lld/ELF/ScriptLexer.cpp

//===- ScriptLexer.cpp ----------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines a lexer for the linker script.
//
// The linker script's grammar is not complex but ambiguous due to the
// lack of the formal specification of the language. What we are trying to
// do in this and other files in LLD is to make a "reasonable" linker
// script processor.
//
// Among simplicity, compatibility and efficiency, we put the most
// emphasis on simplicity when we wrote this lexer. Compatibility with the
// GNU linkers is important, but we did not try to clone every tiny corner
// case of their lexers, as even ld.bfd and ld.gold are subtly different
// in various corner cases. We do not care much about efficiency because
// the time spent in parsing linker scripts is usually negligible.
//
// Overall, this lexer works fine for most linker scripts. There might
// be room for improving compatibility, but that's probably not at the
// top of our todo list.
//
//===----------------------------------------------------------------------===//

#include "ScriptLexer.h"
#include "Config.h"
#include "lld/Common/ErrorHandler.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Path.h"
#include <algorithm>

using namespace llvm;
using namespace lld;
using namespace lld::elf;

ScriptLexer::Buffer::Buffer(MemoryBufferRef mb)
    : s(mb.getBuffer()), filename(mb.getBufferIdentifier()),
      begin(mb.getBufferStart()) {
  if (config->sysroot == "")
    return;
  StringRef path = filename;
  for (; !path.empty(); path = sys::path::parent_path(path)) {
    if (!sys::fs::equivalent(config->sysroot, path))
      continue;
    isUnderSysroot = true;
    return;
  }
}

ScriptLexer::ScriptLexer(MemoryBufferRef mb) : curBuf(mb), mbs(1, mb) {
  activeFilenames.insert(mb.getBufferIdentifier());
}

// Returns a whole line containing the current token.
StringRef ScriptLexer::getLine() {
  StringRef s = getCurrentMB().getBuffer();

  size_t pos = s.rfind('\n', prevTok.data() - s.data());
  if (pos != StringRef::npos)
    s = s.substr(pos + 1);
  return s.substr(0, s.find_first_of("\r\n"));
}

// Returns 0-based column number of the current token.
size_t ScriptLexer::getColumnNumber() {
  return prevTok.data() - getLine().data();
}

std::string ScriptLexer::getCurrentLocation() {
  std::string filename = std::string(getCurrentMB().getBufferIdentifier());
  return (filename + ":" + Twine(prevTokLine)).str();
}

// We don't want to record cascading errors. Keep only the first one.
void ScriptLexer::setError(const Twine &msg) {
  if (errorCount())
    return;

  std::string s = (getCurrentLocation() + ": " + msg).str();
  if (prevTok.size())
    s += "\n>>> " + getLine().str() + "\n>>> " +
         std::string(getColumnNumber(), ' ') + "^";
  error(s);
}

void ScriptLexer::lex() {
  for (;;) {
    StringRef &s = curBuf.s;
    s = skipSpace(s);
    if (s.empty()) {
      // If this buffer is from an INCLUDE command, switch to the "return
      // value"; otherwise, mark EOF.
      if (buffers.empty()) {
        eof = true;
        return;
      }
      activeFilenames.erase(curBuf.filename);
      curBuf = buffers.pop_back_val();
      continue;
    }
    curTokState = inExpr;

    // Quoted token. Note that double-quote characters are parts of a token
    // because, in a glob match context, only unquoted tokens are interpreted
    // as glob patterns. Double-quoted tokens are literal patterns in that
    // context.
    if (s.starts_with("\"")) {
      size_t e = s.find("\"", 1);
      if (e == StringRef::npos) {
        size_t lineno =
            StringRef(curBuf.begin, s.data() - curBuf.begin).count('\n');
        error(curBuf.filename + ":" + Twine(lineno + 1) + ": unclosed quote");
        return;
      }

      curTok = s.take_front(e + 1);
      s = s.substr(e + 1);
      return;
    }

    // Some operators form separate tokens.
    if (s.starts_with("<<=") || s.starts_with(">>=")) {
      curTok = s.substr(0, 3);
      s = s.substr(3);
      return;
    }
    if (s.size() > 1 && (s[1] == '=' && strchr("+-*/!&^|", s[0]))) {
      curTok = s.substr(0, 2);
      s = s.substr(2);
      return;
    }

