From 926a37359107e4146f92be485e771934304b9866 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Tue, 8 Mar 2022 15:03:37 -0500
Subject: [PATCH] Extend SIB test, correct decoder.

---
 InstructionSets/x86/Decoder.cpp                     |  3 +--
 InstructionSets/x86/Decoder.hpp                     |  1 -
 OSBindings/Mac/Clock SignalTests/x86DecoderTests.mm | 11 +++++++----
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/InstructionSets/x86/Decoder.cpp b/InstructionSets/x86/Decoder.cpp
index 432ec8507..19b75c4b7 100644
--- a/InstructionSets/x86/Decoder.cpp
+++ b/InstructionSets/x86/Decoder.cpp
@@ -629,7 +629,7 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(con
 			displacement_size_ = sizes[mod];
 			memreg = Source::Indirect;
 
-			if(allow_sib_) {
+			if(address_size_ == AddressSize::b32) {
 				// 32-bit decoding: the range of potential indirections is expanded,
 				// and may segue into obtaining a SIB.
 				sib_ = ScaleIndexBase(0, Source::None, reg_table[rm]);
@@ -931,7 +931,6 @@ template <Model model> void Decoder<model>::set_32bit_protected_mode(bool enable
 		return;
 	}
 
-	allow_sib_ = enabled;
 	if(enabled) {
 		default_address_size_ = address_size_ = AddressSize::b32;
 		default_data_size_ = data_size_ = DataSize::DWord;
diff --git a/InstructionSets/x86/Decoder.hpp b/InstructionSets/x86/Decoder.hpp
index 7c411423e..6c837df2a 100644
--- a/InstructionSets/x86/Decoder.hpp
+++ b/InstructionSets/x86/Decoder.hpp
@@ -196,7 +196,6 @@ template <Model model> class Decoder {
 		DataSize default_data_size_ = DataSize::Word;
 		AddressSize address_size_ = AddressSize::b16;
 		DataSize data_size_ = DataSize::Word;
-		bool allow_sib_ = false;
 
 		/// Resets size capture and all fields with default values.
 		void reset_parsing() {
diff --git a/OSBindings/Mac/Clock SignalTests/x86DecoderTests.mm b/OSBindings/Mac/Clock SignalTests/x86DecoderTests.mm
index 4cc5bdbbe..78f0689f1 100644
--- a/OSBindings/Mac/Clock SignalTests/x86DecoderTests.mm	
+++ b/OSBindings/Mac/Clock SignalTests/x86DecoderTests.mm	
@@ -333,13 +333,16 @@ std::vector<typename InstructionSet::x86::Decoder<model>::InstructionT> decode(c
 - (void)testSIB {
 	const auto instructions = decode<Model::i80386>({
 		// add edx, -0x7d(ebp + eax*2)
-		0x01, 0x54, 0x45, 0x83
+		0x01, 0x54, 0x45, 0x83,
+
+		// add edx, -0x80(si)
+		0x67, 0x01, 0x54, 0x80,
 	}, true);
 
-	XCTAssertEqual(instructions.size(), 1);
+	XCTAssertEqual(instructions.size(), 2);
 	test(instructions[0], DataSize::DWord, Operation::ADD, Source::eDX, ScaleIndexBase(1, Source::eAX, Source::eBP), 0x00, -125);
-	// Noting that a multiplier of 2 is a scale of 1,
-	// since the scale is in log2.
+	test(instructions[1], DataSize::DWord, Operation::ADD, Source::eDX, ScaleIndexBase(Source::eSI), 0x00, -128);
+	XCTAssertEqual(instructions[1].address_size(), AddressSize::b16);
 }
 
 @end