Add cpuinfo and stack-defining stuff

rust_experiments/src/boot.asm

@@ -1,11 +1,87 @@
 
 global start
 
+%define VRAM 0xb8000
+
+section .bss
+
+stack_bottom:
+    resb 64 ;reserve 64 bytes of stack space
+stack_top:
+
 section .text
 bits 32
 
 start:
-    mov dword [0xb8000], 0x2f4b2f4f ;write OK
+    mov esp, stack_top
+    call test_multiboot
+    call test_cpuid
+    call use_cpuid
+    ;mov dword [VRAM], 0x2f4b2f4f ;write OK
     hlt
 
+error:
+    mov dword [VRAM],   0x4f524f45   ;ER
+    mov dword [VRAM+4], 0x4f3a4f52   ;R:
+    mov dword [VRAM+8], 0x4f204f20   ; <2 spaces>
+    mov byte [VRAM+0xa], al
+    hlt
+
+test_multiboot:
+    cmp eax, 0x36d76289
+    jne no_multiboot
+    ret
+
+    no_multiboot:
+        mov al, "0"
+        jmp error
+
+test_cpuid:
+    pushfd               ; Store the FLAGS-register.
+    pop eax              ; Restore the A-register.
+    mov ecx, eax         ; Set the C-register to the A-register.
+    xor eax, 1 << 21     ; Flip the ID-bit, which is bit 21.
+    push eax             ; Store the A-register.
+    popfd                ; Restore the FLAGS-register.
+    pushfd               ; Store the FLAGS-register.
+    pop eax              ; Restore the A-register.
+    push ecx             ; Store the C-register.
+    popfd                ; Restore the FLAGS-register.
+    xor eax, ecx         ; Do a XOR-operation on the A-register and the C-register.
+    jz no_cpuid          ; The zero flag is set, no CPUID.
+    ret ;CPUID is available
+
+    no_cpuid:
+    mov al, "1"
+    jmp error
+
+use_cpuid:
+    jmp print_cpu_string
+
+print_cpu_string:
+    mov eax, 0x0
+    cpuid
+
+    mov eax, ebx
+    mov [VRAM+0], al
+    mov [VRAM+2], ah
+    shr eax, 16
+    mov [VRAM+4], al
+    mov [VRAM+6], ah
+    mov eax, edx
+
+    mov [VRAM+8], al
+    mov [VRAM+0xa], ah
+    shr eax, 16
+    mov [VRAM+0xc], al
+    mov [VRAM+0xe], ah
+    mov eax, ecx
+
+    mov [VRAM+0x10], al
+    mov [VRAM+0x12], ah
+    shr eax, 16
+    mov [VRAM+0x14], al
+    mov [VRAM+0x16], ah
+    mov [VRAM+0x18], byte ' '
+    ret