linux内核启动第二阶段分析-setup_arch()函数

分手后的思念是犯贱 2022-03-26 14:08 257阅读 0赞

**执行setup\_arch()函数**  
回到start\_kernel当中，488行，调用setup\_arch函数，传给他的参数是那个未被初始化的内部变量command\_line。这个setup\_arch()函数是start\_kernel阶段最重要的一个函数，每个体系都有自己的setup\_arch()函数，是体系结构相关的，具体编译哪个体系的setup\_arch()函数，由顶层Makefile中的ARCH变量决定：  
它首先通过检测出来的处理器类型进行处理器内核的初始化，然后通过 bootmem\_init()函数根据系统定义的 meminfo 结构进行内存结构的初始化，最后调用paging\_init()开启 MMU，创建内核页表，映射所有的物理内存和 IO空间。  
start\_kernel ()  
    --> setup\_arch ()  
       --> paging\_init ()  
          --> bootmem\_init ()  
              --> alloc\_bootmem\_low\_pages ()  
  
arch/arm/kernel/setup.c  
 877 void \_\_init setup\_arch(char \*\*cmdline\_p)  
 878 \{  
 879         struct machine\_desc \*mdesc;  
 880  
 881         unwind\_init(); //本架构中没有用  
 882  
 883         setup\_processor();//汇编的CPU初始化部分  
 884         mdesc = setup\_machine\_fdt(\_\_atags\_pointer);//\_\_atags\_pointer是bootloader传递参数的物理地址  
 885         if (!mdesc)  
 886                 mdesc = setup\_machine\_tags(machine\_arch\_type);  
 887         machine\_desc = mdesc;  
 888         machine\_name = mdesc->name;  
 889  
 890         if (mdesc->soft\_reboot)  
 891                 reboot\_setup("s");  
 892  
 893         init\_mm.start\_code = (unsigned long) \_text;  
 894         init\_mm.end\_code   = (unsigned long) \_etext;  
 895         init\_mm.end\_data   = (unsigned long) \_edata;  
 896         init\_mm.brk        = (unsigned long) \_end;  
 897  
 898         /\* populate cmd\_line too for later use, preserving boot\_command\_line \*/  
 899         strlcpy(cmd\_line, boot\_command\_line, COMMAND\_LINE\_SIZE);  
 900         \*cmdline\_p = cmd\_line;  
 901  
 902         parse\_early\_param();  
 903  
 904         sanity\_check\_meminfo();  
 905         arm\_memblock\_init(&meminfo, mdesc);  
 906  
 907         paging\_init(mdesc);  
 908         request\_standard\_resources(mdesc);  
 909  
 910         unflatten\_device\_tree();  
 911  
 912 \#ifdef CONFIG\_SMP  
 913         if (is\_smp())  
 914                 smp\_init\_cpus();  
 915 \#endif  
 916         reserve\_crashkernel();  
 917  
 918         cpu\_init();//此函数为空  
 919         tcm\_init();  
 920  
 921 \#ifdef CONFIG\_MULTI\_IRQ\_HANDLER  
 922         handle\_arch\_irq = mdesc->handle\_irq;  
 923 \#endif  
 924  
 925 \#ifdef CONFIG\_VT  
 926 \#if defined(CONFIG\_VGA\_CONSOLE)  
 927         conswitchp = &vga\_con;  
 928 \#elif defined(CONFIG\_DUMMY\_CONSOLE)  
 929         conswitchp = &dummy\_con;  
 930 \#endif  
 931 \#endif  
 932         early\_trap\_init();//重定位中断向量，将中断向量代码拷贝到中断向量页，并把信号处理代码指令拷贝到向量页中  
 933  
 934         if (mdesc->init\_early)  
 935                 mdesc->init\_early();  
 936 \}  
  
