linux内核启动时，第一次创建页表

/* * Setup the initial page tables.  We only setup the barest * amount which are required to get the kernel running, which * generally means mapping in the kernel code. * * r8  = machinfo * r9  = cpuid * r10 = procinfo * * Returns: *  r0, r3, r6, r7 corrupted *  r4 = physical page table address */__create_page_tables:pgtblr4@ page table address /*r4为页表的基地址0x30004000*//* * Clear the 16K level 1 swapper page table */ /*清除页表所用的内存为0,0x30004000~0x30007fff*/movr0, r4movr3, #0addr6, r0, #0x40001:strr3, [r0], #4strr3, [r0], #4strr3, [r0], #4strr3, [r0], #4teqr0, r6bne1b/*将内核镜像中的MMU flag数值取出，准备设置page table*/ldrr7, [r10, #PROCINFO_MM_MMUFLAGS] @ mm_mmuflags 假如r7=0xabced/* * Create identity mapping for first MB of kernel to * cater for the MMU enable.  This identity mapping * will be removed by paging_init().  We use our current program * counter to determine corresponding section base address. */movr6, pc@ 取当前pc的值到r6,对当前的地址进行映射movr6, r6, lsr #20@ start of kernel section, 每页的大小为1M，高12位为页表项的索引，mini2440上r6=0x300orrr3, r7, r6, lsl #20@ flags + kernel base <span style="color: rgb(102, 102, 102); font-family: 宋体;font-size:12px; line-height: 26px;">根据上句得出的段计数左移20位算出段地址，并将将低20bit设置成MMU的flag，得到一个map entry，假如r3=0x300abced</span>strr3, [r4, r6, lsl #2]@ identity mapping r4=0x30004000 r6=0x300<<2=0xc00; *(0x30004c00)=0x300abcde/* * Now setup the pagetables for our kernel direct * mapped region. */addr0, r4,  #(KERNEL_START & 0xff000000) >> 18  /*为什么是0xff000000，用r0来作为以后建立一个表项后，来增加4个字节的基地址,右移18位=(<pre name="code" class="cpp">#(KERNEL_START & 0xff000000)

<<20)>>2*/str r3, [r0, #(KERNEL_START & 0x00f00000) >> 18]!ldr r6, =(KERNEL_END - 1)add r0, r0, #4add r6, r4, r6, lsr #181: cmp r0, r6/*对内核虚拟地址的开始KERNEL_START到结束KERNEL_END 做映射*/
add r3, r3, #1 << 20 /*r3的高12位为对应物理页高12位的索引，*/strls r3, [r0], #4/*r0为要将要写页表内容的页表项地址*/bls 1b/* * Then map first 1MB of ram in case it contains our boot params. */add r0, r4, #PAGE_OFFSET >> 18orr r6, r7, #(PHYS_OFFSET & 0xff000000).if (PHYS_OFFSET & 0x00f00000)orr r6, r6, #(PHYS_OFFSET & 0x00f00000).endifstr r6, [r0]#endifmov pc, lrENDPROC(__create_page_tables)