本帖最后由 beyond_笑谈 于 2024-12-19 22:02 编辑
多谢EE提供的这次《Linux内核深度解析》好书共读活动，希望借助本次活动可以深入了解Linux内核知识。
U-Boot下载：u-boot-2017.09.tar
将下载的代码利用FTP服务器传到ubuntu并且解压缩，如下图
利用vim打开uboot的入口文件 start.S，如下图
利用Source Insight 打开start.S文件进行阅读和备注
start.S的代码如下
[/*
* (C) Copyright 2013
* David Feng <fenghua@phytium.com.cn>
* Made notes by Allen Shen - 2024.12
* SPDX-License-Identifier: GPL-2.0+
*/
#include <asm-offsets.h>
#include <config.h>
#include <linux/linkage.h>
#include <asm/macro.h>
#include <asm/armv8/mmu.h>
/*************************************************************************
*
* Startup Code (reset vector)
*
*************************************************************************/
.globl _start /*uboot start from here*/
_start
#ifdef CONFIG_ENABLE_ARM_SOC_BOOT0_HOOK
/*
* Various SoCs need something special and SoC-specific up front in
* order to boot, allow them to set that in their boot0.h file and then
* use it here.
*/
#include <asm/arch/boot0.h>
#else[
b reset /*To reset*/
#endif
.align 3
.globl _TEXT_BASE
_TEXT_BASE:
.quad CONFIG_SYS_TEXT_BASE
/*
* These are defined in the linker script.
*/
.globl _end_ofs
_end_ofs:
.quad _end - _start
.globl _bss_start_ofs
_bss_start_ofs:
.quad __bss_start - _start
.globl _bss_end_ofs
_bss_end_ofs:
.quad __bss_end - _start
reset:
/* Allow the board to save important registers */
b save_boot_params
.globl save_boot_params_ret
save_boot_params_ret:
#ifdef CONFIG_SYS_RESET_SCTRL
bl reset_sctrl
#endif
/*
* Could be EL3/EL2/EL1, Initial State:
* Little Endian, MMU Disabled, i/dCache Disabled
*/
adr x0, vectors
switch_el x1, 3f, 2f, 1f
3: msr vbar_el3, x0
mrs x0, scr_el3
orr x0, x0, #0xf /* SCR_EL3.NS|IRQ|FIQ|EA */
msr scr_el3, x0
msr cptr_el3, xzr /* Enable FP/SIMD */
#ifdef COUNTER_FREQUENCY
ldr x0, =COUNTER_FREQUENCY
msr cntfrq_el0, x0 /* Initialize CNTFRQ */
#endif
b 0f
2: msr vbar_el2, x0
mov x0, #0x33ff
msr cptr_el2, x0 /* Enable FP/SIMD */
b 0f
1: msr vbar_el1, x0
mov x0, #3 << 20
msr cpacr_el1, x0 /* Enable FP/SIMD */
0:
/*
* Enable SMPEN bit for coherency.
* This register is not architectural but at the moment
* this bit should be set for A53/A57/A72.
*/
#ifdef CONFIG_ARMV8_SET_SMPEN
switch_el x1, 3f, 1f, 1f
3:
mrs x0, S3_1_c15_c2_1 /* cpuectlr_el1 */
orr x0, x0, #0x40
msr S3_1_c15_c2_1, x0
1:
#endif
/* Apply ARM core specific erratas */
bl apply_core_errata
/*
* Cache/BPB/TLB Invalidate
* i-cache is invalidated before enabled in icache_enable()
* tlb is invalidated before mmu is enabled in dcache_enable()
* d-cache is invalidated before enabled in dcache_enable()
*/
/* Processor specific initialization */
bl lowlevel_init
#if defined(CONFIG_ARMV8_SPIN_TABLE) && !defined(CONFIG_SPL_BUILD)
branch_if_master x0, x1, master_cpu
b spin_table_secondary_jump
/* never return */
#elif defined(CONFIG_ARMV8_MULTIENTRY)
branch_if_master x0, x1, master_cpu
/*
* Slave CPUs
*/
slave_cpu:
wfe
ldr x1, =CPU_RELEASE_ADDR
ldr x0, [x1]
cbz x0, slave_cpu
br x0 /* branch to the given address */
#endif /* CONFIG_ARMV8_MULTIENTRY */
master_cpu:
bl _main
#ifdef CONFIG_SYS_RESET_SCTRL
reset_sctrl:
switch_el x1, 3f, 2f, 1f
3:
mrs x0, sctlr_el3
b 0f
2:
mrs x0, sctlr_el2
b 0f
1:
mrs x0, sctlr_el1
0:
ldr x1, =0xfdfffffa
and x0, x0, x1
switch_el x1, 6f, 5f, 4f
6:
msr sctlr_el3, x0
b 7f
5:
msr sctlr_el2, x0
b 7f
4:
msr sctlr_el1, x0
7:
dsb sy
isb
b __asm_invalidate_tlb_all
ret
#endif
/*-----------------------------------------------------------------------*/
WEAK(apply_core_errata)
mov x29, lr /* Save LR */
/* For now, we support Cortex-A57 specific errata only */
/* Check if we are running on a Cortex-A57 core */
branch_if_a57_core x0, apply_a57_core_errata
0:
mov lr, x29 /* Restore LR */
ret
apply_a57_core_errata:
#ifdef CONFIG_ARM_ERRATA_828024
mrs x0, S3_1_c15_c2_0 /* cpuactlr_el1 */
/* Disable non-allocate hint of w-b-n-a memory type */
orr x0, x0, #1 << 49
/* Disable write streaming no L1-allocate threshold */
orr x0, x0, #3 << 25
/* Disable write streaming no-allocate threshold */
orr x0, x0, #3 << 27
msr S3_1_c15_c2_0, x0 /* cpuactlr_el1 */
#endif
#ifdef CONFIG_ARM_ERRATA_826974
mrs x0, S3_1_c15_c2_0 /* cpuactlr_el1 */
/* Disable speculative load execution ahead of a DMB */
orr x0, x0, #1 << 59
msr S3_1_c15_c2_0, x0 /* cpuactlr_el1 */
#endif
#ifdef CONFIG_ARM_ERRATA_833471
mrs x0, S3_1_c15_c2_0 /* cpuactlr_el1 */
/* FPSCR write flush.
