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ProgramBuilder.swift
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ProgramBuilder.swift
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// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
/// Builds programs.
///
/// This provides methods for constructing and appending random
/// instances of the different kinds of operations in a program.
public class ProgramBuilder {
/// The fuzzer instance for which this builder is active.
public let fuzzer: Fuzzer
/// The code and type information of the program that is being constructed.
private var code = Code()
public var types = ProgramTypes()
/// Comments for the program that is being constructed.
private var comments = ProgramComments()
/// The parent program for the program being constructed.
private let parent: Program?
public enum Mode {
/// In this mode, the builder will try as hard as possible to generate semantically valid code.
/// However, the generated code is likely not as diverse as in aggressive mode.
case conservative
/// In this mode, the builder tries to generate more diverse code. However, the generated
/// code likely has a lower probability of being semantically correct.
case aggressive
}
/// The mode of this builder
public var mode: Mode
/// Whether to perform splicing as part of the code generation.
public var performSplicingDuringCodeGeneration = true
public var context: Context {
return contextAnalyzer.context
}
/// Counter to quickly determine the next free variable.
private var numVariables = 0
/// Property names and integer values previously seen in the current program.
private var seenPropertyNames = Set<String>()
private var seenIntegers = Set<Int64>()
private var seenFloats = Set<Double>()
/// Keep track of existing variables containing known values. For the reuseOrLoadX APIs.
/// Important: these will contain variables that are no longer in scope. As such, they generally
/// have to be used in combination with the scope analyzer.
private var loadedBuiltins = VariableMap<String>()
private var loadedIntegers = VariableMap<Int64>()
private var loadedFloats = VariableMap<Double>()
/// Various analyzers for the current program.
private var scopeAnalyzer = ScopeAnalyzer()
private var contextAnalyzer = ContextAnalyzer()
/// Abstract interpreter to computer type information.
private var interpreter: AbstractInterpreter?
/// During code generation, contains the minimum number of remaining instructions
/// that should still be generated.
private var currentCodegenBudget = 0
/// Whether there are any variables currently in scope.
public var hasVisibleVariables: Bool {
return scopeAnalyzer.visibleVariables.count > 0
}
/// Constructs a new program builder for the given fuzzer.
init(for fuzzer: Fuzzer, parent: Program?, interpreter: AbstractInterpreter?, mode: Mode) {
self.fuzzer = fuzzer
self.interpreter = interpreter
self.mode = mode
self.parent = parent
}
/// Resets this builder.
public func reset() {
numVariables = 0
seenPropertyNames.removeAll()
seenIntegers.removeAll()
seenFloats.removeAll()
loadedBuiltins.removeAll()
loadedIntegers.removeAll()
loadedFloats.removeAll()
code.removeAll()
types = ProgramTypes()
scopeAnalyzer = ScopeAnalyzer()
contextAnalyzer = ContextAnalyzer()
interpreter?.reset()
currentCodegenBudget = 0
}
/// Finalizes and returns the constructed program, then resets this builder so it can be reused for building another program.
public func finalize() -> Program {
assert(openFunctions.isEmpty)
let program = Program(code: code, parent: parent, types: types, comments: comments)
// TODO set type status to something meaningful?
reset()
return program
}
/// Prints the current program as FuzzIL code to stdout. Useful for debugging.
public func dumpCurrentProgram() {
print(FuzzILLifter().lift(code))
}
/// Returns the index of the next instruction added to the program. This is equal to the current size of the program.
public func indexOfNextInstruction() -> Int {
return code.count
}
/// Add a trace comment to the currently generated program at the current position.
/// This is only done if history inspection is enabled.
public func trace(_ commentGenerator: @autoclosure () -> String) {
if fuzzer.config.inspection.contains(.history) {
// Use an autoclosure here so that template strings are only evaluated when they are needed.
comments.add(commentGenerator(), at: .instruction(code.count))
}
}
/// Add a trace comment at the start of the currently generated program.
