Global Descriptor Table: Difference between revisions
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** For code segments: Readable bit. If clear ('''0'''), read access for this segment is not allowed. If set ('''1''') read access is allowed. Write access is never allowed for code segments. |
** For code segments: Readable bit. If clear ('''0'''), read access for this segment is not allowed. If set ('''1''') read access is allowed. Write access is never allowed for code segments. |
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** For data segments: Writeable bit. If clear ('''0'''), write access for this segment is not allowed. If set ('''1''') write access is allowed. Read access is always allowed for data segments. |
** For data segments: Writeable bit. If clear ('''0'''), write access for this segment is not allowed. If set ('''1''') write access is allowed. Read access is always allowed for data segments. |
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* '''A:''' Accessed bit. The CPU will set it when the segment is accessed unless set to '''1''' in advance. This means that in case the GDT descriptor is stored in read only pages and this bit is set to '''0''', the CPU trying to set this bit will trigger a page fault. Best left set to '''1''' unless otherwise needed. |
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* '''A:''' Accessed bit. Best left clear ('''0'''), the CPU will set it when the segment is accessed. |
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