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//===- LinkerScript.h -------------------------------------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "Config.h"
#include "Writer.h"
#include "lld/Common/LLVM.h"
#include "lld/Common/Strings.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/MemoryBuffer.h"
#include <cstddef>
#include <cstdint>
#include <functional>
#include <memory>
#include <vector>
namespace lld {
namespace elf {
class Defined;
class InputFile;
class InputSection;
class InputSectionBase;
class OutputSection;
class SectionBase;
class Symbol;
class ThunkSection;
// This represents an r-value in the linker script.
struct ExprValue {
ExprValue(SectionBase *sec, bool forceAbsolute, uint64_t val,
const Twine &loc)
: sec(sec), val(val), forceAbsolute(forceAbsolute), loc(loc.str()) {}
ExprValue(uint64_t val) : ExprValue(nullptr, false, val, "") {}
bool isAbsolute() const { return forceAbsolute || sec == nullptr; }
uint64_t getValue() const;
uint64_t getSecAddr() const;
uint64_t getSectionOffset() const;
// If a value is relative to a section, it has a non-null Sec.
SectionBase *sec;
uint64_t val;
uint64_t alignment = 1;
// The original st_type if the expression represents a symbol. Any operation
// resets type to STT_NOTYPE.
uint8_t type = llvm::ELF::STT_NOTYPE;
// True if this expression is enclosed in ABSOLUTE().
// This flag affects the return value of getValue().
bool forceAbsolute;
// Original source location. Used for error messages.
std::string loc;
// This represents an expression in the linker script.
// ScriptParser::readExpr reads an expression and returns an Expr.
// Later, we evaluate the expression by calling the function.
using Expr = std::function<ExprValue()>;
// This enum is used to implement linker script SECTIONS command.
enum SectionsCommandKind {
AssignmentKind, // . = expr or <sym> = expr
ByteKind // BYTE(expr), SHORT(expr), LONG(expr) or QUAD(expr)
struct BaseCommand {
BaseCommand(int k) : kind(k) {}
int kind;
// This represents ". = <expr>" or "<symbol> = <expr>".
struct SymbolAssignment : BaseCommand {
SymbolAssignment(StringRef name, Expr e, std::string loc)
: BaseCommand(AssignmentKind), name(name), expression(e), location(loc) {}
static bool classof(const BaseCommand *c) {
return c->kind == AssignmentKind;
// The LHS of an expression. Name is either a symbol name or ".".
StringRef name;
Defined *sym = nullptr;
// The RHS of an expression.
Expr expression;
// Command attributes for PROVIDE, HIDDEN and PROVIDE_HIDDEN.
bool provide = false;
bool hidden = false;
// Holds file name and line number for error reporting.
std::string location;
// A string representation of this command. We use this for -Map.
std::string commandString;
// Address of this assignment command.
uint64_t addr;
// Size of this assignment command. This is usually 0, but if
// you move '.' this may be greater than 0.
uint64_t size;
// Linker scripts allow additional constraints to be put on output sections.
// If an output section is marked as ONLY_IF_RO, the section is created
// only if its input sections are read-only. Likewise, an output section
// with ONLY_IF_RW is created if all input sections are RW.
enum class ConstraintKind { NoConstraint, ReadOnly, ReadWrite };
// This struct is used to represent the location and size of regions of
// target memory. Instances of the struct are created by parsing the
// MEMORY command.
struct MemoryRegion {
MemoryRegion(StringRef name, Expr origin, Expr length, uint32_t flags,
uint32_t invFlags, uint32_t negFlags, uint32_t negInvFlags)
: name(std::string(name)), origin(origin), length(length), flags(flags),
invFlags(invFlags), negFlags(negFlags), negInvFlags(negInvFlags) {}
std::string name;
Expr origin;
Expr length;
// A section can be assigned to the region if any of these ELF section flags
// are set...
uint32_t flags;
// ... or any of these flags are not set.
// For example, the memory region attribute "r" maps to SHF_WRITE.
uint32_t invFlags;
// A section cannot be assigned to the region if any of these ELF section
// flags are set...
uint32_t negFlags;
// ... or any of these flags are not set.
// For example, the memory region attribute "!r" maps to SHF_WRITE.
uint32_t negInvFlags;
uint64_t curPos = 0;
bool compatibleWith(uint32_t secFlags) const {
if ((secFlags & negFlags) || (~secFlags & negInvFlags))
return false;
return (secFlags & flags) || (~secFlags & invFlags);
// This struct represents one section match pattern in SECTIONS() command.
// It can optionally have negative match pattern for EXCLUDED_FILE command.
// Also it may be surrounded with SORT() command, so contains sorting rules.
class SectionPattern {
StringMatcher excludedFilePat;
// Cache of the most recent input argument and result of excludesFile().
mutable llvm::Optional<std::pair<const InputFile *, bool>> excludesFileCache;
SectionPattern(StringMatcher &&pat1, StringMatcher &&pat2)
: excludedFilePat(pat1), sectionPat(pat2),
sortInner(SortSectionPolicy::Default) {}
bool excludesFile(const InputFile *file) const;
StringMatcher sectionPat;
SortSectionPolicy sortOuter;
SortSectionPolicy sortInner;
class InputSectionDescription : public BaseCommand {
SingleStringMatcher filePat;
// Cache of the most recent input argument and result of matchesFile().
mutable llvm::Optional<std::pair<const InputFile *, bool>> matchesFileCache;
InputSectionDescription(StringRef filePattern, uint64_t withFlags = 0,
uint64_t withoutFlags = 0)
: BaseCommand(InputSectionKind), filePat(filePattern),
withFlags(withFlags), withoutFlags(withoutFlags) {}
static bool classof(const BaseCommand *c) {
return c->kind == InputSectionKind;
bool matchesFile(const InputFile *file) const;
// Input sections that matches at least one of SectionPatterns
// will be associated with this InputSectionDescription.
