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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.
//
//===----------------------------------------------------------------------===//
#include "LinkerScript.h"
#include "Config.h"
#include "Driver.h"
#include "InputSection.h"
#include "Memory.h"
#include "OutputSections.h"
#include "ScriptLexer.h"
#include "Strings.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "Writer.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/Path.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <limits>
#include <memory>
#include <string>
#include <tuple>
#include <vector>
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;
uint64_t ExprValue::getValue() const {
if (Sec)
return Sec->getOffset(Val) + Sec->getOutputSection()->Addr;
return Val;
}
uint64_t ExprValue::getSecAddr() const {
if (Sec)
return Sec->getOffset(0) + Sec->getOutputSection()->Addr;
return 0;
}
// Some operations only support one non absolute value. Move the
// absolute one to the right hand side for convenience.
static void moveAbsRight(ExprValue &A, ExprValue &B) {
if (A.isAbsolute())
std::swap(A, B);
if (!B.isAbsolute())
error("At least one side of the expression must be absolute");
}
static ExprValue add(ExprValue A, ExprValue B) {
moveAbsRight(A, B);
return {A.Sec, A.ForceAbsolute, A.Val + B.getValue()};
}
static ExprValue sub(ExprValue A, ExprValue B) {
return {A.Sec, A.Val - B.getValue()};
}
static ExprValue mul(ExprValue A, ExprValue B) {
return A.getValue() * B.getValue();
}
static ExprValue div(ExprValue A, ExprValue B) {
if (uint64_t BV = B.getValue())
return A.getValue() / BV;
error("division by zero");
return 0;
}
static ExprValue leftShift(ExprValue A, ExprValue B) {
return A.getValue() << B.getValue();
}
static ExprValue rightShift(ExprValue A, ExprValue B) {
return A.getValue() >> B.getValue();
}
static ExprValue lessThan(ExprValue A, ExprValue B) {
return A.getValue() < B.getValue();
}
static ExprValue greaterThan(ExprValue A, ExprValue B) {
return A.getValue() > B.getValue();
}
static ExprValue greaterThanOrEqual(ExprValue A, ExprValue B) {
return A.getValue() >= B.getValue();
}
static ExprValue lessThanOrEqual(ExprValue A, ExprValue B) {
return A.getValue() <= B.getValue();
}
static ExprValue equal(ExprValue A, ExprValue B) {
return A.getValue() == B.getValue();
}
static ExprValue notEqual(ExprValue A, ExprValue B) {
return A.getValue() != B.getValue();
}
static ExprValue bitAnd(ExprValue A, ExprValue B) {
moveAbsRight(A, B);
return {A.Sec, A.ForceAbsolute,
(A.getValue() & B.getValue()) - A.getSecAddr()};
}
static ExprValue bitOr(ExprValue A, ExprValue B) {
moveAbsRight(A, B);
return {A.Sec, A.ForceAbsolute,
(A.getValue() | B.getValue()) - A.getSecAddr()};
}
static ExprValue bitNot(ExprValue A) { return ~A.getValue(); }
static ExprValue minus(ExprValue A) { return -A.getValue(); }
LinkerScriptBase *elf::Script;
ScriptConfiguration *elf::ScriptConfig;
template <class ELFT> static SymbolBody *addRegular(SymbolAssignment *Cmd) {
Symbol *Sym;
uint8_t Visibility = Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT;
std::tie(Sym, std::ignore) = Symtab<ELFT>::X->insert(
Cmd->Name, /*Type*/ 0, Visibility, /*CanOmitFromDynSym*/ false,
/*File*/ nullptr);
Sym->Binding = STB_GLOBAL;
ExprValue Value = Cmd->Expression();
SectionBase *Sec = Value.isAbsolute() ? nullptr : Value.Sec;
replaceBody<DefinedRegular>(Sym, Cmd->Name, /*IsLocal=*/false, Visibility,
STT_NOTYPE, 0, 0, Sec, nullptr);
return Sym->body();
}
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;
}
OutputSection *LinkerScriptBase::getOutputSection(const Twine &Loc,
StringRef Name) {
static OutputSection FakeSec("", 0, 0);
for (OutputSection *Sec : *OutputSections)
if (Sec->Name == Name)
return Sec;
if (ErrorOnMissingSection)
error(Loc + ": undefined section " + Name);
return &FakeSec;
}
// This function is essentially the same as getOutputSection(Name)->Size,
// but it won't print out an error message if a given section is not found.
//
// Linker script does not create an output section if its content is empty.
// We want to allow SIZEOF(.foo) where .foo is a section which happened to
// be empty. That is why this function is different from getOutputSection().
uint64_t LinkerScriptBase::getOutputSectionSize(StringRef Name) {
for (OutputSection *Sec : *OutputSections)
if (Sec->Name == Name)
return Sec->Size;
return 0;
}
void LinkerScriptBase::setDot(Expr E, const Twine &Loc, bool InSec) {
uint64_t Val = E().getValue();
if (Val < Dot) {
if (InSec)
error(Loc + ": unable to move location counter backward for: " +
CurOutSec->Name);
else
error(Loc + ": unable to move location counter backward");
}
Dot = Val;
// Update to location counter means update to section size.
if (InSec)
CurOutSec->Size = Dot - CurOutSec->Addr;
}
// Sets value of a symbol. Two kinds of symbols are processed: synthetic
// symbols, whose value is an offset from beginning of section and regular
// symbols whose value is absolute.
void LinkerScriptBase::assignSymbol(SymbolAssignment *Cmd, bool InSec) {
if (Cmd->Name == ".") {
setDot(Cmd->Expression, Cmd->Location, InSec);
return;
}
if (!Cmd->Sym)
return;
auto *Sym = cast<DefinedRegular>(Cmd->Sym);
ExprValue V = Cmd->Expression();
if (V.isAbsolute()) {
Sym->Value = V.getValue();
} else {
Sym->Section = V.Sec;
if (Sym->Section->Flags & SHF_ALLOC)
Sym->Value = V.Val;
else
Sym->Value = V.getValue();
}
}
static SymbolBody *findSymbol(StringRef S) {
switch (Config->EKind) {
case ELF32LEKind:
return Symtab<ELF32LE>::X->find(S);
case ELF32BEKind:
return Symtab<ELF32BE>::X->find(S);
case ELF64LEKind:
return Symtab<ELF64LE>::X->find(S);
case ELF64BEKind:
return Symtab<ELF64BE>::X->find(S);
default:
llvm_unreachable("unknown Config->EKind");
}
}
static SymbolBody *addRegularSymbol(SymbolAssignment *Cmd) {
switch (Config->EKind) {
case ELF32LEKind:
return addRegular<ELF32LE>(Cmd);
case ELF32BEKind:
return addRegular<ELF32BE>(Cmd);
case ELF64LEKind:
return addRegular<ELF64LE>(Cmd);
case ELF64BEKind:
return addRegular<ELF64BE>(Cmd);
default:
llvm_unreachable("unknown Config->EKind");
}
}
void LinkerScriptBase::addSymbol(SymbolAssignment *Cmd) {
if (Cmd->Name == ".")
return;
// If a symbol was in PROVIDE(), we need to define it only when
// it is a referenced undefined symbol.
SymbolBody *B = findSymbol(Cmd->Name);
if (Cmd->Provide && (!B || B->isDefined()))
return;
Cmd->Sym = addRegularSymbol(Cmd);
}
bool SymbolAssignment::classof(const BaseCommand *C) {
return C->Kind == AssignmentKind;
}
bool OutputSectionCommand::classof(const BaseCommand *C) {
return C->Kind == OutputSectionKind;
}
bool InputSectionDescription::classof(const BaseCommand *C) {
return C->Kind == InputSectionKind;
}
bool AssertCommand::classof(const BaseCommand *C) {
return C->Kind == AssertKind;
}
bool BytesDataCommand::classof(const BaseCommand *C) {
return C->Kind == BytesDataKind;
}
static StringRef basename(InputSectionBase *S) {
if (S->File)
return sys::path::filename(S->File->getName());
return "";
}
bool LinkerScriptBase::shouldKeep(InputSectionBase *S) {
for (InputSectionDescription *ID : Opt.KeptSections)
if (ID->FilePat.match(basename(S)))
for (SectionPattern &P : ID->SectionPatterns)
if (P.SectionPat.match(S->Name))
return true;
return false;
}
static bool comparePriority(InputSectionBase *A, InputSectionBase *B) {
return getPriority(A->Name) < getPriority(B->Name);
}
static bool compareName(InputSectionBase *A, InputSectionBase *B) {
return A->Name < B->Name;
}
static bool compareAlignment(InputSectionBase *A, InputSectionBase *B) {
// ">" is not a mistake. Larger alignments are placed before smaller
// alignments in order to reduce the amount of padding necessary.
