Scala example source code file (ICodeCheckers.scala)
The Scala ICodeCheckers.scala source code
/* NSC -- new Scala compiler
* Copyright 2005-2011 LAMP/EPFL
* @author Martin Odersky
*/
package scala.tools.nsc
package backend
package icode
import scala.collection.mutable
import scala.collection.mutable.ListBuffer
import scala.tools.nsc.symtab._
abstract class ICodeCheckers {
val global: Global
import global._
/** <p>
* This class performs a set of checks similar to what the bytecode
* verifier does. For each basic block, it checks that:
* </p>
* <ul>
* <li>
* for primitive operations: the type and numer of operands match
* the type of the operation
* </li>
* <li>
* for method calls: the method exists in the type of the receiver
* and the number and type of arguments match the declared type of
* the method.
* </li>
* <li>
* for object creation: the constructor can be called.
* </li>
* <li>
* for load/stores: the field/local/param exists and the type
* of the value matches that of the target.
* </li>
* </ul>
* <p>
* For a control flow graph it checks that type stacks at entry to
* each basic block 'agree':
* </p>
* <ul>
* <li>they have the same length
* <li>there exists a lub for all types at the same position in stacks.
* </ul>
*
* @author Iulian Dragos
* @version 1.0, 06/09/2005
*
* @todo Better checks for <code>MONITOR_ENTER/EXIT
* Better checks for local var initializations
*/
class ICodeChecker {
import icodes._
import opcodes._
var clasz: IClass = _
var method: IMethod = _
var code: Code = _
val in: mutable.Map[BasicBlock, TypeStack] = new mutable.HashMap()
val out: mutable.Map[BasicBlock, TypeStack] = new mutable.HashMap()
val emptyStack = new TypeStack() {
override def toString = "<empty>"
}
/** The presence of emptyStack means that path has not yet been checked
* (and may not be empty).
*/
def notChecked(ts: TypeStack) = ts eq emptyStack
def initMaps(bs: Seq[BasicBlock]): Unit = {
in.clear()
out.clear()
bs foreach { b =>
in(b) = emptyStack
out(b) = emptyStack
}
}
/** A wrapper to route log messages to debug output also.
*/
def logChecker(msg: String) = {
log(msg)
checkerDebug(msg)
}
def checkICodes(): Unit = {
if (settings.verbose.value)
println("[[consistency check at the beginning of phase " + globalPhase.name + "]]")
classes.values foreach check
}
private def posStr(p: Position) =
if (p.isDefined) p.line.toString else "<??>"
private def indent(s: String, spaces: Int): String = indent(s, " " * spaces)
private def indent(s: String, prefix: String): String = {
val lines = s split "\\n"
lines map (prefix + _) mkString "\n"
}
/** Only called when m1 < m2, so already known that (m1 ne m2).
*/
private def isConfict(m1: IMember, m2: IMember, canOverload: Boolean) = (
(m1.symbol.name == m2.symbol.name) &&
(!canOverload || (m1.symbol.tpe =:= m2.symbol.tpe))
)
def check(cls: IClass) {
logChecker("\n<<-- Checking class " + cls + " -->>")
clasz = cls
for (f1 <- cls.fields ; f2 <- cls.fields ; if f1 < f2)
if (isConfict(f1, f2, false))
icodeError("Repetitive field name: " + f1.symbol.fullName)
for (m1 <- cls.methods ; m2 <- cls.methods ; if m1 < m2)
if (isConfict(m1, m2, true))
icodeError("Repetitive method: " + m1.symbol.fullName)
clasz.methods foreach check
}
def check(m: IMethod) {
logChecker("\n<< Checking method " + m.symbol.name + " >>")
method = m
if (!m.isAbstractMethod)
check(m.code)
}
def check(c: Code) {
val worklist = new ListBuffer[BasicBlock]
def append(elems: List[BasicBlock]) =
worklist ++= (elems filterNot (worklist contains _))
code = c
worklist += c.startBlock
initMaps(c.blocks)
while (worklist.nonEmpty) {
val block = worklist remove 0
val output = check(block, in(block))
if (output != out(block) || notChecked(out(block))) {
if (block.successors.nonEmpty)
logChecker("** Output change for %s: %s -> %s".format(block, out(block), output))
out(block) = output
append(block.successors)
block.successors foreach meet
}
}
}
/**
* Apply the meet operator of the stack lattice on bl's predecessors.
* :-). Compute the input to bl by checking that all stacks have the
* same length, and taking the lub of types at the same positions.
