llvm-project/lld/ELF/LinkerScript.cpp

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//===- LinkerScript.cpp ---------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the parser/evaluator of the linker script.
// It does not construct an AST but consume linker script directives directly.
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// Results are written to Driver or Config object.
//
//===----------------------------------------------------------------------===//
#include "LinkerScript.h"
#include "Config.h"
#include "Driver.h"
#include "InputSection.h"
#include "OutputSections.h"
#include "ScriptParser.h"
#include "SymbolTable.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/StringSaver.h"
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace lld;
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using namespace lld::elf;
ScriptConfiguration *elf::ScriptConfig;
static bool matchStr(StringRef S, StringRef T);
// This is an operator-precedence parser to parse and evaluate
// a linker script expression. For each linker script arithmetic
// expression (e.g. ". = . + 0x1000"), a new instance of ExprParser
// is created and ran.
namespace {
class ExprParser : public ScriptParserBase {
public:
ExprParser(std::vector<StringRef> &Tokens, uint64_t Dot)
: ScriptParserBase(Tokens), Dot(Dot) {}
uint64_t run();
private:
uint64_t parsePrimary();
uint64_t parseTernary(uint64_t Cond);
uint64_t apply(StringRef Op, uint64_t L, uint64_t R);
uint64_t parseExpr1(uint64_t Lhs, int MinPrec);
uint64_t parseExpr();
uint64_t Dot;
};
}
static int precedence(StringRef Op) {
return StringSwitch<int>(Op)
.Case("*", 4)
.Case("/", 4)
.Case("+", 3)
.Case("-", 3)
.Case("<", 2)
.Case(">", 2)
.Case(">=", 2)
.Case("<=", 2)
.Case("==", 2)
.Case("!=", 2)
.Case("&", 1)
.Default(-1);
}
static uint64_t evalExpr(std::vector<StringRef> &Tokens, uint64_t Dot) {
return ExprParser(Tokens, Dot).run();
}
uint64_t ExprParser::run() {
uint64_t V = parseExpr();
if (!atEOF() && !Error)
setError("stray token: " + peek());
return V;
}
// This is a part of the operator-precedence parser to evaluate
// arithmetic expressions in SECTIONS command. This function evaluates an
// integer literal, a parenthesized expression, the ALIGN function,
// or the special variable ".".
uint64_t ExprParser::parsePrimary() {
StringRef Tok = next();
if (Tok == ".")
return Dot;
if (Tok == "(") {
uint64_t V = parseExpr();
expect(")");
return V;
}
if (Tok == "ALIGN") {
expect("(");
uint64_t V = parseExpr();
expect(")");
return alignTo(Dot, V);
}
uint64_t V = 0;
if (Tok.getAsInteger(0, V))
setError("malformed number: " + Tok);
return V;
}
uint64_t ExprParser::parseTernary(uint64_t Cond) {
next();
uint64_t V = parseExpr();
expect(":");
uint64_t W = parseExpr();
return Cond ? V : W;
}
uint64_t ExprParser::apply(StringRef Op, uint64_t L, uint64_t R) {
if (Op == "*")
return L * R;
if (Op == "/") {
if (R == 0) {
error("division by zero");
return 0;
}
return L / R;
}
if (Op == "+")
return L + R;
if (Op == "-")
return L - R;
if (Op == "<")
return L < R;
if (Op == ">")
return L > R;
if (Op == ">=")
return L >= R;
if (Op == "<=")
return L <= R;
if (Op == "==")
return L == R;
if (Op == "!=")
return L != R;
if (Op == "&")
return L & R;
llvm_unreachable("invalid operator");
return 0;
}
// This is a part of the operator-precedence parser.
// This function assumes that the remaining token stream starts
// with an operator.
uint64_t ExprParser::parseExpr1(uint64_t Lhs, int MinPrec) {
while (!atEOF()) {
// Read an operator and an expression.
StringRef Op1 = peek();
if (Op1 == "?")
return parseTernary(Lhs);
if (precedence(Op1) < MinPrec)
return Lhs;
next();
uint64_t Rhs = parsePrimary();
// Evaluate the remaining part of the expression first if the
// next operator has greater precedence than the previous one.
