Bug Summary

File:tools/lld/ELF/OutputSections.cpp
Warning:line 295, column 19
Called C++ object pointer is null

Annotated Source Code

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clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name OutputSections.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -momit-leaf-frame-pointer -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-8/lib/clang/8.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-8~svn345461/build-llvm/tools/lld/ELF -I /build/llvm-toolchain-snapshot-8~svn345461/tools/lld/ELF -I /build/llvm-toolchain-snapshot-8~svn345461/tools/lld/include -I /build/llvm-toolchain-snapshot-8~svn345461/build-llvm/tools/lld/include -I /build/llvm-toolchain-snapshot-8~svn345461/build-llvm/include -I /build/llvm-toolchain-snapshot-8~svn345461/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/backward -internal-isystem /usr/include/clang/8.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-8/lib/clang/8.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-comment -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-8~svn345461/build-llvm/tools/lld/ELF -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2018-10-27-211344-32123-1 -x c++ /build/llvm-toolchain-snapshot-8~svn345461/tools/lld/ELF/OutputSections.cpp -faddrsig
1//===- OutputSections.cpp -------------------------------------------------===//
2//
3// The LLVM Linker
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9
10#include "OutputSections.h"
11#include "Config.h"
12#include "LinkerScript.h"
13#include "SymbolTable.h"
14#include "SyntheticSections.h"
15#include "Target.h"
16#include "lld/Common/Memory.h"
17#include "lld/Common/Strings.h"
18#include "lld/Common/Threads.h"
19#include "llvm/BinaryFormat/Dwarf.h"
20#include "llvm/Support/Compression.h"
21#include "llvm/Support/MD5.h"
22#include "llvm/Support/MathExtras.h"
23#include "llvm/Support/SHA1.h"
24
25using namespace llvm;
26using namespace llvm::dwarf;
27using namespace llvm::object;
28using namespace llvm::ELF;
29
30using namespace lld;
31using namespace lld::elf;
32
33uint8_t Out::First;
34PhdrEntry *Out::TlsPhdr;
35OutputSection *Out::ElfHeader;
36OutputSection *Out::ProgramHeaders;
37OutputSection *Out::PreinitArray;
38OutputSection *Out::InitArray;
39OutputSection *Out::FiniArray;
40
41std::vector<OutputSection *> elf::OutputSections;
42
43uint32_t OutputSection::getPhdrFlags() const {
44 uint32_t Ret = 0;
45 if (Config->EMachine != EM_ARM || !(Flags & SHF_ARM_PURECODE))
46 Ret |= PF_R;
47 if (Flags & SHF_WRITE)
48 Ret |= PF_W;
49 if (Flags & SHF_EXECINSTR)
50 Ret |= PF_X;
51 return Ret;
52}
53
54template <class ELFT>
55void OutputSection::writeHeaderTo(typename ELFT::Shdr *Shdr) {
56 Shdr->sh_entsize = Entsize;
57 Shdr->sh_addralign = Alignment;
58 Shdr->sh_type = Type;
59 Shdr->sh_offset = Offset;
60 Shdr->sh_flags = Flags;
61 Shdr->sh_info = Info;
62 Shdr->sh_link = Link;
63 Shdr->sh_addr = Addr;
64 Shdr->sh_size = Size;
65 Shdr->sh_name = ShName;
66}
67
68OutputSection::OutputSection(StringRef Name, uint32_t Type, uint64_t Flags)
69 : BaseCommand(OutputSectionKind),
70 SectionBase(Output, Name, Flags, /*Entsize*/ 0, /*Alignment*/ 1, Type,
71 /*Info*/ 0, /*Link*/ 0) {
72 Live = false;
73}
74
75// We allow sections of types listed below to merged into a
76// single progbits section. This is typically done by linker
77// scripts. Merging nobits and progbits will force disk space
78// to be allocated for nobits sections. Other ones don't require
79// any special treatment on top of progbits, so there doesn't
80// seem to be a harm in merging them.
81static bool canMergeToProgbits(unsigned Type) {
82 return Type == SHT_NOBITS || Type == SHT_PROGBITS || Type == SHT_INIT_ARRAY ||
83 Type == SHT_PREINIT_ARRAY || Type == SHT_FINI_ARRAY ||
84 Type == SHT_NOTE;
85}
86
87void OutputSection::addSection(InputSection *IS) {
88 if (!Live) {
89 // If IS is the first section to be added to this section,
