GeekOS源代码学习(0)

梦里梦外; 2022-06-13 10:08 163阅读 0赞

我使用的是geekos-0.3.0，从 [这里][Link 1]下载。  
doc目录下的hacking.pdf有详细的运行说明，只有40页，英文也很简单，稍微仔细的看一下。  
  
  
我们开始  
建立project0  
$startProject project0 ./geekos-0.3.0/src  
这样在当下目录下生成了project0目录  
$cd ./project0/build  
$make depend  
$make  
编译文件，最后生成了fd.img软盘映像文件。  
$file fd.img  
fd.img: Linux kernel  
好，先来试试看再说。  
使用在我的上篇文章《sagalinux学习之/boot目录》中的bochsrc，只要改一下软盘名字就好了。  
先来看看效果！！

![1333765757_6941.png][]

哈哈，看到了吧。

带蓝色背景的字是你需要完成的任务。

pdf上的共有7个project，每一个都会让你完成一个任务，最终任务完成之后，就是一个真正的小型的类unix OS了。。。激动。。。  
project0要求你完成键盘输入的响应，其实源代码函数都已经写好了，只要你调用一下函数就行了。  
  
  
不管project0，我先read the f\*\*king source code...  
来看一下Makefile，对整体有个结构上的理解  
$vi ./build/Makefile

Makefile

# Makefile for GeekOS kernel, userspace, and tools
    # Copyright (c) 2004,2005 David H. Hovemeyer <daveho@cs.umd.edu>
    # $Revision: 1.45 $
    
    # This is free software.  You are permitted to use,
    # redistribute, and modify it as specified in the file "COPYING".
    
    # Required software to build GeekOS:
    # - GNU Make (http://www.gnu.org/software/make)
    # - gcc 2.95.2 generating code for target (i386/ELF) and host platforms
    # - nasm (http://nasm.sourceforge.net)
    # - Perl5, AWK (any version), egrep
    #
    # Cygwin (http://cygwin.com) may be used to build GeekOS.
    # Make sure that gcc, binutils, nasm, and perl are installed.
    
    # NOTES:
    # - This makefile has been written carefully to work correctly
    #   with the -j (parallel make) option.  I regularly use "make -j 2"
    #   to speed the build process on 2 processor systems.
    
    PROJECT_ROOT := ..
    VPATH := $(PROJECT_ROOT)/src
    
    # Figure out if we're compiling with cygwin, http://cygwin.com
    SYSTEM_NAME := $(shell uname -s)
    ifeq ($(findstring CYGWIN,$(SYSTEM_NAME)),CYGWIN)
    SYM_PFX            := _
    EXTRA_C_OPTS       := -DNEED_UNDERSCORE -DGNU_WIN32
    EXTRA_NASM_OPTS    := -DNEED_UNDERSCORE
    NON_ELF_SYSTEM     := yes
    EXTRA_CC_USER_OPTS := -Dmain=geekos_main
    endif
    
    # ----------------------------------------------------------------------
    # Configuration -
    #   Various options specifying how GeekOS should be built,
    #   what source files to build, which user programs to build,
    #   etc.  This is generally the only section of the makefile
    #   that will need to be modified.
    # ----------------------------------------------------------------------
    
    # List of targets to build by default.
    # These targets encompass everything needed to boot
    # and run GeekOS.
    ALL_TARGETS := fd.img
    
    
    # Kernel source files
    KERNEL_C_SRCS := idt.c int.c trap.c irq.c io.c \
    	keyboard.c screen.c timer.c \
    	mem.c crc32.c \
    	gdt.c tss.c segment.c \
    	bget.c malloc.c \
    	synch.c kthread.c \
    	main.c
    
    # Kernel object files built from C source files,将KERNEL_C_SRCS中的xxx.c文件替换成xxx.o并移至当前的geekos目录下
    KERNEL_C_OBJS := $(KERNEL_C_SRCS:%.c=geekos/%.o)
    
    # Kernel assembly files
    KERNEL_ASM_SRCS := lowlevel.asm
    
    
    # Kernel object files build from assembler source files
    KERNEL_ASM_OBJS := \
      $(KERNEL_ASM_SRCS:%.asm=geekos/%.o)
    
    
    # All kernel object files，所有的内核目标文件
    KERNEL_OBJS := $(KERNEL_C_OBJS) \
      $(KERNEL_ASM_OBJS)
    
    # Common library source files.库文件
    # This library is linked into both the kernel and user programs.
    # It provides string functions and generic printf()-style
    # formatted output.
    COMMON_C_SRCS := fmtout.c string.c memmove.c
    
