ARMLinux2.6.18启动过程解析

ARM Linux Boot Sequence
The following traces the Linux boot sequence for ARM-based systems in the 2.6.18 kernel. It looks at just the earliest stages of the boot process, until the generic non-processor-specific start_kernel function is called. The line numbers of each statement are in parenthese at the end of the line; the kernel source itself can be conveniently browsed on the Linux Cross-Reference website.

zImage decompression

    arch/arm/boot/compressed/head.S: start (108)
        First code executed, jumped to by the bootloader, at label "start" (108)
        save contents of registers r1 and r2 in r7 and r8 to save off architecture ID and atags pointer passed in by bootloader (118)
        execute arch-specific code (inserted at 146)
            arch/arm/boot/compressed/head-xscale.S or other arch-specific code file
            added to build in arch/arm/boot/compressed/Makefile
            linked into head.S by linker section declaration:  .section ¡§start¡¨
            flush cache, turn off cache and MMU
        load registers with stored parameters (152)
            sp = stack pointer for decompression code (152)
            r4 = zreladdr = kernel entry point physical address
        check if running at link address, and fix up global offset table if not (196)
        zero decompression bss (205)
        call cache_on to turn on cache (218)
            defined at arch/arm/boot/compressed/head.S (320)
            call call_cache_fn to turn on cache as appropriate for processor variant
                defined at arch/arm/boot/compressed/head.S (505)
                walk through proc_types list (530) until find corresponding processor
                call cache-on function in list item corresponding to processor (511)
                    for ARMv5tej core, cache_on function is __armv4_mmu_cache_on (417)
                        call setup_mmu to set up initial page tables since MMU must be on for cache to be on (419)
                        turn on cache and MMU (426)
        check to make sure won't overwrite image during decompression; assume not for this trace (232)
        call decompress_kernel to decompress kernel to RAM (277)
        branch to call_kernel (278)