mold/linker_script.cc

// On Linux, /usr/lib/x86_64-linux-gnu/libc.so is not actually
// a shared object file but an ASCII text file containing a linker
// script to include a "real" libc.so file. Therefore, we need to
// support a (very limited) subset of the linker script language.

#include "mold.h"

#include <cctype>
#include <iomanip>

static thread_local MemoryMappedFile *current_file;

static std::string_view get_line(std::string_view input, const char *pos) {
  assert(input.data() <= pos);
  assert(pos < input.data() + input.size());

  i64 start = input.rfind('\n', pos - input.data());
  if (start == input.npos)
    start = 0;
  else
    start++;

  i64 end = input.find('\n', pos - input.data());
  if (end == input.npos)
    end = input.size();

  return input.substr(start, end - start);
}

class SyntaxError {
public:
  SyntaxError(std::string_view errpos) {
    std::string_view contents = current_file->get_contents();
    std::string_view line = get_line(contents, errpos.data());

    i64 lineno = 1;
    for (i64 i = 0; contents.data() + i < line.data(); i++)
      if (contents[i] == '\n')
        lineno++;

    i64 column = errpos.data() - line.data();

    std::stringstream ss;
    ss << current_file->name << ":" << lineno << ": ";
    i64 indent = ss.tellp();
    ss << line << "\n" << std::setw(indent + column) << " " << "^ ";
    out << ss.str();
  }

  template <class T> SyntaxError &operator<<(T &&val) {
    out << std::forward<T>(val);
    return *this;
  }

  Fatal out;
};

static std::vector<std::string_view> tokenize(std::string_view input) {
  std::vector<std::string_view> vec;
  while (!input.empty()) {
    if (isspace(input[0])) {
      input = input.substr(1);
      continue;
    }

    if (input.starts_with("/*")) {
      i64 pos = input.find("*/", 2);
      if (pos == std::string_view::npos)
        SyntaxError(input) << "unclosed comment";
      input = input.substr(pos + 2);
      continue;
    }

    if (input[0] == '#') {
      i64 pos = input.find("\n", 1);
      if (pos == std::string_view::npos)
        break;
      input = input.substr(pos + 1);
      continue;
    }

    if (input[0] == '"') {
      i64 pos = input.find('"', 1);
      if (pos == std::string_view::npos)
        SyntaxError(input) << "unclosed string literal";
      vec.push_back(input.substr(0, pos + 1));
      input = input.substr(pos + 1);
      continue;
    }

    i64 pos = input.find_first_not_of(
      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
      "0123456789_.$/\\~=+[]*?-!^:");

    if (pos == 0)
      pos = 1;
    else if (pos == input.npos)
      pos = input.size();

    vec.push_back(input.substr(0, pos));
    input = input.substr(pos);
  }
  return vec;
}

static std::span<std::string_view>
skip(std::span<std::string_view> tok, std::string_view str) {
  if (tok.empty())
    Fatal() << current_file->name << ": expected '" << str << "', but got EOF";
  if (tok[0] != str)
    SyntaxError(tok[0]) << "expected '" << str << "'";
  return tok.subspan(1);
}

static std::string_view unquote(std::string_view s) {
  if (s.size() > 0 && s[0] == '"') {
    assert(s[s.size() - 1] == '"');
    return s.substr(1, s.size() - 2);
  }
  return s;
}

static std::span<std::string_view>
read_output_format(std::span<std::string_view> tok) {
  tok = skip(tok, "(");
  while (!tok.empty() && tok[0] != ")")
    tok = tok.subspan(1);
  if (tok.empty())
    Fatal() << current_file->name << ": expected ')', but got EOF";
  return tok.subspan(1);
}

static MemoryMappedFile *resolve_path(std::string_view tok, ReadContext &rctx) {
  std::string str(unquote(tok));

  if (str.starts_with("/"))
    return MemoryMappedFile::must_open(ctx.arg.sysroot + str);

  if (str.starts_with("-l"))
    return find_library(str.substr(2), ctx.arg.library_paths, rctx);

  if (std::string path = path_dirname(current_file->name) + "/";
      MemoryMappedFile *mb = MemoryMappedFile::open(path + str))
    return mb;

  if (MemoryMappedFile *mb = MemoryMappedFile::open(str))
    return mb;

  for (std::string_view dir : ctx.arg.library_paths) {
    std::string root = dir.starts_with("/") ? ctx.arg.sysroot : "";
    std::string path = root + std::string(dir) + "/" + str;
    if (MemoryMappedFile *mb = MemoryMappedFile::open(path))
      return mb;
  }