*/
def meet(bl: BasicBlock) {
val preds = bl.predecessors
def hasNothingType(s: TypeStack) = s.nonEmpty && (s.head == NothingReference)
def hasNullType(s: TypeStack) = s.nonEmpty && (s.head == NullReference)
/** XXX workaround #1: one stack empty, the other has BoxedUnit.
* One example where this arises is:
*
* def f(b: Boolean): Unit = synchronized { if (b) () }
*/
def allUnits(s: TypeStack) = s.types forall (_ == BoxedUnitReference)
def ifAthenB[T](f: T => Boolean): PartialFunction[(T, T), T] = {
case (x1, x2) if f(x1) => x2
case (x1, x2) if f(x2) => x1
}
/** XXX workaround #2: different stacks heading into an exception
* handler which will clear them anyway. Examples where it arises:
*
* var bippy: Int = synchronized { if (b) 5 else 10 }
*/
def isHandlerBlock() = bl.exceptionHandlerStart
def meet2(s1: TypeStack, s2: TypeStack): TypeStack = {
def workaround(msg: String) = {
checkerDebug(msg + ": " + method + " at block " + bl)
checkerDebug(" s1: " + s1)
checkerDebug(" s2: " + s2)
new TypeStack()
}
def incompatibleString = (
"Incompatible stacks: " + s1 + " and " + s2 + " in " + method + " at entry to block " + bl.label + ":\n" +
indent(bl.predContents, "// ") +
indent(bl.succContents, "// ") +
indent(bl.blockContents, "// ")
)
val f: ((TypeStack, TypeStack)) => TypeStack = {
ifAthenB(notChecked) orElse ifAthenB(hasNothingType) orElse {
case (s1: TypeStack, s2: TypeStack) =>
if (s1.length != s2.length) {
if (allUnits(s1) && allUnits(s2))
workaround("Ignoring mismatched boxed units")
else if (isHandlerBlock)
workaround("Ignoring mismatched stacks entering exception handler")
else
throw new CheckerException(incompatibleString)
}
else {
val newStack = new TypeStack((s1.types, s2.types).zipped map lub)
if (newStack.isEmpty || s1.types == s2.types) () // not interesting to report
else checkerDebug("Checker created new stack:\n (%s, %s) => %s".format(s1, s2, newStack))
newStack
}
}
}
f((s1, s2))
}
if (preds.nonEmpty) {
in(bl) = (preds map out.apply) reduceLeft meet2;
log("Input changed for block: " + bl +" to: " + in(bl));
}
}
private var instruction: Instruction = null
private var basicBlock: BasicBlock = null
private var stringConcatDepth = 0
private def stringConcatIndent() = " " * stringConcatDepth
private def currentInstrString: String = {
val (indent, str) = this.instruction match {
case CALL_PRIMITIVE(StartConcat) =>
val x = stringConcatIndent()
stringConcatDepth += 1
(x, "concat(")
case CALL_PRIMITIVE(EndConcat) =>
if (stringConcatDepth > 0) {
stringConcatDepth -= 1
(stringConcatIndent(), ") // end concat")
}
else ("", "")
case _ =>
(stringConcatIndent(), this.instruction match {
case CALL_PRIMITIVE(StringConcat(el)) => "..."
case null => "null"
case cm @ CALL_METHOD(_, _) => if (clasz.symbol == cm.hostClass) cm.toShortString else cm.toString
case x => x.toString
})
}
indent + str
}
/** A couple closure creators to reduce noise in the output: when multiple
* items are pushed or popped, this lets us print something short and sensible
* for those beyond the first.
*/
def mkInstrPrinter(f: Int => String): () => String = {
var counter = -1
val indent = stringConcatIndent()
() => {
counter += 1
if (counter == 0) currentInstrString
else indent + f(counter)
}
}
def defaultInstrPrinter: () => String = mkInstrPrinter(_ => "\"\"\"")
/**
* Check the basic block to be type correct and return the
* produced type stack.
