1 //===- InputSection.h -------------------------------------------*- C++ -*-===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 #ifndef LLD_ELF_INPUT_SECTION_H
10 #define LLD_ELF_INPUT_SECTION_H
13 #include "Relocations.h"
15 #include "lld/Common/LLVM.h"
16 #include "llvm/ADT/CachedHashString.h"
17 #include "llvm/ADT/DenseSet.h"
18 #include "llvm/ADT/TinyPtrVector.h"
19 #include "llvm/Object/ELF.h"
29 class SyntheticSection;
30 class MergeSyntheticSection;
31 template <class ELFT> class ObjFile;
34 extern std::vector<Partition> partitions;
36 // This is the base class of all sections that lld handles. Some are sections in
37 // input files, some are sections in the produced output file and some exist
38 // just as a convenience for implementing special ways of combining some
42 enum Kind { Regular, EHFrame, Merge, Synthetic, Output };
44 Kind kind() const { return (Kind)sectionKind; }
48 // This pointer points to the "real" instance of this instance.
49 // Usually Repl == this. However, if ICF merges two sections,
50 // Repl pointer of one section points to another section. So,
51 // if you need to get a pointer to this instance, do not use
52 // this but instead this->Repl.
55 unsigned sectionKind : 3;
57 // The next two bit fields are only used by InputSectionBase, but we
58 // put them here so the struct packs better.
62 // Set for sections that should not be folded by ICF.
63 unsigned keepUnique : 1;
65 // The 1-indexed partition that this section is assigned to by the garbage
66 // collector, or 0 if this section is dead. Normally there is only one
67 // partition, so this will either be 0 or 1.
69 elf::Partition &getPartition() const;
71 // These corresponds to the fields in Elf_Shdr.
79 OutputSection *getOutputSection();
80 const OutputSection *getOutputSection() const {
81 return const_cast<SectionBase *>(this)->getOutputSection();
84 // Translate an offset in the input section to an offset in the output
86 uint64_t getOffset(uint64_t offset) const;
88 uint64_t getVA(uint64_t offset = 0) const;
90 bool isLive() const { return partition != 0; }
91 void markLive() { partition = 1; }
92 void markDead() { partition = 0; }
95 SectionBase(Kind sectionKind, StringRef name, uint64_t flags,
96 uint64_t entsize, uint64_t alignment, uint32_t type,
97 uint32_t info, uint32_t link)
98 : name(name), repl(this), sectionKind(sectionKind), bss(false),
99 keepUnique(false), partition(0), alignment(alignment), flags(flags),
100 entsize(entsize), type(type), link(link), info(info) {}
103 // This corresponds to a section of an input file.
104 class InputSectionBase : public SectionBase {
106 template <class ELFT>
107 InputSectionBase(ObjFile<ELFT> &file, const typename ELFT::Shdr &header,
108 StringRef name, Kind sectionKind);
110 InputSectionBase(InputFile *file, uint64_t flags, uint32_t type,
111 uint64_t entsize, uint32_t link, uint32_t info,
112 uint32_t alignment, ArrayRef<uint8_t> data, StringRef name,
115 static bool classof(const SectionBase *s) { return s->kind() != Output; }
117 // Relocations that refer to this section.
118 unsigned numRelocations : 31;
119 unsigned areRelocsRela : 1;
120 const void *firstRelocation = nullptr;
122 // The file which contains this section. Its dynamic type is always
123 // ObjFile<ELFT>, but in order to avoid ELFT, we use InputFile as
127 template <class ELFT> ObjFile<ELFT> *getFile() const {
128 return cast_or_null<ObjFile<ELFT>>(file);
131 // If basic block sections are enabled, many code sections could end up with
132 // one or two jump instructions at the end that could be relaxed to a smaller
133 // instruction. The members below help trimming the trailing jump instruction
134 // and shrinking a section.
135 unsigned bytesDropped = 0;
137 void drop_back(uint64_t num) { bytesDropped += num; }
139 void push_back(uint64_t num) {
140 assert(bytesDropped >= num);
146 rawData = rawData.drop_back(bytesDropped);
151 ArrayRef<uint8_t> data() const {
152 if (uncompressedSize >= 0)
157 uint64_t getOffsetInFile() const;
159 // Input sections are part of an output section. Special sections
160 // like .eh_frame and merge sections are first combined into a
161 // synthetic section that is then added to an output section. In all
162 // cases this points one level up.
163 SectionBase *parent = nullptr;
165 // The next member in the section group if this section is in a group. This is
166 // used by --gc-sections.