/// This is only done if history inspection is enabled.
public func traceHeader(_ commentGenerator: @autoclosure () -> String) {
if fuzzer.config.inspection.contains(.history) {
comments.add(commentGenerator(), at: .header)
}
}
/// Generates a random integer for the current program context.
public func genInt() -> Int64 {
// Either pick a previously seen integer or generate a random one
if probability(0.2) && seenIntegers.count >= 2 {
return chooseUniform(from: seenIntegers)
} else {
return withEqualProbability({
chooseUniform(from: self.fuzzer.environment.interestingIntegers)
}, {
Int64.random(in: -0x100000000...0x100000000)
})
}
}
/// Generates a random regex pattern.
public func genRegExp() -> String {
// Generate a "base" regexp
var regex = ""
let desiredLength = Int.random(in: 1...4)
while regex.count < desiredLength {
regex += withEqualProbability({
String.random(ofLength: 1)
}, {
chooseUniform(from: self.fuzzer.environment.interestingRegExps)
})
}
// Now optionally concatenate with another regexp
if probability(0.3) {
regex += genRegExp()
}
// Or add a quantifier, if there is not already a quantifier in the last position.
if probability(0.2) && !self.fuzzer.environment.interestingRegExpQuantifiers.contains(String(regex.last!)) {
regex += chooseUniform(from: self.fuzzer.environment.interestingRegExpQuantifiers)
}
// Or wrap in brackets
if probability(0.1) {
withEqualProbability({
// optionally invert the character set
if probability(0.2) {
regex = "^" + regex
}
regex = "[" + regex + "]"
}, {
regex = "(" + regex + ")"
})
}
return regex
}
/// Generates a random set of RegExpFlags
public func genRegExpFlags() -> RegExpFlags {
return RegExpFlags.random()
}
/// Generates a random index value for the current program context.
public func genIndex() -> Int64 {
return genInt()
}
/// Generates a random integer for the current program context.
public func genFloat() -> Double {
// TODO improve this
if probability(0.2) && seenFloats.count >= 2 {
return chooseUniform(from: seenFloats)
} else {
return withEqualProbability({
chooseUniform(from: self.fuzzer.environment.interestingFloats)
}, {
Double.random(in: -1000000...1000000)
})
}
}
/// Generates a random string value for the current program context.
public func genString() -> String {
return withEqualProbability({
self.genPropertyNameForRead()
}, {
chooseUniform(from: self.fuzzer.environment.interestingStrings)
}, {
String.random(ofLength: 10)
}, {
String(chooseUniform(from: self.fuzzer.environment.interestingIntegers))
})
}
/// Generates a random builtin name for the current program context.
public func genBuiltinName() -> String {
return chooseUniform(from: fuzzer.environment.builtins)
}
/// Generates a random property name for the current program context.
public func genPropertyNameForRead() -> String {
if probability(0.15) && seenPropertyNames.count >= 2 {
return chooseUniform(from: seenPropertyNames)
} else {
return chooseUniform(from: fuzzer.environment.readPropertyNames)
}
}
/// Generates a random property name for the current program context.
public func genPropertyNameForWrite() -> String {
if probability(0.15) && seenPropertyNames.count >= 2 {
return chooseUniform(from: seenPropertyNames)
} else {
return chooseUniform(from: fuzzer.environment.writePropertyNames)
}
}
/// Generates a random method name for the current program context.
public func genMethodName() -> String {
return chooseUniform(from: fuzzer.environment.methodNames)
}
///
/// Access to variables.
///
/// Returns a random variable.
public func randVar(excludeInnermostScope: Bool = false) -> Variable {
assert(hasVisibleVariables)
return randVarInternal(excludeInnermostScope: excludeInnermostScope)!
}
/// Returns a random variable of the given type.
///
/// In conservative mode, this function fails unless it finds a matching variable.
/// In aggressive mode, this function will also return variables that have unknown type, and may, if no matching variables are available, return variables of any type.
