forked from OSchip/llvm-project
1009 lines
35 KiB
C++
1009 lines
35 KiB
C++
//===- LinkerScript.cpp ---------------------------------------------------===//
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//
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// The LLVM Linker
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains the parser/evaluator of the linker script.
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//
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//===----------------------------------------------------------------------===//
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#include "LinkerScript.h"
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#include "Config.h"
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#include "InputSection.h"
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#include "OutputSections.h"
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#include "Strings.h"
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#include "SymbolTable.h"
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#include "Symbols.h"
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#include "SyntheticSections.h"
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#include "Target.h"
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#include "Writer.h"
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#include "lld/Common/Memory.h"
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#include "lld/Common/Threads.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/BinaryFormat/ELF.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/Endian.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/FileSystem.h"
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#include "llvm/Support/Path.h"
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#include <algorithm>
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#include <cassert>
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#include <cstddef>
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#include <cstdint>
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#include <iterator>
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#include <limits>
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#include <string>
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#include <vector>
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using namespace llvm;
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using namespace llvm::ELF;
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using namespace llvm::object;
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using namespace llvm::support::endian;
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using namespace lld;
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using namespace lld::elf;
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LinkerScript *elf::Script;
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static uint64_t getOutputSectionVA(SectionBase *InputSec, StringRef Loc) {
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if (OutputSection *OS = InputSec->getOutputSection())
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return OS->Addr;
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error(Loc + ": unable to evaluate expression: input section " +
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InputSec->Name + " has no output section assigned");
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return 0;
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}
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uint64_t ExprValue::getValue() const {
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if (Sec)
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return alignTo(Sec->getOffset(Val) + getOutputSectionVA(Sec, Loc),
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Alignment);
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return alignTo(Val, Alignment);
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}
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uint64_t ExprValue::getSecAddr() const {
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if (Sec)
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return Sec->getOffset(0) + getOutputSectionVA(Sec, Loc);
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return 0;
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}
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uint64_t ExprValue::getSectionOffset() const {
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// If the alignment is trivial, we don't have to compute the full
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// value to know the offset. This allows this function to succeed in
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// cases where the output section is not yet known.
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if (Alignment == 1)
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return Val;
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return getValue() - getSecAddr();
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}
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OutputSection *LinkerScript::createOutputSection(StringRef Name,
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StringRef Location) {
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OutputSection *&SecRef = NameToOutputSection[Name];
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OutputSection *Sec;
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if (SecRef && SecRef->Location.empty()) {
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// There was a forward reference.
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Sec = SecRef;
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} else {
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Sec = make<OutputSection>(Name, SHT_PROGBITS, 0);
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if (!SecRef)
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SecRef = Sec;
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}
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Sec->Location = Location;
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return Sec;
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}
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OutputSection *LinkerScript::getOrCreateOutputSection(StringRef Name) {
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OutputSection *&CmdRef = NameToOutputSection[Name];
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if (!CmdRef)
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CmdRef = make<OutputSection>(Name, SHT_PROGBITS, 0);
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return CmdRef;
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}
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void LinkerScript::setDot(Expr E, const Twine &Loc, bool InSec) {
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uint64_t Val = E().getValue();
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if (Val < Dot && InSec)
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error(Loc + ": unable to move location counter backward for: " +
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Ctx->OutSec->Name);
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Dot = Val;
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// Update to location counter means update to section size.
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if (InSec)
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Ctx->OutSec->Size = Dot - Ctx->OutSec->Addr;
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}
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// This function is called from processSectionCommands,
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// while we are fixing the output section layout.
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void LinkerScript::addSymbol(SymbolAssignment *Cmd) {
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if (Cmd->Name == ".")
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return;
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// If a symbol was in PROVIDE(), we need to define it only when
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// it is a referenced undefined symbol.
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Symbol *B = Symtab->find(Cmd->Name);
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if (Cmd->Provide && (!B || B->isDefined()))
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return;
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// Define a symbol.
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Symbol *Sym;
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uint8_t Visibility = Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT;
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std::tie(Sym, std::ignore) = Symtab->insert(Cmd->Name, /*Type*/ 0, Visibility,
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/*CanOmitFromDynSym*/ false,
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/*File*/ nullptr);
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ExprValue Value = Cmd->Expression();
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SectionBase *Sec = Value.isAbsolute() ? nullptr : Value.Sec;
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// When this function is called, section addresses have not been
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// fixed yet. So, we may or may not know the value of the RHS
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// expression.
