此篇博客有很多参考其他文章的内容，由于参考内容繁杂，不一一标注角标了，在末尾会贴上所有参考博客的link，如有侵权，请联系本人处理，谢谢。
深入，并且广泛
-沉默犀牛step1 从哪里开始执行，目前还不清楚，不作分析了。
step2 Bootloader（LK）
LK的代码在bootable/bootloader/lk目录下
在 bootable/bootloadler/lk/arch/arm/ssystem-onesegment.ld 连接文件中ENTRY（_start）指定 LK 从_start 函数开始，_start 在 lk/arch/crt0.S中，下面我们来看一下这个文件中的内容：
.globl _start
_start: //这里就是ENTRY(_start)中的_start
...
/*启动CPU*/
这里的指令都是有关CPU初始化的一些指令，不展开了
/* we are relocated, jump to the right address */
ldrr0, =.Lstack_setup
...
.Lstack_setup:
/*为irq、fiq、abort、undefined、system/user和last supervisor模式设置堆栈*/
/* 清除BSS *
bl kmain //注意这里！上文说过bootloader分为stage1和stage2，从这个汇编文件来看，应该已经包含了stage1，和stage2。只是stage2还没有结束，kmain也算是stage2里面的一部分。如果这里理解有误，请留言告知，感激不尽。
汇编中的最后一个有注释的指令bl kmain，跳转到了如下的代码中，代码路径为 lk/kernel/main.c
void kmain(void) __NO_RETURN __EXTERNALLY_VISIBLE;
void kmain(void) {
thread_t *thr;
thread_init_early(); //初始化thread（lk 中的简单进程）相关结构体。
arch_early_init(); //做一些如 关闭 cache，使能 mmu 的 arm 相关工作。
platform_early_init(); // 相关平台的早期初始化
target_early_init(); // 现在就一个函数跳转，初始化UART（板子相关）
dprintf(INFO, "welcome to lk\n\n");
bs_set_timestamp(BS_BL_START);
dprintf(SPEW, "calling constructors\n");
call_constructors();
dprintf(SPEW, "initializing heap\n");
heap_init(); // lk系统相关的堆栈初始化
__stack_chk_guard_setup();
dprintf(SPEW, "initializing threads\n");
thread_init(); // 线程初始化
dprintf(SPEW, "initializing dpc\n");
dpc_init(); // lk系统控制器初始化（相关事件初始化）
dprintf(SPEW, "initializing timers\n");
timer_init(); // 初始化lk中的定时器
#if (!ENABLE_NANDWRITE)
dprintf(SPEW, "creating bootstrap completion thread\n");
thr = thread_create("bootstrap2",&bootstrap2, NULL, DEFAULT_PRIORITY, DEFAULT_STACK_SIZE); // 新建线程入口函数
if (!thr) {
panic("failed to create thread bootstrap2\n");
}thread_resume(thr);
exit_critical_section(); // 使能中断
thread_become_idle(); // 使自己成为idle进程
#else //对应上面的#if (!ENABLE_NANDWRITE) ，我们一般走if，不会走else
bootstrap_nandwrite();
#endif
}这里可以看到，kmain主要做了两件事：1.本身lk的初始化 2.boot启动初始化
以上与 boot 启动初始化相关函数是arch_early_init、platform_early_init 、bootstrap2，这些是启动的重点，我们下面慢慢来看。
arch_early_init
void arch_early_init(void)
{
/* turn off the cache */
arch_disable_cache(UCACHE); // 关闭 cache
/* set the vector base to our exception vectors so we dont need to double map at 0 */
#if ARM_CPU_CORTEX_A8
set_vector_base(MEMBASE); //设置异常向量基地址
#endif
#if ARM_WITH_MMU
arm_mmu_init(); //初始化MMU
#endif
/* turn the cache back on */
arch_enable_cache(UCACHE); /*开启cache */
#if ARM_WITH_NEON
/* enable cp10 and cp11 */
/* 使能 cp10 和 cp11*/
uint32_t val;
__asm__ volatile("mrc p15, 0, %0, c1, c0, 2" : "=r" (val));
val |= (3<<22)|(3<<20);
__asm__ volatile("mcr p15, 0, %0, c1, c0, 2" :: "r" (val));
isb();
/* set enable bit in fpexc */
/*设置使能 fpexc 位（中断相关）*/
__asm__ volatile("mrc p10, 7, %0, c8, c0, 0" : "=r" (val));
val |= (1<<30);
__asm__ volatile("mcr p10, 7, %0, c8, c0, 0" :: "r" (val));
#endif
#if ARM_CPU_CORTEX_A8
/* enable the cycle count register */
/* 使能循环计数寄存器 */
uint32_t en;
__asm__ volatile("mrc p15, 0, %0, c9, c12, 0" : "=r" (en));
en &= ~(1<<3); /*循环计算每个周期*/
en |= 1; /* 启动所有的 performance 计数器 */
__asm__ volatile("mcr p15, 0, %0, c9, c12, 0" :: "r" (en));
/* enable cycle counter */
en = (1<<31);
__asm__ volatile("mcr p15, 0, %0, c9, c12, 1" :: "r" (en));
#endif
}platform_early_init
void platform_early_init(void)
{
/* initialize the interrupt controller */
/*1.初始化中断*/
platform_init_interrupts();
/* initialize the timer block */
/*初始化定时器*/
platform_init_timer();
}
bootstrap2
static int bootstrap2(void *arg)
{
