Segmentation: Difference between revisions
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*CS = Code Segment |
*CS = Code Segment |
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*DS = Data Segment |
*DS = Data Segment |
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*SS = Stack Segment |
*SS = [[Stack]] Segment |
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*ES = Extra Segment |
*ES = Extra Segment |
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*FS/GS = General Purpose Segments |
*FS/GS = General Purpose Segments |
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Here the new value for CS is encoded in the jump instruction. Eg JMP 0x10:0x100 says to load CS with segment 0x10 and IP with 0x100. CS:IP is the logical address of the instruction to be executed. |
Here the new value for CS is encoded in the jump instruction. Eg JMP 0x10:0x100 says to load CS with segment 0x10 and IP with 0x100. CS:IP is the logical address of the instruction to be executed. |
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====Far Call==== |
====Far Call==== |
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This is exactly the same as a far jump, but the current values of CS/IP are pushed onto the stack before executing at the new position. |
This is exactly the same as a far jump, but the current values of CS/IP are pushed onto the [[stack]] before executing at the new position. |
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====INT==== |
====INT==== |
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The processor reads the new value of CS/IP from the Interrupt Vector Table and then executes what is effectively a far call after pushing EFLAGS onto the stack. |
The processor reads the new value of CS/IP from the Interrupt Vector Table and then executes what is effectively a far call after pushing EFLAGS onto the [[stack]]. |
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====Far Return==== |
====Far Return==== |
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Here the processor pops the return segment/offset from the stack into CS/IP and switches execution to that address. |
Here the processor pops the return segment/offset from the [[stack]] into CS/IP and switches execution to that address. |
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====IRET==== |
====IRET==== |
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This is exactly the same as a far return apart from the processor popping EFLAGS off the stack in addition to CS/IP. |
This is exactly the same as a far return apart from the processor popping EFLAGS off the [[stack]] in addition to CS/IP. |
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Apart from these cases no instruction alters the value of CS. |
Apart from these cases no instruction alters the value of CS. |
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