blob: bff8abb3a4aa0bc5e3cda03f5776a5fee6e08e86 [file] [log] [blame]
Josh Poimboeuf442f04c2016-02-28 22:22:41 -06001/*
2 * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation; either version 2
7 * of the License, or (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, see <http://www.gnu.org/licenses/>.
16 */
17
18/*
19 * This file reads all the special sections which have alternate instructions
20 * which can be patched in or redirected to at runtime.
21 */
22
23#include <stdlib.h>
24#include <string.h>
25
26#include "special.h"
27#include "warn.h"
28
29#define EX_ENTRY_SIZE 12
30#define EX_ORIG_OFFSET 0
31#define EX_NEW_OFFSET 4
32
33#define JUMP_ENTRY_SIZE 24
34#define JUMP_ORIG_OFFSET 0
35#define JUMP_NEW_OFFSET 8
36
37#define ALT_ENTRY_SIZE 13
38#define ALT_ORIG_OFFSET 0
39#define ALT_NEW_OFFSET 4
40#define ALT_FEATURE_OFFSET 8
41#define ALT_ORIG_LEN_OFFSET 10
42#define ALT_NEW_LEN_OFFSET 11
43
44#define X86_FEATURE_POPCNT (4*32+23)
45
46struct special_entry {
47 const char *sec;
48 bool group, jump_or_nop;
49 unsigned char size, orig, new;
50 unsigned char orig_len, new_len; /* group only */
51 unsigned char feature; /* ALTERNATIVE macro CPU feature */
52};
53
54struct special_entry entries[] = {
55 {
56 .sec = ".altinstructions",
57 .group = true,
58 .size = ALT_ENTRY_SIZE,
59 .orig = ALT_ORIG_OFFSET,
60 .orig_len = ALT_ORIG_LEN_OFFSET,
61 .new = ALT_NEW_OFFSET,
62 .new_len = ALT_NEW_LEN_OFFSET,
63 .feature = ALT_FEATURE_OFFSET,
64 },
65 {
66 .sec = "__jump_table",
67 .jump_or_nop = true,
68 .size = JUMP_ENTRY_SIZE,
69 .orig = JUMP_ORIG_OFFSET,
70 .new = JUMP_NEW_OFFSET,
71 },
72 {
73 .sec = "__ex_table",
74 .size = EX_ENTRY_SIZE,
75 .orig = EX_ORIG_OFFSET,
76 .new = EX_NEW_OFFSET,
77 },
78 {},
79};
80
81static int get_alt_entry(struct elf *elf, struct special_entry *entry,
82 struct section *sec, int idx,
83 struct special_alt *alt)
84{
85 struct rela *orig_rela, *new_rela;
86 unsigned long offset;
87
88 offset = idx * entry->size;
89
90 alt->group = entry->group;
91 alt->jump_or_nop = entry->jump_or_nop;
92
93 if (alt->group) {
94 alt->orig_len = *(unsigned char *)(sec->data + offset +
95 entry->orig_len);
96 alt->new_len = *(unsigned char *)(sec->data + offset +
97 entry->new_len);
98 }
99
100 if (entry->feature) {
101 unsigned short feature;
102
103 feature = *(unsigned short *)(sec->data + offset +
104 entry->feature);
105
106 /*
107 * It has been requested that we don't validate the !POPCNT
108 * feature path which is a "very very small percentage of
109 * machines".
110 */
111 if (feature == X86_FEATURE_POPCNT)
112 alt->skip_orig = true;
113 }
114
115 orig_rela = find_rela_by_dest(sec, offset + entry->orig);
116 if (!orig_rela) {
117 WARN_FUNC("can't find orig rela", sec, offset + entry->orig);
118 return -1;
119 }
120 if (orig_rela->sym->type != STT_SECTION) {
121 WARN_FUNC("don't know how to handle non-section rela symbol %s",
122 sec, offset + entry->orig, orig_rela->sym->name);
123 return -1;
124 }
125
126 alt->orig_sec = orig_rela->sym->sec;
127 alt->orig_off = orig_rela->addend;
128
129 if (!entry->group || alt->new_len) {
130 new_rela = find_rela_by_dest(sec, offset + entry->new);
131 if (!new_rela) {
132 WARN_FUNC("can't find new rela",
133 sec, offset + entry->new);
134 return -1;
135 }
136
137 alt->new_sec = new_rela->sym->sec;
138 alt->new_off = (unsigned int)new_rela->addend;
139
140 /* _ASM_EXTABLE_EX hack */
141 if (alt->new_off >= 0x7ffffff0)
142 alt->new_off -= 0x7ffffff0;
143 }
144
145 return 0;
146}
147
148/*
149 * Read all the special sections and create a list of special_alt structs which
150 * describe all the alternate instructions which can be patched in or
151 * redirected to at runtime.
152 */
153int special_get_alts(struct elf *elf, struct list_head *alts)
154{
155 struct special_entry *entry;
156 struct section *sec;
157 unsigned int nr_entries;
158 struct special_alt *alt;
159 int idx, ret;
160
161 INIT_LIST_HEAD(alts);
162
163 for (entry = entries; entry->sec; entry++) {
164 sec = find_section_by_name(elf, entry->sec);
165 if (!sec)
166 continue;
167
168 if (sec->len % entry->size != 0) {
169 WARN("%s size not a multiple of %d",
170 sec->name, entry->size);
171 return -1;
172 }
173
174 nr_entries = sec->len / entry->size;
175
176 for (idx = 0; idx < nr_entries; idx++) {
177 alt = malloc(sizeof(*alt));
178 if (!alt) {
179 WARN("malloc failed");
180 return -1;
181 }
182 memset(alt, 0, sizeof(*alt));
183
184 ret = get_alt_entry(elf, entry, sec, idx, alt);
185 if (ret)
186 return ret;
187
188 list_add_tail(&alt->list, alts);
189 }
190 }
191
192 return 0;
193}