// For example, if we have read "+" and "3", and if the next
// operator is "*", then we'll evaluate 3 * ... part first.
while (!atEOF()) {
StringRef Op2 = peek();
if (precedence(Op2) <= precedence(Op1))
break;
Rhs = parseExpr1(Rhs, precedence(Op2));
}
Lhs = apply(Op1, Lhs, Rhs);
}
return Lhs;
}
// Reads and evaluates an arithmetic expression.
uint64_t ExprParser::parseExpr() { return parseExpr1(parsePrimary(), 0); }
template <class ELFT>
StringRef LinkerScript<ELFT>::getOutputSection(InputSectionBase<ELFT> *S) {
for (SectionRule &R : Opt.Sections)
if (matchStr(R.SectionPattern, S->getSectionName()))
return R.Dest;
return "";
}
template <class ELFT>
bool LinkerScript<ELFT>::isDiscarded(InputSectionBase<ELFT> *S) {
return getOutputSection(S) == "/DISCARD/";
}
template <class ELFT>
bool LinkerScript<ELFT>::shouldKeep(InputSectionBase<ELFT> *S) {
for (StringRef Pat : Opt.KeptSections)
if (matchStr(Pat, S->getSectionName()))
return true;
return false;
}
template <class ELFT>
void LinkerScript<ELFT>::assignAddresses(
ArrayRef<OutputSectionBase<ELFT> *> Sections) {
// Orphan sections are sections present in the input files which
// are not explicitly placed into the output file by the linker script.
// We place orphan sections at end of file.
// Other linkers places them using some heuristics as described in
// https://sourceware.org/binutils/docs/ld/Orphan-Sections.html#Orphan-Sections.
for (OutputSectionBase<ELFT> *Sec : Sections) {
StringRef Name = Sec->getName();
if (getSectionIndex(Name) == INT_MAX)
Opt.Commands.push_back({SectionKind, {}, Name});
}
// Assign addresses as instructed by linker script SECTIONS sub-commands.
Dot = Out<ELFT>::ElfHeader->getSize() + Out<ELFT>::ProgramHeaders->getSize();
uintX_t ThreadBssOffset = 0;
for (SectionsCommand &Cmd : Opt.Commands) {
if (Cmd.Kind == ExprKind) {
Dot = evalExpr(Cmd.Expr, Dot);
continue;
}
// Find all the sections with required name. There can be more than
// ont section with such name, if the alignment, flags or type
// attribute differs.
for (OutputSectionBase<ELFT> *Sec : Sections) {
if (Sec->getName() != Cmd.SectionName)
continue;
if ((Sec->getFlags() & SHF_TLS) && Sec->getType() == SHT_NOBITS) {
uintX_t TVA = Dot + ThreadBssOffset;
TVA = alignTo(TVA, Sec->getAlignment());
Sec->setVA(TVA);
ThreadBssOffset = TVA - Dot + Sec->getSize();
continue;
}
if (Sec->getFlags() & SHF_ALLOC) {
Dot = alignTo(Dot, Sec->getAlignment());
Sec->setVA(Dot);
Dot += Sec->getSize();
continue;
}
}
}
}
template <class ELFT>
ArrayRef<uint8_t> LinkerScript<ELFT>::getFiller(StringRef Name) {
auto I = Opt.Filler.find(Name);
if (I == Opt.Filler.end())
return {};
return I->second;
}
// Returns the index of the given section name in linker script
// SECTIONS commands. Sections are laid out as the same order as they
// were in the script. If a given name did not appear in the script,
// it returns INT_MAX, so that it will be laid out at end of file.
template <class ELFT>
int LinkerScript<ELFT>::getSectionIndex(StringRef Name) {
auto Begin = Opt.Commands.begin();
auto End = Opt.Commands.end();
auto I = std::find_if(Begin, End, [&](SectionsCommand &N) {
return N.Kind == SectionKind && N.SectionName == Name;
});
return I == End ? INT_MAX : (I - Begin);
}
// A compartor to sort output sections. Returns -1 or 1 if
// A or B are mentioned in linker script. Otherwise, returns 0.
template <class ELFT>
int LinkerScript<ELFT>::compareSections(StringRef A, StringRef B) {
int I = getSectionIndex(A);
int J = getSectionIndex(B);
if (I == INT_MAX && J == INT_MAX)
return 0;
return I < J ? -1 : 1;
}
// Returns true if S matches T. S can contain glob meta-characters.
