summaryrefslogtreecommitdiffstats
path: root/openwrt/toolchain/utils/src/sstrip.c
blob: 60c12c972c8ef2979beaac73486ce4d23ff763c0 (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
/* http://www.muppetlabs.com/~breadbox/software/elfkickers.html */

/* sstrip: Copyright (C) 1999-2001 by Brian Raiter, under the GNU
 * General Public License. No warranty. See COPYING for details.
 *
 * Aug 23, 2004 Hacked by Manuel Novoa III <mjn3@codepoet.org> to
 * handle targets of different endianness and/or elf class, making
 * it more useful in a cross-devel environment.
 */

/* ============== original README ===================
 *
 * sstrip is a small utility that removes the contents at the end of an
 * ELF file that are not part of the program's memory image.
 * 
 * Most ELF executables are built with both a program header table and a
 * section header table. However, only the former is required in order
 * for the OS to load, link and execute a program. sstrip attempts to
 * extract the ELF header, the program header table, and its contents,
 * leaving everything else in the bit bucket. It can only remove parts of
 * the file that occur at the end, after the parts to be saved. However,
 * this almost always includes the section header table, and occasionally
 * a few random sections that are not used when running a program.
 * 
 * It should be noted that the GNU bfd library is (understandably)
 * dependent on the section header table as an index to the file's
 * contents. Thus, an executable file that has no section header table
 * cannot be used with gdb, objdump, or any other program based upon the
 * bfd library, at all. In fact, the program will not even recognize the
 * file as a valid executable. (This limitation is noted in the source
 * code comments for bfd, and is marked "FIXME", so this may change at
 * some future date. However, I would imagine that it is a pretty
 * low-priority item, as executables without a section header table are
 * rare in the extreme.) This probably also explains why strip doesn't
 * offer the option to do this.
 * 
 * Shared library files may also have their section header table removed.
 * Such a library will still function; however, it will no longer be
 * possible for a compiler to link a new program against it.
 * 
 * As an added bonus, sstrip also tries to removes trailing zero bytes
 * from the end of the file. (This normally cannot be done with an
 * executable that has a section header table.)
 * 
 * sstrip is a very simplistic program. It depends upon the common
 * practice of putting the parts of the file that contribute to the
 * memory image at the front, and the remaining material at the end. This
 * permits it to discard the latter material without affecting file
 * offsets and memory addresses in what remains. Of course, the ELF
 * standard permits files to be organized in almost any order, so if a
 * pathological linker decided to put its section headers at the top,
 * sstrip would be useless on such executables.
 */

#include	<stdio.h>
#include	<stdlib.h>
#include	<string.h>
#include	<errno.h>
#include	<unistd.h>
#include	<fcntl.h>
#include	<elf.h>

#ifdef __FreeBSD__
/**
 * This seems to work on FreeBSD 5.3, should
 * work on all newer versions as well. I have
 * no idea if it will work on versions < 5.3
 *
 * Joe Estock (guru) <jestock at nutextonline.com>
 */
#include <sys/endian.h>
#define bswap_64 __bswap64
#define bswap_32 __bswap32
#define bswap_16 __bswap16
#elif defined(__APPLE__)
#include	<machine/endian.h>
#include	<machine/byte_order.h>
#define __BYTE_ORDER BYTE_ORDER
#define __BIG_ENDIAN BIG_ENDIAN
#define bswap_16(x) NXSwapShort(x)
#define bswap_32(x) NXSwapInt(x)
#define bswap_64(x) NXSwapLongLong(x)
#else
#include	<endian.h>
#include	<byteswap.h>
#endif 


#ifndef TRUE
#define	TRUE		1
#define	FALSE		0
#endif

/* The name of the program.
 */
static char const	*progname;

/* The name of the current file.
 */
static char const	*filename;


/* A simple error-handling function. FALSE is always returned for the
 * convenience of the caller.
 */
static int err(char const *errmsg)
{
	fprintf(stderr, "%s: %s: %s\n", progname, filename, errmsg);
	return FALSE;
}

/* A flag to signal the need for endian reversal.
 */
static int do_reverse_endian;

