ScriptLexer.cpp
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//===- 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.
//
// Our grammar of the linker script is LL(2), meaning that it needs at
// most two-token lookahead to parse. The only place we need two-token
// lookahead is labels in version scripts, where we need to parse "local :"
// as if "local:".
//
// 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 "lld/Common/ErrorHandler.h"
#include "llvm/ADT/Twine.h"
using namespace llvm;
namespace lld {
namespace elf {
// Returns a whole line containing the current token.
StringRef ScriptLexer::getLine() {
StringRef s = getCurrentMB().getBuffer();
StringRef tok = tokens[pos - 1];
size_t pos = s.rfind('\n', tok.data() - s.data());
if (pos != StringRef::npos)
s = s.substr(pos + 1);
return s.substr(0, s.find_first_of("\r\n"));
}
// Returns 1-based line number of the current token.
size_t ScriptLexer::getLineNumber() {
StringRef s = getCurrentMB().getBuffer();
StringRef tok = tokens[pos - 1];
return s.substr(0, tok.data() - s.data()).count('\n') + 1;
}
// Returns 0-based column number of the current token.
size_t ScriptLexer::getColumnNumber() {
StringRef tok = tokens[pos - 1];
return tok.data() - getLine().data();
}
std::string ScriptLexer::getCurrentLocation() {
std::string filename = getCurrentMB().getBufferIdentifier();
return (filename + ":" + Twine(getLineNumber())).str();
}
ScriptLexer::ScriptLexer(MemoryBufferRef mb) { tokenize(mb); }
// 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 (pos)
s += "\n>>> " + getLine().str() + "\n>>> " +
std::string(getColumnNumber(), ' ') + "^";
error(s);
}
// Split S into linker script tokens.
void ScriptLexer::tokenize(MemoryBufferRef mb) {
std::vector<StringRef> vec;
mbs.push_back(mb);
StringRef s = mb.getBuffer();
StringRef begin = s;
for (;;) {
s = skipSpace(s);
if (s.empty())
break;
// 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.startswith("\"")) {
size_t e = s.find("\"", 1);
if (e == StringRef::npos) {
StringRef filename = mb.getBufferIdentifier();
size_t lineno = begin.substr(0, s.data() - begin.data()).count('\n');
error(filename + ":" + Twine(lineno + 1) + ": unclosed quote");
return;
}
vec.push_back(s.take_front(e + 1));
s = s.substr(e + 1);
continue;
}
// ">foo" is parsed to ">" and "foo", but ">>" is parsed to ">>".
// "|", "||", "&" and "&&" are different operators.
if (s.startswith("<<") || s.startswith("<=") || s.startswith(">>") ||
s.startswith(">=") || s.startswith("||") || s.startswith("&&")) {
vec.push_back(s.substr(0, 2));
s = s.substr(2);
continue;
}
// Unquoted token. This is more relaxed than tokens in C-like language,
// so that you can write "file-name.cpp" as one bare token, for example.
size_t pos = s.find_first_not_of(
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
"0123456789_.$/\\~=+[]*?-!^:");
// A character that cannot start a word (which is usually a
// punctuation) forms a single character token.
if (pos == 0)
pos = 1;
vec.push_back(s.substr(0, pos));
s = s.substr(pos);
}
tokens.insert(tokens.begin() + pos, vec.begin(), vec.end());
}
// Skip leading whitespace characters or comments.
StringRef ScriptLexer::skipSpace(StringRef s) {
for (;;) {
if (s.startswith("/*")) {
size_t e = s.find("*/", 2);
if (e == StringRef::npos) {
error("unclosed comment in a linker script");
return "";
}
s = s.substr(e + 2);
continue;
}
if (s.startswith("#")) {
size_t e = s.find('\n', 1);
if (e == StringRef::npos)
e = s.size() - 1;
s = s.substr(e + 1);
continue;
}
size_t size = s.size();
s = s.ltrim();
if (s.size() == size)
return s;
}
}
// An erroneous token is handled as if it were the last token before EOF.
bool ScriptLexer::atEOF() { return errorCount() || tokens.size() == pos; }
// Split a given string as an expression.
// This function returns "3", "*" and "5" for "3*5" for example.
static std::vector<StringRef> tokenizeExpr(StringRef s) {
StringRef ops = "+-*/:!~=<>"; // List of operators
// Quoted strings are literal strings, so we don't want to split it.
if (s.startswith("\""))
return {s};
// Split S with operators as separators.
std::vector<StringRef> ret;
while (!s.empty()) {
size_t e = s.find_first_of(ops);
// No need to split if there is no operator.
if (e == StringRef::npos) {
ret.push_back(s);
break;
}
// Get a token before the opreator.
if (e != 0)
ret.push_back(s.substr(0, e));
// Get the operator as a token.
// Keep !=, ==, >=, <=, << and >> operators as a single tokens.
if (s.substr(e).startswith("!=") || s.substr(e).startswith("==") ||
s.substr(e).startswith(">=") || s.substr(e).startswith("<=") ||
s.substr(e).startswith("<<") || s.substr(e).startswith(">>")) {
ret.push_back(s.substr(e, 2));
s = s.substr(e + 2);
} else {
ret.push_back(s.substr(e, 1));
s = s.substr(e + 1);
}
}
return ret;
}
// In contexts where expressions are expected, the lexer should apply
// different tokenization rules than the default one. By default,
// arithmetic operator characters are regular characters, but in the
// expression context, they should be independent tokens.
//
// For example, "foo*3" should be tokenized to "foo", "*" and "3" only
// in the expression context.
//
// This function may split the current token into multiple tokens.
void ScriptLexer::maybeSplitExpr() {
if (!inExpr || errorCount() || atEOF())
return;
std::vector<StringRef> v = tokenizeExpr(tokens[pos]);
if (v.size() == 1)
return;
tokens.erase(tokens.begin() + pos);
tokens.insert(tokens.begin() + pos, v.begin(), v.end());
}
StringRef ScriptLexer::next() {
maybeSplitExpr();
if (errorCount())
return "";
if (atEOF()) {
setError("unexpected EOF");
return "";
}
return tokens[pos++];
}
StringRef ScriptLexer::peek() {
StringRef tok = next();
if (errorCount())
return "";
pos = pos - 1;
return tok;
}
StringRef ScriptLexer::peek2() {
skip();
StringRef tok = next();
if (errorCount())
return "";
pos = pos - 2;
return tok;
}
bool ScriptLexer::consume(StringRef tok) {
if (peek() == tok) {
skip();
return true;
}
return false;
}
// Consumes Tok followed by ":". Space is allowed between Tok and ":".
bool ScriptLexer::consumeLabel(StringRef tok) {
if (consume((tok + ":").str()))
return true;
if (tokens.size() >= pos + 2 && tokens[pos] == tok &&
tokens[pos + 1] == ":") {
pos += 2;
return true;
}
return false;
}
void ScriptLexer::skip() { (void)next(); }
void ScriptLexer::expect(StringRef expect) {
if (errorCount())
return;
StringRef tok = next();
if (tok != expect)
setError(expect + " expected, but got " + tok);
}
// 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() && pos > 0);
for (MemoryBufferRef mb : mbs)
if (encloses(mb.getBuffer(), tokens[pos - 1]))
return mb;
llvm_unreachable("getCurrentMB: failed to find a token");
}
} // namespace elf
} // namespace lld