2021年11月24日 | Linux ARMv7中断向量表搬移(2)

一. Linux ARMv7启动阶段对中断向量表的搬移

1、中断向量表和中断处理部分代码的搬移

经历过kernel的汇编阶段，进入C语言start_kernel后对中断向量表的位置进行搬移，搬移函数是early_trap_init。

early_trap_init函数的调用流程为：

 start_kernel(init/main.c)--->setup_arch(arch/arm/kernel/setup.c)--->paging_init(arch/arm/mm/mmu.c)--->devicemaps_init(arch/arm/mm/mmu.c)--->early_trap_init(arch/arm/kernel/traps.c）

/*

* Set up the device mappings. Since we clear out the page tables for all

* mappings above VMALLOC_START, except early fixmap, we might remove debug

* device mappings. This means earlycon can be used to debug this function

* Any other function or debugging method which may touch any device _will_

* crash the kernel.

*/

static void __init devicemaps_init(const struct machine_desc *mdesc)

{

        struct map_desc map;

        unsigned long addr;

        void *vectors;

        /*

         * Allocate the vector page early.

         *分配两个页的内存空间，arm中每个页的大小为4K，这两个页的内存空间，一个是为保存中断向量

         *表，一个是为了保存中断的处理部分代码，这两部分代码的排布可以在

         *(arch/arm/kernel/vmlinux.lds和arch/arm/kernel/entry-armv.S）中可以具体分析出来

         */

        vectors = early_alloc(PAGE_SIZE * 2);

        early_trap_init(vectors);

         /*

          * Clear page table except top pmd used by early fixmaps

          */

         for (addr = VMALLOC_START; addr < (FIXADDR_TOP & PMD_MASK); addr += PMD_SIZE)

                pmd_clear(pmd_off_k(addr));

         /*

          * Map the kernel if it is XIP.

          * It is always first in the modulearea.

          */

#ifdef CONFIG_XIP_KERNEL  //此宏未定义

        map.pfn = __phys_to_pfn(CONFIG_XIP_PHYS_ADDR & SECTION_MASK);

        map.virtual = MODULES_VADDR;

        map.length = ((unsigned long)_etext - map.virtual + ~SECTION_MASK) & SECTION_MASK;

        map.type = MT_ROM;

        create_mapping(&map);

#endif

        /*

         * Map the cache flushing regions.

         */

#ifdef FLUSH_BASE  //此宏未定义

        map.pfn = __phys_to_pfn(FLUSH_BASE_PHYS);

        map.virtual = FLUSH_BASE;

        map.length = SZ_1M;

        map.type = MT_CACHECLEAN;

        create_mapping(&map);

#endif

#ifdef FLUSH_BASE_MINICACHE  //此宏未定义

        map.pfn = __phys_to_pfn(FLUSH_BASE_PHYS + SZ_1M);

        map.virtual = FLUSH_BASE_MINICACHE;

        map.length = SZ_1M;

        map.type = MT_MINICLEAN;

        create_mapping(&map);

#endif

        /*

         * Create a mapping for the machine vectors at the high-vectors

         * location (0xffff0000). If we aren't using high-vectors, also

         * create a mapping at the low-vectors virtual address.

         */

        /*

         *创建一个页的内存地址映射，虚拟地址为0xffff0000，此地址为中断向量表的高端地址

         *设置中断向量表的高端地址在汇编的v7_setup中，使用的v7_crval设置了cp15的c1寄存器

         *v7_crval定义在arch/arm/mm/proc-v7-2level.S。

         */

        map.pfn = __phys_to_pfn(virt_to_phys(vectors));

        map.virtual = 0xffff0000;

        map.length = PAGE_SIZE;

#ifdef CONFIG_KUSER_HELPERS  //此宏有定义

        map.type = MT_HIGH_VECTORS;

#else

        map.type = MT_LOW_VECTORS;

#endif

        create_mapping(&map);

        /*

         *判断中断向量表的位置是否设置在高端地址，如果中断向量表没有设置在高端地址，

         *在映射低端中断向量表地址。

         */

        if (!vectors_high()) {

                map.virtual = 0;

                map.length = PAGE_SIZE * 2;

                map.type = MT_LOW_VECTORS;

            create_mapping(&map);

        }

        /* Now create a kernel read-only mapping */

        map.pfn += 1;

        map.virtual = 0xffff0000 + PAGE_SIZE;

        map.length = PAGE_SIZE;

        map.type = MT_LOW_VECTORS;

        create_mapping(&map);

        /*

         * Ask the machine support to map in the statically mapped devices.

         */

        if (mdesc->map_io)

                mdesc->map_io();

        else

                debug_ll_io_init();

                fill_pmd_gaps();

        /* Reserve fixed i/o space in VMALLOC region */

        pci_reserve_io();

         /*

          * Finally flush the caches and tlb to ensure that we're in a

          * consistent state wrt the writebuffer. This also ensures that

          * any write-allocated cache lines in the vector page are written

          * back. After this point, we can start to touch devices again.

          */

        local_flush_tlb_all();

        flush_cache_all();

        /* Enable asynchronous aborts */

        early_abt_enable();

} 

        /*   AT

         *  TFR   EV X F   I D LR    S

         * .EEE ..EE PUI. .T.T 4RVI ZWRS BLDP WCAM

         * rxxx rrxx xxx0 0101 xxxx xxxx x111 xxxx < forced

         *   01    0 110       0011 1100 .111 1101 < we want

         */

        .align  2

        .type   v7_crval, #object

v7_crval:

        crval   clear=0x2120c302, mmuset=0x10c03c7d, ucset=0x00c01c7c

early_trap_init函数的分析

void __init early_trap_init(void *vectors_base)

{

#ifndef CONFIG_CPU_V7M

        unsigned long vectors = (unsigned long)vectors_base;

        extern char __stubs_start[], __stubs_end[];

        extern char __vectors_start[], __vectors_end[];

        unsigned i;

        vectors_page = vectors_base;

        /*

         * Poison the vectors page with an undefined instruction.  This

         * rly_trap_init instruction is chosen to be undefined for both ARM and Thumb

         * ISAs.  The Thumb version is an undefined instruction with a

         * branch back to the undefined instruction.

         * 将申请的4K先设置为未定义指令，防止在发生其他中断时，没有处理导致cpu错误

         */

        for (i = 0; i < PAGE_SIZE / sizeof(u32); i++)

                ((u32 *)vectors_base)[i] = 0xe7fddef1;/*

         * Copy the vectors, stubs and kuser helpers (in entry-armv.S)

         * into the vector page, mapped at 0xffff0000, and ensure these

         * are visible to the instruction stream.

         */

        /*

         *将中断向量表和中断处理的代码搬移到申请的两页地址空间内

         */

        memcpy((void *)vectors, __vectors_start, __vectors_end - __vectors_start);

        memcpy((void *)vectors + 0x1000, __stubs_start, __stubs_end - __stubs_start);

        kuser_init(vectors_base);

        flush_icache_range(vectors, vectors + PAGE_SIZE * 2);

#else /* ifndef CONFIG_CPU_V7M */

        /*

         * on V7-M there is no need to copy the vector table to a dedicated

         * memory area. The address is configurable and so a table in the kernel

         * image can be used.

         */

#endif

}