A question about PUSHAD

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int0x50

Joined: 19 Jul 2019
Posts: 13

int0x50

PUSHAD pushes all the values of the registers. The registers are stored on the stack in the following order: EAX, ECX, EDX, EBX, EBP, ESP (original value), EBP, ESI, and EDI (if the current operand-size attribute is 32).

How does the original value of ESP is stored?

24 Jul 2019, 09:10

DimonSoft

Joined: 03 Mar 2010
Posts: 632
Location: Belarus

DimonSoft

It’s all there, in Intel SDM:

Intel SDM wrote:

Code:

IF OperandSize = 32 (* PUSHAD instruction *)
THEN
  Temp ← (ESP);
  Push(EAX);
  Push(ECX);
  Push(EDX);
  Push(EBX);
  Push(Temp);
  Push(EBP);
  Push(ESI);
  Push(EDI);
ELSE
...

Saving original value is not a problem, there’s a whole bunch of internal registers inside the processor that are used to ensure operand values are set up on the wires before they get processed. Not even mentioning modern pipelined processors.

24 Jul 2019, 17:25

int0x50

Joined: 19 Jul 2019
Posts: 13

int0x50

Thank you DimonSoft. My bad that I didn't see it before asking. As you rightly said it is in the SDM volume 2b, section 4-510, page number 1194. Thank you for pointing me there.

25 Jul 2019, 07:40

guignol

Joined: 06 Dec 2008
Posts: 666

guignol

EVY

26 Jul 2019, 11:33

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