dprintf(SPEW, "top of bootstrap2()\n");
arch_init(); //此函数为空
// XXX put this somewhere else
#if WITH_LIB_BIO
bio_init();
#endif
#if WITH_LIB_FS
fs_init();
#endif
// initialize the rest of the platform
dprintf(SPEW, "initializing platform\n");
platform_init(); // 平台初始化,不同的平台要做的事情不一样，可以是初始化系统时钟,超频等
// initialize the target
dprintf(SPEW, "initializing target\n");
target_init(); //目标设备初始化,主要初始化Flash,整合分区表等
dprintf(SPEW, "calling apps_init()\n");
apps_init();//应用功能初始化，主要调用aboot_init，启动kernel，加载boot/recovery镜像等
return 0;
}platform_init 中主要是函数 acpu_clock_init，在 acpu_clock_init 对 arm11 进行系统时钟设置，超频 。
target_init 针对硬件平台进行设置。主要对 arm9 和 arm11 的分区表进行整合，初始化flash和读取FLASH信息。
apps_init 是关键，对 LK 中所有 app 初始化并运行起来，而 aboot_init 就将在这里开始被运行，android linux 内核的加载工作就在 aboot_init 中完成的 。
void apps_init(void)
{
const struct app_descriptor *app;
/* call all the init routines */
for (app = &__apps_start; app != &__apps_end; app++) {
if (app->init) //如果app有init成员，就执行app->init
app->init(app);
}
/* start any that want to start on boot */
for (app = &__apps_start; app != &__apps_end; app++) {
if (app->entry && (app->flags & APP_FLAG_DONT_START_ON_BOOT) == 0) {
start_app(app);
}
}
}apps_init()的逻辑很简单，可以猜测aboot_init一定是aboot->init，for循环轮到aboot的时候，就自然调用了aboot_init。
以下代码也证实了我们的猜测：
APP_START(aboot) // 增加一个name为aboot的app
.init = aboot_init, //该app的ini赋值为aboot_init
APP_END
接下来是真正的重头戏：aboot_init()
void aboot_init(const struct app_descriptor *app)
{
unsigned reboot_mode = 0;
int boot_err_type = 0;
int boot_slot = INVALID;
/* Initialise wdog to catch early lk crashes */
#if WDOG_SUPPORT
msm_wdog_init();
#endif
/* Setup page size information for nv storage */
if (target_is_emmc_boot()) //检测是emmc还是flash存储，并设置页大小，一般是2048
{
page_size = mmc_page_size();
page_mask = page_size - 1;
mmc_blocksize = mmc_get_device_blocksize();
mmc_blocksize_mask = mmc_blocksize - 1;
}
else
{
page_size = flash_page_size();
page_mask = page_size - 1;
}
ASSERT((MEMBASE + MEMSIZE) > MEMBASE); //断言，如果内存基地址+内存大小小于内存基地址，则直接终止错误
read_device_info(&device); //从devinfo分区表read data到device结构体
read_allow_oem_unlock(&device); //devinfo分区里记录了unlock状态，从device中读取此信息
/* Detect multi-slot support */
if (partition_multislot_is_supported())
{
boot_slot = partition_find_active_slot();
if (boot_slot == INVALID)
{
boot_into_fastboot = true;
dprintf(INFO, "Active Slot: (INVALID)\n");
}
else
{
/* Setting the state of system to boot active slot */
partition_mark_active_slot(boot_slot);
dprintf(INFO, "Active Slot: (%s)\n", SUFFIX_SLOT(boot_slot));
}
}
/* Display splash screen if enabled */
#if DISPLAY_SPLASH_SCREEN
#if NO_ALARM_DISPLAY
if (!check_alarm_boot()) {
#endif
dprintf(SPEW, "Display Init: Start\n");
#if DISPLAY_HDMI_PRIMARY
if (!strlen(device.display_panel))
strlcpy(device.display_panel, DISPLAY_PANEL_HDMI,
sizeof(device.display_panel));
#endif
#if ENABLE_WBC
/* Wait if the display shutdown is in progress */
while(pm_app_display_shutdown_in_prgs());
if (!pm_appsbl_display_init_done())
target_display_init(device.display_panel);//显示splash，Splash也就是应用程序启动之前先启动一个画面,上面简单的介绍应用程序的厂商,厂商的LOGO,名称和版本等信息,多为一张图片
else
display_image_on_screen();
#else
target_display_init(device.display_panel);
#endif
dprintf(SPEW, "Display Init: Done\n");
#if NO_ALARM_DISPLAY
}
#endif
#endif
target_serialno((unsigned char *) sn_buf);
dprintf(SPEW,"serial number: %s\n",sn_buf);
memset(display_panel_buf, '\0', MAX_PANEL_BUF_SIZE);
/*
* Check power off reason if user force reset,
* if yes phone will do normal boot.
