blob: 161909abf00d0debcc6873cf969f175117dd290e [file] [log] [blame]
//===- 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 "Writer.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringRef.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/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 (Sec->getOutputSection())
return Sec->getOffset(Val) + Sec->getOutputSection()->Addr;
error("unable to evaluate expression: input section " + Sec->Name +
" has no output section assigned");
}
return Val;
}
uint64_t ExprValue::getSecAddr() const {
if (Sec)
return Sec->getOffset(0) + Sec->getOutputSection()->Addr;
return 0;
}
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;
// 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, Cmd->Name, /*IsLocal=*/false, Visibility,
STT_NOTYPE, SymValue, 0, Sec, nullptr);
return Sym->body();
}
OutputSection *LinkerScript::getOutputSection(const Twine &Loc,
StringRef Name) {
for (OutputSection *Sec : *OutputSections)
if (Sec->Name == Name)
return Sec;
static OutputSection Dummy("", 0, 0);
if (ErrorOnMissingSection)
error(Loc + ": undefined section " + Name);
return &Dummy;
}
// 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 LinkerScript::getOutputSectionSize(StringRef Name) {
for (OutputSection *Sec : *OutputSections)
if (Sec->Name == Name)
return Sec->Size;
return 0;
}
void LinkerScript::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 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;
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 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 = 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 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(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.
std::vector<InputSectionBase *>
LinkerScript::computeInputSections(const InputSectionDescription *Cmd) {
std::vector<InputSectionBase *> 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;
// 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(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.
InputSectionBase **Begin = Ret.data() + SizeBefore;
InputSectionBase **End = Ret.data() + Ret.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);
}
}
return Ret;
}
void LinkerScript::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 *>
LinkerScript::createInputSectionList(OutputSectionCommand &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;
CurOutSec = 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 *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I])) {
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(Opt.Commands.begin() + I);
--I;
continue;
}
// A directive may contain symbol definitions like this:
// ".foo : { ...; bar = .; }". Handle them.
for (BaseCommand *Base : Cmd->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 (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, Cmd->Sec);
if (OutputSection *Sec = Cmd->Sec) {
assert(Sec->SectionIndex == INT_MAX);
Sec->SectionIndex = I;
SecToCommand[Sec] = Cmd;
}
}
}
CurOutSec = nullptr;
}
void LinkerScript::fabricateDefaultCommands() {
std::vector<BaseCommand *> Commands;
// Define start address
uint64_t StartAddr = Config->ImageBase + elf::getHeaderSize();
// 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);
Commands.push_back(
make<SymbolAssignment>(".", [=] { return StartAddr; }, ""));
// For each OutputSection that needs a VA fabricate an OutputSectionCommand
// with an InputSectionDescription describing the InputSections
for (OutputSection *Sec : *OutputSections) {
if (!(Sec->Flags & SHF_ALLOC))
continue;
auto *OSCmd = make<OutputSectionCommand>(Sec->Name);
OSCmd->Sec = Sec;
SecToCommand[Sec] = OSCmd;
// Prefer user supplied address over additional alignment constraint
auto I = Config->SectionStartMap.find(Sec->Name);
if (I != Config->SectionStartMap.end())
Commands.push_back(
make<SymbolAssignment>(".", [=] { return I->second; }, ""));
else if (Sec->PageAlign)
OSCmd->AddrExpr = [=] {
return alignTo(Script->getDot(), Config->MaxPageSize);
};
Commands.push_back(OSCmd);
if (Sec->Sections.size()) {
auto *ISD = make<InputSectionDescription>("");
OSCmd->Commands.push_back(ISD);
for (InputSection *ISec : Sec->Sections) {
ISD->Sections.push_back(ISec);
ISec->Assigned = true;
}
}
}
// SECTIONS commands run before other non SECTIONS commands
Commands.insert(Commands.end(), Opt.Commands.begin(), Opt.Commands.end());
Opt.Commands = std::move(Commands);
}
// Add sections that didn't match any sections command.
