3. ATF（ARM Trusted firmware）启动---bl2_arm bl2

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：

 

func bl2_entrypoint
	/*---------------------------------------------
	 * Save from x1 the extents of the tzram
	 * available to BL2 for future use.
	 * x0 is not currently used.
	 * ---------------------------------------------
	 */
	mov	x20, x1
 
	/* ---------------------------------------------
	 * Set the exception vector to something sane.
	 * ---------------------------------------------
	 */
	adr	x0, early_exceptions	//设定异常向量
	msr	vbar_el1, x0
	isb
 
	/* ---------------------------------------------
	 * Enable the SError interrupt now that the
	 * exception vectors have been setup.
	 * ---------------------------------------------
	 */
	msr	daifclr, #DAIF_ABT_BIT
 
	/* ---------------------------------------------
	 * Enable the instruction cache, stack pointer
	 * and data access alignment checks
	 * ---------------------------------------------
	 */
	mov	x1, #(SCTLR_I_BIT | SCTLR_A_BIT | SCTLR_SA_BIT)
	mrs	x0, sctlr_el1
	orr	x0, x0, x1
	msr	sctlr_el1, x0
	isb
 
	/* ---------------------------------------------
	 * Invalidate the RW memory used by the BL2
	 * image. This includes the data and NOBITS
	 * sections. This is done to safeguard against
	 * possible corruption of this memory by dirty
	 * cache lines in a system cache as a result of
	 * use by an earlier boot loader stage.
	 * ---------------------------------------------
	 */
	adr	x0, __RW_START__
	adr	x1, __RW_END__
	sub	x1, x1, x0
	bl	inv_dcache_range
 
	/* ---------------------------------------------
	 * Zero out NOBITS sections. There are 2 of them:
	 *   - the .bss section;
	 *   - the coherent memory section.
	 * ---------------------------------------------
	 */
	ldr	x0, =__BSS_START__
	ldr	x1, =__BSS_SIZE__
	bl	zeromem
 
#if USE_COHERENT_MEM
	ldr	x0, =__COHERENT_RAM_START__
	ldr	x1, =__COHERENT_RAM_UNALIGNED_SIZE__
	bl	zeromem
#endif
 
	/* --------------------------------------------
	 * Allocate a stack whose memory will be marked
	 * as Normal-IS-WBWA when the MMU is enabled.
	 * There is no risk of reading stale stack
	 * memory after enabling the MMU as only the
	 * primary cpu is running at the moment.
	 * --------------------------------------------
	 */
	bl	plat_set_my_stack	//初始化bl2运行的栈
 
	/* ---------------------------------------------
	 * Initialize the stack protector canary before
	 * any C code is called.
	 * ---------------------------------------------
	 */
#if STACK_PROTECTOR_ENABLED
	bl	update_stack_protector_canary
#endif
 
	/* ---------------------------------------------
	 * Perform early platform setup & platform
	 * specific early arch. setup e.g. mmu setup
	 * ---------------------------------------------
	 */
	mov	x0, x20
	bl	bl2_early_platform_setup	//设置平台相关
	bl	bl2_plat_arch_setup	//设置架构相关
 
	/* ---------------------------------------------
	 * Jump to main function.
	 * ---------------------------------------------
	 */
	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,
 
	/* ---------------------------------------------
	 * Should never reach this point.
	 * ---------------------------------------------
	 */
	no_ret	plat_panic_handler
 
endfunc bl2_entrypoint
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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。

void bl2_main(void)
{
	entry_point_info_t *next_bl_ep_info;
 
	NOTICE("BL2: %s\n", version_string);
	NOTICE("BL2: %s\n", build_message);
 
	/* Perform remaining generic architectural setup in S-EL1 */
	bl2_arch_setup();
 
#if TRUSTED_BOARD_BOOT
	/* Initialize authentication module */
	auth_mod_init();	//初始化image验证模块
#endif /* TRUSTED_BOARD_BOOT */
 
	/* Load the subsequent bootloader images. */
	next_bl_ep_info = bl2_load_images();	//加载bl3x image到RAM中并返回bl31的入口地址
 