/* Get a value from the elf header, compensating for endianness.
 */
#define EGET(X) \
	(__extension__ ({ \
		uint64_t __res; \
		if (!do_reverse_endian) { \
			__res = (X); \
		} else if (sizeof(X) == 1) { \
			__res = (X); \
		} else if (sizeof(X) == 2) { \
			__res = bswap_16((X)); \
		} else if (sizeof(X) == 4) { \
			__res = bswap_32((X)); \
		} else if (sizeof(X) == 8) { \
			__res = bswap_64((X)); \
		} else { \
			fprintf(stderr, "%s: %s: EGET failed for size %d\n", \
					progname, filename, sizeof(X)); \
			exit(EXIT_FAILURE); \
		} \
		__res; \
	}))

/* Set a value 'Y' in the elf header to 'X', compensating for endianness.
 */
#define ESET(Y,X) \
		do if (!do_reverse_endian) { \
			Y = (X); \
		} else if (sizeof(Y) == 1) { \
			Y = (X); \
		} else if (sizeof(Y) == 2) { \
			Y = bswap_16((uint16_t)(X)); \
		} else if (sizeof(Y) == 4) { \
			Y = bswap_32((uint32_t)(X)); \
		} else if (sizeof(Y) == 8) { \
			Y = bswap_64((uint64_t)(X)); \
		} else { \
			fprintf(stderr, "%s: %s: ESET failed for size %d\n", \
					progname, filename, sizeof(Y)); \
			exit(EXIT_FAILURE); \
		} while (0)


/* A macro for I/O errors: The given error message is used only when
 * errno is not set.
 */
#define	ferr(msg)	(err(errno ? strerror(errno) : (msg)))



