uboot向kernel的传参机制--bootm与tags ===================================== u-boot在启动内核时，会向内核传递一些参数，可以通过两种方式传递参数给内核，一种是通过参数链表(ttagged list)方式，一种是通过设备树方式。这些参数主要包括 系统的根设备标志，页面大小，内存的起始地址和大小等参数。 struct tag传递参数 ------------------- u-boot把要传递给kernel的参数保存在struct tag数据结构中，启动内核时，把这个结构体的物理地址传递给kernel，kernel会通过这个地址分析出u-boot传递的参数 主要数据结构介绍 ^^^^^^^^^^^^^^^^^ 首先看一下两个比较重要的数据结构 ``struct global_data`` 和 ``struct tag`` **struct global_data** 该数据结构定义在 `include/asm-generic/global_data.h` 中,其中包含了体系相关的数据结构 `struct arch_global_data arch` :: typedef struct global_data { bd_t *bd; unsigned long flags; unsigned int baudrate; unsigned long cpu_clk; /* CPU clock in Hz! */ unsigned long bus_clk; /* We cannot bracket this with CONFIG_PCI due to mpc5xxx */ unsigned long pci_clk; unsigned long mem_clk; #if defined(CONFIG_LCD) || defined(CONFIG_VIDEO) unsigned long fb_base; /* Base address of framebuffer mem */ #endif #if defined(CONFIG_POST) unsigned long post_log_word; /* Record POST activities */ unsigned long post_log_res; /* success of POST test */ unsigned long post_init_f_time; /* When post_init_f started */ #endif #ifdef CONFIG_BOARD_TYPES unsigned long board_type; #endif unsigned long have_console; /* serial_init() was called */ #if CONFIG_IS_ENABLED(PRE_CONSOLE_BUFFER) unsigned long precon_buf_idx; /* Pre-Console buffer index */ #endif unsigned long env_addr; /* Address of Environment struct */ unsigned long env_valid; /* Environment valid? enum env_valid */ unsigned long env_has_init; /* Bitmask of boolean of struct env_location offsets */ int env_load_prio; /* Priority of the loaded environment */ unsigned long ram_base; /* Base address of RAM used by U-Boot */ unsigned long ram_top; /* Top address of RAM used by U-Boot */ unsigned long relocaddr; /* Start address of U-Boot in RAM */ phys_size_t ram_size; /* RAM size */ unsigned long mon_len; /* monitor len */ unsigned long irq_sp; /* irq stack pointer */ unsigned long start_addr_sp; /* start_addr_stackpointer */ unsigned long reloc_off; struct global_data *new_gd; /* relocated global data */ #ifdef CONFIG_DM struct udevice *dm_root; /* Root instance for Driver Model */ struct udevice *dm_root_f; /* Pre-relocation root instance */ struct list_head uclass_root; /* Head of core tree */ #endif #ifdef CONFIG_TIMER struct udevice *timer; /* Timer instance for Driver Model */ #endif const void *fdt_blob; /* Our device tree, NULL if none */ void *new_fdt; /* Relocated FDT */ unsigned long fdt_size; /* Space reserved for relocated FDT */ #ifdef CONFIG_OF_LIVE struct device_node *of_root; #endif struct jt_funcs *jt; /* jump table */ char env_buf[32]; /* buffer for env_get() before reloc. */ #ifdef CONFIG_TRACE void *trace_buff; /* The trace buffer */ #endif #if defined(CONFIG_SYS_I2C) int cur_i2c_bus; /* current used i2c bus */ #endif #ifdef CONFIG_SYS_I2C_MXC void *srdata[10]; #endif unsigned int timebase_h; unsigned int timebase_l; #if CONFIG_VAL(SYS_MALLOC_F_LEN) unsigned long malloc_base; /* base address of early malloc() */ unsigned long malloc_limit; /* limit address */ unsigned long malloc_ptr; /* current address */ #endif #ifdef CONFIG_PCI struct pci_controller *hose; /* PCI hose for early use */ phys_addr_t pci_ram_top; /* top of