*/
if (is_user_force_reset()) //如果强制重启，直接进入normal_boot
goto normal_boot;
/* Check if we should do something other than booting up */
if (keys_get_state(KEY_VOLUMEUP) && keys_get_state(KEY_VOLUMEDOWN)) //如果按下音量上下键，boot_init_fastboot = ture
{
dprintf(ALWAYS,"dload mode key sequence detected\n");
reboot_device(EMERGENCY_DLOAD);
dprintf(CRITICAL,"Failed to reboot into dload mode\n");
boot_into_fastboot = true;
}
if (!boot_into_fastboot)
{
if (keys_get_state(KEY_HOME) || keys_get_state(KEY_VOLUMEUP)) //按下home+音量上 boot_into_recovery = 1
boot_into_recovery = 1;
if (!boot_into_recovery &&
(keys_get_state(KEY_BACK) || keys_get_state(KEY_VOLUMEDOWN))) //按下back+音量下，boot_into_fastboot = true
boot_into_fastboot = true;
}
#if NO_KEYPAD_DRIVER
if (fastboot_trigger())
boot_into_fastboot = true;
#endif
#if USE_PON_REBOOT_REG
reboot_mode = check_hard_reboot_mode();
#else
reboot_mode = check_reboot_mode(); //检测开机原因，修改相应的标志位
#endif
if (reboot_mode == RECOVERY_MODE)
{
boot_into_recovery = 1;
}
else if(reboot_mode == FASTBOOT_MODE)
{
boot_into_fastboot = true;
}
else if(reboot_mode == ALARM_BOOT)
{
boot_reason_alarm = true;
}
#if VERIFIED_BOOT
else if (VB_M <= target_get_vb_version())
{
if (reboot_mode == DM_VERITY_ENFORCING)
{
device.verity_mode = 1;
write_device_info(&device);
}
#if ENABLE_VB_ATTEST
else if (reboot_mode == DM_VERITY_EIO)
#else
else if (reboot_mode == DM_VERITY_LOGGING)
#endif
{
device.verity_mode = 0;
write_device_info(&device);
}
else if (reboot_mode == DM_VERITY_KEYSCLEAR)
{
if(send_delete_keys_to_tz())
ASSERT(0);
}
}
#endif
normal_boot: //正常boot
if (!boot_into_fastboot)
{
if (target_is_emmc_boot())
{
if(emmc_recovery_init())
dprintf(ALWAYS,"error in emmc_recovery_init\n");
if(target_use_signed_kernel())
{
if((device.is_unlocked) || (device.is_tampered))
{
#ifdef TZ_TAMPER_FUSE
set_tamper_fuse_cmd(HLOS_IMG_TAMPER_FUSE);
#endif
#if USE_PCOM_SECBOOT
set_tamper_flag(device.is_tampered);
#endif
}
}
retry_boot:
/* Trying to boot active partition */
if (partition_multislot_is_supported())
{
boot_slot = partition_find_boot_slot();
partition_mark_active_slot(boot_slot);
if (boot_slot == INVALID)
goto fastboot;
}
boot_err_type = boot_linux_from_mmc(); //单独分析这个函数，很重要
switch (boot_err_type)
{
case ERR_INVALID_PAGE_SIZE:
case ERR_DT_PARSE:
case ERR_ABOOT_ADDR_OVERLAP:
case ERR_INVALID_BOOT_MAGIC:
if(partition_multislot_is_supported())
{
/*
* Deactivate current slot, as it failed to
* boot, and retry next slot.
