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3. ATF（ARM Trusted firmware）启动---bl2_atf mmu

作者：不正经 | 2024-05-22 22:00:26

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atf mmu

   

BL2 image将会为后续image的加载执行相关的初始化操作。主要是内存，MMU，串口以及EL3软件运行环境的设置，并且加载bl3x的image到RAM中。通过查看bl2.ld.S文件就可以发现，bl2 image的入口函数是bl2_entrypoint。该函数定义在bl2/aarch64/bl2_entrypoint.S文件中。

1.bl2_entrypoint

该函数的内容如下，该函数最终会出发smc操作，从bl1中将CPU的控制权转交给bl31：

  1. func bl2_entrypoint
  2. 	/*---------------------------------------------
  3. 	 * Save from x1 the extents of the tzram
  4. 	 * available to BL2 for future use.
  5. 	 * x0 is not currently used.
  6. 	 * ---------------------------------------------
  7. 	 */
  8. 	mov	x20, x1
  9.  
  10. 	/* ---------------------------------------------
  11. 	 * Set the exception vector to something sane.
  12. 	 * ---------------------------------------------
  13. 	 */
  14. 	adr	x0, early_exceptions	//设定异常向量
  15. 	msr	vbar_el1, x0
  16. 	isb
  17.  
  18. 	/* ---------------------------------------------
  19. 	 * Enable the SError interrupt now that the
  20. 	 * exception vectors have been setup.
  21. 	 * ---------------------------------------------
  22. 	 */
  23. 	msr	daifclr, #DAIF_ABT_BIT
  24.  
  25. 	/* ---------------------------------------------
  26. 	 * Enable the instruction cache, stack pointer
  27. 	 * and data access alignment checks
  28. 	 * ---------------------------------------------
  29. 	 */
  30. 	mov	x1, #(SCTLR_I_BIT | SCTLR_A_BIT | SCTLR_SA_BIT)
  31. 	mrs	x0, sctlr_el1
  32. 	orr	x0, x0, x1
  33. 	msr	sctlr_el1, x0
  34. 	isb
  35.  
  36. 	/* ---------------------------------------------
  37. 	 * Invalidate the RW memory used by the BL2
  38. 	 * image. This includes the data and NOBITS
  39. 	 * sections. This is done to safeguard against
  40. 	 * possible corruption of this memory by dirty
  41. 	 * cache lines in a system cache as a result of
  42. 	 * use by an earlier boot loader stage.
  43. 	 * ---------------------------------------------
  44. 	 */
  45. 	adr	x0, __RW_START__
  46. 	adr	x1, __RW_END__
  47. 	sub	x1, x1, x0
  48. 	bl	inv_dcache_range
  49.  
  50. 	/* ---------------------------------------------
  51. 	 * Zero out NOBITS sections. There are 2 of them:
  52. 	 *   - the .bss section;
  53. 	 *   - the coherent memory section.
  54. 	 * ---------------------------------------------
  55. 	 */
  56. 	ldr	x0, =__BSS_START__
  57. 	ldr	x1, =__BSS_SIZE__
  58. 	bl	zeromem
  59.  
  60. #if USE_COHERENT_MEM
  61. 	ldr	x0, =__COHERENT_RAM_START__
  62. 	ldr	x1, =__COHERENT_RAM_UNALIGNED_SIZE__
  63. 	bl	zeromem
  64. #endif
  65.  
  66. 	/* --------------------------------------------
  67. 	 * Allocate a stack whose memory will be marked
  68. 	 * as Normal-IS-WBWA when the MMU is enabled.
  69. 	 * There is no risk of reading stale stack
  70. 	 * memory after enabling the MMU as only the
  71. 	 * primary cpu is running at the moment.
  72. 	 * --------------------------------------------
  73. 	 */
  74. 	bl	plat_set_my_stack	//初始化bl2运行的栈
  75.  
  76. 	/* ---------------------------------------------
  77. 	 * Initialize the stack protector canary before
  78. 	 * any C code is called.
  79. 	 * ---------------------------------------------
  80. 	 */
  81. #if STACK_PROTECTOR_ENABLED
  82. 	bl	update_stack_protector_canary
  83. #endif
  84.  
  85. 	/* ---------------------------------------------
  86. 	 * Perform early platform setup & platform
  87. 	 * specific early arch. setup e.g. mmu setup
  88. 	 * ---------------------------------------------
  89. 	 */
  90. 	mov	x0, x20
  91. 	bl	bl2_early_platform_setup	//设置平台相关
  92. 	bl	bl2_plat_arch_setup	//设置架构相关
  93.  
  94. 	/* ---------------------------------------------
  95. 	 * Jump to main function.
  96. 	 * ---------------------------------------------
  97. 	 */
  98. 	bl	bl2_main	//跳转到BL2的主要函数执行，从该函数中跳转到bl31以及bl31,
  99.  
  100. 	/* ---------------------------------------------
  101. 	 * Should never reach this point.
  102. 	 * ---------------------------------------------
  103. 	 */
  104. 	no_ret	plat_panic_handler
  105.  
  106. endfunc bl2_entrypoint

