1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21
22/*
23 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
24 * Use is subject to license terms.
25 */
26
27#include <stdio.h>
28#include <dwarf.h>
29#include <sys/types.h>
30#include <sys/elf.h>
31
32/*
33 * Little Endian Base 128 (LEB128) numbers.
34 * ----------------------------------------
35 *
36 * LEB128 is a scheme for encoding integers densely that exploits the
37 * assumption that most integers are small in magnitude. (This encoding
38 * is equally suitable whether the target machine architecture represents
39 * data in big-endian or little- endian
40 *
41 * Unsigned LEB128 numbers are encoded as follows: start at the low order
42 * end of an unsigned integer and chop it into 7-bit chunks. Place each
43 * chunk into the low order 7 bits of a byte. Typically, several of the
44 * high order bytes will be zero; discard them. Emit the remaining bytes in
45 * a stream, starting with the low order byte; set the high order bit on
46 * each byte except the last emitted byte. The high bit of zero on the last
47 * byte indicates to the decoder that it has encountered the last byte.
48 * The integer zero is a special case, consisting of a single zero byte.
49 *
50 * Signed, 2s complement LEB128 numbers are encoded in a similar except
51 * that the criterion for discarding high order bytes is not whether they
52 * are zero, but whether they consist entirely of sign extension bits.
53 * Consider the 32-bit integer -2. The three high level bytes of the number
54 * are sign extension, thus LEB128 would represent it as a single byte
55 * containing the low order 7 bits, with the high order bit cleared to
56 * indicate the end of the byte stream.
57 *
58 * Note that there is nothing within the LEB128 representation that
59 * indicates whether an encoded number is signed or unsigned. The decoder
60 * must know what type of number to expect.
61 *
62 * DWARF Exception Header Encoding
63 * -------------------------------
64 *
65 * The DWARF Exception Header Encoding is used to describe the type of data
66 * used in the .eh_frame_hdr section. The upper 4 bits indicate how the
67 * value is to be applied. The lower 4 bits indicate the format of the data.
68 *
69 * DWARF Exception Header value format
70 *
71 * Name		Value Meaning
72 * DW_EH_PE_omit	    0xff No value is present.
73 * DW_EH_PE_absptr	    0x00 Value is a void*
74 * DW_EH_PE_uleb128	    0x01 Unsigned value is encoded using the
75 *				 Little Endian Base 128 (LEB128)
76 * DW_EH_PE_udata2	    0x02 A 2 bytes unsigned value.
77 * DW_EH_PE_udata4	    0x03 A 4 bytes unsigned value.
78 * DW_EH_PE_udata8	    0x04 An 8 bytes unsigned value.
79 * DW_EH_PE_signed          0x08 bit on for all signed encodings
80 * DW_EH_PE_sleb128	    0x09 Signed value is encoded using the
81 *				 Little Endian Base 128 (LEB128)
82 * DW_EH_PE_sdata2	    0x0A A 2 bytes signed value.
83 * DW_EH_PE_sdata4	    0x0B A 4 bytes signed value.
84 * DW_EH_PE_sdata8	    0x0C An 8 bytes signed value.
85 *
86 * DWARF Exception Header application
87 *
88 * Name	    Value Meaning
89 * DW_EH_PE_absptr	   0x00 Value is used with no modification.
90 * DW_EH_PE_pcrel	   0x10 Value is reletive to the location of itself
91 * DW_EH_PE_textrel	   0x20
92 * DW_EH_PE_datarel	   0x30 Value is reletive to the beginning of the
93 *				eh_frame_hdr segment ( segment type
94 *			        PT_GNU_EH_FRAME )
95 * DW_EH_PE_funcrel        0x40
96 * DW_EH_PE_aligned        0x50 value is an aligned void*
97 * DW_EH_PE_indirect       0x80 bit to signal indirection after relocation
98 * DW_EH_PE_omit	   0xff No value is present.
99 *
100 */
101
102uint64_t
103uleb_extract(unsigned char *data, uint64_t *dotp)
104{
105	uint64_t	dot = *dotp;
106	uint64_t	res = 0;
107	int		more = 1;
108	int		shift = 0;
109	int		val;
110
111	data += dot;
112
113	while (more) {
114		/*
115		 * Pull off lower 7 bits
116		 */
117		val = (*data) & 0x7f;
118
119		/*
120		 * Add prepend value to head of number.
121		 */
122		res = res | (val << shift);
123
124		/*
125		 * Increment shift & dot pointer
126		 */
127		shift += 7;
128		dot++;
129
130		/*
131		 * Check to see if hi bit is set - if not, this
132		 * is the last byte.
