从uboot中启动的最后一个命令是使用bootm启动kernel,格式如下
bootm $loadaddr $loadaddr $fdtaddr其中，$loadaddr表示boot image在ram中的加载地址，$fdtaddr表示dtb在ram中的加载地址。
bootm命令用于启动操作系统映像；bootm命令从映像文件的头部获取信息；包括：映像文件的CPU架构、操作系统类型、映像类型、压缩方式、映像文件在内存中的加载地址、映像文件运行的入口地址、映像文件名等；
bootm将映像文件加载到指定的地址，解压映像并传递必要的内核启动参数给内核，最后跳转到入口地址进入内核，开始执行内核；
bootm命令执行有三个步骤：
- 解压Linux内核映像并将其加载到RAM中
- 将ramdisk映像加载到RAM中
- 将控制权交给内核，并向内核传递ramdisk在RAM中的位置和大小等信息
将映像文件加载到RAM中时，需要确保映像文件的加载地址，不能与内核的位置有重叠；
本文研究下具体是如何启动的。
bootm命令的使用方法如下：
=> bootm --help
bootm - boot application image from memory
Usage:
bootm [addr [arg ...]]
- boot application image stored in memory
passing arguments 'arg ...'; when booting a Linux kernel,
'arg' can be the address of an initrd image
When booting a Linux kernel which requires a flat device-tree
a third argument is required which is the address of the
device-tree blob. To boot that kernel without an initrd image,
use a '-' for the second argument. If you do not pass a third
a bd_info struct will be passed instead
Sub-commands to do part of the bootm sequence. The sub-commands must be
issued in the order below (it's ok to not issue all sub-commands):
start [addr [arg ...]]
loados - load OS image
ramdisk - relocate initrd, set env initrd_start/initrd_end
fdt - relocate flat device tree
cmdline - OS specific command line processing/setup
bdt - OS specific bd_info processing
prep - OS specific prep before relocation or go
go - start OS
1. do_bootm
// cmd/bootm.c
U_BOOT_CMD(
bootm, CONFIG_SYS_MAXARGS, 1, do_bootm,
"boot application image from memory", bootm_help_text
);do_bootm函数如下,会先对sub commands进行处理，主要处理流程在do_bootm_subcommand,
// cmd/bootm.c
/*******************************************************************/
/* bootm - boot application image from image in memory */
/*******************************************************************/
int do_bootm(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
{
#ifdef CONFIG_NEEDS_MANUAL_RELOC
static int relocated = 0;
if (!relocated) {
int i;
/* relocate names of sub-command table */
for (i = 0; i < ARRAY_SIZE(cmd_bootm_sub); i++)
cmd_bootm_sub[i].name += gd->reloc_off;
relocated = 1;
}
#endif
/* determine if we have a sub command */
argc--; argv++;
if (argc > 0) {
char *endp;
simple_strtoul(argv[0], &endp, 16);
/* endp pointing to NULL means that argv[0] was just a
* valid number, pass it along to the normal bootm processing
*
* If endp is ':' or '#' assume a FIT identifier so pass
* along for normal processing.