    # Common library object files.
    COMMON_C_OBJS := $(COMMON_C_SRCS:%.c=common/%.o)
    
    
    # Base address of kernel，内核在内存中的基址
    KERNEL_BASE_ADDR := 0x00010000
    
    # Kernel entry point function，设置内核入口
    KERNEL_ENTRY = $(SYM_PFX)Main
    
    
    # ----------------------------------------------------------------------
    # Tools -
    #   This section defines programs that are used to build GeekOS.
    # ----------------------------------------------------------------------
    
    # Uncomment if cross compiling
    #TARGET_CC_PREFIX := i386-elf-
    
    # Target C compiler.  gcc 2.95.2 or later should work.
    TARGET_CC := $(TARGET_CC_PREFIX)gcc
    
    # Host C compiler.  This is used to compile programs to execute on
    # the host platform, not the target (x86) platform.  On x86/ELF
    # systems, such as Linux and FreeBSD, it can generally be the same
    # as the target C compiler.
    HOST_CC := gcc
    
    # Target linker.  GNU ld is probably to only one that will work.各种工具
    TARGET_LD := $(TARGET_CC_PREFIX)ld
    
    # Target archiver
    TARGET_AR := $(TARGET_CC_PREFIX)ar
    
    # Target ranlib
    TARGET_RANLIB := $(TARGET_CC_PREFIX)ranlib
    
    # Target nm
    TARGET_NM := $(TARGET_CC_PREFIX)nm
    
    # Target objcopy
    TARGET_OBJCOPY := $(TARGET_CC_PREFIX)objcopy
    
    # Nasm (http://nasm.sourceforge.net)
    NASM := nasm
    
    # Tool to build PFAT filesystem images.
    BUILDFAT := tools/builtFat.exe
    
    # Perl5 or later
    PERL := perl
    
    # Pad a file so its size is a multiple of some unit (i.e., sector size)，以0填充文件使之达到要求的大小
    PAD := $(PERL) $(PROJECT_ROOT)/scripts/pad
    
    # Create a file filled with zeroes.，创建一个内容为‘0’的文件
    ZEROFILE := $(PERL) $(PROJECT_ROOT)/scripts/zerofile
    
    # Calculate size of file in sectors，以扇区计算文件
    NUMSECS := $(PERL) $(PROJECT_ROOT)/scripts/numsecs
    
    
    # ----------------------------------------------------------------------
    # Definitions -
    #   Options passed to the tools.
    # ----------------------------------------------------------------------
    
    # Flags used for all C source files，消除编译器对栈的检查
    GENERAL_OPTS := -O -Wall -fno-stack-protector $(EXTRA_C_OPTS)
    CC_GENERAL_OPTS := $(GENERAL_OPTS)   
    
    # Flags used for kernel C source files
    CC_KERNEL_OPTS := -g -DGEEKOS -I$(PROJECT_ROOT)/include
    
    # Flags user for kernel assembly files
    NASM_KERNEL_OPTS := -I$(PROJECT_ROOT)/src/geekos/ -f elf $(EXTRA_NASM_OPTS)
    
    # Flags used for common library and libc source files
    CC_USER_OPTS := -I$(PROJECT_ROOT)/include -I$(PROJECT_ROOT)/include/libc \
    	$(EXTRA_CC_USER_OPTS)
    
    # Flags passed to objcopy program (strip unnecessary sections from kernel.exe)
    OBJCOPY_FLAGS := -R .dynamic -R .note -R .comment
    
    # ----------------------------------------------------------------------
    # Rules -
    #   Describes how to compile the source files.
    # ----------------------------------------------------------------------
    
    # Compilation of kernel C source files
    #geekos/下的.o目标文件依赖.c源文件
    geekos/%.o : geekos/%.c
    	$(TARGET_CC) -c $(CC_GENERAL_OPTS) $(CC_KERNEL_OPTS) $< -o geekos/$*.o
    
    
    # Compilation of kernel assembly source files
    geekos/%.o : geekos/%.asm
    	$(NASM) $(NASM_KERNEL_OPTS) $< -o geekos/$*.o
    
    geekos/%.o : geekos/%.S
    	$(TARGET_CC) -c $(CC_GENERAL_OPTS) $(CC_KERNEL_OPTS) $< -o geekos/$*.o
    
