xref: /openbmc/u-boot/arch/arm/lib/crt0_64.S (revision 0fa1fc43)
1 /* SPDX-License-Identifier: GPL-2.0+ */
2 /*
3  * crt0 - C-runtime startup Code for AArch64 U-Boot
4  *
5  * (C) Copyright 2013
6  * David Feng <fenghua@phytium.com.cn>
7  *
8  * (C) Copyright 2012
9  * Albert ARIBAUD <albert.u.boot@aribaud.net>
10  */
11 
12 #include <config.h>
13 #include <asm-offsets.h>
14 #include <asm/macro.h>
15 #include <linux/linkage.h>
16 
17 /*
18  * This file handles the target-independent stages of the U-Boot
19  * start-up where a C runtime environment is needed. Its entry point
20  * is _main and is branched into from the target's start.S file.
21  *
22  * _main execution sequence is:
23  *
24  * 1. Set up initial environment for calling board_init_f().
25  *    This environment only provides a stack and a place to store
26  *    the GD ('global data') structure, both located in some readily
27  *    available RAM (SRAM, locked cache...). In this context, VARIABLE
28  *    global data, initialized or not (BSS), are UNAVAILABLE; only
29  *    CONSTANT initialized data are available. GD should be zeroed
30  *    before board_init_f() is called.
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  * 3. Set up intermediate environment where the stack and GD are the
40  *    ones allocated by board_init_f() in system RAM, but BSS and
41  *    initialized non-const data are still not available.
42  *
43  * 4a.For U-Boot proper (not SPL), call relocate_code(). This function
44  *    relocates U-Boot from its current location into the relocation
45  *    destination computed by board_init_f().
46  *
47  * 4b.For SPL, board_init_f() just returns (to crt0). There is no
48  *    code relocation in SPL.
49  *
50  * 5. Set up final environment for calling board_init_r(). This
51  *    environment has BSS (initialized to 0), initialized non-const
52  *    data (initialized to their intended value), and stack in system
53  *    RAM (for SPL moving the stack and GD into RAM is optional - see
54  *    CONFIG_SPL_STACK_R). GD has retained values set by board_init_f().
55  *
56  * TODO: For SPL, implement stack relocation on AArch64.
57  *
58  * 6. For U-Boot proper (not SPL), some CPUs have some work left to do
59  *    at this point regarding memory, so call c_runtime_cpu_setup.
60  *
61  * 7. Branch to board_init_r().
62  *
63  * For more information see 'Board Initialisation Flow in README.
64  */
65 
66 ENTRY(_main)
67 
68 /*
69  * Set up initial C runtime environment and call board_init_f(0).
70  */
71 #if defined(CONFIG_TPL_BUILD) && defined(CONFIG_TPL_NEEDS_SEPARATE_STACK)
72 	ldr	x0, =(CONFIG_TPL_STACK)
73 #elif defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
74 	ldr	x0, =(CONFIG_SPL_STACK)
75 #elif defined(CONFIG_SYS_INIT_SP_BSS_OFFSET)
76 	adr	x0, __bss_start
77 	add	x0, x0, #CONFIG_SYS_INIT_SP_BSS_OFFSET
78 #else
79 	ldr	x0, =(CONFIG_SYS_INIT_SP_ADDR)
80 #endif
81 	bic	sp, x0, #0xf	/* 16-byte alignment for ABI compliance */
82 	mov	x0, sp
83 	bl	board_init_f_alloc_reserve
84 	mov	sp, x0
85 	/* set up gd here, outside any C code */
86 	mov	x18, x0
87 	bl	board_init_f_init_reserve
88 
89 	mov	x0, #0
90 	bl	board_init_f
91 
92 #if !defined(CONFIG_SPL_BUILD)
93 /*
94  * Set up intermediate environment (new sp and gd) and call
95  * relocate_code(addr_moni). Trick here is that we'll return
96  * 'here' but relocated.
97  */
98 	ldr	x0, [x18, #GD_START_ADDR_SP]	/* x0 <- gd->start_addr_sp */
99 	bic	sp, x0, #0xf	/* 16-byte alignment for ABI compliance */
100 	ldr	x18, [x18, #GD_NEW_GD]		/* x18 <- gd->new_gd */
101 
102 	adr	lr, relocation_return
103 #if CONFIG_POSITION_INDEPENDENT
104 	/* Add in link-vs-runtime offset */
105 	adr	x0, _start		/* x0 <- Runtime value of _start */
106 	ldr	x9, _TEXT_BASE		/* x9 <- Linked value of _start */
107 	sub	x9, x9, x0		/* x9 <- Run-vs-link offset */
108 	add	lr, lr, x9
109 #endif
110 	/* Add in link-vs-relocation offset */
111 	ldr	x9, [x18, #GD_RELOC_OFF]	/* x9 <- gd->reloc_off */
112 	add	lr, lr, x9	/* new return address after relocation */
113 	ldr	x0, [x18, #GD_RELOCADDR]	/* x0 <- gd->relocaddr */
114 	b	relocate_code
115 
116 relocation_return:
117 
118 /*
119  * Set up final (full) environment
120  */
121 	bl	c_runtime_cpu_setup		/* still call old routine */
122 #endif /* !CONFIG_SPL_BUILD */
123 #if defined(CONFIG_SPL_BUILD)
124 	bl	spl_relocate_stack_gd           /* may return NULL */
125 	/* set up gd here, outside any C code, if new stack is returned */
126 	cmp	x0, #0
127 	csel	x18, x0, x18, ne
128 	/*
129 	 * Perform 'sp = (x0 != NULL) ? x0 : sp' while working
130 	 * around the constraint that conditional moves can not
131 	 * have 'sp' as an operand
132 	 */
133 	mov	x1, sp
134 	cmp	x0, #0
135 	csel	x0, x0, x1, ne
136 	mov	sp, x0
137 #endif
138 
139 /*
140  * Clear BSS section
141  */
142 	ldr	x0, =__bss_start		/* this is auto-relocated! */
143 	ldr	x1, =__bss_end			/* this is auto-relocated! */
144 clear_loop:
145 	str	xzr, [x0], #8
146 	cmp	x0, x1
147 	b.lo	clear_loop
148 
149 	/* call board_init_r(gd_t *id, ulong dest_addr) */
150 	mov	x0, x18				/* gd_t */
151 	ldr	x1, [x18, #GD_RELOCADDR]	/* dest_addr */
152 	b	board_init_r			/* PC relative jump */
153 
154 	/* NOTREACHED - board_init_r() does not return */
155 
156 ENDPROC(_main)
157