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//
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// For example, if an expression is `x = 42`, we know x is always 42.
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// However, if an expression is `x = .`, there's no way to know its
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// value at the moment.
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//
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// We want to set symbol values early if we can. This allows us to
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// use symbols as variables in linker scripts. Doing so allows us to
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// write expressions like this: `alignment = 16; . = ALIGN(., alignment)`.
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uint64_t SymValue = Value.Sec ? 0 : Value.getValue();
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replaceSymbol<Defined>(Sym, nullptr, Cmd->Name, STB_GLOBAL, Visibility,
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STT_NOTYPE, SymValue, 0, Sec);
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Cmd->Sym = cast<Defined>(Sym);
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}
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// This function is called from assignAddresses, while we are
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// fixing the output section addresses. This function is supposed
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// to set the final value for a given symbol assignment.
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void LinkerScript::assignSymbol(SymbolAssignment *Cmd, bool InSec) {
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if (Cmd->Name == ".") {
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setDot(Cmd->Expression, Cmd->Location, InSec);
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return;
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}
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if (!Cmd->Sym)
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return;
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ExprValue V = Cmd->Expression();
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if (V.isAbsolute()) {
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Cmd->Sym->Section = nullptr;
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Cmd->Sym->Value = V.getValue();
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} else {
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Cmd->Sym->Section = V.Sec;
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Cmd->Sym->Value = V.getSectionOffset();
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}
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}
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static std::string getFilename(InputFile *File) {
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if (!File)
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return "";
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if (File->ArchiveName.empty())
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return File->getName();
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return (File->ArchiveName + "(" + File->getName() + ")").str();
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}
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bool LinkerScript::shouldKeep(InputSectionBase *S) {
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std::string Filename = getFilename(S->File);
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for (InputSectionDescription *ID : KeptSections)
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if (ID->FilePat.match(Filename))
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for (SectionPattern &P : ID->SectionPatterns)
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if (P.SectionPat.match(S->Name))
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return true;
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return false;
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}
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// A helper function for the SORT() command.
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static std::function<bool(InputSectionBase *, InputSectionBase *)>
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getComparator(SortSectionPolicy K) {
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switch (K) {
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case SortSectionPolicy::Alignment:
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return [](InputSectionBase *A, InputSectionBase *B) {
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// ">" is not a mistake. Sections with larger alignments are placed
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// before sections with smaller alignments in order to reduce the
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// amount of padding necessary. This is compatible with GNU.
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return A->Alignment > B->Alignment;
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};
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case SortSectionPolicy::Name:
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return [](InputSectionBase *A, InputSectionBase *B) {
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return A->Name < B->Name;
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};
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case SortSectionPolicy::Priority:
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return [](InputSectionBase *A, InputSectionBase *B) {
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return getPriority(A->Name) < getPriority(B->Name);
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};
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default:
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llvm_unreachable("unknown sort policy");
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}
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}
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// A helper function for the SORT() command.
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static bool matchConstraints(ArrayRef<InputSection *> Sections,
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ConstraintKind Kind) {
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if (Kind == ConstraintKind::NoConstraint)
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return true;
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bool IsRW = llvm::any_of(
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Sections, [](InputSection *Sec) { return Sec->Flags & SHF_WRITE; });
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return (IsRW && Kind == ConstraintKind::ReadWrite) ||
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(!IsRW && Kind == ConstraintKind::ReadOnly);
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}
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static void sortSections(MutableArrayRef<InputSection *> Vec,
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SortSectionPolicy K) {
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if (K != SortSectionPolicy::Default && K != SortSectionPolicy::None)
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std::stable_sort(Vec.begin(), Vec.end(), getComparator(K));
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}
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// Sort sections as instructed by SORT-family commands and --sort-section
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// option. Because SORT-family commands can be nested at most two depth
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// (e.g. SORT_BY_NAME(SORT_BY_ALIGNMENT(.text.*))) and because the command
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// line option is respected even if a SORT command is given, the exact
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// behavior we have here is a bit complicated. Here are the rules.
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//
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// 1. If two SORT commands are given, --sort-section is ignored.
