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Handle prefix ordering correctly

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This commit is contained in:
Alexis Engelke
2019-01-13 20:36:02 +01:00
parent 3ed7cb4a96
commit 2d1a9582b8
2 changed files with 32 additions and 59 deletions
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86
decode.c
View File

@@ -77,11 +77,6 @@ enum PrefixSet
PREFIX_REPNZ = INSTR_FLAG_REPNZ,
PREFIX_REX = INSTR_FLAG_REX,
PREFIX_VEXL = INSTR_FLAG_VEXL,
PREFIX_SEG_FS = 1 << 8,
PREFIX_SEG_GS = 1 << 9,
PREFIX_SEG_CS = 1 << 10,
PREFIX_SEG_DS = 1 << 11,
PREFIX_SEG_ES = 1 << 12,
PREFIX_OPSZ = 1 << 13,
PREFIX_ADDRSZ = 1 << 14,
PREFIX_REXB = 1 << 15,
@@ -101,27 +96,35 @@ typedef enum PrefixSet PrefixSet;
static
int
decode_prefixes(const uint8_t* buffer, int len, DecodeMode mode,
PrefixSet* out_prefixes, uint8_t* out_vex_operand)
PrefixSet* out_prefixes, uint8_t* out_mandatory,
uint8_t* out_segment, uint8_t* out_vex_operand)
{
int off = 0;
PrefixSet prefixes = 0;
uint8_t rep = 0;
*out_mandatory = 0;
*out_segment = RI_NONE;
while (LIKELY(off < len))
{
uint8_t prefix = buffer[off];
switch (prefix)
{
default: goto out;
case 0x2e: prefixes |= PREFIX_SEG_CS; off++; break;
case 0x26: prefixes |= PREFIX_SEG_ES; off++; break;
case 0x3e: prefixes |= PREFIX_SEG_DS; off++; break;
case 0x64: prefixes |= PREFIX_SEG_FS; off++; break;
case 0x65: prefixes |= PREFIX_SEG_GS; off++; break;
case 0x66: prefixes |= PREFIX_OPSZ; off++; break;
// From segment overrides, the last one wins.
case 0x26: *out_segment = RI_ES; off++; break;
case 0x2e: *out_segment = RI_CS; off++; break;
case 0x3e: *out_segment = RI_DS; off++; break;
case 0x64: *out_segment = RI_FS; off++; break;
case 0x65: *out_segment = RI_GS; off++; break;
case 0x67: prefixes |= PREFIX_ADDRSZ; off++; break;
case 0xf0: prefixes |= PREFIX_LOCK; off++; break;
case 0xf2: prefixes |= PREFIX_REPNZ; off++; break;
case 0xf3: prefixes |= PREFIX_REP; off++; break;
case 0x66: prefixes |= PREFIX_OPSZ; off++; break;
// From REP/REPE and REPNZ, the last one wins; and for mandatory
// prefixes they have a higher priority than 66h (handled below).
case 0xf3: rep = PREFIX_REP; *out_mandatory = 2; off++; break;
case 0xf2: rep = PREFIX_REPNZ; *out_mandatory = 3; off++; break;
#if defined(ARCH_X86_64)
case 0x40: case 0x41: case 0x42: case 0x43: case 0x44: case 0x45:
case 0x46: case 0x47: case 0x48: case 0x49: case 0x4a: case 0x4b:
@@ -176,9 +179,7 @@ decode_prefixes(const uint8_t* buffer, int len, DecodeMode mode,
else // 2-byte VEX
prefixes |= PREFIX_ESC_0F;
prefixes |= byte & 0x04 ? PREFIX_VEXL : 0;
prefixes |= (byte & 0x03) == 1 ? PREFIX_OPSZ : 0;
prefixes |= (byte & 0x03) == 2 ? PREFIX_REP : 0;
prefixes |= (byte & 0x03) == 3 ? PREFIX_REPNZ : 0;
*out_mandatory = byte & 0x03;
