1/* 2 * crt0 - C-runtime startup Code for AArch64 U-Boot 3 * 4 * (C) Copyright 2013 5 * David Feng <fenghua@phytium.com.cn> 6 * 7 * (C) Copyright 2012 8 * Albert ARIBAUD <albert.u.boot@aribaud.net> 9 * 10 * SPDX-License-Identifier: GPL-2.0+ 11 */ 12 13#include <config.h> 14#include <asm-offsets.h> 15#include <asm/macro.h> 16#include <linux/linkage.h> 17 18/* 19 * This file handles the target-independent stages of the U-Boot 20 * start-up where a C runtime environment is needed. Its entry point 21 * is _main and is branched into from the target's start.S file. 22 * 23 * _main execution sequence is: 24 * 25 * 1. Set up initial environment for calling board_init_f(). 26 * This environment only provides a stack and a place to store 27 * the GD ('global data') structure, both located in some readily 28 * available RAM (SRAM, locked cache...). In this context, VARIABLE 29 * global data, initialized or not (BSS), are UNAVAILABLE; only 30 * CONSTANT initialized data are available. 31 * 32 * 2. Call board_init_f(). This function prepares the hardware for 33 * execution from system RAM (DRAM, DDR...) As system RAM may not 34 * be available yet, , board_init_f() must use the current GD to 35 * store any data which must be passed on to later stages. These 36 * data include the relocation destination, the future stack, and 37 * the future GD location. 38 * 39 * (the following applies only to non-SPL builds) 40 * 41 * 3. Set up intermediate environment where the stack and GD are the 42 * ones allocated by board_init_f() in system RAM, but BSS and 43 * initialized non-const data are still not available. 44 * 45 * 4. Call relocate_code(). This function relocates U-Boot from its 46 * current location into the relocation destination computed by 47 * board_init_f(). 48 * 49 * 5. Set up final environment for calling board_init_r(). This 50 * environment has BSS (initialized to 0), initialized non-const 51 * data (initialized to their intended value), and stack in system 52 * RAM. GD has retained values set by board_init_f(). Some CPUs 53 * have some work left to do at this point regarding memory, so 54 * call c_runtime_cpu_setup. 55 * 56 * 6. Branch to board_init_r(). 57 */ 58 59ENTRY(_main) 60 61/* 62 * Set up initial C runtime environment and call board_init_f(0). 63 */ 64 ldr x0, =(CONFIG_SYS_INIT_SP_ADDR) 65 sub x0, x0, #GD_SIZE /* allocate one GD above SP */ 66 bic sp, x0, #0xf /* 16-byte alignment for ABI compliance */ 67 mov x18, sp /* GD is above SP */ 68 mov x0, #0 69 bl board_init_f 70 71/* 72 * Set up intermediate environment (new sp and gd) and call 73 * relocate_code(addr_moni). Trick here is that we'll return 74 * 'here' but relocated. 75 */ 76 ldr x0, [x18, #GD_START_ADDR_SP] /* x0 <- gd->start_addr_sp */ 77 bic sp, x0, #0xf /* 16-byte alignment for ABI compliance */ 78 ldr x18, [x18, #GD_BD] /* x18 <- gd->bd */ 79 sub x18, x18, #GD_SIZE /* new GD is below bd */ 80 81 adr lr, relocation_return 82 ldr x9, [x18, #GD_RELOC_OFF] /* x9 <- gd->reloc_off */ 83 add lr, lr, x9 /* new return address after relocation */ 84 ldr x0, [x18, #GD_RELOCADDR] /* x0 <- gd->relocaddr */ 85 b relocate_code 86 87relocation_return: 88 89/* 90 * Set up final (full) environment 91 */ 92 bl c_runtime_cpu_setup /* still call old routine */ 93 94/* 95 * Clear BSS section 96 */ 97 ldr x0, =__bss_start /* this is auto-relocated! */ 98 ldr x1, =__bss_end /* this is auto-relocated! */ 99 mov x2, #0 100clear_loop: 101 str x2, [x0] 102 add x0, x0, #8 103 cmp x0, x1 104 b.lo clear_loop 105 106 /* call board_init_r(gd_t *id, ulong dest_addr) */ 107 mov x0, x18 /* gd_t */ 108 ldr x1, [x18, #GD_RELOCADDR] /* dest_addr */ 109 b board_init_r /* PC relative jump */ 110 111 /* NOTREACHED - board_init_r() does not return */ 112 113ENDPROC(_main) 114