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Update linux-bootstrap-4.md

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0xAX 2015-12-29 13:24:37 +06:00
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Booting/linux-bootstrap-4.md
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@ -389,7 +389,7 @@ Now we can build the top level page table - `PML4` - with:
Here we get the address stored in the `ebx` with `pgtable` offset and put it in `edi`. Next we put this address with offset `0x1007` in the `eax` register. `0x1007` is 4096 bytes (size of the PML4) + 7 (PML4 entry flags - `PRESENT+RW+USER`) and puts `eax` in `edi`. After this manipulation `edi` will contain the address of the first Page Directory Pointer Entry with flags - `PRESENT+RW+USER`.
In the next step we build 4 Page Directory entries in the Page Directory Pointer table, where the first entry will be with `0x7` flags and the others with `0x8`:
In the next step we build 4 Page Directory entries in the Page Directory Pointer table, where the first entry will be with `0x7` flags or present, write, userspace (`PRESENT WRITE | USER`):
```assembly
leal pgtable + 0x1000(%ebx), %edi
@ -404,7 +404,7 @@ In the next step we build 4 Page Directory entries in the Page Directory Pointer
We put the base address of the page directory pointer table in `edi` and the address of the first page directory pointer entry in `eax`. Put `4` in the `ecx` register, it will be a counter in the following loop and write the address of the first page directory pointer table entry to the `edi` register.
After this `edi` will contain the address of the first page directory pointer entry with flags `0x7`. Next we just calculate the address of following page directory pointer entries with flags `0x8` and write their addresses to `edi`.
After this `edi` will contain the address of the first page directory pointer entry with flags `0x7`. Next we just calculate the address of following page directory pointer entries where each entry is 8 bytes, and write their addresses to `eax`.
The next step is building the `2048` page table entries by 2 megabytes:
@ -419,7 +419,7 @@ The next step is building the `2048` page table entries by 2 megabytes:
jnz 1b
```
Here we do almost the same as in the previous example, except the first entry will be with flags - `$0x00000183` - `PRESENT + WRITE + MBZ` and all other entries with `0x8`. In the end we will have 2048 pages by 2 megabytes.
Here we do almost the same as in the previous example, except the first entry will be with flags - `$0x00000183` - `PRESENT + WRITE + MBZ` and all other entries. In the end we will have 2048 pages by 2 megabytes.
Our early page table structure are done, it maps 4 gigabytes of memory and now we can put the address of the high-level page table - `PML4` - in `cr3` control register: