SymbolRewriter.cpp

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//===- SymbolRewriter.cpp - Symbol Rewriter -------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// SymbolRewriter is a LLVM pass which can rewrite symbols transparently within
// existing code.  It is implemented as a compiler pass and is configured via a
// YAML configuration file.
//
// The YAML configuration file format is as follows:
//
// RewriteMapFile := RewriteDescriptors
// RewriteDescriptors := RewriteDescriptor | RewriteDescriptors
// RewriteDescriptor := RewriteDescriptorType ':' '{' RewriteDescriptorFields '}'
// RewriteDescriptorFields := RewriteDescriptorField | RewriteDescriptorFields
// RewriteDescriptorField := FieldIdentifier ':' FieldValue ','
// RewriteDescriptorType := Identifier
// FieldIdentifier := Identifier
// FieldValue := Identifier
// Identifier := [0-9a-zA-Z]+
//
// Currently, the following descriptor types are supported:
//
// - function:          (function rewriting)
//      + Source        (original name of the function)
//      + Target        (explicit transformation)
//      + Transform     (pattern transformation)
//      + Naked         (boolean, whether the function is undecorated)
// - global variable:   (external linkage global variable rewriting)
//      + Source        (original name of externally visible variable)
//      + Target        (explicit transformation)
//      + Transform     (pattern transformation)
// - global alias:      (global alias rewriting)
//      + Source        (original name of the aliased name)
//      + Target        (explicit transformation)
//      + Transform     (pattern transformation)
//
// Note that source and exactly one of [Target, Transform] must be provided
//
// New rewrite descriptors can be created.  Addding a new rewrite descriptor
// involves:
//
//  a) extended the rewrite descriptor kind enumeration
//     (<anonymous>::RewriteDescriptor::RewriteDescriptorType)
//  b) implementing the new descriptor
//     (c.f. <anonymous>::ExplicitRewriteFunctionDescriptor)
//  c) extending the rewrite map parser
//     (<anonymous>::RewriteMapParser::parseEntry)
//
//  Specify to rewrite the symbols using the `-rewrite-symbols` option, and
//  specify the map file to use for the rewriting via the `-rewrite-map-file`
//  option.
//
//===----------------------------------------------------------------------===//
 
#include "llvm/Transforms/Utils/SymbolRewriter.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/ilist.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/IR/Comdat.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalObject.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Regex.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/YAMLParser.h"
#include <memory>
#include <string>
#include <vector>
 
using namespace llvm;
using namespace SymbolRewriter;
 
#define DEBUG_TYPE "symbol-rewriter"
 
static cl::list<std::string> RewriteMapFiles("rewrite-map-file",
                                             cl::desc("Symbol Rewrite Map"),
                                             cl::value_desc("filename"),
                                             cl::Hidden);
 
static void rewriteComdat(Module &M, GlobalObject *GO,
                          const std::string &Source,
                          const std::string &Target) {
  if (Comdat *CD = GO->getComdat()) {
    auto &Comdats = M.getComdatSymbolTable();
 
    Comdat *C = M.getOrInsertComdat(Target);
    C->setSelectionKind(CD->getSelectionKind());
    GO->setComdat(C);
 
    Comdats.erase(Comdats.find(Source));
  }
}
 
namespace {
 
template <RewriteDescriptor::Type DT, typename ValueType,
          ValueType *(Module::*Get)(StringRef) const>
class ExplicitRewriteDescriptor : public RewriteDescriptor {
public:
  const std::string Source;
  const std::string Target;
 
  ExplicitRewriteDescriptor(StringRef S, StringRef T, const bool Naked)
      : RewriteDescriptor(DT),
        Source(std::string(Naked ? StringRef("\01" + S.str()) : S)),
        Target(std::string(T)) {}
 
  bool performOnModule(Module &M) override;
 
  static bool classof(const RewriteDescriptor *RD) {
    return RD->getType() == DT;
  }
};
 
} // end anonymous namespace
 
template <RewriteDescriptor::Type DT, typename ValueType,
          ValueType *(Module::*Get)(StringRef) const>
bool ExplicitRewriteDescriptor<DT, ValueType, Get>::performOnModule(Module &M) {
  bool Changed = false;
  if (ValueType *S = (M.*Get)(Source)) {
    if (GlobalObject *GO = dyn_cast<GlobalObject>(S))
      rewriteComdat(M, GO, Source, Target);
 
    if (Value *T = (M.*Get)(Target))
      S->setValueName(T->getValueName());
    else
      S->setName(Target);
 
