On x86 assembly jump table

Asked Aug 14 '16 at 18:57

Active Aug 14 '16 at 19:02

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Sometimes there are jump table like this:

operations:
    .long operation1, operation2, operation3

Then called by:

jmp *operations(,%ecx,4)

What I don't really understand is since you declare that number to a long, it's 32 bit, so operation + 4*ecx for ecx being 0,1,2 will translate into adding 0,4,8 which doesn't really equal to 0,32,64. So how does this jump actually occurs.

edited Aug 14 '16 at 19:02

Margaret Bloom

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asked Aug 14 '16 at 18:57

Michael Kwan

I have edited `ecs` into `ecx` since you have tagged this question as x86 and there is no such register as `ecs` in x86 assembly. Is that what you meant? If no, feel free to rollback the edit – Margaret Bloom Aug 14 '16 at 19:03
3

Addresses are in bytes not bits. – Ross Ridge Aug 14 '16 at 19:04
Thank you very much. That answered my question – Michael Kwan Aug 14 '16 at 19:29

On x86 assembly jump table

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