123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314 |
- #include "ia32_modrm.h"
- #include "ia32_reg.h"
- #include "x86_imm.h"
- /* NOTE: when decoding ModR/M and SIB, we have to add 1 to all register
- * values obtained from decoding the ModR/M or SIB byte, since they
- * are encoded with eAX = 0 and the tables in ia32_reg.c use eAX = 1.
- * ADDENDUM: this is only the case when the register value is used
- * directly as an index into the register table, not when it is added to
- * a genregs offset. */
- /* -------------------------------- ModR/M, SIB */
- /* ModR/M flags */
- #define MODRM_RM_SIB 0x04 /* R/M == 100 */
- #define MODRM_RM_NOREG 0x05 /* R/B == 101 */
- /* if (MODRM.MOD_NODISP && MODRM.RM_NOREG) then just disp32 */
- #define MODRM_MOD_NODISP 0x00 /* mod == 00 */
- #define MODRM_MOD_DISP8 0x01 /* mod == 01 */
- #define MODRM_MOD_DISP32 0x02 /* mod == 10 */
- #define MODRM_MOD_NOEA 0x03 /* mod == 11 */
- /* 16-bit modrm flags */
- #define MOD16_MOD_NODISP 0
- #define MOD16_MOD_DISP8 1
- #define MOD16_MOD_DISP16 2
- #define MOD16_MOD_REG 3
- #define MOD16_RM_BXSI 0
- #define MOD16_RM_BXDI 1
- #define MOD16_RM_BPSI 2
- #define MOD16_RM_BPDI 3
- #define MOD16_RM_SI 4
- #define MOD16_RM_DI 5
- #define MOD16_RM_BP 6
- #define MOD16_RM_BX 7
- /* SIB flags */
- #define SIB_INDEX_NONE 0x04
- #define SIB_BASE_EBP 0x05
- #define SIB_SCALE_NOBASE 0x00
- /* Convenience struct for modR/M bitfield */
- struct modRM_byte {
- unsigned int mod : 2;
- unsigned int reg : 3;
- unsigned int rm : 3;
- };
- /* Convenience struct for SIB bitfield */
- struct SIB_byte {
- unsigned int scale : 2;
- unsigned int index : 3;
- unsigned int base : 3;
- };
- #if 0
- int modrm_rm[] = {0,1,2,3,MODRM_RM_SIB,MODRM_MOD_DISP32,6,7};
- int modrm_reg[] = {0, 1, 2, 3, 4, 5, 6, 7};
- int modrm_mod[] = {0, MODRM_MOD_DISP8, MODRM_MOD_DISP32, MODRM_MOD_NOEA};
- int sib_scl[] = {0, 2, 4, 8};
- int sib_idx[] = {0, 1, 2, 3, SIB_INDEX_NONE, 5, 6, 7 };
- int sib_bas[] = {0, 1, 2, 3, 4, SIB_SCALE_NOBASE, 6, 7 };
- #endif
- /* this is needed to replace x86_imm_signsized() which does not sign-extend
- * to dest */
- static unsigned int imm32_signsized( unsigned char *buf, size_t buf_len,
- int32_t *dest, unsigned int size ) {
- if ( size > buf_len ) {
- return 0;
- }
- switch (size) {
- case 1:
- *dest = *((signed char *) buf);
- break;
- case 2:
- *dest = *((signed short *) buf);
- break;
- case 4:
- default:
- *dest = *((signed int *) buf);
- break;
- }
- return size;
- }
- static void byte_decode(unsigned char b, struct modRM_byte *modrm) {
- /* generic bitfield-packing routine */
- modrm->mod = b >> 6; /* top 2 bits */
- modrm->reg = (b & 56) >> 3; /* middle 3 bits */
- modrm->rm = b & 7; /* bottom 3 bits */
- }
- static size_t sib_decode( unsigned char *buf, size_t buf_len, x86_ea_t *ea,
- unsigned int mod ) {
- /* set Address Expression fields (scale, index, base, disp)
- * according to the contents of the SIB byte.
