commit 0b05970c71593d94f9b15d30a3a1279de6d28826 Author: Patrick Wuttke Date: Wed Jan 10 18:09:20 2024 +0100 Initial commit. diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..da4ce7b --- /dev/null +++ b/.gitignore @@ -0,0 +1,48 @@ +# Project Folder (at least for now) +.idea + +# Compiled Binaries +*.bin + +# Compile Commands +compile_commands.json + +# Prerequisites +*.d + +# Compiled Object files +*.slo +*.lo +*.o +*.obj + +# Precompiled Headers +*.gch +*.pch + +# Compiled Dynamic libraries +*.so +*.dylib +*.dll + +# Fortran module files +*.mod +*.smod + +# Compiled Static libraries +*.lai +*.la +*.a +*.lib + +# Executables +*.exe +*.out +*.app + +# for projects that use SCons for building: http://http://www.scons.org/ +.sconsign.dblite + +# When configure fails, SCons outputs these +config.log +.sconf_temp diff --git a/SConstruct b/SConstruct new file mode 100644 index 0000000..1145ad3 --- /dev/null +++ b/SConstruct @@ -0,0 +1,39 @@ + +import subprocess + +env = Environment(tools = ['default', 'compilation_db']) +env['AS'] = 'i686-elf-as' +env['CC'] = 'i686-elf-gcc' +env['CXX'] = 'i686-elf-g++' +env['LD'] = 'i686-elf-g++' +env.Append(CXXFLAGS = ['-ffreestanding', '-fno-exceptions', '-fno-rtti', '-std=c++20']) +env.Append(LINKFLAGS = ['-T', 'linker.ld', '-ffreestanding', '-nostdlib']) +env.Append(CPPPATH = ['#include']) + +def get_crt_object(name: str) -> str: + cmd = [env['CXX']] + cmd.extend(env['CXXFLAGS']) + cmd.append(f'-print-file-name={name}') + result = subprocess.run(cmd, stdout=subprocess.PIPE) + return result.stdout.decode('utf-8').strip() +crtbegin_o = get_crt_object('crtbegin.o') +crtend_o = get_crt_object('crtend.o') +crti_o = env.Object('src/crt/crti.s') +crtn_o = env.Object('src/crt/crtn.s') + +os_sources = Split(''' + src/kernel/boot.s + src/kernel/startup.cpp + + src/os/tty.cpp +''') +env['LINKCOM'] = env['LINKCOM'].replace('$_LIBFLAGS', f'{crti_o[0]} {crtbegin_o} $_LIBFLAGS {crtend_o} {crtn_o[0]}') + +prog_os = env.Program( + target = 'os.bin', + source = os_sources +) +env.Depends(prog_os, [crti_o, crtn_o]) +env.Default(prog_os) +comp_db = env.CompilationDatabase(target = '#compile_commands.json') +env.Default(comp_db) diff --git a/boot/grub.cfg b/boot/grub.cfg new file mode 100644 index 0000000..85ccbad --- /dev/null +++ b/boot/grub.cfg @@ -0,0 +1,3 @@ +menuentry "Bad Apple OS" { + multiboot /boot/os.bin +} \ No newline at end of file diff --git a/include/os/tty.hpp b/include/os/tty.hpp new file mode 100644 index 0000000..9ea9367 --- /dev/null +++ b/include/os/tty.hpp @@ -0,0 +1,51 @@ + +#pragma once + +#if !defined(OS_TTY_HPP_INCLUDED) +#define OS_TTY_HPP_INCLUDED 1 + +#include +#include + +namespace tty +{ +enum class VgaColor : uint8_t +{ + BLACK = 0, + BLUE = 1, + GREEN = 2, + CYAN = 3, + RED = 4, + MAGENTA = 5, + BROWN = 6, + LIGHT_GREY = 7, + DARK_GREY = 8, + LIGHT_BLUE = 9, + LIGHT_GREEN = 10, + LIGHT_CYAN = 11, + LIGHT_RED = 12, + LIGHT_MAGENTA = 13, + LIGHT_BROWN = 14, + WHITE = 15 +}; + +struct VgaDoubleColor +{ + VgaColor foreground : 4 = VgaColor::LIGHT_GREY; + VgaColor background : 4 = VgaColor::BLACK; +}; + +[[nodiscard]] size_t strlen(const char* str); // TODO: move to standard lib +void initialize(); +void setColor(VgaDoubleColor color); +void putEntryAt(char chr, VgaDoubleColor color, size_t posX, size_t posY); +void putChar(char chr); +void write(const char* data, size_t size); + +inline void write(const char* data) +{ + write(data, strlen(data)); +} +} // namespace tty + +#endif // OS_TTY_HPP_INCLUDED diff --git a/linker.ld b/linker.ld new file mode 100644 index 0000000..269cda1 --- /dev/null +++ b/linker.ld @@ -0,0 +1,52 @@ +/* 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 +{ + /* It used to be universally recommended to use 1M as a start offset, + as it was effectively guaranteed to be available under BIOS systems. + However, UEFI has made things more complicated, and experimental data + strongly suggests that 