*
* Right now we assume the first arg should never be '-'
*/
if ((*endp != 0) && (*endp != ':') && (*endp != '#'))
return do_bootm_subcommand(cmdtp, flag, argc, argv);
}
return do_bootm_states(cmdtp, flag, argc, argv, BOOTM_STATE_START |
BOOTM_STATE_FINDOS | BOOTM_STATE_FINDOTHER |
BOOTM_STATE_LOADOS |
#ifdef CONFIG_SYS_BOOT_RAMDISK_HIGH
BOOTM_STATE_RAMDISK |
#endif
#if defined(CONFIG_PPC) || defined(CONFIG_MIPS)
BOOTM_STATE_OS_CMDLINE |
#endif
BOOTM_STATE_OS_PREP | BOOTM_STATE_OS_FAKE_GO |
BOOTM_STATE_OS_GO, &images, 1);
}do_bootm_states()函数操作，是由参数states来决定的；
// include/image.h
#define BOOTM_STATE_START (0x00000001)
#define BOOTM_STATE_FINDOS (0x00000002)
#define BOOTM_STATE_FINDOTHER (0x00000004)
#define BOOTM_STATE_LOADOS (0x00000008)
#define BOOTM_STATE_RAMDISK (0x00000010)
#define BOOTM_STATE_FDT (0x00000020)
#define BOOTM_STATE_OS_CMDLINE (0x00000040)
#define BOOTM_STATE_OS_BD_T (0x00000080)
#define BOOTM_STATE_OS_PREP (0x00000100)
#define BOOTM_STATE_OS_FAKE_GO (0x00000200) /* 'Almost' run the OS */
#define BOOTM_STATE_OS_GO (0x00000400)do_bootm_states()函数的参数images，用来表示bootm命令启动kernel的一些信息，包含了指向os、initrd、fdt的映像信息；是全局变量：
// common/bootm.c
bootm_headers_t images; /* pointers to os/initrd/fdt images */2. do_bootm_states
do_bootm_states函数如下：
/**
* Execute selected states of the bootm command.
*
* Note the arguments to this state must be the first argument, Any 'bootm'
* or sub-command arguments must have already been taken.
*
* Note that if states contains more than one flag it MUST contain
* BOOTM_STATE_START, since this handles and consumes the command line args.
*
* Also note that aside from boot_os_fn functions and bootm_load_os no other
* functions we store the return value of in 'ret' may use a negative return
* value, without special handling.
*
* @param cmdtp Pointer to bootm command table entry
* @param flag Command flags (CMD_FLAG_...)
* @param argc Number of subcommand arguments (0 = no arguments)
* @param argv Arguments
* @param states Mask containing states to run (BOOTM_STATE_...)
* @param images Image header information
* @param boot_progress 1 to show boot progress, 0 to not do this
* @return 0 if ok, something else on error. Some errors will cause this
* function to perform a reboot! If states contains BOOTM_STATE_OS_GO
* then the intent is to boot an OS, so this function will not return
* unless the image type is standalone.
*/
int do_bootm_states(struct cmd_tbl *cmdtp, int flag, int argc,
char *const argv[], int states, bootm_headers_t *images,
int boot_progress)
{
boot_os_fn *boot_fn;
ulong iflag = 0;
int ret = 0, need_boot_fn;
images->state |= states;
/*
* Work through the states and see how far we get. We stop on
* any error.
*/
if (states & BOOTM_STATE_START)
ret = bootm_start(cmdtp, flag, argc, argv);
if (!ret && (states & BOOTM_STATE_FINDOS))
ret = bootm_find_os(cmdtp, flag, argc, argv);
if (!ret && (states & BOOTM_STATE_FINDOTHER))
ret = bootm_find_other(cmdtp, flag, argc, argv);
/* Load the OS */
if (!ret && (states & BOOTM_STATE_LOADOS)) {
iflag = bootm_disable_interrupts();
ret = bootm_load_os(images, 0);
if (ret && ret != BOOTM_ERR_OVERLAP)
goto err;
else if (ret == BOOTM_ERR_OVERLAP)
ret = 0;
}
/* Relocate the ramdisk */
#ifdef CONFIG_SYS_BOOT_RAMDISK_HIGH
if (!ret && (states & BOOTM_STATE_RAMDISK)) {
ulong rd_len = images->rd_end - images->rd_start;
ret = boot_ramdisk_high(&images->lmb, images->rd_start,
rd_len, &images->initrd_start, &images->initrd_end);
if (!ret) {
env_set_hex("initrd_start", images->initrd_start);
env_set_hex("initrd_end", images->initrd_end);
}
}
#endif
#if IMAGE_ENABLE_OF_LIBFDT && defined(CONFIG_LMB)
if (!ret && (states & BOOTM_STATE_FDT)) {
boot_fdt_add_mem_rsv_regions(&images->lmb, images->ft_addr);
