1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * MIPS Relocation
4 *
5 * Copyright (c) 2017 Imagination Technologies Ltd.
6 *
7 * Relocation data, found in the .rel section, is generated by the mips-relocs
8 * tool & contains a record of all locations in the U-Boot binary that need to
9 * be fixed up during relocation.
10 *
11 * The data is a sequence of unsigned integers, which are of somewhat arbitrary
12 * size. This is achieved by encoding integers as a sequence of bytes, each of
13 * which contains 7 bits of data with the most significant bit indicating
14 * whether any further bytes need to be read. The least significant bits of the
15 * integer are found in the first byte - ie. it somewhat resembles little
16 * endian.
17 *
18 * Each pair of two integers represents a relocation that must be applied. The
19 * first integer represents the type of relocation as a standard ELF relocation
20 * type (ie. R_MIPS_*). The second integer represents the offset at which to
21 * apply the relocation, relative to the previous relocation or for the first
22 * relocation the start of the relocated .text section.
23 *
24 * The end of the relocation data is indicated when type R_MIPS_NONE (0) is
25 * read, at which point no further integers should be read. That is, the
26 * terminating R_MIPS_NONE reloc includes no offset.
27 */
28
29#include <cpu_func.h>
30#include <init.h>
31#include <asm/relocs.h>
32#include <asm/sections.h>
33#include <linux/bitops.h>
34
35/**
36 * read_uint() - Read an unsigned integer from the buffer
37 * @buf: pointer to a pointer to the reloc buffer
38 *
39 * Read one whole unsigned integer from the relocation data pointed to by @buf,
40 * advancing @buf past the bytes encoding the integer.
41 *
42 * Returns: the integer read from @buf
43 */
44static unsigned long read_uint(uint8_t **buf)
45{
46	unsigned long val = 0;
47	unsigned int shift = 0;
48	uint8_t new;
49
50	do {
51		new = *(*buf)++;
52		val |= (new & 0x7f) << shift;
53		shift += 7;
54	} while (new & 0x80);
55
56	return val;
57}
58
59/**
60 * apply_reloc() - Apply a single relocation
61 * @type: the type of reloc (R_MIPS_*)
62 * @addr: the address that the reloc should be applied to
63 * @off: the relocation offset, ie. number of bytes we're moving U-Boot by
64 *
65 * Apply a single relocation of type @type at @addr. This function is
66 * intentionally simple, and does the bare minimum needed to fixup the
67 * relocated U-Boot - in particular, it does not check for overflows.
68 */
69static void apply_reloc(unsigned int type, void *addr, long off, uint8_t *buf)
70{
71	uint32_t u32;
72
73	switch (type) {
74	case R_MIPS_26:
75		u32 = *(uint32_t *)addr;
76		u32 = (u32 & GENMASK(31, 26)) |
77		      ((u32 + (off >> 2)) & GENMASK(25, 0));
78		*(uint32_t *)addr = u32;
79		break;
80
81	case R_MIPS_32:
82		*(uint32_t *)addr += off;
83		break;
84
85	case R_MIPS_64:
86		*(uint64_t *)addr += off;
87		break;
88
89	case R_MIPS_HI16:
90		*(uint32_t *)addr += off >> 16;
91		break;
92
93	default:
94		panic("Unhandled reloc type %u (@ %p), bss used before relocation?\n",
95		      type, buf);
96	}
97}
98
99/**
100 * relocate_code() - Relocate U-Boot, generally from flash to DDR
101 * @start_addr_sp: new stack pointer
102 * @new_gd: pointer to relocated global data
103 * @relocaddr: the address to relocate to
104 *
105 * Relocate U-Boot from its current location (generally in flash) to a new one
106 * (generally in DDR). This function will copy the U-Boot binary & apply
107 * relocations as necessary, then jump to board_init_r in the new build of
108 * U-Boot. As such, this function does not return.
109 */
110void relocate_code(ulong start_addr_sp, gd_t *new_gd, ulong relocaddr)
111{
112	unsigned long addr, length, bss_len;
113	uint8_t *buf, *bss_start;
114	unsigned int type;
115	long off;
116
117	/*
118	 * Ensure that we're relocating by an offset which is a multiple of
119	 * 64KiB, ie. doesn't change the least significant 16 bits of any
120	 * addresses. This allows us to discard R_MIPS_LO16 relocs, saving
121	 * space in the U-Boot binary & complexity in handling them.
122	 */
123	off = relocaddr - (unsigned long)__text_start;
124	if (off & 0xffff)
125		panic("Mis-aligned relocation\n");
126
127	/* Copy U-Boot to RAM */
128	length = __image_copy_end - __text_start;
129	memcpy((void *)relocaddr, __text_start, length);
130
131	/* Now apply relocations to the copy in RAM */
132	buf = __rel_start;
133	addr = relocaddr;
134	while (true) {
135		type = read_uint(&buf);
136		if (type == R_MIPS_NONE)
137			break;
138
139		addr += read_uint(&buf) << 2;
140		apply_reloc(type, (void *)addr, off, buf);
141	}
142
143	/* Ensure the icache is coherent */
144	flush_cache(relocaddr, length);
145
146	/* Clear the .bss section */
147	bss_start = (uint8_t *)((unsigned long)__bss_start + off);
148	bss_len = (unsigned long)__bss_end - (unsigned long)__bss_start;
149	memset(bss_start, 0, bss_len);
150
151	/* Jump to the relocated U-Boot */
152	asm volatile(
153		       "move	$29, %0\n"
154		"	move	$4, %1\n"
155		"	move	$5, %2\n"
156		"	move	$31, $0\n"
157		"	jr	%3"
158		: /* no outputs */
159		: "r"(start_addr_sp),
160		  "r"(new_gd),
161		  "r"(relocaddr),
162		  "r"((unsigned long)board_init_r + off));
163
164	/* Since we jumped to the new U-Boot above, we won't get here */
165	unreachable();
166}
167