// This is compatible with GNU.
return A->Alignment > B->Alignment;
}
static std::function<bool(InputSectionBase *, InputSectionBase *)>
getComparator(SortSectionPolicy K) {
switch (K) {
case SortSectionPolicy::Alignment:
return compareAlignment;
case SortSectionPolicy::Name:
return compareName;
case SortSectionPolicy::Priority:
return comparePriority;
default:
llvm_unreachable("unknown sort policy");
}
}
static bool matchConstraints(ArrayRef<InputSectionBase *> Sections,
ConstraintKind Kind) {
if (Kind == ConstraintKind::NoConstraint)
return true;
bool IsRW = llvm::any_of(Sections, [=](InputSectionBase *Sec2) {
auto *Sec = static_cast<InputSectionBase *>(Sec2);
return Sec->Flags & SHF_WRITE;
});
return (IsRW && Kind == ConstraintKind::ReadWrite) ||
(!IsRW && Kind == ConstraintKind::ReadOnly);
}
static void sortSections(InputSectionBase **Begin, InputSectionBase **End,
SortSectionPolicy K) {
if (K != SortSectionPolicy::Default && K != SortSectionPolicy::None)
std::stable_sort(Begin, End, getComparator(K));
}
// Compute and remember which sections the InputSectionDescription matches.
void LinkerScriptBase::computeInputSections(InputSectionDescription *I) {
// Collects all sections that satisfy constraints of I
// and attach them to I.
for (SectionPattern &Pat : I->SectionPatterns) {
size_t SizeBefore = I->Sections.size();
for (InputSectionBase *S : InputSections) {
if (S->Assigned)
continue;
// For -emit-relocs we have to ignore entries like
// .rela.dyn : { *(.rela.data) }
// which are common because they are in the default bfd script.
if (S->Type == SHT_REL || S->Type == SHT_RELA)
continue;
StringRef Filename = basename(S);
if (!I->FilePat.match(Filename) || Pat.ExcludedFilePat.match(Filename))
continue;
if (!Pat.SectionPat.match(S->Name))
continue;
I->Sections.push_back(S);
S->Assigned = true;
}
// Sort sections as instructed by SORT-family commands and --sort-section
// option. Because SORT-family commands can be nested at most two depth
// (e.g. SORT_BY_NAME(SORT_BY_ALIGNMENT(.text.*))) and because the command
// line option is respected even if a SORT command is given, the exact
// behavior we have here is a bit complicated. Here are the rules.
//
// 1. If two SORT commands are given, --sort-section is ignored.
// 2. If one SORT command is given, and if it is not SORT_NONE,
// --sort-section is handled as an inner SORT command.
// 3. If one SORT command is given, and if it is SORT_NONE, don't sort.
// 4. If no SORT command is given, sort according to --sort-section.
InputSectionBase **Begin = I->Sections.data() + SizeBefore;
InputSectionBase **End = I->Sections.data() + I->Sections.size();
if (Pat.SortOuter != SortSectionPolicy::None) {
if (Pat.SortInner == SortSectionPolicy::Default)
sortSections(Begin, End, Config->SortSection);
else
sortSections(Begin, End, Pat.SortInner);
sortSections(Begin, End, Pat.SortOuter);
}
}
}
void LinkerScriptBase::discard(ArrayRef<InputSectionBase *> V) {
for (InputSectionBase *S : V) {
S->Live = false;
if (S == InX::ShStrTab)
error("discarding .shstrtab section is not allowed");
discard(S->DependentSections);
}
}
std::vector<InputSectionBase *>
LinkerScriptBase::createInputSectionList(OutputSectionCommand &OutCmd) {
std::vector<InputSectionBase *> Ret;
for (const std::unique_ptr<BaseCommand> &Base : OutCmd.Commands) {
auto *Cmd = dyn_cast<InputSectionDescription>(Base.get());
if (!Cmd)
continue;
computeInputSections(Cmd);
for (InputSectionBase *S : Cmd->Sections)
Ret.push_back(static_cast<InputSectionBase *>(S));
}
return Ret;
}
void LinkerScriptBase::processCommands(OutputSectionFactory &Factory) {
// A symbol can be assigned before any section is mentioned in the linker
// script. In an DSO, the symbol values are addresses, so the only important
// section values are:
// * SHN_UNDEF
// * SHN_ABS
// * Any value meaning a regular section.
// To handle that, create a dummy aether section that fills the void before
// the linker scripts switches to another section. It has an index of one
// which will map to whatever the first actual section is.
Aether = make<OutputSection>("", 0, SHF_ALLOC);
Aether->SectionIndex = 1;
CurOutSec = Aether;
for (unsigned I = 0; I < Opt.Commands.size(); ++I) {
auto Iter = Opt.Commands.begin() + I;
const std::unique_ptr<BaseCommand> &Base1 = *Iter;
// Handle symbol assignments outside of any output section.
if (auto *Cmd = dyn_cast<SymbolAssignment>(Base1.get())) {
addSymbol(Cmd);
continue;
}
if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base1.get())) {
std::vector<InputSectionBase *> V = createInputSectionList(*Cmd);
// The output section name `/DISCARD/' is special.
// Any input section assigned to it is discarded.
if (Cmd->Name == "/DISCARD/") {
discard(V);
continue;
}
// This is for ONLY_IF_RO and ONLY_IF_RW. An output section directive
// ".foo : ONLY_IF_R[OW] { ... }" is handled only if all member input
// sections satisfy a given constraint. If not, a directive is handled
// as if it wasn't present from the beginning.
//
// Because we'll iterate over Commands many more times, the easiest
// way to "make it as if it wasn't present" is to just remove it.
if (!matchConstraints(V, Cmd->Constraint)) {
for (InputSectionBase *S : V)
S->Assigned = false;
Opt.Commands.erase(Iter);
--I;
continue;
}
// A directive may contain symbol definitions like this:
// ".foo : { ...; bar = .; }". Handle them.
for (const std::unique_ptr<BaseCommand> &Base : Cmd->Commands)
if (auto *OutCmd = dyn_cast<SymbolAssignment>(Base.get()))
addSymbol(OutCmd);
// Handle subalign (e.g. ".foo : SUBALIGN(32) { ... }"). If subalign
// is given, input sections are aligned to that value, whether the
// given value is larger or smaller than the original section alignment.
if (Cmd->SubalignExpr) {
uint32_t Subalign = Cmd->SubalignExpr().getValue();
for (InputSectionBase *S : V)
S->Alignment = Subalign;
}
// Add input sections to an output section.
for (InputSectionBase *S : V)
Factory.addInputSec(S, Cmd->Name);
}
}
CurOutSec = nullptr;
}
// Add sections that didn't match any sections command.
void LinkerScriptBase::addOrphanSections(OutputSectionFactory &Factory) {
for (InputSectionBase *S : InputSections)
if (S->Live && !S->OutSec)
Factory.addInputSec(S, getOutputSectionName(S->Name));
}
static bool isTbss(OutputSection *Sec) {
return (Sec->Flags & SHF_TLS) && Sec->Type == SHT_NOBITS;
}
void LinkerScriptBase::output(InputSection *S) {
if (!AlreadyOutputIS.insert(S).second)
return;
bool IsTbss = isTbss(CurOutSec);
uint64_t Pos = IsTbss ? Dot + ThreadBssOffset : Dot;
Pos = alignTo(Pos, S->Alignment);
S->OutSecOff = Pos - CurOutSec->Addr;
Pos += S->getSize();
// Update output section size after adding each section. This is so that
// SIZEOF works correctly in the case below:
// .foo { *(.aaa) a = SIZEOF(.foo); *(.bbb) }
CurOutSec->Size = Pos - CurOutSec->Addr;
// If there is a memory region associated with this input section, then
// place the section in that region and update the region index.
