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
24namespace lld {
25namespace macho {
26
27class InputFile;
28class OutputSection;
29
30class InputSection {
31public:
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 // Return the relocation at \p off, if it exists. This does a linear search.
59 const Reloc *getRelocAt(uint32_t off) const;
60 // Whether the data at \p off in this InputSection is live.
61 virtual bool isLive(uint64_t off) const = 0;
62 virtual void markLive(uint64_t off) = 0;
63 virtual InputSection *canonical() { return this; }
64 virtual const InputSection *canonical() const { return this; }
65
66protected:
67 InputSection(Kind kind, const Section &section, ArrayRef<uint8_t> data,
68 uint32_t align)
69 : sectionKind(kind), keepUnique(false), hasAltEntry(false), align(align),
70 data(data), section(section) {}
71
72 InputSection(const InputSection &rhs)
73 : sectionKind(rhs.sectionKind), keepUnique(false), hasAltEntry(false),
74 align(rhs.align), data(rhs.data), section(rhs.section) {}
75
76 Kind sectionKind;
77
78public:
79 // is address assigned?
80 bool isFinal = false;
81 // keep the address of the symbol(s) in this section unique in the final
82 // binary ?
83 bool keepUnique : 1;
84 // Does this section have symbols at offsets other than zero? (NOTE: only
85 // applies to ConcatInputSections.)
86 bool hasAltEntry : 1;
87 uint32_t align = 1;
88
89 OutputSection *parent = nullptr;
90 ArrayRef<uint8_t> data;
91 std::vector<Reloc> relocs;
92 // The symbols that belong to this InputSection, sorted by value. With
93 // .subsections_via_symbols, there is typically only one element here.
94 llvm::TinyPtrVector<Defined *> symbols;
95
96 const Section &section;
97
98protected:
99 const Defined *getContainingSymbol(uint64_t off) const;
100};
101
102// ConcatInputSections are combined into (Concat)OutputSections through simple
103// concatenation, in contrast with literal sections which may have their
104// contents merged before output.
105class ConcatInputSection final : public InputSection {
106public:
107 ConcatInputSection(const Section &section, ArrayRef<uint8_t> data,
108 uint32_t align = 1)
109 : InputSection(ConcatKind, section, data, align) {}
110
111 uint64_t getOffset(uint64_t off) const override { return outSecOff + off; }
112 uint64_t getVA() const { return InputSection::getVA(off: 0); }
113 // ConcatInputSections are entirely live or dead, so the offset is irrelevant.
114 bool isLive(uint64_t off) const override { return live; }
115 void markLive(uint64_t off) override { live = true; }
116 bool isCoalescedWeak() const { return wasCoalesced && symbols.empty(); }
117 bool shouldOmitFromOutput() const { return !live || isCoalescedWeak(); }
118 void writeTo(uint8_t *buf);
119
120 void foldIdentical(ConcatInputSection *redundant,
121 Symbol::ICFFoldKind foldKind = Symbol::ICFFoldKind::Body);
122 ConcatInputSection *canonical() override {
123 return replacement ? replacement : this;
124 }
125 const InputSection *canonical() const override {
126 return replacement ? replacement : this;
127 }
128
129 static bool classof(const InputSection *isec) {
130 return isec->kind() == ConcatKind;
131 }
132
133 // Points to the surviving section after this one is folded by ICF
134 ConcatInputSection *replacement = nullptr;
135 // Equivalence-class ID for ICF
136 uint32_t icfEqClass[2] = {0, 0};
137
138 // With subsections_via_symbols, most symbols have their own InputSection,
139 // and for weak symbols (e.g. from inline functions), only the
140 // InputSection from one translation unit will make it to the output,
141 // while all copies in other translation units are coalesced into the
142 // first and not copied to the output.
143 bool wasCoalesced = false;
144 bool live = !config->deadStrip;
145 bool hasCallSites = false;
146 // This variable has two usages. Initially, it represents the input order.
147 // After assignAddresses is called, it represents the offset from the
148 // beginning of the output section this section was assigned to.
149 uint64_t outSecOff = 0;
150};
151
152// Initialize a fake InputSection that does not belong to any InputFile.
153// The created ConcatInputSection will always have 'live=true'
154ConcatInputSection *makeSyntheticInputSection(StringRef segName,
155 StringRef sectName,
156 uint32_t flags = 0,
157 ArrayRef<uint8_t> data = {},
158 uint32_t align = 1);
159
160// Helper functions to make it easy to sprinkle asserts.
161
162inline bool shouldOmitFromOutput(InputSection *isec) {
163 return isa<ConcatInputSection>(Val: isec) &&
164 cast<ConcatInputSection>(Val: isec)->shouldOmitFromOutput();
165}
166
167inline bool isCoalescedWeak(InputSection *isec) {
168 return isa<ConcatInputSection>(Val: isec) &&
169 cast<ConcatInputSection>(Val: isec)->isCoalescedWeak();
170}
171
172// We allocate a lot of these and binary search on them, so they should be as
173// compact as possible. Hence the use of 31 rather than 64 bits for the hash.
