diff --git a/Booting/linux-bootstrap-4.md b/Booting/linux-bootstrap-4.md index 72de9e7..539a544 100644 --- a/Booting/linux-bootstrap-4.md +++ b/Booting/linux-bootstrap-4.md @@ -480,7 +480,7 @@ Let's look at how this is implemented. First, we clear the buffer for the page t We put the address of `pgtable` with an offset of `ebx` (remember that `ebx` points to the location in memory where the kernel will be decompressed later) into the `edi` register, clear the `eax` register and set the `ecx` register to `6144`. -The `rep stosl` instruction will write the value of `eax` to `edi`, add `4` to `edi` and decrement `ecx` by `1`. This operation will be repeated while the value of the `ecx` register is greater than zero. That's why we put `6144` or `BOOT_INIT_PGT_SIZE/4` in `ecx`. +The `rep stosl` instruction will write the value of `eax` to the memory location where `edi` points to, increment `edi` by `4`, and decrement `ecx` by `1`. This operation will be repeated while the value of the `ecx` register is greater than zero. That's why we put `6144` or `BOOT_INIT_PGT_SIZE/4` in `ecx`. `pgtable` is defined at the end of the [arch/x86/boot/compressed/head_64.S](https://github.com/torvalds/linux/blob/v4.16/arch/x86/boot/compressed/head_64.S) assembly file: @@ -568,7 +568,7 @@ First of all we need to set the `EFER.LME` flag in the [MSR](http://en.wikipedia wrmsr ``` -Here we put the `MSR_EFER` flag (which is defined in [arch/x86/include/asm/msr-index.h](https://github.com/torvalds/linux/blob/v4.16/arch/x86/include/asm/msr-index.h)) in the `ecx` register and execute the `rdmsr` instruction which reads the [MSR](http://en.wikipedia.org/wiki/Model-specific_register) register. After `rdmsr` executes, the resulting data is stored in `edx:eax` according to the `MSR` register specified in `ecx`. We check the `EFER_LME` bit with the `btsl` instruction and write data from `edx:eax` back to the `MSR` register with the `wrmsr` instruction. +Here we put the `MSR_EFER` flag (which is defined in [arch/x86/include/asm/msr-index.h](https://github.com/torvalds/linux/blob/v4.16/arch/x86/include/asm/msr-index.h)) in the `ecx` register and execute the `rdmsr` instruction which reads the [MSR](http://en.wikipedia.org/wiki/Model-specific_register) register. After `rdmsr` executes, the resulting data is stored in `edx:eax` according to the `MSR` register specified in `ecx`. We check the current `EFER_LME` bit, transfer it into the carry flag and update the bit, all with the `btsl` instruction. Then we write data from `edx:eax` back to the `MSR` register with the `wrmsr` instruction. In the next step, we push the address of the kernel segment code to the stack (we defined it in the GDT) and put the address of the `startup_64` routine in `eax`.