linux2.4.12----2.链接生在bzImage的过程分析

1.bzImage的生成过程
1.1 生成bzImage的过程分析

a. 第1步生成vmlinux,格式是ELF-32
ld -m elf_i386 -T /work/os/linux-2.4.12/arch/i386/vmlinux.lds -e stext arch/i386/kernel/head.o arch/i386/kernel/init_task.o init/main.o init/version.o \
        --start-group \
        arch/i386/kernel/kernel.o arch/i386/mm/mm.o kernel/kernel.o mm/mm.o fs/fs.o ipc/ipc.o \
         drivers/char/char.o drivers/block/block.o drivers/misc/misc.o drivers/net/net.o drivers/media/media.o drivers/char/agp/agp.o drivers/char/drm/drm.o drivers/ide/idedriver.o drivers/scsi/scsidrv.o drivers/cdrom/driver.o drivers/sound/sounddrivers.o drivers/pci/driver.o drivers/pcmcia/pcmcia.o drivers/net/pcmcia/pcmcia_net.o drivers/video/video.o drivers/usb/usbdrv.o \
        net/network.o \
        /work/os/linux-2.4.12/arch/i386/lib/lib.a /work/os/linux-2.4.12/lib/lib.a /work/os/linux-2.4.12/arch/i386/lib/lib.a \
        --end-group \
        -o vmlinux
/work/os/gcc/gcc-3.34/bin/nm vmlinux | grep -v '\(compiled\)\|\(\.o$\)\|\( [aUw] \)\|\(\.\.ng$\)\|\(LASH[RL]DI\)' | sort > System.map

b. 第2步在arch/i386/boot目录下生成bbootsect 与 bsetup
make[1]: Entering directory `/work/os/linux-2.4.12/arch/i386/boot'
/work/os/gcc/gcc-3.34/bin/gcc -E -D__KERNEL__ -I/work/os/linux-2.4.12/include -D__BIG_KERNEL__ -traditional -DSVGA_MODE=NORMAL_VGA  bootsect.S -o bbootsect.s
/work/os/gcc/gcc-3.34/bin/as -o bbootsect.o bbootsect.s
/work/os/gcc/gcc-3.34/bin/ld -m elf_i386 -Ttext 0x0 -s --oformat binary bbootsect.o -o bbootsect
/work/os/gcc/gcc-3.34/bin/gcc -E -D__KERNEL__ -I/work/os/linux-2.4.12/include -D__BIG_KERNEL__ -D__ASSEMBLY__ -traditional -DSVGA_MODE=NORMAL_VGA  setup.S -o bsetup.s
/work/os/gcc/gcc-3.34/bin/as -o bsetup.o bsetup.s
/work/os/gcc/gcc-3.34/bin/ld -m elf_i386 -Ttext 0x0 -s --oformat binary -e begtext -o bsetup bsetup.o

c.compressed目录下-->先把vmlinux用objcopy生成raw-bin格式，然后用gzip压缩生成-->piggy.o
make[2]: Entering directory `/work/os/linux-2.4.12/arch/i386/boot/compressed'
tmppiggy=_tmp_$$piggy; \
    rm -f $tmppiggy $tmppiggy.gz $tmppiggy.lnk; \
    /work/os/gcc/gcc-3.34/bin/objcopy -O binary -R .note -R .comment -S /work/os/linux-2.4.12/vmlinux $tmppiggy; \
    gzip -f -9 < $tmppiggy > $tmppiggy.gz; \
    echo "SECTIONS { .data : { input_len = .; LONG(input_data_end - input_data) input_data = .; *(.data) input_data_end = .; }}" > $tmppiggy.lnk; \
    /work/os/gcc/gcc-3.34/bin/ld -m elf_i386 -r -o piggy.o -b binary $tmppiggy.gz -b elf32-i386 -T $tmppiggy.lnk; \
    rm -f $tmppiggy $tmppiggy.gz $tmppiggy.lnk

d.compressed目录下--> 将解压头head.o与misc.o与压缩过的piggy.o连接到1M处-->bvmlinux
/work/os/gcc/gcc-3.34/bin/gcc -g -D__KERNEL__ -I/work/os/linux-2.4.12/include -Wall -Wstrict-prototypes -Wno-trigraphs -O2 -fomit-frame-pointer -fno-strict-aliasing -fno-common -pipe -mpreferred-stack-boundary=2 -march=i686 -c misc.c
/work/os/gcc/gcc-3.34/bin/ld -m elf_i386 -Ttext 0x100000 -e startup_32 -o bvmlinux head.o misc.o piggy.o
make[2]: Leaving directory `/work/os/linux-2.4.12/arch/i386/boot/compressed'

