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/*
* Copyright © Michael Smith <mikesmiffy128@gmail.com>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
* REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
* AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
* LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
* OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
* PERFORMANCE OF THIS SOFTWARE.
*/
// _Static_assert needs MSVC >= 2019, and this check is irrelevant on Windows
#ifndef _MSC_VER
_Static_assert((unsigned char)-1 == 255, "this code requires 8-bit chars");
#endif
#include "x86.h"
static int mrmsib(const unsigned char *p, int addrlen) {
if (addrlen == 4 || *p & 0xC0) {
int sib = addrlen == 4 && *p < 0xC0 && (*p & 7) == 4;
switch (*p & 0xC0) {
case 0x40: // disp8
return 2 + sib;
case 0: // disp16/32
if ((*p & 7) != 5) {
// disp8/32 via SIB
if (sib && (p[1] & 7) == 5) return *p & 0x40 ? 3 : 6;
return 1 + sib;
}
case 0x80:
return 1 + addrlen + sib;
}
}
if (addrlen == 2 && (*p & 0xC7) == 0x06) return 3;
return 1; // note: include the mrm itself in the byte count
}
enum {
CLASS_UNKNOWN,
CLASS_PFX,
CLASS_NO,
CLASS_I8,
CLASS_IW,
CLASS_IWI,
CLASS_I16,
CLASS_MRM,
CLASS_MRMI8,
CLASS_MRMIW,
CLASS_ENTER,
CLASS_CRAZY8,
CLASS_CRAZYW,
CLASS_2BYTE,
CLASS2B_NO = 1,
CLASS2B_IW,
CLASS2B_MRM,
CLASS2B_MRMI8
};
// note: could theoretically shrink these tables down to 128B each although to
// do it at compile time without the use of _BitInt(4) would be kind of tricky.
static const unsigned char classtab[256] = {
#define TABLEENT(name, val) [val] = CLASS_PFX,
X86_PREFIXES(TABLEENT)
#undef TABLEENT
#define TABLEENT(name, val) [val] = CLASS_NO,
X86_OPS_1BYTE_NO(TABLEENT)
#undef TABLEENT
#define TABLEENT(name, val) [val] = CLASS_I8,
X86_OPS_1BYTE_I8(TABLEENT)
#undef TABLEENT
#define TABLEENT(name, val) [val] = CLASS_IW,
X86_OPS_1BYTE_IW(TABLEENT)
#undef TABLEENT
#define TABLEENT(name, val) [val] = CLASS_IWI,
X86_OPS_1BYTE_IWI(TABLEENT)
#undef TABLEENT
#define TABLEENT(name, val) [val] = CLASS_I16,
X86_OPS_1BYTE_I16(TABLEENT)
#undef TABLEENT
#define TABLEENT(name, val) [val] = CLASS_MRM,
X86_OPS_1BYTE_MRM(TABLEENT)
#undef TABLEENT
#define TABLEENT(name, val) [val] = CLASS_MRMI8,
X86_OPS_1BYTE_MRM_I8(TABLEENT)
#undef TABLEENT
#define TABLEENT(name, val) [val] = CLASS_MRMIW,
X86_OPS_1BYTE_MRM_IW(TABLEENT)
#undef TABLEENT
[X86_ENTER] = CLASS_ENTER,
[X86_CRAZY8] = CLASS_CRAZY8,
[X86_CRAZYW] = CLASS_CRAZYW,
[X86_2BYTE] = CLASS_2BYTE
};
static const unsigned char classtab_2b[256] = {
// we don't support any 3 byte ops for now; implement if ever needed...
[X86_3BYTE1] = CLASS_UNKNOWN,
[X86_3BYTE2] = CLASS_UNKNOWN,
[X86_3DNOW] = CLASS_UNKNOWN,
#define TABLEENT(name, val) [val] = CLASS2B_NO,
X86_OPS_2BYTE_NO(TABLEENT)
#undef TABLEENT
#define TABLEENT(name, val) [val] = CLASS2B_IW,
X86_OPS_2BYTE_IW(TABLEENT)
#undef TABLEENT
#define TABLEENT(name, val) [val] = CLASS2B_MRM,
X86_OPS_2BYTE_MRM(TABLEENT)
#undef TABLEENT
#define TABLEENT(name, val) [val] = CLASS2B_MRMI8,
X86_OPS_2BYTE_MRM_I8(TABLEENT)
#undef TABLEENT
};
#ifndef X86_DISABLE_SIZE_OPT
#if defined(__clang__)
__attribute((minsize))
#elif defined(__GNUC__)
__attribute((optimize("Os")))
#endif
#endif
int x86_len(const unsigned char *insn) {
#define CASES(name, _) case name:
int pfxlen = 0, addrlen = 4, operandlen = 4;
p: switch (classtab[*insn]) {
case CLASS_UNKNOWN: return -1;
case CLASS_PFX:
switch (*insn) {
case X86_PFX_ADSZ: addrlen = 2; goto P; // bit dumb sorry
case X86_PFX_OPSZ: operandlen = 2;
P: X86_SEG_PREFIXES(CASES)
case X86_PFX_LOCK: case X86_PFX_REPN: case X86_PFX_REP:
// instruction can only be 15 bytes. this could go over, oh
// well, just don't want to loop for 8 million years
if (++pfxlen == 14) return -1;
++insn;
goto p;
}
case CLASS_NO: return pfxlen + 1;
case CLASS_I8: operandlen = 1;
case CLASS_IW: return pfxlen + 1 + operandlen;
case CLASS_IWI: return pfxlen + 1 + addrlen;
case CLASS_I16: return pfxlen + 3;
case CLASS_MRM: return pfxlen + 1 + mrmsib(insn + 1, addrlen);
case CLASS_MRMI8: operandlen = 1;
case CLASS_MRMIW:
return pfxlen + 1 + operandlen + mrmsib(insn + 1, addrlen);
case CLASS_ENTER: return pfxlen + 4;
case CLASS_CRAZY8: operandlen = 1;
case CLASS_CRAZYW:
if ((insn[1] & 0x38) >= 0x10) operandlen = 0;
return pfxlen + 1 + operandlen + mrmsib(insn + 1, addrlen);
case CLASS_2BYTE: ++insn; goto b2;
}
#if defined(__GNUC__) || defined(__clang__)
__builtin_unreachable();
#elif defined(_MSC_VER)
__assume(0);
#else
return -1;
#endif
b2: switch (classtab_2b[*insn]) {
case CLASS_UNKNOWN: return -1;
case CLASS2B_NO: return pfxlen + 2;
case CLASS2B_IW: return pfxlen + 2 + operandlen;
case CLASS2B_MRM: return pfxlen + 2 + mrmsib(insn + 1, addrlen);
case CLASS2B_MRMI8: operandlen = 1;
return pfxlen + 2 + operandlen + mrmsib(insn + 1, addrlen);
}
#if defined(__GNUC__) || defined(__clang__)
__builtin_unreachable();
#elif defined(_MSC_VER)
__assume(0);
#else
return -1;
#endif
#undef CASES
}
// vi: sw=4 ts=4 noet tw=80 cc=80
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