2M is a safer place to load. In 2016, a new + feature was introduced to the multiboot2 spec to inform bootloaders + that a kernel can be loaded anywhere within a range of addresses and + will be able to relocate itself to run from such a loader-selected + address, in order to give the loader freedom in selecting a span of + memory which is verified to be available by the firmware, in order to + work around this issue. This does not use that feature, so 2M was + chosen as a safer option than the traditional 1M. */ + . = 2M; + + /* First put the multiboot header, as it is required to be put very 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. */ +} \ No newline at end of file diff --git a/src/crt/crti.s b/src/crt/crti.s new file mode 100644 index 0000000..30dd4ea --- /dev/null +++ b/src/crt/crti.s @@ -0,0 +1,16 @@ +/* x86 crti.s */ +.section .init +.global _init +.type _init, @function +_init: + push %ebp + movl %esp, %ebp + /* gcc will nicely put the contents of crtbegin.o's .init section here. */ + +.section .fini +.global _fini +.type _fini, @function +_fini: + push %ebp + movl %esp, %ebp + /* gcc will nicely put the contents of crtbegin.o's .fini section here. */ diff --git a/src/crt/crtn.s b/src/crt/crtn.s new file mode 100644 index 0000000..1da795d --- /dev/null +++ b/src/crt/crtn.s @@ -0,0 +1,10 @@ +/* x86 crtn.s */ +.section .init + /* gcc will nicely put the contents of crtend.o's .init section here. */ + popl %ebp + ret + +.section .fini + /* gcc will nicely put the contents of crtend.o's .fini section here. */ + popl %ebp + ret diff --git a/src/kernel/boot.s b/src/kernel/boot.s new file mode 100644 index 0000000..66c98bc --- /dev/null +++ b/src/kernel/boot.s @@ -0,0 +1,109 @@ +/* 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 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 diff --git a/src/kernel/startup.cpp b/src/kernel/startup.cpp new file mode 100644 index 0000000..038563e --- /dev/null +++ b/src/kernel/startup.cpp @@ -0,0 +1,23 @@ +#include +#include + +#include "os/tty.hpp" + +/* 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 + +extern "C" void kernel_main(void) +{ + /* Initialize terminal interface */ + tty::initialize(); + + /* Newline support is left as an exercise. */ + tty::write("Hello, kernel World!\n"); +} diff --git a/src/os/tty.cpp b/src/os/tty.cpp new file mode 100644 index 0000000..1bbec74 --- /dev/null +++ b/src/os/tty.cpp @@ -0,0 +1,79 @@ + +#include "os/tty.hpp" + +namespace tty +{ +namespace +{ +inline const size_t VGA_WIDTH = 80; +inline const size_t VGA_HEIGHT = 25; + +constexpr uint8_t vgaEntryColor(VgaDoubleColor color) +{ + return static_cast(color.foreground) | static_cast(color.background) << 4; +} + +constexpr uint16_t vgaEntry(const unsigned char chr, const VgaDoubleColor color) +{ + return static_cast(chr) | static_cast(vgaEntryColor(color) << 8); +} + +size_t gTerminalRow = 0; +size_t gTerminalColumn = 0; +VgaDoubleColor gTerminalColor = VgaDoubleColor(); +uint16_t* gTerminalBuffer = reinterpret_cast(0xB8000); +} + +size_t strlen(const char* str) // TODO: move to standard lib +{ + size_t len = 0; + while (str[len] != '\0') { + ++len; + } + return len; +} + +void initialize() +{ + 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; + gTerminalBuffer[index] = vgaEntry(' ', gTerminalColor); + } + } +} + +void setColor(VgaDoubleColor color) +{ + gTerminalColor = color; +} + +void putEntryAt(char chr, VgaDoubleColor color, size_t posX, size_t posY) +{ + const size_t index = posY * VGA_WIDTH + posX; + gTerminalBuffer[index] = vgaEntry(chr, color); +} + +void putChar(char chr) +{ + putEntryAt(chr, gTerminalColor, gTerminalColumn, gTerminalRow); + if (++gTerminalColumn == VGA_WIDTH) + { + gTerminalColumn = 0; + if (++gTerminalRow == VGA_HEIGHT) + { + gTerminalRow = 0; + } + } +} + +void write(const char* data, size_t size) +{ + for (size_t idx = 0; idx < size; idx++) + { + putChar(data[idx]); + } +} +}