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
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
|
/* ScummVM - Graphic Adventure Engine
*
* ScummVM is the legal property of its developers, whose names
* are too numerous to list here. Please refer to the COPYRIGHT
* file distributed with this source distribution.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* $URL$
* $Id$
*
*/
#include "elf-loader.h"
#define __DEBUG_PLUGINS__
#ifdef __DEBUG_PLUGINS__
#define DBG(x,...) printf(x, ## __VA_ARGS__)
#else
#define DBG(x,...)
#endif
#define seterror(x,...) printf(x, ## __VA_ARGS__)
/**
* Follow the instruction of a relocation section.
*
* @param DLFile SeekableReadStream of File
* @param offset Offset into the File
* @param size Size of relocation section
* @param relSegment Base address of relocated segment in memory (memory offset)
*
*/
bool DLObject::relocate(Common::SeekableReadStream* DLFile, unsigned long offset, unsigned long size, void *relSegment) {
Elf32_Rel *rel = NULL; // relocation entry
// Allocate memory for relocation table
if (!(rel = (Elf32_Rel *)malloc(size))) {
seterror("Out of memory.");
return false;
}
// Read in our relocation table
if (DLFile->seek(offset, SEEK_SET) < 0 ||
DLFile->read(rel, size) != (ssize_t)size) {
seterror("Relocation table load failed.");
free(rel);
return false;
}
// Treat each relocation entry. Loop over all of them
int cnt = size / sizeof(*rel);
DBG("Loaded relocation table. %d entries. base address=%p\n", cnt, relSegment);
bool seenHi16 = false; // For treating HI/LO16 commands
int firstHi16 = -1; // Mark the point of the first hi16 seen
Elf32_Addr ahl = 0; // Calculated addend
int a = 0; // Addend: taken from the target
unsigned int *lastTarget = 0; // For processing hi16 when lo16 arrives
unsigned int relocation = 0;
int debugRelocs[10] = {0}; // For debugging
int extendedHi16 = 0; // Count extended hi16 treatments
Elf32_Addr lastHiSymVal = 0;
bool hi16InShorts = false;
#define DEBUG_NUM 2
// Loop over relocation entries
for (int i = 0; i < cnt; i++) {
// Get the symbol this relocation entry is referring to
Elf32_Sym *sym = (Elf32_Sym *)(_symtab) + (REL_INDEX(rel[i].r_info));
// Get the target instruction in the code
unsigned int *target = (unsigned int *)((char *)relSegment + rel[i].r_offset);
unsigned int origTarget = *target; // Save for debugging
// Act differently based on the type of relocation
switch (REL_TYPE(rel[i].r_info)) {
case R_MIPS_HI16: // Absolute addressing.
if (sym->st_shndx < SHN_LOPROC && // Only shift for plugin section (ie. has a real section index)
firstHi16 < 0) { // Only process first in block of HI16s
firstHi16 = i; // Keep the first Hi16 we saw
seenHi16 = true;
ahl = (*target & 0xffff) << 16; // Take lower 16 bits shifted up
lastHiSymVal = sym->st_value;
hi16InShorts = (ShortsMan.inGeneralSegment((char *)sym->st_value)); // Fix for problem with switching btw segments
if (debugRelocs[0]++ < DEBUG_NUM) // Print only a set number
DBG("R_MIPS_HI16: i=%d, offset=%x, ahl = %x, target = %x\n",
i, rel[i].r_offset, ahl, *target);
}
break;
case R_MIPS_LO16: // Absolute addressing. Needs a HI16 to come before it
if (sym->st_shndx < SHN_LOPROC) { // Only shift for plugin section. (ie. has a real section index)
if (!seenHi16) { // We MUST have seen HI16 first
seterror("R_MIPS_LO16 w/o preceding R_MIPS_HI16 at relocation %d!\n", i);
free(rel);
return false;
}
// Fix: bug in gcc makes LO16s connect to wrong HI16s sometimes (shorts and regular segment)
// Note that we can check the entire shorts segment because the executable's shorts don't belong to this plugin section
// and will be screened out above
bool lo16InShorts = ShortsMan.inGeneralSegment((char *)sym->st_value);
// Correct the bug by getting the proper value in ahl (taken from the current symbol)
if ((hi16InShorts && !lo16InShorts) || (!hi16InShorts && lo16InShorts)) {
ahl -= (lastHiSymVal & 0xffff0000); // We assume gcc meant the same offset
ahl += (sym->st_value & 0xffff0000);
}
ahl &= 0xffff0000; // Clean lower 16 bits for repeated LO16s
a = *target & 0xffff; // Take lower 16 bits of the target
a = (a << 16) >> 16; // Sign extend them
ahl += a; // Add lower 16 bits. AHL is now complete
// Fix: we can have LO16 access to the short segment sometimes
if (lo16InShorts) {
relocation = ahl + _shortsSegment->getOffset(); // Add in the short segment offset
} else // It's in the regular segment
relocation = ahl + (Elf32_Addr)_segment; // Add in the new offset for the segment