    # Compilation of common library C source files
    common/%.o : common/%.c
    	$(TARGET_CC) -c $(CC_GENERAL_OPTS) $(CC_USER_OPTS) $< -o common/$*.o
    
    # ----------------------------------------------------------------------
    # Targets -
    #   Specifies files to be built
    # ----------------------------------------------------------------------
    
    # Default target - see definition of ALL_TARGETS in Configuration section
    all : $(ALL_TARGETS)
    
    # Standard floppy image - just boots the kernel
    fd.img : geekos/fd_boot.bin geekos/setup.bin geekos/kernel.bin
    	cat geekos/fd_boot.bin geekos/setup.bin geekos/kernel.bin > $@
    
    # Floppy boot sector (first stage boot loader).这里动态的计算setup.bin和kernel.bin占软盘扇区大小并插入到boot.asm中的变量中，以将其载入到内存中
    geekos/fd_boot.bin : geekos/setup.bin geekos/kernel.bin $(PROJECT_ROOT)/src/geekos/fd_boot.asm
    	$(NASM) -f bin \
    		-I$(PROJECT_ROOT)/src/geekos/ \
    		-DNUM_SETUP_SECTORS=`$(NUMSECS) geekos/setup.bin` \ #NUM_SETUP_SECTORS是fd_boot.asm中的变量名，在这里赋值
    		-DNUM_KERN_SECTORS=`$(NUMSECS) geekos/kernel.bin` \
    		$(PROJECT_ROOT)/src/geekos/fd_boot.asm \
    		-o $@
    
    # Setup program (second stage boot loader).
    geekos/setup.bin : geekos/kernel.exe $(PROJECT_ROOT)/src/geekos/setup.asm
    	$(NASM) -f bin \
    		-I$(PROJECT_ROOT)/src/geekos/ \
    		-DENTRY_POINT=0x`egrep 'Main$$' geekos/kernel.syms |awk '{print $$1}'` \ #ENTRY_POINT为内核的代码入口，从setup代码跳入
    		$(PROJECT_ROOT)/src/geekos/setup.asm \
    		-o $@
    	$(PAD) $@ 512
    
    # Loadable (flat) kernel image.
    geekos/kernel.bin : geekos/kernel.exe
    	$(TARGET_OBJCOPY) $(OBJCOPY_FLAGS) -S -O binary geekos/kernel.exe geekos/kernel.bin
    	$(PAD) $@ 512
    
    # The kernel executable and symbol map.
    geekos/kernel.exe : $(KERNEL_OBJS) $(COMMON_C_OBJS)
    	$(TARGET_LD) -o geekos/kernel.exe -Ttext $(KERNEL_BASE_ADDR) -e $(KERNEL_ENTRY) \
    		$(KERNEL_OBJS) $(COMMON_C_OBJS)
    	$(TARGET_NM) geekos/kernel.exe > geekos/kernel.syms
    
    # Clean build directories of generated files
    clean :
    	for d in geekos common libc user tools; do \
    		(cd $$d && rm -f *); \
    	done
    
    # Build header file dependencies, so source files are recompiled when
    # header files they depend on are modified.
    depend : $(GENERATED_LIBC_SRCS)
    	$(TARGET_CC) -M $(CC_GENERAL_OPTS) $(CC_KERNEL_OPTS) \
    		$(KERNEL_C_SRCS:%.c=$(PROJECT_ROOT)/src/geekos/%.c) \
    		| $(PERL) -n -e 's,^(\S),geekos/$$1,;print' \
    		> depend.mak
    	$(TARGET_CC) -M $(CC_GENERAL_OPTS) $(CC_USER_OPTS) \
    		$(COMMON_C_SRCS:%.c=$(PROJECT_ROOT)/src/common/%.c) \
    		| $(PERL) -n -e 's,^(\S),common/$$1,;print' \
    		>> depend.mak
    
    # By default, there are no header file dependencies.
    depend.mak :
    	touch $@
    
    include depend.mak

可以看到和sagalinux类似，生成了fd\_boot.bin,setup.bin,kernel.bin文件，并最终通过cat命令生成软盘映像。  
  
我们还是从系统启动开始看起，下一篇来分析./src/geekos/fd\_boot.asm和setup.asm源代码。

[Link 1]: http://sourceforge.net/projects/geekos/files/
[1333765757_6941.png]: https://img-my.csdn.net/uploads/201204/07/1333765757_6941.png