*/
def check(b: BasicBlock, initial: TypeStack): TypeStack = {
this.basicBlock = b
logChecker({
val prefix = "** Checking " + b.fullString
if (initial.isEmpty) prefix
else prefix + " with initial stack " + initial.types.mkString("[", ", ", "]")
})
var stack = new TypeStack(initial)
def checkStack(len: Int) {
if (stack.length < len)
ICodeChecker.this.icodeError("Expected at least " + len + " elements on the stack", stack)
}
def sizeString(push: Boolean) = {
val arrow = if (push) "-> " else "<- "
val sp = " " * stack.length
sp + stack.length + arrow
}
def printStackString(isPush: Boolean, value: TypeKind, instrString: String) = {
val pushString = if (isPush) "+" else "-"
val posString = posStr(this.instruction.pos)
checkerDebug("%-70s %-4s %s %s".format(sizeString(isPush) + value, posString, pushString, instrString))
}
def _popStack: TypeKind = {
if (stack.isEmpty) {
icodeError("Popped empty stack in " + b.fullString + ", throwing a Unit")
return UNIT
}
stack.pop
}
def popStackN(num: Int, instrFn: () => String = defaultInstrPrinter) = {
List.range(0, num) map { _ =>
val res = _popStack
printStackString(false, res, instrFn())
res
}
}
def pushStackN(xs: Seq[TypeKind], instrFn: () => String) = {
xs foreach { x =>
stack push x
printStackString(true, x, instrFn())
}
}
def popStack = { checkStack(1) ; (popStackN(1): @unchecked) match { case List(x) => x } }
def popStack2 = { checkStack(2) ; (popStackN(2): @unchecked) match { case List(x, y) => (x, y) } }
def popStack3 = { checkStack(3) ; (popStackN(3): @unchecked) match { case List(x, y, z) => (x, y, z) } }
/** Called by faux instruction LOAD_EXCEPTION to wipe out the stack. */
def clearStack() = {
if (stack.nonEmpty)
logChecker("Wiping out the " + stack.length + " element stack for exception handler: " + stack)
1 to stack.length foreach (_ => popStack)
}
def pushStack(xs: TypeKind*): Unit = {
pushStackN(xs filterNot (_ == UNIT), defaultInstrPrinter)
}
def typeError(k1: TypeKind, k2: TypeKind) {
icodeError("\n expected: " + k1 + "\n found: " + k2)
}
def isSubtype(k1: TypeKind, k2: TypeKind) = (k1 <:< k2) || {
import platform.isMaybeBoxed
(k1, k2) match {
case (REFERENCE(_), REFERENCE(_)) if k1.isInterfaceType || k2.isInterfaceType =>
logChecker("Considering %s <:< %s because at least one is an interface".format(k1, k2))
true
case (REFERENCE(cls1), REFERENCE(cls2)) if isMaybeBoxed(cls1) || isMaybeBoxed(cls2) =>
logChecker("Considering %s <:< %s because at least one might be a boxed primitive".format(cls1, cls2))
true
case _ =>
false
}
}
/** Return true if k1 is a subtype of any of the following types,
* according to the somewhat relaxed subtyping standards in effect here.
*/
def isOneOf(k1: TypeKind, kinds: TypeKind*) = kinds exists (k => isSubtype(k1, k))
def subtypeTest(k1: TypeKind, k2: TypeKind): Unit =
if (isSubtype(k1, k2)) ()
else typeError(k2, k1)
for (instr <- b) {
this.instruction = instr
def checkLocal(local: Local): Unit = {
method lookupLocal local.sym.name getOrElse {
icodeError(" " + local + " is not defined in method " + method)
}
}
def checkField(obj: TypeKind, field: Symbol): Unit = obj match {
case REFERENCE(sym) =>
if (sym.info.member(field.name) == NoSymbol)
icodeError(" " + field + " is not defined in class " + clasz);
case _ =>
icodeError(" expected reference type, but " + obj + " found");
}
/** Checks that tpe is a subtype of one of the allowed types */
def checkType(tpe: TypeKind, allowed: TypeKind*) = (
if (allowed exists (k => isSubtype(tpe, k))) ()
else icodeError(tpe + " is not one of: " + allowed.mkString("{ ", ", ", " }"))
)
def checkNumeric(tpe: TypeKind) =
checkType(tpe, BYTE, CHAR, SHORT, INT, LONG, FLOAT, DOUBLE)
/** Checks that the 2 topmost elements on stack are of the
* kind TypeKind.
*/
def checkBinop(kind: TypeKind) {
val (a, b) = popStack2
checkType(a, kind)
checkType(b, kind)
}
/** Check that arguments on the stack match method params. */
def checkMethodArgs(method: Symbol) {
val params = method.info.paramTypes
checkStack(params.length)
(
popStackN(params.length, mkInstrPrinter(num => "<arg" + num + ">")),
params.reverse map toTypeKind).zipped foreach ((x, y) => checkType(x, y)
)
}
/** Checks that the object passed as receiver has a method
* <code>method and that it is callable from the current method.
*
* @param receiver ...
