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| 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-field
s */ | |
| 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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Chromium Code Reviews
Issue 1821293002:
Replace libdisasm with capstone
Base URL: https://chromium.googlesource.com/breakpad/breakpad.git@master