1110 lines
36 KiB
C++
1110 lines
36 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 "Memory.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 "Writer.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/Support/Casting.h"
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#include "llvm/Support/ELF.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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uint64_t ExprValue::getValue() const {
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if (Sec) {
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if (Sec->getOutputSection())
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return Sec->getOffset(Val) + Sec->getOutputSection()->Addr;
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error("unable to evaluate expression: input section " + Sec->Name +
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" has no output section assigned");
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}
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return Val;
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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) + Sec->getOutputSection()->Addr;
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return 0;
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}
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template <class ELFT> static SymbolBody *addRegular(SymbolAssignment *Cmd) {
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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<ELFT>::X->insert(
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Cmd->Name, /*Type*/ 0, Visibility, /*CanOmitFromDynSym*/ false,
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/*File*/ nullptr);
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Sym->Binding = STB_GLOBAL;
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ExprValue Value = Cmd->Expression();
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SectionBase *Sec = Value.isAbsolute() ? nullptr : Value.Sec;
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// We want to set symbol values early if we can. This allows us to use symbols
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// as variables in linker scripts. Doing so allows us to write expressions
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// like this: `alignment = 16; . = ALIGN(., alignment)`
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uint64_t SymValue = Value.isAbsolute() ? Value.getValue() : 0;
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replaceBody<DefinedRegular>(Sym, Cmd->Name, /*IsLocal=*/false, Visibility,
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STT_NOTYPE, SymValue, 0, Sec, nullptr);
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return Sym->body();
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}
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OutputSection *LinkerScript::getOutputSection(const Twine &Loc,
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StringRef Name) {
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for (OutputSection *Sec : *OutputSections)
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if (Sec->Name == Name)
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return Sec;
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static OutputSection Dummy("", 0, 0);
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if (ErrorOnMissingSection)
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error(Loc + ": undefined section " + Name);
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return &Dummy;
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}
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// This function is essentially the same as getOutputSection(Name)->Size,
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// but it won't print out an error message if a given section is not found.
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//
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// Linker script does not create an output section if its content is empty.
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// We want to allow SIZEOF(.foo) where .foo is a section which happened to
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// be empty. That is why this function is different from getOutputSection().
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uint64_t LinkerScript::getOutputSectionSize(StringRef Name) {
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for (OutputSection *Sec : *OutputSections)
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if (Sec->Name == Name)
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return Sec->Size;
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return 0;
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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) {
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if (InSec)
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error(Loc + ": unable to move location counter backward for: " +
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CurOutSec->Name);
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else
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error(Loc + ": unable to move location counter backward");
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}
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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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CurOutSec->Size = Dot - CurOutSec->Addr;
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}
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// Sets value of a symbol. Two kinds of symbols are processed: synthetic
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// symbols, whose value is an offset from beginning of section and regular
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// symbols whose value is absolute.
