decode.c

u-boot 源代码

	DECODE_PRINTF("ESI]");
	return M.x86.R_ESI * index;
      case 7:
	DECODE_PRINTF("EDI]");
	return M.x86.R_EDI * index;
    }
    HALT_SYS();
    return 0;			/* NOT REACHED OR REACHED ON ERROR */
}

/****************************************************************************
PARAMETERS:
mod - MOD value of preceding ModR/M byte

RETURNS:
Offset in memory for the address decoding

REMARKS:
Decodes SIB addressing byte and returns calculated effective address.
****************************************************************************/
unsigned decode_sib_address(
    int mod)
{
    int sib   = fetch_byte_imm();
    int ss    = (sib >> 6) & 0x03;
    int index = (sib >> 3) & 0x07;
    int base  = sib & 0x07;
    int offset = 0;
    int displacement;

    switch (base) {
      case 0:
	DECODE_PRINTF("[EAX]");
	offset = M.x86.R_EAX;
	break;
      case 1:
	DECODE_PRINTF("[ECX]");
	offset = M.x86.R_ECX;
	break;
      case 2:
	DECODE_PRINTF("[EDX]");
	offset = M.x86.R_EDX;
	break;
      case 3:
	DECODE_PRINTF("[EBX]");
	offset = M.x86.R_EBX;
	break;
      case 4:
	DECODE_PRINTF("[ESP]");
	offset = M.x86.R_ESP;
	break;
      case 5:
	switch (mod) {
	  case 0:
	    displacement = (s32)fetch_long_imm();
	    DECODE_PRINTF2("[%d]", displacement);
	    offset = displacement;
	    break;
	  case 1:
	    displacement = (s8)fetch_byte_imm();
	    DECODE_PRINTF2("[%d][EBP]", displacement);
	    offset = M.x86.R_EBP + displacement;
	    break;
	  case 2:
	    displacement = (s32)fetch_long_imm();
	    DECODE_PRINTF2("[%d][EBP]", displacement);
	    offset = M.x86.R_EBP + displacement;
	    break;
	  default:
	    HALT_SYS();
	}
	DECODE_PRINTF("[EAX]");
	offset = M.x86.R_EAX;
	break;
      case 6:
	DECODE_PRINTF("[ESI]");
	offset = M.x86.R_ESI;
	break;
      case 7:
	DECODE_PRINTF("[EDI]");
	offset = M.x86.R_EDI;
	break;
      default:
	HALT_SYS();
    }
    offset += decode_sib_si(ss, index);
    return offset;

}

/****************************************************************************
PARAMETERS:
rm  - RM value to decode

RETURNS:
Offset in memory for the address decoding

REMARKS:
Return the offset given by mod=00 addressing.  Also enables the
decoding of instructions.

NOTE:	The code which specifies the corresponding segment (ds vs ss)
	below in the case of [BP+..].  The assumption here is that at the
	point that this subroutine is called, the bit corresponding to
	SYSMODE_SEG_DS_SS will be zero.	 After every instruction
	except the segment override instructions, this bit (as well
	as any bits indicating segment overrides) will be clear.  So
	if a SS access is needed, set this bit.	 Otherwise, DS access
	occurs (unless any of the segment override bits are set).
****************************************************************************/
unsigned decode_rm00_address(
    int rm)
{
    unsigned offset;