region accessible to PCI */ #endif #ifdef CONFIG_PCI_BOOTDELAY int pcidelay_done; #endif struct udevice *cur_serial_dev; /* current serial device */ struct arch_global_data arch; /* architecture-specific data */ #ifdef CONFIG_CONSOLE_RECORD struct membuff console_out; /* console output */ struct membuff console_in; /* console input */ #endif #ifdef CONFIG_DM_VIDEO ulong video_top; /* Top of video frame buffer area */ ulong video_bottom; /* Bottom of video frame buffer area */ #endif #ifdef CONFIG_BOOTSTAGE struct bootstage_data *bootstage; /* Bootstage information */ struct bootstage_data *new_bootstage; /* Relocated bootstage info */ #endif #ifdef CONFIG_LOG int log_drop_count; /* Number of dropped log messages */ int default_log_level; /* For devices with no filters */ struct list_head log_head; /* List of struct log_device */ int log_fmt; /* Mask containing log format info */ #endif } gd_t; 在 `arch/arm/include/asm/global_data.h` :: #ifdef CONFIG_ARM64 #define DECLARE_GLOBAL_DATA_PTR register volatile gd_t *gd asm ("x18") #else #define DECLARE_GLOBAL_DATA_PTR register volatile gd_t *gd asm ("r9") #endif #endif 在需要使用gd指针的时候,只需要加入DECLARE_GLOBAL_DATA_PTR这句话就可以了,可以知道gd指针始终是放在r9或者x18中的 其中的第一个变量,bd_t结构体，定义在 `include/asm-generic/u-boot.h` 中 :: typedef struct bd_info { unsigned long bi_memstart; /* start of DRAM memory */ phys_size_t bi_memsize; /* size of DRAM memory in bytes */ unsigned long bi_flashstart; /* start of FLASH memory */ unsigned long bi_flashsize; /* size of FLASH memory */ unsigned long bi_flashoffset; /* reserved area for startup monitor */ unsigned long bi_sramstart; /* start of SRAM memory */ unsigned long bi_sramsize; /* size of SRAM memory */ #ifdef CONFIG_ARM unsigned long bi_arm_freq; /* arm frequency */ unsigned long bi_dsp_freq; /* dsp core frequency */ unsigned long bi_ddr_freq; /* ddr frequency */ #endif #if defined(CONFIG_MPC8xx) || defined(CONFIG_E500) || defined(CONFIG_MPC86xx) unsigned long bi_immr_base; /* base of IMMR register */ #endif #if defined(CONFIG_M68K) unsigned long bi_mbar_base; /* base of internal registers */ #endif #if defined(CONFIG_MPC83xx) unsigned long bi_immrbar; #endif unsigned long bi_bootflags; /* boot / reboot flag (Unused) */ unsigned long bi_ip_addr; /* IP Address */ unsigned char bi_enetaddr[6]; /* OLD: see README.enetaddr */ unsigned short bi_ethspeed; /* Ethernet speed in Mbps */ unsigned long bi_intfreq; /* Internal Freq, in MHz */ unsigned long bi_busfreq; /* Bus Freq, in MHz */ #if defined(CONFIG_CPM2) unsigned long bi_cpmfreq; /* CPM_CLK Freq, in MHz */ unsigned long bi_brgfreq; /* BRG_CLK Freq, in MHz */ unsigned long bi_sccfreq; /* SCC_CLK Freq, in MHz */ unsigned long bi_vco; /* VCO Out from PLL, in MHz */ #endif #if defined(CONFIG_M68K) unsigned long bi_ipbfreq; /* IPB Bus Freq, in MHz */ unsigned long bi_pcifreq; /* PCI Bus Freq, in MHz */ #endif #if defined(CONFIG_EXTRA_CLOCK) unsigned long bi_inpfreq; /* input Freq in MHz */ unsigned long bi_vcofreq; /* vco Freq in MHz */ unsigned long bi_flbfreq; /* Flexbus Freq in MHz */ #endif #ifdef CONFIG_HAS_ETH1 unsigned char bi_enet1addr[6]; /* OLD: see README.enetaddr */ #endif #ifdef CONFIG_HAS_ETH2 unsigned char bi_enet2addr[6]; /* OLD: see