  
 879行完整的machine\_desc结构描述如下:arch/arm/include/asm/mach/arch.h  
 13 struct tag;  
 14 struct meminfo;  
 15 struct sys\_timer;  
 16  
 17 struct machine\_desc \{  
 18         unsigned int            nr;             /\*  开发板的机器类型ID\*/  
 19         const char              \*name;          /\*  开发板名称 \*/  
 20         unsigned long           boot\_params;    /\*  内核启动参数的地址\*/  
 21         const char              \*\*dt\_compat;    /\* array of device tree  
 22                                                  \* 'compatible' strings \*/  
 23  
 24         unsigned int            nr\_irqs;        /\* number of IRQs \*/  
 25  
 26         unsigned int            video\_start;    /\* start of video RAM   \*/  
 27         unsigned int            video\_end;      /\* end of video RAM     \*/  
 28  
 29         unsigned int            reserve\_lp0 :1; /\* never has lp0        \*/  
 30         unsigned int            reserve\_lp1 :1; /\* never has lp1        \*/  
 31         unsigned int            reserve\_lp2 :1; /\* never has lp2        \*/  
 32         unsigned int            soft\_reboot :1; /\* soft reboot          \*/  
 33         void                    (\*fixup)(struct machine\_desc \*,  
 34                                          struct tag \*, char \*\*,  
 35                                          struct meminfo \*);  
 36         void                    (\*reserve)(void);/\* reserve mem blocks  \*/  
 37         void                    (\*map\_io)(void);/\*  IO 映射函数（在这里修改时钟频率）\*/  
 38         void                    (\*init\_early)(void);  
 39         void                    (\*init\_irq)(void);  /\*  中断初始化函数\*/  
 40         struct sys\_timer        \*timer;         /\* system tick timer    \*/  
 41         void                    (\*init\_machine)(void);  
 42 \#ifdef CONFIG\_MULTI\_IRQ\_HANDLER  
 43         void                    (\*handle\_irq)(struct pt\_regs \*);  
 44 \#endif  
 45 \};  
  
884行\_\_atags\_pointer是bootloader传递参数的物理地址,见第一阶段启动源码第100行(str r2, \[r6\]),此处r6就是\_\_atags\_pointer的地址，它将bootloader通过r2传递过来的地址参数存放到\_\_atags\_pointer。  
  
下面我们来看setup\_machine\_fdt函数，它在arch/arm/kernel/devtree.c中定义如下：  
 71 struct machine\_desc \* \_\_init setup\_machine\_fdt(unsigned int dt\_phys)  
 72 \{  
 73         struct boot\_param\_header \*devtree;  
 74         struct machine\_desc \*mdesc, \*mdesc\_best = NULL;  
 75         unsigned int score, mdesc\_score = ~1;  
 76         unsigned long dt\_root;  
 77         const char \*model;  
 78  
 79         if (!dt\_phys)  
 80                 return NULL;  
 81  
 82         devtree = phys\_to\_virt(dt\_phys);//由于MMU单元已打开，此处\_\_atags\_pointer是物理地址，需要转换成虚拟地址才能访问，因为此时CPU访问的都是虚拟地址  
 83  
 84         /\* check device tree validity \*/  
 85         if (be32\_to\_cpu(devtree->magic) != OF\_DT\_HEADER)  
 86                 return NULL;  
 87  
 88         /\* Search the mdescs for the 'best' compatible value match \*/  
 89         initial\_boot\_params = devtree;  
 90         dt\_root = of\_get\_flat\_dt\_root(); 该函数用来查找在dtb中的根节点  
 91         for\_each\_machine\_desc(mdesc) \{  
 92                 score = of\_flat\_dt\_match(dt\_root, mdesc->dt\_compat);  
 93                 if (score > 0 && score < mdesc\_score) \{  
 94                         mdesc\_best = mdesc;  
 95                         mdesc\_score = score;  
 96                 \}  
 97         \}  
 98         if (!mdesc\_best) \{  
 99                 const char \*prop;  
100                 long size;  
101  
102                 early\_print("\\nError: unrecognized/unsupported "  
103                             "device tree compatible list:\\n\[ ");  
104  
105                 prop = of\_get\_flat\_dt\_prop(dt\_root, "compatible", &size);  
106                 while (size > 0) \{  
107                         early\_print("'%s' ", prop);  
108                         size -= strlen(prop) + 1;  
109                         prop += strlen(prop) + 1;  
110                 \}  
111                 early\_print("\]\\n\\n");  
112  
113                 dump\_machine\_table(); /\* does not return \*/  
114         \}  
115  
116         model = of\_get\_flat\_dt\_prop(dt\_root, "model", NULL);  
117         if (!model)  
118                 model = of\_get\_flat\_dt\_prop(dt\_root, "compatible", NULL);  
119         if (!model)  
120                 model = "<unknown>";  
121         pr\_info("Machine: %s, model: %s\\n", mdesc\_best->name, model);  
122  
123         /\* Retrieve various information from the /chosen node \*/  
124         of\_scan\_flat\_dt(early\_init\_dt\_scan\_chosen, boot\_command\_line);  
125         /\* Initialize \{size,address\}-cells info \*/  
126         of\_scan\_flat\_dt(early\_init\_dt\_scan\_root, NULL);  
127         /\* Setup memory, calling early\_init\_dt\_add\_memory\_arch \*/  
128         of\_scan\_flat\_dt(early\_init\_dt\_scan\_memory, NULL);  
129  
130         /\* Change machine number to match the mdesc we're using \*/  
131         \_\_machine\_arch\_type = mdesc\_best->nr;  
132  
133         return mdesc\_best;  
134 \}  
boot\_param\_header结构在include/linux/of\_fdt.h第44行定义如下：  
struct boot\_param\_header \{  
    \_\_be32    magic;            /\* magic word OF\_DT\_HEADER \*/  
    \_\_be32    totalsize;        /\* total size of DT block \*/  
    \_\_be32    off\_dt\_struct;        /\* offset to structure \*/  
    \_\_be32    off\_dt\_strings;        /\* offset to strings \*/  
    \_\_be32    off\_mem\_rsvmap;        /\* offset to memory reserve map \*/  
    \_\_be32    version;        /\* format version \*/  
    \_\_be32    last\_comp\_version;    /\* last compatible version \*/  
    /\* version 2 fields below \*/  
    \_\_be32    boot\_cpuid\_phys;    /\* Physical CPU id we're booting on \*/  
    /\* version 3 fields below \*/  
    \_\_be32    dt\_strings\_size;    /\* size of the DT strings block \*/  
    /\* version 17 fields below \*/  
    \_\_be32    dt\_struct\_size;        /\* size of the DT structure block \*/  
\};  
第89行initial\_boot\_params在同文件下第436行有定义struct boot\_param\_header \*initial\_boot\_params;  
第90行of\_get\_flat\_dt\_root() 函数用来查找在dtb中的根节点（drivers/of/fdt.c)  
unsigned long \_\_init of\_get\_flat\_dt\_root(void)  
\{  
    unsigned long p = ((unsigned long)initial\_boot\_params) +  
        be32\_to\_cpu(initial\_boot\_params->off\_dt\_struct);  
  
