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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 "InputSection.h"
#include "Memory.h"
#include "OutputSections.h"
#include "Strings.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "Threads.h"
#include "Writer.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Path.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <limits>
#include <string>
#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;
LinkerScript *elf::Script;
uint64_t ExprValue::getValue() const {
if (Sec) {
if (OutputSection *OS = Sec->getOutputSection())
return alignTo(Sec->getOffset(Val) + OS->Addr, Alignment);
error(Loc + ": unable to evaluate expression: input section " + Sec->Name +
" has no output section assigned");
}
return alignTo(Val, Alignment);
}
uint64_t ExprValue::getSecAddr() const {
if (Sec)
return Sec->getOffset(0) + Sec->getOutputSection()->Addr;
return 0;
}
static SymbolBody *addRegular(SymbolAssignment *Cmd) {
Symbol *Sym;
uint8_t Visibility = Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT;
std::tie(Sym, std::ignore) = Symtab->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;
// We want to set symbol values early if we can. This allows us to use symbols
// as variables in linker scripts. Doing so allows us to write expressions
// like this: `alignment = 16; . = ALIGN(., alignment)`
uint64_t SymValue = Value.isAbsolute() ? Value.getValue() : 0;
replaceBody<DefinedRegular>(Sym, nullptr, Cmd->Name, /*IsLocal=*/false,
Visibility, STT_NOTYPE, SymValue, 0, Sec);
return Sym->body();
}
OutputSection *LinkerScript::createOutputSection(StringRef Name,
StringRef Location) {
OutputSection *&SecRef = NameToOutputSection[Name];
OutputSection *Sec;
if (SecRef && SecRef->Location.empty()) {
// There was a forward reference.
Sec = SecRef;
} else {
Sec = make<OutputSection>(Name, SHT_PROGBITS, 0);
if (!SecRef)
SecRef = Sec;
}
Sec->Location = Location;
return Sec;
}
OutputSection *LinkerScript::getOrCreateOutputSection(StringRef Name) {
OutputSection *&CmdRef = NameToOutputSection[Name];
if (!CmdRef)
CmdRef = make<OutputSection>(Name, SHT_PROGBITS, 0);
return CmdRef;
}
void LinkerScript::setDot(Expr E, const Twine &Loc, bool InSec) {
uint64_t Val = E().getValue();
if (Val < Dot && InSec)
error(Loc + ": unable to move location counter backward for: " +
CurAddressState->OutSec->Name);
Dot = Val;
// Update to location counter means update to section size.
if (InSec)
CurAddressState->OutSec->Size = Dot - CurAddressState->OutSec->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 LinkerScript::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;
Sym->Value = alignTo(V.Val, V.Alignment);
}
}
void LinkerScript::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 = Symtab->find(Cmd->Name);
if (Cmd->Provide && (!B || B->isDefined()))
return;
Cmd->Sym = addRegular(Cmd);
}
bool SymbolAssignment::classof(const BaseCommand *C) {
return C->Kind == AssignmentKind;
}
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 LinkerScript::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;
}
// A helper function for the SORT() command.
static std::function<bool(InputSectionBase *, InputSectionBase *)>
getComparator(SortSectionPolicy K) {
switch (K) {
case SortSectionPolicy::Alignment:
return [](InputSectionBase *A, InputSectionBase *B) {
// ">" is not a mistake. Sections with larger alignments are placed
// before sections with smaller alignments in order to reduce the
// amount of padding necessary. This is compatible with GNU.
return A->Alignment > B->Alignment;
};
case SortSectionPolicy::Name:
return [](InputSectionBase *A, InputSectionBase *B) {
return A->Name < B->Name;
};
case SortSectionPolicy::Priority:
return [](InputSectionBase *A, InputSectionBase *B) {
return getPriority(A->Name) < getPriority(B->Name);
};
default:
llvm_unreachable("unknown sort policy");
}
}
// A helper function for the SORT() command.
