Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1624

PUSH—Push Word or Doubleword Onto the Stack (Continued)
#SS(0)
#PF(fault-code)
#AC(0)
Intel Architecture Compatibility
For Intel architecture processors from the Intel 286 on, the PUSH ESP instruction
pushes the value of the ESP register as it existed before the instruction was executed.
(This is also true in the real-address and virtual-8086 modes.) For the Intel 8086
processor, the PUSH SP instruction pushes the new value of the SP register (that is the
value after it has been decremented by 2).
4:322
If a memory operand effective address is outside the SS segment
limit.
If a page fault occurs.
If alignment checking is enabled and an unaligned memory
reference is made.
Volume 4: Base IA-32 Instruction Reference