    if (M.x86.mode & SYSMODE_PREFIX_ADDR) {
	/* 32-bit addressing */
	switch (rm) {
	  case 0:
	    DECODE_PRINTF("[EAX]");
	    return M.x86.R_EAX;
	  case 1:
	    DECODE_PRINTF("[ECX]");
	    return M.x86.R_ECX;
	  case 2:
	    DECODE_PRINTF("[EDX]");
	    return M.x86.R_EDX;
	  case 3:
	    DECODE_PRINTF("[EBX]");
	    return M.x86.R_EBX;
	  case 4:
	    return decode_sib_address(0);
	  case 5:
	    offset = fetch_long_imm();
	    DECODE_PRINTF2("[%08x]", offset);
	    return offset;
	  case 6:
	    DECODE_PRINTF("[ESI]");
	    return M.x86.R_ESI;
	  case 7:
	    DECODE_PRINTF("[EDI]");
	    return M.x86.R_EDI;
	}
    } else {
	/* 16-bit addressing */
	switch (rm) {
	  case 0:
	    DECODE_PRINTF("[BX+SI]");
	    return (M.x86.R_BX + M.x86.R_SI) & 0xffff;
	  case 1:
	    DECODE_PRINTF("[BX+DI]");
	    return (M.x86.R_BX + M.x86.R_DI) & 0xffff;
	  case 2:
	    DECODE_PRINTF("[BP+SI]");
	    M.x86.mode |= SYSMODE_SEG_DS_SS;
	    return (M.x86.R_BP + M.x86.R_SI) & 0xffff;
	  case 3:
	    DECODE_PRINTF("[BP+DI]");
	    M.x86.mode |= SYSMODE_SEG_DS_SS;
	    return (M.x86.R_BP + M.x86.R_DI) & 0xffff;
	  case 4:
	    DECODE_PRINTF("[SI]");
	    return M.x86.R_SI;
	  case 5:
	    DECODE_PRINTF("[DI]");
	    return M.x86.R_DI;
	  case 6:
	    offset = fetch_word_imm();
	    DECODE_PRINTF2("[%04x]", offset);
	    return offset;
	  case 7:
	    DECODE_PRINTF("[BX]");
	    return M.x86.R_BX;
	}
    }
    HALT_SYS();
    return 0;
}

/****************************************************************************
PARAMETERS:
rm  - RM value to decode

RETURNS:
Offset in memory for the address decoding

REMARKS:
Return the offset given by mod=01 addressing.  Also enables the
decoding of instructions.
****************************************************************************/
unsigned decode_rm01_address(
    int rm)
{
    int displacement;

    if (M.x86.mode & SYSMODE_PREFIX_ADDR) {
	/* 32-bit addressing */
	if (rm != 4)
	    displacement = (s8)fetch_byte_imm();
	else
	    displacement = 0;

	switch (rm) {
	  case 0:
	    DECODE_PRINTF2("%d[EAX]", displacement);
	    return M.x86.R_EAX + displacement;
	  case 1:
	    DECODE_PRINTF2("%d[ECX]", displacement);
	    return M.x86.R_ECX + displacement;
	  case 2:
	    DECODE_PRINTF2("%d[EDX]", displacement);
	    return M.x86.R_EDX + displacement;
	  case 3:
	    DECODE_PRINTF2("%d[EBX]", displacement);
	    return M.x86.R_EBX + displacement;
	  case 4: {
	    int offset = decode_sib_address(1);
	    displacement = (s8)fetch_byte_imm();
	    DECODE_PRINTF2("[%d]", displacement);
	    return offset + displacement;
	  }
	  case 5:
	    DECODE_PRINTF2("%d[EBP]", displacement);
	    return M.x86.R_EBP + displacement;
	  case 6:
	    DECODE_PRINTF2("%d[ESI]", displacement);
	    return M.x86.R_ESI + displacement;
	  case 7:
	    DECODE_PRINTF2("%d[EDI]", displacement);
	    return M.x86.R_EDI + displacement;
	}
    } else {
	/* 16-bit addressing */
	displacement = (s8)fetch_byte_imm();
	switch (rm) {
	  case 0:
	    DECODE_PRINTF2("%d[BX+SI]", displacement);
	    return (M.x86.R_BX + M.x86.R_SI + displacement) & 0xffff;
	  case 1:
	    DECODE_PRINTF2("%d[BX+DI]", displacement);
	    return (M.x86.R_BX + M.x86.R_DI + displacement) & 0xffff;
	  case 2:
	    DECODE_PRINTF2("%d[BP+SI]", displacement);
	    M.x86.mode |= SYSMODE_SEG_DS_SS;
	    return (M.x86.R_BP + M.x86.R_SI + displacement) & 0xffff;
	  case 3:
	    DECODE_PRINTF2("%d[BP+DI]", displacement);
	    M.x86.mode |= SYSMODE_SEG_DS_SS;
	    return (M.x86.R_BP + M.x86.R_DI + displacement) & 0xffff;
	  case 4:
	    DECODE_PRINTF2("%d[SI]", displacement);
	    return (M.x86.R_SI + displacement) & 0xffff;
	  case 5:
	    DECODE_PRINTF2("%d[DI]", displacement);
	    return (M.x86.R_DI + displacement) & 0xffff;
	  case 6:
	    DECODE_PRINTF2("%d[BP]", displacement);
	    M.x86.mode |= SYSMODE_SEG_DS_SS;
	    return (M.x86.R_BP + displacement) & 0xffff;
	  case 7:
	    DECODE_PRINTF2("%d[BX]", displacement);
	    return (M.x86.R_BX + displacement) & 0xffff;
	}
    }
    HALT_SYS();
    return 0;			/* SHOULD NOT HAPPEN */
}