static bool matchConstraints(ArrayRef<InputSectionBase *> Sections,
ConstraintKind Kind) {
if (Kind == ConstraintKind::NoConstraint)
return true;
bool IsRW = llvm::any_of(Sections, [](InputSectionBase *Sec) {
return static_cast<InputSectionBase *>(Sec)->Flags & SHF_WRITE;
});
return (IsRW && Kind == ConstraintKind::ReadWrite) ||
(!IsRW && Kind == ConstraintKind::ReadOnly);
}
static void sortSections(InputSection **Begin, InputSection **End,
SortSectionPolicy K) {
if (K != SortSectionPolicy::Default && K != SortSectionPolicy::None)
std::stable_sort(Begin, End, getComparator(K));
}
static llvm::DenseMap<SectionBase *, int> getSectionOrder() {
switch (Config->EKind) {
case ELF32LEKind:
return buildSectionOrder<ELF32LE>();
case ELF32BEKind:
return buildSectionOrder<ELF32BE>();
case ELF64LEKind:
return buildSectionOrder<ELF64LE>();
case ELF64BEKind:
return buildSectionOrder<ELF64BE>();
default:
llvm_unreachable("unknown ELF type");
}
}
static void sortBySymbolOrder(InputSection **Begin, InputSection **End) {
if (Config->SymbolOrderingFile.empty())
return;
static llvm::DenseMap<SectionBase *, int> Order = getSectionOrder();
MutableArrayRef<InputSection *> In(Begin, End - Begin);
sortByOrder(In, [&](InputSectionBase *S) { return Order.lookup(S); });
}
// Compute and remember which sections the InputSectionDescription matches.
std::vector<InputSection *>
LinkerScript::computeInputSections(const InputSectionDescription *Cmd) {
std::vector<InputSection *> Ret;
// Collects all sections that satisfy constraints of Cmd.
for (const SectionPattern &Pat : Cmd->SectionPatterns) {
size_t SizeBefore = Ret.size();
for (InputSectionBase *Sec : InputSections) {
if (Sec->Assigned)
continue;
if (!Sec->Live) {
reportDiscarded(Sec);
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 (Sec->Type == SHT_REL || Sec->Type == SHT_RELA)
continue;
StringRef Filename = basename(Sec);
if (!Cmd->FilePat.match(Filename) ||
Pat.ExcludedFilePat.match(Filename) ||
!Pat.SectionPat.match(Sec->Name))
continue;
Ret.push_back(cast<InputSection>(Sec));
Sec->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.
// 5. If no SORT commands are given and --sort-section is not specified,
// apply sorting provided by --symbol-ordering-file if any exist.
InputSection **Begin = Ret.data() + SizeBefore;
InputSection **End = Ret.data() + Ret.size();
if (Pat.SortOuter == SortSectionPolicy::Default &&
Config->SortSection == SortSectionPolicy::Default) {
sortBySymbolOrder(Begin, End);
continue;
}
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);
}
}
return Ret;
}
void LinkerScript::discard(ArrayRef<InputSectionBase *> V) {
for (InputSectionBase *S : V) {
S->Live = false;
if (S == InX::ShStrTab || S == InX::Common || S == InX::Dynamic ||
S == InX::DynSymTab || S == InX::DynStrTab)
error("discarding " + S->Name + " section is not allowed");
discard(S->DependentSections);
}
}
std::vector<InputSectionBase *>
LinkerScript::createInputSectionList(OutputSection &OutCmd) {
std::vector<InputSectionBase *> Ret;
for (BaseCommand *Base : OutCmd.Commands) {
auto *Cmd = dyn_cast<InputSectionDescription>(Base);
if (!Cmd)
continue;
Cmd->Sections = computeInputSections(Cmd);
Ret.insert(Ret.end(), Cmd->Sections.begin(), Cmd->Sections.end());
}
return Ret;
}
void LinkerScript::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;
auto State = make_unique<AddressState>(Opt);
// CurAddressState captures the local AddressState and makes it accessible
// deliberately. This is needed as there are some cases where we cannot just
// thread the current state through to a lambda function created by the
// script parser.
