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assemblyx86addressing-mode

x86 addressing mode

I am very confused regarding the indirect addressing mode for this instruction:

and $0x0000FF00, 4(%esp)

If this is the current top of stack:

0xBF8DB0B8: 0xDEADBEEF <--- ESP + 4
0xBF8DB0B4: 0xDEADBEEF <--- ESP

and this is the content of memory at 0xDEADBEEF:

0xDEADBEEF: 0x1234ABCD

Which of the following will be performed?

  1. AND 0x0000FF00, 0xDEADBEEF with result: 0x0000BE00 stored in 0xBF8DB0B8.

  2. AND 0x0000FF00, 0x1234ABCD, with result: 0x0000AB00 stored in 0x0000AB00.

  3. AND 0x0000FF00, 0xDEADBEF3. with result: 0x0000BE00 stored in 0xDEADBEF3.

Solution

  • AND 0x0000FF00, 0xDEADBEEF with result: 0x0000BE00 stored in 0xBF8DB0B8:

    Since %esp contains the address 0xBF8DB0B4, 4(%esp) is the address 0xBF8DB0B8 and 0xDEADBEEF is what in that address.