aboutsummaryrefslogtreecommitdiff
path: root/backends/plugins/elf/elf-loader.cpp
blob: f502fa2776cea6eac392b9059511bf27f39bb54e (plain)
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
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
/* 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 "common/scummsys.h"

#if defined(DYNAMIC_MODULES) && defined(USE_ELF_LOADER)

#include "backends/plugins/elf/elf-loader.h"
#include "backends/plugins/elf/memory-manager.h"

#include "common/debug.h"
#include "common/file.h"
#include "common/fs.h"
#include "common/ptr.h"

#include <malloc.h>	// for memalign()

DLObject::DLObject() :
	_file(0),
	_segment(0),
	_symtab(0),
	_strtab(0),
	_segmentSize(0),
	_segmentOffset(0),
	_segmentVMA(0),
	_symbol_cnt(0),
	_symtab_sect(-1),
	_dtors_start(0),
	_dtors_end(0) {
}

DLObject::~DLObject() {
	discardSymtab();
	ELFMemMan.pluginDeallocate(_segment);
	_segment = 0;
}

// Expel the symbol table from memory
void DLObject::discardSymtab() {
	free(_symtab);
	_symtab = 0;

	free(_strtab);
	_strtab = 0;

	_symbol_cnt = 0;
}

// Unload all objects from memory
void DLObject::unload() {
	discardSymtab();

	ELFMemMan.pluginDeallocate(_segment);

	_segment = 0;
	_segmentSize = 0;
	_segmentOffset = 0;
	_segmentVMA = 0;
}

bool DLObject::readElfHeader(Elf32_Ehdr *ehdr) {
	assert(_file);

	// Start reading the elf header. Check for errors and magic
	if (_file->read(ehdr, sizeof(*ehdr)) != sizeof(*ehdr) ||
			memcmp(ehdr->e_ident, ELFMAG, SELFMAG)) {
		warning("elfloader: No ELF file.");
		return false;
	}

	if (ehdr->e_ident[EI_CLASS] != ELFCLASS32) {
		warning("elfloader: Wrong ELF file class.");
		return false;
	}

	if (ehdr->e_ident[EI_DATA] !=
#ifdef SCUMM_BIG_ENDIAN
			ELFDATA2MSB
#else
			ELFDATA2LSB
#endif
			) {
		warning("elfloader: Wrong ELF file endianess.");
		return false;
	}

	if (ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
		warning("elfloader: Wrong ELF file version.");
		return false;
	}

	if (ehdr->e_type != ET_EXEC) {
		warning("elfloader: No executable ELF file.");
		return false;
	}

	if (ehdr->e_machine !=
#ifdef ARM_TARGET
			EM_ARM
#endif
#ifdef MIPS_TARGET
			EM_MIPS
#endif
#ifdef PPC_TARGET
			EM_PPC
#endif
			) {
		warning("elfloader: Wrong ELF file architecture.");
		return false;
	}

	if (ehdr->e_phentsize < sizeof(Elf32_Phdr)	 ||			// Check for size of program header
			ehdr->e_shentsize != sizeof(Elf32_Shdr)) {		// Check for size of section header
		warning("elfloader: Invalid ELF structure sizes.");
		return false;
	}

	debug(2, "elfloader: phoff = %d, phentsz = %d, phnum = %d",
			ehdr->e_phoff, ehdr->e_phentsize, ehdr->e_phnum);

	return true;
}

bool DLObject::readProgramHeaders(Elf32_Ehdr *ehdr, Elf32_Phdr *phdr, Elf32_Half num) {
	assert(_file);

	// Read program header
	if (!_file->seek(ehdr->e_phoff + sizeof(*phdr) * num, SEEK_SET) ||
			_file->read(phdr, sizeof(*phdr)) != sizeof(*phdr)) {
		warning("elfloader: Program header load failed.");
		return false;
	}

	// Check program header values
	if (phdr->p_type != PT_LOAD  || phdr->p_filesz > phdr->p_memsz) {
		warning("elfloader: Invalid program header.");
		return false;
	}

	debug(2, "elfloader: offs = %x, filesz = %x, memsz = %x, align = %x",
			phdr->p_offset, phdr->p_filesz, phdr->p_memsz, phdr->p_align);

	return true;
}

bool DLObject::loadSegment(Elf32_Phdr *phdr) {
	_segment = (byte *)ELFMemMan.pluginAllocate(phdr->p_align, phdr->p_memsz);

	if (!_segment) {
		warning("elfloader: Out of memory.");
		return false;
	}
	
	debug(2, "elfloader: Allocated segment @ %p", _segment);

	// Get offset to load segment into
	_segmentSize = phdr->p_memsz;
	_segmentVMA = phdr->p_vaddr;