CurAddressState = State.get();
CurAddressState->OutSec = Aether;
Dot = 0;
for (size_t I = 0; I < Opt.Commands.size(); ++I) {
// Handle symbol assignments outside of any output section.
if (auto *Cmd = dyn_cast<SymbolAssignment>(Opt.Commands[I])) {
addSymbol(Cmd);
continue;
}
if (auto *Sec = dyn_cast<OutputSection>(Opt.Commands[I])) {
std::vector<InputSectionBase *> V = createInputSectionList(*Sec);
// The output section name `/DISCARD/' is special.
// Any input section assigned to it is discarded.
if (Sec->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, Sec->Constraint)) {
for (InputSectionBase *S : V)
S->Assigned = false;
Opt.Commands.erase(Opt.Commands.begin() + I);
--I;
continue;
}
// A directive may contain symbol definitions like this:
// ".foo : { ...; bar = .; }". Handle them.
for (BaseCommand *Base : Sec->Commands)
if (auto *OutCmd = dyn_cast<SymbolAssignment>(Base))
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 (Sec->SubalignExpr) {
uint32_t Subalign = Sec->SubalignExpr().getValue();
for (InputSectionBase *S : V)
S->Alignment = Subalign;
}
// Add input sections to an output section.
for (InputSectionBase *S : V)
Factory.addInputSec(S, Sec->Name, Sec);
assert(Sec->SectionIndex == INT_MAX);
Sec->SectionIndex = I;
if (Sec->Noload)
Sec->Type = SHT_NOBITS;
}
}
CurAddressState = nullptr;
}
void LinkerScript::fabricateDefaultCommands() {
// Define start address
uint64_t StartAddr = -1;
// The Sections with -T<section> have been sorted in order of ascending
// address. We must lower StartAddr if the lowest -T<section address> as
// calls to setDot() must be monotonically increasing.
for (auto &KV : Config->SectionStartMap)
StartAddr = std::min(StartAddr, KV.second);
Opt.Commands.insert(Opt.Commands.begin(),
make<SymbolAssignment>(".",
[=] {
return std::min(
StartAddr,
Config->ImageBase +
elf::getHeaderSize());
},
""));
}
// Add sections that didn't match any sections command.
void LinkerScript::addOrphanSections(OutputSectionFactory &Factory) {
unsigned NumCommands = Opt.Commands.size();
for (InputSectionBase *S : InputSections) {
if (!S->Live || S->Parent)
continue;
StringRef Name = getOutputSectionName(S->Name);
auto End = Opt.Commands.begin() + NumCommands;
auto I = std::find_if(Opt.Commands.begin(), End, [&](BaseCommand *Base) {
if (auto *Sec = dyn_cast<OutputSection>(Base))
return Sec->Name == Name;
return false;
});
if (I == End) {
Factory.addInputSec(S, Name);
assert(S->getOutputSection()->SectionIndex == INT_MAX);
} else {
OutputSection *Sec = cast<OutputSection>(*I);
Factory.addInputSec(S, Name, Sec);
unsigned Index = std::distance(Opt.Commands.begin(), I);
assert(Sec->SectionIndex == INT_MAX || Sec->SectionIndex == Index);
Sec->SectionIndex = Index;
}
}
}
uint64_t LinkerScript::advance(uint64_t Size, unsigned Align) {
bool IsTbss = (CurAddressState->OutSec->Flags & SHF_TLS) &&
CurAddressState->OutSec->Type == SHT_NOBITS;
uint64_t Start = IsTbss ? Dot + CurAddressState->ThreadBssOffset : Dot;
Start = alignTo(Start, Align);
uint64_t End = Start + Size;
if (IsTbss)
CurAddressState->ThreadBssOffset = End - Dot;
else
Dot = End;
return End;
}
void LinkerScript::output(InputSection *S) {
uint64_t Before = advance(0, 1);
uint64_t Pos = advance(S->getSize(), S->Alignment);
S->OutSecOff = Pos - S->getSize() - CurAddressState->OutSec->Addr;
// 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) }
CurAddressState->OutSec->Size = Pos - CurAddressState->OutSec->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 (CurAddressState->MemRegion) {
uint64_t &CurOffset =
CurAddressState->MemRegionOffset[CurAddressState->MemRegion];
CurOffset += Pos - Before;
uint64_t CurSize = CurOffset - CurAddressState->MemRegion->Origin;
if (CurSize > CurAddressState->MemRegion->Length) {
uint64_t OverflowAmt = CurSize - CurAddressState->MemRegion->Length;
error("section '" + CurAddressState->OutSec->Name +
"' will not fit in region '" + CurAddressState->MemRegion->Name +
"': overflowed by " + Twine(OverflowAmt) + " bytes");
}
}
}
void LinkerScript::switchTo(OutputSection *Sec) {
if (CurAddressState->OutSec == Sec)
return;
CurAddressState->OutSec = Sec;
CurAddressState->OutSec->Addr =
advance(0, CurAddressState->OutSec->Alignment);
// 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 (CurAddressState->LMAOffset)
CurAddressState->OutSec->LMAOffset = CurAddressState->LMAOffset();
}
void LinkerScript::process(BaseCommand &Base) {
// This handles the assignments to symbol or to the dot.
if (auto *Cmd = dyn_cast<SymbolAssignment>(&Base)) {
assignSymbol(Cmd, true);
return;
}
// Handle BYTE(), SHORT(), LONG(), or QUAD().
if (auto *Cmd = dyn_cast<BytesDataCommand>(&Base)) {
Cmd->Offset = Dot - CurAddressState->OutSec->Addr;
Dot += Cmd->Size;
CurAddressState->OutSec->Size = Dot - CurAddressState->OutSec->Addr;
return;
}
// Handle ASSERT().
if (auto *Cmd = dyn_cast<AssertCommand>(&Base)) {
Cmd->Expression();
return;
}
// Handle a single input section description command.
// It calculates and assigns the offsets for each section and also
// updates the output section size.
auto &Cmd = cast<InputSectionDescription>(Base);
for (InputSection *Sec : Cmd.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 *S = dyn_cast<SyntheticSection>(Sec))
if (S->empty())
continue;
if (!Sec->Live)
continue;
assert(CurAddressState->OutSec == Sec->getParent());
output(Sec);
}
}
// 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 *LinkerScript::findMemoryRegion(OutputSection *Sec) {
// If a memory region name was specified in the output section command,
// then try to find that region first.
if (!Sec->MemoryRegionName.empty()) {
auto It = Opt.MemoryRegions.find(Sec->MemoryRegionName);
if (It != Opt.MemoryRegions.end())
return &It->second;
error("memory region '" + Sec->MemoryRegionName + "' not declared");
return nullptr;
}
// If at least one memory region is defined, all sections must
// belong to some memory region. Otherwise, we don't need to do
// anything for memory regions.
if (Opt.MemoryRegions.empty())
return nullptr;
// See if a region can be found by matching section flags.
for (auto &Pair : Opt.MemoryRegions) {
MemoryRegion &M = Pair.second;
if ((M.Flags & Sec->Flags) && (M.NegFlags & Sec->Flags) == 0)
return &M;
}
// 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 LinkerScript::assignOffsets(OutputSection *Sec) {
if (!(Sec->Flags & SHF_ALLOC))
Dot = 0;
else if (Sec->AddrExpr)
setDot(Sec->AddrExpr, Sec->Location, false);
if (Sec->LMAExpr) {
uint64_t D = Dot;
CurAddressState->LMAOffset = [=] { return Sec->LMAExpr().getValue() - D; };
}
CurAddressState->MemRegion = Sec->MemRegion;
if (CurAddressState->MemRegion)
Dot = CurAddressState->MemRegionOffset[CurAddressState->MemRegion];
switchTo(Sec);
// We do not support custom layout for compressed debug sectons.
