ia32_modrm.cpp 9.6 KB

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  1. #include "ia32_modrm.h"
  2. #include "ia32_reg.h"
  3. #include "x86_imm.h"
  4. /* NOTE: when decoding ModR/M and SIB, we have to add 1 to all register
  5. * values obtained from decoding the ModR/M or SIB byte, since they
  6. * are encoded with eAX = 0 and the tables in ia32_reg.c use eAX = 1.
  7. * ADDENDUM: this is only the case when the register value is used
  8. * directly as an index into the register table, not when it is added to
  9. * a genregs offset. */
  10. /* -------------------------------- ModR/M, SIB */
  11. /* ModR/M flags */
  12. #define MODRM_RM_SIB 0x04 /* R/M == 100 */
  13. #define MODRM_RM_NOREG 0x05 /* R/B == 101 */
  14. /* if (MODRM.MOD_NODISP && MODRM.RM_NOREG) then just disp32 */
  15. #define MODRM_MOD_NODISP 0x00 /* mod == 00 */
  16. #define MODRM_MOD_DISP8 0x01 /* mod == 01 */
  17. #define MODRM_MOD_DISP32 0x02 /* mod == 10 */
  18. #define MODRM_MOD_NOEA 0x03 /* mod == 11 */
  19. /* 16-bit modrm flags */
  20. #define MOD16_MOD_NODISP 0
  21. #define MOD16_MOD_DISP8 1
  22. #define MOD16_MOD_DISP16 2
  23. #define MOD16_MOD_REG 3
  24. #define MOD16_RM_BXSI 0
  25. #define MOD16_RM_BXDI 1
  26. #define MOD16_RM_BPSI 2
  27. #define MOD16_RM_BPDI 3
  28. #define MOD16_RM_SI 4
  29. #define MOD16_RM_DI 5
  30. #define MOD16_RM_BP 6
  31. #define MOD16_RM_BX 7
  32. /* SIB flags */
  33. #define SIB_INDEX_NONE 0x04
  34. #define SIB_BASE_EBP 0x05
  35. #define SIB_SCALE_NOBASE 0x00
  36. /* Convenience struct for modR/M bitfield */
  37. struct modRM_byte {
  38. unsigned int mod : 2;
  39. unsigned int reg : 3;
  40. unsigned int rm : 3;
  41. };
  42. /* Convenience struct for SIB bitfield */
  43. struct SIB_byte {
  44. unsigned int scale : 2;
  45. unsigned int index : 3;
  46. unsigned int base : 3;
  47. };
  48. #if 0
  49. int modrm_rm[] = {0,1,2,3,MODRM_RM_SIB,MODRM_MOD_DISP32,6,7};
  50. int modrm_reg[] = {0, 1, 2, 3, 4, 5, 6, 7};
  51. int modrm_mod[] = {0, MODRM_MOD_DISP8, MODRM_MOD_DISP32, MODRM_MOD_NOEA};
  52. int sib_scl[] = {0, 2, 4, 8};
  53. int sib_idx[] = {0, 1, 2, 3, SIB_INDEX_NONE, 5, 6, 7 };
  54. int sib_bas[] = {0, 1, 2, 3, 4, SIB_SCALE_NOBASE, 6, 7 };
  55. #endif
  56. /* this is needed to replace x86_imm_signsized() which does not sign-extend
  57. * to dest */
  58. static unsigned int imm32_signsized( unsigned char *buf, size_t buf_len,
  59. int32_t *dest, unsigned int size ) {
  60. if ( size > buf_len ) {
  61. return 0;
  62. }
  63. switch (size) {
  64. case 1:
  65. *dest = *((signed char *) buf);
  66. break;
  67. case 2:
  68. *dest = *((signed short *) buf);
  69. break;
  70. case 4:
  71. default:
  72. *dest = *((signed int *) buf);
  73. break;
  74. }
  75. return size;
  76. }
  77. static void byte_decode(unsigned char b, struct modRM_byte *modrm) {
  78. /* generic bitfield-packing routine */
  79. modrm->mod = b >> 6; /* top 2 bits */
  80. modrm->reg = (b & 56) >> 3; /* middle 3 bits */
  81. modrm->rm = b & 7; /* bottom 3 bits */
  82. }
  83. static size_t sib_decode( unsigned char *buf, size_t buf_len, x86_ea_t *ea,
  84. unsigned int mod ) {
  85. /* set Address Expression fields (scale, index, base, disp)
  86. * according to the contents of the SIB byte.
