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2. ATF（ARM Trusted firmware）启动---bl1_arm64 启动 bl1 bl2 bl3

作者：从前慢现在也慢 | 2024-05-22 21:53:53

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arm64 启动 bl1 bl2 bl3

   

ATF（ARM Trusted Firmware）是一针对ARM芯片给出的底层的开源固件代码。固件将整个系统分成四种运行等级，分别为：EL0,EL1,EL2,EL3，并规定了每个安全等级中运行的Image名字。本文以ARCH64为示例，介绍冷启动时，ATF的运行过程。ATF的源代码可以从github上获取，具体地址如下：

　　系统上电之后首先会运行SCP boot ROM。之后会跳转到ATF的bl1中继续执行。bl1主要初始化CPU，设定异常向量，将bl2的image加载到安全RAM中，然后跳转到bl2中进行执行。

　　在bl2中将会去加载bl31和bl32以及bl33，其中的cpu状态切换以及跳转将在以下章节详细介绍。

　　bl1的主要代码存放在bl1目录中， bl1的连接脚本是bl1/bl1.ld.s文件，其中可以看到bl1的入口函数是:bl1_entrypoint。

1.1 bl1_entrypoint

　　该函数主要需要执行EL3环境的基本初始化，设定向量表，加载bl2 image并跳转到bl2等操作

  1. func bl1_entrypoint
  2. 	/* ---------------------------------------------------------------------
  3. 	 * If the reset address is programmable then bl1_entrypoint() is
  4. 	 * executed only on the cold boot path. Therefore, we can skip the warm
  5. 	 * boot mailbox mechanism.
  6. 	 * ---------------------------------------------------------------------
  7. 	 */
  8. /* EL3级别运行环境的初始化，该函数定义在   include/common/aarch64/el3_common_macros.S文件中
  9. */
  10. 	el3_entrypoint_common					\
  11. 		_set_endian=1					\
  12. 		_warm_boot_mailbox=!PROGRAMMABLE_RESET_ADDRESS	\
  13. 		_secondary_cold_boot=!COLD_BOOT_SINGLE_CPU	\
  14. 		_init_memory=1					\
  15. 		_init_c_runtime=1				\
  16. 		_exception_vectors=bl1_exceptions
  17.  
  18. 	/* ---------------------------------------------
  19. 	 * Architectural init. can be generic e.g.
  20. 	 * enabling stack alignment and platform spec-
  21. 	 * ific e.g. MMU & page table setup as per the
  22. 	 * platform memory map. Perform the latter here
  23. 	 * and the former in bl1_main.
  24. 	 * ---------------------------------------------
  25. 	 */
  26. 	bl	bl1_early_platform_setup	//调用bl1_early_platform_setup函数完成底层初始化
  27. 	bl	bl1_plat_arch_setup	//调用bl1_plat_arch_setup完成平台初始化
  28.  
  29. 	/* --------------------------------------------------
  30. 	 * Initialize platform and jump to our c-entry point
  31. 	 * for this type of reset.
  32. 	 * --------------------------------------------------
  33. 	 */
  34. 	bl	bl1_main	//调用bl1_main函数，初始化验证模块，加载下一阶段的image到RAM中
  35.  
  36. 	/* --------------------------------------------------
  37. 	 * Do the transition to next boot image.
  38. 	 * --------------------------------------------------
  39. 	 */
  40. 	b	el3_exit	//调用el3_exit函数，跳转到下一个image(bl2)
  41. endfunc bl1_entrypoint