ret = boot_relocate_fdt(&images->lmb, &images->ft_addr,
&images->ft_len);
}
#endif
/* From now on, we need the OS boot function */
if (ret)
return ret;
boot_fn = bootm_os_get_boot_func(images->os.os);
need_boot_fn = states & (BOOTM_STATE_OS_CMDLINE |
BOOTM_STATE_OS_BD_T | BOOTM_STATE_OS_PREP |
BOOTM_STATE_OS_FAKE_GO | BOOTM_STATE_OS_GO);
if (boot_fn == NULL && need_boot_fn) {
if (iflag)
enable_interrupts();
printf("ERROR: booting os '%s' (%d) is not supported\n",
genimg_get_os_name(images->os.os), images->os.os);
bootstage_error(BOOTSTAGE_ID_CHECK_BOOT_OS);
return 1;
}
/* Call various other states that are not generally used */
if (!ret && (states & BOOTM_STATE_OS_CMDLINE))
ret = boot_fn(BOOTM_STATE_OS_CMDLINE, argc, argv, images);
if (!ret && (states & BOOTM_STATE_OS_BD_T))
ret = boot_fn(BOOTM_STATE_OS_BD_T, argc, argv, images);
if (!ret && (states & BOOTM_STATE_OS_PREP)) {
#if defined(CONFIG_SILENT_CONSOLE) && !defined(CONFIG_SILENT_U_BOOT_ONLY)
if (images->os.os == IH_OS_LINUX)
fixup_silent_linux();
#endif
ret = boot_fn(BOOTM_STATE_OS_PREP, argc, argv, images);
}
#ifdef CONFIG_TRACE
/* Pretend to run the OS, then run a user command */
if (!ret && (states & BOOTM_STATE_OS_FAKE_GO)) {
char *cmd_list = env_get("fakegocmd");
ret = boot_selected_os(argc, argv, BOOTM_STATE_OS_FAKE_GO,
images, boot_fn);
if (!ret && cmd_list)
ret = run_command_list(cmd_list, -1, flag);
}
#endif
/* Check for unsupported subcommand. */
if (ret) {
puts("subcommand not supported\n");
return ret;
}
/* Now run the OS! We hope this doesn't return */
if (!ret && (states & BOOTM_STATE_OS_GO))
ret = boot_selected_os(argc, argv, BOOTM_STATE_OS_GO,
images, boot_fn);
/* Deal with any fallout */
err:
if (iflag)
enable_interrupts();
if (ret == BOOTM_ERR_UNIMPLEMENTED)
bootstage_error(BOOTSTAGE_ID_DECOMP_UNIMPL);
else if (ret == BOOTM_ERR_RESET)
do_reset(cmdtp, flag, argc, argv);
return ret;
}其中获取Android boot.img中的kernel流程如下，boot_find_os()-->boot_get_kernel()-->android_image_get_kernel()
/**
* android_image_get_kernel() - processes kernel part of Android boot images
* @hdr: Pointer to image header, which is at the start
* of the image.
* @verify: Checksum verification flag. Currently unimplemented.
* @os_data: Pointer to a ulong variable, will hold os data start
* address.
* @os_len: Pointer to a ulong variable, will hold os data length.
*
* This function returns the os image's start address and length. Also,
* it appends the kernel command line to the bootargs env variable.
*
* Return: Zero, os start address and length on success,
* otherwise on failure.
*/
int android_image_get_kernel(const struct andr_img_hdr *hdr, int verify,
ulong *os_data, ulong *os_len)
{
u32 kernel_addr = android_image_get_kernel_addr(hdr);
uboot_set_rot();
#ifdef CONFIG_TRANSFER_IMGVERSION
/* os_version = ver << 11 | lvl */
u32 os_ver = hdr->os_version >> 11;
u32 os_lvl = hdr->os_version & ((1U << 11) - 1);
u32 android_version =
(((os_ver >> 14) & 0x7F) * 100 + ((os_ver >> 7) & 0x7F)) * 100
+ (os_ver & 0x7F);
u32 android_patchlevel = ((os_lvl >> 4) + 2000) * 100 + (os_lvl & 0x0F);
extern void optee_transfer_imgversion(unsigned long a0, unsigned long a1,
unsigned long a2, unsigned long a3,
unsigned long a4, unsigned long a5,
unsigned long a6, unsigned long a7,
struct arm_smccc_res *res);
struct arm_smccc_res res;
optee_transfer_imgversion(OPTEE_SMC_CALL_TRANSFER_IMGVERSION,
(unsigned long)android_version,
(unsigned long)android_patchlevel, 0, 0, 0, 0, 0, &res);
#endif
const struct image_header *ihdr = (const struct image_header *)
((uintptr_t)hdr + hdr->page_size);
/*
* Not all Android tools use the id field for signing the image with
* sha1 (or anything) so we don't check it. It is not obvious that the
* string is null terminated so we take care of this.
