.set MB_MAGIC, 0xE85250D6
.set MB_ARCH, 0 /* i386 */
.set KERNEL_VIRT_BASE, 0xC0000000
-.set PAGE_SIZE, 4096
/*
* Convert virtual symbols to physical addresses before paging is enabled
* by subtracting KERNEL_VIRT_BASE.
*/
+/* .multiboot_header section (Goes to the .boot file in the linker) */
.section .multiboot_header
.align 8
multiboot_header_start:
.long 8
multiboot_header_end:
-.section .text
+/** .boot_text section (Goes to the .boot file in the linker)
+ * This runs in 1MB (Identity Mapped by the Linker)
+ */
+.section .boot_text
.global _start
.type _start, @function
_start:
+ /* Disable interrupts until the kernel installs a valid IDT */
+ cli
/*
* We are loaded at 1MB physical. Paging is OFF.
* CPU is executing instructions here.
* ESP is unknown.
*/
-
+
/* Setup a temporary stack (using physical address) */
mov $stack_top, %esp
sub $KERNEL_VIRT_BASE, %esp
push %eax
push %ebx
+ /* Mask PIC (disable all IRQs) until kernel remaps/unmasks */
+ movb $0xFF, %al
+ outb %al, $0x21
+ outb %al, $0xA1
+
/*
* SETUP PAGING (Manually)
* We need to map:
* 2. Virt 0xC0000000 -> Phys 0x00000000 (Kernel Space)
*/
- /* 1. Get Physical Address of Page Table 0 (PT0) */
+ /*
+ * Map 0-512MB using 128 page tables.
+ * Multiboot2 info is a physical pointer (EBX) and GRUB may place it high.
+ * Keeping a wide identity + higher-half window avoids early page faults
+ * while PMM/VMM/heap are coming up.
+ */
+
+ /* Fill PTs (boot_pt0..boot_pt127) */
mov $boot_pt0, %edi
- sub $KERNEL_VIRT_BASE, %edi
-
- /* 2. Map 0-4MB to this PT (fill 1024 entries) */
- /* Entry 0: Addr 0 | Present | RW */
- mov $0, %esi
- mov $1023, %ecx
+ sub $KERNEL_VIRT_BASE, %edi /* Physical address of PT0 */
+ xor %ebx, %ebx /* pt_index = 0 */
+
1:
- cmpl $_kernel_physical_end, %esi /* Only map what we need? Nah, map 4MB */
+ /* Fill current PT with 0x003 | (pt_index*4MB + i*4KB) */
+ mov %ebx, %eax
+ shl $22, %eax /* base = pt_index * 4MB */
+ mov %eax, %esi
+
+ mov $1024, %ecx
+2:
mov %esi, %edx
- or $3, %edx /* Present + RW */
+ or $3, %edx
mov %edx, (%edi)
add $4096, %esi
add $4, %edi
- loop 1b
+ loop 2b
+
+ inc %ebx
+ cmp $128, %ebx
+ jne 1b
/* 3. Get Physical Address of Page Directory */
mov $boot_pd, %edi
sub $KERNEL_VIRT_BASE, %edi
- /* 4. Link PT0 to PD at index 0 (Identity Map 0-4MB) */
+ /* Link PT0..PT127 into PD for both identity and higher-half mapping */
mov $boot_pt0, %edx
- sub $KERNEL_VIRT_BASE, %edx
- or $3, %edx
- mov %edx, (%edi)
-
- /* 5. Link PT0 to PD at index 768 (3GB mark -> 0xC0000000) */
- /* 768 * 4MB = 3072MB = 3GB */
- mov %edx, 3072(%edi) /* Offset 768 * 4 bytes = 3072 */
+ sub $KERNEL_VIRT_BASE, %edx /* pt_phys = physical address of PT0 */
+ mov $0, %ebx /* i = 0 */
+
+3:
+ mov %edx, %eax
+ or $3, %eax
+ mov %eax, (%edi,%ebx,4) /* PD[i] */
+ mov %eax, 3072(%edi,%ebx,4) /* PD[768+i] */
+ add $4096, %edx
+ inc %ebx
+ cmp $128, %ebx
+ jne 3b
/* 6. Recursive Mapping (Optional, good for VMM later) at index 1023 */
mov $boot_pd, %edx
/* 8. Enable Paging (Set PG bit in CR0) */
mov %cr0, %ecx
- or $0x80000000, %ecx
+ or $0x80000000, %ecx /* Bit 31 (PG) e Bit 0 (PE - Protection Enable) */
mov %ecx, %cr0
/*
lea higher_half_start, %ecx
jmp *%ecx
+/** From here, we switch to the default .text section.