  87. * b points to the SIB byte in the instruction-stream buffer; the
  88. * byte after b[0] is therefore the byte after the SIB
  89. * returns number of bytes 'used', including the SIB byte */
  90. size_t size = 1; /* start at 1 for SIB byte */
  91. struct SIB_byte sib;
  92. if ( buf_len < 1 ) {
  93. return 0;
  94. }
  95. byte_decode( *buf, (struct modRM_byte *)(void*)&sib ); /* get bit-fields */
  96. if ( sib.base == SIB_BASE_EBP && ! mod ) { /* if base == 101 (ebp) */
  97. /* IF BASE == EBP, deal with exception */
  98. /* IF (ModR/M did not create a Disp */
  99. /* ... create a 32-bit Displacement */
  100. imm32_signsized( &buf[1], buf_len, &ea->disp, sizeof(int32_t));
  101. ea->disp_size = sizeof(int32_t);
  102. ea->disp_sign = (ea->disp < 0) ? 1 : 0;
  103. size += 4; /* add sizeof disp to count */
  104. } else {
  105. /* ELSE BASE refers to a General Register */
  106. ia32_handle_register( &ea->base, sib.base + 1 );
  107. }
  108. /* set scale to 1, 2, 4, 8 */
  109. ea->scale = 1 << sib.scale;
  110. if (sib.index != SIB_INDEX_NONE) {
  111. /* IF INDEX is not 'ESP' (100) */
  112. ia32_handle_register( &ea->index, sib.index + 1 );
  113. }
  114. return (size); /* return number of bytes processed */
  115. }
  116. static size_t modrm_decode16( unsigned char *buf, unsigned int buf_len,
  117. x86_op_t *op, struct modRM_byte *modrm ) {
  118. /* 16-bit mode: hackish, but not as hackish as 32-bit mode ;) */
  119. size_t size = 1; /* # of bytes decoded [1 for modR/M byte] */
  120. x86_ea_t * ea = &op->data.expression;
  121. switch( modrm->rm ) {
  122. case MOD16_RM_BXSI:
  123. ia32_handle_register(&ea->base, REG_WORD_OFFSET + 3);
  124. ia32_handle_register(&ea->index, REG_WORD_OFFSET + 6);
  125. break;
  126. case MOD16_RM_BXDI:
  127. ia32_handle_register(&ea->base, REG_WORD_OFFSET + 3);
  128. ia32_handle_register(&ea->index, REG_WORD_OFFSET + 7);
  129. case MOD16_RM_BPSI:
  130. op->flags.op_seg = x86_op_flags::op_ss_seg>>8;
  131. ia32_handle_register(&ea->base, REG_WORD_OFFSET + 5);
  132. ia32_handle_register(&ea->index, REG_WORD_OFFSET + 6);
  133. break;
  134. case MOD16_RM_BPDI:
  135. op->flags.op_seg = x86_op_flags::op_ss_seg>>8;
  136. ia32_handle_register(&ea->base, REG_WORD_OFFSET + 5);
  137. ia32_handle_register(&ea->index, REG_WORD_OFFSET + 7);
  138. break;
  139. case MOD16_RM_SI:
  140. ia32_handle_register(&ea->base, REG_WORD_OFFSET + 6);
  141. break;
  142. case MOD16_RM_DI:
  143. ia32_handle_register(&ea->base, REG_WORD_OFFSET + 7);
  144. break;
  145. case MOD16_RM_BP:
  146. if ( modrm->mod != MOD16_MOD_NODISP ) {
  147. op->flags.op_seg = x86_op_flags::op_ss_seg>>8;
  148. ia32_handle_register(&ea->base,
  149. REG_WORD_OFFSET + 5);
  150. }
  151. else {
  152. /* There is a special case when
  153. (mod == 0) && (rm == 6) for disp16 */
  154. modrm->mod = MOD16_MOD_DISP16;
  155. }
  156. break;
  157. case MOD16_RM_BX:
  158. ia32_handle_register(&ea->base, REG_WORD_OFFSET + 3);
  159. break;
  160. }
  161. /* move to byte after ModR/M */
  162. ++buf;
  163. --buf_len;
  164. if ( modrm->mod == MOD16_MOD_DISP8 ) {
  165. imm32_signsized( buf, buf_len, &ea->disp, sizeof(char) );
  166. ea->disp_sign = (ea->disp < 0) ? 1 : 0;
  167. ea->disp_size = sizeof(char);
  168. size += sizeof(char);
  169. } else if ( modrm->mod == MOD16_MOD_DISP16 ) {
  170. imm32_signsized( buf, buf_len, &ea->disp, sizeof(short) );
  171. ea->disp_sign = (ea->disp < 0) ? 1 : 0;
  172. ea->disp_size = sizeof(short);
  173. size += sizeof(short);
  174. }
  175. return size;
  176. }
  177. /* TODO : Mark index modes
  178. Use addressing mode flags to imply arrays (index), structure (disp),
  179. two-dimensional arrays [disp + index], classes [ea reg], and so on.