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// 2. If one SORT command is given, and if it is not SORT_NONE,
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// --sort-section is handled as an inner SORT command.
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// 3. If one SORT command is given, and if it is SORT_NONE, don't sort.
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// 4. If no SORT command is given, sort according to --sort-section.
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// 5. If no SORT commands are given and --sort-section is not specified,
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// apply sorting provided by --symbol-ordering-file if any exist.
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static void sortInputSections(
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MutableArrayRef<InputSection *> Vec, const SectionPattern &Pat,
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const DenseMap<SectionBase *, int> &Order) {
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if (Pat.SortOuter == SortSectionPolicy::None)
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return;
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if (Pat.SortOuter == SortSectionPolicy::Default &&
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Config->SortSection == SortSectionPolicy::Default) {
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// If -symbol-ordering-file was given, sort accordingly.
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// Usually, Order is empty.
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if (!Order.empty())
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sortByOrder(Vec, [&](InputSectionBase *S) { return Order.lookup(S); });
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return;
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}
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if (Pat.SortInner == SortSectionPolicy::Default)
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sortSections(Vec, Config->SortSection);
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else
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sortSections(Vec, Pat.SortInner);
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sortSections(Vec, Pat.SortOuter);
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}
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// Compute and remember which sections the InputSectionDescription matches.
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std::vector<InputSection *>
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LinkerScript::computeInputSections(const InputSectionDescription *Cmd,
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const DenseMap<SectionBase *, int> &Order) {
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std::vector<InputSection *> Ret;
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// Collects all sections that satisfy constraints of Cmd.
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for (const SectionPattern &Pat : Cmd->SectionPatterns) {
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size_t SizeBefore = Ret.size();
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for (InputSectionBase *Sec : InputSections) {
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if (!Sec->Live || Sec->Assigned)
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continue;
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// For -emit-relocs we have to ignore entries like
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// .rela.dyn : { *(.rela.data) }
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// which are common because they are in the default bfd script.
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if (Sec->Type == SHT_REL || Sec->Type == SHT_RELA)
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continue;
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std::string Filename = getFilename(Sec->File);
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if (!Cmd->FilePat.match(Filename) ||
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Pat.ExcludedFilePat.match(Filename) ||
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!Pat.SectionPat.match(Sec->Name))
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continue;
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// It is safe to assume that Sec is an InputSection
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// because mergeable or EH input sections have already been
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// handled and eliminated.
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Ret.push_back(cast<InputSection>(Sec));
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Sec->Assigned = true;
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}
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sortInputSections(MutableArrayRef<InputSection *>(Ret).slice(SizeBefore),
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Pat, Order);
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}
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return Ret;
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}
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void LinkerScript::discard(ArrayRef<InputSection *> V) {
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for (InputSection *S : V) {
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if (S == InX::ShStrTab || S == InX::Dynamic || S == InX::DynSymTab ||
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S == InX::DynStrTab)
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error("discarding " + S->Name + " section is not allowed");
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S->Assigned = false;
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S->Live = false;
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discard(S->DependentSections);
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}
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}
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std::vector<InputSection *> LinkerScript::createInputSectionList(
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OutputSection &OutCmd, const DenseMap<SectionBase *, int> &Order) {
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std::vector<InputSection *> Ret;
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for (BaseCommand *Base : OutCmd.SectionCommands) {
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if (auto *Cmd = dyn_cast<InputSectionDescription>(Base)) {
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Cmd->Sections = computeInputSections(Cmd, Order);
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Ret.insert(Ret.end(), Cmd->Sections.begin(), Cmd->Sections.end());
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}
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}
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return Ret;
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}
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void LinkerScript::processSectionCommands() {
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// A symbol can be assigned before any section is mentioned in the linker
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// script. In an DSO, the symbol values are addresses, so the only important
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// section values are:
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// * SHN_UNDEF
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// * SHN_ABS
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// * Any value meaning a regular section.
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// To handle that, create a dummy aether section that fills the void before
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// the linker scripts switches to another section. It has an index of one
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// which will map to whatever the first actual section is.
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Aether = make<OutputSection>("", 0, SHF_ALLOC);
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Aether->SectionIndex = 1;
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// Ctx captures the local AddressState and makes it accessible deliberately.