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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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auto *Sym = cast<DefinedRegular>(Cmd->Sym);
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ExprValue V = Cmd->Expression();
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if (V.isAbsolute()) {
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Sym->Value = V.getValue();
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} else {
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Sym->Section = V.Sec;
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if (Sym->Section->Flags & SHF_ALLOC)
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Sym->Value = V.Val;
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else
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Sym->Value = V.getValue();
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}
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}
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static SymbolBody *findSymbol(StringRef S) {
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switch (Config->EKind) {
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case ELF32LEKind:
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return Symtab<ELF32LE>::X->find(S);
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case ELF32BEKind:
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return Symtab<ELF32BE>::X->find(S);
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case ELF64LEKind:
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return Symtab<ELF64LE>::X->find(S);
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case ELF64BEKind:
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return Symtab<ELF64BE>::X->find(S);
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default:
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llvm_unreachable("unknown Config->EKind");
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}
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}
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static SymbolBody *addRegularSymbol(SymbolAssignment *Cmd) {
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switch (Config->EKind) {
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case ELF32LEKind:
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return addRegular<ELF32LE>(Cmd);
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case ELF32BEKind:
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return addRegular<ELF32BE>(Cmd);
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case ELF64LEKind:
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return addRegular<ELF64LE>(Cmd);
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case ELF64BEKind:
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return addRegular<ELF64BE>(Cmd);
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default:
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llvm_unreachable("unknown Config->EKind");
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}
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}
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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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SymbolBody *B = findSymbol(Cmd->Name);
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if (Cmd->Provide && (!B || B->isDefined()))
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return;
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Cmd->Sym = addRegularSymbol(Cmd);
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}
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bool SymbolAssignment::classof(const BaseCommand *C) {
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return C->Kind == AssignmentKind;
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}
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bool OutputSectionCommand::classof(const BaseCommand *C) {
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return C->Kind == OutputSectionKind;
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}
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bool InputSectionDescription::classof(const BaseCommand *C) {
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return C->Kind == InputSectionKind;
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}
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bool AssertCommand::classof(const BaseCommand *C) {
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return C->Kind == AssertKind;
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}
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bool BytesDataCommand::classof(const BaseCommand *C) {
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return C->Kind == BytesDataKind;
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}
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static StringRef basename(InputSectionBase *S) {
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if (S->File)
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return sys::path::filename(S->File->getName());
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return "";
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}
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bool LinkerScript::shouldKeep(InputSectionBase *S) {
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for (InputSectionDescription *ID : Opt.KeptSections)
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if (ID->FilePat.match(basename(S)))
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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<InputSectionBase *> 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(Sections, [](InputSectionBase *Sec) {
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return static_cast<InputSectionBase *>(Sec)->Flags & SHF_WRITE;
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});
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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(InputSectionBase **Begin, InputSectionBase **End,
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SortSectionPolicy K) {
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if (K != SortSectionPolicy::Default && K != SortSectionPolicy::None)
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std::stable_sort(Begin, End, getComparator(K));
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}
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// Compute and remember which sections the InputSectionDescription matches.
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std::vector<InputSectionBase *>
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LinkerScript::computeInputSections(const InputSectionDescription *Cmd) {
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std::vector<InputSectionBase *> 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->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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StringRef Filename = basename(Sec);
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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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Ret.push_back(Sec);
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Sec->Assigned = true;
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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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InputSectionBase **Begin = Ret.data() + SizeBefore;
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InputSectionBase **End = Ret.data() + Ret.size();
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if (Pat.SortOuter != SortSectionPolicy::None) {
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if (Pat.SortInner == SortSectionPolicy::Default)
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sortSections(Begin, End, Config->SortSection);
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else
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sortSections(Begin, End, Pat.SortInner);
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sortSections(Begin, End, Pat.SortOuter);
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}
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}
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return Ret;
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}
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void LinkerScript::discard(ArrayRef<InputSectionBase *> V) {
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for (InputSectionBase *S : V) {
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S->Live = false;
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if (S == InX::ShStrTab)
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error("discarding .shstrtab section is not allowed");
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discard(S->DependentSections);
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}
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}
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std::vector<InputSectionBase *>
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LinkerScript::createInputSectionList(OutputSectionCommand &OutCmd) {
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std::vector<InputSectionBase *> Ret;
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for (BaseCommand *Base : OutCmd.Commands) {
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auto *Cmd = dyn_cast<InputSectionDescription>(Base);
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if (!Cmd)
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continue;
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Cmd->Sections = computeInputSections(Cmd);
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Ret.insert(Ret.end(), Cmd->Sections.begin(), Cmd->Sections.end());
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}
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return Ret;
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}
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void LinkerScript::processCommands(OutputSectionFactory &Factory) {
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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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CurOutSec = Aether;
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Dot = 0;
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for (size_t I = 0; I < Opt.Commands.size(); ++I) {
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// Handle symbol assignments outside of any output section.
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if (auto *Cmd = dyn_cast<SymbolAssignment>(Opt.Commands[I])) {
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addSymbol(Cmd);
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continue;
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}
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if (auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I])) {
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std::vector<InputSectionBase *> V = createInputSectionList(*Cmd);
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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 (Cmd->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 Commands many more times, the easiest
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// way to "make it as if it wasn't present" is to just remove it.