  SyntaxError(tok) << "library not found: " << str;
}

static std::span<std::string_view>
read_group(std::span<std::string_view> tok, ReadContext &rctx) {
  tok = skip(tok, "(");

  while (!tok.empty() && tok[0] != ")") {
    if (tok[0] == "AS_NEEDED") {
      bool orig = rctx.as_needed;
      rctx.as_needed = true;
      tok = read_group(tok.subspan(1), rctx);
      rctx.as_needed = orig;
      continue;
    }

    MemoryMappedFile *mb = resolve_path(tok[0], rctx);
    read_file(mb, rctx);
    tok = tok.subspan(1);
  }

  if (tok.empty())
    Fatal() << current_file->name << ": expected ')', but got EOF";
  return tok.subspan(1);
}

void parse_linker_script(MemoryMappedFile *mb, ReadContext &rctx) {
  current_file = mb;

  std::vector<std::string_view> vec = tokenize(mb->get_contents());
  std::span<std::string_view> tok = vec;

  while (!tok.empty()) {
    if (tok[0] == "OUTPUT_FORMAT")
      tok = read_output_format(tok.subspan(1));
    else if (tok[0] == "INPUT" || tok[0] == "GROUP")
      tok = read_group(tok.subspan(1), rctx);
    else
      SyntaxError(tok[0]) << "unknown token";
  }
}

static bool read_label(std::span<std::string_view> &tok,
                       std::string label) {
  if (tok.size() >= 1 && tok[0] == label + ":") {
    tok = tok.subspan(1);
    return true;
  }

  if (tok.size() >= 2 && tok[0] == label && tok[1] == ":") {
    tok = tok.subspan(2);
    return true;
  }
  return false;
}

static void parse_version_script_commands(std::span<std::string_view> &tok,
                                          i16 &ver, bool is_extern_cpp) {
  bool is_global = true;

  while (!tok.empty() && tok[0] != "}") {
    if (read_label(tok, "global")) {
      is_global = true;
      continue;
    }

    if (read_label(tok, "local")) {
      is_global = false;
      continue;
    }

    if (tok[0] == "extern") {
      tok = tok.subspan(1);
      tok = skip(tok, "\"C++\"");
      tok = skip(tok, "{");
      parse_version_script_commands(tok, ver, true);
      tok = skip(tok, "}");
      tok = skip(tok, ";");
      continue;
    }

    if (tok[0] == "*")
      ctx.arg.default_version = (is_global ? ver : VER_NDX_LOCAL);
    else
      ctx.arg.version_patterns.push_back({tok[0], ver, is_extern_cpp});
    tok = skip(tok.subspan(1), ";");
  }
}

void parse_version_script(std::string path) {
  current_file = MemoryMappedFile::must_open(path);
  std::vector<std::string_view> vec = tokenize(current_file->get_contents());
  std::span<std::string_view> tok = vec;
  i16 next_ver = VER_NDX_LAST_RESERVED + 1;

  while (!tok.empty()) {
    i16 ver = VER_NDX_GLOBAL;
    if (tok[0] != "{") {
      ver = next_ver++;
      ctx.arg.version_definitions.push_back(tok[0]);
      tok = tok.subspan(1);
    }

    tok = skip(tok, "{");
    parse_version_script_commands(tok, ver, false);
    tok = skip(tok, "}");
    if (!tok.empty() && tok[0] != ";")
      tok = tok.subspan(1);
    tok = skip(tok, ";");
  }

  if (!tok.empty())
    SyntaxError(tok[0]) << "trailing garbage token";
}

void parse_dynamic_list(std::string path) {
  current_file = MemoryMappedFile::must_open(path);
  std::vector<std::string_view> vec = tokenize(current_file->get_contents());
  std::span<std::string_view> tok = vec;

  tok = skip(tok, "{");
  i16 ver = VER_NDX_GLOBAL;

  while (!tok.empty() && tok[0] != "}") {
    if (read_label(tok, "global")) {
      ver = VER_NDX_GLOBAL;
      continue;
    }

    if (read_label(tok, "local")) {
      ver = VER_NDX_LOCAL;
      continue;
    }

    if (tok[0] == "*")
      ctx.arg.default_version = ver;
    else
      ctx.arg.version_patterns.push_back({tok[0], ver, false});
    tok = skip(tok.subspan(1), ";");
  }

  tok = skip(tok, "}");
  tok = skip(tok, ";");

  if (!tok.empty())
    SyntaxError(tok[0]) << "trailing garbage token";
}