers the program's control to a specified location in the code. Unlike function calls, it doesn’t save return information. Instead, it directs execution to a '''target address''', which can be:

* An '''immediate value''',
* A '''general-purpose register''', or
* A '''memory location'''.