1 //===- InputSection.h -------------------------------------------*- C++ -*-===//
2 //
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
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef LLD_MACHO_INPUT_SECTION_H
10 #define LLD_MACHO_INPUT_SECTION_H
11 
12 #include "Config.h"
13 #include "Relocations.h"
14 #include "Symbols.h"
15 
16 #include "lld/Common/LLVM.h"
17 #include "lld/Common/Memory.h"
18 #include "llvm/ADT/ArrayRef.h"
19 #include "llvm/ADT/BitVector.h"
20 #include "llvm/ADT/CachedHashString.h"
21 #include "llvm/ADT/TinyPtrVector.h"
22 #include "llvm/BinaryFormat/MachO.h"
23 
24 namespace lld {
25 namespace macho {
26 
27 class InputFile;
28 class OutputSection;
29 
30 class InputSection {
31 public:
32   enum Kind : uint8_t {
33     ConcatKind,
34     CStringLiteralKind,
35     WordLiteralKind,
36   };
37 
38   Kind kind() const { return sectionKind; }
39   virtual ~InputSection() = default;
40   virtual uint64_t getSize() const { return data.size(); }
41   virtual bool empty() const { return data.empty(); }
42   InputFile *getFile() const { return section.file; }
43   StringRef getName() const { return section.name; }
44   StringRef getSegName() const { return section.segname; }
45   uint32_t getFlags() const { return section.flags; }
46   uint64_t getFileSize() const;
47   // Translates \p off -- an offset relative to this InputSection -- into an
48   // offset from the beginning of its parent OutputSection.
49   virtual uint64_t getOffset(uint64_t off) const = 0;
50   // The offset from the beginning of the file.
51   uint64_t getVA(uint64_t off) const;
52   // Return a user-friendly string for use in diagnostics.
53   // Format: /path/to/object.o:(symbol _func+0x123)
54   std::string getLocation(uint64_t off) const;
55   // Return the source line corresponding to an address, or the empty string.
56   // Format: Source.cpp:123 (/path/to/Source.cpp:123)
57   std::string getSourceLocation(uint64_t off) const;
58   // Whether the data at \p off in this InputSection is live.
59   virtual bool isLive(uint64_t off) const = 0;
60   virtual void markLive(uint64_t off) = 0;
61   virtual InputSection *canonical() { return this; }
62   virtual const InputSection *canonical() const { return this; }
63 
64 protected:
65   InputSection(Kind kind, const Section &section, ArrayRef<uint8_t> data,
66                uint32_t align)
67       : sectionKind(kind), align(align), data(data), section(section) {}
68 
69   InputSection(const InputSection &rhs)
70       : sectionKind(rhs.sectionKind), align(rhs.align), data(rhs.data),
71         section(rhs.section) {}
72 
73   Kind sectionKind;
74 
75 public:
76   // is address assigned?
77   bool isFinal = false;
78   // keep the address of the symbol(s) in this section unique in the final
79   // binary ?
80   bool keepUnique = false;
81   uint32_t align = 1;
82 
83   OutputSection *parent = nullptr;
84   ArrayRef<uint8_t> data;
85   std::vector<Reloc> relocs;
86   // The symbols that belong to this InputSection, sorted by value. With
87   // .subsections_via_symbols, there is typically only one element here.
88   llvm::TinyPtrVector<Defined *> symbols;
89 
90 protected:
91   const Section &section;
92 
93   const Defined *getContainingSymbol(uint64_t off) const;
94 };
95 
96 // ConcatInputSections are combined into (Concat)OutputSections through simple
97 // concatenation, in contrast with literal sections which may have their
98 // contents merged before output.
99 class ConcatInputSection final : public InputSection {
100 public:
101   ConcatInputSection(const Section &section, ArrayRef<uint8_t> data,
102                      uint32_t align = 1)
103       : InputSection(ConcatKind, section, data, align) {}
104 
105   uint64_t getOffset(uint64_t off) const override { return outSecOff + off; }
106   uint64_t getVA() const { return InputSection::getVA(0); }
107   // ConcatInputSections are entirely live or dead, so the offset is irrelevant.
108   bool isLive(uint64_t off) const override { return live; }
109   void markLive(uint64_t off) override { live = true; }
110   bool isCoalescedWeak() const { return wasCoalesced && symbols.empty(); }
111   bool shouldOmitFromOutput() const { return !live || isCoalescedWeak(); }
112   void writeTo(uint8_t *buf);
113 
114   void foldIdentical(ConcatInputSection *redundant);
115   ConcatInputSection *canonical() override {
116     return replacement ? replacement : this;
117   }
118   const InputSection *canonical() const override {
119     return replacement ? replacement : this;
120   }
121 
122   static bool classof(const InputSection *isec) {
123     return isec->kind() == ConcatKind;
124   }
125 
126   // Points to the surviving section after this one is folded by ICF
127   ConcatInputSection *replacement = nullptr;
128   // Equivalence-class ID for ICF
129   uint32_t icfEqClass[2] = {0, 0};
130 
131   // With subsections_via_symbols, most symbols have their own InputSection,
132   // and for weak symbols (e.g. from inline functions), only the
133   // InputSection from one translation unit will make it to the output,
134   // while all copies in other translation units are coalesced into the
135   // first and not copied to the output.