167 InputSectionBase *nextInSectionGroup = nullptr;
169 template <class ELFT> ArrayRef<typename ELFT::Rel> rels() const {
170 assert(!areRelocsRela);
171 return llvm::makeArrayRef(
172 static_cast<const typename ELFT::Rel *>(firstRelocation),
176 template <class ELFT> ArrayRef<typename ELFT::Rela> relas() const {
177 assert(areRelocsRela);
178 return llvm::makeArrayRef(
179 static_cast<const typename ELFT::Rela *>(firstRelocation),
183 // InputSections that are dependent on us (reverse dependency for GC)
184 llvm::TinyPtrVector<InputSection *> dependentSections;
186 // Returns the size of this section (even if this is a common or BSS.)
187 size_t getSize() const;
189 InputSection *getLinkOrderDep() const;
191 // Get the function symbol that encloses this offset from within the
193 template <class ELFT>
194 Defined *getEnclosingFunction(uint64_t offset);
196 // Returns a source location string. Used to construct an error message.
197 template <class ELFT> std::string getLocation(uint64_t offset);
198 std::string getSrcMsg(const Symbol &sym, uint64_t offset);
199 std::string getObjMsg(uint64_t offset);
201 // Each section knows how to relocate itself. These functions apply
202 // relocations, assuming that Buf points to this section's copy in
203 // the mmap'ed output buffer.
204 template <class ELFT> void relocate(uint8_t *buf, uint8_t *bufEnd);
205 void relocateAlloc(uint8_t *buf, uint8_t *bufEnd);
206 static uint64_t getRelocTargetVA(const InputFile *File, RelType Type,
207 int64_t A, uint64_t P, const Symbol &Sym,
210 // The native ELF reloc data type is not very convenient to handle.
211 // So we convert ELF reloc records to our own records in Relocations.cpp.
212 // This vector contains such "cooked" relocations.
213 std::vector<Relocation> relocations;
215 // Indicates that this section needs to be padded with a NOP filler if set to
217 bool nopFiller = false;
219 // These are modifiers to jump instructions that are necessary when basic
220 // block sections are enabled. Basic block sections creates opportunities to
221 // relax jump instructions at basic block boundaries after reordering the
223 std::vector<JumpInstrMod> jumpInstrMods;
225 // A function compiled with -fsplit-stack calling a function
226 // compiled without -fsplit-stack needs its prologue adjusted. Find
227 // such functions and adjust their prologues. This is very similar
228 // to relocation. See https://gcc.gnu.org/wiki/SplitStacks for more
230 template <typename ELFT>
231 void adjustSplitStackFunctionPrologues(uint8_t *buf, uint8_t *end);
234 template <typename T> llvm::ArrayRef<T> getDataAs() const {
235 size_t s = data().size();
236 assert(s % sizeof(T) == 0);
237 return llvm::makeArrayRef<T>((const T *)data().data(), s / sizeof(T));
241 void parseCompressedHeader();
242 void uncompress() const;
244 mutable ArrayRef<uint8_t> rawData;
246 // This field stores the uncompressed size of the compressed data in rawData,
247 // or -1 if rawData is not compressed (either because the section wasn't
248 // compressed in the first place, or because we ended up uncompressing it).
249 // Since the feature is not used often, this is usually -1.
250 mutable int64_t uncompressedSize = -1;
253 // SectionPiece represents a piece of splittable section contents.
254 // We allocate a lot of these and binary search on them. This means that they
255 // have to be as compact as possible, which is why we don't store the size (can
256 // be found by looking at the next one).
257 struct SectionPiece {
258 SectionPiece(size_t off, uint32_t hash, bool live)
259 : inputOff(off), live(live || !config->gcSections), hash(hash >> 1) {}
264 uint64_t outputOff = 0;
267 static_assert(sizeof(SectionPiece) == 16, "SectionPiece is too big");
269 // This corresponds to a SHF_MERGE section of an input file.
270 class MergeInputSection : public InputSectionBase {
272 template <class ELFT>
273 MergeInputSection(ObjFile<ELFT> &f, const typename ELFT::Shdr &header,
275 MergeInputSection(uint64_t flags, uint32_t type, uint64_t entsize,
276 ArrayRef<uint8_t> data, StringRef name);
278 static bool classof(const SectionBase *s) { return s->kind() == Merge; }
279 void splitIntoPieces();
281 // Translate an offset in the input section to an offset in the parent
282 // MergeSyntheticSection.
283 uint64_t getParentOffset(uint64_t offset) const;
285 // Splittable sections are handled as a sequence of data
286 // rather than a single large blob of data.
