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-rw-r--r--src/stem/loader_.asm63
1 files changed, 63 insertions, 0 deletions
diff --git a/src/stem/loader_.asm b/src/stem/loader_.asm
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index 0000000..e1031b4
--- /dev/null
+++ b/src/stem/loader_.asm
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+[GLOBAL loader] ; making entry point visible to linker
+[EXTERN kmain] ; kmain is defined in kmain.c
+
+STACKSIZE equ 0x4000 ; that's 16k.
+
+; setting up the Multiboot header - see GRUB docs for details
+MODULEALIGN equ 1<<0 ; align loaded modules on page boundaries
+MEMINFO equ 1<<1 ; provide memory map
+FLAGS equ MODULEALIGN | MEMINFO ; this is the Multiboot 'flag' field
+MAGIC equ 0x1BADB002 ; 'magic number' lets bootloader find the header
+CHECKSUM equ -(MAGIC + FLAGS) ; checksum required
+
+section .text
+align 4
+MultiBootHeader:
+ dd MAGIC
+ dd FLAGS
+ dd CHECKSUM
+
+section .setup
+loader: ;here, we load our false GDT, used for having the kernel in higher half
+ lgdt [trickgdt]
+ mov cx, 0x10;
+ mov ds, cx;
+ mov es, cx;
+ mov fs, cx;
+ mov gs, cx;
+ mov ss, cx;
+
+ jmp 0x08:higherhalf
+
+section .text
+higherhalf: ; now we're running in higher half
+
+ mov esp, stack+STACKSIZE ; set up the stack
+ push eax ; pass Multiboot magic number
+ add ebx, 0xE0000000 ; update the MB info structure so that it is in the new seg
+ push ebx ; pass Multiboot info structure
+
+ call kmain ; call kernel proper
+
+ cli ; disable interupts
+hang:
+ hlt ; halt machine should kernel return
+ jmp hang
+
+[section .setup] ; this is included in the .setup section, so that it thinks it is at 0x00100000
+
+trickgdt: ; our false GDT
+ dw gdt_end - gdt - 1 ; gdt limit
+ dd gdt ; gdt base
+
+gdt:
+ dd 0, 0 ; null GDT entry
+ db 0xFF, 0xFF, 0, 0, 0, 10011010b, 11001111b, 0x20 ; kernel code segment
+ db 0xFF, 0xFF, 0, 0, 0, 10010010b, 11001111b, 0x20 ; kernel data segment
+
+gdt_end:
+
+[section .bss]
+align 32
+stack:
+ resb STACKSIZE ; reserve 16k stack on a quadword boundary