FLOPPY BOOT SECTOR

本文深入解析了一段用于读取软盘引导扇区的C语言代码,详细介绍了其内部结构和工作流程。
 

/*FLOPPY BOOT SECTOR */
/*       BY     /*
/*   A K A S H*/ 


#include<stdio.h>
#include<dos.h>
#include<conio.h>
typedef unsigned char       BYTE;
typedef unsigned short      WORD;
typedef struct boot
{
  BYTE jump [3];
  char bsOemName [8];
  WORD bytesperSector;
  BYTE sectorspercluster;
  WORD sectorsreservedarea;
  BYTE copiesFAT;
  WORD maxrootdirentries;
  WORD totalSectors;
  BYTE mediaDescriptor;
  WORD sectorsperFAT;
  WORD sectorsperTrack;
  WORD sides;
  WORD hiddenSectors;
  char reserve [480];
};
void main()
{
 clrscr();
 boot rd;
 asm{
 mov dl,0x00
 mov ah,0x00
 int 0x13
 mov dl,0x00
 mov ah,0x01
 int 0x13
 jc next1
 mov dl,0x00
 mov ah,0x02
 mov al,0x01
 mov ch,0x00
 mov cl,0x01
 mov dh,0x00
 lea bx,rd
 int 0x13
 jc next2
 };

 printf("\n\t\t-------------Floppy Boot Sector-------------");
 printf("\n\t\t--------------------B-Y---------------------");
 printf("\n\t\t----------------*A-K-A-S-H*-----------------");
 printf("\n\t\t____________________________________________\n\n\n\n");

 printf("\n\t\t\tJMP instruction:%X%X%X",rd.jump[0],rd.jump[1],rd.jump[2]);
 printf("\n\t\t\t----------------------");
 printf("\n\t\t\tOEM: %s",rd.bsOemName);
 printf("\n\t\t\t-------------");
 printf("\n\t\t\tBytes/Sector:%4d",rd.bytesperSector);
 printf("\n\t\t\t----------------");
 printf("\n\t\t\tSec/Cluster:%X",rd.sectorspercluster);
 printf("\n\t\t\t---------------");
 printf("\n\t\t\tNum Fat:%X",rd.copiesFAT);
 printf("\n\t\t\t----------");
 printf("\n\t\t\tRoot Entry:%4d",rd.maxrootdirentries);
 printf("\n\t\t\t----------------");
 printf("\n\t\t\tTotal Secotrs:%4d",rd.totalSectors);
 printf("\n\t\t\t-------------------");
 printf("\n\t\t\tMedia Desc:%X",rd.mediaDescriptor);
 printf("\n\t\t\t-------------");
 printf("\n\t\t\tSectors/FAT:%4d",rd.sectorsperFAT);
 printf("\n\t\t\t-----------------");
 printf("\n\t\t\tSectors/TRACK:%4d",rd.sectorsperTrack);
 printf("\n\t\t\t-------------------");
 printf("\n\t\t\tSides:%4d",rd.sides);
 printf("\n\t\t\t-----------");
 printf("\n\t\t\tHidden Sector:%4d",rd.hiddenSectors);
 printf("\n\t\t\t-------------------");
 goto end;

next1: printf("\nError: Drive not ready");
 goto end;

next2:
 printf("\nError: Drive cant read");
end:
 getch();
}

 


 

# 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 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 KERNEL_OBJS := $(KERNEL_C_OBJS) \ $(KERNEL_ASM_OBJS) # Common library source files. # 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 KERNEL_BASE_ADDR := 0x00010000 # Kernel entry point function 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. 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) PAD := $(PERL) $(PROJECT_ROOT)/scripts/pad # Create a file filled with zeroes. ZEROFILE := $(PERL) $(PROJECT_ROOT)/scripts/zerofile # Calculate size of file in sectors NUMSECS := $(PERL) $(PROJECT_ROOT)/scripts/numsecs # ---------------------------------------------------------------------- # Definitions - # Options passed to the tools. # ---------------------------------------------------------------------- # Flags used for all C source files GENERAL_OPTS := -O -Wall $(EXTRA_C_OPTS) CC_GENERAL_OPTS := $(GENERAL_OPTS) -Werror # Flags used for kernel C source files CC_KERNEL_OPTS := -g -DGEEKOS -I$(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/%.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). 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=`$(NUMSECS) geekos/setup.bin` \ -DNUM_KERN_SECTORS=`$(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}'` \ $(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 在哪里修改
05-30
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