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if (!matchConstraints(V, Cmd->Constraint)) {
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for (InputSectionBase *S : V)
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S->Assigned = false;
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Opt.Commands.erase(Opt.Commands.begin() + I);
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--I;
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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 : Cmd->Commands)
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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 (Cmd->SubalignExpr) {
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uint32_t Subalign = Cmd->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 (InputSectionBase *S : V)
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Factory.addInputSec(S, Cmd->Name, Cmd->Sec);
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if (OutputSection *Sec = Cmd->Sec) {
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assert(Sec->SectionIndex == INT_MAX);
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Sec->SectionIndex = I;
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SecToCommand[Sec] = Cmd;
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}
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}
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}
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CurOutSec = nullptr;
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}
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void LinkerScript::fabricateDefaultCommands() {
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std::vector<BaseCommand *> Commands;
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// Define start address
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uint64_t StartAddr = Config->ImageBase + elf::getHeaderSize();
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// The Sections with -T<section> have been sorted in order of ascending
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// address. We must lower StartAddr if the lowest -T<section address> as
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// calls to setDot() must be monotonically increasing.
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for (auto& KV : Config->SectionStartMap)
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StartAddr = std::min(StartAddr, KV.second);
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Commands.push_back(
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make<SymbolAssignment>(".", [=] { return StartAddr; }, ""));
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// For each OutputSection that needs a VA fabricate an OutputSectionCommand
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// with an InputSectionDescription describing the InputSections
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for (OutputSection *Sec : *OutputSections) {
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if (!(Sec->Flags & SHF_ALLOC))
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continue;
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auto *OSCmd = make<OutputSectionCommand>(Sec->Name);
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OSCmd->Sec = Sec;
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SecToCommand[Sec] = OSCmd;
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// Prefer user supplied address over additional alignment constraint
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auto I = Config->SectionStartMap.find(Sec->Name);
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if (I != Config->SectionStartMap.end())
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Commands.push_back(
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make<SymbolAssignment>(".", [=] { return I->second; }, ""));
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else if (Sec->PageAlign)
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OSCmd->AddrExpr = [=] {
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return alignTo(Script->getDot(), Config->MaxPageSize);
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};
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Commands.push_back(OSCmd);
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if (Sec->Sections.size()) {
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auto *ISD = make<InputSectionDescription>("");
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OSCmd->Commands.push_back(ISD);
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for (InputSection *ISec : Sec->Sections) {
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ISD->Sections.push_back(ISec);
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ISec->Assigned = true;
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}
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}
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}
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// SECTIONS commands run before other non SECTIONS commands
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Commands.insert(Commands.end(), Opt.Commands.begin(), Opt.Commands.end());
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Opt.Commands = std::move(Commands);
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}
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// Add sections that didn't match any sections command.
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void LinkerScript::addOrphanSections(OutputSectionFactory &Factory) {
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for (InputSectionBase *S : InputSections) {
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if (!S->Live || S->OutSec)
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continue;
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StringRef Name = getOutputSectionName(S->Name);
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auto I = std::find_if(
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Opt.Commands.begin(), Opt.Commands.end(), [&](BaseCommand *Base) {
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if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base))
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return Cmd->Name == Name;
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return false;
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});
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if (I == Opt.Commands.end()) {
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Factory.addInputSec(S, Name);
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} else {
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auto *Cmd = cast<OutputSectionCommand>(*I);
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Factory.addInputSec(S, Name, Cmd->Sec);
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if (OutputSection *Sec = Cmd->Sec) {
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SecToCommand[Sec] = Cmd;
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unsigned Index = std::distance(Opt.Commands.begin(), I);
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assert(Sec->SectionIndex == INT_MAX || Sec->SectionIndex == Index);
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Sec->SectionIndex = Index;
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}
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auto *ISD = make<InputSectionDescription>("");
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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;
|
|
}
|