cmdline
1、向linux kernel添加cmdline的四种方式
(1)、 在dts中的bootargs中添加
(2)、在BoardConfig中添加
(3)、在uboot中添加
(4)、在android的Makefile中添加
2、在uboot中,将cmdline统一放置在FDT中
3、在kernel中,从FDT中解析处cmdline并使用
(1)、跳转linux kernel之前-准备cmdline
(2)、kernel启动-解析cmdline
1、向linux kernel添加cmdline的四种方式
在linux启动时候，串口log中会打印cmdline
[ 0.000000] c0 0 (swapper) Kernel command line: earlycon androidboot.selinux=permissive uart_dma keep_dbgclk_on clk_ignore_unused initrd=0xd0000000,38711808 rw crash_page=0x8f040000 initrd=/recoveryrc boot_reason=0x2000 ota_status=0x1001
在linux启动完成后，通过 cat /proc/cmdline也是可以看到cmdline. 那么cmdline是如何添加的呢？
(1)、 在dts中的bootargs中添加
/ {
model = "yyyyyyy";
compatible = "yyyyyyy", "xxxxxxxx";
chosen {
/*
* initrd parameters not set in dts file since the ramdisk.img size
* need to check in uboot, and the initrd load address and size will
* set in uboot stage.
*/
bootargs = "earlycon androidboot.selinux=permissive uart_dma keep_dbgclk_on clk_ignore_unused";
stdout-path = "serial0:115200";};
......
}
(2)、在BoardConfig中添加
vim device/xxx/xxx_evb/BoardConfigCommon.mk
BOARD_KERNEL_CMDLINE += androidboot.selinux=enforcing androidboot.hardware=xxxx_phone androidboot.dtbo_idx=0
(3)、在uboot中添加
vim u-boot/common/cmd_bootm.c
append_bootargs("recovery=1");
sprintf(dm_buf,"init=/init skip_initramfs rootwait root=/dev/dm-0 dm=\"system none ro,0 1 android-verity /dev/mmcblk0p%d\"",ret);
append_bootargs((const char *)dm_buf);
2、在uboot中,将cmdline统一放置在FDT中
以后再写，哈哈哈哈
3、在kernel中,从FDT中解析处cmdline并使用
(1)、跳转linux kernel之前-准备cmdline
在跳转linux kernel之前(如uboot中)，将cmdline数据放到了FDT中，然后将FDT的地址写入到了X0中。然后再跳转linux kernel.
别问我怎么知道的，请看kernel-4.14/Documentation/arm64/booting.txt
Before jumping into the kernel, the following conditions must be met:
- Quiesce all DMA capable devices so that memory does not get
corrupted by bogus network packets or disk data. This will save
you many hours of debug. - Primary CPU general-purpose register settings
x0 = physical address of device tree blob (dtb) in system RAM.
x1 = 0 (reserved for future use)
x2 = 0 (reserved for future use)
x3 = 0 (reserved for future use)
(2)、kernel启动-解析cmdline
linux kernel从stext开始启动，整个流程大概就是读取X0(FDT地址)保存到X21中，又将X21保存到__fdt_pointer全局变量中
然后再将__fdt_pointer解析处cmdline数据到boot_command_line全局变量中
/*
* The following callee saved general purpose registers are used on the
* primary lowlevel boot path:
*
* Register Scope Purpose
* x21 stext() .. start_kernel() FDT pointer passed at boot in x0
* x23 stext() .. start_kernel() physical misalignment/KASLR offset
* x28 __create_page_tables() callee preserved temp register
* x19/x20 __primary_switch() callee preserved temp registers
*/ENTRY(stext)
bl preserve_boot_args
bl el2_setup // Drop to EL1, w0=cpu_boot_mode
adrp x23, __PHYS_OFFSET
and x23, x23, MIN_KIMG_ALIGN - 1 // KASLR offset, defaults to 0
bl set_cpu_boot_mode_flag
bl __create_page_tables
/*
* The following calls CPU setup code, see arch/arm64/mm/proc.S for
* details.
* On return, the CPU will be ready for the MMU to be turned on and
* the TCR will have been set.