README.enetaddr */ #endif #ifdef CONFIG_HAS_ETH3 unsigned char bi_enet3addr[6]; /* OLD: see README.enetaddr */ #endif #ifdef CONFIG_HAS_ETH4 unsigned char bi_enet4addr[6]; /* OLD: see README.enetaddr */ #endif #ifdef CONFIG_HAS_ETH5 unsigned char bi_enet5addr[6]; /* OLD: see README.enetaddr */ #endif ulong bi_arch_number; /* unique id for this board */ ulong bi_boot_params; /* where this board expects params */ #ifdef CONFIG_NR_DRAM_BANKS struct { /* RAM configuration */ phys_addr_t start; phys_size_t size; } bi_dram[CONFIG_NR_DRAM_BANKS]; #endif /* CONFIG_NR_DRAM_BANKS */ } bd_t; bd_t中的变量 `bi_boot_params` 表示传递给内核的参数的位置，u-boot中命令bdinfo也是查看该结构体的值 global data介绍及背后的思考 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 要理解global data的意义，需要理解以下的事实: u-boot是一个bootloader，有些情况下他可能位于系统的只读存储器(rom或者flash)中，并从那里开始执行。因此，这种情况下，在uboot执行的前期(在将自己copy到可读写的存储器之前)它所在 的存储空间是不可写的，这会有两个问题: - 堆栈无法使用，无法执行函数调用，也就是说C环境不可用 - 没有data段(或正确初始化的data段)可用,不同函数或者代码之间，无法通过全局变量的形式共享数据 针对问题一，通常的解决方案是： u-boot运行起来之后，在那些不需要执行任何初始化动作即可使用的、可读写的存储区域开辟一段堆栈(stack)空间。一般来说，大部分的平台都有自己的sram可用作堆栈空间，如果实在不行，也可借用 CPU的data cache方法 针对问题二,解决方案要稍微复杂一些 首先对于开发者而言，在u-boot被拷贝到可读写的ram(这个动作被称作relacation)之前，永远不要使用全局变量，其次在relocation之前不同模块之间确实有通过全局变量传递数据的需求怎么办，这就是 global data需要解决的事情。。 为了在relocation之前通过全局变量的形式传递数据，u-boot设计了一个巧妙的方法:在堆栈配置好之后，在堆栈开始的位置，为struct global_data预留空间，并将开始地址(就是一个struct global_data指针)保存在 一个寄存器中，后续的传递，都是通过保存在寄存器中的指针实现。对于arm64平台而言,该指针保存在了X18寄存器中 在 `arch/arm/lib/crt0_64.S` 中有如下实现 :: bl board_init_f_alloc_reserve //board_init_f_alloc_reserve的返回值(x0)就是global data的指针 mov sp,x0 /* set up gd here, outside any C code */ mv x18,x0 bl board_init_init_reserve 内核参数链表的格式和说明可以从内核源码目录 `arch/arm/include/asm/setup.h` 中找到，链表必须以ATAG_CORE开始，以ATAG_NONE结束 :: struct tag { struct tag_header hdr; union { struct tag_core core; struct tag_mem32 mem; struct tag_videotext videotext; struct tag_ramdisk ramdisk; struct tag_initrd initrd; struct tag_serialnr serialnr; struct tag_revision revision; struct tag_videolfb videolfb; struct tag_cmdline cmdline; /* * Acorn specific */ struct tag_acorn acorn; /* * DC21285 specific */ struct tag_memclk memclk; } u; }; struct tag_ramdisk { u32 flags; /* bit 0 = load, bit 1 = prompt */ u32 size; /* decompressed ramdisk size in _kilo_ bytes */ u32 start; /* starting block of floppy-based RAM disk image */ }; struct tag_cmdline { char cmdline[1]; /* this is the minimum size */ }; ... 参数结构包括两个部分，一个是tag_header, 一个是u联合体 tag_header结构体定义如下， :: struct tag_header { u32 size; //表示整个tag结构体的大小，用字的个数表示而不是字节，等于tag_header加上u联合体的大小 u32 tag; //整个tag结构体的标记，如ATAG_CORE }; 现在来分析boot_prep_linux函数 :: /* Subcommand: PREP */ static void boot_prep_linux(bootm_headers_t *images) { char *commandline = env_get("bootargs"); //获取环境变量bootargs,这就是要传递给kernel的参数 if (IMAGE_ENABLE_OF_LIBFDT && images->ft_len) { #ifdef CONFIG_OF_LIBFDT debug("using: FDT\n"); if (image_setup_linux(images)) { printf("FDT creation failed! hanging..."); hang(); } #endif } else if (BOOTM_ENABLE_TAGS) { debug("using: ATAGS\n"); setup_start_tag(gd->bd); //通过bd结构体中的参数在内存中的存放位置gd->bd->bi_boot_params来构建初始化tag结构, //表明参数结构的开始 if (BOOTM_ENABLE_SERIAL_TAG) setup_serial_tag(¶ms); //构建串口参数的tag结构 if (BOOTM_ENABLE_CMDLINE_TAG) setup_commandline_tag(gd->bd, commandline); //构建命令行参数的tag结构 