*/
partition_deactivate_slot(boot_slot);
goto retry_boot;
}
else
break;
default:
break;
/* going to fastboot menu */
}
}
else
{
recovery_init();
#if USE_PCOM_SECBOOT
if((device.is_unlocked) || (device.is_tampered))
set_tamper_flag(device.is_tampered);
#endif
boot_linux_from_flash();
}
dprintf(CRITICAL, "ERROR: Could not do normal boot. Reverting "
"to fastboot mode.\n");
}
fastboot: //下面的代码是fastboot的准备工作，从中可以看出，进入fastboot模式是不启动kernel的
/* We are here means regular boot did not happen. Start fastboot. */
/* register aboot specific fastboot commands */
aboot_fastboot_register_commands(); //此函数是fastboot支持的命令，如flash、erase等等
/* dump partition table for debug info */
partition_dump();
/* initialize and start fastboot */
fastboot_init(target_get_scratch_address(), target_get_max_flash_size()); //初始化fastboot
#if FBCON_DISPLAY_MSG
display_fastboot_menu(); //显示fastboot界面
#endif
}device_info是一个用来存放某些信息的结构体：
struct device_info
{
unsigned char magic[DEVICE_MAGIC_SIZE];
bool is_unlocked;
bool is_tampered;
bool is_verified;
bool charger_screen_enabled;
char display_panel[MAX_PANEL_ID_LEN];
char bootloader_version[MAX_VERSION_LEN];
char radio_version[MAX_VERSION_LEN];
};devinfo
Device information including:iis_unlocked, is_tampered, is_verified, charger_screen_enabled, display_panel, bootloader_version, radio_version， All these attirbutes are set based on some specific conditions and written on devinfo partition.
从以上的源码分析中，aboot_init()所做的工作大致如下：
1).确定page_size大小;
2).从devinfo分区获取devinfo信息;
3).通过不同按键选择设置对应标志位boot_into_xxx;
4).如果进入fastboot模式，初始化fastboot命令等。
5).进入boot_linux_from_mmc()函数。
程序走到这，说明没有进入fastboot模式，可能的情况有：正常启动，进入recovery，开机闹钟启动。
boot_linux_from_mmc()主要做下面的事情
1).程序会从boot分区或者recovery分区的header中读取地址等信息，然后把kernel、ramdisk加载到内存中。
2).程序会从misc分区中读取bootloader_message结构体，如果有boot-recovery，则进入recovery模式
3).更新cmdline，然后把cmdline写到tags_addr地址，把参数传给kernel，kernel起来以后会到这个地址读取参数。
int boot_linux_from_mmc(void)
{
//首先创建一个用来保存boot.img文件头信息的变量hdr，buf是一个4096byte的数组，hdr和hdr指向了同一个内存地址
struct boot_img_hdr *hdr = (void*) buf;
struct boot_img_hdr *uhdr;
unsigned offset = 0;
int rcode;
unsigned long long ptn = 0;
int index = INVALID_PTN;
unsigned char *image_addr = 0;
unsigned kernel_actual;
unsigned ramdisk_actual;
unsigned imagesize_actual;
unsigned second_actual = 0;
unsigned int dtb_size = 0;
unsigned int out_len = 0;
unsigned int out_avai_len = 0;
unsigned char *out_addr = NULL;
uint32_t dtb_offset = 0;
unsigned char *kernel_start_addr = NULL;
unsigned int kernel_size = 0;
unsigned int patched_kernel_hdr_size = 0;
int rc;
#if VERIFIED_BOOT_2
int status;
#endif
char *ptn_name = NULL;
#if DEVICE_TREE
struct dt_table *table;
struct dt_entry dt_entry;
unsigned dt_table_offset;
uint32_t dt_actual;
uint32_t dt_hdr_size;
unsigned char *best_match_dt_addr = NULL;
#endif
struct kernel64_hdr *kptr = NULL;
int current_active_slot = INVALID;
if (check_format_bit()) //执行check_format_bit，根据bootselect分区信息判断是否进入recovery模式
boot_into_recovery = 1;
//此时有两种可能，正常开机/进入ffbm（工厂测试）模式，进入ffbm模式是正行启动，但是向kernel传参会多一个字符
//串"androidboot.mode='ffbm_mode_string'"
if (!boot_into_recovery) {
memset(ffbm_mode_string, '\0', sizeof(ffbm_mode_string));
rcode = get_ffbm(ffbm_mode_string, sizeof(ffbm_mode_string));
if (rcode <= 0) {
boot_into_ffbm = false;
if (rcode < 0)
dprintf(CRITICAL,"failed to get ffbm cookie");
} else
boot_into_ffbm = true;
} else
boot_into_ffbm = false;
uhdr = (struct boot_img_hdr *)EMMC_BOOT_IMG_HEADER_ADDR; //uhdr指向boot分区header地址
if (!memcmp(uhdr->magic, BOOT_MAGIC, BOOT_MAGIC_SIZE)) { // //检查uhdr->magic 是否等于 "ANDROID!"
