Initial commit

dev_tools/build_util_src/README

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+This script automatically builds the cross-compiler needed to build FENIX at
+this stage in time. It sets up a cross-compiler for i686-elf in ~/opt/cross.
+
+This version of the script, suitable for building current, unversioned
+pre-releases of FENIX, uses GCC 9.2.0 and Binutils 2.32. You'll need to
+download these from the GNU website:
+    Binutils: https://ftp.gnu.org/gnu/binutils/binutils-2.32.tar.xz
+    GCC: https://ftp.gnu.org/gnu/gcc/gcc-9.2.0/gcc-9.2.0.tar.xz
+Download these tarballs into the same folder as build_cross_compiler.sh
+
+Additionally, you'll need the following:
+    - A suitable C compiler (probably GCC)
+    - make
+    - Bison
+    - Flex
+    - GMP
+    - MPC
+    - MPFR
+    - Texinfo
+
+These correspond to these Fedora packages:
+    - gcc (or whatever C compiler you use, like Clang)
+    - make
+    - bison
+    - flex
+    - gmp-devel
+    - libmpc-devel
+    - mpfr-devel
+    - texinfo
+
+Once you're ready, simply run build_cross_compiler.sh. (You may first need
+to run `chmod +x build_cross_compiler.sh` in order to make it executable.
+
+Once done, you'll probably want to add ~/opt/cross/bin to your PATH. You'll
+probably also want to verify that it worked. To do so, you can start by
+checking if it runs using:
+    `i686-elf-gcc --version`
+You can also try compiling a small test kernel included in cross_compiler_test.
+Simply run `make`. If everything worked, it should successfully compile. You can
+then run `make test` to open the kernel in QEMU. (Note: You'll need
+qemu-system-i386 to test the test kernel.

dev_tools/build_util_src/build_cross_compiler.sh

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+#!/bin/sh
+
+# Extract binutils and gcc
+# You can try changing versions, if you want.
+# The official setup is binutils 2.32 and GCC 9.2.0
+tar -xvf binutils-2.32.tar.xz
+tar -xvf gcc-9.2.0.tar.xz
+
+# We'll eventuall change to, like, i686-fenix or something,
+# but, for now, this is what we'll use.
+# Besides, we'd need patches for a custom OS target
+TARGET=i686-elf
+PREFIX="$HOME/opt-test/cross"
+PATH="$PREFIX/bin:$PATH"
+
+# Go ahead and make sure the prefix exists
+mkdir -p $PREFIX
+
+# Binutils build
+mkdir build-binutils
+cd build-binutils
+# Binutils w/o native language support. Feel free to remove --disable-nls
+# if you want stuff in your native language. Also, enable sysroot support.
+../binutils-2.32/configure --target=$TARGET --prefix="$PREFIX" --with-sysroot --disable-nls --disable-werror
+make
+make install
+
+# GCC build
+cd ..
+mkdir build-gcc
+cd build-gcc
+# Check for $PREFIX/bin in PATH
+which -- $TARGET-as || exit 1
+# GCC w/o NLS and with only C support. Also, it shouldn't rely on having
+# headers available to it. You can optionally remove --disable-nls for
+# nativle language stuffs, or add ,C++ to languages, if you wanna have C++.
+../gcc-9.2.0/configure --target=$TARGET --prefix="$PREFIX" --disable-nls --enable-languages=c --without-headers
+make all-gcc
+make all-target-libgcc
+make install-gcc
+make install-target-libgcc

dev_tools/build_util_src/cross_compiler_test/Makefile

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+# Reminder that you'll need the cross compiler toolchain setup already.
+PREFIX = i686-elf-
+CC = $(PREFIX)gcc
+AS = $(PREFIX)as
+CFLAGS = -ffreestanding -O2
+WARNFLAGS = -Wall -Wextra
+
+all: test.bin
+
+test: test.bin
+	grub-file --is-x86-multiboot test.bin
+	qemu-system-i386 -kernel test.bin
+
+test.bin: boot.o kernel.o linker.ld
+	$(CC) -T linker.ld -o test.bin $(CFLAGS) -nostdlib boot.o kernel.o -lgcc
+
+boot.o: boot.s
+	$(AS) boot.s -o boot.o
+
+kernel.o: kernel.c
+	$(CC) -c kernel.c -o kernel.o -std=gnu99 $(CFLAGS) $(WARNFLAGS)
+
+clean:
+	-rm *.o test.bin

dev_tools/build_util_src/cross_compiler_test/boot.s

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+/* 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 */
+ 
+/* 
+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
+.long MAGIC
+.long FLAGS
+.long 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
+stack_bottom:
+.skip 16384 # 16 KiB
+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
+_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.
+	*/
+ 
+	/*
+	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 $stack_top, %esp
+ 
+	/*
+	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.
+	*/
+ 
+	/*
+	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.
+	*/
+	call kernel_main
+ 
+	/*
+	If the system has nothing more to do, put the computer into an
+	infinite loop. To do that:
+	1) Disable interrupts with cli (clear interrupt enable in eflags).
+	   They are already disabled by the bootloader, so this is not needed.
+	   Mind that you might later enable interrupts and return from
+	   kernel_main (which is sort of nonsensical to do).
+	2) Wait for the next interrupt to arrive with hlt (halt instruction).
+	   Since they are disabled, this will lock up the computer.
+	3) Jump to the hlt instruction if it ever wakes up due to a
+	   non-maskable interrupt occurring or due to system management mode.
+	*/
+	cli
+1:	hlt
+	jmp 1b
+ 
+/*
+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