void LinkerScript::addOrphanSections(OutputSectionFactory &Factory) {
for (InputSectionBase *S : InputSections) {
if (!S->Live || S->OutSec)
continue;
StringRef Name = getOutputSectionName(S->Name);
auto I = std::find_if(
Opt.Commands.begin(), Opt.Commands.end(), [&](BaseCommand *Base) {
if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base))
return Cmd->Name == Name;
return false;
});
if (I == Opt.Commands.end()) {
Factory.addInputSec(S, Name);
} else {
auto *Cmd = cast<OutputSectionCommand>(*I);
Factory.addInputSec(S, Name, Cmd->Sec);
if (OutputSection *Sec = Cmd->Sec) {
SecToCommand[Sec] = Cmd;
unsigned Index = std::distance(Opt.Commands.begin(), I);
assert(Sec->SectionIndex == INT_MAX || Sec->SectionIndex == Index);
Sec->SectionIndex = Index;
}
auto *ISD = make<InputSectionDescription>("");
ISD->Sections.push_back(S);
Cmd->Commands.push_back(ISD);
}
}
}
uint64_t LinkerScript::advance(uint64_t Size, unsigned Align) {
bool IsTbss = (CurOutSec->Flags & SHF_TLS) && CurOutSec->Type == SHT_NOBITS;
uint64_t Start = IsTbss ? Dot + ThreadBssOffset : Dot;
Start = alignTo(Start, Align);
uint64_t End = Start + Size;
if (IsTbss)
ThreadBssOffset = End - Dot;
else
Dot = End;
return End;
}
void LinkerScript::output(InputSection *S) {
uint64_t Pos = advance(S->getSize(), S->Alignment);
S->OutSecOff = Pos - S->getSize() - CurOutSec->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) }
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");
}
}
}
void LinkerScript::switchTo(OutputSection *Sec) {
if (CurOutSec == Sec)
return;
CurOutSec = Sec;
CurOutSec->Addr = advance(0, CurOutSec->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 (LMAOffset)
CurOutSec->LMAOffset = 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 - CurOutSec->Addr;
Dot += Cmd->Size;
CurOutSec->Size = Dot - CurOutSec->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 (InputSectionBase *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(CurOutSec == Sec->OutSec);
output(cast<InputSection>(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(OutputSectionCommand *Cmd) {
// 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;
}
// 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;
OutputSection *Sec = Cmd->Sec;
// 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(OutputSectionCommand *Cmd) {
OutputSection *Sec = Cmd->Sec;
if (!Sec)
return;
if (Cmd->AddrExpr && (Sec->Flags & SHF_ALLOC))
setDot(Cmd->AddrExpr, Cmd->Location, false);
if (Cmd->LMAExpr) {
uint64_t D = Dot;
LMAOffset = [=] { return Cmd->LMAExpr().getValue() - D; };
}
CurMemRegion = Cmd->MemRegion;
if (CurMemRegion)
Dot = CurMemRegion->Offset;
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 (CurOutSec->Flags & SHF_COMPRESSED)
return;
for (BaseCommand *C : Cmd->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 *Cmd = dyn_cast<OutputSectionCommand>(Base))
return std::find(OutputSections->begin(), OutputSections->end(),
Cmd->Sec) == OutputSections->end();
return false;
});
Opt.Commands.erase(Pos, Opt.Commands.end());
}
static bool isAllSectionDescription(const OutputSectionCommand &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;
uint32_t Type = SHT_PROGBITS;
for (int I = 0, E = Opt.Commands.size(); I != E; ++I) {
auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I]);
if (!Cmd)
continue;
if (OutputSection *Sec = Cmd->Sec) {
Flags = Sec->Flags;
Type = Sec->Type;
continue;
}
if (isAllSectionDescription(*Cmd))
continue;
auto *OutSec = make<OutputSection>(Cmd->Name, Type, Flags);
OutSec->SectionIndex = I;
OutputSections->push_back(OutSec);
Cmd->Sec = OutSec;
SecToCommand[OutSec] = Cmd;
}
}
void LinkerScript::adjustSectionsAfterSorting() {
placeOrphanSections();
// Try and find an appropriate memory region to assign offsets in.
for (BaseCommand *Base : Opt.Commands) {
if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base)) {
Cmd->MemRegion = findMemoryRegion(Cmd);
// Handle align (e.g. ".foo : ALIGN(16) { ... }").
if (Cmd->AlignExpr)
Cmd->Sec->updateAlignment(Cmd->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 *Cmd = dyn_cast<OutputSectionCommand>(Base);
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(BaseCommand *Cmd) {
if (isa<OutputSectionCommand>(Cmd))
return false;
if (auto *Assign = dyn_cast<SymbolAssignment>(Cmd))
return Assign->Name != ".";
return true;
}
// 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 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 also 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 LinkerScript::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(),
[](BaseCommand *Cmd) { return !shouldSkip(Cmd); });
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;
}
// If there is no command corresponding to this output section,
// create one and put a InputSectionDescription in it so that both
// representations agree on which input sections to use.
OutputSectionCommand *Cmd = getCmd(Sec);
if (!Cmd) {
Cmd = make<OutputSectionCommand>(Name);
Opt.Commands.insert(CmdIter, Cmd);
++CmdIndex;
Cmd->Sec = Sec;
SecToCommand[Sec] = Cmd;
auto *ISD = make<InputSectionDescription>("");
for (InputSection *IS : Sec->Sections)
ISD->Sections.push_back(IS);
Cmd->Commands.push_back(ISD);
continue;
}
// Continue from where we found it.
while (*CmdIter != Cmd) {
++CmdIter;
++CmdIndex;
}
++CmdIndex;
}
}
void LinkerScript::processNonSectionCommands() {
for (BaseCommand *Base : Opt.Commands) {
if (auto *Cmd = dyn_cast<SymbolAssignment>(Base))
assignSymbol(Cmd, false);
else if (auto *Cmd = dyn_cast<AssertCommand>(Base))
Cmd->Expression();
}
}
// Do a last effort at synchronizing the linker script "AST" and the section
// list. This is needed to account for last minute changes, like adding a
// .ARM.exidx terminator and sorting SHF_LINK_ORDER sections.