*out_vex_operand = ((byte & 0x78) >> 3) ^ 0xf;
// VEX prefix is always the last prefix.
@@ -188,10 +189,12 @@ decode_prefixes(const uint8_t* buffer, int len, DecodeMode mode,
}
out:
if (out_prefixes != NULL)
{
*out_prefixes = prefixes;
}
// If there is no REP/REPNZ prefix and implied opcode extension from a VEX
// prefix, offer 66h as mandatory prefix. If there is a REP prefix, then the
// 66h prefix is ignored when evaluating mandatory prefixes.
if (*out_mandatory == 0 && (prefixes & PREFIX_OPSZ))
*out_mandatory = 1;
*out_prefixes = prefixes | rep;
return off;
}
@@ -375,12 +378,11 @@ decode(const uint8_t* buffer, int len, DecodeMode mode, Instr* instr)
int retval;
int off = 0;
uint8_t vex_operand = 0;
uint8_t mandatory_prefix;
PrefixSet prefixes = 0;
__builtin_memset(instr->operands, 0, sizeof(instr->operands));
retval = decode_prefixes(buffer + off, len - off, mode, &prefixes,
&vex_operand);
&mandatory_prefix, &instr->segment, &vex_operand);
if (UNLIKELY(retval < 0 || off + retval >= len))
{
return -1;
@@ -429,16 +431,8 @@ decode(const uint8_t* buffer, int len, DecodeMode mode, Instr* instr)
// Finally, handle mandatory prefixes (which behave like an opcode ext.).
if (kind == ENTRY_TABLE_PREFIX)
{
uint8_t index = 0;
if (prefixes & PREFIX_OPSZ)
index = 1;
else if (prefixes & PREFIX_REP)
index = 2;
else if (prefixes & PREFIX_REPNZ)
index = 3;
#if defined(ARCH_X86_64)
uint8_t index = mandatory_prefix;
index |= prefixes & PREFIX_REXW ? (1 << 2) : 0;
#endif
index |= prefixes & PREFIX_VEX ? (1 << 3) : 0;
// If a prefix is mandatory and used as opcode extension, it has no
// further effect on the instruction. This is especially important
@@ -461,31 +455,6 @@ decode(const uint8_t* buffer, int len, DecodeMode mode, Instr* instr)
instr->flags |= INSTR_FLAG_64;
instr->address = (uintptr_t) buffer;
if (prefixes & PREFIX_SEG_FS)
{
instr->segment = RI_FS;
}
else if (prefixes & PREFIX_SEG_GS)
{
instr->segment = RI_GS;
}
else if (prefixes & PREFIX_SEG_CS)
{
instr->segment = RI_CS;
}
else if (prefixes & PREFIX_SEG_DS)
{
instr->segment = RI_DS;
}
else if (prefixes & PREFIX_SEG_ES)
{
instr->segment = RI_ES;
}
else
{
instr->segment = RI_DS;
}
uint8_t op_size = 0;
if (desc->gp_size_8)
op_size = 1;
@@ -516,6 +485,7 @@ decode(const uint8_t* buffer, int len, DecodeMode mode, Instr* instr)
0, 1 << desc->gp_fixed_operand_size, op_size, vec_size
};
__builtin_memset(instr->operands, 0, sizeof(instr->operands));
for (int i = 0; i < 4; i++)
{
uint8_t enc_size = (desc->operand_sizes >> 2 * i) & 3;

5
decode.h
View File

@@ -61,13 +61,16 @@ enum RegIndex {
RI_DS,
RI_FS,
RI_GS,
// No register specified
RI_NONE = 0x3f
};
typedef uint8_t Reg;
#define reg_index(reg) (reg)
#define reg_is_none(reg) ((reg) == REG_NONE)
#define REG_NONE (0x3f)
#define REG_NONE RI_NONE
enum
{