- * b points to the SIB byte in the instruction-stream buffer; the
- * byte after b[0] is therefore the byte after the SIB
- * returns number of bytes 'used', including the SIB byte */
- size_t size = 1; /* start at 1 for SIB byte */
- struct SIB_byte sib;
- if ( buf_len < 1 ) {
- return 0;
- }
- byte_decode( *buf, (struct modRM_byte *)(void*)&sib ); /* get bit-fields */
- if ( sib.base == SIB_BASE_EBP && ! mod ) { /* if base == 101 (ebp) */
- /* IF BASE == EBP, deal with exception */
- /* IF (ModR/M did not create a Disp */
- /* ... create a 32-bit Displacement */
- imm32_signsized( &buf[1], buf_len, &ea->disp, sizeof(int32_t));
- ea->disp_size = sizeof(int32_t);
- ea->disp_sign = (ea->disp < 0) ? 1 : 0;
- size += 4; /* add sizeof disp to count */
- } else {
- /* ELSE BASE refers to a General Register */
- ia32_handle_register( &ea->base, sib.base + 1 );
- }
- /* set scale to 1, 2, 4, 8 */
- ea->scale = 1 << sib.scale;
- if (sib.index != SIB_INDEX_NONE) {
- /* IF INDEX is not 'ESP' (100) */
- ia32_handle_register( &ea->index, sib.index + 1 );
- }
- return (size); /* return number of bytes processed */
- }
- static size_t modrm_decode16( unsigned char *buf, unsigned int buf_len,
- x86_op_t *op, struct modRM_byte *modrm ) {
- /* 16-bit mode: hackish, but not as hackish as 32-bit mode ;) */
- size_t size = 1; /* # of bytes decoded [1 for modR/M byte] */
- x86_ea_t * ea = &op->data.expression;
- switch( modrm->rm ) {
- case MOD16_RM_BXSI:
- ia32_handle_register(&ea->base, REG_WORD_OFFSET + 3);
- ia32_handle_register(&ea->index, REG_WORD_OFFSET + 6);
- break;
- case MOD16_RM_BXDI:
- ia32_handle_register(&ea->base, REG_WORD_OFFSET + 3);
- ia32_handle_register(&ea->index, REG_WORD_OFFSET + 7);
- case MOD16_RM_BPSI:
- op->flags.op_seg = x86_op_flags::op_ss_seg;
- ia32_handle_register(&ea->base, REG_WORD_OFFSET + 5);
- ia32_handle_register(&ea->index, REG_WORD_OFFSET + 6);
- break;
- case MOD16_RM_BPDI:
- op->flags.op_seg = x86_op_flags::op_ss_seg;
- ia32_handle_register(&ea->base, REG_WORD_OFFSET + 5);
- ia32_handle_register(&ea->index, REG_WORD_OFFSET + 7);
- break;
- case MOD16_RM_SI:
- ia32_handle_register(&ea->base, REG_WORD_OFFSET + 6);
- break;
- case MOD16_RM_DI:
- ia32_handle_register(&ea->base, REG_WORD_OFFSET + 7);
- break;
- case MOD16_RM_BP:
- if ( modrm->mod != MOD16_MOD_NODISP ) {
- op->flags.op_seg = x86_op_flags::op_ss_seg;
- ia32_handle_register(&ea->base,
- REG_WORD_OFFSET + 5);
- }
- else {
- /* There is a special case when
- (mod == 0) && (rm == 6) for disp16 */
- modrm->mod = MOD16_MOD_DISP16;
- }
- break;
- case MOD16_RM_BX:
- ia32_handle_register(&ea->base, REG_WORD_OFFSET + 3);
- break;
- }
- /* move to byte after ModR/M */
- ++buf;
- --buf_len;
- if ( modrm->mod == MOD16_MOD_DISP8 ) {
- imm32_signsized( buf, buf_len, &ea->disp, sizeof(char) );
- ea->disp_sign = (ea->disp < 0) ? 1 : 0;
- ea->disp_size = sizeof(char);
- size += sizeof(char);
- } else if ( modrm->mod == MOD16_MOD_DISP16 ) {
- imm32_signsized( buf, buf_len, &ea->disp, sizeof(short) );
- ea->disp_sign = (ea->disp < 0) ? 1 : 0;
- ea->disp_size = sizeof(short);
- size += sizeof(short);
- }
- return size;
- }
- /* TODO : Mark index modes
- Use addressing mode flags to imply arrays (index), structure (disp),
- two-dimensional arrays [disp + index], classes [ea reg], and so on.
