src/cc/json_map_decl_visitor.cc

/*
 * Copyright (c) 2017 VMware, Inc.
 *
 * 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
 *
 * http://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.
 */

#include <memory>
#include <string>

#include <clang/AST/ASTContext.h>
#include <clang/AST/RecordLayout.h>
#include <clang/AST/RecursiveASTVisitor.h>
#include <llvm/ADT/StringExtras.h>
#include <llvm/Config/llvm-config.h>
#include "common.h"
#include "table_desc.h"

namespace ebpf {

using std::string;
using std::to_string;
using std::unique_ptr;
using namespace clang;

// Helper visitor for constructing a string representation of a key/leaf decl
class BMapDeclVisitor : public clang::RecursiveASTVisitor<BMapDeclVisitor> {
 public:
  explicit BMapDeclVisitor(clang::ASTContext &C, std::string &result);
  bool TraverseRecordDecl(clang::RecordDecl *Decl);
  bool VisitRecordDecl(clang::RecordDecl *Decl);
  bool VisitFieldDecl(clang::FieldDecl *Decl);
  bool VisitBuiltinType(const clang::BuiltinType *T);
  bool VisitTypedefType(const clang::TypedefType *T);
  bool VisitTagType(const clang::TagType *T);
  bool VisitPointerType(const clang::PointerType *T);
  bool VisitEnumDecl(clang::EnumDecl *D);
  bool VisitAttr(clang::Attr *A);

 private:
  bool shouldSkipPadding(const RecordDecl *D);
  void genJSONForField(FieldDecl *F);

 private:
  clang::ASTContext &C;
  std::string &result_;
};

// Encode the struct layout as a json description
BMapDeclVisitor::BMapDeclVisitor(ASTContext &C, string &result) : C(C), result_(result) {}

bool BMapDeclVisitor::shouldSkipPadding(const RecordDecl *D) {
  if (D->isUnion() || D->field_empty())
    return true;
  for (auto F : D->getDefinition()->fields()) {
    if (F->isBitField())
      return true;
    QualType Ty = F->getType();
    if (Ty->isIncompleteArrayType())
      return true;
  }
  return false;
}

void BMapDeclVisitor::genJSONForField(FieldDecl *F) {
  if (F->isAnonymousStructOrUnion()) {
    if (const RecordType *R = dyn_cast<RecordType>(F->getType()))
      TraverseDecl(R->getDecl());
    result_ += ", ";
    return;
  }
  result_ += "[";
  TraverseDecl(F);
  if (const ConstantArrayType *T = dyn_cast<ConstantArrayType>(F->getType()))
#if LLVM_VERSION_MAJOR >= 13
    result_ += ", [" + toString(T->getSize(), 10, false) + "]";
#else
    result_ += ", [" + T->getSize().toString(10, false) + "]";
#endif
  if (F->isBitField())
    result_ += ", " + to_string(F->getBitWidthValue(C));
  result_ += "], ";
}

bool BMapDeclVisitor::VisitFieldDecl(FieldDecl *D) {
  result_ += "\"";
  result_ += D->getName();
  result_ += "\",";
  return true;
}

bool BMapDeclVisitor::VisitEnumDecl(EnumDecl *D) {
  TraverseType(D->getIntegerType());
  return false;
}

bool BMapDeclVisitor::TraverseRecordDecl(RecordDecl *D) {
  // skip children, handled in Visit...
  if (!WalkUpFromRecordDecl(D))
    return false;
  return true;
}

bool BMapDeclVisitor::VisitRecordDecl(RecordDecl *D) {
  result_ += "[\"";
  result_ += D->getName();
  result_ += "\", [";

  bool SkipPadding = shouldSkipPadding(D);
  if (SkipPadding) {
    for (auto F : D->getDefinition()->fields()) {
      genJSONForField(F);
    }
  } else {
    const ASTRecordLayout &Layout = C.getASTRecordLayout(D);
    CharUnits Offset = C.toCharUnitsFromBits(Layout.getFieldOffset(0));
    for (auto F : D->getDefinition()->fields()) {
      CharUnits FieldSize = C.getTypeSizeInChars(F->getType());
      auto FieldOffsetBits = Layout.getFieldOffset(F->getFieldIndex());
      CharUnits FieldOffset = C.toCharUnitsFromBits(FieldOffsetBits);

      uint64_t Padding = (FieldOffset - Offset).getQuantity();
      if (Padding) {
        /* Padding before this field with "char __pad_<FieldIndex>[Padding]". */
        result_ += "[\"__pad_" + to_string(F->getFieldIndex()) + "\",\"char\",["
                + to_string(Padding) + "]], ";
      }
      Offset = FieldOffset + FieldSize;
      genJSONForField(F);
    }

    /* Additional Padding after the last field so that the Record Size matches */
    CharUnits RecordSize = Layout.getSize();
    if (RecordSize > Offset) {
        result_ += "[\"__pad_end\",\"char\",["
                + to_string((RecordSize - Offset).getQuantity()) + "]], ";
    }
  }

  if (!D->getDefinition()->field_empty())
    result_.erase(result_.end() - 2);
  result_ += "]";
  if (D->isUnion())
    result_ += ", \"union\"";
  else if (D->isStruct()) {
    if (SkipPadding)
      result_ += ", \"struct\"";
    else
      result_ += ", \"struct_packed\"";
  }
  result_ += "]";
  return true;
}
// pointer to anything should be treated as terminal, don't recurse further
bool BMapDeclVisitor::VisitPointerType(const PointerType *T) {
  result_ += "\"unsigned long long\"";
  return false;
}
bool BMapDeclVisitor::VisitTagType(const TagType *T) {
  return TraverseDecl(T->getDecl()->getDefinition());
}
bool BMapDeclVisitor::VisitTypedefType(const TypedefType *T) { return TraverseDecl(T->getDecl()); }
bool BMapDeclVisitor::VisitBuiltinType(const BuiltinType *T) {
  result_ += "\"";
  result_ += T->getName(C.getPrintingPolicy());
  result_ += "\"";
  return true;
}
bool BMapDeclVisitor::VisitAttr(clang::Attr *A) { return false; }

class JsonMapTypesVisitor : public virtual MapTypesVisitor {
 public:
  virtual void Visit(TableDesc &desc, clang::ASTContext &C, clang::QualType key_type,
                     clang::QualType leaf_type) {
    BMapDeclVisitor v1(C, desc.key_desc), v2(C, desc.leaf_desc);
    v1.TraverseType(key_type);
    v2.TraverseType(leaf_type);
  }
};

unique_ptr<MapTypesVisitor> createJsonMapTypesVisitor() {
  return make_unique<JsonMapTypesVisitor>();
}

}  // namespace ebpf