* @param method ...
*/
def checkMethod(receiver: TypeKind, method: Symbol) =
receiver match {
case REFERENCE(sym) =>
checkBool(sym.info.member(method.name) != NoSymbol,
"Method " + method + " does not exist in " + sym.fullName);
if (method.isPrivate)
checkBool(method.owner == clasz.symbol,
"Cannot call private method of " + method.owner.fullName
+ " from " + clasz.symbol.fullName);
else if (method.isProtected) {
val isProtectedOK = (
(clasz.symbol isSubClass method.owner) ||
(clasz.symbol.typeOfThis.typeSymbol isSubClass method.owner) // see pos/bug780.scala
)
checkBool(isProtectedOK,
"Cannot call protected method of " + method.owner.fullName
+ " from " + clasz.symbol.fullName);
}
case ARRAY(_) =>
checkBool(receiver.toType.member(method.name) != NoSymbol,
"Method " + method + " does not exist in " + receiver)
case t =>
icodeError("Not a reference type: " + t)
}
def checkBool(cond: Boolean, msg: String) =
if (!cond) icodeError(msg)
if (settings.debug.value) {
log("PC: " + instr)
log("stack: " + stack)
log("================")
}
instr match {
case THIS(clasz) =>
pushStack(toTypeKind(clasz.tpe))
case CONSTANT(const) =>
pushStack(toTypeKind(const.tpe))
case LOAD_ARRAY_ITEM(kind) =>
popStack2 match {
case (INT, ARRAY(elem)) =>
subtypeTest(elem, kind)
pushStack(elem)
case (a, b) =>
icodeError(" expected and INT and a array reference, but " +
a + ", " + b + " found");
}
case LOAD_LOCAL(local) =>
checkLocal(local)
pushStack(local.kind)
case LOAD_FIELD(field, isStatic) =>
// the symbol's owner should contain it's field, but
// this is already checked by the type checker, no need
// to redo that here
if (isStatic) ()
else checkField(popStack, field)
pushStack(toTypeKind(field.tpe))
case LOAD_MODULE(module) =>
checkBool((module.isModule || module.isModuleClass),
"Expected module: " + module + " flags: " + Flags.flagsToString(module.flags));
pushStack(toTypeKind(module.tpe));
case STORE_THIS(kind) =>
val actualType = popStack
if (actualType.isReferenceType) subtypeTest(actualType, kind)
else icodeError("Expected this reference but found: " + actualType)
case STORE_ARRAY_ITEM(kind) =>
popStack3 match {
case (k, INT, ARRAY(elem)) =>
subtypeTest(k, kind)
subtypeTest(k, elem)
case (a, b, c) =>
icodeError(" expected and array reference, and int and " + kind +
" but " + a + ", " + b + ", " + c + " found");
}
case STORE_LOCAL(local) =>
checkLocal(local)
val actualType = popStack
if (local.kind != NullReference)
subtypeTest(actualType, local.kind)
case STORE_FIELD(field, true) => // static
val fieldType = toTypeKind(field.tpe)
val actualType = popStack
subtypeTest(actualType, fieldType)
case STORE_FIELD(field, false) => // not static
val (value, obj) = popStack2
checkField(obj, field)
val fieldType = toTypeKind(field.tpe)
if (fieldType == NullReference) ()
else subtypeTest(value, fieldType)
case CALL_PRIMITIVE(primitive) =>
checkStack(instr.consumed)
primitive match {
case Negation(kind) =>
checkType(kind, BOOL, BYTE, CHAR, SHORT, INT, LONG, FLOAT, DOUBLE)
checkType(popStack, kind)
pushStack(kind)
case Test(op, kind, zero) =>
if (zero) checkType(popStack, kind)
else checkBinop(kind)
pushStack(BOOL)
case Comparison(op, kind) =>
checkNumeric(kind)
checkBinop(kind)
pushStack(INT)
case Arithmetic(op, kind) =>
checkNumeric(kind)
if (op == NOT)
checkType(popStack, kind)
else
checkBinop(kind)
pushStack(kind)
case Logical(op, kind) =>
checkType(kind, BOOL, BYTE, CHAR, SHORT, INT, LONG)
checkBinop(kind)
pushStack(kind)
case Shift(op, kind) =>
checkType(kind, BYTE, CHAR, SHORT, INT, LONG)
val (a, b) = popStack2
checkType(a, INT)
checkType(b, kind)
pushStack(kind)
case Conversion(src, dst) =>
checkNumeric(src)
checkNumeric(dst)
checkType(popStack, src)
pushStack(dst)
case ArrayLength(kind) =>
popStack match {
case ARRAY(elem) => checkType(elem, kind)
case arr => icodeError(" array reference expected, but " + arr + " found")
}
pushStack(INT)
case StartConcat =>
pushStack(ConcatClass)
case EndConcat =>
checkType(popStack, ConcatClass)
pushStack(StringReference)
case StringConcat(el) =>
checkType(popStack, el)
checkType(popStack, ConcatClass)
pushStack(ConcatClass)
}
case CALL_METHOD(method, style) =>
// PP to ID: I moved the if (!method.isConstructor) check to cover all
// the styles to address checker failure. Can you confirm if the change
// was correct? If I remember right it's a matter of whether some brand
// of supercall should leave a value on the stack, and I know there is some
// trickery performed elsewhere regarding this.