174struct StringPiece {
175 // Offset from the start of the containing input section.
176 uint32_t inSecOff;
177 uint32_t live : 1;
178 // Only set if deduplicating literals
179 uint32_t hash : 31;
180 // Offset from the start of the containing output section.
181 uint64_t outSecOff = 0;
182
183 StringPiece(uint64_t off, uint32_t hash)
184 : inSecOff(off), live(!config->deadStrip), hash(hash) {}
185};
186
187static_assert(sizeof(StringPiece) == 16, "StringPiece is too big!");
188
189// CStringInputSections are composed of multiple null-terminated string
190// literals, which we represent using StringPieces. These literals can be
191// deduplicated and tail-merged, so translating offsets between the input and
192// outputs sections is more complicated.
193//
194// NOTE: One significant difference between LLD and ld64 is that we merge all
195// cstring literals, even those referenced directly by non-private symbols.
196// ld64 is more conservative and does not do that. This was mostly done for
197// implementation simplicity; if we find programs that need the more
198// conservative behavior we can certainly implement that.
199class CStringInputSection final : public InputSection {
200public:
201 CStringInputSection(const Section &section, ArrayRef<uint8_t> data,
202 uint32_t align, bool dedupLiterals)
203 : InputSection(CStringLiteralKind, section, data, align),
204 deduplicateLiterals(dedupLiterals) {}
205
206 uint64_t getOffset(uint64_t off) const override;
207 bool isLive(uint64_t off) const override { return getStringPiece(off).live; }
208 void markLive(uint64_t off) override { getStringPiece(off).live = true; }
209 // Find the StringPiece that contains this offset.
210 StringPiece &getStringPiece(uint64_t off);
211 const StringPiece &getStringPiece(uint64_t off) const;
212 // Split at each null byte.
213 void splitIntoPieces();
214
215 LLVM_ATTRIBUTE_ALWAYS_INLINE
216 StringRef getStringRef(size_t i) const {
217 size_t begin = pieces[i].inSecOff;
218 // The endpoint should be *at* the null terminator, not after. This matches
219 // the behavior of StringRef(const char *Str).
220 size_t end =
221 ((pieces.size() - 1 == i) ? data.size() : pieces[i + 1].inSecOff) - 1;
222 return toStringRef(Input: data.slice(N: begin, M: end - begin));
223 }
224
225 StringRef getStringRefAtOffset(uint64_t off) const {
226 return getStringRef(i: getStringPieceIndex(off));
227 }
228
229 // Returns i'th piece as a CachedHashStringRef. This function is very hot when
230 // string merging is enabled, so we want to inline.
231 LLVM_ATTRIBUTE_ALWAYS_INLINE
232 llvm::CachedHashStringRef getCachedHashStringRef(size_t i) const {
233 assert(deduplicateLiterals);
234 return {getStringRef(i), pieces[i].hash};
235 }
236
237 static bool classof(const InputSection *isec) {
238 return isec->kind() == CStringLiteralKind;
239 }
240
241 bool deduplicateLiterals = false;
242 std::vector<StringPiece> pieces;
243
244private:
245 size_t getStringPieceIndex(uint64_t off) const;
246};
247
248class WordLiteralInputSection final : public InputSection {
249public:
250 WordLiteralInputSection(const Section &section, ArrayRef<uint8_t> data,
251 uint32_t align);
252 uint64_t getOffset(uint64_t off) const override;
253 bool isLive(uint64_t off) const override {
254 return live[off >> power2LiteralSize];
255 }
256 void markLive(uint64_t off) override {
257 live[off >> power2LiteralSize] = true;
258 }
259
260 static bool classof(const InputSection *isec) {
261 return isec->kind() == WordLiteralKind;
262 }
263
264private:
265 unsigned power2LiteralSize;
266 // The liveness of data[off] is tracked by live[off >> power2LiteralSize].
267 llvm::BitVector live;
268};
269
270inline uint8_t sectionType(uint32_t flags) {
271 return flags & llvm::MachO::SECTION_TYPE;
272}
273
274inline bool isZeroFill(uint32_t flags) {
275 return llvm::MachO::isVirtualSection(type: sectionType(flags));
276}
277
278inline bool isThreadLocalVariables(uint32_t flags) {
279 return sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_VARIABLES;
280}
281
282// These sections contain the data for initializing thread-local variables.