/****************************************************************************
PARAMETERS:
rm  - RM value to decode

RETURNS:
Offset in memory for the address decoding

REMARKS:
Return the offset given by mod=10 addressing.  Also enables the
decoding of instructions.
****************************************************************************/
unsigned decode_rm10_address(
    int rm)
{
    if (M.x86.mode & SYSMODE_PREFIX_ADDR) {
	int displacement;

	/* 32-bit addressing */
	if (rm != 4)
	    displacement = (s32)fetch_long_imm();
	else
	    displacement = 0;

	switch (rm) {
	  case 0:
	    DECODE_PRINTF2("%d[EAX]", displacement);
	    return M.x86.R_EAX + displacement;
	  case 1:
	    DECODE_PRINTF2("%d[ECX]", displacement);
	    return M.x86.R_ECX + displacement;
	  case 2:
	    DECODE_PRINTF2("%d[EDX]", displacement);
	    return M.x86.R_EDX + displacement;
	  case 3:
	    DECODE_PRINTF2("%d[EBX]", displacement);
	    return M.x86.R_EBX + displacement;
	  case 4: {
	    int offset = decode_sib_address(2);
	    displacement = (s32)fetch_long_imm();
	    DECODE_PRINTF2("[%d]", displacement);
	    return offset + displacement;
	  }
	  case 5:
	    DECODE_PRINTF2("%d[EBP]", displacement);
	    return M.x86.R_EBP + displacement;
	  case 6:
	    DECODE_PRINTF2("%d[ESI]", displacement);
	    return M.x86.R_ESI + displacement;
	  case 7:
	    DECODE_PRINTF2("%d[EDI]", displacement);
	    return M.x86.R_EDI + displacement;
	}
    } else {
	int displacement = (s16)fetch_word_imm();

	/* 16-bit addressing */
	switch (rm) {
	  case 0:
	    DECODE_PRINTF2("%d[BX+SI]", displacement);
	    return (M.x86.R_BX + M.x86.R_SI + displacement) & 0xffff;
	  case 1:
	    DECODE_PRINTF2("%d[BX+DI]", displacement);
	    return (M.x86.R_BX + M.x86.R_DI + displacement) & 0xffff;
	  case 2:
	    DECODE_PRINTF2("%d[BP+SI]", displacement);
	    M.x86.mode |= SYSMODE_SEG_DS_SS;
	    return (M.x86.R_BP + M.x86.R_SI + displacement) & 0xffff;
	  case 3:
	    DECODE_PRINTF2("%d[BP+DI]", displacement);
	    M.x86.mode |= SYSMODE_SEG_DS_SS;
	    return (M.x86.R_BP + M.x86.R_DI + displacement) & 0xffff;
	  case 4:
	    DECODE_PRINTF2("%d[SI]", displacement);
	    return (M.x86.R_SI + displacement) & 0xffff;
	  case 5:
	    DECODE_PRINTF2("%d[DI]", displacement);
	    return (M.x86.R_DI + displacement) & 0xffff;
	  case 6:
	    DECODE_PRINTF2("%d[BP]", displacement);
	    M.x86.mode |= SYSMODE_SEG_DS_SS;
	    return (M.x86.R_BP + displacement) & 0xffff;
	  case 7:
	    DECODE_PRINTF2("%d[BX]", displacement);
	    return (M.x86.R_BX + displacement) & 0xffff;
	}
    }
    HALT_SYS();
    return 0;			/* SHOULD NOT HAPPEN */
}

/****************************************************************************
PARAMETERS:
mod - modifier
rm  - RM value to decode

RETURNS:
Offset in memory for the address decoding, multiplexing calls to
the decode_rmXX_address functions

REMARKS:
Return the offset given by "mod" addressing.
****************************************************************************/

unsigned decode_rmXX_address(int mod, int rm)
{
  if(mod == 0)
    return decode_rm00_address(rm);
  if(mod == 1)
    return decode_rm01_address(rm);
  return decode_rm10_address(rm);
}

#endif