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>

usingnamespacellvm;
usingnamespacelld;
usingnamespacelld::elf;

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

ScriptLexer::ScriptLexer(Ctx &ctx, MemoryBufferRef mb)
 : ctx(ctx), curBuf(ctx, 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_tScriptLexer::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.
voidScriptLexer::setError(const Twine &msg) {
if (errCount(ctx))
return;

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

voidScriptLexer::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 = lexState;

// 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');
ErrAlways(ctx) << curBuf.filename << ":" << (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;
switch (lexState) {
case State::Script:
 pos = s.find_first_not_of(
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
"0123456789_.$/\\~=+[]*?-!^:");
break;
case State::Expr:
 pos = s.find_first_not_of(
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
"0123456789_.$");
if (pos == 0 && s.size() >= 2 &&
 ((s[0] == s[1] && strchr("<>&|", s[0])) ||
is_contained({"==", "!=", "<=", ">=", "<<", ">>"}, s.substr(0, 2))))
 pos = 2;
break;
 }

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.
boolScriptLexer::atEOF() { return eof || errCount(ctx); }

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;
returnstd::exchange(curTok, StringRef(curBuf.s.data(), 0));
}

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

boolScriptLexer::consume(StringRef tok) {
if (peek() != tok)
returnfalse;
next();
returntrue;
}

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

voidScriptLexer::expect(StringRef expect) {
if (errCount(ctx))
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.
staticboolencloses(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");
}