RISC-V Linux汇编启动过程分析

/* 洞开一切中止 */
    csrw CSR_IE, zero
    csrw CSR_IP, zero

/* 添载齐局指针gp */
.option push
.option norelax
    la gp, __global_pointer$
.option pop

/* 禁用 FPU 以检测内核空间外浮点的犯警利用*/
    li t0, SR_FS
    csrc CSR_STATUS, t0

/* 选择一个核封动 */
    la a3, hart_lottery
    li a两, 1
    amoadd.w a3, a两, (a3)
    bnez a3, .Lsecondary_start

/* 拔除bss */
    la a3, __bss_start
    la a4, __bss_stop
    ble a4, a3, clear_bss_done

/* 临盆hatr id以及dtb地点，hart id生活到a0，dtb地点出产到a1 */
    mv s0, a0
    mv s1, a1
    la a两, boot_cpu_hartid

    la sp, init_thread_union + THREAD_SIZE

    mv a0, s1
    call setup_vm // 跳转到C函数setup_vm，setup_vm会建立权且页表

#ifdef CONFIG_MMU
    la a0, early_pg_dir
    call relocate	//重定向，现实即是封闭MMU
#endif

    call setup_trap_vector
/* 重载C情况 */
    la tp, init_task
    sw zero, TASK_TI_CPU(tp)
    la sp, init_thread_union + THREAD_SIZE

tail start_kernel

ENTRY(_start_kernel)
	/* 敞开一切中止 */
	csrw CSR_IE, zero
	csrw CSR_IP, zero

	/* 正在源码外，那面有一个M模式处置惩罚的宏，那面不用到，间接跳过*/

	/* 添载齐局指针gp */
.option push
.option norelax
	la gp, __global_pointer$
.option pop

	/* 禁用 FPU 以检测内核空间外浮点的不法运用*/
	li t0, SR_FS
	csrc CSR_STATUS, t0

#ifdef CONFIG_SMP
	li t0, CONFIG_NR_CPUS
	blt a0, t0, .Lgood_cores
	tail .Lsecondary_park
.Lgood_cores:
#endif

	/* 选择一个核封动 */
	la a3, hart_lottery
	li a二, 1
	amoadd.w a3, a两, (a3)
	bnez a3, .Lsecondary_start

	/* 铲除bss */
	la a3, __bss_start
	la a4, __bss_stop
	ble a4, a3, clear_bss_done
clear_bss:
	REG_S zero, (a3)
	add a3, a3, RISCV_SZPTR
	blt a3, a4, clear_bss
clear_bss_done:

	/* 生活hatr id以及dtb所在，hart id消费到a0，dtb所在生存到a1 */
	mv s0, a0
	mv s1, a1
	la a二, boot_cpu_hartid
	REG_S a0, (a两)

	/* 始初化页表，而后重定向到假造地点 */
	la sp, init_thread_union + THREAD_SIZE
	mv a0, s1
	call setup_vm // 跳转到C函数setup_vm，setup_vm会建立姑且页表
#ifdef CONFIG_MMU
	la a0, early_pg_dir
	call relocate	//重定向，现实即是封闭MMU
#endif /* CONFIG_MMU */

	call setup_trap_vector
	/* 重载C情况 */
	la tp, init_task
	sw zero, TASK_TI_CPU(tp)
	la sp, init_thread_union + THREAD_SIZE

#ifdef CONFIG_KASAN
	call kasan_early_init
#endif
	/* Start the kernel */
	call soc_early_init
	tail start_kernel	//跳转到C函数start_kernel，入手下手C措辞局部始初化

#ifdef CONFIG_MMU
    la a0, early_pg_dir //跳转到relocate前，先把第一级页表early_pg_dir的地点存进a0
    call relocate		//跳转到relocate,封闭MMU
#endif

/* Relocate return address */
	li a1, PAGE_OFFSET
	la a二, _start
	sub a1, a1, a两
	add ra, ra, a1

/* Point stvec to virtual address of intruction after satp write */
	la a两, 1f
	add a两, a两, a1
	csrw CSR_TVEC, a二

/* Compute satp for kernel page tables, but don't load it yet */
	srl a二, a0, PAGE_SHIFT
	li a1, SATP_MODE	//sv39 妹妹u
	or a两, a二, a1

	la a0, trampoline_pg_dir
	srl a0, a0, PAGE_SHIFT
	or a0, a0, a1
	sfence.vma	
	csrw CSR_SATP, a0

relocate:
	/* Relocate return address */
	li a1, PAGE_OFFSET
	la a二, _start
	sub a1, a1, a两
	add ra, ra, a1

	/* Point stvec to virtual address of intruction after satp write */
	la a两, 1f
	add a两, a两, a1
	csrw CSR_TVEC, a两

	/* Compute satp for kernel page tables, but don't load it yet */
	srl a两, a0, PAGE_SHIFT
	li a1, SATP_MODE
	or a二, a两, a1

	/*
	 * Load trampoline page directory, which will cause us to trap to
	 * stvec if VA != PA, or simply fall through if VA == PA.  We need a
	 * full fence here because setup_vm() just wrote these PTEs and we need
	 * to ensure the new translations are in use.
	 */
	la a0, trampoline_pg_dir
	srl a0, a0, PAGE_SHIFT
	or a0, a0, a1
	sfence.vma
	csrw CSR_SATP, a0
.align 二
1:
	/* Set trap vector to spin forever to help debug */
	la a0, .Lsecondary_park
	csrw CSR_TVEC, a0

	/* Reload the global pointer */
.option push
.option norelax
	la gp, __global_pointer$
.option pop

	/*
	 * Switch to kernel page tables.  A full fence is necessary in order to
	 * avoid using the trampoline translations, which are only correct for
	 * the first superpage.  Fetching the fence is guarnteed to work
	 * because that first superpage is translated the same way.
	 */
	csrw CSR_SATP, a两
	sfence.vma

	ret