///
/// In certain cases, for example in the InputMutator, it might be required to exclude variables from the innermost scopes, which can be achieved by passing excludeInnermostScope: true.
public func randVar(ofType type: Type, excludeInnermostScope: Bool = false) -> Variable? {
var wantedType = type
// As query/input type, .unknown is treated as .anything.
// This for example simplifies code that is attempting to replace a given variable with another one with a "compatible" type.
// If the real type of the replaced variable is unknown, it doesn't make sense to search for another variable of unknown type, so just use .anything.
if wantedType.Is(.unknown) {
wantedType = .anything
}
if mode == .aggressive {
wantedType |= .unknown
}
if let v = randVarInternal(filter: { self.type(of: $0).Is(wantedType) }, excludeInnermostScope: excludeInnermostScope) {
return v
}
// Didn't find a matching variable. If we are in aggressive mode, we now simply return a random variable.
if mode == .aggressive {
return randVar()
}
// Otherwise, we give up
return nil
}
/// Returns a random variable of the given type. This is the same as calling randVar in conservative building mode.
public func randVar(ofConservativeType type: Type) -> Variable? {
let oldMode = mode
mode = .conservative
defer { mode = oldMode }
return randVar(ofType: type)
}
/// Returns a random variable satisfying the given constraints or nil if none is found.
func randVarInternal(filter: ((Variable) -> Bool)? = nil, excludeInnermostScope: Bool = false) -> Variable? {
var candidates = [Variable]()
let scopes = excludeInnermostScope ? scopeAnalyzer.scopes.dropLast() : scopeAnalyzer.scopes
// Prefer inner scopes
withProbability(0.75) {
candidates = chooseBiased(from: scopes, factor: 1.25)
if let f = filter {
candidates = candidates.filter(f)
}
}
if candidates.isEmpty {
let visibleVariables = excludeInnermostScope ? scopes.reduce([], +) : scopeAnalyzer.visibleVariables
if let f = filter {
candidates = visibleVariables.filter(f)
} else {
candidates = visibleVariables
}
}
if candidates.isEmpty {
return nil
}
return chooseUniform(from: candidates)
}
/// Type information access.
public func type(of v: Variable) -> Type {
return types.getType(of: v, after: code.lastInstruction.index)
}
public func type(ofProperty property: String) -> Type {
return interpreter?.type(ofProperty: property) ?? .unknown
}
/// Returns the type of the `super` binding at the current position.
public func currentSuperType() -> Type {
return interpreter?.currentSuperType() ?? .unknown
}
public func methodSignature(of methodName: String, on object: Variable) -> FunctionSignature {
return interpreter?.inferMethodSignature(of: methodName, on: object) ?? FunctionSignature.forUnknownFunction
}
public func methodSignature(of methodName: String, on objType: Type) -> FunctionSignature {
return interpreter?.inferMethodSignature(of: methodName, on: objType) ?? FunctionSignature.forUnknownFunction
}
public func setType(ofProperty propertyName: String, to propertyType: Type) {
trace("Setting global property type: \(propertyName) => \(propertyType)")
interpreter?.setType(ofProperty: propertyName, to: propertyType)
}
public func setType(ofVariable variable: Variable, to variableType: Type) {
interpreter?.setType(of: variable, to: variableType)
}
public func setSignature(ofMethod methodName: String, to methodSignature: FunctionSignature) {
trace("Setting global method signature: \(methodName) => \(methodSignature)")
interpreter?.setSignature(ofMethod: methodName, to: methodSignature)
}
// This expands and collects types for arguments in function signatures.
