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comparison: toolkit/crashreporter/google-breakpad/src/third_party/libdisasm/ia32_modrm.c

toolkit/crashreporter/google-breakpad/src/third_party/libdisasm/ia32_modrm.c

branch
TOR_BUG_9701
changeset 15
b8a032363ba2
equal deleted inserted replaced
-1:000000000000 0:da9b7fa190e6
1 #include "ia32_modrm.h"
2 #include "ia32_reg.h"
3 #include "x86_imm.h"
4
5 /* NOTE: when decoding ModR/M and SIB, we have to add 1 to all register
6 * values obtained from decoding the ModR/M or SIB byte, since they
7 * are encoded with eAX = 0 and the tables in ia32_reg.c use eAX = 1.
8 * ADDENDUM: this is only the case when the register value is used
9 * directly as an index into the register table, not when it is added to
10 * a genregs offset. */
11
12 /* -------------------------------- ModR/M, SIB */
13 /* ModR/M flags */
14 #define MODRM_RM_SIB 0x04 /* R/M == 100 */
15 #define MODRM_RM_NOREG 0x05 /* R/B == 101 */
16
17 /* if (MODRM.MOD_NODISP && MODRM.RM_NOREG) then just disp32 */
18 #define MODRM_MOD_NODISP 0x00 /* mod == 00 */
19 #define MODRM_MOD_DISP8 0x01 /* mod == 01 */
20 #define MODRM_MOD_DISP32 0x02 /* mod == 10 */
21 #define MODRM_MOD_NOEA 0x03 /* mod == 11 */
22
23 /* 16-bit modrm flags */
24 #define MOD16_MOD_NODISP 0
25 #define MOD16_MOD_DISP8 1
26 #define MOD16_MOD_DISP16 2
27 #define MOD16_MOD_REG 3
28
29 #define MOD16_RM_BXSI 0
30 #define MOD16_RM_BXDI 1
31 #define MOD16_RM_BPSI 2
32 #define MOD16_RM_BPDI 3
33 #define MOD16_RM_SI 4
34 #define MOD16_RM_DI 5
35 #define MOD16_RM_BP 6
36 #define MOD16_RM_BX 7
37
38 /* SIB flags */
39 #define SIB_INDEX_NONE 0x04
40 #define SIB_BASE_EBP 0x05
41 #define SIB_SCALE_NOBASE 0x00
42
43 /* Convenience struct for modR/M bitfield */
44 struct modRM_byte {
45 unsigned int mod : 2;
46 unsigned int reg : 3;
47 unsigned int rm : 3;
48 };
49
50 /* Convenience struct for SIB bitfield */
51 struct SIB_byte {
52 unsigned int scale : 2;
53 unsigned int index : 3;
54 unsigned int base : 3;
55 };
56
57
58 #if 0
59 int modrm_rm[] = {0,1,2,3,MODRM_RM_SIB,MODRM_MOD_DISP32,6,7};
60 int modrm_reg[] = {0, 1, 2, 3, 4, 5, 6, 7};
61 int modrm_mod[] = {0, MODRM_MOD_DISP8, MODRM_MOD_DISP32, MODRM_MOD_NOEA};
62 int sib_scl[] = {0, 2, 4, 8};
63 int sib_idx[] = {0, 1, 2, 3, SIB_INDEX_NONE, 5, 6, 7 };
64 int sib_bas[] = {0, 1, 2, 3, 4, SIB_SCALE_NOBASE, 6, 7 };
65 #endif
66
67 /* this is needed to replace x86_imm_signsized() which does not sign-extend
68 * to dest */
69 static unsigned int imm32_signsized( unsigned char *buf, size_t buf_len,
70 int32_t *dest, unsigned int size ) {
71 if ( size > buf_len ) {
72 return 0;
73 }
74
75 switch (size) {
76 case 1:
77 *dest = *((signed char *) buf);
78 break;
79 case 2:
80 *dest = *((signed short *) buf);
81 break;
82 case 4:
83 default:
84 *dest = *((signed int *) buf);
85 break;
86 }
87
88 return size;
89 }
90
91
92
93 static void byte_decode(unsigned char b, struct modRM_byte *modrm) {
94 /* generic bitfield-packing routine */
95
96 modrm->mod = b >> 6; /* top 2 bits */
97 modrm->reg = (b & 56) >> 3; /* middle 3 bits */
98 modrm->rm = b & 7; /* bottom 3 bits */
99 }
100
101
102 static size_t sib_decode( unsigned char *buf, size_t buf_len, x86_ea_t *ea,
103 unsigned int mod ) {
104 /* set Address Expression fields (scale, index, base, disp)
105 * according to the contents of the SIB byte.