std::vector<SectionPattern> sectionPatterns;
// Includes InputSections and MergeInputSections. Used temporarily during
// assignment of input sections to output sections.
std::vector<InputSectionBase *> sectionBases;
// Used after the finalizeInputSections() pass. MergeInputSections have been
// merged into MergeSyntheticSections.
std::vector<InputSection *> sections;
// Temporary record of synthetic ThunkSection instances and the pass that
// they were created in. This is used to insert newly created ThunkSections
// into Sections at the end of a createThunks() pass.
std::vector<std::pair<ThunkSection *, uint32_t>> thunkSections;
// SectionPatterns can be filtered with the INPUT_SECTION_FLAGS command.
uint64_t withFlags;
uint64_t withoutFlags;
// Represents BYTE(), SHORT(), LONG(), or QUAD().
struct ByteCommand : BaseCommand {
ByteCommand(Expr e, unsigned size, std::string commandString)
: BaseCommand(ByteKind), commandString(commandString), expression(e),
size(size) {}
static bool classof(const BaseCommand *c) { return c->kind == ByteKind; }
// Keeps string representing the command. Used for -Map" is perhaps better.
std::string commandString;
Expr expression;
// This is just an offset of this assignment command in the output section.
unsigned offset;
// Size of this data command.
unsigned size;
struct InsertCommand {
std::vector<StringRef> names;
bool isAfter;
StringRef where;
struct PhdrsCommand {
StringRef name;
unsigned type = llvm::ELF::PT_NULL;
bool hasFilehdr = false;
bool hasPhdrs = false;
llvm::Optional<unsigned> flags;
Expr lmaExpr = nullptr;
class LinkerScript final {
// Temporary state used in processSectionCommands() and assignAddresses()
// that must be reinitialized for each call to the above functions, and must
// not be used outside of the scope of a call to the above functions.
struct AddressState {
OutputSection *outSec = nullptr;
MemoryRegion *memRegion = nullptr;
MemoryRegion *lmaRegion = nullptr;
uint64_t lmaOffset = 0;
uint64_t tbssAddr = 0;
llvm::DenseMap<StringRef, OutputSection *> nameToOutputSection;
void addSymbol(SymbolAssignment *cmd);
void assignSymbol(SymbolAssignment *cmd, bool inSec);
void setDot(Expr e, const Twine &loc, bool inSec);
void expandOutputSection(uint64_t size);
void expandMemoryRegions(uint64_t size);
std::vector<InputSectionBase *>
computeInputSections(const InputSectionDescription *,
ArrayRef<InputSectionBase *>);
std::vector<InputSectionBase *> createInputSectionList(OutputSection &cmd);
void discardSynthetic(OutputSection &);
std::vector<size_t> getPhdrIndices(OutputSection *sec);
std::pair<MemoryRegion *, MemoryRegion *>
findMemoryRegion(OutputSection *sec, MemoryRegion *hint);
void switchTo(OutputSection *sec);
uint64_t advance(uint64_t size, unsigned align);
void output(InputSection *sec);
void assignOffsets(OutputSection *sec);
// Ctx captures the local AddressState and makes it accessible
// deliberately. This is needed as there are some cases where we cannot just
// thread the current state through to a lambda function created by the
// script parser.
// This should remain a plain pointer as its lifetime is smaller than
// LinkerScript.
AddressState *ctx = nullptr;
OutputSection *aether;
uint64_t dot;
OutputSection *createOutputSection(StringRef name, StringRef location);
OutputSection *getOrCreateOutputSection(StringRef name);
bool hasPhdrsCommands() { return !phdrsCommands.empty(); }
uint64_t getDot() { return dot; }
void discard(InputSectionBase *s);
ExprValue getSymbolValue(StringRef name, const Twine &loc);
void addOrphanSections();
void diagnoseOrphanHandling() const;
void adjustSectionsBeforeSorting();
void adjustSectionsAfterSorting();
std::vector<PhdrEntry *> createPhdrs();
bool needsInterpSection();
bool shouldKeep(InputSectionBase *s);
const Defined *assignAddresses();
void allocateHeaders(std::vector<PhdrEntry *> &phdrs);
void processSectionCommands();
void processSymbolAssignments();
void declareSymbols();
bool isDiscarded(const OutputSection *sec) const;
// Used to handle INSERT AFTER statements.
void processInsertCommands();
// SECTIONS command list.
std::vector<BaseCommand *> sectionCommands;
// PHDRS command list.
std::vector<PhdrsCommand> phdrsCommands;
bool hasSectionsCommand = false;
bool errorOnMissingSection = false;
// List of section patterns specified with KEEP commands. They will
// be kept even if they are unused and --gc-sections is specified.
std::vector<InputSectionDescription *> keptSections;
// A map from memory region name to a memory region descriptor.
llvm::MapVector<llvm::StringRef, MemoryRegion *> memoryRegions;
// A list of symbols referenced by the script.
std::vector<llvm::StringRef> referencedSymbols;
// Used to implement INSERT [AFTER|BEFORE]. Contains output sections that need
// to be reordered.
std::vector<InsertCommand> insertCommands;
// OutputSections specified by OVERWRITE_SECTIONS.
std::vector<OutputSection *> overwriteSections;
// Sections that will be warned/errored by --orphan-handling.
std::vector<const InputSectionBase *> orphanSections;
extern LinkerScript *script;
} // end namespace elf
} // end namespace lld