    // Unquoted token. The non-expression token is more relaxed than tokens in
    // C-like languages, so that you can write "file-name.cpp" as one bare
    // token.
    size_t pos;
    if (inExpr) {
      pos = s.find_first_not_of(
          "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
          "0123456789_.$");
      if (pos == 0 && s.size() >= 2 &&
          ((s[0] == s[1] && strchr("<>&|", s[0])) ||
           is_contained({"==", "!=", "<=", ">=", "<<", ">>"}, s.substr(0, 2))))
        pos = 2;
    } else {
      pos = s.find_first_not_of(
          "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
          "0123456789_.$/\\~=+[]*?-!^:");
    }

    if (pos == 0)
      pos = 1;
    curTok = s.substr(0, pos);
    s = s.substr(pos);
    break;
  }
}

// Skip leading whitespace characters or comments.
StringRef ScriptLexer::skipSpace(StringRef s) {
  for (;;) {
    if (s.starts_with("/*")) {
      size_t e = s.find("*/", 2);
      if (e == StringRef::npos) {
        setError("unclosed comment in a linker script");
        return "";
      }
      curBuf.lineNumber += s.substr(0, e).count('\n');
      s = s.substr(e + 2);
      continue;
    }
    if (s.starts_with("#")) {
      size_t e = s.find('\n', 1);
      if (e == StringRef::npos)
        e = s.size() - 1;
      else
        ++curBuf.lineNumber;
      s = s.substr(e + 1);
      continue;
    }
    StringRef saved = s;
    s = s.ltrim();
    auto len = saved.size() - s.size();
    if (len == 0)
      return s;
    curBuf.lineNumber += saved.substr(0, len).count('\n');
  }
}

// Used to determine whether to stop parsing. Treat errors like EOF.
bool ScriptLexer::atEOF() { return eof || errorCount(); }

StringRef ScriptLexer::next() {
  prevTok = peek();
  // `prevTokLine` is not updated for EOF so that the line number in `setError`
  // will be more useful.
  if (prevTok.size())
    prevTokLine = curBuf.lineNumber;
  return std::exchange(curTok, StringRef(curBuf.s.data(), 0));
}

StringRef ScriptLexer::peek() {
  // curTok is invalid if curTokState and inExpr mismatch.
  if (curTok.size() && curTokState != inExpr) {
    curBuf.s = StringRef(curTok.data(), curBuf.s.end() - curTok.data());
    curTok = {};
  }
  if (curTok.empty())
    lex();
  return curTok;
}

bool ScriptLexer::consume(StringRef tok) {
  if (peek() != tok)
    return false;
  next();
  return true;
}

void ScriptLexer::skip() { (void)next(); }

void ScriptLexer::expect(StringRef expect) {
  if (errorCount())
    return;
  StringRef tok = next();
  if (tok != expect) {
    if (atEOF())
      setError("unexpected EOF");
    else
      setError(expect + " expected, but got " + tok);
  }
}

ScriptLexer::Token ScriptLexer::till(StringRef tok) {
  StringRef str = next();
  if (str == tok)
    return {};
  if (!atEOF())
    return {str};
  prevTok = {};
  setError("unexpected EOF");
  return {};
}

// Returns true if S encloses T.
static bool encloses(StringRef s, StringRef t) {
  return s.bytes_begin() <= t.bytes_begin() && t.bytes_end() <= s.bytes_end();
}

MemoryBufferRef ScriptLexer::getCurrentMB() {
  // Find input buffer containing the current token.
  assert(!mbs.empty());
  for (MemoryBufferRef mb : mbs)
    if (encloses(mb.getBuffer(), curBuf.s))
      return mb;
  llvm_unreachable("getCurrentMB: failed to find a token");
}