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// This is needed as there are some cases where we cannot just
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// thread the current state through to a lambda function created by the
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// script parser.
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auto Deleter = make_unique<AddressState>();
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Ctx = Deleter.get();
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Ctx->OutSec = Aether;
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size_t I = 0;
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DenseMap<SectionBase *, int> Order = buildSectionOrder();
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// Add input sections to output sections.
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for (BaseCommand *Base : SectionCommands) {
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// Handle symbol assignments outside of any output section.
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if (auto *Cmd = dyn_cast<SymbolAssignment>(Base)) {
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addSymbol(Cmd);
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continue;
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}
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if (auto *Sec = dyn_cast<OutputSection>(Base)) {
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std::vector<InputSection *> V = createInputSectionList(*Sec, Order);
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// The output section name `/DISCARD/' is special.
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// Any input section assigned to it is discarded.
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if (Sec->Name == "/DISCARD/") {
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discard(V);
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continue;
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}
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// This is for ONLY_IF_RO and ONLY_IF_RW. An output section directive
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// ".foo : ONLY_IF_R[OW] { ... }" is handled only if all member input
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// sections satisfy a given constraint. If not, a directive is handled
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// as if it wasn't present from the beginning.
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//
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// Because we'll iterate over SectionCommands many more times, the easy
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// way to "make it as if it wasn't present" is to make it empty.
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if (!matchConstraints(V, Sec->Constraint)) {
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for (InputSectionBase *S : V)
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S->Assigned = false;
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Sec->SectionCommands.clear();
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continue;
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}
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// A directive may contain symbol definitions like this:
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// ".foo : { ...; bar = .; }". Handle them.
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for (BaseCommand *Base : Sec->SectionCommands)
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if (auto *OutCmd = dyn_cast<SymbolAssignment>(Base))
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addSymbol(OutCmd);
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// Handle subalign (e.g. ".foo : SUBALIGN(32) { ... }"). If subalign
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// is given, input sections are aligned to that value, whether the
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// given value is larger or smaller than the original section alignment.
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if (Sec->SubalignExpr) {
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uint32_t Subalign = Sec->SubalignExpr().getValue();
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for (InputSectionBase *S : V)
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S->Alignment = Subalign;
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}
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// Add input sections to an output section.
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for (InputSection *S : V)
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Sec->addSection(S);
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Sec->SectionIndex = I++;
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if (Sec->Noload)
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Sec->Type = SHT_NOBITS;
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}
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}
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Ctx = nullptr;
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}
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static OutputSection *findByName(ArrayRef<BaseCommand *> Vec,
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StringRef Name) {
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for (BaseCommand *Base : Vec)
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if (auto *Sec = dyn_cast<OutputSection>(Base))
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if (Sec->Name == Name)
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return Sec;
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return nullptr;
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}
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static OutputSection *createSection(InputSectionBase *IS,
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StringRef OutsecName) {
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OutputSection *Sec = Script->createOutputSection(OutsecName, "<internal>");
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Sec->addSection(cast<InputSection>(IS));
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return Sec;
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}
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static OutputSection *addInputSec(StringMap<OutputSection *> &Map,
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InputSectionBase *IS, StringRef OutsecName) {
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// Sections with SHT_GROUP or SHF_GROUP attributes reach here only when the -r
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// option is given. A section with SHT_GROUP defines a "section group", and
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// its members have SHF_GROUP attribute. Usually these flags have already been
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// stripped by InputFiles.cpp as section groups are processed and uniquified.
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// However, for the -r option, we want to pass through all section groups
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// as-is because adding/removing members or merging them with other groups
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// change their semantics.
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if (IS->Type == SHT_GROUP || (IS->Flags & SHF_GROUP))
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return createSection(IS, OutsecName);
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// Imagine .zed : { *(.foo) *(.bar) } script. Both foo and bar may have
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// relocation sections .rela.foo and .rela.bar for example. Most tools do
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// not allow multiple REL[A] sections for output section. Hence we
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// should combine these relocation sections into single output.
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// We skip synthetic sections because it can be .rela.dyn/.rela.plt or any
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// other REL[A] sections created by linker itself.
