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1 //===- ScriptLexer.cpp ----------------------------------------------------===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8 //
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9 // This file defines a lexer for the linker script.
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10 //
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11 // The linker script's grammar is not complex but ambiguous due to the
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12 // lack of the formal specification of the language. What we are trying to
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13 // do in this and other files in LLD is to make a "reasonable" linker
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14 // script processor.
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15 //
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16 // Among simplicity, compatibility and efficiency, we put the most
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17 // emphasis on simplicity when we wrote this lexer. Compatibility with the
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18 // GNU linkers is important, but we did not try to clone every tiny corner
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19 // case of their lexers, as even ld.bfd and ld.gold are subtly different
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20 // in various corner cases. We do not care much about efficiency because
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21 // the time spent in parsing linker scripts is usually negligible.
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22 //
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23 // Our grammar of the linker script is LL(2), meaning that it needs at
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24 // most two-token lookahead to parse. The only place we need two-token
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25 // lookahead is labels in version scripts, where we need to parse "local :"
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26 // as if "local:".
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27 //
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28 // Overall, this lexer works fine for most linker scripts. There might
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29 // be room for improving compatibility, but that's probably not at the
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30 // top of our todo list.
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31 //
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32 //===----------------------------------------------------------------------===//
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33
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34 #include "ScriptLexer.h"
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35 #include "lld/Common/ErrorHandler.h"
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36 #include "llvm/ADT/Twine.h"
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37
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38 using namespace llvm;
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173
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39 using namespace lld;
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40 using namespace lld::elf;
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150
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41
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42 // Returns a whole line containing the current token.
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43 StringRef ScriptLexer::getLine() {
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44 StringRef s = getCurrentMB().getBuffer();
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45 StringRef tok = tokens[pos - 1];
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46
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47 size_t pos = s.rfind('\n', tok.data() - s.data());
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48 if (pos != StringRef::npos)
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49 s = s.substr(pos + 1);
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50 return s.substr(0, s.find_first_of("\r\n"));
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51 }
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52
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53 // Returns 1-based line number of the current token.
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54 size_t ScriptLexer::getLineNumber() {
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55 StringRef s = getCurrentMB().getBuffer();
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56 StringRef tok = tokens[pos - 1];
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57 return s.substr(0, tok.data() - s.data()).count('\n') + 1;
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58 }
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59
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60 // Returns 0-based column number of the current token.
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61 size_t ScriptLexer::getColumnNumber() {
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62 StringRef tok = tokens[pos - 1];
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63 return tok.data() - getLine().data();
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64 }
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65
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66 std::string ScriptLexer::getCurrentLocation() {
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67 std::string filename = std::string(getCurrentMB().getBufferIdentifier());
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68 return (filename + ":" + Twine(getLineNumber())).str();
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69 }
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70
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71 ScriptLexer::ScriptLexer(MemoryBufferRef mb) { tokenize(mb); }
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72
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73 // We don't want to record cascading errors. Keep only the first one.
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74 void ScriptLexer::setError(const Twine &msg) {
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75 if (errorCount())
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76 return;
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77
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78 std::string s = (getCurrentLocation() + ": " + msg).str();
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79 if (pos)
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80 s += "\n>>> " + getLine().str() + "\n>>> " +
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81 std::string(getColumnNumber(), ' ') + "^";
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82 error(s);
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83 }
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84
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85 // Split S into linker script tokens.
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86 void ScriptLexer::tokenize(MemoryBufferRef mb) {
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87 std::vector<StringRef> vec;
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88 mbs.push_back(mb);
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89 StringRef s = mb.getBuffer();
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90 StringRef begin = s;
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91
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92 for (;;) {
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93 s = skipSpace(s);
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94 if (s.empty())
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95 break;
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96
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97 // Quoted token. Note that double-quote characters are parts of a token
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98 // because, in a glob match context, only unquoted tokens are interpreted
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99 // as glob patterns. Double-quoted tokens are literal patterns in that
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100 // context.
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101 if (s.startswith("\"")) {
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102 size_t e = s.find("\"", 1);
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103 if (e == StringRef::npos) {
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104 StringRef filename = mb.getBufferIdentifier();
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105 size_t lineno = begin.substr(0, s.data() - begin.data()).count('\n');
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106 error(filename + ":" + Twine(lineno + 1) + ": unclosed quote");
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107 return;
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108 }
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109
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110 vec.push_back(s.take_front(e + 1));
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111 s = s.substr(e + 1);
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112 continue;
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113 }
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114
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115 // ">foo" is parsed to ">" and "foo", but ">>" is parsed to ">>".
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116 // "|", "||", "&" and "&&" are different operators.
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117 if (s.startswith("<<") || s.startswith("<=") || s.startswith(">>") ||
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118 s.startswith(">=") || s.startswith("||") || s.startswith("&&")) {
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119 vec.push_back(s.substr(0, 2));
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120 s = s.substr(2);
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121 continue;
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122 }
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123
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124 // Unquoted token. This is more relaxed than tokens in C-like language,
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125 // so that you can write "file-name.cpp" as one bare token, for example.
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126 size_t pos = s.find_first_not_of(
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127 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
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128 "0123456789_.$/\\~=+[]*?-!^:");
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129
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130 // A character that cannot start a word (which is usually a
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131 // punctuation) forms a single character token.
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132 if (pos == 0)
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133 pos = 1;
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134 vec.push_back(s.substr(0, pos));
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135 s = s.substr(pos);
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136 }
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137
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138 tokens.insert(tokens.begin() + pos, vec.begin(), vec.end());
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139 }
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140
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141 // Skip leading whitespace characters or comments.