e.用objcopy对添加了解压头的compressed/bvmlinux去符号生成raw-bin格式的 -->bvmlinux.out
gcc -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -o tools/build tools/build.c -I/work/os/linux-2.4.12/include
/work/os/gcc/gcc-3.34/bin/objcopy -O binary -R .note -R .comment -S compressed/bvmlinux compressed/bvmlinux.out

f. 将arch/i386/boot下的bbootsect bsetup 与加上解压头的bvmlinux.out 合并到bzImage中
tools/build -b bbootsect bsetup compressed/bvmlinux.out CURRENT > bzImage
Root device is (8, 7)
Boot sector 512 bytes.
Setup is 2385 bytes.
System is 790 kB
make[1]: Leaving directory `/work/os/linux-2.4.12/arch/i386/boot

1.2 关于tools/build.c的作用
a. 如果没有加-b参数,则认为是普通的内核，其最大长度是#define DEF_SYSSIZE 0x7F00,内核长度最大为:7F00*16=508K
b. bbootsect-->arch/i386/boot/bootsect.S编译出来的,就是一个512字节的MBR-->写到bzImage开头
c. bsetup-->arch/i386/boot/Setup.S编译出来的-->按512个字节为单位写到bzImage中去,接着bbootsect
d. compressed/bvmlinux.out
e. CURRENT-->代表major_root与minor_root,即文件系统的设备结点-->这会写到bzImage的buf[508-509]去。



2. 各个部分的运行地址分析








附录1: tools/build.c的分析

cong@msi:/work/os/linux-2.4.12/arch/i386/boot$ cat tools/build.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdarg.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <unistd.h>
#include <fcntl.h>
#include <asm/boot.h>

typedef unsigned char byte;
typedef unsigned short word;
typedef unsigned long u32;

#define DEFAULT_MAJOR_ROOT 0
#define DEFAULT_MINOR_ROOT 0

/* Minimal number of setup sectors (see also bootsect.S) */
#define SETUP_SECTS 4

byte buf[1024];
int fd;
int is_big_kernel;

void die(const char * str, ...)
{
    va_list args;
    va_start(args, str);
    vfprintf(stderr, str, args);
    fputc('\n', stderr);
    exit(1);
}
//对open进行封装
void file_open(const char *name)
{
    if ((fd = open(name, O_RDONLY, 0)) < 0)
        die("Unable to open `%s': %m", name);
}

void usage(void)
{
    die("Usage: build [-b] bootsect setup system [rootdev] [> image]");
}

int main(int argc, char ** argv)
{
    unsigned int i, c, sz, setup_sectors;
    u32 sys_size;
    byte major_root, minor_root;
    struct stat sb;

    if (argc > 2 && !strcmp(argv[1], "-b"))
    {
         is_big_kernel = 1;    //-b的意思是big，有了-b说明允许生成超过508K的内核
         argc--, argv++;
    }
    if ((argc < 4) || (argc > 5))
        usage();
//下面这个if是确定major_root与minor_root，即确定rootfs是在哪个设备上
    if (argc > 4) {
        if (!strcmp(argv[4], "CURRENT")) {
            if (stat("/", &sb)) {
                perror("/");
                die("Couldn't stat /");
            }
            major_root = major(sb.st_dev);
            minor_root = minor(sb.st_dev);
        } else if (strcmp(argv[4], "FLOPPY")) {
            if (stat(argv[4], &sb)) {
                perror(argv[4]);
                die("Couldn't stat root device.");
            }
            major_root = major(sb.st_rdev);
            minor_root = minor(sb.st_rdev);
        } else {
            major_root = 0;
            minor_root = 0;
        }
    } else {
        major_root = DEFAULT_MAJOR_ROOT;
        minor_root = DEFAULT_MINOR_ROOT;
    }
    fprintf(stderr, "Root device is (%d, %d)\n", major_root, minor_root);
//第1步-->打开512个字节的bootsect，然后写到bzImage的开头,bootsect的位置[0-0x200]
    file_open(argv[1]);
    i = read(fd, buf, sizeof(buf));
    fprintf(stderr,"Boot sector %d bytes.\n",i);
    if (i != 512)
        die("Boot block must be exactly 512 bytes");
    if (buf[510] != 0x55 || buf[511] != 0xaa)               -->0x55aa启动标志
        die("Boot block hasn't got boot flag (0xAA55)");
    buf[508] = minor_root;                                  -->将rootfs设备号写到508,509处
    buf[509] = major_root;
    if (write(1, buf, 512) != 512)                          -->修改好buf之后真正的写在bzImage上
        die("Write call failed");
    close (fd);

