armv8 kernel boot process

linux kernel version: 4.8.0 -rc5

1. first core boot process:
arch/arm64/kernel/head.S 
    

70         __HEAD
 71 _head:
 72         /*
 73 * DO NOT MODIFY. Image header expected by Linux boot-loaders.
 74 */
 75 #ifdef CONFIG_EFI
 76         /*
 77 * This add instruction has no meaningful effect except that
 78 * its opcode forms the magic "MZ" signature required by UEFI.
 79 */
 80 add x13, x18, #0x16
 81         b       stext
 82 #else
 83         b       stext                                       // branch to kernel start, magic
 84 .long   0                                           // reserved
 85 #endif

211 ENTRY(stext)
212 bl preserve_boot_args
213 bl el2_setup                                           // Drop to EL1, w20=cpu_boot_mode
214         adrp    x24, __PHYS_OFFSET
215 and x23, x24, MIN_KIMG_ALIGN - 1        // KASLR offset, defaults to 0
216 bl set_cpu_boot_mode_flag
217 bl __create_page_tables            // x25=TTBR0, x26=TTBR1
218         /*
219 * The following calls CPU setup code, see arch/arm64/mm/proc.S for
220 * details.
221 * On return, the CPU will be ready for the MMU to be turned on and
222 * the TCR will have been set.
223 */
224 bl __cpu_setup                                 // initialise processor
225         adr_l   x27, __primary_switch           // address to jump to after
226                                                                             // MMU has been enabled
227         b       __enable_mmu
228 ENDPROC(stext)

781 __primary_switch:
782 #ifdef CONFIG_RELOCATABLE
783         /*
784 * Iterate over each entry in the relocation table, and apply the
785 * relocations in place.
786 */
787         ldr     w9, =__rela_offset                          // offset to reloc table
788         ldr     w10, =__rela_size                           // size of reloc table
789
790         mov_q   x11, KIMAGE_VADDR               // default virtual offset
791 add x11, x11, x23                               // actual virtual offset
792 add x9, x9, x11                                 // __va(.rela)
793 add x10, x9, x10                                // __va(.rela) + sizeof(.rela)
794
795 0: cmp x9, x10
796         b.hs    1f
797         ldp     x11, x12, [x9], #24
798         ldr     x13, [x9, #-8]
799 cmp w12, #R_AARCH64_RELATIVE
800         b.ne 0b
801 add x13, x13, x23                           // relocate
802 str x13, [x11, x23]
803         b       0b
804
805 1:
806 #endif
807         ldr     x8, =__primary_switched
808         br      x8
809 ENDPROC(__primary_switch)

421 __primary_switched:
422 mov x28, lr                         // preserve LR
423         adr_l   x8, vectors                     // load VBAR_EL1 with virtual
424         msr     vbar_el1, x8                    // vector table address
425         isb
426
427         // Clear BSS
428         adr_l   x0, __bss_start
429 mov x1, xzr
430         adr_l   x2, __bss_stop
431 sub x2, x2, x0
432 bl __pi_memset
433         dsb     ishst                           // Make zero page visible to PTW
434
435         adr_l   sp, initial_sp, x4
436 mov x4, sp
437 and x4, x4, #~(THREAD_SIZE - 1)
438         msr     sp_el0, x4                      // Save thread_info
439         str_l   x21, __fdt_pointer, x5          // Save FDT pointer
440
441         ldr_l   x4, kimage_vaddr                // Save the offset between
442 sub x4, x4, x24                     // the kernel virtual and
443         str_l   x4, kimage_voffset, x5          // physical mappings
444
445 mov x29, #0
446 #ifdef CONFIG_KASAN
447 bl kasan_early_init
448 #endif
449 #ifdef CONFIG_RANDOMIZE_BASE
450         tst     x23, ~(MIN_KIMG_ALIGN - 1) // already running randomized?
451         b.ne 0f
452 mov x0, x21                         // pass FDT address in x0
453 mov x1, x23                         // pass modulo offset in x1
454 bl kaslr_early_init                // parse FDT for KASLR options
455         cbz     x0, 0f                          // KASLR disabled? just proceed
456         orr     x23, x23, x0                    // record KASLR offset
457 ret x28                             // we must enable KASLR, return
458                                                 // to __enable_mmu()
459 0:
460 #endif
461         b       start_kernel
462 ENDPROC(__primary_switched)

from here, enter C code function: start_kernel().

2. secondary core boot process:

init/main.c  ---> start_kernel() --> rest_init(); -> kernel_thread(kernel_init, NULL, CLONE_FS); ---- >
            kernel_init(void *unused)  ---> kernel_init_freeable();  ----> smp_init();(kernel/smp.c)--> 
            cpu_up(cpu);