    Changed = true;
  }
  return Changed;
}
 
namespace {
 
template <RewriteDescriptor::Type DT, typename ValueType,
          ValueType *(Module::*Get)(StringRef) const,
          iterator_range<typename iplist<ValueType>::iterator>
          (Module::*Iterator)()>
class PatternRewriteDescriptor : public RewriteDescriptor {
public:
  const std::string Pattern;
  const std::string Transform;
 
  PatternRewriteDescriptor(StringRef P, StringRef T)
      : RewriteDescriptor(DT), Pattern(std::string(P)),
        Transform(std::string(T)) {}
 
  bool performOnModule(Module &M) override;
 
  static bool classof(const RewriteDescriptor *RD) {
    return RD->getType() == DT;
  }
};
 
} // end anonymous namespace
 
template <RewriteDescriptor::Type DT, typename ValueType,
          ValueType *(Module::*Get)(StringRef) const,
          iterator_range<typename iplist<ValueType>::iterator>
          (Module::*Iterator)()>
bool PatternRewriteDescriptor<DT, ValueType, Get, Iterator>::
performOnModule(Module &M) {
  bool Changed = false;
  for (auto &C : (M.*Iterator)()) {
    std::string Error;
 
    std::string Name = Regex(Pattern).sub(Transform, C.getName(), &Error);
    if (!Error.empty())
      report_fatal_error(Twine("unable to transforn ") + C.getName() + " in " +
                         M.getModuleIdentifier() + ": " + Error);
 
    if (C.getName() == Name)
      continue;
 
    if (GlobalObject *GO = dyn_cast<GlobalObject>(&C))
      rewriteComdat(M, GO, std::string(C.getName()), Name);
 
    if (Value *V = (M.*Get)(Name))
      C.setValueName(V->getValueName());
    else
      C.setName(Name);
 
    Changed = true;
  }
  return Changed;
}
 
namespace {
 
/// Represents a rewrite for an explicitly named (function) symbol.  Both the
/// source function name and target function name of the transformation are
/// explicitly spelt out.
using ExplicitRewriteFunctionDescriptor =
    ExplicitRewriteDescriptor<RewriteDescriptor::Type::Function, Function,
                              &Module::getFunction>;
 
/// Represents a rewrite for an explicitly named (global variable) symbol.  Both
/// the source variable name and target variable name are spelt out.  This
/// applies only to module level variables.
using ExplicitRewriteGlobalVariableDescriptor =
    ExplicitRewriteDescriptor<RewriteDescriptor::Type::GlobalVariable,
                              GlobalVariable, &Module::getGlobalVariable>;
 
/// Represents a rewrite for an explicitly named global alias.  Both the source
/// and target name are explicitly spelt out.
using ExplicitRewriteNamedAliasDescriptor =
    ExplicitRewriteDescriptor<RewriteDescriptor::Type::NamedAlias, GlobalAlias,
                              &Module::getNamedAlias>;
 
/// Represents a rewrite for a regular expression based pattern for functions.
/// A pattern for the function name is provided and a transformation for that
/// pattern to determine the target function name create the rewrite rule.
using PatternRewriteFunctionDescriptor =
    PatternRewriteDescriptor<RewriteDescriptor::Type::Function, Function,
                             &Module::getFunction, &Module::functions>;
 
/// Represents a rewrite for a global variable based upon a matching pattern.
/// Each global variable matching the provided pattern will be transformed as
/// described in the transformation pattern for the target.  Applies only to
/// module level variables.
using PatternRewriteGlobalVariableDescriptor =
    PatternRewriteDescriptor<RewriteDescriptor::Type::GlobalVariable,
                             GlobalVariable, &Module::getGlobalVariable,
                             &Module::globals>;
 
/// PatternRewriteNamedAliasDescriptor - represents a rewrite for global
/// aliases which match a given pattern.  The provided transformation will be
/// applied to each of the matching names.
using PatternRewriteNamedAliasDescriptor =
    PatternRewriteDescriptor<RewriteDescriptor::Type::NamedAlias, GlobalAlias,
                             &Module::getNamedAlias, &Module::aliases>;
 
} // end anonymous namespace
 
bool RewriteMapParser::parse(const std::string &MapFile,
                             RewriteDescriptorList *DL) {
  ErrorOr<std::unique_ptr<MemoryBuffer>> Mapping =
      MemoryBuffer::getFile(MapFile);
 
  if (!Mapping)
    report_fatal_error(Twine("unable to read rewrite map '") + MapFile +
                       "': " + Mapping.getError().message());
 
  if (!parse(*Mapping, DL))
    report_fatal_error(Twine("unable to parse rewrite map '") + MapFile + "'");
 
  return true;
}
 
bool RewriteMapParser::parse(std::unique_ptr<MemoryBuffer> &MapFile,
                             RewriteDescriptorList *DL) {
  SourceMgr SM;
  yaml::Stream YS(MapFile->getBuffer(), SM);
 
  for (auto &Document : YS) {
    yaml::MappingNode *DescriptorList;
 