*/
bl __cpu_setup // initialise processor
b __primary_switchENDPROC(stext)
这里调用了：
preserve_boot_args
__primary_switch
在preserve_boot_args将X0(fdt地址)暂时先保存到了X21中
preserve_boot_args:
mov x21, x0 // x21=FDT
adr_l x0, boot_args // record the contents of
stp x21, x1, [x0] // x0 .. x3 at kernel entry
stp x2, x3, [x0, #16]
dmb sy // needed before dc ivac with
// MMU off
mov x1, #0x20 // 4 x 8 bytes
b __inval_dcache_area // tail callENDPROC(preserve_boot_args)
__primary_switch调用了__primary_switched
__primary_switch:
ifdef CONFIG_RANDOMIZE_BASE
mov x19, x0 // preserve new SCTLR_EL1 value
mrs x20, sctlr_el1 // preserve old SCTLR_EL1 valueendif
bl __enable_mmuifdef CONFIG_RELOCATABLE
bl __relocate_kernelifdef CONFIG_RANDOMIZE_BASE
ldr x8, =__primary_switched
adrp x0, __PHYS_OFFSET
blr x8
__primary_switched将X21(fdt地址)保存到了__fdt_pointer全局变量中
__primary_switched:
adrp x4, init_thread_union
add sp, x4, #THREAD_SIZE
adr_l x5, init_task
msr sp_el0, x5 // Save thread_info
adr_l x8, vectors // load VBAR_EL1 with virtual
msr vbar_el1, x8 // vector table address
isb
stp xzr, x30, [sp, #-16]!
mov x29, sp
str_l x21, __fdt_pointer, x5 // Save FDT pointer
ldr_l x4, kimage_vaddr // Save the offset between
sub x4, x4, x0 // the kernel virtual and
str_l x4, kimage_voffset, x5 // physical mappings
// Clear BSS
adr_l x0, __bss_start
mov x1, xzr
adr_l x2, __bss_stop
sub x2, x2, x0
bl __pi_memset
dsb ishst // Make zero page visible to PTW
在setup_arch()的时候，调用setup_machine_fdt将fdt解析到了boot_command_line全局变量中
void __init setup_arch(char **cmdline_p)
{
pr_info("Boot CPU: AArch64 Processor [%08x]\n", read_cpuid_id());......
*cmdline_p = boot_command_line;......
setup_machine_fdt(__fdt_pointer);......
}
setup_machine_fdt()—>early_init_dt_scan()—>early_init_dt_scan_nodes()
在中，将fdt解析到了boot_command_line中
of_scan_flat_dt(early_init_dt_scan_chosen, boot_command_line)
static void __init setup_machine_fdt(phys_addr_t dt_phys)
{
void *dt_virt = fixmap_remap_fdt(dt_phys);
const char *name;
if (!dt_virt || !early_init_dt_scan(dt_virt)) {
pr_crit("\n"
"Error: invalid device tree blob at physical address %pa (virtual address 0x%p)\n"
"The dtb must be 8-byte aligned and must not exceed 2 MB in size\n"
"\nPlease check your bootloader.",
&dt_phys, dt_virt);
while (true)
cpu_relax();
}
name = of_flat_dt_get_machine_name();
if (!name)
return;
/* backward-compatibility for third-party applications */
machine_desc_set(name);
pr_info("Machine model: %s\n", name);
dump_stack_set_arch_desc("%s (DT)", name);}
bool __init early_init_dt_scan(void *params)
{
bool status;
status = early_init_dt_verify(params);
if (!status)
return false;
early_init_dt_scan_nodes();
return true;}
void __init early_init_dt_scan_nodes(void)
{
/* Retrieve various information from the /chosen node */
of_scan_flat_dt(early_init_dt_scan_chosen, boot_command_line);
/* Initialize {size,address}-cells info */
of_scan_flat_dt(early_init_dt_scan_root, NULL);
/* Setup memory, calling early_init_dt_add_memory_arch */
of_scan_flat_dt(early_init_dt_scan_memory, NULL);}
在start_kernel()打印了cmdline.
asmlinkage __visible void __init start_kernel(void)
{
…
pr_notice(“Kernel command line: %s\n”, boot_command_line);
…
}