//第2步-->把setup写到bzImage中,不足一个扇区部分的补0。setup紧接着bootsect-->setup的位置[0x200-0x200*n]
    file_open(argv[2]);                 /* Copy the setup code */
    for (i=0 ; (c=read(fd, buf, sizeof(buf)))>0 ; i+=c )   //把setup写到bzImage中
        if (write(1, buf, c) != c)
            die("Write call failed");
    if (c != 0)
        die("read-error on `setup'");
    close (fd);
    setup_sectors = (i + 511) / 512;    /* Pad unused space with zeros */
    /* for compatibility with ancient versions of LILO. */
    if (setup_sectors < SETUP_SECTS)      //不到4个扇区凑够4个扇区
        setup_sectors = SETUP_SECTS;
    fprintf(stderr, "Setup is %d bytes.\n", i);
    memset(buf, 0, sizeof(buf));
    while (i < setup_sectors * 512) {        //把不到1个扇区的内容补0
        c = setup_sectors * 512 - i;
        if (c > sizeof(buf))
            c = sizeof(buf);
        if (write(1, buf, c) != c)
            die("Write call failed");
        i += c;
    }

//第3步-->把bvmlinux.out写到bzImage中。vmlinux紧接着sectup
    file_open(argv[3]);
    if (fstat (fd, &sb))
        die("Unable to stat `%s': %m", argv[3]);
    sz = sb.st_size;
    fprintf (stderr, "System is %d kB\n", sz/1024);
    sys_size = (sz + 15) / 16;
    /* 0x28000*16 = 2.5 MB, conservative estimate for the current maximum */
    if (sys_size > (is_big_kernel ? 0x28000 : DEF_SYSSIZE))         -->普通内核508K,bzImage的内核可达2.5M
        die("System is too big. Try using %smodules.", is_big_kernel ? "" : "bzImage or ");
    if (sys_size > 0xefff)
        fprintf(stderr,"warning: kernel is too big for standalone boot " "from floppy\n");
    while (sz > 0) {
        int l, n;

        l = (sz > sizeof(buf)) ? sizeof(buf) : sz;
        if ((n=read(fd, buf, l)) != l) {
            if (n < 0)
                die("Error reading %s: %m", argv[3]);
            else
                die("%s: Unexpected EOF", argv[3]);
        }
        if (write(1, buf, l) != l)
            die("Write failed");
        sz -= l;
    }
    close(fd);
//到bootsect中写入一些值
    if (lseek(1, 497, SEEK_SET) != 497)         /* Write sizes to the bootsector */
        die("Output: seek failed");
    buf[0] = setup_sectors;                      -->497字节是setup的sector数目
    if (write(1, buf, 1) != 1)
        die("Write of setup sector count failed");
    if (lseek(1, 500, SEEK_SET) != 500)          -->500字节是bvmliux.out的字节数/16的大小
        die("Output: seek failed");
    buf[0] = (sys_size & 0xff);
    buf[1] = ((sys_size >> 8) & 0xff);
    if (write(1, buf, 2) != 2)
        die("Write of image length failed");

    return 0;                     /* Everything is OK */
}

a. 说明--> 这是./arch/i386/boot/bzImage的前512个字节的最后

b. 0005是setup的扇区数
cong@msi:/work/os/linux-2.4.12$ ls arch/i386/boot/bsetup -l
-rwxrwxr-x 1 cong cong 2385 Oct 29 10:10 arch/i386/boot/bsetup
(2385+512)/512=5
c. b4c5 0000 是vmlinux.out的segment数
cong@msi:/work/os/linux-2.4.12$ ls arch/i386/boot/compressed/bvmlinux.out  -l
-rwxrwxr-x 1 cong cong 809790 Oct 29 10:10 arch/i386/boot/compressed/bvmlinux.out
(809790+15)/16=50612=C5B4