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Merge pull request #753 from Mutated1994/patch-2

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feat: Add some comments
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0xAX 2020-11-17 13:51:16 +06:00 committed by GitHub
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Initialization/linux-initialization-2.md
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@ -336,15 +336,39 @@ Next we save general registers on the stack:
UNWIND_HINT_REGS
```
Okay, now the stack contains following data:
```
High |-------------------------|
| %rflags |
| %cs |
| %rip |
| error code |
| %rdi |
| %rsi |
| %rdx |
| %rax |
| %r8 |
| %r9 |
| %r10 |
| %r11 |
| %rbx |
| %rbp |
| %r12 |
| %r13 |
| %r14 |
| %r15 |<-- %rsp
Low |-------------------------|
```
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):
```assembly
cmpq $14,%rsi
cmpq $14,%rsi /* Page fault? */
jnz 10f
GET_CR2_INTO(%rdi)
call early_make_pgtable
andl %eax,%eax
jz 20f
andl %eax,%eax /* It is more efficient, the opcode is shorter than movl 1, %eax, only 2 bytes. */
jz 20f /* All good */
```
otherwise we call `early_fixup_exception` function by passing kernel stack pointer: