back to nasm

README.md

@@ -7,7 +7,7 @@
 - `make`
 - `i386-elf-gcc`
 - `i386-elf-ld`
-- `i386-elf-as`
+- `nasm`
 
 ### Creating a disk image
 

makefile

@@ -1,16 +1,14 @@
 CC = i386-elf-gcc
-AS = i386-elf-as
 LD = i386-elf-ld
 
 CFLAGS 	= -m32 -ffreestanding -fno-builtin -Wall -Wextra -Wshadow -std=c23
 LDFLAGS = 
-ASFLAGS = 
 
 SRC_C   := src/kernel.c src/string.c src/vga.c
-SRC_ASM := src/boot.s
+SRC_ASM := src/boot.asm
 
 OBJ_C   := $(SRC_C:src/%.c=.build/%.o)
-OBJ_ASM := $(SRC_ASM:src/%.s=.build/%.o)
+OBJ_ASM := $(SRC_ASM:src/%.asm=.build/%.o)
 OBJS    := $(OBJ_C) $(OBJ_ASM)
 
 kernel: .build/kernel
@@ -37,5 +35,5 @@ build-dir:
 .build/%.o: src/%.c | build-dir
 	$(CC) $(CFLAGS) -c -o $@ $<
 
-.build/%.o: src/%.s | build-dir
+.build/%.o: src/%.asm | build-dir
-	$(AS) $(ASFLAGS) -o $@ $<
+	nasm -f elf32 -o $@ $<

src/boot.asm

@@ -0,0 +1,106 @@
+global _start
+extern kernel_main
+
+%define FLAGS       0b10
+%define MAGIC       0x1BADB002
+%define CHECKSUM    -(MAGIC + FLAGS)
+
+section .multiboot
+    align 4
+    dd MAGIC
+    dd FLAGS
+    dd CHECKSUM
+
+section .bss
+    align 4096
+    pml4_table:
+        resb 4096
+    pdpt_table:
+        resb 4096
+    pd_table:
+        resb 4096
+
+section .bss
+    align 16
+    stack_bottom:
+        resb 16384
+    stack_top:
+
+section .data
+    align 8
+    gdt64:
+        dq 0x0000000000000000
+    .code:
+        dq 0x00AF9A000000FFFF
+    .descriptor:
+        dw .end - gdt64 - 1
+        dq gdt64
+    .end:
+
+section .text
+    bits 32
+    _start:
+        mov esp, stack_top
+
+        ; Multiboot will place a magic value in eax
+        ; If this magic value is not present, then we might not have multiboot info in ebx,
+        ; therefore we throw an error
+        cmp eax, 0x2BADB002
+        jne error
+
+        ; Check if cpuid is available by flipping the 22-nth youngest bit
+        ; in the eflags register and checking if the cpu flipped it back
+        pushfd
+        pop eax
+        mov ecx, eax
+        xor eax, 1 << 21
+        push eax
+        popfd
+        pushfd
+        pop eax
+        ; If cpuid is available, eax should be different than ecx
+        xor eax, ecx
+        jz error
+        ; Finally restore eflags register to the original value
+        push ecx
+        popfd
+
+        ; Check if extended cpuid is available by calling cpuid with 0x80000000,
+        ; If cpuid is available, eax will be greater than 0x80000000 after the call
+        mov eax, 0x80000000
+        cpuid
+        cmp eax, 0x80000001
+        jb error
+
+        ; Check if long mode is available by calling cpuid with 0x80000001
+        ; this will place the extended features of the cpu in edx
+        ; The 30-nth youngest bit tells us if long mode is supported or not
+        mov eax, 0x80000001
+        cpuid
+        test edx, 1 << 29
+        jz error
+
+        ; todo(nub31): setup paging
+        ; todo(nub31): enter long mode
+
+        ; Load global descriptor table which is set up for 64 bit
+        lgdt [gdt64.descriptor]
+
+        call kernel_main
+        jmp error
+
+    error:
+        cli
+        mov byte [0xb8000], 'B'
+        mov byte [0xb8002], 'O'
+        mov byte [0xb8004], 'O'
+        mov byte [0xb8006], 'T'
+        mov byte [0xb8008], ' '
+        mov byte [0xb800a], 'E'
+        mov byte [0xb800c], 'R'
+        mov byte [0xb800e], 'R'
+        mov byte [0xb8010], 'O'
+        mov byte [0xb8012], 'R'
+    hang:
+        hlt
+        jmp hang

src/boot.s

@@ -1,108 +0,0 @@
-.intel_syntax noprefix
-
-.set ALIGN,    1<<0
-.set MEMINFO,  1<<1
-.set FLAGS,    ALIGN | MEMINFO
-.set MAGIC,    0x1BADB002
-.set CHECKSUM, -(MAGIC + FLAGS)
-
-.section .multiboot
-.align 4
-.long MAGIC
-.long FLAGS
-.long CHECKSUM
-
-.section .bss
-.align 4096
-pml4_table:
-    .zero 4096
-pdpt_table:
-    .zero 4096
-pd_table:
-    .zero 4096
-
-.section .bss
-.align 16
-stack_bottom:
-    .skip 16384
-stack_top:
-
-.section .data
-.align 8
-gdt64:
-    .quad 0x0000000000000000
-gdt64_code:
-    .quad 0x00AF9A000000FFFF
-gdt64_descriptor:
-    .word gdt64_end - gdt64 - 1
-    .long gdt64
-gdt64_end:
-
-.section .text
-.code32
-.global _start
-_start:
-	mov esp, stack_top
-
-    // Multiboot will place a magic value in eax
-    // If this magic value is not present, then we might not have multiboot info in ebx,
-    // therefore we throw an error
-	cmp eax, 0x2BADB002
-	jne error
-
-    // Check if cpuid is available by flipping the 22-nth youngest bit
-    // in the eflags register and checking if the cpu flipped it back
-    pushfd
-    pop eax
-    mov ecx, eax
-    xor eax, 1 << 21
-    push eax
-    popfd
-    pushfd
-    pop eax
-    // If cpuid is available, eax should be different than ecx
-    xor eax, ecx
-    jz error
-    // Finally restore eflags register to the original value
-    push ecx
-    popfd
-
-    // Check if extended cpuid is available by calling cpuid with 0x80000000,
-    // If cpuid is available, eax will be greater than 0x80000000 after the call
-    mov eax, 0x80000000
-    cpuid
-    cmp eax, 0x80000001
-    jb error
-
-    // Check if long mode is available by calling cpuid with 0x80000001
-    // this will place the extended features of the cpu in edx
-    // The 30-nth youngest bit tells us if long mode is supported or not
-    mov eax, 0x80000001
-    cpuid
-    test edx, 1 << 29
-    jz error
-
-    // todo(nub31): setup paging
-    // todo(nub31): enter long mode
-
-    // Load global descriptor table which is set up for 64 bit
-    lgdt [gdt64_descriptor]
-
-	call kernel_main
-	jmp error
-
-error:
-    cli
-    mov byte ptr [0xb8000], 'B'
-    mov byte ptr [0xb8002], 'O'
-    mov byte ptr [0xb8004], 'O'
-    mov byte ptr [0xb8006], 'T'
-    mov byte ptr [0xb8008], ' '
-    mov byte ptr [0xb800a], 'E'
-    mov byte ptr [0xb800c], 'R'
-    mov byte ptr [0xb800e], 'R'
-    mov byte ptr [0xb8010], 'O'
-    mov byte ptr [0xb8012], 'R'
-hang:
-    hlt
-    jmp hang