private func prepareArgumentTypes(forSignature signature: FunctionSignature) -> [Type] {
var parameterTypes = signature.inputTypes
var argumentTypes = [Type]()
// "Expand" varargs parameters first
if signature.hasVarargsParameter() {
let varargsParam = parameterTypes.removeLast()
assert(varargsParam.isList)
for _ in 0..<Int.random(in: 0...5) {
parameterTypes.append(varargsParam.removingFlagTypes())
}
}
for var param in parameterTypes {
if param.isOptional {
// It's an optional argument, so stop here in some cases
if probability(0.25) {
break
}
// Otherwise, "unwrap" the optional
param = param.removingFlagTypes()
}
assert(!param.hasFlags)
argumentTypes.append(param)
}
return argumentTypes
}
public func generateCallArguments(for signature: FunctionSignature) -> [Variable] {
let argumentTypes = prepareArgumentTypes(forSignature: signature)
var arguments = [Variable]()
for argumentType in argumentTypes {
if let v = randVar(ofConservativeType: argumentType) {
arguments.append(v)
} else {
let argument = generateVariable(ofType: argumentType)
// make sure, that now after generation we actually have a
// variable of that type available.
assert(randVar(ofType: argumentType) != nil)
arguments.append(argument)
}
}
return arguments
}
public func randCallArguments(for signature: FunctionSignature) -> [Variable]? {
let argumentTypes = prepareArgumentTypes(forSignature: signature)
var arguments = [Variable]()
for argumentType in argumentTypes {
guard let v = randVar(ofType: argumentType) else { return nil }
arguments.append(v)
}
return arguments
}
public func randCallArguments(for function: Variable) -> [Variable]? {
let signature = type(of: function).signature ?? FunctionSignature.forUnknownFunction
return randCallArguments(for: signature)
}
public func generateCallArguments(for function: Variable) -> [Variable] {
let signature = type(of: function).signature ?? FunctionSignature.forUnknownFunction
return generateCallArguments(for: signature)
}
public func randCallArguments(forMethod methodName: String, on object: Variable) -> [Variable]? {
let signature = methodSignature(of: methodName, on: object)
return randCallArguments(for: signature)
}
public func randCallArguments(forMethod methodName: String, on objType: Type) -> [Variable]? {
let signature = methodSignature(of: methodName, on: objType)
return randCallArguments(for: signature)
}
public func randCallArgumentsWithSpreading(n: Int) -> (arguments: [Variable], spreads: [Bool]) {
var arguments: [Variable] = []
var spreads: [Bool] = []
for _ in 0...n {
let val = randVar()
arguments.append(val)
// Prefer to spread values that we know are iterable, as non-iterable values will lead to exceptions ("TypeError: Found non-callable @@iterator")
if type(of: val).Is(.iterable) {
spreads.append(probability(0.9))
} else {
spreads.append(probability(0.1))
}
}
return (arguments, spreads)
}
public func generateCallArguments(forMethod methodName: String, on object: Variable) -> [Variable] {
let signature = methodSignature(of: methodName, on: object)
return generateCallArguments(for: signature)
}
/// Generates a sequence of instructions that generate the desired type.
/// This function can currently generate:
/// - primitive types
/// - arrays
/// - objects of certain types
/// - plain objects with properties that are either generated or selected
/// and methods that are selected from the environment.
/// It currently cannot generate:
/// - methods for objects
func generateVariable(ofType type: Type) -> Variable {
trace("Generating variable of type \(type)")
// Check primitive types
if type.Is(.integer) || type.Is(fuzzer.environment.intType) {
return loadInt(genInt())
}
if type.Is(.float) || type.Is(fuzzer.environment.floatType) {
return loadFloat(genFloat())
}
if type.Is(.string) || type.Is(fuzzer.environment.stringType) {
return loadString(genString())
}
if type.Is(.boolean) || type.Is(fuzzer.environment.booleanType) {
return loadBool(Bool.random())
}
if type.Is(.bigint) || type.Is(fuzzer.environment.bigIntType) {
return loadBigInt(genInt())
}
if type.Is(.function()) {
let signature = type.signature ?? FunctionSignature(withParameterCount: Int.random(in: 2...5), hasRestParam: probability(0.1))
return definePlainFunction(withSignature: signature, isStrict: probability(0.1)) { _ in
generateRecursive()
doReturn(value: randVar())
}
}
if type.Is(.regexp) || type.Is(fuzzer.environment.regExpType) {
return loadRegExp(genRegExp(), genRegExpFlags())
}
assert(type.Is(.object()), "Unexpected type encountered \(type)")
// The variable that we will return.
var obj: Variable
// Fast path for array creation.
if type.Is(fuzzer.environment.arrayType) && probability(0.9) {
let value = randVar()
return createArray(with: Array(repeating: value, count: Int.random(in: 1...5)))
}
if let group = type.group {
// Objects with predefined groups must be constructable through a Builtin exposed by the Environment.