#ifdef AARCH32
	/*
	 * For AArch32 state BL1 and BL2 share the MMU setup.
	 * Given that BL2 does not map BL1 regions, MMU needs
	 * to be disabled in order to go back to BL1.
	 */
	disable_mmu_icache_secure();
#endif /* AARCH32 */
 
	console_flush();
 
	/*
	 * Run next BL image via an SMC to BL1. Information on how to pass
	 * control to the BL32 (if present) and BL33 software images will
	 * be passed to next BL image as an argument.
	 */
/* 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 */
	smc(BL1_SMC_RUN_IMAGE, (unsigned long)next_bl_ep_info, 0, 0, 0, 0, 0, 0);
}
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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
 

entry_point_info_t *bl2_load_images(void)
{
	bl_params_t *bl2_to_next_bl_params;
	bl_load_info_t *bl2_load_info;
	const bl_load_info_node_t *bl2_node_info;
	int plat_setup_done = 0;
	int err;
 
	/*
	 * Get information about the images to load.
	 */
/* 获取bl3x image的加载和入口信息 */
	bl2_load_info = plat_get_bl_image_load_info();
 
/* 检查返回的bl2_load_info中的信息是否正确 */
	assert(bl2_load_info);
	assert(bl2_load_info->head);
	assert(bl2_load_info->h.type == PARAM_BL_LOAD_INFO);
	assert(bl2_load_info->h.version >= VERSION_2);
 
/* 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 */
	bl2_node_info = bl2_load_info->head;
 
/* 进入loop循环， */
	while (bl2_node_info) {
		/*
		 * Perform platform setup before loading the image,
		 * if indicated in the image attributes AND if NOT
		 * already done before.
		 */
/* 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 */
		if (bl2_node_info->image_info->h.attr & IMAGE_ATTRIB_PLAT_SETUP) {
			if (plat_setup_done) {
				WARN("BL2: Platform setup already done!!\n");
			} else {
				INFO("BL2: Doing platform setup\n");
				bl2_platform_setup();
				plat_setup_done = 1;
			}
		}
 
/* 对bl3x image进行电子验签，如果通过则执行加载操作 */
		if (!(bl2_node_info->image_info->h.attr & IMAGE_ATTRIB_SKIP_LOADING)) {
			INFO("BL2: Loading image id %d\n", bl2_node_info->image_id);
			err = load_auth_image(bl2_node_info->image_id,
				bl2_node_info->image_info);
			if (err) {
				ERROR("BL2: Failed to load image (%i)\n", err);
				plat_error_handler(err);
			}
		} else {
			INFO("BL2: Skip loading image id %d\n", bl2_node_info->image_id);
		}
 
		/* Allow platform to handle image information. */
/* 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 */
		err = bl2_plat_handle_post_image_load(bl2_node_info->image_id);
		if (err) {
			ERROR("BL2: Failure in post image load handling (%i)\n", err);
			plat_error_handler(err);
		}
 
		/* Go to next image */
		bl2_node_info = bl2_node_info->next_load_info;
	}
 
	/*
	 * Get information to pass to the next image.
	 */
/* 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*/
	bl2_to_next_bl_params = plat_get_next_bl_params();
	assert(bl2_to_next_bl_params);
	assert(bl2_to_next_bl_params->head);
	assert(bl2_to_next_bl_params->h.type == PARAM_BL_PARAMS);
	assert(bl2_to_next_bl_params->h.version >= VERSION_2);
 
	/* Flush the parameters to be passed to next image */
	plat_flush_next_bl_params();
 
/* 返回下一个进入的image的入口信息,即bl31的入口信息 */
	return bl2_to_next_bl_params->head->ep_info;
}
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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：

 

static bl_mem_params_node_t bl2_mem_params_descs[] = {
#ifdef SCP_BL2_BASE
	/* Fill SCP_BL2 related information if it exists */
    {
	    .image_id = SCP_BL2_IMAGE_ID,
 
	    SET_STATIC_PARAM_HEAD(ep_info, PARAM_IMAGE_BINARY,
		    VERSION_2, entry_point_info_t, SECURE | NON_EXECUTABLE),
 
	    SET_STATIC_PARAM_HEAD(image_info, PARAM_IMAGE_BINARY,
		    VERSION_2, image_info_t, 0),
	    .image_info.image_base = SCP_BL2_BASE,
	    .image_info.image_max_size = PLAT_CSS_MAX_SCP_BL2_SIZE,
 
