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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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221
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55 if (pos == 0)
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56 return 1;
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150
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57 StringRef s = getCurrentMB().getBuffer();
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58 StringRef tok = tokens[pos - 1];
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59 return s.substr(0, tok.data() - s.data()).count('\n') + 1;
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60 }
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61
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62 // Returns 0-based column number of the current token.
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63 size_t ScriptLexer::getColumnNumber() {
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64 StringRef tok = tokens[pos - 1];
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65 return tok.data() - getLine().data();
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66 }
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67
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68 std::string ScriptLexer::getCurrentLocation() {
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69 std::string filename = std::string(getCurrentMB().getBufferIdentifier());
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70 return (filename + ":" + Twine(getLineNumber())).str();
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71 }
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72
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73 ScriptLexer::ScriptLexer(MemoryBufferRef mb) { tokenize(mb); }
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74
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75 // We don't want to record cascading errors. Keep only the first one.
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76 void ScriptLexer::setError(const Twine &msg) {
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77 if (errorCount())
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78 return;
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79
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80 std::string s = (getCurrentLocation() + ": " + msg).str();
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81 if (pos)
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82 s += "\n>>> " + getLine().str() + "\n>>> " +
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83 std::string(getColumnNumber(), ' ') + "^";
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84 error(s);
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85 }
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86
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87 // Split S into linker script tokens.
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88 void ScriptLexer::tokenize(MemoryBufferRef mb) {
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89 std::vector<StringRef> vec;
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90 mbs.push_back(mb);
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91 StringRef s = mb.getBuffer();
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92 StringRef begin = s;
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93
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94 for (;;) {
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95 s = skipSpace(s);
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96 if (s.empty())
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97 break;
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98
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99 // Quoted token. Note that double-quote characters are parts of a token
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100 // because, in a glob match context, only unquoted tokens are interpreted
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101 // as glob patterns. Double-quoted tokens are literal patterns in that
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102 // context.
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103 if (s.startswith("\"")) {
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104 size_t e = s.find("\"", 1);
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105 if (e == StringRef::npos) {
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106 StringRef filename = mb.getBufferIdentifier();
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107 size_t lineno = begin.substr(0, s.data() - begin.data()).count('\n');
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108 error(filename + ":" + Twine(lineno + 1) + ": unclosed quote");
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109 return;
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110 }
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111
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112 vec.push_back(s.take_front(e + 1));
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113 s = s.substr(e + 1);
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114 continue;
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115 }
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116
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117 // ">foo" is parsed to ">" and "foo", but ">>" is parsed to ">>".
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118 // "|", "||", "&" and "&&" are different operators.
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119 if (s.startswith("<<") || s.startswith("<=") || s.startswith(">>") ||
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120 s.startswith(">=") || s.startswith("||") || s.startswith("&&")) {
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121 vec.push_back(s.substr(0, 2));
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122 s = s.substr(2);
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123 continue;
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124 }
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125
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126 // Unquoted token. This is more relaxed than tokens in C-like language,
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127 // so that you can write "file-name.cpp" as one bare token, for example.
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128 size_t pos = s.find_first_not_of(
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129 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
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130 "0123456789_.$/\\~=+[]*?-!^:");
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131
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132 // A character that cannot start a word (which is usually a
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133 // punctuation) forms a single character token.
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134 if (pos == 0)
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135 pos = 1;
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136 vec.push_back(s.substr(0, pos));
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137 s = s.substr(pos);
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138 }
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139
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140 tokens.insert(tokens.begin() + pos, vec.begin(), vec.end());
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141 }
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142
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143 // Skip leading whitespace characters or comments.
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144 StringRef ScriptLexer::skipSpace(StringRef s) {
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145 for (;;) {
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146 if (s.startswith("/*")) {
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147 size_t e = s.find("*/", 2);
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148 if (e == StringRef::npos) {
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221
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149 setError("unclosed comment in a linker script");
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150
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150 return "";
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151 }
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152 s = s.substr(e + 2);
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153 continue;
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154 }
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155 if (s.startswith("#")) {
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156 size_t e = s.find('\n', 1);
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157 if (e == StringRef::npos)
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158 e = s.size() - 1;
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159 s = s.substr(e + 1);
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160 continue;
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161 }
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162 size_t size = s.size();
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163 s = s.ltrim();
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164 if (s.size() == size)
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165 return s;
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166 }
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167 }
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168
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169 // An erroneous token is handled as if it were the last token before EOF.
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170 bool ScriptLexer::atEOF() { return errorCount() || tokens.size() == pos; }
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171
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172 // Split a given string as an expression.