	// Set .bss segment to 0 if necessary
	if (phdr->p_memsz > phdr->p_filesz) {
		debug(2, "elfloader: Setting %p to %p to 0 for bss",
				_segment + phdr->p_filesz, _segment + phdr->p_memsz);
		memset(_segment + phdr->p_filesz, 0, phdr->p_memsz - phdr->p_filesz);
	}

	debug(2, "elfloader: Reading the segment into memory");

	// Read the segment into memory
	if (!_file->seek(phdr->p_offset, SEEK_SET) ||
			_file->read(_segment, phdr->p_filesz) != phdr->p_filesz) {
		warning("elfloader: Segment load failed.");
		return false;
	}

	debug(2, "elfloader: Segment has been read into memory");

	return true;
}

Elf32_Shdr * DLObject::loadSectionHeaders(Elf32_Ehdr *ehdr) {
	assert(_file);

	Elf32_Shdr *shdr = 0;

	// Allocate memory for section headers
	if (!(shdr = (Elf32_Shdr *)malloc(ehdr->e_shnum * sizeof(*shdr)))) {
		warning("elfloader: Out of memory.");
		return 0;
	}

	// Read from file into section headers
	if (!_file->seek(ehdr->e_shoff, SEEK_SET) ||
			_file->read(shdr, ehdr->e_shnum * sizeof(*shdr)) !=
			ehdr->e_shnum * sizeof(*shdr)) {
		warning("elfloader: Section headers load failed.");
		free(shdr);
		return 0;
	}

	return shdr;
}

int DLObject::findSymbolTableSection(Elf32_Ehdr *ehdr, Elf32_Shdr *shdr) {
	int SymbolTableSection = -1;
	
	// Loop over sections, looking for symbol table linked to a string table
	for (uint32 i = 0; i < ehdr->e_shnum; i++) {
		if (shdr[i].sh_type == SHT_SYMTAB &&
				shdr[i].sh_entsize == sizeof(Elf32_Sym) &&
				shdr[i].sh_link < ehdr->e_shnum &&
				shdr[shdr[i].sh_link].sh_type == SHT_STRTAB) {
			SymbolTableSection = i;
			break;
		}
	}
	
	return SymbolTableSection;
}

int DLObject::loadSymbolTable(Elf32_Ehdr *ehdr, Elf32_Shdr *shdr) {
	assert(_file);

	_symtab_sect = findSymbolTableSection(ehdr, shdr);

	// Check for no symbol table
	if (_symtab_sect < 0) {
		warning("elfloader: No symbol table.");
		return -1;
	}

	debug(2, "elfloader: Symbol section at section %d, size %x",
			_symtab_sect, shdr[_symtab_sect].sh_size);

	// Allocate memory for symbol table
	if (!(_symtab = (Elf32_Sym *)malloc(shdr[_symtab_sect].sh_size))) {
		warning("elfloader: Out of memory.");
		return -1;
	}

	// Read symbol table into memory
	if (!_file->seek(shdr[_symtab_sect].sh_offset, SEEK_SET) ||
			_file->read(_symtab, shdr[_symtab_sect].sh_size) !=
			shdr[_symtab_sect].sh_size) {
		warning("elfloader: Symbol table load failed.");
		free(_symtab);
		_symtab = 0;
		return -1;
	}

	// Set number of symbols
	_symbol_cnt = shdr[_symtab_sect].sh_size / sizeof(Elf32_Sym);
	debug(2, "elfloader: Loaded %d symbols.", _symbol_cnt);

	return _symtab_sect;
}

bool DLObject::loadStringTable(Elf32_Shdr *shdr) {
	assert(_file);

	uint32 string_sect = shdr[_symtab_sect].sh_link;

	// Allocate memory for string table
	if (!(_strtab = (char *)malloc(shdr[string_sect].sh_size))) {
		warning("elfloader: Out of memory.");
		return false;
	}

	// Read string table into memory
	if (!_file->seek(shdr[string_sect].sh_offset, SEEK_SET) ||
			_file->read(_strtab, shdr[string_sect].sh_size) !=
			shdr[string_sect].sh_size) {
		warning("elfloader: Symbol table strings load failed.");
		free(_strtab);
		_strtab = 0;
		return false;
	}

	return true;
}

void DLObject::relocateSymbols(ptrdiff_t offset) {
	// Loop over symbols, add relocation offset
	Elf32_Sym *s = _symtab;

	for (uint32 c = _symbol_cnt; c--; s++) {
		// Make sure we don't relocate special valued symbols
		if (s->st_shndx < SHN_LOPROC) {
			s->st_value += offset;

			if (s->st_value < Elf32_Addr(_segment) ||
					s->st_value > Elf32_Addr(_segment) + _segmentSize)
				warning("elfloader: Symbol out of bounds! st_value = %x", s->st_value);
		}
	}
}