dprintf(INFO, "Unified boot method!\n");
hdr = uhdr;
goto unified_boot;
}
if (boot_into_recovery &&
(!partition_multislot_is_supported()))
ptn_name = "recovery"; 支持recovery分区
else
ptn_name = "boot"; //支持boot分区
index = partition_get_index(ptn_name); //读取对应分区
ptn = partition_get_offset(index); //读取对应分区的偏移量
if(ptn == 0) {
dprintf(CRITICAL, "ERROR: No %s partition found\n", ptn_name);
return -1;
}
/* Set Lun for boot & recovery partitions */
mmc_set_lun(partition_get_lun(index)); //调用mmc_set_lun设置boot或recovery分区的lun号
//调用mmc_read，从boot或者recovery分区读取1字节的内容到buf(hdr)中
//我们知道在boot/recovery中开始的1字节存放的是hdr的内容
if (mmc_read(ptn + offset, (uint32_t *) buf, page_size)) {
dprintf(CRITICAL, "ERROR: Cannot read boot image header\n");
return -1;
}
//上面已经从boot/recovery分区读取了header到hdr，这里对比magic是否等于"ANDROID！"
//如果不是，则表明读取的header是错误的，也算是校验吧
if (memcmp(hdr->magic, BOOT_MAGIC, BOOT_MAGIC_SIZE)) {
dprintf(CRITICAL, "ERROR: Invalid boot image header\n");
return ERR_INVALID_BOOT_MAGIC;
}
//比较也的大小是否相同（应该都是相同的2048字节），判断是否需要更新页大小。
if (hdr->page_size && (hdr->page_size != page_size)) {
if (hdr->page_size > BOOT_IMG_MAX_PAGE_SIZE) {
dprintf(CRITICAL, "ERROR: Invalid page size\n");
return -1;
}
page_size = hdr->page_size;
page_mask = page_size - 1;
}
//kernel、ramdisk，second大小向上页对齐
kernel_actual = ROUND_TO_PAGE(hdr->kernel_size, page_mask);
ramdisk_actual = ROUND_TO_PAGE(hdr->ramdisk_size, page_mask);
second_actual = ROUND_TO_PAGE(hdr->second_size, page_mask);
image_addr = (unsigned char *)target_get_scratch_address();
memcpy(image_addr, (void *)buf, page_size);
/* ensure commandline is terminated */
hdr->cmdline[BOOT_ARGS_SIZE-1] = 0;
#if DEVICE_TREE //如果有DEVICE_TREE
#ifndef OSVERSION_IN_BOOTIMAGE
dt_size = hdr->dt_size;
#endif
dt_actual = ROUND_TO_PAGE(dt_size, page_mask); //计算出dt所占的页的大小
if (UINT_MAX < ((uint64_t)kernel_actual + (uint64_t)ramdisk_actual+ (uint64_t)second_actual + (uint64_t)dt_actual + page_size)) {
dprintf(CRITICAL, "Integer overflow detected in bootimage header fields at %u in %s\n",__LINE__,__FILE__);
return -1;
}
// image占的页的总大小
imagesize_actual = (page_size + kernel_actual + ramdisk_actual + second_actual + dt_actual);
#else
if (UINT_MAX < ((uint64_t)kernel_actual + (uint64_t)ramdisk_actual + (uint64_t)second_actual + page_size)) {
dprintf(CRITICAL, "Integer overflow detected in bootimage header fields at %u in %s\n",__LINE__,__FILE__);
return -1;
}
imagesize_actual = (page_size + kernel_actual + ramdisk_actual + second_actual);
#endif
#if VERIFIED_BOOT
boot_verifier_init(); //初始化boot.img的鉴权，读取OEM 和User Keystore（即校验boot）
#endif
//检查boot.img是否与aboot的内存空间有重叠
if (check_aboot_addr_range_overlap((uintptr_t) image_addr, imagesize_actual))
{
dprintf(CRITICAL, "Boot image buffer address overlaps with aboot addresses.\n");
return -1;
}
/*
* Update loading flow of bootimage to support compressed/uncompressed
* bootimage on both 64bit and 32bit platform.
* 1. Load bootimage from emmc partition onto DDR.
* 2. Check if bootimage is gzip format. If yes, decompress compressed kernel
* 3. Check kernel header and update kernel load addr for 64bit and 32bit
* platform accordingly.
* 4. Sanity Check on kernel_addr and ramdisk_addr and copy data.