dev_tools/build_util_src/cross_compiler_test/kernel.c

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+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+ 
+/* Check if the compiler thinks you are targeting the wrong operating system. */
+#if defined(__linux__)
+#error "You are not using a cross-compiler, you will most certainly run into trouble"
+#endif
+ 
+/* This tutorial will only work for the 32-bit ix86 targets. */
+#if !defined(__i386__)
+#error "This tutorial needs to be compiled with a ix86-elf compiler"
+#endif
+ 
+/* Hardware text mode color constants. */
+enum vga_color {
+	VGA_COLOR_BLACK = 0,
+	VGA_COLOR_BLUE = 1,
+	VGA_COLOR_GREEN = 2,
+	VGA_COLOR_CYAN = 3,
+	VGA_COLOR_RED = 4,
+	VGA_COLOR_MAGENTA = 5,
+	VGA_COLOR_BROWN = 6,
+	VGA_COLOR_LIGHT_GREY = 7,
+	VGA_COLOR_DARK_GREY = 8,
+	VGA_COLOR_LIGHT_BLUE = 9,
+	VGA_COLOR_LIGHT_GREEN = 10,
+	VGA_COLOR_LIGHT_CYAN = 11,
+	VGA_COLOR_LIGHT_RED = 12,
+	VGA_COLOR_LIGHT_MAGENTA = 13,
+	VGA_COLOR_LIGHT_BROWN = 14,
+	VGA_COLOR_WHITE = 15,
+};
+ 
+static inline uint8_t vga_entry_color(enum vga_color fg, enum vga_color bg) 
+{
+	return fg | bg << 4;
+}
+ 
+static inline uint16_t vga_entry(unsigned char uc, uint8_t color) 
+{
+	return (uint16_t) uc | (uint16_t) color << 8;
+}
+ 
+size_t strlen(const char* str) 
+{
+	size_t len = 0;
+	while (str[len])
+		len++;
+	return len;
+}
+ 
+static const size_t VGA_WIDTH = 80;
+static const size_t VGA_HEIGHT = 25;
+ 
+size_t terminal_row;
+size_t terminal_column;
+uint8_t terminal_color;
+uint16_t* terminal_buffer;
+ 
+void terminal_initialize(void) 
+{
+	terminal_row = 0;
+	terminal_column = 0;
+	terminal_color = vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
+	terminal_buffer = (uint16_t*) 0xB8000;
+	for (size_t y = 0; y < VGA_HEIGHT; y++) {
+		for (size_t x = 0; x < VGA_WIDTH; x++) {
+			const size_t index = y * VGA_WIDTH + x;
+			terminal_buffer[index] = vga_entry(' ', terminal_color);
+		}
+	}
+}
+ 
+void terminal_setcolor(uint8_t color) 
+{
+	terminal_color = color;
+}
+ 
+void terminal_putentryat(char c, uint8_t color, size_t x, size_t y) 
+{
+	const size_t index = y * VGA_WIDTH + x;
+	terminal_buffer[index] = vga_entry(c, color);
+}
+ 
+void terminal_putchar(char c) 
+{
+	terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
+	if (++terminal_column == VGA_WIDTH) {
+		terminal_column = 0;
+		if (++terminal_row == VGA_HEIGHT)
+			terminal_row = 0;
+	}
+}
+ 
+void terminal_write(const char* data, size_t size) 
+{
+	for (size_t i = 0; i < size; i++)
+		terminal_putchar(data[i]);
+}
+ 
+void terminal_writestring(const char* data) 
+{
+	terminal_write(data, strlen(data));
+}
+ 
+void kernel_main(void) 
+{
+	/* Initialize terminal interface */
+	terminal_initialize();
+ 
+	/* Newline support is left as an exercise. */
+	terminal_writestring("Hello, kernel World!\n");
+}

dev_tools/build_util_src/cross_compiler_test/linker.ld

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+/* The bootloader will look at this image and start execution at the symbol
+   designated as the entry point. */
+ENTRY(_start)
+ 
+/* Tell where the various sections of the object files will be put in the final
+   kernel image. */
+SECTIONS
+{
+	/* Begin putting sections at 1 MiB, a conventional place for kernels to be
+	   loaded at by the bootloader. */
+	. = 1M;
+ 
+	/* First put the multiboot header, as it is required to be put very early
+	   early in the image or the bootloader won't recognize the file format.
+	   Next we'll put the .text section. */
+	.text BLOCK(4K) : ALIGN(4K)
+	{
+		*(.multiboot)
+		*(.text)
+	}
+ 
+	/* Read-only data. */
+	.rodata BLOCK(4K) : ALIGN(4K)
+	{
+		*(.rodata)
+	}
+ 
+	/* Read-write data (initialized) */
+	.data BLOCK(4K) : ALIGN(4K)
+	{
+		*(.data)
+	}
+ 
+	/* Read-write data (uninitialized) and stack */
+	.bss BLOCK(4K) : ALIGN(4K)
+	{
+		*(COMMON)
+		*(.bss)
+	}
+ 
+	/* The compiler may produce other sections, by default it will put them in
+	   a segment with the same name. Simply add stuff here as needed. */
+}