// Normally, that builtin is a .constructor(), but we also allow just a .function() for constructing object.
// This is for example necessary for JavaScript Symbols, as the Symbol builtin is not a constructor.
let constructorType = fuzzer.environment.type(ofBuiltin: group)
assert(constructorType.Is(.function() | .constructor()), "We don't know how to construct \(group)")
assert(constructorType.signature != nil, "We don't know how to construct \(group) (missing signature for constructor)")
assert(constructorType.signature!.outputType.group == group, "We don't know how to construct \(group) (invalid signature for constructor)")
let constructorSignature = constructorType.signature!
let arguments = generateCallArguments(for: constructorSignature)
let constructor = loadBuiltin(group)
if !constructorType.Is(.constructor()) {
obj = callFunction(constructor, withArgs: arguments)
} else {
obj = construct(constructor, withArgs: arguments)
}
} else {
// Either generate a literal or use the store property stuff.
if probability(0.8) { // Do the literal
var initialProperties: [String: Variable] = [:]
// gather properties of the correct types
for prop in type.properties {
var value: Variable?
let type = self.type(ofProperty: prop)
if type != .unknown {
// TODO Here and elsewhere in this function: turn this pattern into a new helper function,
// e.g. reuseOrGenerateVariable(ofType: ...). See also the discussions in
// https://github.com/googleprojectzero/fuzzilli/blob/main/Docs/HowFuzzilliWorks.md#when-to-instantiate
// TODO I don't think we need to use the ofConservativeType version. The regular ofType version should
// be fine since the ProgramTemplates/HybridEngine do the code generation in conservative mode anyway.
value = randVar(ofConservativeType: type) ?? generateVariable(ofType: type)
} else {
if !hasVisibleVariables {
value = loadInt(genInt())
} else {
value = randVar()
}
}
initialProperties[prop] = value
}
// TODO: This should take the method type/signature into account!
_ = type.methods.map { initialProperties[$0] = randVar(ofType: .function()) ?? generateVariable(ofType: .function()) }
obj = createObject(with: initialProperties)
} else { // Do it with storeProperty
obj = construct(loadBuiltin("Object"), withArgs: [])
for method in type.methods {
// TODO: This should take the method type/signature into account!
let methodVar = randVar(ofType: .function()) ?? generateVariable(ofType: .function())
storeProperty(methodVar, as: method, on: obj)
}
// These types might have been defined in the interpreter
for prop in type.properties {
var value: Variable?
let type = self.type(ofProperty: prop)
if type != .unknown {
value = randVar(ofConservativeType: type) ?? generateVariable(ofType: type)
} else {
value = randVar()
}
storeProperty(value!, as: prop, on: obj)
}
}
}
return obj
}
///
/// Adoption of variables from a different program.
/// Required when copying instructions between program.
///
private var varMaps = [VariableMap<Variable>]()
/// Formatted ProgramTypes structure for easier adopting of runtimeTypes
private var runtimeTypesMaps = [[[(Variable, Type)]]]()
/// Prepare for adoption of variables from the given program.
///
/// This sets up a mapping for variables from the given program to the
/// currently constructed one to avoid collision of variable names.
public func beginAdoption(from program: Program) {
varMaps.append(VariableMap())
runtimeTypesMaps.append(program.types.onlyRuntimeTypes().indexedByInstruction(for: program))
}
/// Finishes the most recently started adoption.
public func endAdoption() {
varMaps.removeLast()
runtimeTypesMaps.removeLast()
}
/// Executes the given block after preparing for adoption from the provided program.
public func adopting(from program: Program, _ block: () -> Void) {
beginAdoption(from: program)
block()
endAdoption()
}
/// Maps a variable from the program that is currently configured for adoption into the program being constructed.
public func adopt(_ variable: Variable) -> Variable {
if !varMaps.last!.contains(variable) {
varMaps[varMaps.count - 1][variable] = nextVariable()
}
return varMaps.last![variable]!