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if (!isa<SyntheticSection>(IS) &&
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(IS->Type == SHT_REL || IS->Type == SHT_RELA)) {
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auto *Sec = cast<InputSection>(IS);
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OutputSection *Out = Sec->getRelocatedSection()->getOutputSection();
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if (Out->RelocationSection) {
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Out->RelocationSection->addSection(Sec);
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return nullptr;
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}
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Out->RelocationSection = createSection(IS, OutsecName);
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return Out->RelocationSection;
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}
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// When control reaches here, mergeable sections have already been merged into
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// synthetic sections. For relocatable case we want to create one output
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// section per syntetic section so that they have a valid sh_entsize.
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if (Config->Relocatable && (IS->Flags & SHF_MERGE))
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return createSection(IS, OutsecName);
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// The ELF spec just says
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// ----------------------------------------------------------------
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// In the first phase, input sections that match in name, type and
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// attribute flags should be concatenated into single sections.
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// ----------------------------------------------------------------
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//
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// However, it is clear that at least some flags have to be ignored for
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// section merging. At the very least SHF_GROUP and SHF_COMPRESSED have to be
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// ignored. We should not have two output .text sections just because one was
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// in a group and another was not for example.
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//
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// It also seems that that wording was a late addition and didn't get the
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// necessary scrutiny.
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//
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// Merging sections with different flags is expected by some users. One
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// reason is that if one file has
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//
|
|
// int *const bar __attribute__((section(".foo"))) = (int *)0;
|
|
//
|
|
// gcc with -fPIC will produce a read only .foo section. But if another
|
|
// file has
|
|
//
|
|
// int zed;
|
|
// int *const bar __attribute__((section(".foo"))) = (int *)&zed;
|
|
//
|
|
// gcc with -fPIC will produce a read write section.
|
|
//
|
|
// Last but not least, when using linker script the merge rules are forced by
|
|
// the script. Unfortunately, linker scripts are name based. This means that
|
|
// expressions like *(.foo*) can refer to multiple input sections with
|
|
// different flags. We cannot put them in different output sections or we
|
|
// would produce wrong results for
|
|
//
|
|
// start = .; *(.foo.*) end = .; *(.bar)
|
|
//
|
|
// and a mapping of .foo1 and .bar1 to one section and .foo2 and .bar2 to
|
|
// another. The problem is that there is no way to layout those output
|
|
// sections such that the .foo sections are the only thing between the start
|
|
// and end symbols.
|
|
//
|
|
// Given the above issues, we instead merge sections by name and error on
|
|
// incompatible types and flags.
|
|
OutputSection *&Sec = Map[OutsecName];
|
|
if (Sec) {
|
|
Sec->addSection(cast<InputSection>(IS));
|
|
return nullptr;
|
|
}
|
|
|
|
Sec = createSection(IS, OutsecName);
|
|
return Sec;
|
|
}
|
|
|
|
// Add sections that didn't match any sections command.
|
|
void LinkerScript::addOrphanSections() {
|
|
unsigned End = SectionCommands.size();
|
|
StringMap<OutputSection *> Map;
|
|
|
|
std::vector<OutputSection *> V;
|
|
for (InputSectionBase *S : InputSections) {
|
|
if (!S->Live || S->Parent)
|
|
continue;
|
|
|
|
StringRef Name = getOutputSectionName(S->Name);
|
|
|
|
if (Config->OrphanHandling == OrphanHandlingPolicy::Error)
|
|
error(toString(S) + " is being placed in '" + Name + "'");
|
|
else if (Config->OrphanHandling == OrphanHandlingPolicy::Warn)
|
|
warn(toString(S) + " is being placed in '" + Name + "'");
|
|
|
|
if (OutputSection *Sec =
|
|
findByName(makeArrayRef(SectionCommands).slice(0, End), Name)) {
|
|
Sec->addSection(cast<InputSection>(S));
|
|
continue;
|
|
}
|
|
|
|
if (OutputSection *OS = addInputSec(Map, S, Name))
|
|
V.push_back(OS);
|
|
assert(S->getOutputSection()->SectionIndex == INT_MAX);
|
|
}
|
|
|
|
// If no SECTIONS command was given, we should insert sections commands
|
|
// before others, so that we can handle scripts which refers them,
|
|
// for example: "foo = ABSOLUTE(ADDR(.text)));".
|
|
// When SECTIONS command is present we just add all orphans to the end.