if (CurMemRegion) {
CurMemRegion->Offset += CurOutSec->Size;
uint64_t CurSize = CurMemRegion->Offset - CurMemRegion->Origin;
if (CurSize > CurMemRegion->Length) {
uint64_t OverflowAmt = CurSize - CurMemRegion->Length;
error("section '" + CurOutSec->Name + "' will not fit in region '" +
CurMemRegion->Name + "': overflowed by " + Twine(OverflowAmt) +
" bytes");
}
}
if (IsTbss)
ThreadBssOffset = Pos - Dot;
else
Dot = Pos;
}
void LinkerScriptBase::flush() {
assert(CurOutSec);
if (!AlreadyOutputOS.insert(CurOutSec).second)
return;
for (InputSection *I : CurOutSec->Sections)
output(I);
}
void LinkerScriptBase::switchTo(OutputSection *Sec) {
if (CurOutSec == Sec)
return;
if (AlreadyOutputOS.count(Sec))
return;
CurOutSec = Sec;
Dot = alignTo(Dot, CurOutSec->Alignment);
CurOutSec->Addr = isTbss(CurOutSec) ? Dot + ThreadBssOffset : Dot;
// If neither AT nor AT> is specified for an allocatable section, the linker
// will set the LMA such that the difference between VMA and LMA for the
// section is the same as the preceding output section in the same region
// https://sourceware.org/binutils/docs-2.20/ld/Output-Section-LMA.html
if (LMAOffset)
CurOutSec->LMAOffset = LMAOffset();
}
void LinkerScriptBase::process(BaseCommand &Base) {
// This handles the assignments to symbol or to a location counter (.)
if (auto *AssignCmd = dyn_cast<SymbolAssignment>(&Base)) {
assignSymbol(AssignCmd, true);
return;
}
// Handle BYTE(), SHORT(), LONG(), or QUAD().
if (auto *DataCmd = dyn_cast<BytesDataCommand>(&Base)) {
DataCmd->Offset = Dot - CurOutSec->Addr;
Dot += DataCmd->Size;
CurOutSec->Size = Dot - CurOutSec->Addr;
return;
}
if (auto *AssertCmd = dyn_cast<AssertCommand>(&Base)) {
AssertCmd->Expression();
return;
}
// It handles single input section description command,
// calculates and assigns the offsets for each section and also
// updates the output section size.
auto &ICmd = cast<InputSectionDescription>(Base);
for (InputSectionBase *IB : ICmd.Sections) {
// We tentatively added all synthetic sections at the beginning and removed
// empty ones afterwards (because there is no way to know whether they were
// going be empty or not other than actually running linker scripts.)
// We need to ignore remains of empty sections.
if (auto *Sec = dyn_cast<SyntheticSection>(IB))
if (Sec->empty())
continue;
if (!IB->Live)
continue;
assert(CurOutSec == IB->OutSec || AlreadyOutputOS.count(IB->OutSec));
output(cast<InputSection>(IB));
}
}
static OutputSection *
findSection(StringRef Name, const std::vector<OutputSection *> &Sections) {
auto End = Sections.end();
auto HasName = [=](OutputSection *Sec) { return Sec->Name == Name; };
auto I = std::find_if(Sections.begin(), End, HasName);
std::vector<OutputSection *> Ret;
if (I == End)
return nullptr;
assert(std::find_if(I + 1, End, HasName) == End);
return *I;
}
// This function searches for a memory region to place the given output
// section in. If found, a pointer to the appropriate memory region is
// returned. Otherwise, a nullptr is returned.
MemoryRegion *LinkerScriptBase::findMemoryRegion(OutputSectionCommand *Cmd,
OutputSection *Sec) {
// If a memory region name was specified in the output section command,
// then try to find that region first.
if (!Cmd->MemoryRegionName.empty()) {
auto It = Opt.MemoryRegions.find(Cmd->MemoryRegionName);
if (It != Opt.MemoryRegions.end())
return &It->second;
error("memory region '" + Cmd->MemoryRegionName + "' not declared");
return nullptr;
}
// The memory region name is empty, thus a suitable region must be
// searched for in the region map. If the region map is empty, just
// return. Note that this check doesn't happen at the very beginning
// so that uses of undeclared regions can be caught.
if (!Opt.MemoryRegions.size())
return nullptr;
// See if a region can be found by matching section flags.
for (auto &MRI : Opt.MemoryRegions) {
MemoryRegion &MR = MRI.second;
if ((MR.Flags & Sec->Flags) != 0 && (MR.NegFlags & Sec->Flags) == 0)
return &MR;
}
// Otherwise, no suitable region was found.
if (Sec->Flags & SHF_ALLOC)
error("no memory region specified for section '" + Sec->Name + "'");
return nullptr;
}
// This function assigns offsets to input sections and an output section
// for a single sections command (e.g. ".text { *(.text); }").
void LinkerScriptBase::assignOffsets(OutputSectionCommand *Cmd) {
OutputSection *Sec = findSection(Cmd->Name, *OutputSections);
if (!Sec)
return;
if (Cmd->AddrExpr && Sec->Flags & SHF_ALLOC)
setDot(Cmd->AddrExpr, Cmd->Location);
if (Cmd->LMAExpr) {
uint64_t D = Dot;
LMAOffset = [=] { return Cmd->LMAExpr().getValue() - D; };
}
// Handle align (e.g. ".foo : ALIGN(16) { ... }").
if (Cmd->AlignExpr)
Sec->updateAlignment(Cmd->AlignExpr().getValue());
// Try and find an appropriate memory region to assign offsets in.
CurMemRegion = findMemoryRegion(Cmd, Sec);
if (CurMemRegion)
Dot = CurMemRegion->Offset;
switchTo(Sec);
// Find the last section output location. We will output orphan sections
// there so that end symbols point to the correct location.
auto E = std::find_if(Cmd->Commands.rbegin(), Cmd->Commands.rend(),
[](const std::unique_ptr<BaseCommand> &Cmd) {
return !isa<SymbolAssignment>(*Cmd);
})
.base();
for (auto I = Cmd->Commands.begin(); I != E; ++I)
process(**I);
flush();
std::for_each(E, Cmd->Commands.end(),
[this](std::unique_ptr<BaseCommand> &B) { process(*B.get()); });
}
void LinkerScriptBase::removeEmptyCommands() {
// It is common practice to use very generic linker scripts. So for any
// given run some of the output sections in the script will be empty.
// We could create corresponding empty output sections, but that would
// clutter the output.
// We instead remove trivially empty sections. The bfd linker seems even
// more aggressive at removing them.
auto Pos = std::remove_if(
Opt.Commands.begin(), Opt.Commands.end(),
[&](const std::unique_ptr<BaseCommand> &Base) {
if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base.get()))
return !findSection(Cmd->Name, *OutputSections);
return false;
});
Opt.Commands.erase(Pos, Opt.Commands.end());
}
static bool isAllSectionDescription(const OutputSectionCommand &Cmd) {
for (const std::unique_ptr<BaseCommand> &I : Cmd.Commands)
if (!isa<InputSectionDescription>(*I))
return false;
return true;
}
void LinkerScriptBase::adjustSectionsBeforeSorting() {
// If the output section contains only symbol assignments, create a
// corresponding output section. The bfd linker seems to only create them if
// '.' is assigned to, but creating these section should not have any bad
// consequeces and gives us a section to put the symbol in.
uint64_t Flags = SHF_ALLOC;
uint32_t Type = SHT_NOBITS;
for (const std::unique_ptr<BaseCommand> &Base : Opt.Commands) {
auto *Cmd = dyn_cast<OutputSectionCommand>(Base.get());
if (!Cmd)
continue;
if (OutputSection *Sec = findSection(Cmd->Name, *OutputSections)) {
Flags = Sec->Flags;
Type = Sec->Type;
continue;
}
if (isAllSectionDescription(*Cmd))
continue;
auto *OutSec = make<OutputSection>(Cmd->Name, Type, Flags);
OutputSections->push_back(OutSec);
}
}
void LinkerScriptBase::adjustSectionsAfterSorting() {
placeOrphanSections();
// If output section command doesn't specify any segments,
// and we haven't previously assigned any section to segment,
// then we simply assign section to the very first load segment.
// Below is an example of such linker script:
// PHDRS { seg PT_LOAD; }
// SECTIONS { .aaa : { *(.aaa) } }
std::vector<StringRef> DefPhdrs;
auto FirstPtLoad =
std::find_if(Opt.PhdrsCommands.begin(), Opt.PhdrsCommands.end(),
[](const PhdrsCommand &Cmd) { return Cmd.Type == PT_LOAD; });
if (FirstPtLoad != Opt.PhdrsCommands.end())
DefPhdrs.push_back(FirstPtLoad->Name);
// Walk the commands and propagate the program headers to commands that don't
// explicitly specify them.
for (const std::unique_ptr<BaseCommand> &Base : Opt.Commands) {
auto *Cmd = dyn_cast<OutputSectionCommand>(Base.get());
if (!Cmd)
continue;
if (Cmd->Phdrs.empty())
Cmd->Phdrs = DefPhdrs;
else
DefPhdrs = Cmd->Phdrs;
}
removeEmptyCommands();
}
// When placing orphan sections, we want to place them after symbol assignments
// so that an orphan after
// begin_foo = .;
// foo : { *(foo) }
// end_foo = .;
// doesn't break the intended meaning of the begin/end symbols.
