i386/i386.reference/ARPL.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Opcode ARPL</TITLE>
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  14 <H1>ARPL -- Adjust RPL Field of Selector</H1>
  15
  16 <PRE>
  17 Opcode    Instruction          Clocks    Description
  18
  19 63 /r     ARPL r/m16,r16       pm=20/21  Adjust RPL of r/m16 to not
  20                                          less than RPL of r16
  21 </PRE>
  22
  23 <H2>Operation</H2>
  24
  25 <PRE>
  26 IF RPL bits(0,1) of DEST < RPL bits(0,1) of SRC
  27 THEN
  28    ZF := 1;
  29    RPL bits(0,1) of DEST := RPL bits(0,1) of SRC;
  30 ELSE
  31    ZF := 0;
  32 FI;
  33 </PRE>
  34
  35 <H2>Description</H2>
  36
  37 The ARPL instruction has two operands. The first operand is a 16-bit
  38 memory variable or word register that contains the value of a selector. The
  39 second operand is a word register. If the RPL field ("requested privilege
  40 level"--bottom two bits) of the first operand is less than the RPL field of
  41 the second operand, the zero flag is set to 1 and the RPL field of the
  42 first operand is increased to match the second operand. Otherwise, the zero
  43 flag is set to 0 and no change is made to the first operand.
  44 <P>
  45 ARPL appears in operating system software, not in application programs. It
  46 is used to guarantee that a selector parameter to a subroutine does not
  47 request more privilege than the caller is allowed. The second operand of
  48 ARPL is normally a register that contains the CS selector value of the
  49 caller.
  50
  51 <H2>Flags Affected</H2>
  52
  53 ZF as described above
  54
  55 <H2>Protected Mode Exceptions</H2>
  56
  57 #GP(0) if the result is in a nonwritable segment; #GP(0) for an illegal
  58 memory operand effective address in the CS, DS, ES, FS, or GS segments;
  59 #SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page
  60 fault
  61
  62 <H2>Real Address Mode Exceptions</H2>
  63
  64 Interrupt 6; ARPL is not recognized in Real Address Mode
  65
  66 <H2>Virtual 8086 Mode Exceptions</H2>
  67
  68 Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault
  69
  70
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  73 <P>
  74 <B>up:</B> <A HREF="c17.htm">
  75 Chapter 17 -- 80386 Instruction Set</A><BR>
  76 <B>prev:</B><A HREF="AND.htm"> AND Logical AND</A><BR>
  77 <B>next:</B><A HREF="BOUND.htm"> BOUND Check Array Index Against Bounds</A>
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