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/*
prefix.c
diStorm3 - Powerful disassembler for X86/AMD64
http://ragestorm.net/distorm/
distorm at gmail dot com
Copyright (C) 2003-2012 Gil Dabah
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>
*/
#include "prefix.h"
#include "x86defs.h"
#include "instructions.h"
#include "../include/mnemonics.h"
/*
* The main purpose of this module is to keep track of all kind of prefixes a single instruction may have.
* The problem is that a single instruction may have up to six different prefix-types.
* That's why I have to detect such cases and drop those excess prefixes.
*/
int prefixes_is_valid(unsigned int ch, _DecodeType dt)
{
switch (ch) {
/* for i in xrange(0x40, 0x50): print "case 0x%2x:" % i */
case 0x40: /* REX: */
case 0x41:
case 0x42:
case 0x43:
case 0x44:
case 0x45:
case 0x46:
case 0x47:
case 0x48:
case 0x49:
case 0x4a:
case 0x4b:
case 0x4c:
case 0x4d:
case 0x4e:
case 0x4f: return (dt == Decode64Bits);
case PREFIX_LOCK: return TRUE;
case PREFIX_REPNZ: return TRUE;
case PREFIX_REP: return TRUE;
case PREFIX_CS: return TRUE;
case PREFIX_SS: return TRUE;
case PREFIX_DS: return TRUE;
case PREFIX_ES: return TRUE;
case PREFIX_FS: return TRUE;
case PREFIX_GS: return TRUE;
case PREFIX_OP_SIZE: return TRUE;
case PREFIX_ADDR_SIZE: return TRUE;
/* The VEXs might be false positives, the decode_perfixes will determine for sure. */
case PREFIX_VEX2b: /* VEX is supported for all modes, because 16 bits Pmode is included. */
case PREFIX_VEX3b: return TRUE;
}
return FALSE;
}
/* Ignore a specific prefix type. */
void prefixes_ignore(_PrefixState* ps, _PrefixIndexer pi)
{
/*
* If that type of prefix appeared already, set the bit of that *former* prefix.
* Anyway, set the new index of that prefix type to the current index, so next time we know its position.
*/
if (ps->pfxIndexer[pi] != PFXIDX_NONE) ps->unusedPrefixesMask |= (1 << ps->pfxIndexer[pi]);
}
/* Ignore all prefix. */
void prefixes_ignore_all(_PrefixState* ps)
{
int i;
for (i = 0; i < PFXIDX_MAX; i++)
prefixes_ignore(ps, i);
}
/* Calculates which prefixes weren't used and accordingly sets the bits in the unusedPrefixesMask. */
uint16_t prefixes_set_unused_mask(_PrefixState* ps)
{
/*
* The decodedPrefixes represents the prefixes that were *read* from the binary stream for the instruction.
* The usedPrefixes represents the prefixes that were actually used by the instruction in the *decode* phase.
* Xoring between the two will result in a 'diff' which returns the prefixes that were read
* from the stream *and* that were never used in the actual decoding.
*
* Only one prefix per type can be set in decodedPrefixes from the stream.
* Therefore it's enough to check each type once and set the flag accordingly.
* That's why we had to book-keep each prefix type and its position.
* So now we know which bits we need to set exactly in the mask.
*/
_iflags unusedPrefixesDiff = ps->decodedPrefixes ^ ps->usedPrefixes;
/* Examine unused prefixes by type: */
/*
* About REX: it might be set in the diff although it was never in the stream itself.
* This is because the vrex is shared between VEX and REX and some places flag it as REX usage, while
* we were really decoding an AVX instruction.
* It's not a big problem, because the prefixes_ignore func will ignore it anyway,
* since it wasn't seen earlier. But it's important to know this.
*/
if (unusedPrefixesDiff & INST_PRE_REX) prefixes_ignore(ps, PFXIDX_REX);
if (unusedPrefixesDiff & INST_PRE_SEGOVRD_MASK) prefixes_ignore(ps, PFXIDX_SEG);
if (unusedPrefixesDiff & INST_PRE_LOKREP_MASK) prefixes_ignore(ps, PFXIDX_LOREP);
if (unusedPrefixesDiff & INST_PRE_OP_SIZE) prefixes_ignore(ps, PFXIDX_OP_SIZE);
if (unusedPrefixesDiff & INST_PRE_ADDR_SIZE) prefixes_ignore(ps, PFXIDX_ADRS);
/* If a VEX instruction was found, its prefix is considered as used, therefore no point for checking for it. */
return ps->unusedPrefixesMask;
}
/*
* Mark a prefix as unused, and bookkeep where we last saw this same type,
* because in the future we might want to disable it too.