*/
if (partition_multislot_is_supported())
{
current_active_slot = partition_find_active_slot();
dprintf(INFO, "Loading boot image (%d) active_slot(%s): start\n",
imagesize_actual, SUFFIX_SLOT(current_active_slot));
}
else
{
dprintf(INFO, "Loading (%s) image (%d): start\n",
(!boot_into_recovery ? "boot" : "recovery"),imagesize_actual);
}
bs_set_timestamp(BS_KERNEL_LOAD_START);
if ((target_get_max_flash_size() - page_size) < imagesize_actual)
{
dprintf(CRITICAL, "booimage size is greater than DDR can hold\n");
return -1;
}
offset = page_size;
/* Read image without signature and header*/
if (mmc_read(ptn + offset, (void *)(image_addr + offset), imagesize_actual - page_size))
{
dprintf(CRITICAL, "ERROR: Cannot read boot image\n");
return -1;
}
if (partition_multislot_is_supported())
{
dprintf(INFO, "Loading boot image (%d) active_slot(%s): done\n",
imagesize_actual, SUFFIX_SLOT(current_active_slot));
}
else
{
dprintf(INFO, "Loading (%s) image (%d): done\n",
(!boot_into_recovery ? "boot" : "recovery"),imagesize_actual);
}
bs_set_timestamp(BS_KERNEL_LOAD_DONE);
/* Authenticate Kernel */
dprintf(INFO, "use_signed_kernel=%d, is_unlocked=%d, is_tampered=%d.\n",
(int) target_use_signed_kernel(),
device.is_unlocked,
device.is_tampered);
#if VERIFIED_BOOT_2
offset = imagesize_actual;
if (check_aboot_addr_range_overlap((uintptr_t)image_addr + offset, page_size))
{
dprintf(CRITICAL, "Signature read buffer address overlaps with aboot addresses.\n");
return -1;
}
/* Read signature */
if(mmc_read(ptn + offset, (void *)(image_addr + offset), page_size))
{
dprintf(CRITICAL, "ERROR: Cannot read boot image signature\n");
return -1;
}
memset(&info, 0, sizeof(bootinfo));
info.images[0].image_buffer = image_addr;
info.images[0].imgsize = imagesize_actual;
info.images[0].name = "boot";
info.num_loaded_images = 0;
info.multi_slot_boot = partition_multislot_is_supported();
info.bootreason_alarm = boot_reason_alarm;
info.bootinto_recovery = boot_into_recovery;
status = load_image_and_auth(&info);
if(status)
return -1;
vbcmdline = info.vbcmdline;
#else
/* Change the condition a little bit to include the test framework support.
* We would never reach this point if device is in fastboot mode, even if we did
* that means we are in test mode, so execute kernel authentication part for the
* tests */
if((target_use_signed_kernel() && (!device.is_unlocked)) || is_test_mode_enabled()) //这里是false
{
offset = imagesize_actual;
if (check_aboot_addr_range_overlap((uintptr_t)image_addr + offset, page_size))
{
dprintf(CRITICAL, "Signature read buffer address overlaps with aboot addresses.\n");
return -1;
}
/* Read signature */
if(mmc_read(ptn + offset, (void *)(image_addr + offset), page_size))
{
dprintf(CRITICAL, "ERROR: Cannot read boot image signature\n");
return -1;
}
verify_signed_bootimg((uint32_t)image_addr, imagesize_actual);
/* The purpose of our test is done here */
if(is_test_mode_enabled() && auth_kernel_img)
return 0;
} else {
second_actual = ROUND_TO_PAGE(hdr->second_size, page_mask);
#ifdef TZ_SAVE_KERNEL_HASH
aboot_save_boot_hash_mmc((uint32_t) image_addr, imagesize_actual);
#endif /* TZ_SAVE_KERNEL_HASH */
#ifdef MDTP_SUPPORT
{
/* Verify MDTP lock.
* For boot & recovery partitions, MDTP will use boot_verifier APIs,
* since verification was skipped in aboot. The signature is not part of the loaded image.
*/
mdtp_ext_partition_verification_t ext_partition;
ext_partition.partition = boot_into_recovery ? MDTP_PARTITION_RECOVERY : MDTP_PARTITION_BOOT;
ext_partition.integrity_state = MDTP_PARTITION_STATE_UNSET;
ext_partition.page_size = page_size;
ext_partition.image_addr = (uint32)image_addr;
ext_partition.image_size = imagesize_actual;
ext_partition.sig_avail = FALSE;
mdtp_fwlock_verify_lock(&ext_partition);
}
#endif /* MDTP_SUPPORT */
}
#endif
#if VERIFIED_BOOT
if((boot_verify_get_state() == ORANGE) && (!boot_into_ffbm)) //校验boot
{
#if FBCON_DISPLAY_MSG
display_bootverify_menu(DISPLAY_MENU_ORANGE);
wait_for_users_action();
#else
//dprintf(CRITICAL,
// "Your device has been unlocked and can't be trusted.\nWait for 5 seconds before proceeding\n");
//mdelay(5000);
#endif
}
#endif
#if VERIFIED_BOOT
if (VB_M == target_get_vb_version())
{
/* set boot and system versions. */
set_os_version((unsigned char *)image_addr);
// send root of trust
if(!send_rot_command((uint32_t)device.is_unlocked))
ASSERT(0);
}
#endif
/*
* Check if the kernel image is a gzip package. If yes, need to decompress it.
* If not, continue booting.
*/
if (is_gzip_package((unsigned char *)(image_addr + page_size), hdr->kernel_size))
{
out_addr = (unsigned char *)(image_addr + imagesize_actual + page_size);
out_avai_len = target_get_max_flash_size() - imagesize_actual - page_size;
dprintf(INFO, "decompressing kernel image: start\n");
rc = decompress((unsigned char *)(image_addr + page_size),
hdr->kernel_size, out_addr, out_avai_len,
&dtb_offset, &out_len);
if (rc)
{
dprintf(CRITICAL, "decompressing kernel image failed!!!\n");
ASSERT(0);
}
dprintf(INFO, "decompressing kernel image: done\n");
kptr = (struct kernel64_hdr *)out_addr;
kernel_start_addr = out_addr;
kernel_size = out_len;
} else {
dprintf(INFO, "Uncpmpressed kernel in use\n");
if (!strncmp((char*)(image_addr + page_size),
PATCHED_KERNEL_MAGIC,
sizeof(PATCHED_KERNEL_MAGIC) - 1)) {
dprintf(INFO, "Patched kernel detected\n");
kptr = (struct kernel64_hdr *)(image_addr + page_size +
PATCHED_KERNEL_HEADER_SIZE);
//The size of the kernel is stored at start of kernel image + 16
//The dtb would start just after the kernel
dtb_offset = *((uint32_t*)((unsigned char*)
(image_addr + page_size +
sizeof(PATCHED_KERNEL_MAGIC) -
1)));
//The actual kernel starts after the 20 byte header.
kernel_start_addr = (unsigned char*)(image_addr +
page_size + PATCHED_KERNEL_HEADER_SIZE);
kernel_size = hdr->kernel_size;
patched_kernel_hdr_size = PATCHED_KERNEL_HEADER_SIZE;
} else {
dprintf(INFO, "Kernel image not patched..Unable to locate dt offset\n");
kptr = (struct kernel64_hdr *)(image_addr + page_size);
kernel_start_addr = (unsigned char *)(image_addr + page_size);
kernel_size = hdr->kernel_size;
}
}
/*
* Update the kernel/ramdisk/tags address if the boot image header
* has default values, these default values come from mkbootimg when
* the boot image is flashed using fastboot flash:raw
*/
update_ker_tags_rdisk_addr(hdr, IS_ARM64(kptr));
/* Get virtual addresses since the hdr saves physical addresses. */
//将hdr中保存的物理地址转化为虚拟地址
hdr->kernel_addr = VA((addr_t)(hdr->kernel_addr));
hdr->ramdisk_addr = VA((addr_t)(hdr->ramdisk_addr));
hdr->tags_addr = VA((addr_t)(hdr->tags_addr));
kernel_size = ROUND_TO_PAGE(kernel_size, page_mask);
/* Check if the addresses in the header are valid. */
if (check_aboot_addr_range_overlap(hdr->kernel_addr, kernel_size) ||
check_ddr_addr_range_bound(hdr->kernel_addr, kernel_size) ||
check_aboot_addr_range_overlap(hdr->ramdisk_addr, ramdisk_actual) ||
check_ddr_addr_range_bound(hdr->ramdisk_addr, ramdisk_actual))
{
dprintf(CRITICAL, "kernel/ramdisk addresses are not valid.\n");
return -1;
}
#ifndef DEVICE_TREE
if (check_aboot_addr_range_overlap(hdr->tags_addr, MAX_TAGS_SIZE) ||
check_ddr_addr_range_bound(hdr->tags_addr, MAX_TAGS_SIZE))
{
dprintf(CRITICAL, "Tags addresses are not valid.\n");
return -1;
}
#endif
/* Move kernel, ramdisk and device tree to correct address */
memmove((void*) hdr->kernel_addr, kernel_start_addr, kernel_size);
memmove((void*) hdr->ramdisk_addr, (char *)(image_addr + page_size + kernel_actual), hdr->ramdisk_size);
#if DEVICE_TREE
if(dt_size) {
dt_table_offset = ((uint32_t)image_addr + page_size + kernel_actual + ramdisk_actual + second_actual);
table = (struct dt_table*) dt_table_offset;
if (dev_tree_validate(table, hdr->page_size, &dt_hdr_size) != 0) {
