elf_loader.h

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// -*- mode: C++ -*-
//
// Copyright 2022 Google LLC
//
// Licensed under the Apache License v2.0 with LLVM Exceptions (the
// "License"); you may not use this file except in compliance with the
// License.  You may obtain a copy of the License at
//
//     https://llvm.org/LICENSE.txt
//
// 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.
//
// Author: Aleksei Vetrov

#ifndef STG_ELF_LOADER_H_
#define STG_ELF_LOADER_H_

#include <gelf.h>

#include <cstddef>
#include <cstdint>
#include <functional>
#include <string>
#include <string_view>
#include <vector>

#include "stg.h"

namespace stg {
namespace elf {

struct SymbolTableEntry {
  enum class SymbolType {
    NOTYPE = 0,
    OBJECT,
    FUNCTION,
    SECTION,
    FILE,
    COMMON,
    TLS,
    GNU_IFUNC
  };

  enum class ValueType {
    UNDEFINED = 0,
    ABSOLUTE,
    COMMON,
    RELATIVE_TO_SECTION,
  };

  using Binding = ElfSymbol::Binding;
  using Visibility = ElfSymbol::Visibility;

  std::string_view name;
  uint64_t value;
  uint64_t size;
  SymbolType symbol_type;
  Binding binding;
  Visibility visibility;
  ValueType value_type;
};

class ElfLoader final {
 public:
  explicit ElfLoader(const std::string& path, bool verbose = false);
  ElfLoader(char* data, size_t size, bool verbose = false);
  ElfLoader(const ElfLoader&) = delete;
  ElfLoader& operator=(const ElfLoader&) = delete;
  ~ElfLoader();

  std::string_view GetBtfRawData() const;
  std::vector<SymbolTableEntry> GetElfSymbols() const;

 private:
  std::vector<Elf_Scn*> GetSectionsIf(
      std::function<bool(const GElf_Shdr&)> predicate) const;
  std::vector<Elf_Scn*> GetSectionsByName(const std::string& name) const;
  Elf_Scn* GetSectionByName(const std::string& name) const;
  Elf_Scn* GetSectionByType(Elf64_Word type) const;
  Elf_Scn* GetSymbolTableSection() const;

  struct SectionInfo {
    GElf_Shdr header;
    Elf_Data* data;
  };
  SectionInfo GetSectionInfo(Elf_Scn* section) const;
  size_t GetNumberOfEntries(const GElf_Shdr& section_header) const;

  std::string_view GetString(uint32_t section, size_t offset) const;

  const bool verbose_;
  int fd_;
  Elf* elf_;
};

}  // namespace elf
}  // namespace stg

#endif  // STG_ELF_LOADER_H_