    // ignore empty documents
    if (isa<yaml::NullNode>(Document.getRoot()))
      continue;
 
    DescriptorList = dyn_cast<yaml::MappingNode>(Document.getRoot());
    if (!DescriptorList) {
      YS.printError(Document.getRoot(), "DescriptorList node must be a map");
      return false;
    }
 
    for (auto &Descriptor : *DescriptorList)
      if (!parseEntry(YS, Descriptor, DL))
        return false;
  }
 
  return true;
}
 
bool RewriteMapParser::parseEntry(yaml::Stream &YS, yaml::KeyValueNode &Entry,
                                  RewriteDescriptorList *DL) {
  yaml::ScalarNode *Key;
  yaml::MappingNode *Value;
  SmallString<32> KeyStorage;
  StringRef RewriteType;
 
  Key = dyn_cast<yaml::ScalarNode>(Entry.getKey());
  if (!Key) {
    YS.printError(Entry.getKey(), "rewrite type must be a scalar");
    return false;
  }
 
  Value = dyn_cast<yaml::MappingNode>(Entry.getValue());
  if (!Value) {
    YS.printError(Entry.getValue(), "rewrite descriptor must be a map");
    return false;
  }
 
  RewriteType = Key->getValue(KeyStorage);
  if (RewriteType.equals("function"))
    return parseRewriteFunctionDescriptor(YS, Key, Value, DL);
  else if (RewriteType.equals("global variable"))
    return parseRewriteGlobalVariableDescriptor(YS, Key, Value, DL);
  else if (RewriteType.equals("global alias"))
    return parseRewriteGlobalAliasDescriptor(YS, Key, Value, DL);
 
  YS.printError(Entry.getKey(), "unknown rewrite type");
  return false;
}
 
bool RewriteMapParser::
parseRewriteFunctionDescriptor(yaml::Stream &YS, yaml::ScalarNode *K,
                               yaml::MappingNode *Descriptor,
                               RewriteDescriptorList *DL) {
  bool Naked = false;
  std::string Source;
  std::string Target;
  std::string Transform;
 
  for (auto &Field : *Descriptor) {
    yaml::ScalarNode *Key;
    yaml::ScalarNode *Value;
    SmallString<32> KeyStorage;
    SmallString<32> ValueStorage;
    StringRef KeyValue;
 
    Key = dyn_cast<yaml::ScalarNode>(Field.getKey());
    if (!Key) {
      YS.printError(Field.getKey(), "descriptor key must be a scalar");
      return false;
    }
 
    Value = dyn_cast<yaml::ScalarNode>(Field.getValue());
    if (!Value) {
      YS.printError(Field.getValue(), "descriptor value must be a scalar");
      return false;
    }
 
    KeyValue = Key->getValue(KeyStorage);
    if (KeyValue.equals("source")) {
      std::string Error;
 
      Source = std::string(Value->getValue(ValueStorage));
      if (!Regex(Source).isValid(Error)) {
        YS.printError(Field.getKey(), "invalid regex: " + Error);
        return false;
      }
    } else if (KeyValue.equals("target")) {
      Target = std::string(Value->getValue(ValueStorage));
    } else if (KeyValue.equals("transform")) {
      Transform = std::string(Value->getValue(ValueStorage));
    } else if (KeyValue.equals("naked")) {
      std::string Undecorated;
 
      Undecorated = std::string(Value->getValue(ValueStorage));
      Naked = StringRef(Undecorated).lower() == "true" || Undecorated == "1";
    } else {
      YS.printError(Field.getKey(), "unknown key for function");
      return false;
    }
  }
 
  if (Transform.empty() == Target.empty()) {
    YS.printError(Descriptor,
                  "exactly one of transform or target must be specified");
    return false;
  }
 
  // TODO see if there is a more elegant solution to selecting the rewrite
  // descriptor type
  if (!Target.empty())
    DL->push_back(std::make_unique<ExplicitRewriteFunctionDescriptor>(
        Source, Target, Naked));
  else
    DL->push_back(
        std::make_unique<PatternRewriteFunctionDescriptor>(Source, Transform));
 
  return true;
}
 
bool RewriteMapParser::
parseRewriteGlobalVariableDescriptor(yaml::Stream &YS, yaml::ScalarNode *K,
                                     yaml::MappingNode *Descriptor,
                                     RewriteDescriptorList *DL) {
  std::string Source;
  std::string Target;
  std::string Transform;
 
  for (auto &Field : *Descriptor) {
    yaml::ScalarNode *Key;
    yaml::ScalarNode *Value;
    SmallString<32> KeyStorage;
    SmallString<32> ValueStorage;
    StringRef KeyValue;
 