if (firstHi16 >= 0) { // We haven't treated the HI16s yet so do it now
for (int j = firstHi16; j < i; j++) {
if (REL_TYPE(rel[j].r_info) != R_MIPS_HI16) continue; // Skip over non-Hi16s
lastTarget = (unsigned int *)((char *)relSegment + rel[j].r_offset); // get hi16 target
*lastTarget &= 0xffff0000; // Clear the lower 16 bits of the last target
*lastTarget |= (relocation >> 16) & 0xffff; // Take the upper 16 bits of the relocation
if (relocation & 0x8000)(*lastTarget)++; // Subtle: we need to add 1 to the HI16 in this case
}
firstHi16 = -1; // Reset so we'll know we treated it
} else {
extendedHi16++;
}
*target &= 0xffff0000; // Clear the lower 16 bits of current target
*target |= relocation & 0xffff; // Take the lower 16 bits of the relocation
if (debugRelocs[1]++ < DEBUG_NUM)
DBG("R_MIPS_LO16: i=%d, offset=%x, a=%x, ahl = %x, lastTarget = %x, origt = %x, target = %x\n",
i, rel[i].r_offset, a, ahl, *lastTarget, origTarget, *target);
if (lo16InShorts && debugRelocs[2]++ < DEBUG_NUM)
DBG("R_MIPS_LO16s: i=%d, offset=%x, a=%x, ahl = %x, lastTarget = %x, origt = %x, target = %x\n",
i, rel[i].r_offset, a, ahl, *lastTarget, origTarget, *target);
}
break;
case R_MIPS_26: // Absolute addressing (for jumps and branches only)
if (sym->st_shndx < SHN_LOPROC) { // Only relocate for main segment
a = *target & 0x03ffffff; // Get 26 bits' worth of the addend
a = (a << 6) >> 6; // Sign extend a
relocation = ((a << 2) + (Elf32_Addr)_segment) >> 2; // a already points to the target. Subtract our offset
*target &= 0xfc000000; // Clean lower 26 target bits
*target |= (relocation & 0x03ffffff);
if (debugRelocs[3]++ < DEBUG_NUM)
DBG("R_MIPS_26: i=%d, offset=%x, symbol=%d, stinfo=%x, a=%x, origTarget=%x, target=%x\n",
i, rel[i].r_offset, REL_INDEX(rel[i].r_info), sym->st_info, a, origTarget, *target);
} else {
if (debugRelocs[4]++ < DEBUG_NUM)
DBG("R_MIPS_26: i=%d, offset=%x, symbol=%d, stinfo=%x, a=%x, origTarget=%x, target=%x\n",
i, rel[i].r_offset, REL_INDEX(rel[i].r_info), sym->st_info, a, origTarget, *target);
}
break;
case R_MIPS_GPREL16: // GP Relative addressing
if (_shortsSegment->getOffset() != 0 && // Only relocate if we shift the shorts section
ShortsMan.inGeneralSegment((char *)sym->st_value)) { // Only relocate things in the plugin hole
a = *target & 0xffff; // Get 16 bits' worth of the addend
a = (a << 16) >> 16; // Sign extend it
relocation = a + _shortsSegment->getOffset();
*target &= 0xffff0000; // Clear the lower 16 bits of the target
*target |= relocation & 0xffff;
if (debugRelocs[5]++ < DEBUG_NUM)
DBG("R_MIPS_GPREL16: i=%d, a=%x, gpVal=%x, origTarget=%x, target=%x, offset=%x\n",
i, a, _gpVal, origTarget, *target, _shortsSegment->getOffset());
}
break;
case R_MIPS_32: // Absolute addressing
if (sym->st_shndx < SHN_LOPROC) { // Only shift for plugin section.
a = *target; // Get full 32 bits of addend
if (ShortsMan.inGeneralSegment((char *)sym->st_value)) // Check if we're in the shorts segment
relocation = a + _shortsSegment->getOffset(); // Shift by shorts offset
else // We're in the main section
relocation = a + (Elf32_Addr)_segment; // Shift by main offset
*target = relocation;
if (debugRelocs[6]++ < DEBUG_NUM)
DBG("R_MIPS_32: i=%d, a=%x, origTarget=%x, target=%x\n", i, a, origTarget, *target);
}
break;
default:
seterror("Unknown relocation type %x at relocation %d.\n", REL_TYPE(rel[i].r_info), i);
free(rel);
return false;
}
}
DBG("Done with relocation. extendedHi16=%d\n\n", extendedHi16);
free(rel);
return true;
}
bool DLObject::relocateRels(Common::SeekableReadStream* DLFile, Elf32_Ehdr *ehdr, Elf32_Shdr *shdr) {
// Loop over sections, finding relocation sections
for (int i = 0; i < ehdr->e_shnum; i++) {
Elf32_Shdr *curShdr = &(shdr[i]);
//Elf32_Shdr *linkShdr = &(shdr[curShdr->sh_info]);
if (curShdr->sh_type == SHT_REL && // Check for a relocation section
curShdr->sh_entsize == sizeof(Elf32_Rel) && // Check for proper relocation size
(int)curShdr->sh_link == _symtab_sect && // Check that the sh_link connects to our symbol table
curShdr->sh_info < ehdr->e_shnum && // Check that the relocated section exists
(shdr[curShdr->sh_info].sh_flags & SHF_ALLOC)) { // Check if relocated section resides in memory
if (!ShortsMan.inGeneralSegment((char *)shdr[curShdr->sh_info].sh_addr)) { // regular segment
if (!relocate(DLFile, curShdr->sh_offset, curShdr->sh_size, _segment)) {
return false;
}
} else { // In Shorts segment
if (!relocate(DLFile, curShdr->sh_offset, curShdr->sh_size, (void *)_shortsSegment->getOffset())) {
return false;
}
}
}
}
return true;
}
|
