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

source code of lld/MachO/InputSection.h