diff --git a/Booting/linux-bootstrap-3.md b/Booting/linux-bootstrap-3.md index f1ca82f..613b670 100644 --- a/Booting/linux-bootstrap-3.md +++ b/Booting/linux-bootstrap-3.md @@ -483,20 +483,20 @@ asm volatile("lgdtl %0" : : "m" (gdt)); Actual transition into protected mode -------------------------------------------------------------------------------- -It is the end of `go_to_protected_mode` function. We loaded IDT, GDT, disable interruptions and now can switch CPU into protected mode. The last step we call `protected_mode_jump` function with two parameters: +This is the end of the `go_to_protected_mode` function. We loaded IDT, GDT, disable interruptions and now can switch the CPU into protected mode. The last step is calling the `protected_mode_jump` function with two parameters: ```C protected_mode_jump(boot_params.hdr.code32_start, (u32)&boot_params + (ds() << 4)); ``` -which is defined in the [arch/x86/boot/pmjump.S](https://github.com/torvalds/linux/blob/master/arch/x86/boot/pmjump.S#L26). It takes two parameters: +which is defined in [arch/x86/boot/pmjump.S](https://github.com/torvalds/linux/blob/master/arch/x86/boot/pmjump.S#L26). It takes two parameters: * address of protected mode entry point * address of `boot_params` -Let's look inside `protected_mode_jump`. As I wrote above, you can find it in the `arch/x86/boot/pmjump.S`. First parameter will be in `eax` register and second is in `edx`. +Let's look inside `protected_mode_jump`. As I wrote above, you can find it in `arch/x86/boot/pmjump.S`. The first parameter will be in the `eax` register and second is in `edx`. -First of all we put address of `boot_params` in the `esi` register and address of code segment register `cs` (0x1000) in the `bx`. After this we shift `bx` by 4 bits and add address of label `2` to it (we will have physical address of label `2` in the `bx` after it) and jump to label `1`. Next we put data segment and task state segment in the `cs` and `di` registers with: +First of all we put the address of `boot_params` in the `esi` register and the address of code segment register `cs` (0x1000) in `bx`. After this we shift `bx` by 4 bits and add the address of label `2` to it (we will have the physical address of label `2` in the `bx` after this) and jump to label `1`. Next we put data segment and task state segment in the `cs` and `di` registers with: ```assembly movw $__BOOT_DS, %cx @@ -505,7 +505,7 @@ movw $__BOOT_TSS, %di As you can read above `GDT_ENTRY_BOOT_CS` has index 2 and every GDT entry is 8 byte, so `CS` will be `2 * 8 = 16`, `__BOOT_DS` is 24 etc. -Next we set `PE` (Protection Enable) bit in the `CR0` control register: +Next we set the `PE` (Protection Enable) bit in the `CR0` control register: ```assembly movl %cr0, %edx @@ -513,7 +513,7 @@ orb $X86_CR0_PE, %dl movl %edx, %cr0 ``` -and make long jump to the protected mode: +and make a long jump to protected mode: ```assembly .byte 0x66, 0xea @@ -522,7 +522,7 @@ and make long jump to the protected mode: ``` where -* `0x66` is the operand-size prefix which allows to mix 16-bit and 32-bit code, +* `0x66` is the operand-size prefix which allows us to mix 16-bit and 32-bit code, * `0xea` - is the jump opcode, * `in_pm32` is the segment offset * `__BOOT_CS` is the code segment. @@ -534,7 +534,7 @@ After this we are finally in the protected mode: .section ".text32","ax" ``` -Let's look at the first steps in the protected mode. First of all we setup data segment with: +Let's look at the first steps in protected mode. First of all we set up the data segment with: ```assembly movl %ecx, %ds @@ -544,7 +544,7 @@ movl %ecx, %gs movl %ecx, %ss ``` -If you read with attention, you can remember that we saved `$__BOOT_DS` in the `cx` register. Now we fill with it all segment registers besides `cs` (`cs` is already `__BOOT_CS`). Next we zero out all general purpose registers besides `eax` with: +If you paid attention, you can remember that we saved `$__BOOT_DS` in the `cx` register. Now we fill it with all segment registers besides `cs` (`cs` is already `__BOOT_CS`). Next we zero out all general purpose registers besides `eax` with: ```assembly xorl %ecx, %ecx @@ -560,9 +560,9 @@ And jump to the 32-bit entry point in the end: jmpl *%eax ``` -Remember that `eax` contains address of the 32-bit entry (we passed it as first parameter into `protected_mode_jump`). +Remember that `eax` contains the address of the 32-bit entry (we passed it as first parameter into `protected_mode_jump`). -That's all we're in the protected mode and stop at it's entry point. What happens next, we will see in the next part. +That's all. We're in the protected mode and stop at it's entry point. We will see what happens next in the next part. Conclusion --------------------------------------------------------------------------------