aboutsummaryrefslogtreecommitdiff
path: root/arch/arm/lib/crt0_64.S
blob: e76b25a03e8c7621717cc9595c7b2fd5be9807e9 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
/* SPDX-License-Identifier: GPL-2.0+ */
/*
 * crt0 - C-runtime startup Code for AArch64 U-Boot
 *
 * (C) Copyright 2013
 * David Feng <fenghua@phytium.com.cn>
 *
 * (C) Copyright 2012
 * Albert ARIBAUD <albert.u.boot@aribaud.net>
 */

#include <config.h>
#include <asm-offsets.h>
#include <asm/macro.h>
#include <linux/linkage.h>

/*
 * This file handles the target-independent stages of the U-Boot
 * start-up where a C runtime environment is needed. Its entry point
 * is _main and is branched into from the target's start.S file.
 *
 * _main execution sequence is:
 *
 * 1. Set up initial environment for calling board_init_f().
 *    This environment only provides a stack and a place to store
 *    the GD ('global data') structure, both located in some readily
 *    available RAM (SRAM, locked cache...). In this context, VARIABLE
 *    global data, initialized or not (BSS), are UNAVAILABLE; only
 *    CONSTANT initialized data are available. GD should be zeroed
 *    before board_init_f() is called.
 *
 * 2. Call board_init_f(). This function prepares the hardware for
 *    execution from system RAM (DRAM, DDR...) As system RAM may not
 *    be available yet, , board_init_f() must use the current GD to
 *    store any data which must be passed on to later stages. These
 *    data include the relocation destination, the future stack, and
 *    the future GD location.
 *
 * 3. Set up intermediate environment where the stack and GD are the
 *    ones allocated by board_init_f() in system RAM, but BSS and
 *    initialized non-const data are still not available.
 *
 * 4a.For U-Boot proper (not SPL), call relocate_code(). This function
 *    relocates U-Boot from its current location into the relocation
 *    destination computed by board_init_f().
 *
 * 4b.For SPL, board_init_f() just returns (to crt0). There is no
 *    code relocation in SPL.
 *
 * 5. Set up final environment for calling board_init_r(). This
 *    environment has BSS (initialized to 0), initialized non-const
 *    data (initialized to their intended value), and stack in system
 *    RAM (for SPL moving the stack and GD into RAM is optional - see
 *    CONFIG_SPL_STACK_R). GD has retained values set by board_init_f().
 *
 * TODO: For SPL, implement stack relocation on AArch64.
 *
 * 6. For U-Boot proper (not SPL), some CPUs have some work left to do
 *    at this point regarding memory, so call c_runtime_cpu_setup.
 *
 * 7. Branch to board_init_r().
 *
 * For more information see 'Board Initialisation Flow in README.
 */

ENTRY(_main)

/*
 * Set up initial C runtime environment and call board_init_f(0).
 */
#if defined(CONFIG_TPL_BUILD) && defined(CONFIG_TPL_NEEDS_SEPARATE_STACK)
	ldr	x0, =(CONFIG_TPL_STACK)
#elif defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
	ldr	x0, =(CONFIG_SPL_STACK)
#elif defined(CONFIG_INIT_SP_RELATIVE)
	adr	x0, __bss_start
	add	x0, x0, #CONFIG_SYS_INIT_SP_BSS_OFFSET
#else
	ldr	x0, =(CONFIG_SYS_INIT_SP_ADDR)
#endif
	bic	sp, x0, #0xf	/* 16-byte alignment for ABI compliance */
	mov	x0, sp
	bl	board_init_f_alloc_reserve
	mov	sp, x0
	/* set up gd here, outside any C code */
	mov	x18, x0
	bl	board_init_f_init_reserve

	mov	x0, #0
	bl	board_init_f

#if !defined(CONFIG_SPL_BUILD)
/*
 * Set up intermediate environment (new sp and gd) and call
 * relocate_code(addr_moni). Trick here is that we'll return
 * 'here' but relocated.
 */
	ldr	x0, [x18, #GD_START_ADDR_SP]	/* x0 <- gd->start_addr_sp */
	bic	sp, x0, #0xf	/* 16-byte alignment for ABI compliance */
	ldr	x18, [x18, #GD_NEW_GD]		/* x18 <- gd->new_gd */

	adr	lr, relocation_return
#if CONFIG_POSITION_INDEPENDENT
	/* Add in link-vs-runtime offset */
	adr	x0, _start		/* x0 <- Runtime value of _start */
	ldr	x9, _TEXT_BASE		/* x9 <- Linked value of _start */
	sub	x9, x9, x0		/* x9 <- Run-vs-link offset */
	add	lr, lr, x9
#endif
	/* Add in link-vs-relocation offset */
	ldr	x9, [x18, #GD_RELOC_OFF]	/* x9 <- gd->reloc_off */
	add	lr, lr, x9	/* new return address after relocation */
	ldr	x0, [x18, #GD_RELOCADDR]	/* x0 <- gd->relocaddr */
	b	relocate_code

relocation_return:

/*
 * Set up final (full) environment
 */
	bl	c_runtime_cpu_setup		/* still call old routine */
#endif /* !CONFIG_SPL_BUILD */
#if defined(CONFIG_SPL_BUILD)
	bl	spl_relocate_stack_gd           /* may return NULL */
	/* set up gd here, outside any C code, if new stack is returned */
	cmp	x0, #0
	csel	x18, x0, x18, ne
	/*
	 * Perform 'sp = (x0 != NULL) ? x0 : sp' while working
	 * around the constraint that conditional moves can not
	 * have 'sp' as an operand
	 */
	mov	x1, sp
	cmp	x0, #0
	csel	x0, x0, x1, ne
	mov	sp, x0
#endif

/*
 * Clear BSS section
 */
	ldr	x0, =__bss_start		/* this is auto-relocated! */
	ldr	x1, =__bss_end			/* this is auto-relocated! */
clear_loop:
	str	xzr, [x0], #8
	cmp	x0, x1
	b.lo	clear_loop

	/* call board_init_r(gd_t *id, ulong dest_addr) */
	mov	x0, x18				/* gd_t */
	ldr	x1, [x18, #GD_RELOCADDR]	/* dest_addr */
	b	board_init_r			/* PC relative jump */

	/* NOTREACHED - board_init_r() does not return */

ENDPROC(_main)