xref: /openbmc/u-boot/arch/mips/lib/reloc.c (revision 3aa4b703)
1 /*
2  * MIPS Relocation
3  *
4  * Copyright (c) 2017 Imagination Technologies Ltd.
5  *
6  * SPDX-License-Identifier:	GPL-2.0+
7  *
8  * Relocation data, found in the .rel section, is generated by the mips-relocs
9  * tool & contains a record of all locations in the U-Boot binary that need to
10  * be fixed up during relocation.
11  *
12  * The data is a sequence of unsigned integers, which are of somewhat arbitrary
13  * size. This is achieved by encoding integers as a sequence of bytes, each of
14  * which contains 7 bits of data with the most significant bit indicating
15  * whether any further bytes need to be read. The least significant bits of the
16  * integer are found in the first byte - ie. it somewhat resembles little
17  * endian.
18  *
19  * Each pair of two integers represents a relocation that must be applied. The
20  * first integer represents the type of relocation as a standard ELF relocation
21  * type (ie. R_MIPS_*). The second integer represents the offset at which to
22  * apply the relocation, relative to the previous relocation or for the first
23  * relocation the start of the relocated .text section.
24  *
25  * The end of the relocation data is indicated when type R_MIPS_NONE (0) is
26  * read, at which point no further integers should be read. That is, the
27  * terminating R_MIPS_NONE reloc includes no offset.
28  */
29 
30 #include <common.h>
31 #include <asm/relocs.h>
32 #include <asm/sections.h>
33 
34 /**
35  * read_uint() - Read an unsigned integer from the buffer
36  * @buf: pointer to a pointer to the reloc buffer
37  *
38  * Read one whole unsigned integer from the relocation data pointed to by @buf,
39  * advancing @buf past the bytes encoding the integer.
40  *
41  * Returns: the integer read from @buf
42  */
43 static unsigned long read_uint(uint8_t **buf)
44 {
45 	unsigned long val = 0;
46 	unsigned int shift = 0;
47 	uint8_t new;
48 
49 	do {
50 		new = *(*buf)++;
51 		val |= (new & 0x7f) << shift;
52 		shift += 7;
53 	} while (new & 0x80);
54 
55 	return val;
56 }
57 
58 /**
59  * apply_reloc() - Apply a single relocation
60  * @type: the type of reloc (R_MIPS_*)
61  * @addr: the address that the reloc should be applied to
62  * @off: the relocation offset, ie. number of bytes we're moving U-Boot by
63  *
64  * Apply a single relocation of type @type at @addr. This function is
65  * intentionally simple, and does the bare minimum needed to fixup the
66  * relocated U-Boot - in particular, it does not check for overflows.
67  */
68 static void apply_reloc(unsigned int type, void *addr, long off)
69 {
70 	uint32_t u32;
71 
72 	switch (type) {
73 	case R_MIPS_26:
74 		u32 = *(uint32_t *)addr;
75 		u32 = (u32 & GENMASK(31, 26)) |
76 		      ((u32 + (off >> 2)) & GENMASK(25, 0));
77 		*(uint32_t *)addr = u32;
78 		break;
79 
80 	case R_MIPS_32:
81 		*(uint32_t *)addr += off;
82 		break;
83 
84 	case R_MIPS_64:
85 		*(uint64_t *)addr += off;
86 		break;
87 
88 	case R_MIPS_HI16:
89 		*(uint32_t *)addr += off >> 16;
90 		break;
91 
92 	default:
93 		panic("Unhandled reloc type %u\n", type);
94 	}
95 }
96 
97 /**
98  * relocate_code() - Relocate U-Boot, generally from flash to DDR
99  * @start_addr_sp: new stack pointer
100  * @new_gd: pointer to relocated global data
101  * @relocaddr: the address to relocate to
102  *
103  * Relocate U-Boot from its current location (generally in flash) to a new one
104  * (generally in DDR). This function will copy the U-Boot binary & apply
105  * relocations as necessary, then jump to board_init_r in the new build of
106  * U-Boot. As such, this function does not return.
107  */
108 void relocate_code(ulong start_addr_sp, gd_t *new_gd, ulong relocaddr)
109 {
110 	unsigned long addr, length, bss_len;
111 	uint8_t *buf, *bss_start;
112 	unsigned int type;
113 	long off;
114 
115 	/*
116 	 * Ensure that we're relocating by an offset which is a multiple of
117 	 * 64KiB, ie. doesn't change the least significant 16 bits of any
118 	 * addresses. This allows us to discard R_MIPS_LO16 relocs, saving
119 	 * space in the U-Boot binary & complexity in handling them.
120 	 */
121 	off = relocaddr - (unsigned long)__text_start;
122 	if (off & 0xffff)
123 		panic("Mis-aligned relocation\n");
124 
125 	/* Copy U-Boot to RAM */
126 	length = __image_copy_end - __text_start;
127 	memcpy((void *)relocaddr, __text_start, length);
128 
129 	/* Now apply relocations to the copy in RAM */
130 	buf = __rel_start;
131 	addr = relocaddr;
132 	while (true) {
133 		type = read_uint(&buf);
134 		if (type == R_MIPS_NONE)
135 			break;
136 
137 		addr += read_uint(&buf) << 2;
138 		apply_reloc(type, (void *)addr, off);
139 	}
140 
141 	/* Ensure the icache is coherent */
142 	flush_cache(relocaddr, length);
143 
144 	/* Clear the .bss section */
145 	bss_start = (uint8_t *)((unsigned long)__bss_start + off);
146 	bss_len = (unsigned long)&__bss_end - (unsigned long)__bss_start;
147 	memset(bss_start, 0, bss_len);
148 
149 	/* Jump to the relocated U-Boot */
150 	asm volatile(
151 		       "move	$29, %0\n"
152 		"	move	$4, %1\n"
153 		"	move	$5, %2\n"
154 		"	move	$31, $0\n"
155 		"	jr	%3"
156 		: /* no outputs */
157 		: "r"(start_addr_sp),
158 		  "r"(new_gd),
159 		  "r"(relocaddr),
160 		  "r"((unsigned long)board_init_r + off));
161 
162 	/* Since we jumped to the new U-Boot above, we won't get here */
163 	unreachable();
164 }
165