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Fix typo (#1023)

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2021-06-21 18:33:26 +10:00
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blog/content/edition-2/posts/05-cpu-exceptions/index.md
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@@ -180,7 +180,7 @@ On a normal function call (using the `call` instruction), the CPU pushes the ret
For exception and interrupt handlers, however, pushing a return address would not suffice, since interrupt handlers often run in a different context (stack pointer, CPU flags, etc.). Instead, the CPU performs the following steps when an interrupt occurs:
1. **Aligning the stack pointer**: An interrupt can occur at any instructions, so the stack pointer can have any value, too. However, some CPU instructions (e.g. some SSE instructions) require that the stack pointer is aligned on a 16 byte boundary, therefore the CPU performs such an alignment right after the interrupt.
2. **Switching stacks** (in some cases): A stack switch occurs when the CPU privilege level changes, for example when a CPU exception occurs in an user mode program. It is also possible to configure stack switches for specific interrupts using the so-called _Interrupt Stack Table_ (described in the next post).
2. **Switching stacks** (in some cases): A stack switch occurs when the CPU privilege level changes, for example when a CPU exception occurs in a user mode program. It is also possible to configure stack switches for specific interrupts using the so-called _Interrupt Stack Table_ (described in the next post).
3. **Pushing the old stack pointer**: The CPU pushes the values of the stack pointer (`rsp`) and the stack segment (`ss`) registers at the time when the interrupt occurred (before the alignment). This makes it possible to restore the original stack pointer when returning from an interrupt handler.
4. **Pushing and updating the `RFLAGS` register**: The [`RFLAGS`] register contains various control and status bits. On interrupt entry, the CPU changes some bits and pushes the old value.
5. **Pushing the instruction pointer**: Before jumping to the interrupt handler function, the CPU pushes the instruction pointer (`rip`) and the code segment (`cs`). This is comparable to the return address push of a normal function call.