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Use special root table for VEX

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Some instruction opcodes have an entirely different encoding when a VEX
prefix is present. For example, 0f41 is CMOVNO without mandatory
prefixes while VEX.NP.W0.L1.0f41 is KANDW with a mandatory prefix. To
avoid collisions, the VEX prefix is better handled as a completely
separate decode tree, at the cost of a slight increase in table size.
This commit is contained in:
Alexis Engelke
2020-02-10 20:29:05 +01:00
parent b376d0d0f8
commit f6a66ea4fb
3 changed files with 42 additions and 30 deletions
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38
decode.c
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@@ -39,6 +39,7 @@ typedef enum DecodeMode DecodeMode;
#define ENTRY_TABLE_PREFIX 5
#define ENTRY_TABLE_VEX 6
#define ENTRY_TABLE_PREFIX_REP 7
#define ENTRY_TABLE_ROOT 8
#define ENTRY_MASK 7
#define ENTRY_UNPACK(table,kind,entry) do { \
@@ -348,25 +349,24 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
return FD_ERR_PARTIAL;
off += retval;
uint32_t kind = ENTRY_TABLE256;
uint32_t kind = ENTRY_TABLE_ROOT;
// "Legacy" walk through table and escape opcodes
if (LIKELY(opcode_escape < 0))
while (kind == ENTRY_TABLE256 && LIKELY(off < len))
ENTRY_UNPACK(table, kind, 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)
if (LIKELY(!(prefixes & PREFIX_VEX)))
{
ENTRY_UNPACK(table, kind, table[0x0F]);
if (opcode_escape == 2)
ENTRY_UNPACK(table, kind, table[0x38]);
if (opcode_escape == 3)
ENTRY_UNPACK(table, kind, table[0x3A]);
if (LIKELY(off < len))
// "Legacy" walk through table and escape opcodes
ENTRY_UNPACK(table, kind, table[0]);
while (kind == ENTRY_TABLE256 && LIKELY(off < len))
ENTRY_UNPACK(table, kind, table[buffer[off++]]);
}
else
return FD_ERR_UD;
{
// VEX/EVEX compact escapes; the prefix precedes the single opcode byte
if (opcode_escape < 0 || opcode_escape > 3)
return FD_ERR_UD;
ENTRY_UNPACK(table, kind, table[4 | opcode_escape]);
if (LIKELY(off < len))
ENTRY_UNPACK(table, kind, table[buffer[off++]]);
}
// Then, walk through ModR/M-encoded opcode extensions.
if ((kind == ENTRY_TABLE8 || kind == ENTRY_TABLE72) && LIKELY(off < len))
@@ -389,18 +389,12 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
// Handle mandatory prefixes (which behave like an opcode ext.).
if (kind == ENTRY_TABLE_PREFIX)
{
uint8_t index = mandatory_prefix;
index |= prefixes & PREFIX_VEX ? (1 << 2) : 0;
// If a prefix is mandatory and used as opcode extension, it has no
// further effect on the instruction. This is especially important
// for the 0x66 prefix, which could otherwise override the operand
// size of general purpose registers.
prefixes &= ~(PREFIX_OPSZ | PREFIX_REPNZ | PREFIX_REP);
ENTRY_UNPACK(table, kind, table[index]);
}
else if (prefixes & PREFIX_VEX)
{
return FD_ERR_UD;
ENTRY_UNPACK(table, kind, table[mandatory_prefix]);
}
if (kind == ENTRY_TABLE_PREFIX_REP)
@@ -519,7 +513,6 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
{
FdOp* operand = &instr->operands[DESC_IMM_IDX(desc)];
operand->type = FD_OT_IMM;
operand->size = 1;
instr->imm = 1;
}
else if (imm_control == 2)
@@ -527,7 +520,6 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
FdOp* operand = &instr->operands[DESC_IMM_IDX(desc)];
operand->type = FD_OT_MEM;
operand->reg = FD_REG_NONE;
operand->size = op_size;
instr->idx_reg = FD_REG_NONE;
if (UNLIKELY(off + addr_size > len))