136   bool wasCoalesced = false;
137   bool live = !config->deadStrip;
138   bool hasCallSites = false;
139   // This variable has two usages. Initially, it represents the input order.
140   // After assignAddresses is called, it represents the offset from the
141   // beginning of the output section this section was assigned to.
142   uint64_t outSecOff = 0;
143 };
144 
145 // Initialize a fake InputSection that does not belong to any InputFile.
146 ConcatInputSection *makeSyntheticInputSection(StringRef segName,
147                                               StringRef sectName,
148                                               uint32_t flags = 0,
149                                               ArrayRef<uint8_t> data = {},
150                                               uint32_t align = 1);
151 
152 // Helper functions to make it easy to sprinkle asserts.
153 
154 inline bool shouldOmitFromOutput(InputSection *isec) {
155   return isa<ConcatInputSection>(isec) &&
156          cast<ConcatInputSection>(isec)->shouldOmitFromOutput();
157 }
158 
159 inline bool isCoalescedWeak(InputSection *isec) {
160   return isa<ConcatInputSection>(isec) &&
161          cast<ConcatInputSection>(isec)->isCoalescedWeak();
162 }
163 
164 // We allocate a lot of these and binary search on them, so they should be as
165 // compact as possible. Hence the use of 31 rather than 64 bits for the hash.
166 struct StringPiece {
167   // Offset from the start of the containing input section.
168   uint32_t inSecOff;
169   uint32_t live : 1;
170   // Only set if deduplicating literals
171   uint32_t hash : 31;
172   // Offset from the start of the containing output section.
173   uint64_t outSecOff = 0;
174 
175   StringPiece(uint64_t off, uint32_t hash)
176       : inSecOff(off), live(!config->deadStrip), hash(hash) {}
177 };
178 
179 static_assert(sizeof(StringPiece) == 16, "StringPiece is too big!");
180 
181 // CStringInputSections are composed of multiple null-terminated string
182 // literals, which we represent using StringPieces. These literals can be
183 // deduplicated and tail-merged, so translating offsets between the input and
184 // outputs sections is more complicated.
185 //
186 // NOTE: One significant difference between LLD and ld64 is that we merge all
187 // cstring literals, even those referenced directly by non-private symbols.
188 // ld64 is more conservative and does not do that. This was mostly done for
189 // implementation simplicity; if we find programs that need the more
190 // conservative behavior we can certainly implement that.
191 class CStringInputSection final : public InputSection {
192 public:
193   CStringInputSection(const Section &section, ArrayRef<uint8_t> data,
194                       uint32_t align)
195       : InputSection(CStringLiteralKind, section, data, align) {}
196   uint64_t getOffset(uint64_t off) const override;
197   bool isLive(uint64_t off) const override { return getStringPiece(off).live; }
198   void markLive(uint64_t off) override { getStringPiece(off).live = true; }
199   // Find the StringPiece that contains this offset.
200   StringPiece &getStringPiece(uint64_t off);
201   const StringPiece &getStringPiece(uint64_t off) const;
202   // Split at each null byte.
203   void splitIntoPieces();
204 
205   LLVM_ATTRIBUTE_ALWAYS_INLINE
206   StringRef getStringRef(size_t i) const {
207     size_t begin = pieces[i].inSecOff;
208     size_t end =
209         (pieces.size() - 1 == i) ? data.size() : pieces[i + 1].inSecOff;
210     return toStringRef(data.slice(begin, end - begin));
211   }
212 
213   // Returns i'th piece as a CachedHashStringRef. This function is very hot when
214   // string merging is enabled, so we want to inline.
215   LLVM_ATTRIBUTE_ALWAYS_INLINE
216   llvm::CachedHashStringRef getCachedHashStringRef(size_t i) const {
217     assert(config->dedupLiterals);
218     return {getStringRef(i), pieces[i].hash};
219   }
220 
221   static bool classof(const InputSection *isec) {
222     return isec->kind() == CStringLiteralKind;
223   }
224 
225   std::vector<StringPiece> pieces;
226 };
227 
228 class WordLiteralInputSection final : public InputSection {
229 public:
230   WordLiteralInputSection(const Section &section, ArrayRef<uint8_t> data,
231                           uint32_t align);
232   uint64_t getOffset(uint64_t off) const override;
233   bool isLive(uint64_t off) const override {
234     return live[off >> power2LiteralSize];
235   }
236   void markLive(uint64_t off) override {
237     live[off >> power2LiteralSize] = true;
238   }
239 
240   static bool classof(const InputSection *isec) {
241     return isec->kind() == WordLiteralKind;
242   }
243 
244 private:
245   unsigned power2LiteralSize;
246   // The liveness of data[off] is tracked by live[off >> power2LiteralSize].