}
private func createVariableMapping(from sourceVariable: Variable, to hostVariable: Variable) {
assert(!varMaps.last!.contains(sourceVariable))
varMaps[varMaps.count - 1][sourceVariable] = hostVariable
}
/// Maps a list of variables from the program that is currently configured for adoption into the program being constructed.
public func adopt<Variables: Collection>(_ variables: Variables) -> [Variable] where Variables.Element == Variable {
return variables.map(adopt)
}
private func adoptTypes(at origInstrIndex: Int) {
for (variable, type) in runtimeTypesMaps.last![origInstrIndex] {
// No need to keep unknown type nor type of not adopted variable
if let adoptedVariable = varMaps.last![variable] {
// Unknown runtime types should not be saved in ProgramTypes
assert(type != .unknown)
interpreter?.setType(of: adoptedVariable, to: type)
// We should save this type even if we do not have interpreter
// This way we can use runtime types without interpreter
types.setType(of: adoptedVariable, to: type, after: code.lastInstruction.index, quality: .runtime)
}
}
}
/// Adopts an instruction from the program that is currently configured for adoption into the program being constructed.
public func adopt(_ instr: Instruction, keepTypes: Bool) {
internalAppend(Instruction(instr.op, inouts: adopt(instr.inouts)))
if keepTypes {
adoptTypes(at: instr.index)
}
}
/// Append an instruction at the current position.
public func append(_ instr: Instruction) {
for v in instr.allOutputs {
numVariables = max(v.number + 1, numVariables)
}
internalAppend(instr)
}
/// Append a program at the current position.
///
/// This also renames any variable used in the given program so all variables
/// from the appended program refer to the same values in the current program.
public func append(_ program: Program) {
adopting(from: program) {
for instr in program.code {
adopt(instr, keepTypes: true)
}
}
}
/// Append a splice from another program.
public func splice(from program: Program, at index: Int) {
trace("Splicing instruction \(index) (\(program.code[index].op.name)) from \(program.id)")
beginAdoption(from: program)
let source = program.code
// The slice of the given program that will be inserted into the current program.
var slice = Set<Int>()
// Determine all necessary input instructions for the choosen instruction
// We need special handling for blocks:
// If the choosen instruction is a block instruction then copy the whole block
// If we need an inner output of a block instruction then only copy the block instructions, not the content
// Otherwise copy the whole block including its content
var requiredInputs = VariableSet()
// A Set of variables that have yet to be included in the slice
var remainingInputs = VariableSet()
// A stack of contexts that are required by the instruction in the slice
var requiredContextStack = [Context.empty]
// Helper function to handle context updates when handling block instructions
func handleBlockInstruction(instruction instr: Instruction, shouldAdd: Bool = false){
// When we encounter a block begin:
// 1. We ensure that the context being opened removes at least one required context
// 2. The default context (.script) isn't the only context being removed
// 3. The required context is not empty
if instr.isBlockBegin {
var requiredContext = requiredContextStack.removeLast()
if requiredContext.subtracting(instr.op.contextOpened) != requiredContext && requiredContext.intersection(instr.op.contextOpened) != .script && requiredContext != .empty {
requiredContextStack.append(requiredContext)
if shouldAdd {
add(instr)
}
requiredContext = requiredContextStack.removeLast()
}
requiredContext = requiredContext.subtracting(instr.op.contextOpened)
// If the required context is not a subset of the current stack top, then we have contexts that should be propagated to the current stack top
// We must have at least one context on the stack
if requiredContextStack.count >= 1 {
var currentTop = requiredContextStack.removeLast()
requiredContext = requiredContext.subtracting(currentTop)
if requiredContext != .empty {
currentTop.formUnion(requiredContext)
}
requiredContextStack.append(currentTop)
} else {
requiredContextStack.append(requiredContext)
}
}
if instr.isBlockEnd {
requiredContextStack.append([])
}
}
// Helper function to add a context to the context stack
func addContextRequired(requiredContext: Context) {
var currentContext = requiredContextStack.removeLast()
currentContext.formUnion(requiredContext)
requiredContextStack.append(currentContext)
}
// Helper function to add an instruction, or possibly multiple instruction in the case of blocks, to the slice.
