1. 确定 processor type
arch/arm/kernel/head.S中:
00075: mrcp15, 0, r9, c0, c0@ get processor id
00076: bl__lookup_processor_type@ r5=procinfo r9=cpuid
00077: movsr10, r5@ invalid processor (r5=0)?
00078: beq__error_p@ yes, error p
75行: 通过cp15协处理器的c0寄存器来获得processor id的指令. 关于cp15的详细内容可参考相关的arm手册
76行: 跳转到__lookup_processor_type.在__lookup_processor_type中,会把processor type 存储在r5中
77,78行: 判断r5中的processor type是否是0,如果是0,说明是无效的processor type,跳转到__error_p(出错)
__lookup_processor_type 函数主要是根据从cpu中获得的processor id和系统中的proc_info进行匹配,将匹配到的proc_info_list的基地址存到r5中, 0表示没有找到对应的processor type.
下面我们分析__lookup_processor_type函数
arch/arm/kernel/head-common.S中:
00145: .type__lookup_processor_type, %function
00146: __lookup_processor_type:
00147: adrr3, 3f
00148: ldmdar3, {r5 - r7}
00149: subr3, r3, r7@ get offset between virt&phys
00150: addr5, r5, r3@ convert virt addresses to
00151: addr6, r6, r3@ physical address space
00152: 1:ldmiar5, {r3, r4}@ value, mask
00153: andr4, r4, r9@ mask wanted bits
00154: teqr3, r4
00155: beq2f
00156: addr5, r5, #PROC_INFO_SZ@ sizeof(proc_info_list)
00157: cmpr5, r6
00158: blo1b
00159: movr5, #0@ unknown processor
00160: 2:movpc, lr
00161:
00162:
00165: ENTRY(lookup_processor_type)
00166: stmfdsp!, {r4 - r7, r9, lr}
00167: movr9, r0
00168: bl__lookup_processor_type
00169: movr0, r5
00170: ldmfdsp!, {r4 - r7, r9, pc}
00171:
00172:
00176: .long__proc_info_begin
00177: .long__proc_info_end
00178: 3:.long.
00179: .long__arch_info_begin
00180: .long__arch_info_end
145, 146行是函数定义
147行: 取地址指令,这里的3f是向前symbol名称是3的位置,即第178行,将该地址存入r3.
这里需要注意的是,adr指令取址,获得的是基于pc的一个地址,要格外注意,这个地址是3f处的"运行时地址",由于此时MMU还没有打开,也可以理解成物理地址(实地址).(详细内容可参考arm指令手册)
148行: 因为r3中的地址是178行的位置的地址,因而执行完后:
r5存的是176行符号 __proc_info_begin的地址;
r6存的是177行符号 __proc_info_end的地址;
r7存的是3f处的地址.
这里需要注意链接地址和运行时地址的区别. r3存储的是运行时地址(物理地址),而r7中存储的是链接地址(虚拟地址).
__proc_info_begin和__proc_info_end是在arch/arm/kernel/vmlinux.lds.S中:
00031:__proc_info_begin = .;
00032:*(.proc.info.init)
00033:__proc_info_end = .;
这里是声明了两个变量:__proc_info_begin 和 __proc_info_end,其中等号后面的"."是location counter(详细内容请参考ld.info)
这三行的意思是: __proc_info_begin 的位置上,放置所有文件中的 ".proc.info.init" 段的内容,然后紧接着是 __proc_info_end 的位置.
kernel 使用struct proc_info_list来描述processor type.
在 include/asm-arm/procinfo.h 中:
00029: struct proc_info_list {
00030: unsigned intcpu_val;
00031: unsigned intcpu_mask;
00032: unsigned long__cpu_mm_mmu_flags;
00033: unsigned long__cpu_io_mmu_flags;
00034: unsigned long__cpu_flush;
00035: const char*arch_name;
00036: const char*elf_name;
00037: unsigned intelf_hwcap;
00038: const char*cpu_name;
00039: struct processor*proc;
00040: struct cpu_tlb_fns*tlb;
00041: struct cpu_user_fns*user;
00042: struct cpu_cache_fns*cache;
00043: };
我们当前以at91为例,其processor是926的.
在arch/arm/mm/proc-arm926.S 中:
00464: .section ".proc.info.init", #alloc, #execinstr
00465:
00466: .type__arm926_proc_info,#object
00467: __arm926_proc_info:
00468: .long0x41069260@ ARM926EJ-S (v5TEJ)
00469: .long0xff0ffff0
00470: .long PMD_TYPE_SECT | \
00471: PMD_SECT_BUFFERABLE | \
00472: PMD_SECT_CACHEABLE | \
00473: PMD_BIT4 | \
00474: PMD_SECT_AP_WRITE | \
00475: PMD_SECT_AP_READ
00476: .long PMD_TYPE_SECT | \
00477: PMD_BIT4 | \
00478: PMD_SECT_AP_WRITE | \
00479: PMD_SECT_AP_READ
00480: b__arm926_setup
00481: .longcpu_arch_name
00482: .longcpu_elf_name
00483: .longHWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_VFP|HWCAP_E
