ap-boot.S

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/*
 * Okay, this file contains the code that's going to bootstrap the AP cpus
 */


        .globl  ap_trampoline_start,ap_trampoline_end
        .text
        .code16
ap_trampoline_start:
        cli
        cld

        movw    %cs,%ax         // The CPU knows its CS already, so lets use it for the other segments
        movw    %ax,%ds
        movw    %ax,%es
        movw    %ax,%ss

        // Do some bochs-specific bullshit
        mov     $0x31,%al // '1'
        mov     $0xe9,%dx
        outb    %al,%dx
        //lgdt    ap_gdt;       
        lgdt    ap_trampoline_gdt_limit - ap_trampoline_start
        movl    %cr0,%eax
        orl     $0x1,%eax
        movl    %eax,%cr0       // PMODE!

.code32
        .byte 0x66
        ljmp    $0x08,$(ap_trampoline_32 - ap_trampoline_start)         // 0x08 == KERNEL_CS

ap_trampoline_32:
        mov     $0x32,%al // '2'
        mov     $0xe9,%dx
        outb    %al,%dx

        mov     $0x10,%ax
        mov     %ax,%ds
        mov     %ax,%es
        mov     %ax,%fs
        mov     %ax,%gs
        mov     %ax,%ss

        // Spinlock
        mov     ap_trampoline_spl - ap_trampoline_start,%edi
ap_spl:
        //cmp   $1,(%edi)
        //je    ap_spl

        mov     $1,%eax      // Value to be set
        xchgl   (%edi),%eax
        cmp     $0,%eax
        je      ap_spl
        // /Spinlock

        mov     $0x30,%al // '0'
        mov     $0xe9,%dx
        outb    %al,%dx
                
        mov     ap_trampoline_stackptr - ap_trampoline_start,%ebx
        mov     %ebx,%esp
        add     $0x1000,%ebx
        mov     %ebx,ap_trampoline_stackptr - ap_trampoline_start

        mov     $0x31,%al // '1'
        mov     $0xe9,%dx
        outb    %al,%dx

        // spinunlock
        mov     $0,%eax
        mov     ap_trampoline_spl - ap_trampoline_start,%edi
        xchgl   (%edi),%eax
        // /spinunlock

        mov     $0x33,%al // '3'
        mov     $0xe9,%dx
        outb    %al,%dx

        mov     ap_trampoline_epoint,%eax
        call    *%eax
1:
        hlt
        jmp     1b              // Halt if we ever get here somehow

        // Stack.. This sucks, since CPU initialization isn't serialized
ap_trampoline_stackptr:
        .long   0x10000         // 256KB
ap_trampoline_epoint:
        .long   c_ap_boot

ap_trampoline_spl:
        .long   0
ap_gdt:
        .long ubixGDT
        
        // GDT
ap_trampoline_gdt:
        .word   0
ap_trampoline_gdt_limit:
        .word   128     // Room for 32 descriptors
ap_trampoline_gdt_base:
        .long   0x20000         // 128KB (move this later)


ap_trampoline_end:

---