*/
strncpy(andr_tmp_str, hdr->name, ANDR_BOOT_NAME_SIZE);
andr_tmp_str[ANDR_BOOT_NAME_SIZE] = '\0';
if (strlen(andr_tmp_str))
printf("Android's image name: %s\n", andr_tmp_str);
printf("Kernel load addr 0x%08x size %u KiB\n",
kernel_addr, DIV_ROUND_UP(hdr->kernel_size, 1024));
int len = 0;
if (*hdr->cmdline) {
printf("Kernel command line: %s\n", hdr->cmdline);
len += strlen(hdr->cmdline);
}
char *bootargs = env_get("bootargs");
if (bootargs)
len += strlen(bootargs);
int add_Factory_Flag = false;
if(is_Factory_Mode()) {
add_Factory_Flag = true;
printf("is facotry mode add flag to cmdline \n");
len = len + strlen(" i_isFactory=true");
}
char *newbootargs = malloc(len + 2);
if (!newbootargs) {
puts("Error: malloc in android_image_get_kernel failed!\n");
return -ENOMEM;
}
*newbootargs = '\0';
if (bootargs) {
printf("bootargs: %s\n", bootargs);
strcpy(newbootargs, bootargs);
strcat(newbootargs, " ");
}
if (*hdr->cmdline)
strcat(newbootargs, hdr->cmdline);
if(add_Factory_Flag) {
strcat(newbootargs, " i_isFactory=true");
printf("add factory flag newbootargs: [%s]\n", newbootargs);
}
env_set("bootargs", newbootargs);
#ifdef ESWIN_FCT_RES_APP
if(need_reserve_app() && parse_misc_for_wipedata()) {
printf("newbootargs: [%s]\n", newbootargs);
const char *match = NULL;
char *fixbootargs;
match = strstr(newbootargs, "androidboot.selinux=enforcing");
if(match) {
printf("wipe_data and fix selinux to permissive\n");
fixbootargs = malloc(len + 4);
if(!fixbootargs)
goto malloc_fixbootargs_fail;
memset(fixbootargs,'\0',len+4);
strncpy(fixbootargs, newbootargs, match - newbootargs);
strcat(fixbootargs, "androidboot.selinux=permissive");
strcat(fixbootargs, match + strlen("androidboot.selinux=enforcing"));
} else {
printf("wipe_data and add selinux permissive\n");
fixbootargs = malloc(len + 2 + strlen( "androidboot.selinux=permissive"));
*fixbootargs = '\0';
if(!fixbootargs)
goto malloc_fixbootargs_fail;
strcpy(fixbootargs, newbootargs);
strcat(fixbootargs, " androidboot.selinux=permissive");
}
printf("fixbootargs: [%s]\n", fixbootargs);
env_set("bootargs", fixbootargs);
malloc_fixbootargs_fail:
printf("wipe_data parse done\n");
}
#endif
if (os_data) {
if (image_get_magic(ihdr) == IH_MAGIC) {
*os_data = image_get_data(ihdr);
} else {
*os_data = (ulong)hdr;
*os_data += hdr->page_size;
}
}
if (os_len) {
if (image_get_magic(ihdr) == IH_MAGIC)
*os_len = image_get_data_size(ihdr);
else
*os_len = hdr->kernel_size;
}
return 0;
}获取ramdisk的流程如下，bootm_find_other()-->bootm_find_images()--boot_get_randisk()
获取dtb的流程如下，bootm_find_other()-->bootm_find_images()--boot_get_fdt()
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