- */
- size_t Ia32_Decoder::ia32_modrm_decode( unsigned char *buf, unsigned int buf_len,
- x86_op_t *op, size_t gen_regs ) {
- /* create address expression and/or fill operand based on value of
- * ModR/M byte. Calls sib_decode as appropriate.
- * flags specifies whether Reg or mod+R/M fields are being decoded
- * returns the number of bytes in the instruction, including modR/M */
- struct modRM_byte modrm;
- size_t size = 1; /* # of bytes decoded [1 for modR/M byte] */
- x86_ea_t * ea;
- byte_decode(*buf, &modrm); /* get bitfields */
- /* first, handle the case where the mod field is a register only */
- if ( modrm.mod == MODRM_MOD_NOEA ) {
- op->type = op_register;
- ia32_handle_register(&op->data.reg, modrm.rm + gen_regs);
- /* increase insn size by 1 for modrm byte */
- return 1;
- }
- /* then deal with cases where there is an effective address */
- ea = &op->data.expression;
- op->type = op_expression;
- op->flags.op_pointer=true;
- if ( m_decoded->addr_size == 2 ) {
- /* gah! 16 bit mode! */
- return modrm_decode16( buf, buf_len, op, &modrm);
- }
- /* move to byte after ModR/M */
- ++buf;
- --buf_len;
- if (modrm.mod == MODRM_MOD_NODISP) { /* if mod == 00 */
- /* IF MOD == No displacement, just Indirect Register */
- if (modrm.rm == MODRM_RM_NOREG) { /* if r/m == 101 */
- /* IF RM == No Register, just Displacement */
- /* This is an Intel Moronic Exception TM */
- imm32_signsized( buf, buf_len, &ea->disp,
- sizeof(int32_t) );
- ea->disp_size = sizeof(int32_t);
- ea->disp_sign = (ea->disp < 0) ? 1 : 0;
- size += 4; /* add sizeof disp to count */
- } else if (modrm.rm == MODRM_RM_SIB) { /* if r/m == 100 */
- /* ELSE IF an SIB byte is present */
- /* TODO: check for 0 retval */
- size += sib_decode( buf, buf_len, ea, modrm.mod);
- /* move to byte after SIB for displacement */
- ++buf;
- --buf_len;
- } else { /* modR/M specifies base register */
- /* ELSE RM encodes a general register */
- ia32_handle_register( &ea->base, modrm.rm + 1 );
- }
- } else { /* mod is 01 or 10 */
- if (modrm.rm == MODRM_RM_SIB) { /* rm == 100 */
- /* IF base is an AddrExpr specified by an SIB byte */
- /* TODO: check for 0 retval */
- size += sib_decode( buf, buf_len, ea, modrm.mod);
- /* move to byte after SIB for displacement */
- ++buf;
- --buf_len;
- } else {
- /* ELSE base is a general register */
- ia32_handle_register( &ea->base, modrm.rm + 1 );
- }
- /* ELSE mod + r/m specify a disp##[base] or disp##(SIB) */
- if (modrm.mod == MODRM_MOD_DISP8) { /* mod == 01 */
- /* If this is an 8-bit displacement */
- imm32_signsized( buf, buf_len, &ea->disp,
- sizeof(char));
- ea->disp_size = sizeof(char);
- ea->disp_sign = (ea->disp < 0) ? 1 : 0;
- size += 1; /* add sizeof disp to count */
- } else {
- /* Displacement is dependent on address size */
- imm32_signsized( buf, buf_len, &ea->disp, m_decoded->addr_size);
- ea->disp_size = m_decoded->addr_size;
- ea->disp_sign = (ea->disp < 0) ? 1 : 0;
- size += 4;
- }
- }
- return size; /* number of bytes found in instruction */
- }
- void ia32_reg_decode( unsigned char byte, x86_op_t *op, size_t gen_regs ) {
- struct modRM_byte modrm;
- byte_decode( byte, &modrm ); /* get bitfields */
- /* set operand to register ID */
- op->type = op_register;
- ia32_handle_register(&op->data.reg, modrm.reg + gen_regs);
- return;
- }
|