wrote a basic bootloader

examples and stuff/booting stuff/uefi_funcs.S

@@ -0,0 +1,94 @@
+.section .efi.text
+
+// Function to get UEFI memory map
+get_memory_map:
+    push %rbp
+    mov %rsp, %rbp
+
+    // Local variables for memory map
+    sub $48, %rsp
+    mov $0, -8(%rbp)   // memory_map_size
+    mov $0, -16(%rbp)  // memory_map_buffer
+    mov $0, -24(%rbp)  // map_key
+    mov $0, -32(%rbp)  // descriptor_size
+    mov $0, -40(%rbp)  // descriptor_version
+
+    // First call to get size
+    lea -8(%rbp), %rcx    // memory_map_size
+    mov $0, %rdx          // memory_map
+    lea -24(%rbp), %r8    // map_key
+    lea -32(%rbp), %r9    // descriptor_size
+    push $0               // descriptor_version
+    call boot_services_get_memory_map
+    
+    // Allocate buffer
+    mov -8(%rbp), %rcx    // size
+    add $1000, %rcx       // Add some extra space
+    mov $8, %rdx          // alignment
+    lea -16(%rbp), %r8    // buffer pointer
+    call boot_services_allocate_pool
+
+    // Get actual map
+    mov -8(%rbp), %rcx
+    mov -16(%rbp), %rdx
+    lea -24(%rbp), %r8
+    lea -32(%rbp), %r9
+    push -40(%rbp)
+    call boot_services_get_memory_map
+
+    // Save map key
+    mov -24(%rbp), %rax
+    mov %rax, memory_map_key
+
+    leave
+    ret
+
+// Function to exit boot services
+exit_boot_services:
+    push %rbp
+    mov %rsp, %rbp
+    
+    // Parameters already in rcx (image_handle) and rdx (map_key)
+    call boot_services_exit
+
+    leave
+    ret
+
+// Function to set up page tables
+setup_page_tables:
+    push %rbp
+    mov %rsp, %rbp
+
+    // Clear tables
+    mov $pml4_table, %rdi
+    mov $12288, %ecx      // 3 pages (PML4, PDPT, PD)
+    xor %eax, %eax
+    rep stosb
+
+    // Set up identity mapping for first 2MB
+    // PML4[0] -> PDPT
+    mov $pdpt_table, %eax
+    or $3, %eax           // Present + Write
+    mov %eax, pml4_table
+
+    // PDPT[0] -> PD
+    mov $pd_table, %eax
+    or $3, %eax
+    mov %eax, pdpt_table
+
+    // PD[0] -> 2MB page
+    mov $0x83, %eax       // Present + Write + Huge
+    mov %eax, pd_table
+
+    // Map kernel to higher half
+    // PML4[511] -> PDPT
+    mov $pdpt_table, %eax
+    or $3, %eax
+    mov %eax, pml4_table + 4088
+
+    // Load CR3
+    mov $pml4_table, %rax
+    mov %rax, %cr3
+
+    leave
+    ret