// At this point we already know their size and have compressed content.
if (CurAddressState->OutSec->Flags & SHF_COMPRESSED)
return;
for (BaseCommand *C : Sec->Commands)
process(*C);
}
void LinkerScript::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(),
[&](BaseCommand *Base) {
if (auto *Sec = dyn_cast<OutputSection>(Base))
return !Sec->Live;
return false;
});
Opt.Commands.erase(Pos, Opt.Commands.end());
}
static bool isAllSectionDescription(const OutputSection &Cmd) {
for (BaseCommand *Base : Cmd.Commands)
if (!isa<InputSectionDescription>(*Base))
return false;
return true;
}
void LinkerScript::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;
for (int I = 0, E = Opt.Commands.size(); I != E; ++I) {
auto *Sec = dyn_cast<OutputSection>(Opt.Commands[I]);
if (!Sec)
continue;
if (Sec->Live) {
Flags = Sec->Flags;
continue;
}
if (isAllSectionDescription(*Sec))
continue;
Sec->Live = true;
Sec->SectionIndex = I;
Sec->Flags = Flags;
}
}
void LinkerScript::adjustSectionsAfterSorting() {
// Try and find an appropriate memory region to assign offsets in.
for (BaseCommand *Base : Opt.Commands) {
if (auto *Sec = dyn_cast<OutputSection>(Base)) {
Sec->MemRegion = findMemoryRegion(Sec);
// Handle align (e.g. ".foo : ALIGN(16) { ... }").
if (Sec->AlignExpr)
Sec->updateAlignment(Sec->AlignExpr().getValue());
}
}
// 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 (BaseCommand *Base : Opt.Commands) {
auto *Sec = dyn_cast<OutputSection>(Base);
if (!Sec)
continue;
if (Sec->Phdrs.empty()) {
// To match the bfd linker script behaviour, only propagate program
// headers to sections that are allocated.
if (Sec->Flags & SHF_ALLOC)
Sec->Phdrs = DefPhdrs;
} else {
DefPhdrs = Sec->Phdrs;
}
}
removeEmptyCommands();
}
void LinkerScript::allocateHeaders(std::vector<PhdrEntry *> &Phdrs) {
uint64_t Min = std::numeric_limits<uint64_t>::max();
for (OutputSection *Sec : OutputSections)
if (Sec->Flags & SHF_ALLOC)
Min = std::min<uint64_t>(Min, Sec->Addr);
auto It = llvm::find_if(
Phdrs, [](const PhdrEntry *E) { return E->p_type == PT_LOAD; });
if (It == Phdrs.end())
return;
PhdrEntry *FirstPTLoad = *It;
uint64_t HeaderSize = getHeaderSize();
if (HeaderSize <= Min || Script->hasPhdrsCommands()) {
Min = alignDown(Min - HeaderSize, Config->MaxPageSize);
Out::ElfHeader->Addr = Min;
Out::ProgramHeaders->Addr = Min + Out::ElfHeader->Size;
return;
}
assert(FirstPTLoad->First == Out::ElfHeader);
OutputSection *ActualFirst = nullptr;
for (OutputSection *Sec : OutputSections) {
if (Sec->FirstInPtLoad == Out::ElfHeader) {
ActualFirst = Sec;
break;
}
}
if (ActualFirst) {
for (OutputSection *Sec : OutputSections)
if (Sec->FirstInPtLoad == Out::ElfHeader)
Sec->FirstInPtLoad = ActualFirst;
FirstPTLoad->First = ActualFirst;
} else {
Phdrs.erase(It);
}
auto PhdrI = llvm::find_if(
Phdrs, [](const PhdrEntry *E) { return E->p_type == PT_PHDR; });
if (PhdrI != Phdrs.end())
Phdrs.erase(PhdrI);
}
LinkerScript::AddressState::AddressState(const ScriptConfiguration &Opt) {
for (auto &MRI : Opt.MemoryRegions) {
const MemoryRegion *MR = &MRI.second;
MemRegionOffset[MR] = MR->Origin;
}
}
void LinkerScript::assignAddresses() {
// Assign addresses as instructed by linker script SECTIONS sub-commands.