* Note that in some cases where a flush is unnecessary this
could impact performance. */
orr x0, x0, #1 << 38
msr S3_1_c15_c2_0, x0 /* cpuactlr_el1 */
#endif
#ifdef CONFIG_ARM_ERRATA_829520
mrs x0, S3_1_c15_c2_0 /* cpuactlr_el1 */
/* Disable Indirect Predictor bit will prevent this erratum
from occurring
* Note that in some cases where a flush is unnecessary this
could impact performance. */
orr x0, x0, #1 << 4
msr S3_1_c15_c2_0, x0 /* cpuactlr_el1 */
#endif
#ifdef CONFIG_ARM_ERRATA_833069
mrs x0, S3_1_c15_c2_0 /* cpuactlr_el1 */
/* Disable Enable Invalidates of BTB bit */
and x0, x0, #0xE
msr S3_1_c15_c2_0, x0 /* cpuactlr_el1 */
#endif
b 0b
ENDPROC(apply_core_errata)
/*-----------------------------------------------------------------------*/
WEAK(lowlevel_init)
mov x29, lr /* Save LR */
#if defined(CONFIG_GICV2) || defined(CONFIG_GICV3)
branch_if_slave x0, 1f
ldr x0, =GICD_BASE
bl gic_init_secure
1:
#if defined(CONFIG_GICV3)
ldr x0, =GICR_BASE
bl gic_init_secure_percpu
#elif defined(CONFIG_GICV2)
ldr x0, =GICD_BASE
ldr x1, =GICC_BASE
bl gic_init_secure_percpu
#endif
#endif
#ifdef CONFIG_ARMV8_MULTIENTRY
branch_if_master x0, x1, 2f
/*
* Slave should wait for master clearing spin table.
* This sync prevent salves observing incorrect
* value of spin table and jumping to wrong place.
*/
#if defined(CONFIG_GICV2) || defined(CONFIG_GICV3)
#ifdef CONFIG_GICV2
ldr x0, =GICC_BASE
#endif
bl gic_wait_for_interrupt
#endif
/*
* All slaves will enter EL2 and optionally EL1.
*/
adr x4, lowlevel_in_el2
ldr x5, =ES_TO_AARCH64
bl armv8_switch_to_el2
lowlevel_in_el2:
#ifdef CONFIG_ARMV8_SWITCH_TO_EL1
adr x4, lowlevel_in_el1
ldr x5, =ES_TO_AARCH64
bl armv8_switch_to_el1
lowlevel_in_el1:
#endif
#endif /* CONFIG_ARMV8_MULTIENTRY */
2:
mov lr, x29 /* Restore LR */
ret
ENDPROC(lowlevel_init)
WEAK(smp_kick_all_cpus)
/* Kick secondary cpus up by SGI 0 interrupt */
#if defined(CONFIG_GICV2) || defined(CONFIG_GICV3)
ldr x0, =GICD_BASE
b gic_kick_secondary_cpus
#endif
ret
ENDPROC(smp_kick_all_cpus)
/*-----------------------------------------------------------------------*/
ENTRY(c_runtime_cpu_setup)
/* Relocate vBAR */
adr x0, vectors
switch_el x1, 3f, 2f, 1f
3: msr vbar_el3, x0
b 0f
2: msr vbar_el2, x0
b 0f
1: msr vbar_el1, x0
0:
ret
ENDPROC(c_runtime_cpu_setup)
WEAK(save_boot_params)
b save_boot_params_ret /* back to my caller */
ENDPROC(save_boot_params)
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