build: Use the custom linker and nasm

6 files changed, 183 insertions, 201 deletions

diff --git a/cmake/toolchain.cmake b/cmake/toolchain.cmake
index 716b5e7..5107848 100644
--- a/cmake/toolchain.cmake
+++ b/cmake/toolchain.cmake
@@ -1,8 +1,18 @@
 set(CMAKE_C_COMPILER clang)
 set(CMAKE_CXX_COMPILER clang++)
+set(CMAKE_LINKER ld.lld)
 set(CMAKE_ASM_COMPILER nasm)
+# Hacky, yes.
+set(CMAKE_CXX_LINK_EXECUTABLE
+  "<CMAKE_LINKER> <FLAGS> <CMAKE_CXX_LINK_FLAGS> <LINK_FLAGS> <OBJECTS> -o <TARGET> <LINK_LIBRARIES>"
+)
+
+set(CMAKE_ASM_NASM_COMPILER /usr/bin/nasm)
+set(CMAKE_ASM_NASM_SOURCE_FILE_EXTENSIONS s)
+set(CMAKE_ASM_NASM_OBJECT_FORMAT elf)
 
-set(CMAKE_SYSTEM_PROCESSOR i686)
 set(CMAKE_C_COMPILER_TARGET i686-elf)
 set(CMAKE_CXX_COMPILER_TARGET i686-elf)
 set(CMAKE_ASM_COMPILER_TARGET i686-elf)
+
+set(CMAKE_SYSTEM_PROCESSOR i686)
diff --git a/kernel/CMakeLists.txt b/kernel/CMakeLists.txt
index bab610e..3af9102 100644
--- a/kernel/CMakeLists.txt
+++ b/kernel/CMakeLists.txt
@@ -1,7 +1,9 @@
 cmake_minimum_required(VERSION 3.21)
-project(kernel C ASM)
+project(kernel C ASM_NASM)
 
 set(SRC
+  boot/init/crti.s
+  
   boot/gdt/gdt.cc
   boot/gdt/gdt.s
   boot/init/boot.s
@@ -25,6 +27,8 @@ set(SRC
   mm/physical_mm/physical_mm.cc
   mm/virtual_mm/virtual_mm.cc
   mm/virtual_mm/pages.cc
+
+  boot/init/crtn.s
 )
 
 add_executable(kernel ${SRC})
@@ -62,32 +66,7 @@ target_compile_options(kernel PRIVATE
 )
 
 set(LINKER_SCRIPT "${CMAKE_CURRENT_SOURCE_DIR}/boot/linker.ld")
-set(LINKER_FLAGS
+target_link_options(kernel PRIVATE
   -T ${LINKER_SCRIPT}
   -nostdlib
-  -fuse-ld=lld
-  --target=i686-elf
 )
-
-add_library(crti OBJECT boot/init/crti.s)
-add_library(crtn OBJECT boot/init/crtn.s)
-add_dependencies(kernel crti crtn)
-
-get_target_property(CRTI_SRC crti SOURCES)
-get_target_property(CRTN_SRC crtn SOURCES)
-get_target_property(CRTI_OUT crti BINARY_DIR)
-get_target_property(CRTN_OUT crtn BINARY_DIR)
-
-set(CRTI_O "${CRTI_OUT}/CMakeFiles/crti.dir/${CRTI_SRC}.o")
-set(CRTN_O "${CRTN_OUT}/CMakeFiles/crtn.dir/${CRTN_SRC}.o")
-
-# FIXME: This isn't a good way of setting the link order.
-set(CMAKE_CXX_LINK_EXECUTABLE "${CMAKE_CXX_COMPILER} <CMAKE_CXX_LINK_FLAGS> <FLAGS> <LINK_FLAGS> \
-  ${CRTI_O} \
-  <OBJECTS> \
-  ${CRTN_O} \
-  -o <TARGET> <LINK_LIBRARIES>"
-)
-
-target_link_options(kernel PRIVATE ${LINKER_FLAGS})
-target_link_libraries(kernel PRIVATE gcc)
diff --git a/kernel/boot/gdt/gdt.s b/kernel/boot/gdt/gdt.s
index d1d768c..73ebed1 100644
--- a/kernel/boot/gdt/gdt.s
+++ b/kernel/boot/gdt/gdt.s
@@ -1,24 +1,41 @@
-.global _GDT_flush
-.type _GDT_flush, @function
+;;
+;; bubbl
+;; Copyright (C) 2024-2025  Raghuram Subramani <raghus2247@gmail.com>
+;;
+;; This program is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+;;
+
+global _GDT_flush
 _GDT_flush:
-  /* First Argument (Pointer to the GDT) */
-  movl 4(%esp), %eax
+  ;; First Argument (Pointer to the GDT)
+  mov eax, [esp + 4]
   