// We don't want to go over sections since Writer<ELFT>::sortSections is the
// one in charge of deciding the order of the sections.
// We don't want to go over alignments, since doing so in
// rx_sec : { *(rx_sec) }
// . = ALIGN(0x1000);
// /* The RW PT_LOAD starts here*/
// rw_sec : { *(rw_sec) }
// would mean that the RW PT_LOAD would become unaligned.
static bool shouldSkip(const BaseCommand &Cmd) {
if (isa<OutputSectionCommand>(Cmd))
return false;
const auto *Assign = dyn_cast<SymbolAssignment>(&Cmd);
if (!Assign)
return true;
return Assign->Name != ".";
}
// Orphan sections are sections present in the input files which are
// not explicitly placed into the output file by the linker script.
//
// When the control reaches this function, Opt.Commands contains
// output section commands for non-orphan sections only. This function
// adds new elements for orphan sections to Opt.Commands so that all
// sections are explicitly handled by Opt.Commands.
//
// Writer<ELFT>::sortSections has already sorted output sections.
// What we need to do is to scan OutputSections vector and
// Opt.Commands in parallel to find orphan sections. If there is an
// output section that doesn't have a corresponding entry in
// Opt.Commands, we will insert a new entry to Opt.Commands.
//
// There is some ambiguity as to where exactly a new entry should be
// inserted, because Opt.Commands contains not only output section
// commands but other types of commands such as symbol assignment
// expressions. There's no correct answer here due to the lack of the
// formal specification of the linker script. We use heuristics to
// determine whether a new output command should be added before or
// after another commands. For the details, look at shouldSkip
// function.
void LinkerScriptBase::placeOrphanSections() {
// The OutputSections are already in the correct order.
// This loops creates or moves commands as needed so that they are in the
// correct order.
int CmdIndex = 0;
// As a horrible special case, skip the first . assignment if it is before any
// section. We do this because it is common to set a load address by starting
// the script with ". = 0xabcd" and the expectation is that every section is
// after that.
auto FirstSectionOrDotAssignment =
std::find_if(Opt.Commands.begin(), Opt.Commands.end(),
[](const std::unique_ptr<BaseCommand> &Cmd) {
if (isa<OutputSectionCommand>(*Cmd))
return true;
const auto *Assign = dyn_cast<SymbolAssignment>(Cmd.get());
if (!Assign)
return false;
return Assign->Name == ".";
});
if (FirstSectionOrDotAssignment != Opt.Commands.end()) {
CmdIndex = FirstSectionOrDotAssignment - Opt.Commands.begin();
if (isa<SymbolAssignment>(**FirstSectionOrDotAssignment))
++CmdIndex;
}
for (OutputSection *Sec : *OutputSections) {
StringRef Name = Sec->Name;
// Find the last spot where we can insert a command and still get the
// correct result.
auto CmdIter = Opt.Commands.begin() + CmdIndex;
auto E = Opt.Commands.end();
while (CmdIter != E && shouldSkip(**CmdIter)) {
++CmdIter;
++CmdIndex;
}
auto Pos =
std::find_if(CmdIter, E, [&](const std::unique_ptr<BaseCommand> &Base) {
auto *Cmd = dyn_cast<OutputSectionCommand>(Base.get());
return Cmd && Cmd->Name == Name;
});
if (Pos == E) {
Opt.Commands.insert(CmdIter,
llvm::make_unique<OutputSectionCommand>(Name));
++CmdIndex;
continue;
}
// Continue from where we found it.
CmdIndex = (Pos - Opt.Commands.begin()) + 1;
}
}
void LinkerScriptBase::processNonSectionCommands() {
for (const std::unique_ptr<BaseCommand> &Base : Opt.Commands) {
if (auto *Cmd = dyn_cast<SymbolAssignment>(Base.get()))
assignSymbol(Cmd);
else if (auto *Cmd = dyn_cast<AssertCommand>(Base.get()))
Cmd->Expression();
}
}
void LinkerScriptBase::assignAddresses(std::vector<PhdrEntry> &Phdrs) {
// Assign addresses as instructed by linker script SECTIONS sub-commands.
Dot = 0;
ErrorOnMissingSection = true;
switchTo(Aether);
for (const std::unique_ptr<BaseCommand> &Base : Opt.Commands) {
if (auto *Cmd = dyn_cast<SymbolAssignment>(Base.get())) {
assignSymbol(Cmd);
continue;
}
if (auto *Cmd = dyn_cast<AssertCommand>(Base.get())) {
Cmd->Expression();
continue;
}
auto *Cmd = cast<OutputSectionCommand>(Base.get());
assignOffsets(Cmd);
}
uint64_t MinVA = std::numeric_limits<uint64_t>::max();
for (OutputSection *Sec : *OutputSections) {
if (Sec->Flags & SHF_ALLOC)
MinVA = std::min<uint64_t>(MinVA, Sec->Addr);
else
Sec->Addr = 0;
}
allocateHeaders(Phdrs, *OutputSections, MinVA);
}
// Creates program headers as instructed by PHDRS linker script command.
std::vector<PhdrEntry> LinkerScriptBase::createPhdrs() {
std::vector<PhdrEntry> Ret;
// Process PHDRS and FILEHDR keywords because they are not
// real output sections and cannot be added in the following loop.
for (const PhdrsCommand &Cmd : Opt.PhdrsCommands) {
Ret.emplace_back(Cmd.Type, Cmd.Flags == UINT_MAX ? PF_R : Cmd.Flags);
PhdrEntry &Phdr = Ret.back();
if (Cmd.HasFilehdr)
Phdr.add(Out::ElfHeader);
if (Cmd.HasPhdrs)
Phdr.add(Out::ProgramHeaders);
if (Cmd.LMAExpr) {
Phdr.p_paddr = Cmd.LMAExpr().getValue();
Phdr.HasLMA = true;
}
}
// Add output sections to program headers.
for (OutputSection *Sec : *OutputSections) {
if (!(Sec->Flags & SHF_ALLOC))
break;
// Assign headers specified by linker script
for (size_t Id : getPhdrIndices(Sec->Name)) {
Ret[Id].add(Sec);
if (Opt.PhdrsCommands[Id].Flags == UINT_MAX)
Ret[Id].p_flags |= Sec->getPhdrFlags();
}
}
return Ret;
}
bool LinkerScriptBase::ignoreInterpSection() {
// Ignore .interp section in case we have PHDRS specification
// and PT_INTERP isn't listed.
return !Opt.PhdrsCommands.empty() &&
llvm::find_if(Opt.PhdrsCommands, [](const PhdrsCommand &Cmd) {
return Cmd.Type == PT_INTERP;
}) == Opt.PhdrsCommands.end();
}
uint32_t LinkerScriptBase::getFiller(StringRef Name) {
for (const std::unique_ptr<BaseCommand> &Base : Opt.Commands)
if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base.get()))
if (Cmd->Name == Name)
return Cmd->Filler;
return 0;
}
static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
const endianness E =
(Config->EKind == ELF32LEKind || Config->EKind == ELF64LEKind)
? llvm::support::endianness::little
: llvm::support::endianness::big;
switch (Size) {
case 1:
*Buf = (uint8_t)Data;
break;
case 2:
write16(Buf, Data, E);
break;
case 4:
write32(Buf, Data, E);
break;
case 8:
write64(Buf, Data, E);
break;
default:
llvm_unreachable("unsupported Size argument");
}
}
void LinkerScriptBase::writeDataBytes(StringRef Name, uint8_t *Buf) {
int I = getSectionIndex(Name);
if (I == INT_MAX)
return;
auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I].get());
for (const std::unique_ptr<BaseCommand> &Base : Cmd->Commands)
if (auto *Data = dyn_cast<BytesDataCommand>(Base.get()))
writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size);
}
bool LinkerScriptBase::hasLMA(StringRef Name) {
for (const std::unique_ptr<BaseCommand> &Base : Opt.Commands)
if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base.get()))
if (Cmd->LMAExpr && Cmd->Name == Name)
return true;
return false;
}
// 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.