+ * The linker will place this in the 3GB area.
+ */
+.section .text
higher_half_start:
/*
* We are now running at 0xC0xxxxxx.
* but let's leave it for C code to clean up.
*/
- /* Unmap the low 4MB (Security: Null pointer deref should fault now!) */
- movl $0, boot_pd
- invlpg 0
-
/* Update Stack Pointer to be Virtual */
/* (Currently ESP points to physical, which is valid mapped,
- but let's fix it to use the virtual range) */
+ * but let's fix it to use the virtual range) */
add $KERNEL_VIRT_BASE, %esp
/* Restore Multiboot args (popped from stack) */
- pop %ebx
- pop %eax
+ pop %ebx /* EBX now has the Multiboot Info address */
+ pop %eax /* EAX now has the Magic Number */
- /*
- * Pass args to kernel_main.
- * NOTE: 'ebx' (multiboot info) is a PHYSICAL address.
- * kernel_main might need to map it or we identity map enough RAM.
- * Since we kept identity mapping for now (or just unmapped 0-4MB?),
- * Wait, I unmapped 0. If multiboot struct is in low mem, we lost access.
- * Let's Re-map 0 temporarily inside C or pass physical address and let C handle it.
- * For now, let's NOT unmap 0 in asm to be safe, let C do it.
- */
-
- /* Re-map low memory for safety until PMM parses tags */
- mov $boot_pt0, %edx
- sub $KERNEL_VIRT_BASE, %edx
- or $3, %edx
- mov %edx, boot_pd
+ /* Build arch_boot_args (in .bss) and call arch_start(args) */
+ mov $arch_boot_args, %ecx
+ mov %eax, 0(%ecx) /* args->a0 = multiboot magic */
+ mov %ebx, 4(%ecx) /* args->a1 = multiboot info phys */
+ movl $0, 8(%ecx) /* args->a2 = 0 */
+ movl $0, 12(%ecx) /* args->a3 = 0 */
- /* Call C Kernel */
- /* void kernel_main(uint32_t magic, uint32_t phys_addr) */
- push %ebx
- push %eax
- call kernel_main
+ push %ecx
+ call arch_start
+ add $4, %esp
/* Hang */
cli
.skip 4096
.global boot_pt0
boot_pt0:
- .skip 4096
+ .skip 4096*128
+
+.align 16
+.global arch_boot_args
+arch_boot_args:
+ .skip 16
.align 16
stack_bottom:
stack_top:
/* Helper symbol for map loop limit */
-_kernel_physical_end:
+_kernel_physical_end:
\ No newline at end of file
* AdrOS - x86 Linker Script (Higher Half)
*/
+/* The entry point reverts to the default _start */
ENTRY(_start)
/* The bootloader loads us at 1MB physical */
{
/*
* We start at 1MB physical.
- * The symbol '.' tracks the VIRTUAL address.
- * We offset it to 3GB + 1MB.
*/
- . = KERNEL_VIRT_BASE + PHYSICAL_BASE;
+ . = PHYSICAL_BASE;
- _start = .;
-
- /*
- * The AT(...) keyword tells the linker:
- * "Put this section at PHYSICAL address X in the file,
- * but calculate symbols as if it were at VIRTUAL address Y"
+ /** TEXT SECTION:
+ * VMA = 0xC0100000 (3GB + 1MB)
+ * LMA = 0x00100000 (1MB) - Defined by AT()
*/
-
- .text : AT(ADDR(.text) - KERNEL_VIRT_BASE)
+ .text KERNEL_VIRT_BASE + PHYSICAL_BASE : AT(PHYSICAL_BASE)
{
- /* Multiboot header must be very early physically */
+ /* REQUIRED: The Header MUST be the first thing */
KEEP(*(.multiboot_header))
+ /* Boot code (boot.o) */
+ *(.boot_text)
+ /* Rest of the kernel code */
*(.text)
}
projects / AdrOS.git / commitdiff