Dot = 0;
auto State = make_unique<AddressState>(Opt);
// CurAddressState captures the local AddressState and makes it accessible
// deliberately. This is needed as there are some cases where we cannot just
// thread the current state through to a lambda function created by the
// script parser.
CurAddressState = State.get();
ErrorOnMissingSection = true;
switchTo(Aether);
for (BaseCommand *Base : Opt.Commands) {
if (auto *Cmd = dyn_cast<SymbolAssignment>(Base)) {
assignSymbol(Cmd, false);
continue;
}
if (auto *Cmd = dyn_cast<AssertCommand>(Base)) {
Cmd->Expression();
continue;
}
assignOffsets(cast<OutputSection>(Base));
}
CurAddressState = nullptr;
}
// Creates program headers as instructed by PHDRS linker script command.
std::vector<PhdrEntry *> LinkerScript::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) {
PhdrEntry *Phdr =
make<PhdrEntry>(Cmd.Type, Cmd.Flags == UINT_MAX ? PF_R : Cmd.Flags);
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;
}
Ret.push_back(Phdr);
}
// Add output sections to program headers.
for (OutputSection *Sec : OutputSections) {
// Assign headers specified by linker script
for (size_t Id : getPhdrIndices(Sec)) {
Ret[Id]->add(Sec);
if (Opt.PhdrsCommands[Id].Flags == UINT_MAX)
Ret[Id]->p_flags |= Sec->getPhdrFlags();
}
}
return Ret;
}
bool LinkerScript::ignoreInterpSection() {
// Ignore .interp section in case we have PHDRS specification
// and PT_INTERP isn't listed.
if (Opt.PhdrsCommands.empty())
return false;
for (PhdrsCommand &Cmd : Opt.PhdrsCommands)
if (Cmd.Type == PT_INTERP)
return false;
return true;
}
ExprValue LinkerScript::getSymbolValue(const Twine &Loc, StringRef S) {
if (S == ".")
return {CurAddressState->OutSec, Dot - CurAddressState->OutSec->Addr, Loc};
if (SymbolBody *B = Symtab->find(S)) {
if (auto *D = dyn_cast<DefinedRegular>(B))
return {D->Section, D->Value, Loc};
if (auto *C = dyn_cast<DefinedCommon>(B))
return {InX::Common, C->Offset, Loc};
}
error(Loc + ": symbol not found: " + S);
return 0;
}
bool LinkerScript::isDefined(StringRef S) { return Symtab->find(S) != nullptr; }
static const size_t NoPhdr = -1;
// Returns indices of ELF headers containing specific section. Each index is a
// zero based number of ELF header listed within PHDRS {} script block.
std::vector<size_t> LinkerScript::getPhdrIndices(OutputSection *Cmd) {
std::vector<size_t> Ret;
for (StringRef PhdrName : Cmd->Phdrs) {
size_t Index = getPhdrIndex(Cmd->Location, PhdrName);
if (Index != NoPhdr)
Ret.push_back(Index);
}
return Ret;
}
// Returns the index of the segment named PhdrName if found otherwise
// NoPhdr. When not found, if PhdrName is not the special case value 'NONE'
// (which can be used to explicitly specify that a section isn't assigned to a
// segment) then error.
size_t LinkerScript::getPhdrIndex(const Twine &Loc, StringRef PhdrName) {
size_t I = 0;
for (PhdrsCommand &Cmd : Opt.PhdrsCommands) {
if (Cmd.Name == PhdrName)
return I;
++I;
}
if (PhdrName != "NONE")
error(Loc + ": section header '" + PhdrName + "' is not listed in PHDRS");
return NoPhdr;
}
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