int LinkerScriptBase::getSectionIndex(StringRef Name) {
for (int I = 0, E = Opt.Commands.size(); I != E; ++I)
if (auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I].get()))
if (Cmd->Name == Name)
return I;
return INT_MAX;
}
ExprValue LinkerScriptBase::getSymbolValue(const Twine &Loc, StringRef S) {
if (S == ".")
return {CurOutSec, Dot - CurOutSec->Addr};
if (SymbolBody *B = findSymbol(S)) {
if (auto *D = dyn_cast<DefinedRegular>(B))
return {D->Section, D->Value};
auto *C = cast<DefinedCommon>(B);
return {InX::Common, C->Offset};
}
error(Loc + ": symbol not found: " + S);
return 0;
}
bool LinkerScriptBase::isDefined(StringRef S) {
return findSymbol(S) != nullptr;
}
// Returns indices of ELF headers containing specific section, identified
// by Name. Each index is a zero based number of ELF header listed within
// PHDRS {} script block.
std::vector<size_t> LinkerScriptBase::getPhdrIndices(StringRef SectionName) {
for (const std::unique_ptr<BaseCommand> &Base : Opt.Commands) {
auto *Cmd = dyn_cast<OutputSectionCommand>(Base.get());
if (!Cmd || Cmd->Name != SectionName)
continue;
std::vector<size_t> Ret;
for (StringRef PhdrName : Cmd->Phdrs)
Ret.push_back(getPhdrIndex(Cmd->Location, PhdrName));
return Ret;
}
return {};
}
size_t LinkerScriptBase::getPhdrIndex(const Twine &Loc, StringRef PhdrName) {
size_t I = 0;
for (PhdrsCommand &Cmd : Opt.PhdrsCommands) {
if (Cmd.Name == PhdrName)
return I;
++I;
}
error(Loc + ": section header '" + PhdrName + "' is not listed in PHDRS");
return 0;
}
class elf::ScriptParser final : public ScriptLexer {
typedef void (ScriptParser::*Handler)();
public:
ScriptParser(MemoryBufferRef MB)
: ScriptLexer(MB),
IsUnderSysroot(isUnderSysroot(MB.getBufferIdentifier())) {}
void readLinkerScript();
void readVersionScript();
void readDynamicList();
private:
void addFile(StringRef Path);
void readAsNeeded();
void readEntry();
void readExtern();
void readGroup();
void readInclude();
void readMemory();
void readOutput();
void readOutputArch();
void readOutputFormat();
void readPhdrs();
void readSearchDir();
void readSections();
void readVersion();
void readVersionScriptCommand();
SymbolAssignment *readAssignment(StringRef Name);
BytesDataCommand *readBytesDataCommand(StringRef Tok);
uint32_t readFill();
OutputSectionCommand *readOutputSectionDescription(StringRef OutSec);
uint32_t readOutputSectionFiller(StringRef Tok);
std::vector<StringRef> readOutputSectionPhdrs();
InputSectionDescription *readInputSectionDescription(StringRef Tok);
StringMatcher readFilePatterns();
std::vector<SectionPattern> readInputSectionsList();
InputSectionDescription *readInputSectionRules(StringRef FilePattern);
unsigned readPhdrType();
SortSectionPolicy readSortKind();
SymbolAssignment *readProvideHidden(bool Provide, bool Hidden);
SymbolAssignment *readProvideOrAssignment(StringRef Tok);
void readSort();
Expr readAssert();
uint64_t readMemoryAssignment(StringRef, StringRef, StringRef);
std::pair<uint32_t, uint32_t> readMemoryAttributes();
Expr readExpr();
Expr readExpr1(Expr Lhs, int MinPrec);
StringRef readParenLiteral();
Expr readPrimary();
Expr readTernary(Expr Cond);
Expr readParenExpr();
// For parsing version script.
std::vector<SymbolVersion> readVersionExtern();
void readAnonymousDeclaration();
void readVersionDeclaration(StringRef VerStr);
std::pair<std::vector<SymbolVersion>, std::vector<SymbolVersion>>
readSymbols();
ScriptConfiguration &Opt = *ScriptConfig;
bool IsUnderSysroot;
};
void ScriptParser::readDynamicList() {
expect("{");
readAnonymousDeclaration();
if (!atEOF())
setError("EOF expected, but got " + next());
}
void ScriptParser::readVersionScript() {
readVersionScriptCommand();
if (!atEOF())
setError("EOF expected, but got " + next());
}
void ScriptParser::readVersionScriptCommand() {
if (consume("{")) {
readAnonymousDeclaration();
return;
}
while (!atEOF() && !Error && peek() != "}") {
StringRef VerStr = next();
if (VerStr == "{") {
setError("anonymous version definition is used in "
"combination with other version definitions");
return;
}
expect("{");
readVersionDeclaration(VerStr);
}
}
void ScriptParser::readVersion() {
expect("{");
readVersionScriptCommand();
expect("}");
}
void ScriptParser::readLinkerScript() {
while (!atEOF()) {
StringRef Tok = next();
if (Tok == ";")
continue;
if (Tok == "ASSERT") {
Opt.Commands.emplace_back(new AssertCommand(readAssert()));
} else if (Tok == "ENTRY") {
readEntry();
} else if (Tok == "EXTERN") {
readExtern();
} else if (Tok == "GROUP" || Tok == "INPUT") {
readGroup();
} else if (Tok == "INCLUDE") {
readInclude();
} else if (Tok == "MEMORY") {
readMemory();
} else if (Tok == "OUTPUT") {
readOutput();
} else if (Tok == "OUTPUT_ARCH") {
readOutputArch();
} else if (Tok == "OUTPUT_FORMAT") {
readOutputFormat();
} else if (Tok == "PHDRS") {
readPhdrs();
} else if (Tok == "SEARCH_DIR") {
readSearchDir();
} else if (Tok == "SECTIONS") {
readSections();
} else if (Tok == "VERSION") {
readVersion();
} else if (SymbolAssignment *Cmd = readProvideOrAssignment(Tok)) {
Opt.Commands.emplace_back(Cmd);
} else {
setError("unknown directive: " + Tok);
}
}
}
void ScriptParser::addFile(StringRef S) {
if (IsUnderSysroot && S.startswith("/")) {
SmallString<128> PathData;
StringRef Path = (Config->Sysroot + S).toStringRef(PathData);
if (sys::fs::exists(Path)) {
Driver->addFile(Saver.save(Path));
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 {
if (Optional<std::string> Path = findFromSearchPaths(S))
Driver->addFile(Saver.save(*Path));
else
setError("unable to find " + S);
}
}
void ScriptParser::readAsNeeded() {
expect("(");
bool Orig = Config->AsNeeded;
Config->AsNeeded = true;
while (!Error && !consume(")"))
addFile(unquote(next()));
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 && !consume(")"))
Config->Undefined.push_back(next());
}
void ScriptParser::readGroup() {
expect("(");
while (!Error && !consume(")")) {
StringRef Tok = next();
if (Tok == "AS_NEEDED")
readAsNeeded();
else
addFile(unquote(Tok));
}
}
void ScriptParser::readInclude() {
StringRef Tok = unquote(next());
// https://sourceware.org/binutils/docs/ld/File-Commands.html:
// The file will be searched for in the current directory, and in any
// directory specified with the -L option.
if (sys::fs::exists(Tok)) {
if (Optional<MemoryBufferRef> MB = readFile(Tok))
tokenize(*MB);
return;
}
if (Optional<std::string> Path = findFromSearchPaths(Tok)) {
if (Optional<MemoryBufferRef> MB = readFile(*Path))
tokenize(*MB);
return;
}
setError("cannot open " + Tok);
}
void ScriptParser::readOutput() {
// -o <file> takes predecence over OUTPUT(<file>).
expect("(");
StringRef Tok = next();
if (Config->OutputFile.empty())
Config->OutputFile = unquote(Tok);
expect(")");
}
void ScriptParser::readOutputArch() {
// OUTPUT_ARCH is ignored for now.
expect("(");
while (!Error && !consume(")"))
skip();
}
void ScriptParser::readOutputFormat() {
// Error checking only for now.
expect("(");
skip();
StringRef Tok = next();
if (Tok == ")")
return;
if (Tok != ",") {
setError("unexpected token: " + Tok);
return;
}
skip();
expect(",");
skip();
expect(")");
}
void ScriptParser::readPhdrs() {
expect("{");
while (!Error && !consume("}")) {
StringRef Tok = next();
Opt.PhdrsCommands.push_back(
{Tok, PT_NULL, false, false, UINT_MAX, nullptr});
PhdrsCommand &PhdrCmd = Opt.PhdrsCommands.back();
PhdrCmd.Type = readPhdrType();
do {
Tok = next();
if (Tok == ";")
break;
if (Tok == "FILEHDR")
PhdrCmd.HasFilehdr = true;
else if (Tok == "PHDRS")
PhdrCmd.HasPhdrs = true;
else if (Tok == "AT")
PhdrCmd.LMAExpr = readParenExpr();
else if (Tok == "FLAGS") {
expect("(");
// Passing 0 for the value of dot is a bit of a hack. It means that
// we accept expressions like ".|1".