if (BOOTM_ENABLE_REVISION_TAG) setup_revision_tag(¶ms); if (BOOTM_ENABLE_MEMORY_TAGS) setup_memory_tags(gd->bd); if (BOOTM_ENABLE_INITRD_TAG) { /* * In boot_ramdisk_high(), it may relocate ramdisk to * a specified location. And set images->initrd_start & * images->initrd_end to relocated ramdisk's start/end * addresses. So use them instead of images->rd_start & * images->rd_end when possible. */ if (images->initrd_start && images->initrd_end) { setup_initrd_tag(gd->bd, images->initrd_start, images->initrd_end); } else if (images->rd_start && images->rd_end) { setup_initrd_tag(gd->bd, images->rd_start, images->rd_end); } } setup_board_tags(¶ms); setup_end_tag(gd->bd); } else { printf("FDT and ATAGS support not compiled in - hanging\n"); hang(); } } - setup_start_tag :: static void setup_start_tag (bd_t *bd) { params = (struct tag *)bd->bi_boot_params; //获取struct tag指针 params->hdr.tag = ATAG_CORE; //设置参数链表开始标签 params->hdr.size = tag_size (tag_core); params->u.core.flags = 0; params->u.core.pagesize = 0; params->u.core.rootdev = 0; params = tag_next (params); } #define tag_next(t) ((struct tag *)((u32 *)(t) + (t)->hdr.size)) - setup_commandline_tag :: static void setup_commandline_tag(bd_t *bd, char *commandline) { char *p; printf("set cmd line ...\n"); if (!commandline) return; /* eat leading white space */ for (p = commandline; *p == ' '; p++); /* skip non-existent command lines so the kernel will still * use its default command line. */ if (*p == '\0') return; params->hdr.tag = ATAG_CMDLINE; params->hdr.size = (sizeof (struct tag_header) + strlen (p) + 1 + 4) >> 2; strcpy (params->u.cmdline.cmdline, p); params = tag_next (params); } 设备树传参 ----------- 新版本的linux内核都采用设备树的方式进行板级设备信息描述，uboot在启动内核的时候需要将设备树的地址传递给kernel。跟以前的方式不同，采用设备树时 不再使用struct tag进行参数传递，设备数中本身有对需要传递参数的描述，uboot中将设备树进行解析并设置对应参数。kernel直接解析uboot传递的设备树并从中 找到要传递参数 boot_prep_linux函数中有两个主分支，定义设备树时运行分支一,没有定义时采用struct tag进行参数传递 :: int image_setup_linux(bootm_headers_t *images) { ulong of_size = images->ft_len; char **of_flat_tree = &images->ft_addr; struct lmb *lmb = &images->lmb; int ret; if (IMAGE_ENABLE_OF_LIBFDT) boot_fdt_add_mem_rsv_regions(lmb, *of_flat_tree); if (IMAGE_BOOT_GET_CMDLINE) { ret = boot_get_cmdline(lmb, &images->cmdline_start, &images->cmdline_end); if (ret) { puts("ERROR with allocation of cmdline\n"); return ret; } } if (IMAGE_ENABLE_OF_LIBFDT) { ret = boot_relocate_fdt(lmb, of_flat_tree, &of_size); if (ret) return ret; } if (IMAGE_ENABLE_OF_LIBFDT && of_size) { ret = image_setup_libfdt(images, *of_flat_tree, of_size, lmb); //此函数中会调用fdt_chosen进行参数传递 if (ret) return ret; } return 0; } int fdt_chosen(void *fdt) { int nodeoffset; int err; char *str; /* used to set string properties */ err = fdt_check_header(fdt); if (err < 0) { printf("fdt_chosen: %s\n", fdt_strerror(err)); return err; } /* find or create "/chosen" node. */ nodeoffset = fdt_find_or_add_subnode(fdt, 0, "chosen"); if (nodeoffset < 0) return nodeoffset; str = env_get("bootargs"); if (str) { err = fdt_setprop(fdt, nodeoffset, "bootargs", str, strlen(str) + 1); if (err < 0) { printf("WARNING: could not set bootargs %s.\n", fdt_strerror(err)); return err; } } return fdt_fixup_stdout(fdt, nodeoffset); }