    Key = dyn_cast<yaml::ScalarNode>(Field.getKey());
    if (!Key) {
      YS.printError(Field.getKey(), "descriptor Key must be a scalar");
      return false;
    }
 
    Value = dyn_cast<yaml::ScalarNode>(Field.getValue());
    if (!Value) {
      YS.printError(Field.getValue(), "descriptor value must be a scalar");
      return false;
    }
 
    KeyValue = Key->getValue(KeyStorage);
    if (KeyValue.equals("source")) {
      std::string Error;
 
      Source = std::string(Value->getValue(ValueStorage));
      if (!Regex(Source).isValid(Error)) {
        YS.printError(Field.getKey(), "invalid regex: " + Error);
        return false;
      }
    } else if (KeyValue.equals("target")) {
      Target = std::string(Value->getValue(ValueStorage));
    } else if (KeyValue.equals("transform")) {
      Transform = std::string(Value->getValue(ValueStorage));
    } else {
      YS.printError(Field.getKey(), "unknown Key for Global Variable");
      return false;
    }
  }
 
  if (Transform.empty() == Target.empty()) {
    YS.printError(Descriptor,
                  "exactly one of transform or target must be specified");
    return false;
  }
 
  if (!Target.empty())
    DL->push_back(std::make_unique<ExplicitRewriteGlobalVariableDescriptor>(
        Source, Target,
        /*Naked*/ false));
  else
    DL->push_back(std::make_unique<PatternRewriteGlobalVariableDescriptor>(
        Source, Transform));
 
  return true;
}
 
bool RewriteMapParser::
parseRewriteGlobalAliasDescriptor(yaml::Stream &YS, yaml::ScalarNode *K,
                                  yaml::MappingNode *Descriptor,
                                  RewriteDescriptorList *DL) {
  std::string Source;
  std::string Target;
  std::string Transform;
 
  for (auto &Field : *Descriptor) {
    yaml::ScalarNode *Key;
    yaml::ScalarNode *Value;
    SmallString<32> KeyStorage;
    SmallString<32> ValueStorage;
    StringRef KeyValue;
 
    Key = dyn_cast<yaml::ScalarNode>(Field.getKey());
    if (!Key) {
      YS.printError(Field.getKey(), "descriptor key must be a scalar");
      return false;
    }
 
    Value = dyn_cast<yaml::ScalarNode>(Field.getValue());
    if (!Value) {
      YS.printError(Field.getValue(), "descriptor value must be a scalar");
      return false;
    }
 
    KeyValue = Key->getValue(KeyStorage);
    if (KeyValue.equals("source")) {
      std::string Error;
 
      Source = std::string(Value->getValue(ValueStorage));
      if (!Regex(Source).isValid(Error)) {
        YS.printError(Field.getKey(), "invalid regex: " + Error);
        return false;
      }
    } else if (KeyValue.equals("target")) {
      Target = std::string(Value->getValue(ValueStorage));
    } else if (KeyValue.equals("transform")) {
      Transform = std::string(Value->getValue(ValueStorage));
    } else {
      YS.printError(Field.getKey(), "unknown key for Global Alias");
      return false;
    }
  }
 
  if (Transform.empty() == Target.empty()) {
    YS.printError(Descriptor,
                  "exactly one of transform or target must be specified");
    return false;
  }
 
  if (!Target.empty())
    DL->push_back(std::make_unique<ExplicitRewriteNamedAliasDescriptor>(
        Source, Target,
        /*Naked*/ false));
  else
    DL->push_back(std::make_unique<PatternRewriteNamedAliasDescriptor>(
        Source, Transform));
 
  return true;
}
 
PreservedAnalyses RewriteSymbolPass::run(Module &M, ModuleAnalysisManager &AM) {
  if (!runImpl(M))
    return PreservedAnalyses::all();
 
  return PreservedAnalyses::none();
}
 
bool RewriteSymbolPass::runImpl(Module &M) {
  bool Changed;
 
  Changed = false;
  for (auto &Descriptor : Descriptors)
    Changed |= Descriptor->performOnModule(M);
 
  return Changed;
}
 
void RewriteSymbolPass::loadAndParseMapFiles() {
  const std::vector<std::string> MapFiles(RewriteMapFiles);
  SymbolRewriter::RewriteMapParser Parser;
 
  for (const auto &MapFile : MapFiles)
    Parser.parse(MapFile, &Descriptors);
}