283inline bool isThreadLocalData(uint32_t flags) {
284 return sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_REGULAR ||
285 sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_ZEROFILL;
286}
287
288inline bool isDebugSection(uint32_t flags) {
289 return (flags & llvm::MachO::SECTION_ATTRIBUTES_USR) ==
290 llvm::MachO::S_ATTR_DEBUG;
291}
292
293inline bool isWordLiteralSection(uint32_t flags) {
294 return sectionType(flags) == llvm::MachO::S_4BYTE_LITERALS ||
295 sectionType(flags) == llvm::MachO::S_8BYTE_LITERALS ||
296 sectionType(flags) == llvm::MachO::S_16BYTE_LITERALS;
297}
298
299bool isCodeSection(const InputSection *);
300bool isCfStringSection(const InputSection *);
301bool isClassRefsSection(const InputSection *);
302bool isSelRefsSection(const InputSection *);
303bool isEhFrameSection(const InputSection *);
304bool isGccExceptTabSection(const InputSection *);
305
306extern std::vector<ConcatInputSection *> inputSections;
307// This is used as a counter for specyfing input order for input sections
308extern int inputSectionsOrder;
309
310namespace section_names {
311
312constexpr const char authGot[] = "__auth_got";
313constexpr const char authPtr[] = "__auth_ptr";
314constexpr const char binding[] = "__binding";
315constexpr const char bitcodeBundle[] = "__bundle";
316constexpr const char cString[] = "__cstring";
317constexpr const char cfString[] = "__cfstring";
318constexpr const char cgProfile[] = "__cg_profile";
319constexpr const char chainFixups[] = "__chainfixups";
320constexpr const char codeSignature[] = "__code_signature";
321constexpr const char common[] = "__common";
322constexpr const char compactUnwind[] = "__compact_unwind";
323constexpr const char data[] = "__data";
324constexpr const char debugAbbrev[] = "__debug_abbrev";
325constexpr const char debugInfo[] = "__debug_info";
326constexpr const char debugLine[] = "__debug_line";
327constexpr const char debugStr[] = "__debug_str";
328constexpr const char debugStrOffs[] = "__debug_str_offs";
329constexpr const char ehFrame[] = "__eh_frame";
330constexpr const char gccExceptTab[] = "__gcc_except_tab";
331constexpr const char export_[] = "__export";
332constexpr const char dataInCode[] = "__data_in_code";
333constexpr const char functionStarts[] = "__func_starts";
334constexpr const char got[] = "__got";
335constexpr const char header[] = "__mach_header";
336constexpr const char indirectSymbolTable[] = "__ind_sym_tab";
337constexpr const char initOffsets[] = "__init_offsets";
338constexpr const char const_[] = "__const";
339constexpr const char lazySymbolPtr[] = "__la_symbol_ptr";
340constexpr const char lazyBinding[] = "__lazy_binding";
341constexpr const char literals[] = "__literals";
342constexpr const char functionMap[] = "__llvm_merge";
343constexpr const char moduleInitFunc[] = "__mod_init_func";
344constexpr const char moduleTermFunc[] = "__mod_term_func";
345constexpr const char nonLazySymbolPtr[] = "__nl_symbol_ptr";
346constexpr const char objcCatList[] = "__objc_catlist";
347constexpr const char objcClassList[] = "__objc_classlist";
348constexpr const char objcMethList[] = "__objc_methlist";
349constexpr const char objcClassRefs[] = "__objc_classrefs";
350constexpr const char objcConst[] = "__objc_const";
351constexpr const char objCImageInfo[] = "__objc_imageinfo";
352constexpr const char objcStubs[] = "__objc_stubs";
353constexpr const char objcSelrefs[] = "__objc_selrefs";
354constexpr const char objcMethname[] = "__objc_methname";
355constexpr const char objcNonLazyCatList[] = "__objc_nlcatlist";
356constexpr const char objcNonLazyClassList[] = "__objc_nlclslist";
357constexpr const char objcProtoList[] = "__objc_protolist";
358constexpr const char outlinedHashTree[] = "__llvm_outline";
359constexpr const char pageZero[] = "__pagezero";
360constexpr const char pointers[] = "__pointers";
361constexpr const char rebase[] = "__rebase";
362constexpr const char staticInit[] = "__StaticInit";
363constexpr const char stringTable[] = "__string_table";
364constexpr const char stubHelper[] = "__stub_helper";
365constexpr const char stubs[] = "__stubs";
366constexpr const char swift[] = "__swift";
367constexpr const char symbolTable[] = "__symbol_table";
368constexpr const char textCoalNt[] = "__textcoal_nt";
369constexpr const char text[] = "__text";
370constexpr const char threadPtrs[] = "__thread_ptrs";
371constexpr const char threadVars[] = "__thread_vars";
372constexpr const char unwindInfo[] = "__unwind_info";
373constexpr const char weakBinding[] = "__weak_binding";
374constexpr const char zeroFill[] = "__zerofill";
375constexpr const char addrSig[] = "__llvm_addrsig";
376
377} // namespace section_names
378
379void addInputSection(InputSection *inputSection);
380} // namespace macho
381
382std::string toString(const macho::InputSection *);
383
384} // namespace lld
385
386#endif
387