|
|
if (HasSectionsCommand)
|
|
SectionCommands.insert(SectionCommands.end(), V.begin(), V.end());
|
|
else
|
|
SectionCommands.insert(SectionCommands.begin(), V.begin(), V.end());
|
|
}
|
|
|
|
uint64_t LinkerScript::advance(uint64_t Size, unsigned Alignment) {
|
|
bool IsTbss =
|
|
(Ctx->OutSec->Flags & SHF_TLS) && Ctx->OutSec->Type == SHT_NOBITS;
|
|
uint64_t Start = IsTbss ? Dot + Ctx->ThreadBssOffset : Dot;
|
|
Start = alignTo(Start, Alignment);
|
|
uint64_t End = Start + Size;
|
|
|
|
if (IsTbss)
|
|
Ctx->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() - Ctx->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) }
|
|
Ctx->OutSec->Size = Pos - Ctx->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 (Ctx->MemRegion) {
|
|
uint64_t &CurOffset = Ctx->MemRegionOffset[Ctx->MemRegion];
|
|
CurOffset += Pos - Before;
|
|
uint64_t CurSize = CurOffset - Ctx->MemRegion->Origin;
|
|
if (CurSize > Ctx->MemRegion->Length) {
|
|
uint64_t OverflowAmt = CurSize - Ctx->MemRegion->Length;
|
|
error("section '" + Ctx->OutSec->Name + "' will not fit in region '" +
|
|
Ctx->MemRegion->Name + "': overflowed by " + Twine(OverflowAmt) +
|
|
" bytes");
|
|
}
|
|
}
|
|
}
|
|
|
|
void LinkerScript::switchTo(OutputSection *Sec) {
|
|
if (Ctx->OutSec == Sec)
|
|
return;
|
|
|
|
Ctx->OutSec = Sec;
|
|
Ctx->OutSec->Addr = advance(0, Ctx->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 (Ctx->LMAOffset)
|
|
Ctx->OutSec->LMAOffset = Ctx->LMAOffset();
|
|
}
|
|
|
|
// 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 = MemoryRegions.find(Sec->MemoryRegionName);
|
|
if (It != 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 (MemoryRegions.empty())
|
|
return nullptr;
|
|
|
|
// See if a region can be found by matching section flags.
|
|
for (auto &Pair : 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);
|
|
|
|
Ctx->MemRegion = Sec->MemRegion;
|
|
if (Ctx->MemRegion)
|
|
Dot = Ctx->MemRegionOffset[Ctx->MemRegion];
|
|
|
|
if (Sec->LMAExpr) {
|
|
uint64_t D = Dot;
|
|
Ctx->LMAOffset = [=] { return Sec->LMAExpr().getValue() - D; };
|
|
}
|
|
|
|
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 (Ctx->OutSec->Flags & SHF_COMPRESSED)
|
|
return;
|
|
|
|
// We visited SectionsCommands from processSectionCommands to
|
|
// layout sections. Now, we visit SectionsCommands again to fix
|
|
// section offsets.
|
|
for (BaseCommand *Base : Sec->SectionCommands) {
|
|
// This handles the assignments to symbol or to the dot.
|
|
if (auto *Cmd = dyn_cast<SymbolAssignment>(Base)) {
|
|
assignSymbol(Cmd, true);
|
|
continue;
|
|
}
|
|
|
|
// Handle BYTE(), SHORT(), LONG(), or QUAD().
|
|
if (auto *Cmd = dyn_cast<ByteCommand>(Base)) {
|
|
Cmd->Offset = Dot - Ctx->OutSec->Addr;
|
|
Dot += Cmd->Size;
|
|
Ctx->OutSec->Size = Dot - Ctx->OutSec->Addr;
|
|
continue;
|
|
}
|
|
|
|
// Handle ASSERT().
|
|
if (auto *Cmd = dyn_cast<AssertCommand>(Base)) {
|
|
Cmd->Expression();
|
|
continue;
|
|
}
|
|
|
|
// 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(Ctx->OutSec == Sec->getParent());
|
|
output(Sec);
|
|
}
|
|
}
|
|
}
|
|
|
|
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.