247   llvm::BitVector live;
248 };
249 
250 inline uint8_t sectionType(uint32_t flags) {
251   return flags & llvm::MachO::SECTION_TYPE;
252 }
253 
254 inline bool isZeroFill(uint32_t flags) {
255   return llvm::MachO::isVirtualSection(sectionType(flags));
256 }
257 
258 inline bool isThreadLocalVariables(uint32_t flags) {
259   return sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_VARIABLES;
260 }
261 
262 // These sections contain the data for initializing thread-local variables.
263 inline bool isThreadLocalData(uint32_t flags) {
264   return sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_REGULAR ||
265          sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_ZEROFILL;
266 }
267 
268 inline bool isDebugSection(uint32_t flags) {
269   return (flags & llvm::MachO::SECTION_ATTRIBUTES_USR) ==
270          llvm::MachO::S_ATTR_DEBUG;
271 }
272 
273 inline bool isWordLiteralSection(uint32_t flags) {
274   return sectionType(flags) == llvm::MachO::S_4BYTE_LITERALS ||
275          sectionType(flags) == llvm::MachO::S_8BYTE_LITERALS ||
276          sectionType(flags) == llvm::MachO::S_16BYTE_LITERALS;
277 }
278 
279 bool isCodeSection(const InputSection *);
280 bool isCfStringSection(const InputSection *);
281 bool isClassRefsSection(const InputSection *);
282 bool isEhFrameSection(const InputSection *);
283 
284 extern std::vector<ConcatInputSection *> inputSections;
285 
286 namespace section_names {
287 
288 constexpr const char authGot[] = "__auth_got";
289 constexpr const char authPtr[] = "__auth_ptr";
290 constexpr const char binding[] = "__binding";
291 constexpr const char bitcodeBundle[] = "__bundle";
292 constexpr const char cString[] = "__cstring";
293 constexpr const char cfString[] = "__cfstring";
294 constexpr const char cgProfile[] = "__cg_profile";
295 constexpr const char codeSignature[] = "__code_signature";
296 constexpr const char common[] = "__common";
297 constexpr const char compactUnwind[] = "__compact_unwind";
298 constexpr const char data[] = "__data";
299 constexpr const char debugAbbrev[] = "__debug_abbrev";
300 constexpr const char debugInfo[] = "__debug_info";
301 constexpr const char debugLine[] = "__debug_line";
302 constexpr const char debugStr[] = "__debug_str";
303 constexpr const char ehFrame[] = "__eh_frame";
304 constexpr const char gccExceptTab[] = "__gcc_except_tab";
305 constexpr const char export_[] = "__export";
306 constexpr const char dataInCode[] = "__data_in_code";
307 constexpr const char functionStarts[] = "__func_starts";
308 constexpr const char got[] = "__got";
309 constexpr const char header[] = "__mach_header";
310 constexpr const char indirectSymbolTable[] = "__ind_sym_tab";
311 constexpr const char const_[] = "__const";
312 constexpr const char lazySymbolPtr[] = "__la_symbol_ptr";
313 constexpr const char lazyBinding[] = "__lazy_binding";
314 constexpr const char literals[] = "__literals";
315 constexpr const char moduleInitFunc[] = "__mod_init_func";
316 constexpr const char moduleTermFunc[] = "__mod_term_func";
317 constexpr const char nonLazySymbolPtr[] = "__nl_symbol_ptr";
318 constexpr const char objcCatList[] = "__objc_catlist";
319 constexpr const char objcClassList[] = "__objc_classlist";
320 constexpr const char objcClassRefs[] = "__objc_classrefs";
321 constexpr const char objcConst[] = "__objc_const";
322 constexpr const char objcImageInfo[] = "__objc_imageinfo";
323 constexpr const char objcNonLazyCatList[] = "__objc_nlcatlist";
324 constexpr const char objcNonLazyClassList[] = "__objc_nlclslist";
325 constexpr const char objcProtoList[] = "__objc_protolist";
326 constexpr const char pageZero[] = "__pagezero";
327 constexpr const char pointers[] = "__pointers";
328 constexpr const char rebase[] = "__rebase";
329 constexpr const char staticInit[] = "__StaticInit";
330 constexpr const char stringTable[] = "__string_table";
331 constexpr const char stubHelper[] = "__stub_helper";
332 constexpr const char stubs[] = "__stubs";
333 constexpr const char swift[] = "__swift";
334 constexpr const char symbolTable[] = "__symbol_table";
335 constexpr const char textCoalNt[] = "__textcoal_nt";
336 constexpr const char text[] = "__text";
337 constexpr const char threadPtrs[] = "__thread_ptrs";
338 constexpr const char threadVars[] = "__thread_vars";
339 constexpr const char unwindInfo[] = "__unwind_info";
340 constexpr const char weakBinding[] = "__weak_binding";
341 constexpr const char zeroFill[] = "__zerofill";
342 constexpr const char addrSig[] = "__llvm_addrsig";
343 
344 } // namespace section_names
345 
346 } // namespace macho
347 
348 std::string toString(const macho::InputSection *);
349 
350 } // namespace lld
351 
352 #endif
353