106 * b points to the SIB byte in the instruction-stream buffer; the
107 * byte after b[0] is therefore the byte after the SIB
108 * returns number of bytes 'used', including the SIB byte */
109 size_t size = 1; /* start at 1 for SIB byte */
110 struct SIB_byte sib;
111
112 if ( buf_len < 1 ) {
113 return 0;
114 }
115
116 byte_decode( *buf, (struct modRM_byte *)(void*)&sib ); /* get bit-fields */
117
118 if ( sib.base == SIB_BASE_EBP && ! mod ) { /* if base == 101 (ebp) */
119 /* IF BASE == EBP, deal with exception */
120 /* IF (ModR/M did not create a Disp */
121 /* ... create a 32-bit Displacement */
122 imm32_signsized( &buf[1], buf_len, &ea->disp, sizeof(int32_t));
123 ea->disp_size = sizeof(int32_t);
124 ea->disp_sign = (ea->disp < 0) ? 1 : 0;
125 size += 4; /* add sizeof disp to count */
126
127 } else {
128 /* ELSE BASE refers to a General Register */
129 ia32_handle_register( &ea->base, sib.base + 1 );
130 }
131
132 /* set scale to 1, 2, 4, 8 */
133 ea->scale = 1 << sib.scale;
134
135 if (sib.index != SIB_INDEX_NONE) {
136 /* IF INDEX is not 'ESP' (100) */
137 ia32_handle_register( &ea->index, sib.index + 1 );
138 }
139
140 return (size); /* return number of bytes processed */
141 }
142
143 static size_t modrm_decode16( unsigned char *buf, unsigned int buf_len,
144 x86_op_t *op, struct modRM_byte *modrm ) {
145 /* 16-bit mode: hackish, but not as hackish as 32-bit mode ;) */
146 size_t size = 1; /* # of bytes decoded [1 for modR/M byte] */
147 x86_ea_t * ea = &op->data.expression;
148
149 switch( modrm->rm ) {
150 case MOD16_RM_BXSI:
151 ia32_handle_register(&ea->base, REG_WORD_OFFSET + 3);
152 ia32_handle_register(&ea->index, REG_WORD_OFFSET + 6);
153 break;
154 case MOD16_RM_BXDI:
155 ia32_handle_register(&ea->base, REG_WORD_OFFSET + 3);
156 ia32_handle_register(&ea->index, REG_WORD_OFFSET + 7);
157 case MOD16_RM_BPSI:
158 op->flags |= op_ss_seg;
159 ia32_handle_register(&ea->base, REG_WORD_OFFSET + 5);
160 ia32_handle_register(&ea->index, REG_WORD_OFFSET + 6);
161 break;
162 case MOD16_RM_BPDI:
163 op->flags |= op_ss_seg;
164 ia32_handle_register(&ea->base, REG_WORD_OFFSET + 5);
165 ia32_handle_register(&ea->index, REG_WORD_OFFSET + 7);
166 break;
167 case MOD16_RM_SI:
168 ia32_handle_register(&ea->base, REG_WORD_OFFSET + 6);
169 break;
170 case MOD16_RM_DI:
171 ia32_handle_register(&ea->base, REG_WORD_OFFSET + 7);
172 break;
173 case MOD16_RM_BP:
174 if ( modrm->mod != MOD16_MOD_NODISP ) {
175 op->flags |= op_ss_seg;
176 ia32_handle_register(&ea->base,
177 REG_WORD_OFFSET + 5);
178 }
179 break;
180 case MOD16_RM_BX:
181 ia32_handle_register(&ea->base, REG_WORD_OFFSET + 3);
182 break;
183 }
184
185 /* move to byte after ModR/M */
186 ++buf;
187 --buf_len;
188
189 if ( modrm->mod == MOD16_MOD_DISP8 ) {
190 imm32_signsized( buf, buf_len, &ea->disp, sizeof(char) );
191 ea->disp_sign = (ea->disp < 0) ? 1 : 0;
192 ea->disp_size = sizeof(char);
193 size += sizeof(char);
194 } else if ( modrm->mod == MOD16_MOD_DISP16 ) {
195 imm32_signsized( buf, buf_len, &ea->disp, sizeof(short) );
196 ea->disp_sign = (ea->disp < 0) ? 1 : 0;
197 ea->disp_size = sizeof(short);
198 size += sizeof(short);
199 }
200
201 return size;
202 }
203
204 /* TODO : Mark index modes
205 Use addressing mode flags to imply arrays (index), structure (disp),
206 two-dimensional arrays [disp + index], classes [ea reg], and so on.