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142 StringRef ScriptLexer::skipSpace(StringRef s) {
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143 for (;;) {
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144 if (s.startswith("/*")) {
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145 size_t e = s.find("*/", 2);
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146 if (e == StringRef::npos) {
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147 error("unclosed comment in a linker script");
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148 return "";
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149 }
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150 s = s.substr(e + 2);
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151 continue;
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152 }
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153 if (s.startswith("#")) {
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154 size_t e = s.find('\n', 1);
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155 if (e == StringRef::npos)
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156 e = s.size() - 1;
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157 s = s.substr(e + 1);
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158 continue;
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159 }
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160 size_t size = s.size();
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161 s = s.ltrim();
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162 if (s.size() == size)
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163 return s;
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164 }
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165 }
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166
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167 // An erroneous token is handled as if it were the last token before EOF.
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168 bool ScriptLexer::atEOF() { return errorCount() || tokens.size() == pos; }
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169
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170 // Split a given string as an expression.
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171 // This function returns "3", "*" and "5" for "3*5" for example.
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172 static std::vector<StringRef> tokenizeExpr(StringRef s) {
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173 StringRef ops = "+-*/:!~=<>"; // List of operators
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174
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175 // Quoted strings are literal strings, so we don't want to split it.
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176 if (s.startswith("\""))
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177 return {s};
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178
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179 // Split S with operators as separators.
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180 std::vector<StringRef> ret;
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181 while (!s.empty()) {
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182 size_t e = s.find_first_of(ops);
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183
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184 // No need to split if there is no operator.
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185 if (e == StringRef::npos) {
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186 ret.push_back(s);
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187 break;
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188 }
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189
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173
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190 // Get a token before the operator.
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150
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191 if (e != 0)
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192 ret.push_back(s.substr(0, e));
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193
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194 // Get the operator as a token.
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195 // Keep !=, ==, >=, <=, << and >> operators as a single tokens.
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196 if (s.substr(e).startswith("!=") || s.substr(e).startswith("==") ||
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197 s.substr(e).startswith(">=") || s.substr(e).startswith("<=") ||
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198 s.substr(e).startswith("<<") || s.substr(e).startswith(">>")) {
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199 ret.push_back(s.substr(e, 2));
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200 s = s.substr(e + 2);
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201 } else {
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202 ret.push_back(s.substr(e, 1));
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203 s = s.substr(e + 1);
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204 }
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205 }
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206 return ret;
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207 }
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208
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209 // In contexts where expressions are expected, the lexer should apply
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210 // different tokenization rules than the default one. By default,
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211 // arithmetic operator characters are regular characters, but in the
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212 // expression context, they should be independent tokens.
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213 //
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214 // For example, "foo*3" should be tokenized to "foo", "*" and "3" only
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215 // in the expression context.
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216 //
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217 // This function may split the current token into multiple tokens.
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218 void ScriptLexer::maybeSplitExpr() {
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219 if (!inExpr || errorCount() || atEOF())
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220 return;
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221
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222 std::vector<StringRef> v = tokenizeExpr(tokens[pos]);
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223 if (v.size() == 1)
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224 return;
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225 tokens.erase(tokens.begin() + pos);
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226 tokens.insert(tokens.begin() + pos, v.begin(), v.end());
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227 }
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228
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229 StringRef ScriptLexer::next() {
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230 maybeSplitExpr();
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231
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232 if (errorCount())
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233 return "";
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234 if (atEOF()) {
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235 setError("unexpected EOF");
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236 return "";
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237 }
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238 return tokens[pos++];
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239 }
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240
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241 StringRef ScriptLexer::peek() {
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242 StringRef tok = next();
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243 if (errorCount())
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244 return "";
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245 pos = pos - 1;
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246 return tok;
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247 }
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248
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249 StringRef ScriptLexer::peek2() {
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250 skip();
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251 StringRef tok = next();
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252 if (errorCount())
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253 return "";
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254 pos = pos - 2;
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255 return tok;
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256 }
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257
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258 bool ScriptLexer::consume(StringRef tok) {
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259 if (peek() == tok) {
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260 skip();
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261 return true;
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262 }
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263 return false;
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264 }
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265
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266 // Consumes Tok followed by ":". Space is allowed between Tok and ":".
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267 bool ScriptLexer::consumeLabel(StringRef tok) {
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268 if (consume((tok + ":").str()))
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269 return true;
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270 if (tokens.size() >= pos + 2 && tokens[pos] == tok &&
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271 tokens[pos + 1] == ":") {
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272 pos += 2;
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273 return true;
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274 }
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275 return false;
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276 }
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277
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278 void ScriptLexer::skip() { (void)next(); }
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279
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280 void ScriptLexer::expect(StringRef expect) {
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281 if (errorCount())
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282 return;
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283 StringRef tok = next();
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284 if (tok != expect)
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285 setError(expect + " expected, but got " + tok);
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286 }
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287
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288 // Returns true if S encloses T.
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289 static bool encloses(StringRef s, StringRef t) {
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290 return s.bytes_begin() <= t.bytes_begin() && t.bytes_end() <= s.bytes_end();
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291 }
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292
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293 MemoryBufferRef ScriptLexer::getCurrentMB() {
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294 // Find input buffer containing the current token.
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295 assert(!mbs.empty() && pos > 0);
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296 for (MemoryBufferRef mb : mbs)
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297 if (encloses(mb.getBuffer(), tokens[pos - 1]))
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298 return mb;
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299 llvm_unreachable("getCurrentMB: failed to find a token");
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300 }
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