287 std::vector<SectionPiece> pieces;
289 // Returns I'th piece's data. This function is very hot when
290 // string merging is enabled, so we want to inline.
291 LLVM_ATTRIBUTE_ALWAYS_INLINE
292 llvm::CachedHashStringRef getData(size_t i) const {
293 size_t begin = pieces[i].inputOff;
295 (pieces.size() - 1 == i) ? data().size() : pieces[i + 1].inputOff;
296 return {toStringRef(data().slice(begin, end - begin)), pieces[i].hash};
299 // Returns the SectionPiece at a given input section offset.
300 SectionPiece *getSectionPiece(uint64_t offset);
301 const SectionPiece *getSectionPiece(uint64_t offset) const {
302 return const_cast<MergeInputSection *>(this)->getSectionPiece(offset);
305 SyntheticSection *getParent() const;
308 void splitStrings(ArrayRef<uint8_t> a, size_t size);
309 void splitNonStrings(ArrayRef<uint8_t> a, size_t size);
312 struct EhSectionPiece {
313 EhSectionPiece(size_t off, InputSectionBase *sec, uint32_t size,
314 unsigned firstRelocation)
315 : inputOff(off), sec(sec), size(size), firstRelocation(firstRelocation) {}
317 ArrayRef<uint8_t> data() {
318 return {sec->data().data() + this->inputOff, size};
322 ssize_t outputOff = -1;
323 InputSectionBase *sec;
325 unsigned firstRelocation;
328 // This corresponds to a .eh_frame section of an input file.
329 class EhInputSection : public InputSectionBase {
331 template <class ELFT>
332 EhInputSection(ObjFile<ELFT> &f, const typename ELFT::Shdr &header,
334 static bool classof(const SectionBase *s) { return s->kind() == EHFrame; }
335 template <class ELFT> void split();
336 template <class ELFT, class RelTy> void split(ArrayRef<RelTy> rels);
338 // Splittable sections are handled as a sequence of data
339 // rather than a single large blob of data.
340 std::vector<EhSectionPiece> pieces;
342 SyntheticSection *getParent() const;
345 // This is a section that is added directly to an output section
346 // instead of needing special combination via a synthetic section. This
347 // includes all input sections with the exceptions of SHF_MERGE and
348 // .eh_frame. It also includes the synthetic sections themselves.
349 class InputSection : public InputSectionBase {
351 InputSection(InputFile *f, uint64_t flags, uint32_t type, uint32_t alignment,
352 ArrayRef<uint8_t> data, StringRef name, Kind k = Regular);
353 template <class ELFT>
354 InputSection(ObjFile<ELFT> &f, const typename ELFT::Shdr &header,
357 // Write this section to a mmap'ed file, assuming Buf is pointing to
358 // beginning of the output section.
359 template <class ELFT> void writeTo(uint8_t *buf);
361 uint64_t getOffset(uint64_t offset) const { return outSecOff + offset; }
363 OutputSection *getParent() const;
365 // This variable has two usages. Initially, it represents an index in the
366 // OutputSection's InputSection list, and is used when ordering SHF_LINK_ORDER
367 // sections. After assignAddresses is called, it represents the offset from
368 // the beginning of the output section this section was assigned to.
369 uint64_t outSecOff = 0;
371 static bool classof(const SectionBase *s);
373 InputSectionBase *getRelocatedSection() const;
375 template <class ELFT, class RelTy>
376 void relocateNonAlloc(uint8_t *buf, llvm::ArrayRef<RelTy> rels);
379 uint32_t eqClass[2] = {0, 0};
381 // Called by ICF to merge two input sections.
382 void replace(InputSection *other);
384 static InputSection discarded;
387 template <class ELFT, class RelTy>
388 void copyRelocations(uint8_t *buf, llvm::ArrayRef<RelTy> rels);
390 template <class ELFT> void copyShtGroup(uint8_t *buf);
393 inline bool isDebugSection(const InputSectionBase &sec) {
394 return (sec.flags & llvm::ELF::SHF_ALLOC) == 0 &&
395 (sec.name.startswith(".debug") || sec.name.startswith(".zdebug"));
398 // The list of all input sections.
399 extern std::vector<InputSectionBase *> inputSections;
401 // The set of TOC entries (.toc + addend) for which we should not apply
402 // toc-indirect to toc-relative relaxation. const Symbol * refers to the
403 // STT_SECTION symbol associated to the .toc input section.
404 extern llvm::DenseSet<std::pair<const Symbol *, uint64_t>> ppc64noTocRelax;
408 std::string toString(const elf::InputSectionBase *);