T0b1/fadec
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Decode VEX compact escapes more precisely

Browse Source 
The single opcode byte follows the VEX prefix immediately.
This commit is contained in:
Alexis Engelke
2019-02-24 10:07:18 +01:00
parent b2b29239b1
commit 9cdd35f82f
1 changed files with 23 additions and 30 deletions
Download Patch File Download Diff File Expand all files Collapse all files

53
decode.c
View File

@@ -84,11 +84,6 @@ enum PrefixSet
PREFIX_REXX = 1 << 16, PREFIX_REXX = 1 << 16,
PREFIX_REXR = 1 << 17, PREFIX_REXR = 1 << 17,
PREFIX_REXW = 1 << 18, PREFIX_REXW = 1 << 18,
PREFIX_ESC_NONE = 0 << 19,
PREFIX_ESC_0F = 1 << 19,
PREFIX_ESC_0F38 = 2 << 19,
PREFIX_ESC_0F3A = 3 << 19,
PREFIX_ESC_MASK = 3 << 19,
PREFIX_VEX = 1 << 21, PREFIX_VEX = 1 << 21,
}; };
@@ -98,7 +93,8 @@ static
int int
decode_prefixes(const uint8_t* buffer, int len, DecodeMode mode, decode_prefixes(const uint8_t* buffer, int len, DecodeMode mode,
PrefixSet* out_prefixes, uint8_t* out_mandatory, PrefixSet* out_prefixes, uint8_t* out_mandatory,
uint8_t* out_segment, uint8_t* out_vex_operand) uint8_t* out_segment, uint8_t* out_vex_operand,
int* out_opcode_escape)
{ {
int off = 0; int off = 0;
PrefixSet prefixes = 0; PrefixSet prefixes = 0;
@@ -106,6 +102,7 @@ decode_prefixes(const uint8_t* buffer, int len, DecodeMode mode,
uint8_t rep = 0; uint8_t rep = 0;
*out_mandatory = 0; *out_mandatory = 0;
*out_segment = FD_REG_NONE; *out_segment = FD_REG_NONE;
*out_opcode_escape = -1;
while (LIKELY(off < len)) while (LIKELY(off < len))
{ {
@@ -158,13 +155,7 @@ decode_prefixes(const uint8_t* buffer, int len, DecodeMode mode,
prefixes |= byte & 0x40 ? 0 : PREFIX_REXX; prefixes |= byte & 0x40 ? 0 : PREFIX_REXX;
// SDM Vol 2A 2-15 (Dec. 2016): Ignored in 32-bit mode // SDM Vol 2A 2-15 (Dec. 2016): Ignored in 32-bit mode
prefixes |= mode == DECODE_64 || (byte & 0x20) ? 0 : PREFIX_REXB; prefixes |= mode == DECODE_64 || (byte & 0x20) ? 0 : PREFIX_REXB;
switch (byte & 0x1f) *out_opcode_escape = (byte & 0x1f);
{
case 0x01: prefixes |= PREFIX_ESC_0F; break;
case 0x02: prefixes |= PREFIX_ESC_0F38; break;
case 0x03: prefixes |= PREFIX_ESC_0F3A; break;
default: return -1;
}
// Load third byte of VEX prefix // Load third byte of VEX prefix
if (UNLIKELY(off + 2 >= len)) if (UNLIKELY(off + 2 >= len))
@@ -178,7 +169,7 @@ decode_prefixes(const uint8_t* buffer, int len, DecodeMode mode,
prefixes |= byte & 0x80 ? PREFIX_REXW : 0; prefixes |= byte & 0x80 ? PREFIX_REXW : 0;
} }
else // 2-byte VEX else // 2-byte VEX
prefixes |= PREFIX_ESC_0F; *out_opcode_escape = 1;
prefixes |= byte & 0x04 ? PREFIX_VEXL : 0; prefixes |= byte & 0x04 ? PREFIX_VEXL : 0;
*out_mandatory = byte & 0x03; *out_mandatory = byte & 0x03;
*out_vex_operand = ((byte & 0x78) >> 3) ^ 0xf; *out_vex_operand = ((byte & 0x78) >> 3) ^ 0xf;
@@ -343,10 +334,12 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
int off = 0; int off = 0;
uint8_t vex_operand = 0; uint8_t vex_operand = 0;
uint8_t mandatory_prefix; uint8_t mandatory_prefix;
int opcode_escape;
PrefixSet prefixes = 0; PrefixSet prefixes = 0;
retval = decode_prefixes(buffer + off, len - off, mode, &prefixes, retval = decode_prefixes(buffer + off, len - off, mode, &prefixes,
&mandatory_prefix, &instr->segment, &vex_operand); &mandatory_prefix, &instr->segment, &vex_operand,
&opcode_escape);
if (UNLIKELY(retval < 0 || off + retval >= len)) if (UNLIKELY(retval < 0 || off + retval >= len))
{ {
return -1; return -1;
@@ -355,23 +348,23 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
uint32_t kind = ENTRY_TABLE256; uint32_t kind = ENTRY_TABLE256;
if (UNLIKELY(prefixes & PREFIX_ESC_MASK)) // "Legacy" walk through table and escape opcodes
if (LIKELY(opcode_escape < 0))
while (kind == ENTRY_TABLE256 && LIKELY(off < len))
ENTRY_UNPACK(table, kind, _decode_table, table[buffer[off++]]);
// VEX/EVEX compact escapes; the prefix precedes the single opcode byte
else if (opcode_escape == 1 || opcode_escape == 2 || opcode_escape == 3)
{ {
uint32_t escape = prefixes & PREFIX_ESC_MASK; ENTRY_UNPACK(table, kind, _decode_table, table[0x0F]);
table = (uint16_t*) &_decode_table[table[0x0F] & ~7]; if (opcode_escape == 2)
if (escape == PREFIX_ESC_0F38) ENTRY_UNPACK(table, kind, _decode_table, table[0x38]);
{ if (opcode_escape == 3)
table = (uint16_t*) &_decode_table[table[0x38] & ~7]; ENTRY_UNPACK(table, kind, _decode_table, table[0x3A]);
} if (LIKELY(off < len))
else if (escape == PREFIX_ESC_0F3A) ENTRY_UNPACK(table, kind, _decode_table, table[buffer[off++]]);
{
table = (uint16_t*) &_decode_table[table[0x3A] & ~7];
}
} }
else
// First walk through full-byte opcodes. We do at most three iterations. return -1;
while (kind == ENTRY_TABLE256 && LIKELY(off < len))
ENTRY_UNPACK(table, kind, _decode_table, table[buffer[off++]]);
// Then, walk through ModR/M-encoded opcode extensions. // Then, walk through ModR/M-encoded opcode extensions.
if ((kind == ENTRY_TABLE8 || kind == ENTRY_TABLE72) && LIKELY(off < len)) if ((kind == ENTRY_TABLE8 || kind == ENTRY_TABLE72) && LIKELY(off < len))