PhdrCmd.Flags = readExpr()().getValue();
expect(")");
} else
setError("unexpected header attribute: " + Tok);
} while (!Error);
}
}
void ScriptParser::readSearchDir() {
expect("(");
StringRef Tok = next();
if (!Config->Nostdlib)
Config->SearchPaths.push_back(unquote(Tok));
expect(")");
}
void ScriptParser::readSections() {
Opt.HasSections = true;
// -no-rosegment is used to avoid placing read only non-executable sections in
// their own segment. We do the same if SECTIONS command is present in linker
// script. See comment for computeFlags().
Config->SingleRoRx = true;
expect("{");
while (!Error && !consume("}")) {
StringRef Tok = next();
BaseCommand *Cmd = readProvideOrAssignment(Tok);
if (!Cmd) {
if (Tok == "ASSERT")
Cmd = new AssertCommand(readAssert());
else
Cmd = readOutputSectionDescription(Tok);
}
Opt.Commands.emplace_back(Cmd);
}
}
static int precedence(StringRef Op) {
return StringSwitch<int>(Op)
.Cases("*", "/", 5)
.Cases("+", "-", 4)
.Cases("<<", ">>", 3)
.Cases("<", "<=", ">", ">=", "==", "!=", 2)
.Cases("&", "|", 1)
.Default(-1);
}
StringMatcher ScriptParser::readFilePatterns() {
std::vector<StringRef> V;
while (!Error && !consume(")"))
V.push_back(next());
return StringMatcher(V);
}
SortSectionPolicy ScriptParser::readSortKind() {
if (consume("SORT") || consume("SORT_BY_NAME"))
return SortSectionPolicy::Name;
if (consume("SORT_BY_ALIGNMENT"))
return SortSectionPolicy::Alignment;
if (consume("SORT_BY_INIT_PRIORITY"))
return SortSectionPolicy::Priority;
if (consume("SORT_NONE"))
return SortSectionPolicy::None;
return SortSectionPolicy::Default;
}
// Method reads a list of sequence of excluded files and section globs given in
// a following form: ((EXCLUDE_FILE(file_pattern+))? section_pattern+)+
// Example: *(.foo.1 EXCLUDE_FILE (*a.o) .foo.2 EXCLUDE_FILE (*b.o) .foo.3)
// The semantics of that is next:
// * Include .foo.1 from every file.
// * Include .foo.2 from every file but a.o
// * Include .foo.3 from every file but b.o
std::vector<SectionPattern> ScriptParser::readInputSectionsList() {
std::vector<SectionPattern> Ret;
while (!Error && peek() != ")") {
StringMatcher ExcludeFilePat;
if (consume("EXCLUDE_FILE")) {
expect("(");
ExcludeFilePat = readFilePatterns();
}
std::vector<StringRef> V;
while (!Error && peek() != ")" && peek() != "EXCLUDE_FILE")
V.push_back(next());
if (!V.empty())
Ret.push_back({std::move(ExcludeFilePat), StringMatcher(V)});
else
setError("section pattern is expected");
}
return Ret;
}
// Reads contents of "SECTIONS" directive. That directive contains a
// list of glob patterns for input sections. The grammar is as follows.
//
// <patterns> ::= <section-list>
// | <sort> "(" <section-list> ")"
// | <sort> "(" <sort> "(" <section-list> ")" ")"
//
// <sort> ::= "SORT" | "SORT_BY_NAME" | "SORT_BY_ALIGNMENT"
// | "SORT_BY_INIT_PRIORITY" | "SORT_NONE"
//
// <section-list> is parsed by readInputSectionsList().
InputSectionDescription *
ScriptParser::readInputSectionRules(StringRef FilePattern) {
auto *Cmd = new InputSectionDescription(FilePattern);
expect("(");
while (!Error && !consume(")")) {
SortSectionPolicy Outer = readSortKind();
SortSectionPolicy Inner = SortSectionPolicy::Default;
std::vector<SectionPattern> V;
if (Outer != SortSectionPolicy::Default) {
expect("(");
Inner = readSortKind();
if (Inner != SortSectionPolicy::Default) {
expect("(");
V = readInputSectionsList();
expect(")");
} else {
V = readInputSectionsList();
}
expect(")");
} else {
V = readInputSectionsList();
}
for (SectionPattern &Pat : V) {
Pat.SortInner = Inner;
Pat.SortOuter = Outer;
}
std::move(V.begin(), V.end(), std::back_inserter(Cmd->SectionPatterns));
}
return Cmd;
}
InputSectionDescription *
ScriptParser::readInputSectionDescription(StringRef Tok) {
// Input section wildcard can be surrounded by KEEP.
// https://sourceware.org/binutils/docs/ld/Input-Section-Keep.html#Input-Section-Keep
if (Tok == "KEEP") {
expect("(");
StringRef FilePattern = next();
InputSectionDescription *Cmd = readInputSectionRules(FilePattern);
expect(")");
Opt.KeptSections.push_back(Cmd);
return Cmd;
}
return readInputSectionRules(Tok);
}
void ScriptParser::readSort() {
expect("(");
expect("CONSTRUCTORS");
expect(")");
}
Expr ScriptParser::readAssert() {
expect("(");
Expr E = readExpr();
expect(",");
StringRef Msg = unquote(next());
expect(")");
return [=] {
if (!E().getValue())
error(Msg);
return Script->getDot();
};
}
// Reads a FILL(expr) command. We handle the FILL command as an
// alias for =fillexp section attribute, which is different from
// what GNU linkers do.
// https://sourceware.org/binutils/docs/ld/Output-Section-Data.html
uint32_t ScriptParser::readFill() {
expect("(");
uint32_t V = readOutputSectionFiller(next());
expect(")");
expect(";");
return V;
}
OutputSectionCommand *
ScriptParser::readOutputSectionDescription(StringRef OutSec) {
OutputSectionCommand *Cmd = new OutputSectionCommand(OutSec);
Cmd->Location = getCurrentLocation();
// Read an address expression.
// https://sourceware.org/binutils/docs/ld/Output-Section-Address.html#Output-Section-Address
if (peek() != ":")
Cmd->AddrExpr = readExpr();
expect(":");
if (consume("AT"))
Cmd->LMAExpr = readParenExpr();
if (consume("ALIGN"))
Cmd->AlignExpr = readParenExpr();
if (consume("SUBALIGN"))
Cmd->SubalignExpr = readParenExpr();
// Parse constraints.
if (consume("ONLY_IF_RO"))
Cmd->Constraint = ConstraintKind::ReadOnly;
if (consume("ONLY_IF_RW"))
Cmd->Constraint = ConstraintKind::ReadWrite;
expect("{");
while (!Error && !consume("}")) {
StringRef Tok = next();
if (Tok == ";") {
// Empty commands are allowed. Do nothing here.
} else if (SymbolAssignment *Assignment = readProvideOrAssignment(Tok)) {
Cmd->Commands.emplace_back(Assignment);
} else if (BytesDataCommand *Data = readBytesDataCommand(Tok)) {
Cmd->Commands.emplace_back(Data);
} else if (Tok == "ASSERT") {
Cmd->Commands.emplace_back(new AssertCommand(readAssert()));
expect(";");
} else if (Tok == "CONSTRUCTORS") {
// CONSTRUCTORS is a keyword to make the linker recognize C++ ctors/dtors
// by name. This is for very old file formats such as ECOFF/XCOFF.
// For ELF, we should ignore.
} else if (Tok == "FILL") {
Cmd->Filler = readFill();
} else if (Tok == "SORT") {
readSort();
} else if (peek() == "(") {
Cmd->Commands.emplace_back(readInputSectionDescription(Tok));
} else {
setError("unknown command " + Tok);
}
}
if (consume(">"))
Cmd->MemoryRegionName = next();
Cmd->Phdrs = readOutputSectionPhdrs();
if (consume("="))
Cmd->Filler = readOutputSectionFiller(next());
else if (peek().startswith("="))
Cmd->Filler = readOutputSectionFiller(next().drop_front());
// Consume optional comma following output section command.
consume(",");
return Cmd;
}
// Read "=<number>" where <number> is an octal/decimal/hexadecimal number.