#define HEADER_FUNCTIONS(CLASS) \
 \
/* readelfheader() reads the ELF header into our global variable, and \
 * checks to make sure that this is in fact a file that we should be \
 * munging. \
 */ \
static int readelfheader ## CLASS (int fd, Elf ## CLASS ## _Ehdr *ehdr) \
{ \
	 if (read(fd, ((char *)ehdr)+EI_NIDENT, sizeof(*ehdr) - EI_NIDENT) \
		!= sizeof(*ehdr) - EI_NIDENT) \
		return ferr("missing or incomplete ELF header."); \
 \
	/* Verify the sizes of the ELF header and the program segment \
	 * header table entries. \
	 */ \
	if (EGET(ehdr->e_ehsize) != sizeof(Elf ## CLASS ## _Ehdr)) \
		return err("unrecognized ELF header size."); \
	if (EGET(ehdr->e_phentsize) != sizeof(Elf ## CLASS ## _Phdr)) \
		return err("unrecognized program segment header size."); \
 \
	/* Finally, check the file type. \
	 */ \
	if (EGET(ehdr->e_type) != ET_EXEC && EGET(ehdr->e_type) != ET_DYN) \
		return err("not an executable or shared-object library."); \
 \
	return TRUE; \
} \
 \
/* readphdrtable() loads the program segment header table into memory. \
 */ \
static int readphdrtable ## CLASS (int fd, Elf ## CLASS ## _Ehdr const *ehdr, \
								   Elf ## CLASS ## _Phdr **phdrs) \
{ \
	size_t	size; \
 \
	if (!EGET(ehdr->e_phoff) || !EGET(ehdr->e_phnum) \
)		return err("ELF file has no program header table."); \
 \
	size = EGET(ehdr->e_phnum) * sizeof **phdrs; \
	if (!(*phdrs = malloc(size))) \
		return err("Out of memory!"); \
 \
	errno = 0; \
	if (read(fd, *phdrs, size) != (ssize_t)size) \
		return ferr("missing or incomplete program segment header table."); \
 \
	return TRUE; \
} \
 \
/* getmemorysize() determines the offset of the last byte of the file \
 * that is referenced by an entry in the program segment header table. \
 * (Anything in the file after that point is not used when the program \
 * is executing, and thus can be safely discarded.) \
 */ \
static int getmemorysize ## CLASS (Elf ## CLASS ## _Ehdr const *ehdr, \
								   Elf ## CLASS ## _Phdr const *phdrs, \
						 unsigned long *newsize) \
{ \
	Elf ## CLASS ## _Phdr const   *phdr; \
	unsigned long	size, n; \
	int			i; \
 \
	/* Start by setting the size to include the ELF header and the \
	 * complete program segment header table. \
	 */ \
	size = EGET(ehdr->e_phoff) + EGET(ehdr->e_phnum) * sizeof *phdrs; \
	if (size < sizeof *ehdr) \
		size = sizeof *ehdr; \
 \
	/* Then keep extending the size to include whatever data the \
	 * program segment header table references. \
	 */ \
	for (i = 0, phdr = phdrs ; i < EGET(ehdr->e_phnum) ; ++i, ++phdr) { \
		if (EGET(phdr->p_type) != PT_NULL) { \
			n = EGET(phdr->p_offset) + EGET(phdr->p_filesz); \
			if (n > size) \
				size = n; \
		} \
	} \
 \
	*newsize = size; \
	return TRUE; \
} \
 \
/* modifyheaders() removes references to the section header table if \
 * it was stripped, and reduces program header table entries that \
 * included truncated bytes at the end of the file. \
 */ \
static int modifyheaders ## CLASS (Elf ## CLASS ## _Ehdr *ehdr, \
								   Elf ## CLASS ## _Phdr *phdrs, \
								   unsigned long newsize) \
{ \
	Elf ## CLASS ## _Phdr *phdr; \
	int		i; \
 \
	/* If the section header table is gone, then remove all references \
	 * to it in the ELF header. \
	 */ \
	if (EGET(ehdr->e_shoff) >= newsize) { \
		ESET(ehdr->e_shoff,0); \
		ESET(ehdr->e_shnum,0); \
		ESET(ehdr->e_shentsize,0); \
		ESET(ehdr->e_shstrndx,0); \
	} \
 \
	/* The program adjusts the file size of any segment that was \
	 * truncated. The case of a segment being completely stripped out \
	 * is handled separately. \
	 */ \
	for (i = 0, phdr = phdrs ; i < EGET(ehdr->e_phnum) ; ++i, ++phdr) { \
		if (EGET(phdr->p_offset) >= newsize) { \
			ESET(phdr->p_offset,newsize); \
			ESET(phdr->p_filesz,0); \
		} else if (EGET(phdr->p_offset) + EGET(phdr->p_filesz) > newsize) { \
			newsize -= EGET(phdr->p_offset); \
			ESET(phdr->p_filesz, newsize); \
		} \
	} \
 \
	return TRUE; \
} \
 \
/* commitchanges() writes the new headers back to the original file \
 * and sets the file to its new size. \
 */ \
static int commitchanges ## CLASS (int fd, Elf ## CLASS ## _Ehdr const *ehdr, \
								   Elf ## CLASS ## _Phdr *phdrs, \
								   unsigned long newsize) \
{ \
	size_t	n; \
 \
	/* Save the changes to the ELF header, if any. \
	 */ \
	if (lseek(fd, 0, SEEK_SET)) \
		return ferr("could not rewind file"); \
	errno = 0; \
	if (write(fd, ehdr, sizeof *ehdr) != sizeof *ehdr) \
		return err("could not modify file"); \
 \
	/* Save the changes to the program segment header table, if any. \
	 */ \
	if (lseek(fd, EGET(ehdr->e_phoff), SEEK_SET) == (off_t)-1) { \
		err("could not seek in file."); \
		goto warning; \
	} \
	n = EGET(ehdr->e_phnum) * sizeof *phdrs; \
	if (write(fd, phdrs, n) != (ssize_t)n) { \
		err("could not write to file"); \
		goto warning; \
	} \
 \
	/* Eleventh-hour sanity check: don't truncate before the end of \
	 * the program segment header table. \
	 */ \
	if (newsize < EGET(ehdr->e_phoff) + n) \
		newsize = EGET(ehdr->e_phoff) + n; \
 \
	/* Chop off the end of the file. \
	 */ \
	if (ftruncate(fd, newsize)) { \
		err("could not resize file"); \
		goto warning; \
	} \
 \
	return TRUE; \
 \
 warning: \
	return err("ELF file may have been corrupted!"); \
}


/* First elements of Elf32_Ehdr and Elf64_Ehdr are common.
 */
static int readelfheaderident(int fd, Elf32_Ehdr *ehdr)
{
	errno = 0;
	if (read(fd, ehdr, EI_NIDENT) != EI_NIDENT)
		return ferr("missing or incomplete ELF header.");

	/* Check the ELF signature.
	 */
	if (!(ehdr->e_ident[EI_MAG0] == ELFMAG0 &&
		  ehdr->e_ident[EI_MAG1] == ELFMAG1 &&
		  ehdr->e_ident[EI_MAG2] == ELFMAG2 &&
		  ehdr->e_ident[EI_MAG3] == ELFMAG3))
	{
		err("missing ELF signature.");
		return -1;
	}

