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@@ -336,15 +336,39 @@ Next we save general registers on the stack:
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UNWIND_HINT_REGS
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```
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+Okay, now the stack contains following data:
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+```
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+High |-------------------------|
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+ | %rflags |
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+ | %cs |
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+ | %rip |
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+ | error code |
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+ | %rdi |
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+ | %rsi |
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+ | %rdx |
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+ | %rax |
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+ | %r8 |
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+ | %r9 |
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+ | %r10 |
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+ | %r11 |
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+ | %rbx |
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+ | %rbp |
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+ | %r12 |
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+ | %r13 |
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+ | %r14 |
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+ | %r15 |<-- %rsp
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+Low |-------------------------|
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+```
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+
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We need to do it to prevent wrong values of registers when we return from the interrupt handler. After this we check the vector number, and if it is `#PF` or [Page Fault](https://en.wikipedia.org/wiki/Page_fault), we put value from the `cr2` to the `rdi` register and call `early_make_pgtable` (we'll see it soon):
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```assembly
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- cmpq $14,%rsi
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+ cmpq $14,%rsi /* Page fault? */
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jnz 10f
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GET_CR2_INTO(%rdi)
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call early_make_pgtable
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- andl %eax,%eax
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- jz 20f
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+ andl %eax,%eax /* It is more efficient, the opcode is shorter than movl 1, %eax, only 2 bytes. */
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+ jz 20f /* All good */
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```
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otherwise we call `early_fixup_exception` function by passing kernel stack pointer:
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0xAX