*/
_INLINE_ void prefixes_track_unused(_PrefixState* ps, int index, _PrefixIndexer pi)
{
prefixes_ignore(ps, pi);
/* Book-keep the current index for this type. */
ps->pfxIndexer[pi] = index;
}
/*
* Read as many prefixes as possible, up to 15 bytes, and halt when we encounter non-prefix byte.
* This algorithm tries to imitate a real processor, where the same prefix can appear a few times, etc.
* The tiny complexity is that we want to know when a prefix was superfluous and mark any copy of it as unused.
* Note that the last prefix of its type will be considered as used, and all the others (of same type) before it as unused.
*/
void prefixes_decode(const uint8_t* code, int codeLen, _PrefixState* ps, _DecodeType dt)
{
int index, done;
uint8_t vex;
/*
* First thing to do, scan for prefixes, there are six types of prefixes.
* There may be up to six prefixes before a single instruction, not the same type, no special order,
* except REX/VEX must precede immediately the first opcode byte.
* BTW - This is the reason why I didn't make the REP prefixes part of the instructions (STOS/SCAS/etc).
*
* Another thing, the instruction maximum size is 15 bytes, thus if we read more than 15 bytes, we will halt.
*
* We attach all prefixes to the next instruction, there might be two or more occurrences from the same prefix.
* Also, since VEX can be allowed only once we will test it separately.
*/
for (index = 0, done = FALSE;
(codeLen > 0) && (code - ps->start < INST_MAXIMUM_SIZE);
code++, codeLen--, index++) {
/*
NOTE: AMD treat lock/rep as two different groups... But I am based on Intel.
- Lock and Repeat:
- 0xF0 — LOCK
- 0xF2 — REPNE/REPNZ
- 0xF3 - REP/REPE/REPZ
- Segment Override:
- 0x2E - CS
- 0x36 - SS
- 0x3E - DS
- 0x26 - ES
- 0x64 - FS
- 0x65 - GS
- Operand-Size Override: 0x66, switching default size.
- Address-Size Override: 0x67, switching default size.
64 Bits:
- REX: 0x40 - 0x4f, extends register access.
- 2 Bytes VEX: 0xc4
- 3 Bytes VEX: 0xc5
32 Bits:
- 2 Bytes VEX: 0xc4 11xx-xxxx
- 3 Bytes VEX: 0xc5 11xx-xxxx
*/
/* Examine what type of prefix we got. */
switch (*code)
{
/* REX type, 64 bits decoding mode only: */
case 0x40:
case 0x41:
case 0x42:
case 0x43:
case 0x44:
case 0x45:
case 0x46:
case 0x47:
case 0x48:
case 0x49:
case 0x4a:
case 0x4b:
case 0x4c:
case 0x4d:
case 0x4e:
case 0x4f:
if (dt == Decode64Bits) {
ps->decodedPrefixes |= INST_PRE_REX;
ps->vrex = *code & 0xf; /* Keep only BXRW. */
ps->rexPos = code;
ps->prefixExtType = PET_REX;
prefixes_track_unused(ps, index, PFXIDX_REX);
} else done = TRUE; /* If we are not in 64 bits mode, it's an instruction, then halt. */
break;
/* LOCK and REPx type: */
case PREFIX_LOCK:
ps->decodedPrefixes |= INST_PRE_LOCK;
prefixes_track_unused(ps, index, PFXIDX_LOREP);
break;
case PREFIX_REPNZ:
ps->decodedPrefixes |= INST_PRE_REPNZ;
prefixes_track_unused(ps, index, PFXIDX_LOREP);
break;
case PREFIX_REP:
ps->decodedPrefixes |= INST_PRE_REP;
prefixes_track_unused(ps, index, PFXIDX_LOREP);
break;
/* Seg Overide type: */
case PREFIX_CS:
ps->decodedPrefixes |= INST_PRE_CS;
prefixes_track_unused(ps, index, PFXIDX_SEG);
break;
case PREFIX_SS:
ps->decodedPrefixes |= INST_PRE_SS;
prefixes_track_unused(ps, index, PFXIDX_SEG);
break;
case PREFIX_DS:
ps->decodedPrefixes |= INST_PRE_DS;
prefixes_track_unused(ps, index, PFXIDX_SEG);
break;
case PREFIX_ES:
ps->decodedPrefixes |= INST_PRE_ES;
prefixes_track_unused(ps, index, PFXIDX_SEG);
break;
case PREFIX_FS:
ps->decodedPrefixes |= INST_PRE_FS;
prefixes_track_unused(ps, index, PFXIDX_SEG);
break;
case PREFIX_GS:
ps->decodedPrefixes |= INST_PRE_GS;
prefixes_track_unused(ps, index, PFXIDX_SEG);
break;
/* Op Size type: */
case PREFIX_OP_SIZE:
ps->decodedPrefixes |= INST_PRE_OP_SIZE;
prefixes_track_unused(ps, index, PFXIDX_OP_SIZE);
break;
/* Addr Size type: */
case PREFIX_ADDR_SIZE:
ps->decodedPrefixes |= INST_PRE_ADDR_SIZE;
prefixes_track_unused(ps, index, PFXIDX_ADRS);
break;
/* Non-prefix byte now, so break 2. */
default: done = TRUE; break;
}
if (done) break;
}
/* 2 Bytes VEX: */
if ((codeLen >= 2) &&
(*code == PREFIX_VEX2b) &&
((code - ps->start) <= INST_MAXIMUM_SIZE - 2)) {
/*
* In 32 bits the second byte has to be in the special range of Mod=11.