2. bl2_main

该函数主要实现将bl3x的image加载RAM中，并通过smc调用执行bl1中指定的smc handle将CPU的全向交给bl31。

  1. void bl2_main(void)
  2. {
  3. 	entry_point_info_t *next_bl_ep_info;
  4.  
  5. 	NOTICE("BL2: %s\n", version_string);
  6. 	NOTICE("BL2: %s\n", build_message);
  7.  
  8. 	/* Perform remaining generic architectural setup in S-EL1 */
  9. 	bl2_arch_setup();
  10.  
  11. #if TRUSTED_BOARD_BOOT
  12. 	/* Initialize authentication module */
  13. 	auth_mod_init();	//初始化image验证模块
  14. #endif /* TRUSTED_BOARD_BOOT */
  15.  
  16. 	/* Load the subsequent bootloader images. */
  17. 	next_bl_ep_info = bl2_load_images();	//加载bl3x image到RAM中并返回bl31的入口地址
  18.  
  19. #ifdef AARCH32
  20. 	/*
  21. 	 * For AArch32 state BL1 and BL2 share the MMU setup.
  22. 	 * Given that BL2 does not map BL1 regions, MMU needs
  23. 	 * to be disabled in order to go back to BL1.
  24. 	 */
  25. 	disable_mmu_icache_secure();
  26. #endif /* AARCH32 */
  27.  
  28. 	console_flush();
  29.  
  30. 	/*
  31. 	 * Run next BL image via an SMC to BL1. Information on how to pass
  32. 	 * control to the BL32 (if present) and BL33 software images will
  33. 	 * be passed to next BL image as an argument.
  34. 	 */
  35. /* 调用smc指令，触发在bl1中设定的smc异常中断处理函数，跳转到bl31 */
  36. 	smc(BL1_SMC_RUN_IMAGE, (unsigned long)next_bl_ep_info, 0, 0, 0, 0, 0, 0);
  37. }