1.2 el3_entrypoint_common函数

该函数是以宏的形式被定义的，主要完成el3基本设置和向量表注册

  1. .macro el3_entrypoint_common					\
  2. 		_set_endian, _warm_boot_mailbox, _secondary_cold_boot,	\
  3. 		_init_memory, _init_c_runtime, _exception_vectors
  4. /* 设定大小端 */
  5. 	.if \_set_endian
  6. 		/* -------------------------------------------------------------
  7. 		 * Set the CPU endianness before doing anything that might
  8. 		 * involve memory reads or writes.
  9. 		 * -------------------------------------------------------------
  10. 		 */
  11. 		mrs	x0, sctlr_el3
  12. 		bic	x0, x0, #SCTLR_EE_BIT
  13. 		msr	sctlr_el3, x0
  14. 		isb
  15. 	.endif /* _set_endian */
  16.  
  17. /* 判定是否需要调用do_cold_boot流程 */
  18. 	.if \_warm_boot_mailbox
  19. 		/* -------------------------------------------------------------
  20. 		 * This code will be executed for both warm and cold resets.
  21. 		 * Now is the time to distinguish between the two.
  22. 		 * Query the platform entrypoint address and if it is not zero
  23. 		 * then it means it is a warm boot so jump to this address.
  24. 		 * -------------------------------------------------------------
  25. 		 */
  26. 		bl	plat_get_my_entrypoint
  27. 		cbz	x0, do_cold_boot
  28. 		br	x0
  29.  
  30. 	do_cold_boot:
  31. 	.endif /* _warm_boot_mailbox */
  32.  
  33. 	/* ---------------------------------------------------------------------
  34. 	 * It is a cold boot.
  35. 	 * Perform any processor specific actions upon reset e.g. cache, TLB
  36. 	 * invalidations etc.
  37. 	 * ---------------------------------------------------------------------
  38. 	 */
  39. 	bl	reset_handler		//执行reset handle操作
  40.  
  41. /* 初始化异常向量 */
  42. 	el3_arch_init_common \_exception_vectors
  43.  
  44. /* 判定当前CPU是否是主CPU，如果是则做主CPU的初始化 */
  45. 	.if \_secondary_cold_boot
  46. 		/* -------------------------------------------------------------
  47. 		 * Check if this is a primary or secondary CPU cold boot.
  48. 		 * The primary CPU will set up the platform while the
  49. 		 * secondaries are placed in a platform-specific state until the
  50. 		 * primary CPU performs the necessary actions to bring them out
  51. 		 * of that state and allows entry into the OS.
  52. 		 * -------------------------------------------------------------
  53. 		 */
  54. 		bl	plat_is_my_cpu_primary
  55. 		cbnz	w0, do_primary_cold_boot
  56.  
  57. 		/* This is a cold boot on a secondary CPU */
  58. 		bl	plat_secondary_cold_boot_setup
  59. 		/* plat_secondary_cold_boot_setup() is not supposed to return */
  60. 		bl	el3_panic
  61.  
  62. 	do_primary_cold_boot:
  63. 	.endif /* _secondary_cold_boot */
  64.  
  65. 	/* ---------------------------------------------------------------------
  66. 	 * Initialize memory now. Secondary CPU initialization won't get to this
  67. 	 * point.
  68. 	 * ---------------------------------------------------------------------
  69. 	 */
  70. /* 初始化memory */
  71. 	.if \_init_memory
  72. 		bl	platform_mem_init
  73. 	.endif /* _init_memory */
  74.  
  75. 	/* ---------------------------------------------------------------------
  76. 	 * Init C runtime environment:
  77. 	 *   - Zero-initialise the NOBITS sections. There are 2 of them:
  78. 	 *       - the .bss section;
  79. 	 *       - the coherent memory section (if any).
  80. 	 *   - Relocate the data section from ROM to RAM, if required.
  81. 	 * ---------------------------------------------------------------------
  82. 	 */
  83. /* 初始化C语言的运行环境 */
  84. 	.if \_init_c_runtime
  85. #ifdef IMAGE_BL31
  86. 		/* -------------------------------------------------------------
  87. 		 * Invalidate the RW memory used by the BL31 image. This
  88. 		 * includes the data and NOBITS sections. This is done to
  89. 		 * safeguard against possible corruption of this memory by
  90. 		 * dirty cache lines in a system cache as a result of use by
  91. 		 * an earlier boot loader stage.
  92. 		 * -------------------------------------------------------------
  93. 		 */
  94. 		adr	x0, __RW_START__
  95. 		adr	x1, __RW_END__
  96. 		sub	x1, x1, x0
  97. 		bl	inv_dcache_range
  98. #endif /* IMAGE_BL31 */
  99.  
  100. 		ldr	x0, =__BSS_START__
  101. 		ldr	x1, =__BSS_SIZE__
  102. 		bl	zeromem
  103.  
  104. #if USE_COHERENT_MEM
  105. 		ldr	x0, =__COHERENT_RAM_START__
  106. 		ldr	x1, =__COHERENT_RAM_UNALIGNED_SIZE__
  107. 		bl	zeromem
  108. #endif
  109.  
  110. #ifdef IMAGE_BL1
  111. 		ldr	x0, =__DATA_RAM_START__
  112. 		ldr	x1, =__DATA_ROM_START__
  113. 		ldr	x2, =__DATA_SIZE__
  114. 		bl	memcpy16
  115. #endif
  116. 	.endif /* _init_c_runtime */
  117.  
  118. 	/* ---------------------------------------------------------------------
  119. 	 * Use SP_EL0 for the C runtime stack.
  120. 	 * ---------------------------------------------------------------------
  121. 	 */
  122. 	msr	spsel, #0
  123.  
  124. 	/* ---------------------------------------------------------------------
  125. 	 * Allocate a stack whose memory will be marked as Normal-IS-WBWA when
  126. 	 * the MMU is enabled. There is no risk of reading stale stack memory
  127. 	 * after enabling the MMU as only the primary CPU is running at the
  128. 	 * moment.
  129. 	 * ---------------------------------------------------------------------
  130. 	 */
  131. 	bl	plat_set_my_stack	//设定堆栈
  132.  
  133. #if STACK_PROTECTOR_ENABLED
  134. 	.if \_init_c_runtime
  135. 	bl	update_stack_protector_canary
  136. 	.endif /* _init_c_runtime */
  137. #endif
  138. 	.endm
  139.  
  140. #endif /* __EL3_COMMON_MACROS_S__ */


