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The double faults post is the 10th post now

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Philipp Oppermann
2017-03-25 16:38:35 +01:00
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blog/content/post/12-double-faults.md → blog/content/post/10-double-faults.md
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@@ -17,7 +17,7 @@ As always, the complete source code is available on [Github]. Please file [issue
## What is a Double Fault? ## What is a Double Fault?
In simplified terms, a double fault is a special exception that occurs when the CPU fails to invoke an exception handler. For example, it occurs when a page fault is triggered but there is no page fault handler registered in the [Interrupt Descriptor Table][IDT] (IDT). So it's kind of similar to catch-all blocks in programming languages with exceptions, e.g. `catch(...)` in C++ or `catch(Exception e)` in Java or C#. In simplified terms, a double fault is a special exception that occurs when the CPU fails to invoke an exception handler. For example, it occurs when a page fault is triggered but there is no page fault handler registered in the [Interrupt Descriptor Table][IDT] (IDT). So it's kind of similar to catch-all blocks in programming languages with exceptions, e.g. `catch(...)` in C++ or `catch(Exception e)` in Java or C#.
[IDT]: {{% relref "09-catching-exceptions.md#the-interrupt-descriptor-table" %}} [IDT]: {{% relref "09-handling-exceptions.md#the-interrupt-descriptor-table" %}}
A double fault behaves like a normal exception. It has the vector number `8` and we can define a normal handler function for it in the IDT. It is really important to provide a double fault handler, because if a double fault is unhandled a fatal _triple fault_ occurs. Triple faults can't be caught and most hardware reacts with a system reset. A double fault behaves like a normal exception. It has the vector number `8` and we can define a normal handler function for it in the IDT. It is really important to provide a double fault handler, because if a double fault is unhandled a fatal _triple fault_ occurs. Triple faults can't be caught and most hardware reacts with a system reset.
@@ -208,7 +208,7 @@ struct InterruptStackTable {
For each exception handler, we can choose an stack from the IST through the `options` field in the corresponding [IDT entry]. For example, we could use the first stack in the IST for our double fault handler. Then the CPU would automatically switch to this stack whenever a double fault occurs. This switch would happen before anything is pushed, so it would prevent the triple fault. For each exception handler, we can choose an stack from the IST through the `options` field in the corresponding [IDT entry]. For example, we could use the first stack in the IST for our double fault handler. Then the CPU would automatically switch to this stack whenever a double fault occurs. This switch would happen before anything is pushed, so it would prevent the triple fault.
[IDT entry]: {{% relref "09-catching-exceptions.md#the-interrupt-descriptor-table" %}} [IDT entry]: {{% relref "09-handling-exceptions.md#the-interrupt-descriptor-table" %}}
### Allocating a new Stack ### Allocating a new Stack
In order to fill an Interrupt Stack Table later, we need a way to allocate new stacks. Therefore we extend our `memory` module with a new `stack_allocator` submodule: In order to fill an Interrupt Stack Table later, we need a way to allocate new stacks. Therefore we extend our `memory` module with a new `stack_allocator` submodule: