Lk启动流程分析
Posted feisonzl
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1 Lk概述
LK是(L)ittle(K)ernel的缩写。目前android平台普遍采用lk作为其bootloader，LK是一个开源项目。但是，LK只是整个系统的引导部分，所以它不是独立存在。LK是一个功能及其强大的bootloader，但现在只支持arm和x86平台。
LK的一个显著的特点就是它实现了一个简单的线程机制（thread），和对高通处理器的深度定制和使用。
2 源代码目录
app //主函数启动app执行的目录，第一个app在app/aboot/aboot.c中
arch //体系代码包含x86和arm
dev //设备目录，包含显示器，键盘，net,usb等设备的初始化代码
include //头文件
kernel //kernel/main.c主函数以及kernel/thread.c线程函数
lib //库文件
make //编译规则
platform //不同平台代码mdmxxx，msmxxx，apqxxx，qsdxxx，还有共享的目录msm_shared
project //整个工程的编译规则
target //通用init.c,具体目标板的初始化(主要为板子设备资源init.c代码中)
3 Lk入口
3.1 bootable\\bootloader\\lk\\arch\\arm\\rule.mk文件下相关部分：
# potentially generated files that should be cleaned out with clean make rule
GENERATED += \\
$(BUILDDIR)/system-onesegment.ld \\
$(BUILDDIR)/system-twosegment.ld
# rules for generating the linker scripts
$(BUILDDIR)/trustzone-test-system-onesegment.ld: $(LOCAL_DIR)/trustzone-test-system-onesegment.ld $(LK_TOP_DIR)/target/$(TARGET)/rules.mk .FORCE
@echo generating $@
@$(MKDIR)
$(NOECHO)sed "s/%MEMBASE%/$(MEMBASE)/;s/%MEMSIZE%/$(MEMSIZE)/;s/%ROMLITE_PREFLASHED_DATA%/$(ROMLITE_PREFLASHED_DATA)/" < $< > $@
$(BUILDDIR)/trustzone-system-onesegment.ld: $(LOCAL_DIR)/trustzone-system-onesegment.ld $(LK_TOP_DIR)/target/$(TARGET)/rules.mk .FORCE
@echo generating $@
@$(MKDIR)
$(NOECHO)sed "s/%MEMBASE%/$(MEMBASE)/;s/%MEMSIZE%/$(MEMSIZE)/" < $< > $@
$(BUILDDIR)/system-onesegment.ld: $(LOCAL_DIR)/system-onesegment.ld $(LK_TOP_DIR)/target/$(TARGET)/rules.mk .FORCE
@echo generating $@
@$(MKDIR)
$(NOECHO)sed "s/%MEMBASE%/$(MEMBASE)/;s/%MEMSIZE%/$(MEMSIZE)/" < $< > $@
$(BUILDDIR)/system-twosegment.ld: $(LOCAL_DIR)/system-twosegment.ld $(LK_TOP_DIR)/target/$(TARGET)/rules.mk .FORCE
@echo generating $@
@$(MKDIR)
$(NOECHO)sed "s/%ROMBASE%/$(ROMBASE)/;s/%MEMBASE%/$(MEMBASE)/;s/%MEMSIZE%/$(MEMSIZE)/" < $< > $@3.2 arch/arm/system-onesegment.ld
OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
OUTPUT_ARCH(arm)
ENTRY(_start) /*跳入crt0.S文件执行代码*/
3.3 arch/arm/crt0.S
.section ".text.boot"
.globl _start
_start:
b reset
b arm_undefined
b arm_syscall
b arm_prefetch_abort
b arm_data_abort
b arm_reserved
b arm_irq
b arm_fiq
reset:
……
bl kmain
b
……4 kmain函数
bootable/bootloader/lk/kernel/main.c
/* called from crt0.S */
void kmain(void) __NO_RETURN __EXTERNALLY_VISIBLE;
void kmain(void)
// get us into some sort of thread context
thread_init_early(); //初始化线程上下文
// early arch stuff
arch_early_init(); //架构初始化，如关闭cache，使能mmu
// do any super early platform initialization
platform_early_init(); //平台早期初始化
// do any super early target initialization
target_early_init(); //目标设备早期初始化,初始化串口
dprintf(INFO, "welcome to lk\\n\\n");
bs_set_timestamp(BS_BL_START);
// deal with any static constructors
dprintf(SPEW, "calling constructors\\n");
call_constructors();
// bring up the kernel heap
dprintf(SPEW, "initializing heap\\n");
heap_init(); //堆初始化
__stack_chk_guard_setup();
// initialize the threading system
dprintf(SPEW, "initializing threads\\n");
thread_init(); //线程初始化
// initialize the dpc system
dprintf(SPEW, "initializing dpc\\n");
dpc_init(); //lk系统控制器初始化
// initialize kernel timers
dprintf(SPEW, "initializing timers\\n");
timer_init(); //kernel时钟初始化
#if (!ENABLE_NANDWRITE)
// create a thread to complete system initialization
dprintf(SPEW, "creating bootstrap completion thread\\n");
thread_resume(thread_create("bootstrap2", &bootstrap2, NULL, DEFAULT_PRIORITY, DEFAULT_STACK_SIZE)); //创建一个线程初始化系统
// enable interrupts
exit_critical_section(); //使能中断
// become the idle thread
thread_become_idle(); //本线程切换成idle线程，idle为空闲线程，当没有更高优先级的线程时才执行
#else
bootstrap_nandwrite();
#endif
4.1 arch_early_init函数
bootable/bootloader/lk/arch/arm/arch.c
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(); //mmu初始化
#endif
/* turn the cache back on */
arch_enable_cache(UCACHE); //使能cache
#if ARM_WITH_NEON
/* enable cp10 and 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 */
__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 */
uint32_t en;
__asm__ volatile("mrc p15, 0, %0, c9, c12, 0" : "=r" (en));
en &= ~(1<<3); /* cycle count every cycle */
en |= 1; /* enable all performance counters */
__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
4.2 platform_early_init函数
bootable/bootloader/lk/platform/msm8953/platform.c
void platform_early_init(void)
board_init(); //主板初始化
platform_clock_init(); //平台时钟初始化
qgic_init(); //中断控制器初始化
qtimer_init(); //定时器初始化
scm_init(); //
4.3 target_early_init函数
bootable/bootloader/lk/ target/msm8953/init.c
void target_early_init(void)
#if WITH_DEBUG_UART
uart_dm_init(1, 0, BLSP1_UART0_BASE); //串口初始化
#endif
5. timer_init函数
bootable/bootloader/lk/ kernel/timer.c
void timer_init(void)
list_initialize(&timer_queue);
/* register for a periodic timer tick */
platform_set_periodic_timer(timer_tick, NULL, 10); /* 10ms */
4.4 bootstrap2函数分析
bootable/bootloader/lk/kernel/main.c
static int bootstrap2(void *arg)
dprintf(SPEW, "top of bootstrap2()\\n");
arch_init(); //架构初始化，空函数
// 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(); //板级设备初始化，空函数
// initialize the target
dprintf(SPEW, "initializing target\\n");
target_init(); //目标设备初始化，见1.1
dprintf(SPEW, "calling apps_init()\\n");
apps_init(); //lk应用初始化，见1.2
return 0;
4.4.1 target_init函数
bootable/bootloader/lk/target/msm8953/init.c
void target_init(void)
#if VERIFIED_BOOT
#if !VBOOT_MOTA
int ret = 0;
#endif
#endif
dprintf(INFO, "target_init()\\n");
spmi_init(PMIC_ARB_CHANNEL_NUM, PMIC_ARB_OWNER_ID); //初始化spmi 控制器
target_keystatus();
target_sdc_init(); //sd card 初始化，内部包含了mmc的初始化
if (partition_read_table()) //读取分区表
dprintf(CRITICAL, "Error reading the partition table info\\n");
ASSERT(0);
#if LONG_PRESS_POWER_ON
shutdown_detect();
#endif
#if PON_VIB_SUPPORT
vib_timed_turn_on(VIBRATE_TIME);
#endif
if (target_use_signed_kernel())
target_crypto_init_params();
#if VERIFIED_BOOT
#if !VBOOT_MOTA
clock_ce_enable(CE1_INSTANCE);
/* Initialize Qseecom */
ret = qseecom_init(); //qse 初始化
if (ret < 0)
dprintf(CRITICAL, "Failed to initialize qseecom, error: %d\\n", ret);
ASSERT(0);
/* Start Qseecom */
ret = qseecom_tz_init(); //qse tz初始化
if (ret < 0)
dprintf(CRITICAL, "Failed to start qseecom, error: %d\\n", ret);
ASSERT(0);
if (rpmb_init() < 0) //rpmb 初始化（Replay Protected Memory Block，emmc中的一个分区，总共五个分区：BOOT Area Partition 1，BOOT Area Partition 2，RPMB，User Data Area，Vender private area）
dprintf(CRITICAL, "RPMB init failed\\n");
ASSERT(0);
/*
* Load the sec app for first time
*/
if (load_sec_app() < 0) //加载安全app
dprintf(CRITICAL, "Failed to load App for verified\\n");
ASSERT(0);
#endif
#endif
#if SMD_SUPPORT
rpm_smd_init(); //smd 初始化
#endif
4.4.2 apps_init函数
bootable/bootloader/lk/ app/app.c
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)
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);
代码段：
for (app = &__apps_start; app != &__apps_end; app++)
if (app->init)
app->init(app);
表示进入各自的app init函数，通过下面的代码段可以分析出具体有哪些app init函数。
bootable/bootloader/lk/ arch/arm/system-onesegment.ld
.rodata :
……..
__apps_start = .;
KEEP (*(.apps))
__apps_end = .;
……..
bootable/bootloader/lk/ include/app.h
struct app_descriptor
const char *name;
app_init init;
app_entry entry;
unsigned int flags;
;
#define APP_START(appname) struct app_descriptor _app_##appname __SECTION(".apps") = .name = #appname,
#define APP_END ;
bootable/bootloader/lk/app/aboot/aboot.c
APP_START(aboot)
.init = aboot_init,
APP_END
上面的过程表示了如何将aboot模块的aboot_init函数加入到.apps代码段。这种方式也用在clocktests 、shell、pcitests、stringtests、tests模块中，请参见一下文件：
bootable/bootloader/lk/app/clocktests/clock_tests.c:APP_START(clocktests)
bootable/bootloader/lk/app/aboot/aboot.c:APP_START(aboot)
bootable/bootloader/lk/app/shell/shell.c:APP_START(shell)
bootable/bootloader/lk/app/pcitests/pci_tests.c:APP_START(pcitests)
bootable/bootloader/lk/app/stringtests/string_tests.c:APP_START(stringtests)
bootable/bootloader/lk/app/tests/tests.c:APP_START(tests)5 aboot_init函数分析
/bootable/bootloader/lk/app/aboot/aboot.c
void aboot_init(const struct app_descriptor *app)
unsigned reboot_mode = 0;
/* Initialise wdog to catch early lk crashes */
#if WDOG_SUPPORT
msm_wdog_init(); //看门狗初始化
#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);
read_device_info(&device); //读取device info分区的信息到device结构体中
read_allow_oem_unlock(&device); //devinfo分区里记录了unlock状态，从device中读取此信息
/* Display splash screen if enabled */
#if DISPLAY_SPLASH_SCREEN
#if NO_ALARM_DISPLAY
if (!check_alarm_boot()) //判断是否是因为闹钟导致的重启
#endif
dprintf(SPEW, "Display Init: Start\\n");
#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);
else
display_image_on_screen();
#else
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
#endif
dprintf(SPEW, "Display Init: Done\\n");
#if NO_ALARM_DISPLAY
#endif
#endif
target_serialno((unsigned char *) sn_buf); //读取序列号
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()) //判断是否是用户设置的重启
goto normal_boot;
/* Check if we should do something other than booting up */
//判断是否进入各种模式
if (keys_get_state(KEY_VOLUMEUP) && keys_get_state(KEY_VOLUMEDOWN))
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))
boot_into_recovery = 1;
if (!boot_into_recovery &&
(keys_get_state(KEY_BACK) || keys_get_state(KEY_VOLUMEDOWN)))
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();
#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
#if !VBOOT_MOTA
else if (reboot_mode == DM_VERITY_ENFORCING)
device.verity_mode = 1;
write_device_info(&device);
else if (reboot_mode == DM_VERITY_LOGGING)
device.verity_mode = 0;
write_device_info(&device);
else if (reboot_mode == DM_VERITY_KEYSCLEAR)
if(send_delete_keys_to_tz())
ASSERT(0);
#endif
#endif
normal_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();
#endif
#if USE_PCOM_SECBOOT
set_tamper_flag(device.is_tampered);
#endif
boot_linux_from_mmc(); //跳入linux kernel启动，后面深入分析
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(); //跳入linux kernel启动，后面深入分析
dprintf(CRITICAL, "ERROR: Could not do normal boot. Reverting "
"to fastboot mode.\\n");
/* We are here means regular boot did not happen. Start fastboot. */
/* register aboot specific fastboot commands */
aboot_fastboot_register_commands();
/* dump partition table for debug info */
partition_dump();
/* initialize and start fastboot */
fastboot_init(target_get_scratch_address(), target_get_max_flash_size());
#if FBCON_DISPLAY_MSG
display_fastboot_menu(); //显示fastboot菜单
#endif
5.1 read_device_info函数分析
- device_info结构体
bootable/bootloader/lk/ app/aboot/devinfo.h
struct device_info
unsigned char magic[DEVICE_MAGIC_SIZE];
bool is_unlocked;
bool is_tampered;
bool is_unlock_critical;
bool charger_screen_enabled;
char display_panel[MAX_PANEL_ID_LEN];
char bootloader_version[MAX_VERSION_LEN];
char radio_version[MAX_VERSION_LEN];
;2 read_device_info函数
bootable/bootloader/lk/ app/aboot/aboot.c
void read_device_info(device_info *dev)
if(target_is_emmc_boot())
struct device_info *info = memalign(PAGE_SIZE, ROUNDUP(BOOT_IMG_MAX_PAGE_SIZE, PAGE_SIZE)); //开辟一片内存，其大小是对齐的倍数，必须是2的幂
if(info == NULL)
dprintf(CRITICAL, "Failed to allocate memory for device info struct\\n");
ASSERT(0);
info_buf = info;
#if USE_RPMB_FOR_DEVINFO //从rpmb中读取devinfo
if (is_secure_boot_enable())
if((read_device_info_rpmb((void*) info, PAGE_SIZE)) < 0)
ASSERT(0);
else
read_device_info_mmc(info);
#else
read_device_info_mmc(info); //从mmc中读取devinfo
#endif
if (memcmp(info->magic, DEVICE_MAGIC, DEVICE_MAGIC_SIZE))
memcpy(info->magic, DEVICE_MAGIC, DEVICE_MAGIC_SIZE);
if (is_secure_boot_enable()) //是否为安全启动
info->is_unlocked = 0;
#if !VBOOT_MOTA
info->is_unlock_critical = 0;
#endif
else
info->is_unlocked = 1;
#if !VBOOT_MOTA
info->is_unlock_critical = 1;
#endif
info->is_tampered = 0;
info->charger_screen_enabled = 0;
#if !VBOOT_MOTA
info->verity_mode = 1; //enforcing by default
#endif
write_device_info(info);
memcpy(dev, info, sizeof(device_info)); //回写devinfo
free(info);
else
read_device_info_flash(dev); //从flash中读取devinfo
5.2 boot_linux_from_mmc分析
/bootable/bootloader/lk/app/aboot/aboot.c
int boot_linux_from_mmc(void)
// buf由前面BUF_DMA_ALIGN(buf, BOOT_IMG_MAX_PAGE_SIZE); 表示声明一个buf数组，并将boot img copy到其中
//Equal to max-supported pagesize
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;
int rc;
#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;
if (check_format_bit()) //查找bootselect分区，并判断其是否存在相应的标志位，否则返回false
boot_into_recovery = 1;
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;
//有前面定义确定uhdr的位置
uhdr = (struct boot_img_hdr *)EMMC_BOOT_IMG_HEADER_ADDR;
if (!memcmp(uhdr->magic, BOOT_MAGIC, BOOT_MAGIC_SIZE)) //校验magic是否为"ANDROID! "
dprintf(INFO, "Unified boot method!\\n");
hdr = uhdr; //将uhdr的值赋给hdr，即buf
goto unified_boot;
if (!boot_into_recovery) //正常启动
index = partition_get_index("boot");
ptn = partition_get_offset(index);
if(ptn == 0)
dprintf(CRITICAL, "ERROR: No boot partition found\\n");
return -1;
else
index = partition_get_index("recovery");//进入recovery模式
ptn = partition_get_offset(index);
if(ptn == 0)
dprintf(CRITICAL, "ERROR: No recovery partition found\\n");
return -1;
/* Set Lun for boot & recovery partitions */
mmc_set_lun(partition_get_lun(index));
if (mmc_read(ptn + offset, (uint32_t *) buf, page_size)) //将bootimg读取到buf中
dprintf(CRITICAL, "ERROR: Cannot read boot image header\\n");
return -1;
if (memcmp(hdr->magic, BOOT_MAGIC, BOOT_MAGIC_SIZE)) //校验
dprintf(CRITICAL, "ERROR: Invalid boot image header\\n");
return -1;
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;
/* ensure commandline is terminated */
hdr->cmdline[BOOT_ARGS_SIZE-1] = 0;
kernel_actual = ROUND_TO_PAGE(hdr->kernel_size, page_mask); //kernel所占页的总大小
ramdisk_actual = ROUND_TO_PAGE(hdr->ramdisk_size, page_mask); //ramdisk所占页的总大小
image_addr = (unsigned char *)target_get_scratch_address();
#if DEVICE_TREE
dt_actual = ROUND_TO_PAGE(hdr->dt_size, page_mask); //dt所占页的总大小
imagesize_actual = (page_size + kernel_actual + ramdisk_actual + dt_actual); //image所占页的总大小
#else
imagesize_actual = (page_size + kernel_actual + ramdisk_actual);
#endif
#if VERIFIED_BOOT
boot_verifier_init(); //校验boot
#endif
if (check_aboot_addr_range_overlap((uintptr_t) image_addr, imagesize_actual)) //aboot和bootimage地址是否重合
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.
*/
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)//判断image能否完全放入ddr
dprintf(CRITICAL, "booimage size is greater than DDR can hold\\n");
return -1;
/* Read image without signature */
if (mmc_read(ptn + offset, (void *)image_addr, imagesize_actual))
dprintf(CRITICAL, "ERROR: Cannot read boot image\\n");
return -1;
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);
/* 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())
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);//校验bootimg
/* 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); //second_size所占页的总大小
#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 */
#if VERIFIED_BOOT
if(boot_verify_get_state() == ORANGE)
#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 !VBOOT_MOTA
// send root of trust
if(!send_rot_command((uint32_t)device.is_unlocked))
ASSERT(0);
#endif
#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)) //判断内核格式并解压
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
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)); //更新kernel/ramdisk/tags地址
/* Get virtual addresses since the hdr saves physical addresses. */
hdr->kernel_addr = VA((addr_t)(hdr->kernel_addr)); //转换为虚拟地址
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_aboot_addr_range_overlap(hdr->ramdisk_addr, ramdisk_actual))
dprintf(CRITICAL, "kernel/ramdisk addresses overlap with aboot addresses.\\n");
return -1;
#ifndef DEVICE_TREE
if (check_aboot_addr_range_overlap(hdr->tags_addr, MAX_TAGS_SIZE))
dprintf(CRITICAL, "Tags addresses overlap with aboot addresses.\\n");
return -1;
#endif
/* Move kernel, ramdisk and device tree to correct address */
memmove((void*) hdr->kernel_addr, kernel_start_addr, kernel_size); //移动kernel, ramdisk and device tree到相应的地址
memmove((void*) hdr->ramdisk_addr, (char *)(image_addr + page_size + kernel_actual), hdr->ramdisk_size);
#if DEVICE_TREE
if(hdr->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(hdr->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) > hdr->dt_size)
dprintf(CRITICAL, "ERROR: Device tree contents are Invalid\\n");
return -1;
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 */
if (check_aboot_addr_range_overlap(hdr->tags_addr, dtb_size))
dprintf(CRITICAL, "Device tree addresses overlap with aboot addresses.\\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))
dprintf(CRITICAL, "Device tree addresses overlap with aboot addresses.\\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),
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:
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;
主要完成的工作：
1.将uhdr存入hdr/buf
2.读取bootimg到内存buf/hdr中
3.判断内核是否为gzip格式，如果是则解压
4.boot linux并通过boot_linux函数传递内核的地址，tags的地址，命令行参数，ramdisk地址和大小
5.2.1 boot_img_hdr结构分析
boot_img_hdr主要存储了bootimg、ramdisk、dt的地址
bootable/bootloader/lk /app/aboot/bootimg.h
#ifndef _BOOT_IMAGE_H_
#define _BOOT_IMAGE_H_
typedef struct boot_img_hdr boot_img_hdr;
#define BOOT_MAGIC "ANDROID!"
#define BOOT_MAGIC_SIZE 8
#define BOOT_NAME_SIZE 16
#define BOOT_ARGS_SIZE 512
#define BOOT_IMG_MAX_PAGE_SIZE 4096
struct boot_img_hdr
unsigned char magic[BOOT_MAGIC_SIZE];
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