// https://sourceware.org/binutils/docs/ld/Output-Section-Fill.html
//
// ld.gold is not fully compatible with ld.bfd. ld.bfd handles
// hexstrings as blobs of arbitrary sizes, while ld.gold handles them
// as 32-bit big-endian values. We will do the same as ld.gold does
// because it's simpler than what ld.bfd does.
uint32_t ScriptParser::readOutputSectionFiller(StringRef Tok) {
uint32_t V;
if (!Tok.getAsInteger(0, V))
return V;
setError("invalid filler expression: " + Tok);
return 0;
}
SymbolAssignment *ScriptParser::readProvideHidden(bool Provide, bool Hidden) {
expect("(");
SymbolAssignment *Cmd = readAssignment(next());
Cmd->Provide = Provide;
Cmd->Hidden = Hidden;
expect(")");
expect(";");
return Cmd;
}
SymbolAssignment *ScriptParser::readProvideOrAssignment(StringRef Tok) {
SymbolAssignment *Cmd = nullptr;
if (peek() == "=" || peek() == "+=") {
Cmd = readAssignment(Tok);
expect(";");
} else if (Tok == "PROVIDE") {
Cmd = readProvideHidden(true, false);
} else if (Tok == "HIDDEN") {
Cmd = readProvideHidden(false, true);
} else if (Tok == "PROVIDE_HIDDEN") {
Cmd = readProvideHidden(true, true);
}
return Cmd;
}
SymbolAssignment *ScriptParser::readAssignment(StringRef Name) {
StringRef Op = next();
assert(Op == "=" || Op == "+=");
Expr E = readExpr();
if (Op == "+=") {
std::string Loc = getCurrentLocation();
E = [=] { return add(Script->getSymbolValue(Loc, Name), E()); };
}
return new SymbolAssignment(Name, E, getCurrentLocation());
}
// This is an operator-precedence parser to parse a linker
// script expression.
Expr ScriptParser::readExpr() {
// Our lexer is context-aware. Set the in-expression bit so that
// they apply different tokenization rules.
bool Orig = InExpr;
InExpr = true;
Expr E = readExpr1(readPrimary(), 0);
InExpr = Orig;
return E;
}
static Expr combine(StringRef Op, Expr L, Expr R) {
if (Op == "*")
return [=] { return mul(L(), R()); };
if (Op == "/") {
return [=] { return div(L(), R()); };
}
if (Op == "+")
return [=] { return add(L(), R()); };
if (Op == "-")
return [=] { return sub(L(), R()); };
if (Op == "<<")
return [=] { return leftShift(L(), R()); };
if (Op == ">>")
return [=] { return rightShift(L(), R()); };
if (Op == "<")
return [=] { return lessThan(L(), R()); };
if (Op == ">")
return [=] { return greaterThan(L(), R()); };
if (Op == ">=")
return [=] { return greaterThanOrEqual(L(), R()); };
if (Op == "<=")
return [=] { return lessThanOrEqual(L(), R()); };
if (Op == "==")
return [=] { return ::equal(L(), R()); };
if (Op == "!=")
return [=] { return notEqual(L(), R()); };
if (Op == "&")
return [=] { return bitAnd(L(), R()); };
if (Op == "|")
return [=] { return bitOr(L(), R()); };
llvm_unreachable("invalid operator");
}
// This is a part of the operator-precedence parser. This function
// assumes that the remaining token stream starts with an operator.
Expr ScriptParser::readExpr1(Expr Lhs, int MinPrec) {
while (!atEOF() && !Error) {
// Read an operator and an expression.
if (consume("?"))
return readTernary(Lhs);
StringRef Op1 = peek();
if (precedence(Op1) < MinPrec)
break;
skip();
Expr Rhs = readPrimary();
// 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 = readExpr1(Rhs, precedence(Op2));
}
Lhs = combine(Op1, Lhs, Rhs);
}
return Lhs;
}
uint64_t static getConstant(StringRef S) {
if (S == "COMMONPAGESIZE")
return Target->PageSize;
if (S == "MAXPAGESIZE")
return Config->MaxPageSize;
error("unknown constant: " + S);
return 0;
}
// Parses Tok as an integer. Returns true if successful.
// It recognizes hexadecimal (prefixed with "0x" or suffixed with "H")
// and decimal numbers. Decimal numbers may have "K" (kilo) or
// "M" (mega) prefixes.
static bool readInteger(StringRef Tok, uint64_t &Result) {
// Negative number
if (Tok.startswith("-")) {
if (!readInteger(Tok.substr(1), Result))
return false;
Result = -Result;
return true;
}
// Hexadecimal
if (Tok.startswith_lower("0x"))
return !Tok.substr(2).getAsInteger(16, Result);
if (Tok.endswith_lower("H"))
return !Tok.drop_back().getAsInteger(16, Result);
// Decimal
int Suffix = 1;
if (Tok.endswith_lower("K")) {
Suffix = 1024;
Tok = Tok.drop_back();
} else if (Tok.endswith_lower("M")) {
Suffix = 1024 * 1024;
Tok = Tok.drop_back();
}
if (Tok.getAsInteger(10, Result))
return false;
Result *= Suffix;
return true;
}
BytesDataCommand *ScriptParser::readBytesDataCommand(StringRef Tok) {
int Size = StringSwitch<unsigned>(Tok)
.Case("BYTE", 1)
.Case("SHORT", 2)
.Case("LONG", 4)
.Case("QUAD", 8)
.Default(-1);
if (Size == -1)
return nullptr;
return new BytesDataCommand(readParenExpr(), Size);
}
StringRef ScriptParser::readParenLiteral() {
expect("(");
StringRef Tok = next();
expect(")");
return Tok;
}
Expr ScriptParser::readPrimary() {
if (peek() == "(")
return readParenExpr();
StringRef Tok = next();
std::string Location = getCurrentLocation();
if (Tok == "~") {
Expr E = readPrimary();
return [=] { return bitNot(E()); };
}
if (Tok == "-") {
Expr E = readPrimary();
return [=] { return minus(E()); };
}
// Built-in functions are parsed here.
// https://sourceware.org/binutils/docs/ld/Builtin-Functions.html.
if (Tok == "ABSOLUTE") {
Expr Inner = readParenExpr();
return [=] {
ExprValue I = Inner();
I.ForceAbsolute = true;
return I;
};
}
if (Tok == "ADDR") {
StringRef Name = readParenLiteral();
return [=]() -> ExprValue {
return {Script->getOutputSection(Location, Name), 0};
};
}
if (Tok == "LOADADDR") {
StringRef Name = readParenLiteral();
return [=] { return Script->getOutputSection(Location, Name)->getLMA(); };
}
if (Tok == "ASSERT")
return readAssert();
if (Tok == "ALIGN") {
expect("(");
Expr E = readExpr();
if (consume(",")) {
Expr E2 = readExpr();
expect(")");
return [=] { return alignTo(E().getValue(), E2().getValue()); };
}
expect(")");
return [=] { return alignTo(Script->getDot(), E().getValue()); };
}
if (Tok == "CONSTANT") {
StringRef Name = readParenLiteral();
return [=] { return getConstant(Name); };
}
if (Tok == "DEFINED") {
StringRef Name = readParenLiteral();
return [=] { return Script->isDefined(Name) ? 1 : 0; };
}
if (Tok == "SEGMENT_START") {
expect("(");
skip();
expect(",");
Expr E = readExpr();
expect(")");
return [=] { return E(); };
}
if (Tok == "DATA_SEGMENT_ALIGN") {
expect("(");
Expr E = readExpr();
expect(",");
readExpr();
expect(")");
return [=] { return alignTo(Script->getDot(), E().getValue()); };
}
if (Tok == "DATA_SEGMENT_END") {
expect("(");
expect(".");
expect(")");
return [] { return Script->getDot(); };
}
// GNU linkers implements more complicated logic to handle
// DATA_SEGMENT_RELRO_END. We instead ignore the arguments and just align to
// the next page boundary for simplicity.
if (Tok == "DATA_SEGMENT_RELRO_END") {
expect("(");
readExpr();
expect(",");
readExpr();
expect(")");
return [] { return alignTo(Script->getDot(), Target->PageSize); };
}
if (Tok == "SIZEOF") {
StringRef Name = readParenLiteral();
return [=] { return Script->getOutputSectionSize(Name); };
}
if (Tok == "ALIGNOF") {
StringRef Name = readParenLiteral();
return [=] { return Script->getOutputSection(Location, Name)->Alignment; };
}
if (Tok == "SIZEOF_HEADERS")
return [=] { return elf::getHeaderSize(); };
// Tok is a literal number.