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173 // This function returns "3", "*" and "5" for "3*5" for example.
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174 static std::vector<StringRef> tokenizeExpr(StringRef s) {
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175 StringRef ops = "+-*/:!~=<>"; // List of operators
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176
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177 // Quoted strings are literal strings, so we don't want to split it.
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178 if (s.startswith("\""))
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179 return {s};
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180
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181 // Split S with operators as separators.
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182 std::vector<StringRef> ret;
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183 while (!s.empty()) {
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184 size_t e = s.find_first_of(ops);
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185
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186 // No need to split if there is no operator.
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187 if (e == StringRef::npos) {
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188 ret.push_back(s);
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189 break;
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190 }
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191
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173
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192 // Get a token before the operator.
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150
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193 if (e != 0)
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194 ret.push_back(s.substr(0, e));
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195
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196 // Get the operator as a token.
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197 // Keep !=, ==, >=, <=, << and >> operators as a single tokens.
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198 if (s.substr(e).startswith("!=") || s.substr(e).startswith("==") ||
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199 s.substr(e).startswith(">=") || s.substr(e).startswith("<=") ||
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200 s.substr(e).startswith("<<") || s.substr(e).startswith(">>")) {
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201 ret.push_back(s.substr(e, 2));
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202 s = s.substr(e + 2);
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203 } else {
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204 ret.push_back(s.substr(e, 1));
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205 s = s.substr(e + 1);
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206 }
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207 }
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208 return ret;
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209 }
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210
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211 // In contexts where expressions are expected, the lexer should apply
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212 // different tokenization rules than the default one. By default,
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213 // arithmetic operator characters are regular characters, but in the
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214 // expression context, they should be independent tokens.
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215 //
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216 // For example, "foo*3" should be tokenized to "foo", "*" and "3" only
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217 // in the expression context.
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218 //
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219 // This function may split the current token into multiple tokens.
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220 void ScriptLexer::maybeSplitExpr() {
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221 if (!inExpr || errorCount() || atEOF())
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222 return;
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223
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224 std::vector<StringRef> v = tokenizeExpr(tokens[pos]);
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225 if (v.size() == 1)
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226 return;
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227 tokens.erase(tokens.begin() + pos);
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228 tokens.insert(tokens.begin() + pos, v.begin(), v.end());
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229 }
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230
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231 StringRef ScriptLexer::next() {
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232 maybeSplitExpr();
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233
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234 if (errorCount())
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235 return "";
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236 if (atEOF()) {
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237 setError("unexpected EOF");
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238 return "";
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239 }
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240 return tokens[pos++];
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241 }
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242
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243 StringRef ScriptLexer::peek() {
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244 StringRef tok = next();
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245 if (errorCount())
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246 return "";
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247 pos = pos - 1;
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248 return tok;
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249 }
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250
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251 StringRef ScriptLexer::peek2() {
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252 skip();
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253 StringRef tok = next();
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254 if (errorCount())
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255 return "";
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256 pos = pos - 2;
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257 return tok;
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258 }
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259
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260 bool ScriptLexer::consume(StringRef tok) {
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261 if (peek() == tok) {
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262 skip();
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263 return true;
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264 }
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265 return false;
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266 }
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267
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268 // Consumes Tok followed by ":". Space is allowed between Tok and ":".
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269 bool ScriptLexer::consumeLabel(StringRef tok) {
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270 if (consume((tok + ":").str()))
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271 return true;
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272 if (tokens.size() >= pos + 2 && tokens[pos] == tok &&
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273 tokens[pos + 1] == ":") {
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274 pos += 2;
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275 return true;
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276 }
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277 return false;
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278 }
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279
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280 void ScriptLexer::skip() { (void)next(); }
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281
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282 void ScriptLexer::expect(StringRef expect) {
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283 if (errorCount())
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284 return;
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285 StringRef tok = next();
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286 if (tok != expect)
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287 setError(expect + " expected, but got " + tok);
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288 }
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289
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290 // Returns true if S encloses T.
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291 static bool encloses(StringRef s, StringRef t) {
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292 return s.bytes_begin() <= t.bytes_begin() && t.bytes_end() <= s.bytes_end();
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293 }
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294
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295 MemoryBufferRef ScriptLexer::getCurrentMB() {
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296 // Find input buffer containing the current token.
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221
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297 assert(!mbs.empty());
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298 if (pos == 0)
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299 return mbs.back();
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150
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300 for (MemoryBufferRef mb : mbs)
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301 if (encloses(mb.getBuffer(), tokens[pos - 1]))
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302 return mb;
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303 llvm_unreachable("getCurrentMB: failed to find a token");
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304 }
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