func add(_ instr: Instruction, includeBlockContent: Bool = false) {
guard !slice.contains(instr.index) else { return }
func internalAdd(_ instr: Instruction) {
remainingInputs.subtract(instr.allOutputs)
requiredInputs.formUnion(instr.inputs)
remainingInputs.formUnion(instr.inputs)
addContextRequired(requiredContext: instr.op.requiredContext)
handleBlockInstruction(instruction: instr)
slice.insert(instr.index)
}
if instr.isBlock {
let group = BlockGroup(around: instr, in: source)
let instructions = includeBlockContent ? group.includingContent() : group.excludingContent()
// Instructions within blocks are evaluated in reverse order so that the evaluation is consistent with the caller loop
for instr in instructions.reversed() {
internalAdd(instr)
}
} else {
internalAdd(instr)
}
}
// Compute the slice...
var idx = index
// First, add the selected instruction.
add(source[idx], includeBlockContent: true)
// Then add all instructions that the slice has data dependencies on.
while idx > 0 {
// This is the exit condition from the loop
// We have no remaining inputs to account for and
// There's only one context on the stack which must be a subset of self.context (i.e. context of the host program)
if remainingInputs.isEmpty && requiredContextStack.count == 1 {
let requiredContext = requiredContextStack.last!
if requiredContext.isSubset(of: self.context) {
break
}
}
idx -= 1
let instr = source[idx]
if !requiredInputs.isDisjoint(with: instr.allOutputs) {
let onlyNeedsInnerOutputs = requiredInputs.isDisjoint(with: instr.outputs)
// If we only need inner outputs (e.g. function parameters), then we don't include
// the block's content in the slice. Otherwise we do.
add(instr, includeBlockContent: !onlyNeedsInnerOutputs)
}
// If we perform a potentially mutating operation (such as a property store or a method call)
// on a required variable, then we may decide to keep that instruction as well.
if mode == .conservative || (mode == .aggressive && probability(0.5)) {
if instr.mayMutate(requiredInputs) {
add(instr)
}
}
handleBlockInstruction(instruction: instr, shouldAdd: true)
}
// If, after the loop, the current context does not contain the required context (e.g. because we are just after a BeginSwitch), abort the splicing
let stillRequired = requiredContextStack.removeLast()
guard stillRequired.isSubset(of: self.context) else {
endAdoption()
return
}
// Finally, insert the slice into the current program.
for instr in source {
if slice.contains(instr.index) {
adopt(instr, keepTypes: true)
}
}
endAdoption()
trace("Splicing done")
}
func splice(from program: Program) {
// Pick a starting instruction from the selected program.
// For that, prefer dataflow "sinks" whose outputs are not used for anything else,
// as these are probably the most interesting instructions.
var idx = 0
var counter = 0
repeat {
counter += 1
idx = Int.random(in: 0..<program.size)
// Some instructions are less suited to be the start of a splice. Skip them.
} while counter < 25 && (program.code[idx].isJump || program.code[idx].isBlockEnd || !program.code[idx].hasInputs)
splice(from: program, at: idx)
}
private var openFunctions = [Variable]()
private func callLikelyRecurses(function: Variable) -> Bool {
return openFunctions.contains(function)
}
/// Executes a code generator.
///
/// - Parameter generators: The code generator to run at the current position.