该函数是需要带参数调用，参数说明如下：

_set_endian：设定大小端

_warm_boot_mailbox：检查当前是属于冷启动还是热启动(power on or reset)

_secondary_cold_boot: 确定当前的CPU是主CPU还是从属CPU

_init_memory：是否需要初始化memory

_init_c_runtime: 是否需要初始化C语言的执行环境

_exception_vectors: 异常向量表地址

1.3 bl1_early_patform_setup

该函数用来完成早期的初始化操作，主要包括memory, page table, 所需外围设备的初始化以及相关状态设定等；

  1. void bl1_early_platform_setup(void)
  2. {
  3. /* 使能看门狗，初始化console,初始化memory */
  4. 	arm_bl1_early_platform_setup();
  5.  
  6. 	/*
  7. 	 * Initialize Interconnect for this cluster during cold boot.
  8. 	 * No need for locks as no other CPU is active.
  9. 	 */
  10. 	plat_arm_interconnect_init();//初始化外围设备
  11. 	/*
  12. 	 * Enable Interconnect coherency for the primary CPU's cluster.
  13. 	 */
  14. 	plat_arm_interconnect_enter_coherency();//使能外围设备
  15. }

1.4 bl_main

该函数完成bl2 image的加载和运行环境的设置，如果开启了trusted boot，则需要对image进行verify操作

  1. void bl1_main(void)
  2. {
  3. 	unsigned int image_id;
  4.  
  5. 	/* Announce our arrival */
  6. 	NOTICE(FIRMWARE_WELCOME_STR);
  7. 	NOTICE("BL1: %s\n", version_string);
  8. 	NOTICE("BL1: %s\n", build_message);
  9.  
  10. 	INFO("BL1: RAM %p - %p\n", (void *)BL1_RAM_BASE,
  11. 					(void *)BL1_RAM_LIMIT);
  12.  
  13. 	print_errata_status();
  14.  
  15. #if DEBUG
  16. 	u_register_t val;
  17. 	/*
  18. 	 * Ensure that MMU/Caches and coherency are turned on
  19. 	 */
  20. #ifdef AARCH32
  21. 	val = read_sctlr();
  22. #else
  23. 	val = read_sctlr_el3();
  24. #endif
  25. 	assert(val & SCTLR_M_BIT);
  26. 	assert(val & SCTLR_C_BIT);
  27. 	assert(val & SCTLR_I_BIT);
  28. 	/*
  29. 	 * Check that Cache Writeback Granule (CWG) in CTR_EL0 matches the
  30. 	 * provided platform value
  31. 	 */
  32. 	val = (read_ctr_el0() >> CTR_CWG_SHIFT) & CTR_CWG_MASK;
  33. 	/*
  34. 	 * If CWG is zero, then no CWG information is available but we can
  35. 	 * at least check the platform value is less than the architectural
  36. 	 * maximum.
  37. 	 */
  38. 	if (val != 0)
  39. 		assert(CACHE_WRITEBACK_GRANULE == SIZE_FROM_LOG2_WORDS(val));
  40. 	else
  41. 		assert(CACHE_WRITEBACK_GRANULE <= MAX_CACHE_LINE_SIZE);
  42. #endif
  43.  
  44. 	/* Perform remaining generic architectural setup from EL3 */
  45. 	bl1_arch_setup();	//设置下一个image的EL级别
  46.  
  47. #if TRUSTED_BOARD_BOOT
  48. 	/* Initialize authentication module */
  49. 	auth_mod_init();	//初始化image的验证模块
  50. #endif /* TRUSTED_BOARD_BOOT */
  51.  
  52. 	/* Perform platform setup in BL1. */
  53. 	bl1_platform_setup();	//平台相关设置，主要是IO的设置
  54.  
  55. 	/* Get the image id of next image to load and run. */
  56. 	image_id = bl1_plat_get_next_image_id();	//获取下一个阶段image的ID值。默认返回值为BL2_IMAGE_ID
  57.  
  58. 	/*
  59. 	 * We currently interpret any image id other than
  60. 	 * BL2_IMAGE_ID as the start of firmware update.
  61. 	 */
  62. 	if (image_id == BL2_IMAGE_ID)
  63. 		bl1_load_bl2();		//将bl2 image加载到安全RAM中
  64. 	else
  65. 		NOTICE("BL1-FWU: *******FWU Process Started*******\n");
  66.  
  67. 	bl1_prepare_next_image(image_id);	//获取bl2 image的描述信息，包括名字，ID，entry potin info等，并将这些信息保存到bl1_cpu_context的上下文中
  68. 	console_flush();
  69. }

