Reverting to continue using GNU.

Makefile

@@ -17,18 +17,17 @@
 # General options
 TARGET=i686
 ARCH=$(shell echo $(TARGET) | sed s/i.86/x86/)
-CROSSFLAGS=--target=$(TARGET)-pc-none-elf -march=$(TARGET)
 # Assembly options
-AS=nasm
+AS=i686-elf-as
-AFLAGS=-felf32 -Isrc/kernel/arch/$(ARCH)/ -Isrc/
+AFLAGS=
 # C options
-CC=clang
+CC=i686-elf-gcc
 CFLAGS?=-O0 -g
-CFLAGS:=$(CFLAGS) $(CROSSFLAGS) -std=c99 -ffreestanding -fno-builtin -nostdlibinc -Wall -Wextra -Isrc/
+CFLAGS:=$(CFLAGS) -std=gnu99 -ffreestanding -Wall -Wextra -Isrc/
 # Linker options
 LDFLAGS?=-O0
-LDFLAGS:=$(LDFLAGS) $(CROSSFLAGS) -ffreestanding -nostdlib
+LDFLAGS:=$(LDFLAGS) -ffreestanding -nostdlib
-LIBS=
+LIBS=-lgcc
 
 # Binary variables
 OBJS=src/kernel/arch/$(ARCH)/boot.o src/kernel/kernel.o src/kernel/arch/$(ARCH)/tty.o

README

@@ -1,17 +1,17 @@
 ===============
 *** Colonel ***
 ===============
-Colonel (pronounced as it is spelt) is a small hobby kernel project
+This is a small OS project I'm working on. It's slow progress and
-that I'm working on. It currently supports the following architectures:
+probably shouldn't be run anywhere except in an emulator. It currently
-
+supports the following architectures:
  - x86
 
 # Compiling
 -----------
-This project uses Clang (https://clang.llvm.org/) and NASM
+You'll want to setup a cross-compilation toolchain with GCC
-(http://www.nasm.us/) for building. You will also require GNU Make
+(https://gcc.gnu.org/) for your target architecture, along with
-(https://www.gnu.org/software/make/), unless you want to manually go
+GNU Make (https://www.gnu.org/software/make/) (I'll switch to the
-through and compile the files.
+GNU autotools as soon as I can get them to work properly).
 
 To compile a full image you can run `make build-iso`, which will use
 GNU GRUB (https://www.gnu.org/software/grub/) as the bootloader. Else,

src/kernel/arch/x86/boot.s

@@ -1,65 +1,139 @@
-; Copyright (C) 2018  Ortega Froysa, Nicolás <nortega@themusicinnoise.net>
+/*
-; Author: Ortega Froysa, Nicolás <nortega@themusicinnoise.net>
+ * Copyright (C) 2018  Ortega Froysa, Nicolás <nortega@themusicinnoise.net>
-;
+ * Author: Ortega Froysa, Nicolás <nortega@themusicinnoise.net>
-; 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
+ * This program is free software: you can redistribute it and/or modify
-; the Free Software Foundation, either version 3 of the License, or
+ * it under the terms of the GNU General Public License as published by
-; (at your option) any later version.
+ * 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
+ * This program is distributed in the hope that it will be useful,
-; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
-; GNU General Public License for more details.
+ * 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/>.
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
 
-MBALIGN equ 1<<0               ; align loaded modules on page boundaries
+# declare constants for the multiboot header
-MEMINFO equ 1<<1               ; provide memory map
+.set ALIGN,      1 << 0            # align loaded modules on page boundaries
-FLAGS equ MBALIGN | MEMINFO    ; multiboot flag field
+.set MEMINFO,    1 << 1            # provide memory map
-MAGIC equ 0x1BADB002           ; magic number to help bootloader find the header
+.set FLAGS,      ALIGN | MEMINFO   # the multiboot `FLAG' field
-CHECKSUM equ -(MAGIC + FLAGS)  ; checksum of the above data
+.set MAGIC,      0x1BADB002        # 'magic number' letting the boot loader know we're here
+.set CHECKSUM ,  -(MAGIC + FLAGS)  # checksum of the above to prove we're multiboot
 
-section .multiboot
+/*
-align 4
+ * Declare the multiboot header marking this program as a kernel. The bootloader
-	dd MAGIC
+ * will search for these values in the first 8 KiB of the kernel file aligned at
-	dd FLAGS
+ * 32-bit boundaries (4 bytes). We put the signature in its own section to force
-	dd CHECKSUM
+ * it within the first 8 KiB of the kernel file.
+ */
+.section .multiboot
+.align 4
+.long MAGIC
+.long FLAGS
+.long CHECKSUM
 
-section .bss
+/*
-align 16
+ * Create a 16 byte aligned stack with 16 KiB of size. We create labels at the
+ * bottom and top of the stack.
+ */
+.section .bss
+.align 16
 stack_bottom:
-	resb 16384  ; 16KiB
+.skip 16384  # 16 KiB
 stack_top:
 