* Otherwise it might be a normal LDS instruction.
*/
if ((dt == Decode64Bits) || (*(code + 1) >= INST_DIVIDED_MODRM)) {
ps->vexPos = code + 1;
ps->decodedPrefixes |= INST_PRE_VEX;
ps->prefixExtType = PET_VEX2BYTES;
/*
* VEX 1 byte bits:
* |7-6--3-2-10|
* |R|vvvv|L|pp|
* |-----------|
*/
/* -- Convert from VEX prefix to VREX flags -- */
vex = *ps->vexPos;
if (~vex & 0x80 && dt == Decode64Bits) ps->vrex |= PREFIX_EX_R; /* Convert VEX.R. */
if (vex & 4) ps->vrex |= PREFIX_EX_L; /* Convert VEX.L. */
code += 2;
}
}
/* 3 Bytes VEX: */
if ((codeLen >= 3) &&
(*code == PREFIX_VEX3b) &&
((code - ps->start) <= INST_MAXIMUM_SIZE - 3) &&
(~ps->decodedPrefixes & INST_PRE_VEX)) {
/*
* In 32 bits the second byte has to be in the special range of Mod=11.
* Otherwise it might be a normal LES instruction.
* And we don't care now about the 3rd byte.
*/
if ((dt == Decode64Bits) || (*(code + 1) >= INST_DIVIDED_MODRM)) {
ps->vexPos = code + 1;
ps->decodedPrefixes |= INST_PRE_VEX;
ps->prefixExtType = PET_VEX3BYTES;
/*
* VEX first and second bytes:
* |7-6-5-4----0| |7-6--3-2-10|
* |R|X|B|m-mmmm| |W|vvvv|L|pp|
* |------------| |-----------|
*/
/* -- Convert from VEX prefix to VREX flags -- */
vex = *ps->vexPos;
ps->vrex |= ((~vex >> 5) & 0x7); /* Shift and invert VEX.R/X/B to their place */
vex = *(ps->vexPos + 1);
if (vex & 4) ps->vrex |= PREFIX_EX_L; /* Convert VEX.L. */
if (vex & 0x80) ps->vrex |= PREFIX_EX_W; /* Convert VEX.W. */
/* Clear some flags if the mode isn't 64 bits. */
if (dt != Decode64Bits) ps->vrex &= ~(PREFIX_EX_B | PREFIX_EX_X | PREFIX_EX_R | PREFIX_EX_W);
code += 3;
}
}
/*
* Save last byte scanned address, so the decoder could keep on scanning from this point and on and on and on.
* In addition the decoder is able to know that the last byte could lead to MMX/SSE instructions (preceding REX if exists).
*/
ps->last = code; /* ps->last points to an opcode byte. */
}
/*
* For every memory-indirection operand we want to set its corresponding default segment.
* If the segment is being overrided, we need to see whether we use it or not.
* We will use it only if it's not the default one already.
*/
void prefixes_use_segment(_iflags defaultSeg, _PrefixState* ps, _DecodeType dt, _DInst* di)
{
_iflags flags = 0;
if (dt == Decode64Bits) flags = ps->decodedPrefixes & INST_PRE_SEGOVRD_MASK64;
else flags = ps->decodedPrefixes & INST_PRE_SEGOVRD_MASK;
if ((flags == 0) || (flags == defaultSeg)) {
flags = defaultSeg;
di->segment |= SEGMENT_DEFAULT;
} else if (flags != defaultSeg) {
/* Use it only if it's non-default segment. */
ps->usedPrefixes |= flags;
}
/* ASSERT: R_XX must be below 128. */
switch (flags)
{
case INST_PRE_ES: di->segment |= R_ES; break;
case INST_PRE_CS: di->segment |= R_CS; break;
case INST_PRE_SS: di->segment |= R_SS; break;
case INST_PRE_DS: di->segment |= R_DS; break;
case INST_PRE_FS: di->segment |= R_FS; break;
case INST_PRE_GS: di->segment |= R_GS; break;
}
/* If it's one of the CS,SS,DS,ES and the mode is 64 bits, set segment it to none, since it's ignored. */
if ((dt == Decode64Bits) && (flags & INST_PRE_SEGOVRD_MASK32)) di->segment = R_NONE;
}

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