	/* Compare the file's class and endianness with the program's.
	 */
#if __BYTE_ORDER == __LITTLE_ENDIAN
	if (ehdr->e_ident[EI_DATA] == ELFDATA2LSB) {
		do_reverse_endian = 0;
	} else if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB) {
/* 		fprintf(stderr, "ELF file has different endianness.\n"); */
		do_reverse_endian = 1;
	}
#elif __BYTE_ORDER == __BIG_ENDIAN
	if (ehdr->e_ident[EI_DATA] == ELFDATA2LSB) {
/* 		fprintf(stderr, "ELF file has different endianness.\n"); */
		do_reverse_endian = 1;
	} else if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB) {
		do_reverse_endian = 0;
	}
#else
#error unkown endianness
#endif
	else {
		err("Unsupported endianness");
		return -1;
	}

	/* Check the target architecture.
	 */
/*	 if (EGET(ehdr->e_machine) != ELF_ARCH) { */
/* 		/\* return err("ELF file created for different architecture."); *\/ */
/* 		fprintf(stderr, "ELF file created for different architecture.\n"); */
/* 	} */
	return ehdr->e_ident[EI_CLASS];
}


HEADER_FUNCTIONS(32)

HEADER_FUNCTIONS(64)

/* truncatezeros() examines the bytes at the end of the file's
 * size-to-be, and reduces the size to exclude any trailing zero
 * bytes.
 */
static int truncatezeros(int fd, unsigned long *newsize)
{
	unsigned char	contents[1024];
	unsigned long	size, n;

	size = *newsize;
	do {
		n = sizeof contents;
		if (n > size)
			n = size;
		if (lseek(fd, size - n, SEEK_SET) == (off_t)-1)
			return ferr("cannot seek in file.");
		if (read(fd, contents, n) != (ssize_t)n)
			return ferr("cannot read file contents");
		while (n && !contents[--n])
			--size;
	} while (size && !n);

	/* Sanity check.
	 */
	if (!size)
		return err("ELF file is completely blank!");

	*newsize = size;
	return TRUE;
}

/* main() loops over the cmdline arguments, leaving all the real work
 * to the other functions.
 */
int main(int argc, char *argv[])
{
	int				fd;
	union {
		Elf32_Ehdr	ehdr32;
		Elf64_Ehdr	ehdr64;
	} e;
	union {
		Elf32_Phdr	*phdrs32;
		Elf64_Phdr	*phdrs64;
	} p;
	unsigned long	newsize;
	char			**arg;
	int				failures = 0;

	if (argc < 2 || argv[1][0] == '-') {
		printf("Usage: sstrip FILE...\n"
			   "sstrip discards all nonessential bytes from an executable.\n\n"
			   "Version 2.0-X Copyright (C) 2000,2001 Brian Raiter.\n"
			   "Cross-devel hacks Copyright (C) 2004 Manuel Novoa III.\n"
			   "This program is free software, licensed under the GNU\n"
			   "General Public License. There is absolutely no warranty.\n");
		return EXIT_SUCCESS;
	}

	progname = argv[0];

	for (arg = argv + 1 ; *arg != NULL ; ++arg) {
		filename = *arg;

		fd = open(*arg, O_RDWR);
		if (fd < 0) {
			ferr("can't open");
			++failures;
			continue;
		}

		switch (readelfheaderident(fd, &e.ehdr32)) {
			case ELFCLASS32:
				if (!(readelfheader32(fd, &e.ehdr32)					&&
					  readphdrtable32(fd, &e.ehdr32, &p.phdrs32)		&&
					  getmemorysize32(&e.ehdr32, p.phdrs32, &newsize)	&&
					  truncatezeros(fd, &newsize)						&&
					  modifyheaders32(&e.ehdr32, p.phdrs32, newsize)	&&
					  commitchanges32(fd, &e.ehdr32, p.phdrs32, newsize)))
					++failures;
				break;
			case ELFCLASS64:
				if (!(readelfheader64(fd, &e.ehdr64)					&&
					  readphdrtable64(fd, &e.ehdr64, &p.phdrs64)		&&
					  getmemorysize64(&e.ehdr64, p.phdrs64, &newsize)	&&
					  truncatezeros(fd, &newsize)						&&
					  modifyheaders64(&e.ehdr64, p.phdrs64, newsize)	&&
					  commitchanges64(fd, &e.ehdr64, p.phdrs64, newsize)))
					++failures;
				break;
			default:
				++failures;
				break;
		}
		close(fd);
	}

	return failures ? EXIT_FAILURE : EXIT_SUCCESS;
}