|
|
llvm::erase_if(SectionCommands, [&](BaseCommand *Base) {
|
|
if (auto *Sec = dyn_cast<OutputSection>(Base))
|
|
return !Sec->Live;
|
|
return false;
|
|
});
|
|
}
|
|
|
|
static bool isAllSectionDescription(const OutputSection &Cmd) {
|
|
for (BaseCommand *Base : Cmd.SectionCommands)
|
|
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 issue is what to do with linker script
|
|
// like ".foo : { symbol = 42; }". One option would be to convert it to
|
|
// "symbol = 42;". That is, move the symbol out of the empty section
|
|
// description. That seems to be what bfd does for this simple case. The
|
|
// problem is that this is not completely general. bfd will give up and
|
|
// create a dummy section too if there is a ". = . + 1" inside the section
|
|
// for example.
|
|
// Given that we want to create the section, we have to worry what impact
|
|
// it will have on the link. For example, if we just create a section with
|
|
// 0 for flags, it would change which PT_LOADs are created.
|
|
// We could remember that that particular section is dummy and ignore it in
|
|
// other parts of the linker, but unfortunately there are quite a few places
|
|
// that would need to change:
|
|
// * The program header creation.
|
|
// * The orphan section placement.
|
|
// * The address assignment.
|
|
// The other option is to pick flags that minimize the impact the section
|
|
// will have on the rest of the linker. That is why we copy the flags from
|
|
// the previous sections. Only a few flags are needed to keep the impact low.
|
|
uint64_t Flags = SHF_ALLOC;
|
|
|
|
for (BaseCommand *Cmd : SectionCommands) {
|
|
auto *Sec = dyn_cast<OutputSection>(Cmd);
|
|
if (!Sec)
|
|
continue;
|
|
if (Sec->Live) {
|
|
Flags = Sec->Flags & (SHF_ALLOC | SHF_WRITE | SHF_EXECINSTR);
|
|
continue;
|
|
}
|
|
|
|
if (isAllSectionDescription(*Sec))
|
|
continue;
|
|
|
|
Sec->Live = true;
|
|
Sec->Flags = Flags;
|
|
}
|
|
}
|
|
|
|
void LinkerScript::adjustSectionsAfterSorting() {
|
|
// Try and find an appropriate memory region to assign offsets in.
|
|
for (BaseCommand *Base : SectionCommands) {
|
|
if (auto *Sec = dyn_cast<OutputSection>(Base)) {
|
|
if (!Sec->Live)
|
|
continue;
|
|
Sec->MemRegion = findMemoryRegion(Sec);
|
|
// Handle align (e.g. ".foo : ALIGN(16) { ... }").
|
|
if (Sec->AlignExpr)
|
|
Sec->Alignment =
|
|
std::max<uint32_t>(Sec->Alignment, 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(PhdrsCommands.begin(), PhdrsCommands.end(),
|
|
[](const PhdrsCommand &Cmd) { return Cmd.Type == PT_LOAD; });
|
|
if (FirstPtLoad != 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 : SectionCommands) {
|
|
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;
|
|
}
|
|
}
|
|
}
|
|
|
|
static OutputSection *findFirstSection(PhdrEntry *Load) {
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec->PtLoad == Load)
|
|
return Sec;
|
|
return nullptr;
|
|
}
|
|
|
|
// Try to find an address for the file and program headers output sections,
|
|
// which were unconditionally added to the first PT_LOAD segment earlier.
|
|
//
|
|
// When using the default layout, we check if the headers fit below the first
|
|
// allocated section. When using a linker script, we also check if the headers
|
|
// are covered by the output section. This allows omitting the headers by not
|
|
// leaving enough space for them in the linker script; this pattern is common
|
|
// in embedded systems.
|
|
//
|
|
// If there isn't enough space for these sections, we'll remove them from the
|
|
// PT_LOAD segment, and we'll also remove the PT_PHDR segment.
|
|
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();
|
|
// When linker script with SECTIONS is being used, don't output headers
|
|
// unless there's a space for them.
