Format of a jump table

Question

I am reading an example on a course about jump tables. They call gdb x/8g 0x123456

The resulting output looks like:

0x123456    0x000000000000134234    0x0000000000005f424
0x123487    0x0000000000001dd1ac    0x000000000000ef327

I thought a jump table maps an address to the address of the code it should execute. Why then are there 3 columns (shouldn't it be 2?).

Have you read a gdb manual to see what `x` does? – Kerrek SB Jun 14 '14 at 13:33 — Kerrek SB, Jun 14 '14 at 13:33

score 1 · Accepted Answer · answered Jun 14 '14 at 21:11

Why then are there 3 columns (shouldn't it be 2?)

You didn't paste the real GDB output, which looked something like:

0x123450    0x000000000000134234    0x0000000000005f424
0x123460    0x0000000000001dd1ac    0x000000000000ef327

(the first column is different). In programming, details matter.

If you make the terminal narrower, then you'll get 2 columns, like this:

0x123450    0x000000000000134234
0x123458    0x0000000000005f424
0x123460    0x0000000000001dd1ac
0x123468    0x000000000000ef327

As KerrekSB suggested, read the GDB manual to understand what x does. Hint: the first column doesn't really matter -- it's where the table itself is stored.

Format of a jump table

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