i386/i386.reference/PUSH.htm

   1 <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
   2 <HTML>
   3 <HEAD>
   4 <TITLE>80386 Programmer's Reference Manual -- Opcode PUSH</TITLE>
   5 </HEAD>
   6 <BODY>
   7 <B>up:</B> <A HREF="c17.htm">
   8 Chapter 17 -- 80386 Instruction Set</A><BR>
   9 <B>prev:</B><A HREF="POPF.htm"> POPF/POPFD Pop Stack into FLAGS or EFLAGS Register</A><BR>
  10 <B>next:</B><A HREF="PUSHA.htm"> PUSHA/PUSHAD Push all General Registers</A>
  11 <P>
  12 <HR>
  13 <P>
  14 <H1>PUSH -- Push Operand onto the Stack</H1>
  15
  16 <PRE>
  17 Opcode     Instruction   Clocks   Description
  18
  19 FF   /6    PUSH m16      5        Push memory word
  20 FF   /6    PUSH m32      5        Push memory dword
  21 50 + /r    PUSH r16      2        Push register word
  22 50 + /r    PUSH r32      2        Push register dword
  23 6A         PUSH imm8     2        Push immediate byte
  24 68         PUSH imm16    2        Push immediate word
  25 68         PUSH imm32    2        Push immediate dword
  26 0E         PUSH CS       2        Push CS
  27 16         PUSH SS       2        Push SS
  28 1E         PUSH DS       2        Push DS
  29 06         PUSH ES       2        Push ES
  30 0F   A0    PUSH FS       2        Push FS
  31 OF   A8    PUSH GS       2        Push GS
  32 </PRE>
  33
  34
  35 <H2>Operation</H2>
  36
  37 <PRE>
  38 IF StackAddrSize = 16
  39 THEN
  40    IF OperandSize = 16 THEN
  41       SP := SP - 2;
  42       (SS:SP) := (SOURCE); (* word assignment *)
  43    ELSE
  44       SP := SP - 4;
  45       (SS:SP) := (SOURCE); (* dword assignment *)
  46    FI;
  47 ELSE (* StackAddrSize = 32 *)
  48    IF OperandSize = 16
  49    THEN
  50       ESP := ESP - 2;
  51       (SS:ESP) := (SOURCE); (* word assignment *)
  52    ELSE
  53       ESP := ESP - 4;
  54       (SS:ESP) := (SOURCE); (* dword assignment *)
  55    FI;
  56 FI;
  57 </PRE>
  58
  59 <H2>Description</H2>
  60
  61 PUSH decrements the stack pointer by 2 if the operand-size attribute of
  62 the instruction is 16 bits; otherwise, it decrements the stack pointer by
  63 4. PUSH then places the operand on the new top of stack, which is
  64 pointed to by the stack pointer.
  65 <P>
  66 The 80386 PUSH eSP instruction pushes the value of eSP as it existed
  67 before the instruction. This differs from the 8086, where PUSH SP
  68 pushes the new value (decremented by 2).
  69
  70 <H2>Flags Affected</H2>
  71
  72 None
  73
  74 <H2>Protected Mode Exceptions</H2>
  75
  76 #SS(0) if the new value of SP or ESP is outside the stack segment limit;
  77 #GP(0) for an illegal memory operand effective address in the CS, DS,
  78 ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment;
  79 #PF(fault-code) for a page fault
  80
  81 <H2>Real Address Mode Exceptions</H2>
  82
  83 None; if SP or ESP is 1, the 80386 shuts down due to a lack of stack
  84 space
  85
  86 <H2>Virtual 8086 Mode Exceptions</H2>
  87
  88 Same exceptions as in real-address mode; #PF(fault-code) for a page
  89 fault
  90
  91
  92 <P>
  93 <HR>
  94 <P>
  95 <B>up:</B> <A HREF="c17.htm">
  96 Chapter 17 -- 80386 Instruction Set</A><BR>
  97 <B>prev:</B><A HREF="POPF.htm"> POPF/POPFD Pop Stack into FLAGS or EFLAGS Register</A><BR>
  98 <B>next:</B><A HREF="PUSHA.htm"> PUSHA/PUSHAD Push all General Registers</A>
  99 </BODY>