i386/i386.reference/LSL.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Opcode LSL</TITLE>
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   8 Chapter 17 -- 80386 Instruction Set</A><BR>
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  13 <P>
  14 <H1>LSL -- Load Segment Limit</H1>
  15
  16 <PRE>
  17 Opcode       Instruction      Clocks      Description
  18
  19 0F  03 /r    LSL r16,r/m16    pm=20/21    Load: r16 := segment limit,
  20                                           selector r/m16 (byte granular)
  21 0F  03 /r    LSL r32,r/m32    pm=20/21    Load: r32 := segment limit,
  22                                           selector r/m32 (byte granular)
  23 0F  03 /r    LSL r16,r/m16    pm=25/26    Load: r16 := segment limit,
  24                                           selector r/m16 (page granular)
  25 0F  03 /r    LSL r32,r/m32    pm=25/26    Load: r32 := segment limit,
  26                                           selector r/m32 (page granular)
  27 </PRE>
  28
  29 <H2>Description</H2>
  30
  31 The LSL instruction loads a register with an unscrambled segment limit,
  32 and sets ZF to 1, provided that the source selector is visible at the CPL
  33 weakened by RPL, and that the descriptor is a type accepted by LSL.
  34 Otherwise, ZF is cleared to 0, and the destination register is unchanged.
  35 The segment limit is loaded as a byte granular value. If the descriptor
  36 has a page granular segment limit, LSL will translate it to a byte limit
  37 before loading it in the destination register (shift left 12 the 20-bit
  38 "raw" limit from descriptor, then OR with 00000FFFH).
  39 <P>
  40 The 32-bit forms of this instruction store the 32-bit byte granular limit
  41 in the 16-bit destination register.
  42 <P>
  43 Code and data segment descriptors are valid for LSL.
  44 <P>
  45 The valid special segment and gate descriptor types for LSL are given
  46 in the following table:
  47
  48 <PRE>
  49 Type   Name                      Valid/Invalid
  50
  51   0    Invalid                   Invalid
  52   1    Available 80286 TSS       Valid
  53   2    LDT                       Valid
  54   3    Busy 80286 TSS            Valid
  55   4    80286 call gate           Invalid
  56   5    80286/80386 task gate     Invalid
  57   6    80286 trap gate           Invalid
  58   7    80286 interrupt gate      Invalid
  59   8    Invalid                   Valid
  60   9    Available 80386 TSS       Valid
  61   A    Invalid                   Invalid
  62   B    Busy 80386 TSS            Valid
  63   C    80386 call gate           Invalid
  64   D    Invalid                   Invalid
  65   E    80386 trap gate           Invalid
  66   F    80386 interrupt gate      Invalid
  67 </PRE>
  68
  69 <H2>Flags Affected</H2>
  70
  71 ZF as described above
  72
  73 <H2>Protected Mode Exceptions</H2>
  74
  75 #GP(0) for an illegal memory operand effective address in the CS, DS,
  76 ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment;
  77 #PF(fault-code) for a page fault
  78
  79 <H2>Real Address Mode Exceptions</H2>
  80
  81 Interrupt 6; LSL is not recognized in Real Address Mode
  82
  83 <H2>Virtual 8086 Mode Exceptions</H2>
  84
  85 Same exceptions as in Real Address Mode
  86
  87
  88 <P>
  89 <HR>
  90 <P>
  91 <B>up:</B> <A HREF="c17.htm">
  92 Chapter 17 -- 80386 Instruction Set</A><BR>
  93 <B>prev:</B><A HREF="LOOP.htm"> LOOP/LOOPcond Loop Control with CX Counter</A><BR>
  94 <B>next:</B><A HREF="LTR.htm"> LTR Load Task Register</A>
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