/// - Returns: the number of instructions added by all generators.
public func run(_ generator: CodeGenerator, recursiveCodegenBudget: Int? = nil) {
assert(generator.requiredContext.isSubset(of: context))
if let budget = recursiveCodegenBudget {
currentCodegenBudget = budget
}
var inputs: [Variable] = []
for type in generator.inputTypes {
guard let val = randVar(ofType: type) else { return }
// In conservative mode, attempt to prevent direct recursion to reduce the number of timeouts
// This is a very crude mechanism. It might be worth implementing a more sophisticated one.
if mode == .conservative && type.Is(.function()) && callLikelyRecurses(function: val) { return }
inputs.append(val)
}
self.trace("Executing code generator \(generator.name)")
generator.run(in: self, with: inputs)
self.trace("Code generator finished")
}
private func generateInternal() {
assert(!fuzzer.corpus.isEmpty)
while currentCodegenBudget > 0 {
// There are two modes of code generation:
// 1. Splice code from another program in the corpus
// 2. Pick a CodeGenerator, find or generate matching variables, and execute it
withEqualProbability({
guard self.performSplicingDuringCodeGeneration else { return }
let program = self.fuzzer.corpus.randomElementForSplicing()
self.splice(from: program)
}, {
// We can't run code generators if we don't have any visible variables.
if self.scopeAnalyzer.visibleVariables.isEmpty {
// Generate some variables
self.run(chooseUniform(from: self.fuzzer.trivialCodeGenerators))
assert(!self.scopeAnalyzer.visibleVariables.isEmpty)
}
// Enumerate generators that have the required context
// TODO: To improve performance it may be beneficial to implement a caching mechanism for these results
var availableGenerators: [CodeGenerator] = []
for generator in self.fuzzer.codeGenerators {
if generator.requiredContext.isSubset(of: self.context) {
availableGenerators.append(generator)
}
}
guard !availableGenerators.isEmpty else { return }
// Select a generator at random and run it
let generator = chooseUniform(from: availableGenerators)
self.run(generator)
})
// This effectively limits the size of recursively generated code fragments.
if probability(0.25) {
return
}
}
}
/// Generates random code at the current position.
///
/// Code generation involves executing the configured code generators as well as splicing code from other
/// programs in the corpus into the current one.
public func generate(n: Int = 1) {
currentCodegenBudget = n
while currentCodegenBudget > 0 {
generateInternal()
}
}
/// Called by a code generator to generate more additional code, for example inside a newly created block.
public func generateRecursive() {
// Generate at least one instruction, even if already below budget
if currentCodegenBudget <= 0 {
currentCodegenBudget = 1
}
generateInternal()
}
//
// Variable reuse APIs.
//
// These attempt to find an existing variable containing the desired value.
// If none exist, a new instruction is emitted to create it.
//
// This is generally an O(n) operation in the number of currently visible
// varialbes (~= current size of program). This should be fine since it is
// not too frequently used. Also, this way of implementing it keeps the
// overhead in internalAppend to a minimum, which is probably more important.
public func reuseOrLoadBuiltin(_ name: String) -> Variable {
for v in scopeAnalyzer.visibleVariables {
if let builtin = loadedBuiltins[v], builtin == name {
return v
}
}
return loadBuiltin(name)
}
public func reuseOrLoadInt(_ value: Int64) -> Variable {
for v in scopeAnalyzer.visibleVariables {
if let val = loadedIntegers[v], val == value {
return v
}
}
return loadInt(value)
}
public func reuseOrLoadAnyInt() -> Variable {
// This isn't guaranteed to succeed, but that's probably fine.
let val = seenIntegers.randomElement() ?? genInt()
return reuseOrLoadInt(val)
}
public func reuseOrLoadFloat(_ value: Double) -> Variable {
for v in scopeAnalyzer.visibleVariables {
if let val = loadedFloats[v], val == value {
return v
}
}
return loadFloat(value)
}
public func reuseOrLoadAnyFloat() -> Variable {
let val = seenFloats.randomElement() ?? genFloat()
return reuseOrLoadFloat(val)
}
//