-  /* Load GDT */
-  lgdt (%eax)
+  ;; Load GDT
+  lgdt [eax]
 
-  /* Offset For Kernel Data Segment (16 bits) */
-  mov $0x10, %eax
+  ;; Offset For Kernel Data Segment (16 bits)
+  mov eax, 0x10
 
-  /* Set the Data Segment Selectors */
-  mov %ax, %ds
-  mov %ax, %es
-  mov %ax, %fs
-  mov %ax, %gs
-  mov %ax, %ss
+  ;; Set the Data Segment Selectors
+  mov ds, ax
+  mov es, ax
+  mov fs, ax
+  mov gs, ax
+  mov ss, ax
 
-  /* Set the Code Segment Selector */
-  jmp $0x08, $.flush
+  ;; Set the Code Segment Selector
+  jmp 0x08:.flush
 
 .flush:
   ret
diff --git a/kernel/boot/init/boot.s b/kernel/boot/init/boot.s
index 8a134c4..c558c97 100644
--- a/kernel/boot/init/boot.s
+++ b/kernel/boot/init/boot.s
@@ -1,120 +1,102 @@
-/*
- * bubbl
- * Copyright (C) 2024-2025  Raghuram Subramani <raghus2247@gmail.com>
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
+;;
+;; bubbl
+;; Copyright (C) 2024-2025  Raghuram Subramani <raghus2247@gmail.com>
+;;
+;; This program is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+;;
 
-/* Adapted from https://wiki.osdev.org/Bare_Bones */
+;; Adapted from https://wiki.osdev.org/Bare_Bones
 
-/* Declare constants for the multiboot header. */
-.set ALIGN,    1<<0             /* align loaded modules on page boundaries */
-.set MEMINFO,  1<<1             /* provide memory map */
-.set FLAGS,    ALIGN | MEMINFO  /* this is the Multiboot 'flag' field */
-.set MAGIC,    0x1BADB002       /* 'magic number' lets bootloader find the header */
-.set CHECKSUM, -(MAGIC + FLAGS) /* checksum of above, to prove we are multiboot */
+MBALIGN  equ  1 << 0              ;; align loaded modules on page boundaries
+MEMINFO  equ  1 << 1              ;; provide memory map
+MBFLAGS  equ  MBALIGN | MEMINFO   ;; this is the Multiboot 'flag' field
+MAGIC    equ  0x1BADB002          ;; 'magic number' lets bootloader find the header
+CHECKSUM equ -(MAGIC + MBFLAGS)   ;; checksum of above, to prove we are multiboot
 
-/* 
-  Declare a multiboot header that marks the program as a kernel. These are magic
-  values that are documented in the multiboot standard. The bootloader will
-  search for this signature in the first 8KiB of the kernel file, aligned at a
-  32-bit boundary. The signature is in its own section so the header can be
-  forced to be within the first 8KiB of the kernel file.
-*/
-.section .multiboot
-.align 4
-.long MAGIC
-.long FLAGS
-.long CHECKSUM
+; Declare a multiboot header that marks the program as a kernel. These are magic
+; values that are documented in the multiboot standard. The bootloader will
+; search for this signature in the first 8 KiB of the kernel file, aligned at a
+; 32-bit boundary. The signature is in its own section so the header can be
+; forced to be within the first 8 KiB of the kernel file.
+section .multiboot
+align 4
+dd MAGIC
+dd MBFLAGS
+dd CHECKSUM
 