1.5 bl1_prepare_next_image

该函数用来获取bl2 image的描述信息，获取bl2的入口地址，这只下个阶段的CPU上下文，以备执行从bl1跳转到bl2的操作使用

  1. void bl1_prepare_next_image(unsigned int image_id)
  2. {
  3. 	unsigned int security_state;
  4. 	image_desc_t *image_desc;
  5. 	entry_point_info_t *next_bl_ep;
  6.  
  7. #if CTX_INCLUDE_AARCH32_REGS
  8. 	/*
  9. 	 * Ensure that the build flag to save AArch32 system registers in CPU
  10. 	 * context is not set for AArch64-only platforms.
  11. 	 */
  12. 	if (((read_id_aa64pfr0_el1() >> ID_AA64PFR0_EL1_SHIFT)
  13. 			& ID_AA64PFR0_ELX_MASK) == 0x1) {
  14. 		ERROR("EL1 supports AArch64-only. Please set build flag "
  15. 				"CTX_INCLUDE_AARCH32_REGS = 0");
  16. 		panic();
  17. 	}
  18. #endif
  19.  
  20. 	/* Get the image descriptor. */
  21. /* 获取bl2 image的描述信息，主要包括入口地址，名字等信息 */
  22. 	image_desc = bl1_plat_get_image_desc(image_id);
  23. 	assert(image_desc);
  24.  
  25. 	/* Get the entry point info. */
  26. /* 获取image的入口地址信息 */
  27. 	next_bl_ep = &image_desc->ep_info;
  28.  
  29. 	/* Get the image security state. */
  30. /* 获取bl2 image的安全状态（判定该image是属于安全态的image的还是非安全态的image） */
  31. 	security_state = GET_SECURITY_STATE(next_bl_ep->h.attr);
  32.  
  33. 	/* Setup the Secure/Non-Secure context if not done already. */
  34. /* 设定用于存放CPU context的变量 */
  35. 	if (!cm_get_context(security_state))
  36. 		cm_set_context(&bl1_cpu_context[security_state], security_state);
  37.  
  38. 	/* Prepare the SPSR for the next BL image. */
  39. /* 为下个阶段的image准备好SPSR数据 */
  40. 	if (security_state == SECURE) {
  41. 		next_bl_ep->spsr = SPSR_64(MODE_EL1, MODE_SP_ELX,
  42. 				   DISABLE_ALL_EXCEPTIONS);
  43. 	} else {
  44. 		/* Use EL2 if supported else use EL1. */
  45. 		if (read_id_aa64pfr0_el1() &
  46. 			(ID_AA64PFR0_ELX_MASK << ID_AA64PFR0_EL2_SHIFT)) {
  47. 			next_bl_ep->spsr = SPSR_64(MODE_EL2, MODE_SP_ELX,
  48. 				DISABLE_ALL_EXCEPTIONS);
  49. 		} else {
  50. 			next_bl_ep->spsr = SPSR_64(MODE_EL1, MODE_SP_ELX,
  51. 			   DISABLE_ALL_EXCEPTIONS);
  52. 		}
  53. 	}
  54.  
  55. 	/* Allow platform to make change */
  56. 	bl1_plat_set_ep_info(image_id, next_bl_ep);
  57.  
  58. 	/* Prepare the context for the next BL image. */
  59. /* 使用获取到的bl2 image的entrypoint info数据来初始化cpu context */
  60. 	cm_init_my_context(next_bl_ep);
  61. /* 为进入到下个EL级别做准备 */
  62. 	cm_prepare_el3_exit(security_state);
  63.  
  64. 	/* Indicate that image is in execution state. */
  65. /* 设定image的执行状态 */
  66. 	image_desc->state = IMAGE_STATE_EXECUTED;
  67.  
  68. /* 打印出bl2 image的入口信息 */
  69. 	print_entry_point_info(next_bl_ep);
  70. }

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