// The asterisk ('*') matches zero or more characacters, and the question
// mark ('?') matches one character.
static bool matchStr(StringRef S, StringRef T) {
for (;;) {
if (S.empty())
return T.empty();
if (S[0] == '*') {
S = S.substr(1);
if (S.empty())
// Fast path. If a pattern is '*', it matches anything.
return true;
for (size_t I = 0, E = T.size(); I < E; ++I)
if (matchStr(S, T.substr(I)))
return true;
return false;
}
if (T.empty() || (S[0] != T[0] && S[0] != '?'))
return false;
S = S.substr(1);
T = T.substr(1);
}
}
class elf::ScriptParser : public ScriptParserBase {
typedef void (ScriptParser::*Handler)();
public:
ScriptParser(StringRef S, bool B) : ScriptParserBase(S), IsUnderSysroot(B) {}
void run();
private:
void addFile(StringRef Path);
void readAsNeeded();
void readEntry();
void readExtern();
void readGroup();
void readInclude();
void readNothing() {}
void readOutput();
void readOutputArch();
void readOutputFormat();
void readSearchDir();
void readSections();
void readLocationCounterValue();
void readOutputSectionDescription();
const static StringMap<Handler> Cmd;
ScriptConfiguration &Opt = *ScriptConfig;
StringSaver Saver = {ScriptConfig->Alloc};
bool IsUnderSysroot;
};
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const StringMap<elf::ScriptParser::Handler> elf::ScriptParser::Cmd = {
{"ENTRY", &ScriptParser::readEntry},
{"EXTERN", &ScriptParser::readExtern},
{"GROUP", &ScriptParser::readGroup},
{"INCLUDE", &ScriptParser::readInclude},
{"INPUT", &ScriptParser::readGroup},
{"OUTPUT", &ScriptParser::readOutput},
{"OUTPUT_ARCH", &ScriptParser::readOutputArch},
{"OUTPUT_FORMAT", &ScriptParser::readOutputFormat},
{"SEARCH_DIR", &ScriptParser::readSearchDir},
{"SECTIONS", &ScriptParser::readSections},
{";", &ScriptParser::readNothing}};
void ScriptParser::run() {
while (!atEOF()) {
StringRef Tok = next();
if (Handler Fn = Cmd.lookup(Tok))
(this->*Fn)();
else
setError("unknown directive: " + Tok);
}
}
void ScriptParser::addFile(StringRef S) {
if (IsUnderSysroot && S.startswith("/")) {
SmallString<128> Path;
(Config->Sysroot + S).toStringRef(Path);
if (sys::fs::exists(Path)) {
Driver->addFile(Saver.save(Path.str()));
return;
}
}
if (sys::path::is_absolute(S)) {
Driver->addFile(S);
} else if (S.startswith("=")) {
if (Config->Sysroot.empty())
Driver->addFile(S.substr(1));
else
Driver->addFile(Saver.save(Config->Sysroot + "/" + S.substr(1)));
} else if (S.startswith("-l")) {
Driver->addLibrary(S.substr(2));
} else if (sys::fs::exists(S)) {
Driver->addFile(S);
} else {
std::string Path = findFromSearchPaths(S);
if (Path.empty())
setError("unable to find " + S);
else
Driver->addFile(Saver.save(Path));
}
}
void ScriptParser::readAsNeeded() {
expect("(");
bool Orig = Config->AsNeeded;
Config->AsNeeded = true;
while (!Error) {
StringRef Tok = next();
if (Tok == ")")
break;
addFile(Tok);
}
Config->AsNeeded = Orig;
}
void ScriptParser::readEntry() {
// -e <symbol> takes predecence over ENTRY(<symbol>).