-/*
-  The multiboot standard does not define the value of the stack pointer register
-  (esp) and it is up to the kernel to provide a stack. This allocates room for a
-  small stack by creating a symbol at the bottom of it, then allocating 16384
-  bytes for it, and finally creating a symbol at the top. The stack grows
-  downwards on x86. The stack is in its own section so it can be marked nobits,
-  which means the kernel file is smaller because it does not contain an
-  uninitialized stack. The stack on x86 must be 16-byte aligned according to the
-  System V ABI standard and de-facto extensions. The compiler will assume the
-  stack is properly aligned and failure to align the stack will result in
-  undefined behavior.
-*/
-.section .bss
-.align 16
+;; The multiboot standard does not define the value of the stack pointer register
+;; (esp) and it is up to the kernel to provide a stack. This allocates room for a
+;; small stack by creating a symbol at the bottom of it, then allocating 16384
+;; bytes for it, and finally creating a symbol at the top. The stack grows
+;; downwards on x86. The stack is in its own section so it can be marked nobits,
+;; which means the kernel file is smaller because it does not contain an
+;; uninitialized stack. The stack on x86 must be 16-byte aligned according to the
+;; System V ABI standard and de-facto extensions. The compiler will assume the
+;; stack is properly aligned and failure to align the stack will result in
+;; undefined behavior.
+
+section .bss
+align 16
 stack_bottom:
-.skip 16384 # 16KiB
+resb 16384 ;;16KiB	
 stack_top:
 
-/*
-  The linker script specifies _start as the entry point to the kernel and the
-  bootloader will jump to this position once the kernel has been loaded. It
-  doesn't make sense to return from this function as the bootloader is gone.
-*/
-.section .text
-.global _start
-.type _start, @function
+;; The linker script specifies _start as the entry point to the kernel and the
+;; bootloader will jump to this position once the kernel has been loaded. It
+;; doesn't make sense to return from this function as the bootloader is gone.
+section .text
+global _start
 _start:
-  /*
-  The bootloader has loaded us into 32-bit protected mode on a x86
-  machine. Interrupts are disabled. Paging is disabled. The processor
-  state is as defined in the multiboot standard. The kernel has full
-  control of the CPU. The kernel can only make use of hardware features
-  and any code it provides as part of itself. There's no printf
-  function, unless the kernel provides its own <stdio.h> header and a
-  printf implementation. There are no security restrictions, no
-  safeguards, no debugging mechanisms, only what the kernel provides
-  itself. It has absolute and complete power over the
-  machine.
-  */
+  ;; The bootloader has loaded us into 32-bit protected mode on a x86
+  ;; machine. Interrupts are disabled. Paging is disabled. The processor
+  ;; state is as defined in the multiboot standard. The kernel has full
+  ;; control of the CPU. The kernel can only make use of hardware features
+  ;; and any code it provides as part of itself. There's no printf
+  ;; function, unless the kernel provides its own <stdio.h> header and a
+  ;; printf implementation. There are no security restrictions, no
+  ;; safeguards, no debugging mechanisms, only what the kernel provides
+  ;; itself. It has absolute and complete power over the
+  ;; machine.
 
-  /*
-  To set up a stack, we set the esp register to point to the top of the
-  stack (as it grows downwards on x86 systems). This is necessarily done
-  in assembly as languages such as C cannot function without a stack.
-  */
-  movl $stack_top, %esp
+  ;; To set up a stack, we set the esp register to point to the top of the
+  ;; stack (as it grows downwards on x86 systems). This is necessarily done
+  ;; in assembly as languages such as C cannot function without a stack.
+  mov esp, stack_top
 
-  /* Push Multiboot values to stack for kernel_main */
-  push %ebx
-  push %eax
+  ;; Push Multiboot values to stack for kernel_main
+  push ebx
+  push eax
 
