1 /* SPDX-License-Identifier: GPL-2.0-only */ 2 /* 3 * linux/arch/arm/boot/bootp/init.S 4 * 5 * Copyright (C) 2000-2003 Russell King. 6 * 7 * "Header" file for splitting kernel + initrd. Note that we pass 8 * r0 through to r3 straight through. 9 * 10 * This demonstrates how to append code to the start of the kernel 11 * zImage, and boot the kernel without copying it around. This 12 * example would be simpler; if we didn't have an object of unknown 13 * size immediately following the kernel, we could build this into 14 * a binary blob, and concatenate the zImage using the cat command. 15 */ 16 .section .start, "ax" 17 .type _start, #function 18 .globl _start 19 20 _start: add lr, pc, #-0x8 @ lr = current load addr 21 adr r13, data 22 ldmia r13!, {r4-r6} @ r5 = dest, r6 = length 23 add r4, r4, lr @ r4 = initrd_start + load addr 24 bl move @ move the initrd 25 26 /* 27 * Setup the initrd parameters to pass to the kernel. This can only be 28 * passed in via the tagged list. 29 */ 30 ldmia r13, {r5-r9} @ get size and addr of initrd 31 @ r5 = ATAG_CORE 32 @ r6 = ATAG_INITRD2 33 @ r7 = initrd start 34 @ r8 = initrd end 35 @ r9 = param_struct address 36 37 ldr r10, [r9, #4] @ get first tag 38 teq r10, r5 @ is it ATAG_CORE? 39 /* 40 * If we didn't find a valid tag list, create a dummy ATAG_CORE entry. 41 */ 42 movne r10, #0 @ terminator 43 movne r4, #2 @ Size of this entry (2 words) 44 stmiane r9, {r4, r5, r10} @ Size, ATAG_CORE, terminator 45 46 /* 47 * find the end of the tag list, and then add an INITRD tag on the end. 48 * If there is already an INITRD tag, then we ignore it; the last INITRD 49 * tag takes precedence. 50 */ 51 taglist: ldr r10, [r9, #0] @ tag length 52 teq r10, #0 @ last tag (zero length)? 53 addne r9, r9, r10, lsl #2 54 bne taglist 55 56 mov r5, #4 @ Size of initrd tag (4 words) 57 stmia r9, {r5, r6, r7, r8, r10} 58 b kernel_start @ call kernel 59 60 /* 61 * Move the block of memory length r6 from address r4 to address r5 62 */ 63 move: ldmia r4!, {r7 - r10} @ move 32-bytes at a time 64 stmia r5!, {r7 - r10} 65 ldmia r4!, {r7 - r10} 66 stmia r5!, {r7 - r10} 67 subs r6, r6, #8 * 4 68 bcs move 69 mov pc, lr 70 71 .size _start, . - _start 72 73 .align 74 75 .type data,#object 76 data: .word initrd_start @ source initrd address 77 .word initrd_phys @ destination initrd address 78 .word initrd_size @ initrd size 79 80 .word 0x54410001 @ r5 = ATAG_CORE 81 .word 0x54420005 @ r6 = ATAG_INITRD2 82 .word initrd_phys @ r7 83 .word initrd_size @ r8 84 .word params_phys @ r9 85 .size data, . - data 86