expect("(");
StringRef Tok = next();
if (Config->Entry.empty())
Config->Entry = Tok;
expect(")");
}
void ScriptParser::readExtern() {
expect("(");
while (!Error) {
StringRef Tok = next();
if (Tok == ")")
return;
Config->Undefined.push_back(Tok);
}
}
void ScriptParser::readGroup() {
expect("(");
while (!Error) {
StringRef Tok = next();
if (Tok == ")")
return;
if (Tok == "AS_NEEDED") {
readAsNeeded();
continue;
}
addFile(Tok);
}
}
void ScriptParser::readInclude() {
StringRef Tok = next();
auto MBOrErr = MemoryBuffer::getFile(Tok);
if (!MBOrErr) {
setError("cannot open " + Tok);
return;
}
std::unique_ptr<MemoryBuffer> &MB = *MBOrErr;
StringRef S = Saver.save(MB->getMemBufferRef().getBuffer());
std::vector<StringRef> V = tokenize(S);
Tokens.insert(Tokens.begin() + Pos, V.begin(), V.end());
}
void ScriptParser::readOutput() {
// -o <file> takes predecence over OUTPUT(<file>).
expect("(");
StringRef Tok = next();
if (Config->OutputFile.empty())
Config->OutputFile = Tok;
expect(")");
}
void ScriptParser::readOutputArch() {
// Error checking only for now.
expect("(");
next();
expect(")");
}
void ScriptParser::readOutputFormat() {
// Error checking only for now.
expect("(");
next();
StringRef Tok = next();
if (Tok == ")")
return;
if (Tok != ",") {
setError("unexpected token: " + Tok);
return;
}
next();
expect(",");
next();
expect(")");
}
void ScriptParser::readSearchDir() {
expect("(");
Config->SearchPaths.push_back(next());
expect(")");
}
void ScriptParser::readSections() {
Opt.DoLayout = true;
expect("{");
while (!Error && !skip("}")) {
StringRef Tok = peek();
if (Tok == ".")
readLocationCounterValue();
else
readOutputSectionDescription();
}
}
void ScriptParser::readLocationCounterValue() {
expect(".");
expect("=");
Opt.Commands.push_back({ExprKind, {}, ""});
SectionsCommand &Cmd = Opt.Commands.back();
while (!Error) {
StringRef Tok = next();
if (Tok == ";")
break;
Cmd.Expr.push_back(Tok);
}
if (Cmd.Expr.empty())
error("error in location counter expression");
}
void ScriptParser::readOutputSectionDescription() {
StringRef OutSec = next();
Opt.Commands.push_back({SectionKind, {}, OutSec});
expect(":");
expect("{");
while (!Error && !skip("}")) {
StringRef Tok = next();
if (Tok == "*") {
expect("(");
while (!Error && !skip(")"))
Opt.Sections.emplace_back(OutSec, next());
} else if (Tok == "KEEP") {
expect("(");
expect("*");
expect("(");
while (!Error && !skip(")")) {
StringRef Sec = next();
Opt.Sections.emplace_back(OutSec, Sec);
Opt.KeptSections.push_back(Sec);
}
expect(")");
} else {
setError("unknown command " + Tok);
}
}
StringRef Tok = peek();
if (Tok.startswith("=")) {
if (!Tok.startswith("=0x")) {
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setError("filler should be a hexadecimal value");
return;
}
Tok = Tok.substr(3);
Opt.Filler[OutSec] = parseHex(Tok);
next();
}
}
static bool isUnderSysroot(StringRef Path) {
if (Config->Sysroot == "")
return false;
for (; !Path.empty(); Path = sys::path::parent_path(Path))
if (sys::fs::equivalent(Config->Sysroot, Path))
return true;
return false;
}
// Entry point.
void elf::readLinkerScript(MemoryBufferRef MB) {
StringRef Path = MB.getBufferIdentifier();
ScriptParser(MB.getBuffer(), isUnderSysroot(Path)).run();
}
template class elf::LinkerScript<ELF32LE>;
template class elf::LinkerScript<ELF32BE>;
template class elf::LinkerScript<ELF64LE>;
template class elf::LinkerScript<ELF64BE>;