Support b/bl instructions

modify_arc.go

@@ -54,7 +54,7 @@ func generateTag(tag Tag, tagContents []byte) []byte {
 		byte(tag),
 	}
 	// Tag length
-	contents = append(contents, toLength(len(tagContents))...)
+	contents = append(contents, fourByte(uint32(len(tagContents)))...)
 	// Tag contents
 	contents = append(contents, tagContents...)
 
@@ -120,9 +120,9 @@ func generateOperaCertStore() {
 	file.Write(append(header, caCertTag...))
 }
 
-// toLength returns 4 bytes, suitable for the given length.
+// fourByte returns 4 bytes, suitable for the given length.
-func toLength(value int) []byte {
+func fourByte(value uint32) []byte {
 	holder := make([]byte, 4)
-	binary.BigEndian.PutUint32(holder, uint32(value))
+	binary.BigEndian.PutUint32(holder, value)
 	return holder
 }

patch_custom_ca.go

@@ -36,7 +36,7 @@ func LoadCustomCA() PatchSet {
 				LWZ(R3, 0xac, R28),
 				LWZ(R5, 0xc4, R28),
 				// SSLSetRootCA(ssl_fd, ca_cert, cert_index)
-				Instruction{0x48, 0x01, 0x59, 0x49},
+				BL(0x800acae4, 0x800c242c),
 
 				// Check if successful
 				CMPWI(R3, 0),
@@ -46,7 +46,7 @@ func LoadCustomCA() PatchSet {
 				// Return error -1004 if failed
 				LI(R3, 0xfc14),
 				// b FUNCTION_PROLOG
-				Instruction{0x48, 0x00, 0x00, 0xbc},
+				B(0x800acaf4, 0x800acbb0),
 
 				// ----
 
@@ -56,7 +56,7 @@ func LoadCustomCA() PatchSet {
 				LWZ(R3, 0xac, R28),
 				LWZ(R4, 0xd8, R28),
 				// SSLSetBuiltinRootCA(ssl_fd, cert_index)
-				Instruction{0x48, 0x01, 0x5a, 0x75},
+				BL(0x800acb00, 0x800c2574),
 
 				// Check if successful
 				CMPWI(R3, 0),
@@ -66,7 +66,7 @@ func LoadCustomCA() PatchSet {
 				// Return error -1004 if failed
 				LI(R3, 0xfc14),
 				// b FUNCTION_PROLOG
-				Instruction{0x48, 0x00, 0x00, 0xa0},
+				B(0x800acb10, 0x800acbb0),
 			}.toBytes(),
 			After: Instructions{
 				// Our certificate is present at 0x802e97b8.
@@ -84,7 +84,7 @@ func LoadCustomCA() PatchSet {
 				LWZ(R3, 0xac, R28),
 
 				// SSLSetRootCA(ssl_fd, ca_cert, cert_index)
-				Instruction{0x48, 0x01, 0x59, 0x49},
+				BL(0x800acae4, 0x800c242c),
 
 				// Check for errors
 				CMPWI(R3, 0),
@@ -94,7 +94,7 @@ func LoadCustomCA() PatchSet {
 				// Return error -1004 if failed
 				LI(R3, 0xfc14),
 				// b FUNCTION_PROLOG
-				Instruction{0x48, 0x00, 0x00, 0xbc},
+				B(0x800acaf4, 0x800acbb0),
 
 				// NOP the rest in order to allow execution to continue.
 				NOP(), NOP(), NOP(), NOP(), NOP(), NOP(), NOP(),

powerpc.go

@@ -1,5 +1,15 @@
 package main
 
+// uint24 returns
+func uint24(num uint32) [3]byte {
+	if num > 0x00FFFFFF {
+		panic("invalid uint24 passed")
+	}
+
+	result := fourByte(num)
+	return [3]byte{result[1], result[2], result[3]}
+}
+
 // Instruction represents a 4-byte PowerPC instruction.
 type Instruction [4]byte
 
@@ -102,3 +112,28 @@ func MFSPR() Instruction {
 func STWU(rS Register, rA Register, offset uint16) Instruction {
 	return EncodeInstrDForm(37, rS, rA, offset)
 }
+
+// calcDestination determines the proper offset from a given
+// calling address and target address.
+func calcDestination(from uint, target uint) [3]byte {
+	// TODO(spotlightishere): Handle negative offsets properly
+	offset := target - from
+
+	// Sign-extend by two bytes
+	calc := uint32(offset >> 2)
+	return uint24(calc)
+}
+
+// BL represents the bl PowerPC instruction.
+// It calculates the offset from the given current address and the given
+// target address, saving the current address in the link register. It then branches.
+func BL(current uint, target uint) Instruction {
+	return EncodeInstrIForm(18, calcDestination(current, target), false, true)
+}
+
+// B represents the b PowerPC instruction.
+// It calculates the offset from the given current address
+// and the given target address, and then branches.
+func B(current uint, target uint) Instruction {
+	return EncodeInstrIForm(18, calcDestination(current, target), false, false)
+}

powerpc_encoding.go

@@ -116,6 +116,42 @@ func EncodeInstrDForm(opcode byte, rT Register, rA Register, value uint16) Instr
 	return Instruction{firstInstr, secondInstr, valByte[0], valByte[1]}
 }
 
+// EncodeInstrIForm handles encoding a given opcode, LI, AA and LK.
+// I-form assumes:
+//   - 6 bits for the opcode
+//   - 24 bits for LI
+//   - 1 bit for absolute (AA)
+//   - 1 bit for should store in link register (LK)
+func EncodeInstrIForm(opcode byte, LI [3]byte, AA bool, LK bool) Instruction {
+	opBits := getBits(opcode)
+	liOne := getBits(LI[0])
+	liTwo := getBits(LI[1])
+	liThree := getBits(LI[2])
+
+	instr := [4]Bits{
+		{
+			// We need the upper six bits for our opcode.
+			opBits[2], opBits[3], opBits[4], opBits[5], opBits[6], opBits[7],
+			// Otherwise, copy LI as-is.
+			liOne[0], liOne[1],
+		},
+		{
+			liOne[2], liOne[3], liOne[4], liOne[5], liOne[6], liOne[7], liTwo[0], liTwo[1],
+		},
+		{
+			liTwo[2], liTwo[3], liTwo[4], liTwo[5], liTwo[6], liTwo[7], liThree[0], liThree[1],
+		},
+		{
+			liThree[2], liThree[3], liThree[4], liThree[5], liThree[6], liThree[7],
+			// Copy AA and LK as-is.
+			AA,
+			LK,
+		},
+	}
+
+	return Instruction{instr[0].getByte(), instr[1].getByte(), instr[2].getByte(), instr[3].getByte()}
+}
+
 // twoByte converts a uint16 to two big-endian bytes.
 func twoByte(passed uint16) [2]byte {
 	result := make([]byte, 2)