hw/i386.reference/SGDT.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Opcode SGDT</TITLE>
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  14 <H1>SGDT/SIDT -- Store Global/Interrupt Descriptor Table Register</H1>
  15
  16 <PRE>
  17 Opcode       Instruction   Clocks   Description
  18
  19 0F  01 /0    SGDT m        9        Store GDTR to m
  20 0F  01 /1    SIDT m        9        Store IDTR to m
  21 </PRE>
  22
  23 <H2>Operation</H2>
  24
  25 <PRE>
  26 DEST := 48-bit BASE/LIMIT register contents;
  27 </PRE>
  28
  29 <H2>Description</H2>
  30
  31 SGDT/SIDT copies the contents of the descriptor table register the six
  32 bytes of memory indicated by the operand. The LIMIT field of the
  33 register is assigned to the first word at the effective address. If the
  34 operand-size attribute is 32 bits, the next three bytes are assigned the
  35 BASE field of the register, and the fourth byte is written with zero. The
  36 last byte is undefined. Otherwise, if the operand-size attribute is 16
  37 bits, the next four bytes are assigned the 32-bit BASE field of the
  38 register.
  39 <P>
  40 SGDT and SIDT are used only in operating system software; they are
  41 not used in application programs.
  42
  43 <H2>Flags Affected</H2>
  44
  45 None
  46
  47 <H2>Protected Mode Exceptions</H2>
  48
  49 Interrupt 6 if the destination operand is a register; #GP(0) if the
  50 destination is in a nonwritable segment; #GP(0) for an illegal memory
  51 operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for
  52 an illegal address in the SS segment; #PF(fault-code) for a page fault
  53
  54 <H2>Real Address Mode Exceptions</H2>
  55
  56 Interrupt 6 if the destination operand is a register; Interrupt 13 if any
  57 part of the operand would lie outside of the effective address space from
  58 0 to 0FFFFH
  59
  60 <H2>Virtual 8086 Mode Exceptions</H2>
  61
  62 Same exceptions as in Real Address Mode; #PF(fault-code) for a page
  63 fault
  64
  65 <H2>Compatability Note</H2>
  66
  67 The 16-bit forms of the SGDT/SIDT instructions are compatible with
  68 the 80286, if the value in the upper eight bits is not referenced. The
  69 80286 stores 1's in these upper bits, whereas the 80386 stores 0's if the
  70 operand-size attribute is 16 bits. These bits were specified as undefined
  71 by the SGDT/SIDT instructions in the iAPX 286 Programmer's
  72 Reference Manual.
  73
  74
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  79 Chapter 17 -- 80386 Instruction Set</A><BR>
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