centipede/symbol_table.cc

// Copyright 2022 The Centipede Authors.
//
// 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
//
//      https://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 "./centipede/symbol_table.h"

#include <cstdlib>
#include <filesystem>
#include <fstream>
#include <string>
#include <string_view>

#include "absl/strings/str_cat.h"
#include "absl/strings/strip.h"
#include "./centipede/command.h"
#include "./centipede/control_flow.h"
#include "./centipede/logging.h"
#include "./centipede/util.h"

namespace centipede {

void SymbolTable::ReadFromLLVMSymbolizer(std::istream &in) {
  // We remove some useless file prefixes for better human readability.
  const std::string_view file_prefixes_to_remove[] = {"/proc/self/cwd/", "./"};
  while (in) {
    // We (mostly) blindly trust the input format is correct.
    std::string func, file, empty;
    std::getline(in, func);
    std::getline(in, file);
    std::getline(in, empty);
    CHECK(empty.empty()) << "Unexpected symbolizer output format: " << VV(func)
                         << VV(file) << VV(empty);
    if (!in) break;
    for (auto &bad_prefix : file_prefixes_to_remove) {
      file = absl::StripPrefix(file, bad_prefix);
    }
    AddEntry(func, file);
  }
}

void SymbolTable::GetSymbolsFromBinary(const PCTable &pc_table,
                                       std::string_view binary_path,
                                       std::string_view symbolizer_path,
                                       std::string_view tmp_path1,
                                       std::string_view tmp_path2) {
  // NOTE: --symbolizer_path=/dev/null is a somewhat expected alternative to ""
  // that users might pass.
  if (symbolizer_path.empty() || symbolizer_path == "/dev/null") {
    LOG(WARNING) << "Symbolizer unspecified: debug symbols will not be used";
  } else {
    auto pcs_path(tmp_path1);
    auto symbols_path(tmp_path2);
    // Create the input file (one PC per line).
    std::string pcs_string;
    for (auto &pc_info : pc_table) {
      absl::StrAppend(&pcs_string, "0x", absl::Hex(pc_info.pc), "\n");
    }
    WriteToLocalFile(pcs_path, pcs_string);
    // Run the symbolizer.
    Command cmd(symbolizer_path,
                {
                    "--no-inlines",
                    "-e",
                    std::string(binary_path),
                    "<",
                    std::string(pcs_path),
                },
                /*env=*/{}, symbols_path);
    int exit_code = cmd.Execute();
    if (exit_code != EXIT_SUCCESS) {
      LOG(ERROR) << "system() failed: " << VV(cmd.ToString()) << VV(exit_code);
    } else {
      // Get and process the symbolizer output.
      std::ifstream symbolizer_output(std::string{symbols_path});
      ReadFromLLVMSymbolizer(symbolizer_output);
      std::filesystem::remove(pcs_path);
      std::filesystem::remove(symbols_path);
      if (size() != pc_table.size()) {
        LOG(ERROR) << "Symbolization failed: debug symbols will not be used";
      }
    }
  }

  if (size() != pc_table.size()) {
    // Something went wrong. Set symbols to unknown so the sizes of pc_table and
    // symbols always match.
    SetAllToUnknown(pc_table.size());
  }
}

void SymbolTable::SetAllToUnknown(size_t size) {
  entries_.resize(size);
  for (auto &entry : entries_) {
    entry = {"?", "?"};
  }
}

}  // namespace centipede