Intel 64 and IA-32 Architectures Software Developers Manual Volume 2B, Instruction Set Reference, N-Z

Vol. 2B 4-217
INSTRUCTION SET REFERENCE, N-Z
PUSHA/PUSHAD—Push All General-Purpose Registers
Description
Pushes the contents of the general-purpose registers onto the stack. The registers
are stored on the stack in the following order: EAX, ECX, EDX, EBX, ESP (original
value), EBP, ESI, and EDI (if the current operand-size attribute is 32) and AX, CX, DX,
BX, SP (original value), BP, SI, and DI (if the operand-size attribute is 16). These
instructions perform the reverse operation of the POPA/POPAD instructions. The
value pushed for the ESP or SP register is its value before prior to pushing the first
register (see the “Operation” section below).
The PUSHA (push all) and PUSHAD (push all double) mnemonics reference the same
opcode. The PUSHA instruction is intended for use when the operand-size attribute is
16 and the PUSHAD instruction for when the operand-size attribute is 32. Some
assemblers may force the operand size to 16 when PUSHA is used and to 32 when
PUSHAD is used. Others may treat these mnemonics as synonyms (PUSHA/PUSHAD)
and use the current setting of the operand-size attribute to determine the size of
values to be pushed from the stack, regardless of the mnemonic used.
In the real-address mode, if the ESP or SP register is 1, 3, or 5 when PUSHA/PUSHAD
executes: an #SS exception is generated but not delivered (the stack error reported
prevents #SS delivery). Next, the processor generates a #DF exception and enters a
shutdown state as described in the #DF discussion in Chapter 5 of the Intel
®
64 and
IA-32 Architectures Software Developer’s Manual, Volume 3A.
This instruction executes as described in compatibility mode and legacy mode. It is
not valid in 64-bit mode.
Operation
IF 64-bit Mode
THEN #UD
FI;
IF OperandSize
= 32 (* PUSHAD instruction *)
THEN
Temp ← (ESP);
Push(EAX);
Opcode Instruction
64-Bit
Mode
Compat/
Leg Mode Description
60 PUSHA Invalid Valid Push AX, CX, DX, BX, original SP, BP, SI,
and DI.
60 PUSHAD Invalid Valid Push EAX, ECX, EDX, EBX, original ESP,
EBP, ESI, and EDI.