|
|
uint64_t Base = HasSectionsCommand ? alignDown(Min, Config->MaxPageSize) : 0;
|
|
if (HeaderSize <= Min - Base || Script->hasPhdrsCommands()) {
|
|
Min = alignDown(Min - HeaderSize, Config->MaxPageSize);
|
|
Out::ElfHeader->Addr = Min;
|
|
Out::ProgramHeaders->Addr = Min + Out::ElfHeader->Size;
|
|
return;
|
|
}
|
|
|
|
Out::ElfHeader->PtLoad = nullptr;
|
|
Out::ProgramHeaders->PtLoad = nullptr;
|
|
FirstPTLoad->FirstSec = findFirstSection(FirstPTLoad);
|
|
|
|
llvm::erase_if(Phdrs,
|
|
[](const PhdrEntry *E) { return E->p_type == PT_PHDR; });
|
|
}
|
|
|
|
LinkerScript::AddressState::AddressState() {
|
|
for (auto &MRI : Script->MemoryRegions) {
|
|
const MemoryRegion *MR = MRI.second;
|
|
MemRegionOffset[MR] = MR->Origin;
|
|
}
|
|
}
|
|
|
|
static uint64_t getInitialDot() {
|
|
// By default linker scripts use an initial value of 0 for '.',
|
|
// but prefer -image-base if set.
|
|
if (Script->HasSectionsCommand)
|
|
return Config->ImageBase ? *Config->ImageBase : 0;
|
|
|
|
uint64_t StartAddr = UINT64_MAX;
|
|
// 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);
|
|
return std::min(StartAddr, Target->getImageBase() + elf::getHeaderSize());
|
|
}
|
|
|
|
// Here we assign addresses as instructed by linker script SECTIONS
|
|
// sub-commands. Doing that allows us to use final VA values, so here
|
|
// we also handle rest commands like symbol assignments and ASSERTs.
|
|
void LinkerScript::assignAddresses() {
|
|
Dot = getInitialDot();
|
|
|
|
auto Deleter = make_unique<AddressState>();
|
|
Ctx = Deleter.get();
|
|
ErrorOnMissingSection = true;
|
|
switchTo(Aether);
|
|
|
|
for (BaseCommand *Base : SectionCommands) {
|
|
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));
|
|
}
|
|
Ctx = 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 : PhdrsCommands) {
|
|
PhdrEntry *Phdr = make<PhdrEntry>(Cmd.Type, Cmd.Flags ? *Cmd.Flags : PF_R);
|
|
|
|
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 (!PhdrsCommands[Id].Flags.hasValue())
|
|
Ret[Id]->p_flags |= Sec->getPhdrFlags();
|
|
}
|
|
}
|
|
return Ret;
|
|
}
|
|
|
|
// Returns true if we should emit an .interp section.
|
|
//
|
|
// We usually do. But if PHDRS commands are given, and
|
|
// no PT_INTERP is there, there's no place to emit an
|
|
// .interp, so we don't do that in that case.
|
|
bool LinkerScript::needsInterpSection() {
|
|
if (PhdrsCommands.empty())
|
|
return true;
|
|
for (PhdrsCommand &Cmd : PhdrsCommands)
|
|
if (Cmd.Type == PT_INTERP)
|
|
return true;
|
|
return false;
|
|
}
|
|
|
|
ExprValue LinkerScript::getSymbolValue(StringRef Name, const Twine &Loc) {
|
|
if (Name == ".") {
|
|
if (Ctx)
|
|
return {Ctx->OutSec, false, Dot - Ctx->OutSec->Addr, Loc};
|
|
error(Loc + ": unable to get location counter value");
|
|
return 0;
|
|
}
|
|
|
|
if (auto *Sym = dyn_cast_or_null<Defined>(Symtab->find(Name)))
|
|
return {Sym->Section, false, Sym->Value, Loc};
|
|
|
|
error(Loc + ": symbol not found: " + Name);
|
|
return 0;
|
|
}
|
|
|
|
// Returns the index of the segment named Name.
|
|
static Optional<size_t> getPhdrIndex(ArrayRef<PhdrsCommand> Vec,
|
|
StringRef Name) {
|
|
for (size_t I = 0; I < Vec.size(); ++I)
|
|
if (Vec[I].Name == Name)
|
|
return I;
|
|
return None;
|
|
}
|
|
|
|
// 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 S : Cmd->Phdrs) {
|
|
if (Optional<size_t> Idx = getPhdrIndex(PhdrsCommands, S))
|
|
Ret.push_back(*Idx);
|
|
else if (S != "NONE")
|
|
error(Cmd->Location + ": section header '" + S +
|
|
"' is not listed in PHDRS");
|
|
}
|
|
return Ret;
|
|
}
|