Writing C in Protected Mode

.gitignore

@@ -1,3 +1,4 @@
 .DS_Store
 *.code-workspace
-*.bin
+bin/*
+build/*

Makefile

@@ -1,4 +1,6 @@
-FILES = ./build/kernel.asm.o
+FILES = ./build/kernel.asm.o ./build/kernel.o
+INCLUDES = -I./src
+FLAGS = -g -ffreestanding -falign-jumps -falign-functions -falign-labels -falign-loops -fstrength-reduce -fomit-frame-pointer -finline-functions -Wno-unused-function -fno-builtin -Werror -Wno-unused-label -Wno-cpp -Wno-unused-parammeter -nostdlib -nostartfiles -nodefaultlibs -Wall -O0 -Iinc
 
 all: ./bin/boot.bin ./bin/kernel.bin
 	rm -rf ./bin/os.bin
@@ -11,11 +13,14 @@ all: ./bin/boot.bin ./bin/kernel.bin
 
 ./bin/kernel.bin: $(FILES)
 	i686-elf-ld -g -relocatable $(FILES) -o ./build/kernelfull.o
-	i686-elf-gcc -T ./src/linker.ld -o ./bin/kernel.bin -ffreestanding -O0 -nostdlib ./build/kernelfull.o
+	i686-elf-gcc $(FLAGS) -T ./src/linker.ld -o ./bin/kernel.bin ./build/kernelfull.o
 
 ./build/kernel.asm.o: ./src/kernel.asm
 	nasm -f elf -g ./src/kernel.asm -o ./build/kernel.asm.o
 
+./build/kernel.o: ./src/kernel.c
+	i686-elf-gcc $(INCLUDES) $(FLAGS) -std=gnu99 -c ./src/kernel.c -o ./build/kernel.o
+
 run:
 	qemu-system-x86_64 -hda ./bin/os.bin
 

doc/protected_mode_development.md

@@ -81,7 +81,7 @@ general:
 
 ---
 
-## Notes
+## References
 
 - [GDB to LLDB command map](https://lldb.llvm.org/use/map.html#examining-thread-state)
 - [Entering Protected Mode tutorial](http://www.osdever.net/tutorials/view/the-world-of-protected-mode)

doc/protected_mode_development_2.md

@@ -112,3 +112,7 @@ Quick summary of how our code works with memory.
     - Note that aligning `boot.asm` to 512 bytes is unrelated to the memory alignment issue we talk about here. The bootloader must have the boot signature 0x55AA at 511 and 512 byte.
   - Make sure that `kernel.asm.o` is the first file to be linked. That ensures `kernel.asm.o` is located in the `.text` section ([`linker.ld`](../src/linker.ld)) when linked, and always starts at 0x100000. `kernel.asm.o` is 512 bytes long, so any other C object files linked after that are automatically aligned.
   - In other kernel assembly files, specify `.asm` section so that they are linked at the end of the object file. If the assembled code is not a multiple of 4 bytes, that's okay because those files are at the end.
+
+---
+
+[continue](./protected_mode_development_3.md)

doc/protected_mode_development_3.md

@@ -0,0 +1,7 @@
+# Protected Mode Development - Part 3
+
+## Writing C program in Protected Mode
+
+Now, we start writing our kernel in C. [commit]()
+
+Debugging steps are the same as what we did in the [previous note](./protected_mode_development_2.md) "5. Build, run, and debug".

src/kernel.asm

@@ -2,6 +2,8 @@
 
 global _start
 
+extern kernel_main
+
 CODE_SEG equ 0x08
 DATA_SEG equ 0x10
 
@@ -20,6 +22,8 @@ _start:
     or al, 2
     out 0x92, al                ; Write to the bus line 92
 
+    call kernel_main
+
     cld                         ; Clears direction flag
     cli                         ; Disables interrupts
     hlt                         ; This hangs the computer

src/kernel.c

@@ -0,0 +1,5 @@
+#include "kernel.h"
+
+void kernel_main()
+{
+}

src/kernel.h

@@ -0,0 +1,6 @@
+#ifndef KERNEL_H
+#define KERNEL_H
+
+void kernel_main();
+
+#endif