-section .data
+/*
-%include "gdt.s"
+ * Create the GDT
+ */
+.section .data
+gdt_start:
+gdt_null:
+.long 0x0
+.long 0x0
 
-section .text
+gdt_kcode:
-global _start:function (_start.end - _start)
+.word 0xFFFF             # limit
+.word 0x0                # base
+.byte 0x0                # base
+.byte 0b10011010         # 1st flags | type flags
+.byte 0b11001111         # 2nd flags | limit
+.byte 0x0                # base
+
+gdt_kdata:
+.word 0xFFFF             # limit
+.word 0x0                # base
+.byte 0x0                # base
+.byte 0b10010010         # 1st flags | type flags
+.byte 0b11001111         # 2nd flags | limit
+.byte 0x0                # base
+
+gdt_ucode:
+.word 0xFFFF             # limit
+.word 0x0                # base
+.byte 0x0                # base
+.byte 0b11111010         # 1st flags | type flags
+.byte 0b11001111         # 2nd flags | limit
+.byte 0x0                # base
+
+gdt_udata:
+.word 0xFFFF             # limit
+.word 0x0                # base
+.byte 0x0                # base
+.byte 0b11110010         # 1st flags | type flags
+.byte 0b11001111         # 2nd flags | limit
+.byte 0x0                # base
+
+# TODO: setup the TSS
+gdt_tss:
+.word 0x0                # size of TSS (set later)
+.word 0x0                # address of TSS (set later)
+.byte 0x0                # address of TSS (set later)
+.byte 0b10010001         # 1st flags | type flags
+.byte 0b01000000         # 2nd flags | size of TSS (set later
+.byte 0x0                # address of TSS (set later)
+
+gdt_end:
+
+gdtr:
+.word (gdt_end - gdt_start - 1)
+.long gdt_start
+
+/*
+ * The linker script specifies the `_start' label as the entry point to the kernel
+ * and the bootloader will jump to this position. That is, this is where the kernel
+ * starts.
+ */
+.section .text
+.global _start
+.type _start, @function
 _start:
-	; setup the stack
+	# set the position of `%esp' to the top of the stack
-	mov esp, stack_top
+	mov $stack_top, %esp
 
-	; TODO: setup GDT, IDT, paging, etc. here
+	# GDT, paging, and other features
+flush_gdt:
 	cli
-	lgdt [gdtr]
+	lgdt (gdtr)
-	jmp 0x08:.reload_segs
+	movw $0x10, %ax
-.reload_segs:
+	movw %ax, %ds
-	mov ax, 0x10
+	movw %ax, %es
-	mov ds, ax
+	movw %ax, %fs
-	mov es, ax
+	movw %ax, %gs
-	mov fs, ax
+	movw %ax, %ss
-	mov gs, ax
+	ljmp $0x08, $flush_end
-	mov ss, ax
+flush_end:
 
-	; call the kernel
+boot_kernel:
-	extern kernel_main
+	# enter high-level kernel (C)
 	call kernel_main
 
-	; hang
+	# put computer into infinite loop
-	cli
+	cli                    # disable interrupts by clearing the interrupt flag in `eflags'
-.hang:
+end_loop:
-	hlt
+	hlt                    # wait for next interrupt
-	jmp .hang
+	jmp end_loop           # jump to the `hlt' instruction if it ever leaves it
-.end:
+
+.size _start, . - _start

src/kernel/arch/x86/gdt.s

@@ -1,68 +0,0 @@
-; Copyright (C) 2018  Ortega Froysa, Nicolás <nortega@themusicinnoise.net>
-; Author: Ortega Froysa, Nicolás <nortega@themusicinnoise.net>
-;
-; 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/>.
-
-gdt_start:
-
-gdt_null:
-	dd 0x0
-	dd 0x0
-
-gdt_kcode:
-	dw 0xFFFF     ; limit (bits 0-15)
-	dw 0x0        ; base (bits 0-15)
-
-	db 0x0        ; base (bits 16-23)
-	db 10011010b  ; 1st flags | type flags
-	db 11001111b  ; 2nd flags | limit (bits 16-19)
-	db 0x0        ; base (bits 24-31)
-
-gdt_kdata:
-	dw 0xFFFF
-	dw 0x0
-
-	db 0x0
-	db 10010010b
-	db 11001111b
-	db 0x0
-
-gdt_ucode:
-	dw 0xFFFF
-	dw 0x0
-
-	db 0x0
-	db 11111010b
-	db 11001111b
-	db 0x0
-
-gdt_udata:
-	dw 0xFFFF
-	dw 0x0
-
-	db 0x0
-	db 11110010b
-	db 11001111b
-	db 0x0
-
-; TODO: fill this in later
-gdt_tss:
-	dd 0x0
-	dd 0x0
-
-gdt_end:
-
-gdtr:
-	dw gdt_end  - gdt_start - 1
-	dd gdt_start

src/kernel/arch/x86/tss.h

@@ -18,7 +18,7 @@
 
 #pragma once
 
-struct tss {
+volatile struct tss {
 	uint16_t link;
 	uint16_t link_r;    // reserved