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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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30
parseinstrs.py
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@@ -142,6 +142,7 @@ class EntryKind(Enum):
TABLE_PREFIX = 5
TABLE_VEX = 6
TABLE_PREFIX_REP = 7
TABLE_ROOT = -1
class TrieEntry(namedtuple("TrieEntry", "kind,items,payload")):
__slots__ = ()
@@ -149,9 +150,10 @@ class TrieEntry(namedtuple("TrieEntry", "kind,items,payload")):
EntryKind.TABLE256: 256,
EntryKind.TABLE8: 8,
EntryKind.TABLE72: 72,
EntryKind.TABLE_PREFIX: 8,
EntryKind.TABLE_PREFIX: 4,
EntryKind.TABLE_VEX: 4,
EntryKind.TABLE_PREFIX_REP: 4,
EntryKind.TABLE_ROOT: 8,
}
@classmethod
def table(cls, kind):
@@ -184,7 +186,19 @@ def parse_opcode(opcode_string):
if match is None:
raise Exception("invalid opcode: '%s'" % opcode_string)
opcode = [(EntryKind.TABLE256, [x]) for x in unhexlify(match.group("opcode"))]
opcode = []
opcode_bytes = unhexlify(match.group("opcode"))
# root table, VEX prefix already consumes escape opcode bytes
if match.group("vex"):
idx = [b"", b"\x0f", b"\x0f\x38", b"\x0f\x3a"].index(opcode_bytes[:-1])
opcode.append((EntryKind.TABLE_ROOT, [4 | idx]))
opcode_bytes = opcode_bytes[-1:]
else:
opcode.append((EntryKind.TABLE_ROOT, [0]))
# normal opcode bytes
opcode += [(EntryKind.TABLE256, [x]) for x in opcode_bytes]
opcext = match.group("modrm")
if opcext:
@@ -208,8 +222,7 @@ def parse_opcode(opcode_string):
if match.group("prefixes"):
legacy = {"NP": 0, "66": 1, "F3": 2, "F2": 3}[match.group("legacy")]
entry = legacy | ((1 << 2) if match.group("vex") else 0)
opcode.append((EntryKind.TABLE_PREFIX, [entry]))
opcode.append((EntryKind.TABLE_PREFIX, [legacy]))
if match.group("vexl") or match.group("rexw"):
rexw = match.group("rexw")
@@ -230,7 +243,10 @@ def format_opcode(opcode):
opcode_string = ""
prefix = ""
for kind, byte in opcode:
if kind == EntryKind.TABLE256:
if kind == EntryKind.TABLE_ROOT:
opcode_string += ["", "0f", "0f38", "0f3a"][byte & 3]
prefix += ["", "VEX."][byte >> 2]
elif kind == EntryKind.TABLE256:
opcode_string += "{:02x}".format(byte)
elif kind in (EntryKind.TABLE8, EntryKind.TABLE72):
opcode_string += "/{:x}".format(byte)
@@ -251,7 +267,7 @@ class Table:
self.data = OrderedDict()
self.roots = ["root%d"%i for i in range(root_count)]
for i in range(root_count):
self.data["root%d"%i] = TrieEntry.table(EntryKind.TABLE256)
self.data["root%d"%i] = TrieEntry.table(EntryKind.TABLE_ROOT)
self.offsets = {}
self.annotations = {}
@@ -273,7 +289,7 @@ class Table:
# An opcode can occur once only.
if table.items[opcode[-1][1]]:
raise Exception("opcode_collision for {}".format(name))
raise Exception("opcode collision for {}".format(name))
table.items[opcode[-1][1]] = name
self.data[name] = TrieEntry.instr(instr_encoding)