dprintf(CRITICAL, "ERROR: Cannot validate Device Tree Table \n");
return -1;
}
/* Its Error if, dt_hdr_size (table->num_entries * dt_entry size + Dev_Tree Header)
goes beyound hdr->dt_size*/
if (dt_hdr_size > ROUND_TO_PAGE(dt_size,hdr->page_size)) {
dprintf(CRITICAL, "ERROR: Invalid Device Tree size \n");
return -1;
}
/* Find index of device tree within device tree table */
if(dev_tree_get_entry_info(table, &dt_entry) != 0){
dprintf(CRITICAL, "ERROR: Getting device tree address failed\n");
return -1;
}
if(dt_entry.offset > (UINT_MAX - dt_entry.size)) {
dprintf(CRITICAL, "ERROR: Device tree contents are Invalid\n");
return -1;
}
/* Ensure we are not overshooting dt_size with the dt_entry selected */
if ((dt_entry.offset + dt_entry.size) > dt_size) {
dprintf(CRITICAL, "ERROR: Device tree contents are Invalid\n");
return -1;
}
//检测kernel image是否是gzip的包，如果是，解压，如果不是，继续boot。得到kernel的起始地址和大小
if (is_gzip_package((unsigned char *)dt_table_offset + dt_entry.offset, dt_entry.size))
{
unsigned int compressed_size = 0;
out_addr += out_len;
out_avai_len -= out_len;
dprintf(INFO, "decompressing dtb: start\n");
rc = decompress((unsigned char *)dt_table_offset + dt_entry.offset,
dt_entry.size, out_addr, out_avai_len,
&compressed_size, &dtb_size);
if (rc)
{
dprintf(CRITICAL, "decompressing dtb failed!!!\n");
ASSERT(0);
}
dprintf(INFO, "decompressing dtb: done\n");
best_match_dt_addr = out_addr;
} else {
best_match_dt_addr = (unsigned char *)dt_table_offset + dt_entry.offset;
dtb_size = dt_entry.size;
}
/* Validate and Read device device tree in the tags_addr */
//检测kernel/ramdisk/tags地址是否超出emmc地址
if (check_aboot_addr_range_overlap(hdr->tags_addr, dtb_size) ||
check_ddr_addr_range_bound(hdr->tags_addr, dtb_size))
{
dprintf(CRITICAL, "Device tree addresses are not valid\n");
return -1;
}
memmove((void *)hdr->tags_addr, (char *)best_match_dt_addr, dtb_size);
} else {
/* Validate the tags_addr */
if (check_aboot_addr_range_overlap(hdr->tags_addr, kernel_actual) ||
check_ddr_addr_range_bound(hdr->tags_addr, kernel_actual))
{
dprintf(CRITICAL, "Device tree addresses are not valid.\n");
return -1;
}
/*
* If appended dev tree is found, update the atags with
* memory address to the DTB appended location on RAM.
* Else update with the atags address in the kernel header
*/
void *dtb;
dtb = dev_tree_appended(
(void*)(image_addr + page_size +
patched_kernel_hdr_size),
hdr->kernel_size, dtb_offset,
(void *)hdr->tags_addr);
if (!dtb) {
dprintf(CRITICAL, "ERROR: Appended Device Tree Blob not found\n");
return -1;
}
}
#endif
if (boot_into_recovery && !device.is_unlocked && !device.is_tampered)
target_load_ssd_keystore();
unified_boot:
//最后在函数返回前，将会执行到boot_linux，在boot_linux中将会完成跳转到内核的操作。
boot_linux((void *)hdr->kernel_addr, (void *)hdr->tags_addr,
(const char *)hdr->cmdline, board_machtype(),
(void *)hdr->ramdisk_addr, hdr->ramdisk_size);
return 0;
}至此LK的源码分析完毕。还需要补充emmc，boot.img , recovery.img 和各种分区部分的知识。
参考文章：
Android 开发之 —- bootloader （LK）https://blog.csdn.net/jmq_0000/article/details/7378348
Android启动流程分析之二：内核的引导 https://blog.csdn.net/ffmxnjm/article/details/70598711
MSM8909+Android5.1.1启动流程(7)—boot_linux_from_mmc() https://www.2cto.com/kf/201608/543311.html
lk启动流程详细分析 https://www.cnblogs.com/xiaolei-kaiyuan/p/5458145.html