Minimized multiboot works!

Makefile

@@ -2,6 +2,7 @@
 
 IN_EXT ?= .S
 LD ?= ld
+LINKER_SCRIPT ?= linker.ld
 # Use gcc so that the preprocessor will run first.
 MYAS ?= gcc
 OBJ_EXT ?= .o
@@ -16,8 +17,8 @@ OUTS := $(patsubst %$(IN_EXT),%$(OUT_EXT),$(INS))
 
 all: $(OUTS)
 
-%$(OUT_EXT): %$(OBJ_EXT) a.ld
-	$(LD) --oformat binary -o '$@' '$<' -T a.ld #-Ttext 0x7C00
+%$(OUT_EXT): %$(OBJ_EXT) $(LINKER_SCRIPT)
+	$(LD) --oformat binary -o '$@' '$<' -T '$(LINKER_SCRIPT)' #-Ttext 0x7C00
 
 %$(OBJ_EXT): %$(IN_EXT)
 	$(MYAS) -c -o '$@' '$<'

README.md

@@ -9,8 +9,8 @@ Hello world examples of programs without an OS. A.K.A. bare bones.
     1.  [bios_one_char](bios_one_char.S)
     1.  [bios_hello_world](bios_hello_world.S)
     1.  [shutdown_apm](shutdown_apm.S)
+    1.  [multiboot/](multiboot/)
     1.  TODO not working
-        1. [multiboot-c/](multiboot-c/)
         1. [UEFI](uefi/)
         1. [hajji](hajji)
     1.  [nasm](nasm/)
@@ -21,13 +21,17 @@ Hello world examples of programs without an OS. A.K.A. bare bones.
 ## Getting started
 
     sudo apt-get install build-essential gnu-efi qemu
+
+    # Run the default program on QEMU.
     make run
+
+    # Run a given program.
     make run RUN=min
     make run RUN=bios_one_char
 
 Tested on Ubuntu 14.04.
 
-Run on real hardware: insert as USB, determine its device (`/dev/sdX`) with:
+Run on real hardware: for insert as USB, determine its device (`/dev/sdX`) with:
 
     sudo lsblk
     sudo fdisk -l

multiboot/README.md

@@ -1,5 +1,11 @@
 # Multiboot
 
+1.  [hello-world](hello-world/)
+1.  TODO not working
+    1.  [osdev](osdev/)
+
+## Introduction
+
 <https://en.wikipedia.org/wiki/Multiboot_Specification>
 
 Standard created by GRUB for booting OSes.

multiboot/hello-world/Makefile

@@ -0,0 +1,16 @@
+main.elf: entry.o main.o
+	ld -m elf_i386 -nostdlib -T linker.ld -o '$@' $^
+
+entry.o: entry.asm
+	nasm -f elf '$<' -o '$@'
+
+main.o: main.c
+	gcc -c -m32 -std=c99 -ffreestanding -fno-builtin -Os -Wall -Wextra -o '$@' '$<'
+
+clean:
+	rm -f *.elf *.o
+
+run: main.elf
+	qemu-system-i386 -kernel '$<'
+
+.PHONY: clean run

multiboot/hello-world/README.md

@@ -0,0 +1,7 @@
+# Hello World
+
+Multiboot hello world.
+
+Uses VGA output because we cannot use BIOS calls from protected mode: <http://stackoverflow.com/questions/5794991/why-cant-i-call-bios-interrupts-from-protected-mode>
+
+Originally minimized from <https://github.com/programble/bare-metal-tetris>

multiboot/hello-world/entry.asm

@@ -0,0 +1,40 @@
+global loader
+global stack_ptr
+
+extern main
+
+MODULEALIGN equ 1<<0
+MEMINFO equ 1<<1
+FLAGS equ MODULEALIGN | MEMINFO
+MAGIC equ 0x1BADB002
+CHECKSUM equ -(MAGIC + FLAGS)
+
+section .mbheader
+align 4
+MultiBootHeader:
+  dd MAGIC
+  dd FLAGS
+  dd CHECKSUM
+
+section .text
+
+STACKSIZE equ 0x4000
+
+loader:
+  mov esp, stack+STACKSIZE
+  push eax
+  push ebx
+
+  call main
+
+  cli
+
+hang:
+  hlt
+  jmp hang
+
+section .bss
+align 4
+stack:
+  resb STACKSIZE
+stack_ptr:

multiboot/hello-world/linker.ld

@@ -0,0 +1,23 @@
+ENTRY (loader)
+SECTIONS
+{
+  . = 0x00100000;
+  .mbheader : {
+    *(.mbheader)
+  }
+  .text : {
+    *(.text)
+  }
+  .rodata ALIGN (0x1000) : {
+    *(.rodata)
+  }
+  .data ALIGN (0x1000) : {
+    *(.data)
+  }
+  .bss : {
+    sbss = .;
+    *(COMMON)
+    *(.bss)
+    ebss = .;
+  }
+}

multiboot/hello-world/main.c

@@ -0,0 +1,36 @@
+#include "stdint.h"
+
+enum color {
+    BLACK = 0,
+    BRIGHT = 7
+};
+
+enum size {
+    COLS = 80,
+    ROWS = 25
+};
+
+uint16_t *const video = (uint16_t*) 0xB8000;
+
+void putc(uint8_t x, uint8_t y, enum color fg, enum color bg, char c) {
+    video[y * COLS + x] = (bg << 12) | (fg << 8) | c;
+}
+
+void puts(uint8_t x, uint8_t y, enum color fg, enum color bg, const char *s) {
+    for (; *s; s++, x++)
+        putc(x, y, fg, bg, *s);
+}
+
+void clear(enum color bg) {
+    uint8_t x, y;
+    for (y = 0; y < ROWS; y++)
+        for (x = 0; x < COLS; x++)
+            putc(x, y, bg, bg, ' ');
+}
+
+
+int __attribute__((noreturn)) main() {
+    clear(BLACK);
+    puts(0, 0, BRIGHT, BLACK, "hello world");
+    while (1);
+}

multiboot/osdev/README.md

@@ -2,8 +2,6 @@
 
 Originally from: <http://wiki.osdev.org/Bare_Bones>, should be a reasonable way to start a serious OS.
 
-## TODO get working
-
     sudo aptitude install -y build-essential gcc-multilib qemu xorriso
     make run