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Move setup_SSE to boot.asm

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Philipp Oppermann
2015-12-12 14:21:15 +01:00
parent e272cc9257
commit 953704f103
3 changed files with 31 additions and 57 deletions
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30
posts/2015-09-02-setup-rust.md
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@@ -273,41 +273,27 @@ Through `objdump -D` we disassemble our whole kernel and `grep` picks the releva
The rough translation of this cryptic definition is: _If SSE isn't enabled_. So apparently Rust uses SSE instructions by default and we didn't enable SSE before. So the fix for this bug is enabling SSE.
### Enabling SSE
To enable SSE, assembly code is needed again. We want to add a function that tests if SSE is available and enables it then. Else we want to print an error message. But we can't use our existing `error` procedure because it uses (now invalid) 32-bit instructions. So we need a new one (in `long_mode_init.asm`):
To enable SSE, assembly code is needed again. We want to add a function that tests if SSE is available and enables it then. Else we want to print an error message.
```nasm
; Prints `ERROR: ` and the given error code to screen and hangs.
; parameter: error code (in ascii) in al
error:
mov rbx, 0x4f4f4f524f524f45
mov [0xb8000], rbx
mov rbx, 0x4f204f204f3a4f52
mov [0xb8008], rbx
mov byte [0xb800e], al
hlt
jmp error
```
It's the nearly the same as the 32-bit procedure in the [previous post][32-bit error function] (instead of `ERR:` we print `ERROR:` here).
Now we can add a function that checks for SSE and enables it:
We add it to the `boot.asm` file:
```nasm
; Check for SSE and enable it. If it's not supported throw error "a".
setup_SSE:
; check for SSE
mov rax, 0x1
mov eax, 0x1
cpuid
test edx, 1<<25
jz .no_SSE
; enable SSE
mov rax, cr0
mov eax, cr0
and ax, 0xFFFB ; clear coprocessor emulation CR0.EM
or ax, 0x2 ; set coprocessor monitoring CR0.MP
mov cr0, rax
mov rax, cr4
mov cr0, eax
mov eax, cr4
or ax, 3 << 9 ; set CR4.OSFXSR and CR4.OSXMMEXCPT at the same time
mov cr4, rax
mov cr4, eax
ret
.no_SSE:
@@ -316,7 +302,7 @@ setup_SSE:
```
The code is from the great [OSDev Wiki][osdev sse] again. Notice that it sets/unsets exactly the bits that can cause the `Invalid Opcode` exception.
When we insert a `call setup_SSE` right before calling `rust_main`, our Rust code will finally work.
When we insert a `call setup_SSE` somewhere in the `start` function (for example after `call enable_paging`), our Rust code will finally work.
[32-bit error function]: {{ page.previous.url }}#some-tests
[osdev sse]: http://wiki.osdev.org/SSE#Checking_for_SSE