How to jump by using x64 memory address, stored at x64 location?

Question

As far as I know 'jmp' by using a 64bit address as operand is impossible but I believe using a x64 memory location is (from here JMP r/m64). But how can I write this in hex?

Illustration of what instruction I want hex opcode of:

qword memAddress

jmp far qword ptr [memAddress]

You didn't specify processor type but I figure I'd point out that JMP m16:64 is only available on Intel x64 and not available on AMD's x64 — Michael Petch, Jan 04 '15 at 19:06

Sep Roland · Answer 1 · 2015-01-04T19:59:58.807

1

jmp far qword ptr [memAddress]

For what it is worth. My assembler produces this : 48h,FFh,2Ch,25h,00h,00h,00h,00h

edited Jan 04 '15 at 19:59

answered Jan 04 '15 at 19:19

Sep Roland

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score 1 · Answer 2 · answered Apr 15 '19 at 23:03

jmp far doesn't take a qword memory operand, it takes an 80-bit m16:64 operand to be loaded into CS:RIP.

I think you want to leave out the far and use an indirect near jump that only modifies RIP, not CS. You say you want JMP r/m64, and that's what this is.

In NASM syntax, qword is the default operand-size for indirect jumps:

default rel
label:
    jmp [rel label]

Assembles + disassembles (objdump -drwC -MIntel) to this:

ff 25 fa ff ff ff jmp QWORD PTR [rip+0xfffffffffffffffa] # 401000 <label>

See also Call an absolute pointer in x86 machine code if you pointer is an assemble-time constant, e.g. for JIT. (e.g. mov rax, 0x123456789ab / jmp rax or call rax is also an option.)

How to jump by using x64 memory address, stored at x64 location?

2 Answers2

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