-  /*
-  This is a good place to initialize crucial processor state before the
-  high-level kernel is entered. It's best to minimize the early
-  environment where crucial features are offline. Note that the
-  processor is not fully initialized yet: Features such as floating
-  point instructions and instruction set extensions are not initialized
-  yet. The GDT should be loaded here. Paging should be enabled here.
-  C++ features such as global constructors and exceptions will require
-  runtime support to work as well.
-  */
+  ;;
+  ;; This is a good place to initialize crucial processor state before the
+  ;; high-level kernel is entered. It's best to minimize the early
+  ;; environment where crucial features are offline. Note that the
+  ;; processor is not fully initialized yet: Features such as floating
+  ;; point instructions and instruction set extensions are not initialized
+  ;; yet. The GDT should be loaded here. Paging should be enabled here.
+  ;; C++ features such as global constructors and exceptions will require
+  ;; runtime support to work as well.
 
-  /* Call the global constructors. */
+  ;; Call the global constructors.
+  extern _init
   call _init
 
-  /*
-  Enter the high-level kernel. The ABI requires the stack is 16-byte
-  aligned at the time of the call instruction (which afterwards pushes
-  the return pointer of size 4 bytes). The stack was originally 16-byte
-  aligned above and we've pushed a multiple of 16 bytes to the
-  stack since (pushed 0 bytes so far), so the alignment has thus been
-  preserved and the call is well defined.
-  */
+  ;; Enter the high-level kernel. The ABI requires the stack is 16-byte
+  ;; aligned at the time of the call instruction (which afterwards pushes
+  ;; the return pointer of size 4 bytes). The stack was originally 16-byte
+  ;; aligned above and we've pushed a multiple of 16 bytes to the
+  ;; stack since (pushed 0 bytes so far), so the alignment has thus been
+  ;; preserved and the call is well defined.
+  extern kernel_main
   call kernel_main
-
-/*
-Set the size of the _start symbol to the current location '.' minus its start.
-This is useful when debugging or when you implement call tracing.
-*/
-.size _start, . - _start
diff --git a/kernel/boot/init/crti.s b/kernel/boot/init/crti.s
index 8f86ffa..e3ddc32 100644
--- a/kernel/boot/init/crti.s
+++ b/kernel/boot/init/crti.s
@@ -1,33 +1,29 @@
-/*
- * bubbl
- * Copyright (C) 2024-2025  Raghuram Subramani <raghus2247@gmail.com>
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
+;; 
+;; bubbl
+;; Copyright (C) 2024-2025  Raghuram Subramani <raghus2247@gmail.com>
+;;
+;; This program is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+;;
 
-.section .init
-.global _init
-.type _init, @function
+section .init
+global _init
 _init:
-  push %ebp
-  mov %esp, %ebp
-  /* gcc will nicely put the contents of crtbegin.o's .init section here. */
+  push ebp
+  mov ebp, esp
 
-.section .fini
-.global _fini
-.type _fini, @function
+section .fini
+global _fini
 _fini:
-  push %ebp
-  mov %esp, %ebp
-  /* gcc will nicely put the contents of crtbegin.o's .fini section here. */
+  push ebp
+  mov ebp, esp
diff --git a/kernel/boot/init/crtn.s b/kernel/boot/init/crtn.s
index 8a20b9e..d585bfe 100644
--- a/kernel/boot/init/crtn.s
+++ b/kernel/boot/init/crtn.s
@@ -1,27 +1,25 @@
-/*
- * bubbl
- * Copyright (C) 2024-2025  Raghuram Subramani <raghus2247@gmail.com>
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
+;;
+;; bubbl
+;; Copyright (C) 2024-2025  Raghuram Subramani <raghus2247@gmail.com>
+;;
+;; This program is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+;;
 
-.section .init
-  /* gcc will nicely put the contents of crtend.o's .init section here. */
-  popl %ebp
+section .init
+  pop ebp
   ret
 
-.section .fini
-  /* gcc will nicely put the contents of crtend.o's .fini section here. */
-  popl %ebp
+section .fini
+  pop ebp
   ret