From 0bb08a980d52db277a6da8758486bac22342a882 Mon Sep 17 00:00:00 2001
From: iximeow <me@iximeow.net>
Date: Sat, 30 Nov 2019 17:22:05 -0800
Subject: more careful prefix handling
---
src/lib.rs | 58 ++++++++++++++++++++++++++++------------------------------
1 file changed, 28 insertions(+), 30 deletions(-)
(limited to 'src')
diff --git a/src/lib.rs b/src/lib.rs
index d03a952..bf94dbe 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2911,6 +2911,23 @@ pub fn read_instr<T: Iterator<Item=u8>>(mut bytes_iter: T, instruction: &mut Ins
let mut alternate_opcode_map: Option<OpcodeMap> = None;
// use std::intrinsics::unlikely;
let mut prefixes = Prefixes::new(0);
+
+ fn escapes_are_prefixes_actually(prefixes: &mut Prefixes, opc_map: &mut Option<OpcodeMap>) {
+ match opc_map {
+ Some(OpcodeMap::Map66) => {
+ prefixes.set_operand_size();
+ },
+ Some(OpcodeMap::MapF2) => {
+ prefixes.set_repnz();
+ },
+ Some(OpcodeMap::MapF3) => {
+ prefixes.set_rep();
+ },
+ None => {}
+ }
+ *opc_map = None;
+ }
+
let record: OpcodeRecord = loop {
// let operand_code = loop {
match bytes_iter.next() {
@@ -2934,17 +2951,7 @@ pub fn read_instr<T: Iterator<Item=u8>>(mut bytes_iter: T, instruction: &mut Ins
},
};
if rec.0 == Interpretation::Instruction(Opcode::Invalid) {
- match opcode_map {
- OpcodeMap::Map66 => {
- prefixes.set_operand_size();
- },
- OpcodeMap::MapF2 => {
- prefixes.set_repnz();
- },
- OpcodeMap::MapF3 => {
- prefixes.set_rep();
- },
- }
+ escapes_are_prefixes_actually(&mut prefixes, &mut Some(opcode_map));
OPCODE_0F_MAP[opcode_byte as usize]
} else {
rec
@@ -2957,51 +2964,42 @@ pub fn read_instr<T: Iterator<Item=u8>>(mut bytes_iter: T, instruction: &mut Ins
break record;
} else if let Interpretation::Instruction(_) = record.0 {
- match alternate_opcode_map {
- Some(OpcodeMap::Map66) => {
- prefixes.set_operand_size();
- },
- Some(OpcodeMap::MapF2) => {
- prefixes.set_repnz();
- },
- Some(OpcodeMap::MapF3) => {
- prefixes.set_rep();
- },
- None => {}
- }
+ escapes_are_prefixes_actually(&mut prefixes, &mut alternate_opcode_map);
break record;
} else {
+ // some prefix seen after we saw rex, but before the 0f escape or an actual
+ // opcode. so we must forget the rex prefix!
+ // this is to handle sequences like 41660f21cf
+ // where if 660f21 were a valid opcode, 41 would apply a rex.b
+ // prefix, but since 660f21 is not valid, the opcode is interpreted
+ // as 0f21, where 66 is a prefix, which makes 41 not the last
+ // prefix before the opcode, and it's discarded.
+ prefixes.rex_mut().from(0);
+ escapes_are_prefixes_actually(&mut prefixes, &mut alternate_opcode_map);
match b {
0x26 => {
prefixes.set_es();
- alternate_opcode_map = None;
},
0x2e => {
prefixes.set_cs();
- alternate_opcode_map = None;
},
0x36 => {
prefixes.set_ss();
- alternate_opcode_map = None;
},
0x3e => {
prefixes.set_ds();
- alternate_opcode_map = None;
},
0x64 => {
prefixes.set_fs();
- alternate_opcode_map = None;
},
0x65 => {
prefixes.set_gs();
- alternate_opcode_map = None;
},
0x66 => {
alternate_opcode_map = Some(OpcodeMap::Map66);
},
0x67 => {
prefixes.set_address_size();
- alternate_opcode_map = None;
},
0xf0 => {
prefixes.set_lock();
--
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