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.section .text
.global _start
.type _start, @function
_start:
cli
mov $_stack_top, %esp
push %ebx // save the address of the multiboot struct
mov $0x80000000, %eax // check CPUID extended functions
cpuid
cmp $0x80000001, %eax
jb panic_early
mov $0x80000001, %eax
cpuid
test $(1<<29), %edx // check long mode support
jz panic_early
mov %cr4, %eax
or $(1<<5 | 1<<9 | 1<<10), %eax // PAE | SSE | SSE
mov %eax, %cr4
call pml4_identity_init
mov $pml4_identity, %eax
mov %eax, %cr3
mov $0xC0000080, %ecx // EFER MSR
rdmsr
or $(1 | 1<<8 | 1<<11), %eax // syscall/ret | long mode | NX
wrmsr
mov %cr0, %eax
or $0x80000002, %eax // enable paging, coprocessor monitoring
and $(~4), %eax // disable coprocessor emulation
mov %eax, %cr0
/* fill out the TSS's address */
movw $TSS, (GdtTss + 2)
lgdt (GdtPointer)
pop %edi
mov $(2 << 3), %eax // SEG_r0data
mov %eax, %ds
mov %eax, %ss
mov %eax, %es
mov %eax, %fs
mov %eax, %gs
ljmp $(1 << 3), $boot64 // SEG_r0code
panic_early:
// output a vga Fuck
movl $0x4F754F46, 0xB872A
movl $0x4F6B4F63, 0xB872E
jmp cpu_halt
.global cpu_shutdown
.type cpu_shutdown, @function
cpu_shutdown:
/* This quits QEMU. While I couldn't find this officially documented anywhere,
* it is used by QEMU in tests/tcg/i386/system/boot.S (as of commit 40d6ee), so
* I assume that this is safe-ish to use */
mov $0x604, %edx
mov $0x2000, %eax
outw %ax, %dx
.global cpu_halt
.type cpu_halt, @function
cpu_halt:
cli
1: hlt
jmp 1b
.global cpu_pause
.type cpu_pause, @function
cpu_pause:
sti
hlt
cli
ret
.section .shared
.global GDT
.align 8
GDT:
#define GdtLimit(p) (p & 0xFFFF) | ((p >> 16) << 48) /* doesn't check if p fits in 20 bits */
#define GdtAccessed (1<<40)
#define GdtReadWrite (1<<41)
#define GdtCode (1<<43)
#define GdtCodeOrData (1<<44)
#define GdtRing(r) (r<<45)
#define GdtPresent (1<<47)
#define GdtAvailable (1<<52)
#define GdtLongMode (1<<53)
#define GdtPageGran (1<<55) /* limit is in pages */
#define GdtCommon (GdtLimit(0xFFFFF) | GdtPageGran | GdtAccessed | \
GdtReadWrite | GdtCodeOrData | GdtPresent | GdtAvailable)
.8byte 0 /* [0] = SEG_null */
.8byte GdtCommon | GdtRing(0) | GdtLongMode | GdtCode /* [1] = SEG_r0code */
.8byte GdtCommon | GdtRing(0) | GdtLongMode /* [2] = SEG_r0data */
.8byte GdtCommon | GdtRing(3) | GdtCode /* [3] = SEG_r3code32 */
.8byte GdtCommon | GdtRing(3) | GdtLongMode /* [4] = SEG_r3data */
.8byte GdtCommon | GdtRing(3) | GdtLongMode | GdtCode /* [5] = SEG_r3code */
GdtTss:
.8byte GdtLimit(104) | (9<<40) | GdtPresent | GdtAvailable /* [6] = SEG_TSS */
.8byte 0 /* [7] = SEG_TSS2 */
.section .data
.global GdtPointer
GdtPointer:
.2byte 63 /* size of the GDT - 1 */
.4byte GDT /* address of the GDT */
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