  180. */
  181. size_t Ia32_Decoder::ia32_modrm_decode( unsigned char *buf, unsigned int buf_len,
  182. x86_op_t *op, size_t gen_regs ) {
  183. /* create address expression and/or fill operand based on value of
  184. * ModR/M byte. Calls sib_decode as appropriate.
  185. * flags specifies whether Reg or mod+R/M fields are being decoded
  186. * returns the number of bytes in the instruction, including modR/M */
  187. struct modRM_byte modrm;
  188. size_t size = 1; /* # of bytes decoded [1 for modR/M byte] */
  189. x86_ea_t * ea;
  190. byte_decode(*buf, &modrm); /* get bitfields */
  191. /* first, handle the case where the mod field is a register only */
  192. if ( modrm.mod == MODRM_MOD_NOEA ) {
  193. op->type = op_register;
  194. ia32_handle_register(&op->data.reg, modrm.rm + gen_regs);
  195. /* increase insn size by 1 for modrm byte */
  196. return 1;
  197. }
  198. /* then deal with cases where there is an effective address */
  199. ea = &op->data.expression;
  200. op->type = op_expression;
  201. op->flags.op_pointer=true;
  202. if ( m_decoded->addr_size == 2 ) {
  203. /* gah! 16 bit mode! */
  204. return modrm_decode16( buf, buf_len, op, &modrm);
  205. }
  206. /* move to byte after ModR/M */
  207. ++buf;
  208. --buf_len;
  209. if (modrm.mod == MODRM_MOD_NODISP) { /* if mod == 00 */
  210. /* IF MOD == No displacement, just Indirect Register */
  211. if (modrm.rm == MODRM_RM_NOREG) { /* if r/m == 101 */
  212. /* IF RM == No Register, just Displacement */
  213. /* This is an Intel Moronic Exception TM */
  214. imm32_signsized( buf, buf_len, &ea->disp,
  215. sizeof(int32_t) );
  216. ea->disp_size = sizeof(int32_t);
  217. ea->disp_sign = (ea->disp < 0) ? 1 : 0;
  218. size += 4; /* add sizeof disp to count */
  219. } else if (modrm.rm == MODRM_RM_SIB) { /* if r/m == 100 */
  220. /* ELSE IF an SIB byte is present */
  221. /* TODO: check for 0 retval */
  222. size += sib_decode( buf, buf_len, ea, modrm.mod);
  223. /* move to byte after SIB for displacement */
  224. ++buf;
  225. --buf_len;
  226. } else { /* modR/M specifies base register */
  227. /* ELSE RM encodes a general register */
  228. ia32_handle_register( &ea->base, modrm.rm + 1 );
  229. }
  230. } else { /* mod is 01 or 10 */
  231. if (modrm.rm == MODRM_RM_SIB) { /* rm == 100 */
  232. /* IF base is an AddrExpr specified by an SIB byte */
  233. /* TODO: check for 0 retval */
  234. size += sib_decode( buf, buf_len, ea, modrm.mod);
  235. /* move to byte after SIB for displacement */
  236. ++buf;
  237. --buf_len;
  238. } else {
  239. /* ELSE base is a general register */
  240. ia32_handle_register( &ea->base, modrm.rm + 1 );
  241. }
  242. /* ELSE mod + r/m specify a disp##[base] or disp##(SIB) */
  243. if (modrm.mod == MODRM_MOD_DISP8) { /* mod == 01 */
  244. /* If this is an 8-bit displacement */
  245. imm32_signsized( buf, buf_len, &ea->disp,
  246. sizeof(char));
  247. ea->disp_size = sizeof(char);
  248. ea->disp_sign = (ea->disp < 0) ? 1 : 0;
  249. size += 1; /* add sizeof disp to count */
  250. } else {
  251. /* Displacement is dependent on address size */
  252. imm32_signsized( buf, buf_len, &ea->disp, m_decoded->addr_size);
  253. ea->disp_size = m_decoded->addr_size;
  254. ea->disp_sign = (ea->disp < 0) ? 1 : 0;
  255. size += 4;
  256. }
  257. }
  258. return size; /* number of bytes found in instruction */
  259. }
  260. void ia32_reg_decode( unsigned char byte, x86_op_t *op, size_t gen_regs ) {
  261. struct modRM_byte modrm;
  262. byte_decode( byte, &modrm ); /* get bitfields */
  263. /* set operand to register ID */
  264. op->type = op_register;
  265. ia32_handle_register(&op->data.reg, modrm.reg + gen_regs);
  266. return;
  267. }