    while (be32\_to\_cpup((\_\_be32 \*)p) == OF\_DT\_NOP)  
        p += 4;  
    BUG\_ON(be32\_to\_cpup((\_\_be32 \*)p) != OF\_DT\_BEGIN\_NODE);  
    p += 4;  
    return ALIGN(p + strlen((char \*)p) + 1, 4);  
\}  
  
第91行在arch/arm/include/asm/mach/arch.h中定义如下  
 55 extern struct machine\_desc \_\_arch\_info\_begin\[\], \_\_arch\_info\_end\[\];  
 56 \#define for\_each\_machine\_desc(p)                        \\  
 57         for (p = \_\_arch\_info\_begin; p < \_\_arch\_info\_end; p++)  
 58  
 59 /\*  
 60  \* Set of macros to define architecture features.  This is built into  
 61  \* a table by the linker.  
 62  \*/  
 63 \#define MACHINE\_START(\_type,\_name)                      \\  
 64 static const struct machine\_desc \_\_mach\_desc\_\#\#\_type    \\  
 65  \_\_used                                                 \\  
 66  \_\_attribute\_\_((\_\_section\_\_(".arch.info.init"))) = \{    \\  
 67         .nr             = MACH\_TYPE\_\#\#\_type,            \\  
 68         .name           = \_name,  
 69  
 70 \#define MACHINE\_END                             \\  
 71 \};  
  
int \_\_init of\_flat\_dt\_match(unsigned long node, const char \*\*compat)  
\{  
    return of\_fdt\_match(initial\_boot\_params, node, compat);  
\}  
如果node与兼容表中的值匹配则返回真  
int of\_fdt\_match(struct boot\_param\_header \*blob, unsigned long node,  
                 const char \*\*compat)  
\{  
    unsigned int tmp, score = 0;  
  
    if (!compat)  
        return 0;  
  
    while (\*compat) \{  
        tmp = of\_fdt\_is\_compatible(blob, node, \*compat);  
        if (tmp && (score == 0 || (tmp < score)))  
            score = tmp;  
        compat++;  
    \}  
  
    return score;  
\}