133		 */
134		more = ((*data++) & 0x80) >> 7;
135	}
136	*dotp = dot;
137	return (res);
138}
139
140int64_t
141sleb_extract(unsigned char *data, uint64_t *dotp)
142{
143	uint64_t	dot = *dotp;
144	int64_t		res = 0;
145	int		more = 1;
146	int		shift = 0;
147	int		val;
148
149	data += dot;
150
151	while (more) {
152		/*
153		 * Pull off lower 7 bits
154		 */
155		val = (*data) & 0x7f;
156
157		/*
158		 * Add prepend value to head of number.
159		 */
160		res = res | (val << shift);
161
162		/*
163		 * Increment shift & dot pointer
164		 */
165		shift += 7;
166		dot++;
167
168		/*
169		 * Check to see if hi bit is set - if not, this
170		 * is the last byte.
171		 */
172		more = ((*data++) & 0x80) >> 7;
173	}
174	*dotp = dot;
175
176	/*
177	 * Make sure value is properly sign extended.
178	 */
179	res = (res << (64 - shift)) >> (64 - shift);
180
181	return (res);
182}
183
184/*
185 * Extract a DWARF encoded datum
186 *
187 * entry:
188 *	data - Base of data buffer containing encoded bytes
189 *	dotp - Address of variable containing index within data
190 *		at which the desired datum starts.
191 *	ehe_flags - DWARF encoding
192 *	eident - ELF header e_ident[] array for object being processed
193 *	sh_base - Base address of ELF section containing desired datum
194 *	sh_offset - Offset relative to sh_base of desired datum.
195 */
196uint64_t
197dwarf_ehe_extract(unsigned char *data, uint64_t *dotp, uint_t ehe_flags,
198    unsigned char *eident, uint64_t sh_base, uint64_t sh_offset)
199{
200	uint64_t    dot = *dotp;
201	uint_t	    lsb;
202	uint_t	    wordsize;
203	uint_t	    fsize;
204	uint64_t    result;
205
206	if (eident[EI_DATA] == ELFDATA2LSB)
207		lsb = 1;
208	else
209		lsb = 0;
210
211	if (eident[EI_CLASS] == ELFCLASS64)
212		wordsize = 8;
213	else
214		wordsize = 4;
215
216	switch (ehe_flags & 0x0f) {
217	case DW_EH_PE_omit:
218		return (0);
219	case DW_EH_PE_absptr:
220		fsize = wordsize;
221		break;
222	case DW_EH_PE_udata8:
223	case DW_EH_PE_sdata8:
224		fsize = 8;
225		break;
226	case DW_EH_PE_udata4:
227	case DW_EH_PE_sdata4:
228		fsize = 4;
229		break;
230	case DW_EH_PE_udata2:
231	case DW_EH_PE_sdata2:
232		fsize = 2;
233		break;
234	case DW_EH_PE_uleb128:
235		return (uleb_extract(data, dotp));
236	case DW_EH_PE_sleb128:
237		return ((uint64_t)sleb_extract(data, dotp));
238	default:
239		return (0);
240	}
241
242	if (lsb) {
243		/*
244		 * Extract unaligned LSB formated data
245		 */
246		uint_t	cnt;
247
248		result = 0;
249		for (cnt = 0; cnt < fsize;
250		    cnt++, dot++) {
251			uint64_t val;
252			val = data[dot];
253			result |= val << (cnt * 8);
254		}
255	} else {
256		/*
257		 * Extract unaligned MSB formated data
258		 */
259		uint_t	cnt;
260		result = 0;
261		for (cnt = 0; cnt < fsize;
262		    cnt++, dot++) {
263			uint64_t	val;
264			val = data[dot];
265			result |= val << ((fsize - cnt - 1) * 8);
266		}
267	}
268	/*
269	 * perform sign extension
270	 */
271	if ((ehe_flags & DW_EH_PE_signed) &&
272	    (fsize < sizeof (uint64_t))) {
273		int64_t	sresult;
274		uint_t	bitshift;
275		sresult = result;
276		bitshift = (sizeof (uint64_t) - fsize) * 8;
277		sresult = (sresult << bitshift) >> bitshift;
278		result = sresult;
279	}
280
281	/*
282	 * If value is relative to a base address, adjust it
283	 */
284	if (result) {
285		switch (ehe_flags & 0xf0) {
286		case DW_EH_PE_pcrel:
287			result += sh_base + sh_offset;
288			break;
289
290		case DW_EH_PE_datarel:
291			result += sh_base;
292			break;
293		}
294	}
295	*dotp = dot;
296	return (result);
297}
298