3. bl2_load_images

该函数用来加载bl3x的image到RAM中，返回一个具有image入口信息的变量。smc handle根据该变量跳转到bl31进行执行
 

  1. entry_point_info_t *bl2_load_images(void)
  2. {
  3. 	bl_params_t *bl2_to_next_bl_params;
  4. 	bl_load_info_t *bl2_load_info;
  5. 	const bl_load_info_node_t *bl2_node_info;
  6. 	int plat_setup_done = 0;
  7. 	int err;
  8.  
  9. 	/*
  10. 	 * Get information about the images to load.
  11. 	 */
  12. /* 获取bl3x image的加载和入口信息 */
  13. 	bl2_load_info = plat_get_bl_image_load_info();
  14.  
  15. /* 检查返回的bl2_load_info中的信息是否正确 */
  16. 	assert(bl2_load_info);
  17. 	assert(bl2_load_info->head);
  18. 	assert(bl2_load_info->h.type == PARAM_BL_LOAD_INFO);
  19. 	assert(bl2_load_info->h.version >= VERSION_2);
  20.  
  21. /* 将bl2_load_info中的head变量的值赋值为bl2_node_info，即将bl31 image的入口信息传递給bl2_node_info变量 */
  22. 	bl2_node_info = bl2_load_info->head;
  23.  
  24. /* 进入loop循环， */
  25. 	while (bl2_node_info) {
  26. 		/*
  27. 		 * Perform platform setup before loading the image,
  28. 		 * if indicated in the image attributes AND if NOT
  29. 		 * already done before.
  30. 		 */
  31. /* 在加载特定的bl3x image到RAM之前先确定是否需要做平台的初始化 */
  32. 		if (bl2_node_info->image_info->h.attr & IMAGE_ATTRIB_PLAT_SETUP) {
  33. 			if (plat_setup_done) {
  34. 				WARN("BL2: Platform setup already done!!\n");
  35. 			} else {
  36. 				INFO("BL2: Doing platform setup\n");
  37. 				bl2_platform_setup();
  38. 				plat_setup_done = 1;
  39. 			}
  40. 		}
  41.  
  42. /* 对bl3x image进行电子验签，如果通过则执行加载操作 */
  43. 		if (!(bl2_node_info->image_info->h.attr & IMAGE_ATTRIB_SKIP_LOADING)) {
  44. 			INFO("BL2: Loading image id %d\n", bl2_node_info->image_id);
  45. 			err = load_auth_image(bl2_node_info->image_id,
  46. 				bl2_node_info->image_info);
  47. 			if (err) {
  48. 				ERROR("BL2: Failed to load image (%i)\n", err);
  49. 				plat_error_handler(err);
  50. 			}
  51. 		} else {
  52. 			INFO("BL2: Skip loading image id %d\n", bl2_node_info->image_id);
  53. 		}
  54.  
  55. 		/* Allow platform to handle image information. */
  56. /* 可以根据实际需要更改，通过给定image ID来更改image的加载信息 */
  57. 		err = bl2_plat_handle_post_image_load(bl2_node_info->image_id);
  58. 		if (err) {
  59. 			ERROR("BL2: Failure in post image load handling (%i)\n", err);
  60. 			plat_error_handler(err);
  61. 		}
  62.  
  63. 		/* Go to next image */
  64. 		bl2_node_info = bl2_node_info->next_load_info;
  65. 	}
  66.  
  67. 	/*
  68. 	 * Get information to pass to the next image.
  69. 	 */
  70. /* 获取下一个执行的Image的入口信息，并且将以后会被执行的image的入口信息组合成链表 ,t通过判断image des中的ep_info.h.attr的值是否为（EXECUTABLE|EP_FIRST_EX）来确定接下来第一个被执行的image*/
  71. 	bl2_to_next_bl_params = plat_get_next_bl_params();
  72. 	assert(bl2_to_next_bl_params);
  73. 	assert(bl2_to_next_bl_params->head);
  74. 	assert(bl2_to_next_bl_params->h.type == PARAM_BL_PARAMS);
  75. 	assert(bl2_to_next_bl_params->h.version >= VERSION_2);
  76.  
  77. 	/* Flush the parameters to be passed to next image */
  78. 	plat_flush_next_bl_params();
  79.  
  80. /* 返回下一个进入的image的入口信息,即bl31的入口信息 */
  81. 	return bl2_to_next_bl_params->head->ep_info;
  82. }


4.REGISTER_BL_IMAGE_DESCS(bl2_mem_params_descs)