val paramCount = method.info.paramTypes.length match {
case x if style.hasInstance => x + 1
case x => x
}
if (style == Static(true))
checkBool(method.isPrivate || method.isConstructor, "Static call to non-private method.")
checkStack(paramCount)
checkMethodArgs(method)
if (style.hasInstance)
checkMethod(popStack, method)
if (!method.isConstructor)
pushStack(toTypeKind(method.info.resultType))
case NEW(kind) =>
pushStack(kind)
case CREATE_ARRAY(elem, dims) =>
checkStack(dims)
stack.pop(dims) foreach (checkType(_, INT))
pushStack(ARRAY(elem))
case IS_INSTANCE(tpe) =>
val ref = popStack
checkBool(!ref.isValueType, "IS_INSTANCE on primitive type: " + ref)
checkBool(!tpe.isValueType, "IS_INSTANCE on primitive type: " + tpe)
pushStack(BOOL)
case CHECK_CAST(tpe) =>
val ref = popStack
checkBool(!ref.isValueType, "CHECK_CAST to primitive type: " + ref)
checkBool(!tpe.isValueType, "CHECK_CAST to primitive type: " + tpe)
pushStack(tpe)
case SWITCH(tags, labels) =>
checkType(popStack, INT)
checkBool(tags.length == labels.length - 1,
"The number of tags and labels does not coincide.")
checkBool(labels forall (b => code.blocks contains b),
"Switch target cannot be found in code.")
case JUMP(whereto) =>
checkBool(code.blocks contains whereto,
"Jump to non-existant block " + whereto)
case CJUMP(success, failure, cond, kind) =>
checkBool(code.blocks contains success,
"Jump to non-existant block " + success)
checkBool(code.blocks contains failure,
"Jump to non-existant block " + failure)
checkBinop(kind)
case CZJUMP(success, failure, cond, kind) =>
checkBool(code.blocks contains success,
"Jump to non-existant block " + success)
checkBool(code.blocks contains failure,
"Jump to non-existant block " + failure)
checkType(popStack, kind)
case RETURN(UNIT) => ()
case RETURN(kind) =>
val top = popStack
if (kind.isValueType) checkType(top, kind)
else checkBool(!top.isValueType, "" + kind + " is a reference type, but " + top + " is not");
case THROW(clasz) =>
checkType(popStack, toTypeKind(clasz.tpe))
pushStack(NothingReference)
case DROP(kind) =>
checkType(popStack, kind)
case DUP(kind) =>
val top = popStack
checkType(top, kind)
pushStack(top)
pushStack(top)
case MONITOR_ENTER() =>
checkBool(popStack.isReferenceType, "MONITOR_ENTER on non-reference type")
case MONITOR_EXIT() =>
checkBool(popStack.isReferenceType, "MONITOR_EXIT on non-reference type")
case BOX(kind) =>
checkType(popStack, kind)
pushStack(REFERENCE(definitions.boxedClass(kind.toType.typeSymbol)))
case UNBOX(kind) =>
popStack
pushStack(kind)
case LOAD_EXCEPTION(clasz) =>
clearStack()
pushStack(REFERENCE(clasz))
case SCOPE_ENTER(_) | SCOPE_EXIT(_) =>
()
case _ =>
abort("Unknown instruction: " + instr)
}
}
stack
}
//////////////// Error reporting /////////////////////////
def icodeError(msg: String) {
ICodeCheckers.this.global.globalError(
"!! ICode checker fatality in " + method +
"\n at: " + basicBlock.fullString +
"\n error message: " + msg
)
}
def icodeError(msg: String, stack: TypeStack) {
icodeError(msg + "\n type stack: " + stack)
}
}
}
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