SymbolRewriter.h   [plain text]

//===-- SymbolRewriter.h - Symbol Rewriting Pass ----------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file provides the prototypes and definitions related to the Symbol
// Rewriter pass.
//
// The Symbol Rewriter pass takes a set of rewrite descriptors which define
// transformations for symbol names.  These can be either single name to name
// trnsformation or more broad regular expression based transformations.
//
// All the functions are re-written at the IR level.  The Symbol Rewriter itself
// is exposed as a module level pass.  All symbols at the module level are
// iterated.  For any matching symbol, the requested transformation is applied,
// updating references to it as well (a la RAUW).  The resulting binary will
// only contain the rewritten symbols.
//
// By performing this operation in the compiler, we are able to catch symbols
// that would otherwise not be possible to catch (e.g. inlined symbols).
//
// This makes it possible to cleanly transform symbols without resorting to
// overly-complex macro tricks and the pre-processor.  An example of where this
// is useful is the sanitizers where we would like to intercept a well-defined
// set of functions across the module.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_TRANSFORMS_UTILS_SYMBOL_REWRITER_H
#define LLVM_TRANSFORMS_UTILS_SYMBOL_REWRITER_H

#include "llvm/ADT/ilist.h"
#include "llvm/ADT/ilist_node.h"
#include "llvm/IR/Module.h"

namespace llvm {
class MemoryBuffer;

namespace yaml {
class KeyValueNode;
class MappingNode;
class ScalarNode;
class Stream;
}

namespace SymbolRewriter {
/// The basic entity representing a rewrite operation.  It serves as the base
/// class for any rewrite descriptor.  It has a certain set of specializations
/// which describe a particular rewrite.
///
/// The RewriteMapParser can be used to parse a mapping file that provides the
/// mapping for rewriting the symbols.  The descriptors individually describe
/// whether to rewrite a function, global variable, or global alias.  Each of
/// these can be selected either by explicitly providing a name for the ones to
/// be rewritten or providing a (posix compatible) regular expression that will
/// select the symbols to rewrite.  This descriptor list is passed to the
/// SymbolRewriter pass.
class RewriteDescriptor : public ilist_node<RewriteDescriptor> {
  RewriteDescriptor(const RewriteDescriptor &) = delete;

  const RewriteDescriptor &
  operator=(const RewriteDescriptor &) = delete;

public:
  enum class Type {
    Invalid,        /// invalid
    Function,       /// function - descriptor rewrites a function
    GlobalVariable, /// global variable - descriptor rewrites a global variable
    NamedAlias,     /// named alias - descriptor rewrites a global alias
  };

  virtual ~RewriteDescriptor() {}

  Type getType() const { return Kind; }

  virtual bool performOnModule(Module &M) = 0;

protected:
  explicit RewriteDescriptor(Type T) : Kind(T) {}

private:
  const Type Kind;
};

typedef iplist<RewriteDescriptor> RewriteDescriptorList;

class RewriteMapParser {
public:
  bool parse(const std::string &MapFile, RewriteDescriptorList *Descriptors);

private:
  bool parse(std::unique_ptr<MemoryBuffer> &MapFile, RewriteDescriptorList *DL);
  bool parseEntry(yaml::Stream &Stream, yaml::KeyValueNode &Entry,
                  RewriteDescriptorList *DL);
  bool parseRewriteFunctionDescriptor(yaml::Stream &Stream,
                                      yaml::ScalarNode *Key,
                                      yaml::MappingNode *Value,
                                      RewriteDescriptorList *DL);
  bool parseRewriteGlobalVariableDescriptor(yaml::Stream &Stream,
                                            yaml::ScalarNode *Key,
                                            yaml::MappingNode *Value,
                                            RewriteDescriptorList *DL);
  bool parseRewriteGlobalAliasDescriptor(yaml::Stream &YS, yaml::ScalarNode *K,
                                         yaml::MappingNode *V,
                                         RewriteDescriptorList *DL);
};
}

template <>
struct ilist_traits<SymbolRewriter::RewriteDescriptor>
    : public ilist_default_traits<SymbolRewriter::RewriteDescriptor> {
  mutable ilist_half_node<SymbolRewriter::RewriteDescriptor> Sentinel;

public:
  // createSentinel is used to get a reference to a node marking the end of
  // the list.  Because the sentinel is relative to this instance, use a
  // non-static method.
  SymbolRewriter::RewriteDescriptor *createSentinel() const {
    // since i[p] lists always publicly derive from the corresponding
    // traits, placing a data member in this class will augment the
    // i[p]list.  Since the NodeTy is expected to publicly derive from
    // ilist_node<NodeTy>, there is a legal viable downcast from it to
    // NodeTy.  We use this trick to superpose i[p]list with a "ghostly"
    // NodeTy, which becomes the sentinel.  Dereferencing the sentinel is
    // forbidden (save the ilist_node<NodeTy>) so no one will ever notice
    // the superposition.
    return static_cast<SymbolRewriter::RewriteDescriptor *>(&Sentinel);
  }
  void destroySentinel(SymbolRewriter::RewriteDescriptor *) {}

  SymbolRewriter::RewriteDescriptor *provideInitialHead() const {
    return createSentinel();
  }

  SymbolRewriter::RewriteDescriptor *
  ensureHead(SymbolRewriter::RewriteDescriptor *&) const {
    return createSentinel();
  }

  static void noteHead(SymbolRewriter::RewriteDescriptor *,
                       SymbolRewriter::RewriteDescriptor *) {}
};

ModulePass *createRewriteSymbolsPass();
ModulePass *createRewriteSymbolsPass(SymbolRewriter::RewriteDescriptorList &);
}

#endif