GDT Tutorial: Difference between revisions
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: a register of your CPU that refers to a segment for a special use (e.g. <tt>SS</tt>, <tt>CS</tt>, <tt>DS</tt> ...) |
: a register of your CPU that refers to a segment for a special use (e.g. <tt>SS</tt>, <tt>CS</tt>, <tt>DS</tt> ...) |
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; Selector |
; Selector |
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: a reference to a descriptor you can load into a segment register; the selector is an offset of a descriptor table entry. These entries are 8 bytes long. Therefore, bits 3 and up only declare the descriptor table entry offset, while bit 2 specifies if this selector is a GDT or LDT selector (LDT - bit set, GDT - bit cleared), and bits 0 - 1 declare the ring level that needs to |
: a reference to a descriptor you can load into a segment register; the selector is an offset of a descriptor table entry. These entries are 8 bytes long. Therefore, bits 3 and up only declare the descriptor table entry offset, while bit 2 specifies if this selector is a GDT or LDT selector (LDT - bit set, GDT - bit cleared), and bits 0 - 1 declare the ring level that needs to correspond to the descriptor table entry's DPL field. If it doesn't, a General Protection Fault occurs; if it does correspond then the CPL level of the selector used is changed accordingly. |
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; Descriptor |
; Descriptor |
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: a memory structure (part of a table) that tells the CPU the attributes of a given segment |
: a memory structure (part of a table) that tells the CPU the attributes of a given segment |
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