	    .next_handoff_image_id = INVALID_IMAGE_ID,
    },
#endif /* SCP_BL2_BASE */
 
#ifdef EL3_PAYLOAD_BASE
	/* Fill EL3 payload related information (BL31 is EL3 payload)*/
    {
	    .image_id = BL31_IMAGE_ID,
 
	    SET_STATIC_PARAM_HEAD(ep_info, PARAM_EP,
		    VERSION_2, entry_point_info_t,
		    SECURE | EXECUTABLE | EP_FIRST_EXE),
	    .ep_info.pc = EL3_PAYLOAD_BASE,
	    .ep_info.spsr = SPSR_64(MODE_EL3, MODE_SP_ELX,
		    DISABLE_ALL_EXCEPTIONS),
 
	    SET_STATIC_PARAM_HEAD(image_info, PARAM_EP,
		    VERSION_2, image_info_t,
		    IMAGE_ATTRIB_PLAT_SETUP | IMAGE_ATTRIB_SKIP_LOADING),
 
	    .next_handoff_image_id = INVALID_IMAGE_ID,
    },
 
#else /* EL3_PAYLOAD_BASE */
 
	/* Fill BL31 related information */
    {
	    .image_id = BL31_IMAGE_ID,
 
	    SET_STATIC_PARAM_HEAD(ep_info, PARAM_EP,
		    VERSION_2, entry_point_info_t,
		    SECURE | EXECUTABLE | EP_FIRST_EXE),
	    .ep_info.pc = BL31_BASE,
	    .ep_info.spsr = SPSR_64(MODE_EL3, MODE_SP_ELX,
		    DISABLE_ALL_EXCEPTIONS),
#if DEBUG
	    .ep_info.args.arg1 = ARM_BL31_PLAT_PARAM_VAL,
#endif
 
	    SET_STATIC_PARAM_HEAD(image_info, PARAM_EP,
		    VERSION_2, image_info_t, IMAGE_ATTRIB_PLAT_SETUP),
	    .image_info.image_base = BL31_BASE,
	    .image_info.image_max_size = BL31_LIMIT - BL31_BASE,
 
# ifdef BL32_BASE
	    .next_handoff_image_id = BL32_IMAGE_ID,
# else
	    .next_handoff_image_id = BL33_IMAGE_ID,
# endif
    },
 
# ifdef BL32_BASE
	/* Fill BL32 related information */
    {
	    .image_id = BL32_IMAGE_ID,
 
	    SET_STATIC_PARAM_HEAD(ep_info, PARAM_EP,
		    VERSION_2, entry_point_info_t, SECURE | EXECUTABLE),
	    .ep_info.pc = BL32_BASE,
 
	    SET_STATIC_PARAM_HEAD(image_info, PARAM_EP,
		    VERSION_2, image_info_t, 0),
	    .image_info.image_base = BL32_BASE,
	    .image_info.image_max_size = BL32_LIMIT - BL32_BASE,
 
	    .next_handoff_image_id = BL33_IMAGE_ID,
    },
# endif /* BL32_BASE */
 
	/* Fill BL33 related information */
    {
	    .image_id = BL33_IMAGE_ID,
	    SET_STATIC_PARAM_HEAD(ep_info, PARAM_EP,
		    VERSION_2, entry_point_info_t, NON_SECURE | EXECUTABLE),
# ifdef PRELOADED_BL33_BASE
	    .ep_info.pc = PRELOADED_BL33_BASE,
 
	    SET_STATIC_PARAM_HEAD(image_info, PARAM_EP,
		    VERSION_2, image_info_t, IMAGE_ATTRIB_SKIP_LOADING),
# else
	    .ep_info.pc = PLAT_ARM_NS_IMAGE_OFFSET,
 
	    SET_STATIC_PARAM_HEAD(image_info, PARAM_EP,
		    VERSION_2, image_info_t, 0),
	    .image_info.image_base = PLAT_ARM_NS_IMAGE_OFFSET,
	    .image_info.image_max_size = ARM_DRAM1_SIZE,
# endif /* PRELOADED_BL33_BASE */
 
	    .next_handoff_image_id = INVALID_IMAGE_ID,
    }
#endif /* EL3_PAYLOAD_BASE */
};
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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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