uint64_t V;
if (readInteger(Tok, V))
return [=] { return V; };
// Tok is a symbol name.
if (Tok != "." && !isValidCIdentifier(Tok))
setError("malformed number: " + Tok);
return [=] { return Script->getSymbolValue(Location, Tok); };
}
Expr ScriptParser::readTernary(Expr Cond) {
Expr L = readExpr();
expect(":");
Expr R = readExpr();
return [=] { return Cond().getValue() ? L() : R(); };
}
Expr ScriptParser::readParenExpr() {
expect("(");
Expr E = readExpr();
expect(")");
return E;
}
std::vector<StringRef> ScriptParser::readOutputSectionPhdrs() {
std::vector<StringRef> Phdrs;
while (!Error && peek().startswith(":")) {
StringRef Tok = next();
Phdrs.push_back((Tok.size() == 1) ? next() : Tok.substr(1));
}
return Phdrs;
}
// Read a program header type name. The next token must be a
// name of a program header type or a constant (e.g. "0x3").
unsigned ScriptParser::readPhdrType() {
StringRef Tok = next();
uint64_t Val;
if (readInteger(Tok, Val))
return Val;
unsigned Ret = StringSwitch<unsigned>(Tok)
.Case("PT_NULL", PT_NULL)
.Case("PT_LOAD", PT_LOAD)
.Case("PT_DYNAMIC", PT_DYNAMIC)
.Case("PT_INTERP", PT_INTERP)
.Case("PT_NOTE", PT_NOTE)
.Case("PT_SHLIB", PT_SHLIB)
.Case("PT_PHDR", PT_PHDR)
.Case("PT_TLS", PT_TLS)
.Case("PT_GNU_EH_FRAME", PT_GNU_EH_FRAME)
.Case("PT_GNU_STACK", PT_GNU_STACK)
.Case("PT_GNU_RELRO", PT_GNU_RELRO)
.Case("PT_OPENBSD_RANDOMIZE", PT_OPENBSD_RANDOMIZE)
.Case("PT_OPENBSD_WXNEEDED", PT_OPENBSD_WXNEEDED)
.Case("PT_OPENBSD_BOOTDATA", PT_OPENBSD_BOOTDATA)
.Default(-1);
if (Ret == (unsigned)-1) {
setError("invalid program header type: " + Tok);
return PT_NULL;
}
return Ret;
}
// Reads an anonymous version declaration.
void ScriptParser::readAnonymousDeclaration() {
std::vector<SymbolVersion> Locals;
std::vector<SymbolVersion> Globals;
std::tie(Locals, Globals) = readSymbols();
for (SymbolVersion V : Locals) {
if (V.Name == "*")
Config->DefaultSymbolVersion = VER_NDX_LOCAL;
else
Config->VersionScriptLocals.push_back(V);
}
for (SymbolVersion V : Globals)
Config->VersionScriptGlobals.push_back(V);
expect(";");
}
// Reads a non-anonymous version definition,
// e.g. "VerStr { global: foo; bar; local: *; };".
void ScriptParser::readVersionDeclaration(StringRef VerStr) {
// Read a symbol list.
std::vector<SymbolVersion> Locals;
std::vector<SymbolVersion> Globals;
std::tie(Locals, Globals) = readSymbols();
for (SymbolVersion V : Locals) {
if (V.Name == "*")
Config->DefaultSymbolVersion = VER_NDX_LOCAL;
else
Config->VersionScriptLocals.push_back(V);
}
// Create a new version definition and add that to the global symbols.
VersionDefinition Ver;
Ver.Name = VerStr;
Ver.Globals = Globals;
// User-defined version number starts from 2 because 0 and 1 are
// reserved for VER_NDX_LOCAL and VER_NDX_GLOBAL, respectively.
Ver.Id = Config->VersionDefinitions.size() + 2;
Config->VersionDefinitions.push_back(Ver);
// Each version may have a parent version. For example, "Ver2"
// defined as "Ver2 { global: foo; local: *; } Ver1;" has "Ver1"
// as a parent. This version hierarchy is, probably against your
// instinct, purely for hint; the runtime doesn't care about it
// at all. In LLD, we simply ignore it.
if (peek() != ";")
skip();
expect(";");
}
// Reads a list of symbols, e.g. "{ global: foo; bar; local: *; };".
std::pair<std::vector<SymbolVersion>, std::vector<SymbolVersion>>
ScriptParser::readSymbols() {
std::vector<SymbolVersion> Locals;
std::vector<SymbolVersion> Globals;
std::vector<SymbolVersion> *V = &Globals;
while (!Error) {
if (consume("}"))
break;
if (consumeLabel("local")) {
V = &Locals;
continue;
}
if (consumeLabel("global")) {
V = &Globals;
continue;
}
if (consume("extern")) {
std::vector<SymbolVersion> Ext = readVersionExtern();
V->insert(V->end(), Ext.begin(), Ext.end());
} else {
StringRef Tok = next();
V->push_back({unquote(Tok), false, hasWildcard(Tok)});
}
expect(";");
}
return {Locals, Globals};
}
// Reads an "extern C++" directive, e.g.,
// "extern "C++" { ns::*; "f(int, double)"; };"
std::vector<SymbolVersion> ScriptParser::readVersionExtern() {
StringRef Tok = next();
bool IsCXX = Tok == "\"C++\"";
if (!IsCXX && Tok != "\"C\"")
setError("Unknown language");
expect("{");
std::vector<SymbolVersion> Ret;
while (!Error && peek() != "}") {
StringRef Tok = next();
bool HasWildcard = !Tok.startswith("\"") && hasWildcard(Tok);
Ret.push_back({unquote(Tok), IsCXX, HasWildcard});
expect(";");
}
expect("}");
return Ret;
}
uint64_t ScriptParser::readMemoryAssignment(StringRef S1, StringRef S2,
StringRef S3) {
if (!(consume(S1) || consume(S2) || consume(S3))) {
setError("expected one of: " + S1 + ", " + S2 + ", or " + S3);
return 0;
}
expect("=");
// TODO: Fully support constant expressions.
uint64_t Val;
if (!readInteger(next(), Val))
setError("nonconstant expression for " + S1);
return Val;
}
// Parse the MEMORY command as specified in:
// https://sourceware.org/binutils/docs/ld/MEMORY.html
//
// MEMORY { name [(attr)] : ORIGIN = origin, LENGTH = len ... }
void ScriptParser::readMemory() {
expect("{");
while (!Error && !consume("}")) {
StringRef Name = next();
uint32_t Flags = 0;
uint32_t NegFlags = 0;
if (consume("(")) {
std::tie(Flags, NegFlags) = readMemoryAttributes();
expect(")");
}
expect(":");
uint64_t Origin = readMemoryAssignment("ORIGIN", "org", "o");
expect(",");
uint64_t Length = readMemoryAssignment("LENGTH", "len", "l");
// Add the memory region to the region map (if it doesn't already exist).
auto It = Opt.MemoryRegions.find(Name);
if (It != Opt.MemoryRegions.end())
setError("region '" + Name + "' already defined");
else
Opt.MemoryRegions[Name] = {Name, Origin, Length, Origin, Flags, NegFlags};
}
}
// This function parses the attributes used to match against section
// flags when placing output sections in a memory region. These flags
// are only used when an explicit memory region name is not used.
std::pair<uint32_t, uint32_t> ScriptParser::readMemoryAttributes() {
uint32_t Flags = 0;
uint32_t NegFlags = 0;
bool Invert = false;
for (char C : next().lower()) {
uint32_t Flag = 0;
if (C == '!')
Invert = !Invert;
else if (C == 'w')
Flag = SHF_WRITE;
else if (C == 'x')
Flag = SHF_EXECINSTR;
else if (C == 'a')
Flag = SHF_ALLOC;
else if (C != 'r')
setError("invalid memory region attribute");
if (Invert)
NegFlags |= Flag;
else
Flags |= Flag;
}
return {Flags, NegFlags};
}
void elf::readLinkerScript(MemoryBufferRef MB) {
ScriptParser(MB).readLinkerScript();
}
void elf::readVersionScript(MemoryBufferRef MB) {
ScriptParser(MB).readVersionScript();
}
void elf::readDynamicList(MemoryBufferRef MB) {
ScriptParser(MB).readDynamicList();
}
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