// Track the size of the plugin through memory manager without loading
// the plugin into memory. 
//
void DLObject::trackSize(const char *path) {
	
	_file = Common::FSNode(path).createReadStream();
	
	if (!_file) {
		warning("elfloader: File %s not found.", path);
		return;
	}

	Elf32_Ehdr ehdr;
	Elf32_Phdr phdr;

	if (!readElfHeader(&ehdr)) {
		delete _file;
		_file = 0;
		return;
	}
	
	ELFMemMan.trackPlugin(true);	// begin tracking the plugin size
	
	// Load the segments
	for (uint32 i = 0; i < ehdr.e_phnum; i++) {	
		debug(2, "elfloader: Loading segment %d", i);

		if (!readProgramHeaders(&ehdr, &phdr, i)) {
			delete _file;
			_file = 0;
			return;
		}

		if (phdr.p_flags & PF_X) {	// check for executable, allocated segment
			ELFMemMan.trackAlloc(phdr.p_align, phdr.p_memsz);
		}
	}
	
	ELFMemMan.trackPlugin(false);	// we're done tracking the plugin size

	delete _file;
	_file = 0;
	// No need to track the symbol table sizes -- they get discarded
}

bool DLObject::load() {
	Elf32_Ehdr ehdr;
	Elf32_Phdr phdr;

	if (readElfHeader(&ehdr) == false)
		return false;

	//Load the segments
	for (uint32 i = 0; i < ehdr.e_phnum; i++) {	
		debug(2, "elfloader: Loading segment %d", i);

		if (readProgramHeaders(&ehdr, &phdr, i) == false)
			return false;

		if (!loadSegment(&phdr))
			return false;
	}

	Elf32_Shdr *shdr = loadSectionHeaders(&ehdr);
	if (!shdr)
		return false;

	_symtab_sect = loadSymbolTable(&ehdr, shdr);
	if (_symtab_sect < 0) {
		free(shdr);
		return false;
	}
		
	if (!loadStringTable(shdr)) {
		free(shdr);
		return false;
	}
	
	// Offset by our segment allocated address
	// must use _segmentVMA here for multiple segments (MIPS)
	_segmentOffset = ptrdiff_t(_segment) - _segmentVMA;
	relocateSymbols(_segmentOffset);

	if (!relocateRels(&ehdr, shdr)) {
		free(shdr);
		return false;
	}

	return true;
}

bool DLObject::open(const char *path) {
	void *ctors_start, *ctors_end;

	debug(2, "elfloader: open(\"%s\")", path);

	_file = Common::FSNode(path).createReadStream();

	if (!_file) {
		warning("elfloader: File %s not found.", path);
		return false;
	}

	debug(2, "elfloader: %s found!", path);

	/*Try to load and relocate*/
	if (!load()) {
		unload();
		return false;
	}

	debug(2, "elfloader: Loaded!");

	delete _file;
	_file = 0;

	flushDataCache(_segment, _segmentSize);

	ctors_start = symbol("___plugin_ctors");
	ctors_end = symbol("___plugin_ctors_end");
	_dtors_start = symbol("___plugin_dtors");
	_dtors_end = symbol("___plugin_dtors_end");

	if (!ctors_start || !ctors_end || !_dtors_start || !_dtors_end) {
		warning("elfloader: Missing ctors/dtors.");
		_dtors_start = _dtors_end = 0;
		unload();
		return false;
	}

	debug(2, "elfloader: Calling constructors.");
	for (void (**f)(void) = (void (**)(void))ctors_start; f != ctors_end; f++)
		(**f)();

	debug(2, "elfloader: %s opened ok.", path);

	return true;
}

bool DLObject::close() {
	if (_dtors_start && _dtors_end)
		for (void (**f)(void) = (void (**)(void))_dtors_start; f != _dtors_end; f++)
			(**f)();

	_dtors_start = _dtors_end = 0;
	unload();
	return true;
}

void *DLObject::symbol(const char *name) {
	debug(2, "elfloader: Symbol(\"%s\")", name);

	if (!_symtab || !_strtab || _symbol_cnt < 1) {
		warning("elfloader: No symbol table loaded.");
		return 0;
	}

	Elf32_Sym *s = _symtab;

	for (uint32 c = _symbol_cnt; c--; s++)
		// We can only import symbols that are global or weak in the plugin
		if ((SYM_BIND(s->st_info) == STB_GLOBAL ||
				SYM_BIND(s->st_info) == STB_WEAK) &&
				!strcmp(name, _strtab + s->st_name)) {
			// We found the symbol
			debug(2, "elfloader: => 0x%08x", s->st_value);
			return (void*)s->st_value;
		}

	// We didn't find the symbol
	warning("elfloader: Symbol \"%s\" not found.", name);
	return 0;
}

#endif /* defined(DYNAMIC_MODULES) && defined(USE_ELF_LOADER) */