//
// FIXME: We should instead create the "AST" earlier and the above changes would
// be done directly in the "AST".
//
// This can only handle new sections being added and sections being reordered.
void LinkerScript::synchronize() {
for (BaseCommand *Base : Opt.Commands) {
auto *Cmd = dyn_cast<OutputSectionCommand>(Base);
if (!Cmd)
continue;
ArrayRef<InputSection *> Sections = Cmd->Sec->Sections;
std::vector<InputSectionBase **> ScriptSections;
DenseSet<InputSectionBase *> ScriptSectionsSet;
for (BaseCommand *Base : Cmd->Commands) {
auto *ISD = dyn_cast<InputSectionDescription>(Base);
if (!ISD)
continue;
for (InputSectionBase *&IS : ISD->Sections) {
if (IS->Live) {
ScriptSections.push_back(&IS);
ScriptSectionsSet.insert(IS);
}
}
}
std::vector<InputSectionBase *> Missing;
for (InputSection *IS : Sections)
if (!ScriptSectionsSet.count(IS))
Missing.push_back(IS);
if (!Missing.empty()) {
auto ISD = make<InputSectionDescription>("");
ISD->Sections = Missing;
Cmd->Commands.push_back(ISD);
for (InputSectionBase *&IS : ISD->Sections)
if (IS->Live)
ScriptSections.push_back(&IS);
}
assert(ScriptSections.size() == Sections.size());
for (int I = 0, N = Sections.size(); I < N; ++I)
*ScriptSections[I] = Sections[I];
}
}
static bool allocateHeaders(std::vector<PhdrEntry> &Phdrs,
ArrayRef<OutputSection *> OutputSections,
uint64_t Min) {
auto FirstPTLoad =
std::find_if(Phdrs.begin(), Phdrs.end(),
[](const PhdrEntry &E) { return E.p_type == PT_LOAD; });
if (FirstPTLoad == Phdrs.end())
return false;
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 true;
}
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(FirstPTLoad);
}
auto PhdrI = std::find_if(Phdrs.begin(), Phdrs.end(), [](const PhdrEntry &E) {
return E.p_type == PT_PHDR;
});
if (PhdrI != Phdrs.end())
Phdrs.erase(PhdrI);
return false;
}
void LinkerScript::assignAddresses(std::vector<PhdrEntry> &Phdrs) {
// Assign addresses as instructed by linker script SECTIONS sub-commands.
Dot = 0;
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;
}
auto *Cmd = cast<OutputSectionCommand>(Base);
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> 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) {
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)) {
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;
}
OutputSectionCommand *LinkerScript::getCmd(OutputSection *Sec) const {
auto I = SecToCommand.find(Sec);
if (I == SecToCommand.end())
return nullptr;
return I->second;
}
Optional<uint32_t> LinkerScript::getFiller(OutputSection *Sec) {
if (OutputSectionCommand *Cmd = getCmd(Sec))
return Cmd->Filler;
return None;
}
static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
if (Size == 1)
*Buf = Data;
else if (Size == 2)
write16(Buf, Data, Config->Endianness);
else if (Size == 4)
write32(Buf, Data, Config->Endianness);
else if (Size == 8)
write64(Buf, Data, Config->Endianness);
else
llvm_unreachable("unsupported Size argument");
}
void LinkerScript::writeDataBytes(OutputSection *Sec, uint8_t *Buf) {
if (OutputSectionCommand *Cmd = getCmd(Sec))
for (BaseCommand *Base : Cmd->Commands)
if (auto *Data = dyn_cast<BytesDataCommand>(Base))
writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size);
}
bool LinkerScript::hasLMA(OutputSection *Sec) {
if (OutputSectionCommand *Cmd = getCmd(Sec))
if (Cmd->LMAExpr)
return true;
return false;
}
ExprValue LinkerScript::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};
if (auto *C = dyn_cast<DefinedCommon>(B))
return {InX::Common, C->Offset};
}
error(Loc + ": symbol not found: " + S);
return 0;
}
bool LinkerScript::isDefined(StringRef S) { return findSymbol(S) != nullptr; }
// 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 *Sec) {
if (OutputSectionCommand *Cmd = getCmd(Sec)) {
std::vector<size_t> Ret;
for (StringRef PhdrName : Cmd->Phdrs)
Ret.push_back(getPhdrIndex(Cmd->Location, PhdrName));
return Ret;
}
return {};
}
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;
}
error(Loc + ": section header '" + PhdrName + "' is not listed in PHDRS");
return 0;
}