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//===-- FunctionAliasPass.cpp -----------------------------------*- C++ -*-===//
//
// The KLEE Symbolic Virtual Machine
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "Passes.h"
#include "klee/Support/Casting.h"
#include "klee/Support/ErrorHandling.h"
#include "klee/Support/OptionCategories.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Regex.h"
using namespace llvm;
namespace {
cl::list<std::string>
FunctionAlias("function-alias",
cl::desc("Replace functions that match name or regular "
"expression pattern with an alias to the function "
"whose name is given by replacement"),
cl::value_desc("name|pattern>:<replacement"),
cl::cat(klee::ModuleCat));
} // namespace
namespace klee {
bool FunctionAliasPass::runOnModule(Module &M) {
bool modified = false;
assert((M.ifunc_size() == 0) && "Unexpected ifunc");
for (const auto &pair : FunctionAlias) {
bool matchFound = false;
// regex pattern can contain colons, e.g. in character classes,
// but replacement function name cannot
std::size_t lastColon = pair.rfind(':');
if (lastColon == std::string::npos) {
klee_error("function-alias: no replacement given");
}
std::string pattern = pair.substr(0, lastColon);
std::string replacement = pair.substr(lastColon + 1);
if (pattern.empty())
klee_error("function-alias: name or pattern cannot be empty");
if (replacement.empty())
klee_error("function-alias: replacement cannot be empty");
if (pattern == replacement) {
klee_error("function-alias: @%s cannot replace itself", pattern.c_str());
}
// check if replacement function exists
GlobalValue *replacementValue = M.getNamedValue(replacement);
if (!isFunctionOrGlobalFunctionAlias(replacementValue))
klee_error("function-alias: replacement function @%s could not be found",
replacement.c_str());
// directly replace if pattern is not a regex
GlobalValue *match = M.getNamedValue(pattern);
if (isFunctionOrGlobalFunctionAlias(match)) {
if (tryToReplace(match, replacementValue)) {
modified = true;
klee_message("function-alias: replaced @%s with @%s", pattern.c_str(),
replacement.c_str());
continue;
}
}
if (match != nullptr) {
// pattern is not a regex, but no replacement was found
klee_error("function-alias: no (replacable) match for '%s' found",
pattern.c_str());
}
Regex regex(pattern);
std::string error;
if (!regex.isValid(error)) {
klee_error("function-alias: '%s' is not a valid regex: %s",
pattern.c_str(), error.c_str());
}
std::vector<GlobalValue *> matches;
// find matches for regex
for (GlobalValue &global : M.global_values()) {
if (!global.hasName())
continue;
if (!isFunctionOrGlobalFunctionAlias(&global))
continue;
SmallVector<StringRef, 8> matchVec;
bool match = regex.match(global.getName(), &matchVec);
if (match && matchVec[0].str() == global.getName().str()) {
if (global.getName().str() == replacement) {
klee_warning("function-alias: do not replace @%s (matching '%s') "
"with @%s: cannot replace itself",
global.getName().str().c_str(), pattern.c_str(),
replacement.c_str());
continue;
}
matches.push_back(&global);
}
}
// replace all found regex matches
for (GlobalValue *global : matches) {
// name will be invalidated by tryToReplace
std::string name = global->getName().str();
if (tryToReplace(global, replacementValue)) {
modified = true;
matchFound = true;
klee_message("function-alias: replaced @%s (matching '%s') with @%s",
name.c_str(), pattern.c_str(), replacement.c_str());
}
}
if (!matchFound) {
klee_error("function-alias: no (replacable) match for '%s' found",
pattern.c_str());
}
}
return modified;
}
const FunctionType *FunctionAliasPass::getFunctionType(const GlobalValue *gv) {
#if LLVM_VERSION_CODE >= LLVM_VERSION(15, 0)
if (auto *ft = dyn_cast<FunctionType>(gv->getType()))
return ft;
return dyn_cast<FunctionType>(gv->getValueType());
#else
const Type *type = gv->getType();
while (type->isPointerTy())
type = type->getPointerElementType();
return dyn_cast<FunctionType>(type);
#endif
}
bool FunctionAliasPass::checkType(const GlobalValue *match,
const GlobalValue *replacement) {
const FunctionType *MFT = getFunctionType(match);
const FunctionType *RFT = getFunctionType(replacement);
assert(MFT != nullptr && RFT != nullptr);
if (MFT->getReturnType() != RFT->getReturnType()) {
klee_warning("function-alias: @%s could not be replaced with @%s: "
"return type differs",
match->getName().str().c_str(),
replacement->getName().str().c_str());
return false;
}
if (MFT->isVarArg() != RFT->isVarArg()) {
klee_warning("function-alias: @%s could not be replaced with @%s: "
"one has varargs while the other does not",
match->getName().str().c_str(),
replacement->getName().str().c_str());
return false;
}
if (MFT->getNumParams() != RFT->getNumParams()) {
klee_warning("function-alias: @%s could not be replaced with @%s: "
"number of parameters differs",
match->getName().str().c_str(),
replacement->getName().str().c_str());
return false;
}
std::size_t numParams = MFT->getNumParams();
for (std::size_t i = 0; i < numParams; ++i) {
if (MFT->getParamType(i) != RFT->getParamType(i)) {
klee_warning("function-alias: @%s could not be replaced with @%s: "
"parameter types differ",
match->getName().str().c_str(),
replacement->getName().str().c_str());
return false;
}
}
return true;
}
bool FunctionAliasPass::tryToReplace(GlobalValue *match,
GlobalValue *replacement) {
if (!checkType(match, replacement))
return false;
GlobalAlias *alias = GlobalAlias::create("", replacement);
match->replaceAllUsesWith(alias);
alias->takeName(match);
match->eraseFromParent();
return true;
}
bool FunctionAliasPass::isFunctionOrGlobalFunctionAlias(const GlobalValue *gv) {
if (isa_and_nonnull<Function>(gv))
return true;
if (const auto *ga = dyn_cast_or_null<GlobalAlias>(gv)) {
const auto *aliasee = dyn_cast<GlobalValue>(ga->getAliasee());
if (!aliasee) {
// check if GlobalAlias is alias bitcast
const auto *cexpr = dyn_cast<ConstantExpr>(ga->getAliasee());
if (!cexpr || !cexpr->isCast())
return false;
aliasee = dyn_cast<GlobalValue>(cexpr->getOperand(0));
}
return isFunctionOrGlobalFunctionAlias(aliasee);
}
return false;
}
char FunctionAliasPass::ID = 0;
} // namespace klee
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