该宏的执行将会初始化组成bl2加载bl3x image的列表使用到的重要全局变量，其中bl2_mem_params_descs变量的定义如下：

  1. static bl_mem_params_node_t bl2_mem_params_descs[] = {
  2. #ifdef SCP_BL2_BASE
  3. 	/* Fill SCP_BL2 related information if it exists */
  4.     {
  5. 	    .image_id = SCP_BL2_IMAGE_ID,
  6.  
  7. 	    SET_STATIC_PARAM_HEAD(ep_info, PARAM_IMAGE_BINARY,
  8. 		    VERSION_2, entry_point_info_t, SECURE | NON_EXECUTABLE),
  9.  
  10. 	    SET_STATIC_PARAM_HEAD(image_info, PARAM_IMAGE_BINARY,
  11. 		    VERSION_2, image_info_t, 0),
  12. 	    .image_info.image_base = SCP_BL2_BASE,
  13. 	    .image_info.image_max_size = PLAT_CSS_MAX_SCP_BL2_SIZE,
  14.  
  15. 	    .next_handoff_image_id = INVALID_IMAGE_ID,
  16.     },
  17. #endif /* SCP_BL2_BASE */
  18.  
  19. #ifdef EL3_PAYLOAD_BASE
  20. 	/* Fill EL3 payload related information (BL31 is EL3 payload)*/
  21.     {
  22. 	    .image_id = BL31_IMAGE_ID,
  23.  
  24. 	    SET_STATIC_PARAM_HEAD(ep_info, PARAM_EP,
  25. 		    VERSION_2, entry_point_info_t,
  26. 		    SECURE | EXECUTABLE | EP_FIRST_EXE),
  27. 	    .ep_info.pc = EL3_PAYLOAD_BASE,
  28. 	    .ep_info.spsr = SPSR_64(MODE_EL3, MODE_SP_ELX,
  29. 		    DISABLE_ALL_EXCEPTIONS),
  30.  
  31. 	    SET_STATIC_PARAM_HEAD(image_info, PARAM_EP,
  32. 		    VERSION_2, image_info_t,
  33. 		    IMAGE_ATTRIB_PLAT_SETUP | IMAGE_ATTRIB_SKIP_LOADING),
  34.  
  35. 	    .next_handoff_image_id = INVALID_IMAGE_ID,
  36.     },
  37.  
  38. #else /* EL3_PAYLOAD_BASE */
  39.  
  40. 	/* Fill BL31 related information */
  41.     {
  42. 	    .image_id = BL31_IMAGE_ID,
  43.  
  44. 	    SET_STATIC_PARAM_HEAD(ep_info, PARAM_EP,
  45. 		    VERSION_2, entry_point_info_t,
  46. 		    SECURE | EXECUTABLE | EP_FIRST_EXE),
  47. 	    .ep_info.pc = BL31_BASE,
  48. 	    .ep_info.spsr = SPSR_64(MODE_EL3, MODE_SP_ELX,
  49. 		    DISABLE_ALL_EXCEPTIONS),
  50. #if DEBUG
  51. 	    .ep_info.args.arg1 = ARM_BL31_PLAT_PARAM_VAL,
  52. #endif
  53.  
  54. 	    SET_STATIC_PARAM_HEAD(image_info, PARAM_EP,
  55. 		    VERSION_2, image_info_t, IMAGE_ATTRIB_PLAT_SETUP),
  56. 	    .image_info.image_base = BL31_BASE,
  57. 	    .image_info.image_max_size = BL31_LIMIT - BL31_BASE,
  58.  
  59. # ifdef BL32_BASE
  60. 	    .next_handoff_image_id = BL32_IMAGE_ID,
  61. # else
  62. 	    .next_handoff_image_id = BL33_IMAGE_ID,
  63. # endif
  64.     },
  65.  
  66. # ifdef BL32_BASE
  67. 	/* Fill BL32 related information */
  68.     {
  69. 	    .image_id = BL32_IMAGE_ID,
  70.  
  71. 	    SET_STATIC_PARAM_HEAD(ep_info, PARAM_EP,
  72. 		    VERSION_2, entry_point_info_t, SECURE | EXECUTABLE),
  73. 	    .ep_info.pc = BL32_BASE,
  74.  
  75. 	    SET_STATIC_PARAM_HEAD(image_info, PARAM_EP,
  76. 		    VERSION_2, image_info_t, 0),
  77. 	    .image_info.image_base = BL32_BASE,
  78. 	    .image_info.image_max_size = BL32_LIMIT - BL32_BASE,
  79.  
  80. 	    .next_handoff_image_id = BL33_IMAGE_ID,
  81.     },
  82. # endif /* BL32_BASE */
  83.  
  84. 	/* Fill BL33 related information */
  85.     {
  86. 	    .image_id = BL33_IMAGE_ID,
  87. 	    SET_STATIC_PARAM_HEAD(ep_info, PARAM_EP,
  88. 		    VERSION_2, entry_point_info_t, NON_SECURE | EXECUTABLE),
  89. # ifdef PRELOADED_BL33_BASE
  90. 	    .ep_info.pc = PRELOADED_BL33_BASE,
  91.  
  92. 	    SET_STATIC_PARAM_HEAD(image_info, PARAM_EP,
  93. 		    VERSION_2, image_info_t, IMAGE_ATTRIB_SKIP_LOADING),
  94. # else
  95. 	    .ep_info.pc = PLAT_ARM_NS_IMAGE_OFFSET,
  96.  
  97. 	    SET_STATIC_PARAM_HEAD(image_info, PARAM_EP,
  98. 		    VERSION_2, image_info_t, 0),
  99. 	    .image_info.image_base = PLAT_ARM_NS_IMAGE_OFFSET,
  100. 	    .image_info.image_max_size = ARM_DRAM1_SIZE,
  101. # endif /* PRELOADED_BL33_BASE */
  102.  
  103. 	    .next_handoff_image_id = INVALID_IMAGE_ID,
  104.     }
  105. #endif /* EL3_PAYLOAD_BASE */
  106. };


在该变量中规定了SCP_BL2， EL3_payload, bl32, bl33 image的相关信息，例如：

image的入口地址信息：ep_info

image在RAM中的基地址：image_base

image的基本信息：image_info

image的ID值：image_id

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