207 */
208 size_t ia32_modrm_decode( unsigned char *buf, unsigned int buf_len,
209 x86_op_t *op, x86_insn_t *insn, size_t gen_regs ) {
210 /* create address expression and/or fill operand based on value of
211 * ModR/M byte. Calls sib_decode as appropriate.
212 * flags specifies whether Reg or mod+R/M fields are being decoded
213 * returns the number of bytes in the instruction, including modR/M */
214 struct modRM_byte modrm;
215 size_t size = 1; /* # of bytes decoded [1 for modR/M byte] */
216 x86_ea_t * ea;
217
218
219 byte_decode(*buf, &modrm); /* get bitfields */
220
221 /* first, handle the case where the mod field is a register only */
222 if ( modrm.mod == MODRM_MOD_NOEA ) {
223 op->type = op_register;
224 ia32_handle_register(&op->data.reg, modrm.rm + gen_regs);
225 /* increase insn size by 1 for modrm byte */
226 return 1;
227 }
228
229 /* then deal with cases where there is an effective address */
230 ea = &op->data.expression;
231 op->type = op_expression;
232 op->flags |= op_pointer;
233
234 if ( insn->addr_size == 2 ) {
235 /* gah! 16 bit mode! */
236 return modrm_decode16( buf, buf_len, op, &modrm);
237 }
238
239 /* move to byte after ModR/M */
240 ++buf;
241 --buf_len;
242
243 if (modrm.mod == MODRM_MOD_NODISP) { /* if mod == 00 */
244
245 /* IF MOD == No displacement, just Indirect Register */
246 if (modrm.rm == MODRM_RM_NOREG) { /* if r/m == 101 */
247 /* IF RM == No Register, just Displacement */
248 /* This is an Intel Moronic Exception TM */
249 imm32_signsized( buf, buf_len, &ea->disp,
250 sizeof(int32_t) );
251 ea->disp_size = sizeof(int32_t);
252 ea->disp_sign = (ea->disp < 0) ? 1 : 0;
253 size += 4; /* add sizeof disp to count */
254
255 } else if (modrm.rm == MODRM_RM_SIB) { /* if r/m == 100 */
256 /* ELSE IF an SIB byte is present */
257 /* TODO: check for 0 retval */
258 size += sib_decode( buf, buf_len, ea, modrm.mod);
259 /* move to byte after SIB for displacement */
260 ++buf;
261 --buf_len;
262 } else { /* modR/M specifies base register */
263 /* ELSE RM encodes a general register */
264 ia32_handle_register( &ea->base, modrm.rm + 1 );
265 }
266 } else { /* mod is 01 or 10 */
267 if (modrm.rm == MODRM_RM_SIB) { /* rm == 100 */
268 /* IF base is an AddrExpr specified by an SIB byte */
269 /* TODO: check for 0 retval */
270 size += sib_decode( buf, buf_len, ea, modrm.mod);
271 /* move to byte after SIB for displacement */
272 ++buf;
273 --buf_len;
274 } else {
275 /* ELSE base is a general register */
276 ia32_handle_register( &ea->base, modrm.rm + 1 );
277 }
278
279 /* ELSE mod + r/m specify a disp##[base] or disp##(SIB) */
280 if (modrm.mod == MODRM_MOD_DISP8) { /* mod == 01 */
281 /* If this is an 8-bit displacement */
282 imm32_signsized( buf, buf_len, &ea->disp,
283 sizeof(char));
284 ea->disp_size = sizeof(char);
285 ea->disp_sign = (ea->disp < 0) ? 1 : 0;
286 size += 1; /* add sizeof disp to count */
287
288 } else {
289 /* Displacement is dependent on address size */
290 imm32_signsized( buf, buf_len, &ea->disp,
291 insn->addr_size);
292 ea->disp_size = insn->addr_size;
293 ea->disp_sign = (ea->disp < 0) ? 1 : 0;
294 size += 4;
295 }
296 }
297
298 return size; /* number of bytes found in instruction */
299 }
300
301 void ia32_reg_decode( unsigned char byte, x86_op_t *op, size_t gen_regs ) {
302 struct modRM_byte modrm;
303 byte_decode( byte, &modrm ); /* get bitfields */
304
305 /* set operand to register ID */
306 op->type = op_register;
307 ia32_handle_register(&op->data.reg, modrm.reg + gen_regs);
308
309 return;
310 }

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