90 // initialize Type, Entsize and flags from IS.
91 Live = true;
92 Type = IS->Type;
93 Entsize = IS->Entsize;
94 Flags = IS->Flags;
95 } else {
96 // Otherwise, check if new type or flags are compatible with existing ones.
97 unsigned Mask = SHF_ALLOC | SHF_TLS | SHF_LINK_ORDER;
98 if ((Flags & Mask) != (IS->Flags & Mask))
99 error("incompatible section flags for " + Name + "\n>>> " + toString(IS) +
100 ": 0x" + utohexstr(IS->Flags) + "\n>>> output section " + Name +
101 ": 0x" + utohexstr(Flags));
102
103 if (Type != IS->Type) {
104 if (!canMergeToProgbits(Type) || !canMergeToProgbits(IS->Type))
105 error("section type mismatch for " + IS->Name + "\n>>> " +
106 toString(IS) + ": " +
107 getELFSectionTypeName(Config->EMachine, IS->Type) +
108 "\n>>> output section " + Name + ": " +
109 getELFSectionTypeName(Config->EMachine, Type));
110 Type = SHT_PROGBITS;
111 }
112 }
113
114 IS->Parent = this;
115 uint64_t AndMask =
116 Config->EMachine == EM_ARM ? (uint64_t)SHF_ARM_PURECODE : 0;
117 uint64_t OrMask = ~AndMask;
118 uint64_t AndFlags = (Flags & IS->Flags) & AndMask;
119 uint64_t OrFlags = (Flags | IS->Flags) & OrMask;
120 Flags = AndFlags | OrFlags;
121
122 Alignment = std::max(Alignment, IS->Alignment);
123
124 // If this section contains a table of fixed-size entries, sh_entsize
125 // holds the element size. If it contains elements of different size we
126 // set sh_entsize to 0.
127 if (Entsize != IS->Entsize)
128 Entsize = 0;
129
130 if (!IS->Assigned) {
131 IS->Assigned = true;
132 if (SectionCommands.empty() ||
133 !isa<InputSectionDescription>(SectionCommands.back()))
134 SectionCommands.push_back(make<InputSectionDescription>(""));
135 auto *ISD = cast<InputSectionDescription>(SectionCommands.back());
136 ISD->Sections.push_back(IS);
137 }
138}
139
140static void sortByOrder(MutableArrayRef<InputSection *> In,
141 llvm::function_ref<int(InputSectionBase *S)> Order) {
142 typedef std::pair<int, InputSection *> Pair;
143 auto Comp = [](const Pair &A, const Pair &B) { return A.first < B.first; };
144
145 std::vector<Pair> V;
146 for (InputSection *S : In)
147 V.push_back({Order(S), S});
148 std::stable_sort(V.begin(), V.end(), Comp);
149
150 for (size_t I = 0; I < V.size(); ++I)
151 In[I] = V[I].second;
152}
153
154uint64_t elf::getHeaderSize() {
155 if (Config->OFormatBinary)
156 return 0;
157 return Out::ElfHeader->Size + Out::ProgramHeaders->Size;
158}
159
160bool OutputSection::classof(const BaseCommand *C) {
161 return C->Kind == OutputSectionKind;
162}
163
164void OutputSection::sort(llvm::function_ref<int(InputSectionBase *S)> Order) {
165 assert(Live)((Live) ? static_cast<void> (0) : __assert_fail ("Live"
, "/build/llvm-toolchain-snapshot-8~svn345461/tools/lld/ELF/OutputSections.cpp"
, 165, __PRETTY_FUNCTION__))
;
166 for (BaseCommand *B : SectionCommands)
167 if (auto *ISD = dyn_cast<InputSectionDescription>(B))
168 sortByOrder(ISD->Sections, Order);
169}
170
171// Fill [Buf, Buf + Size) with Filler.
172// This is used for linker script "=fillexp" command.
173static void fill(uint8_t *Buf, size_t Size, uint32_t Filler) {
174 size_t I = 0;
175 for (; I + 4 < Size; I += 4)
176 memcpy(Buf + I, &Filler, 4);
177 memcpy(Buf + I, &Filler, Size - I);
178}
179
180// Compress section contents if this section contains debug info.
181template <class ELFT> void OutputSection::maybeCompress() {
182 typedef typename ELFT::Chdr Elf_Chdr;
183
184 // Compress only DWARF debug sections.
185 if (!Config->CompressDebugSections || (Flags & SHF_ALLOC) ||
186 !Name.startswith(".debug_"))
187 return;
188
189 // Create a section header.
190 ZDebugHeader.resize(sizeof(Elf_Chdr));
191 auto *Hdr = reinterpret_cast<Elf_Chdr *>(ZDebugHeader.data());
192 Hdr->ch_type = ELFCOMPRESS_ZLIB;
193 Hdr->ch_size = Size;
194 Hdr->ch_addralign = Alignment;
195
196 // Write section contents to a temporary buffer and compress it.
197 std::vector<uint8_t> Buf(Size);
198 writeTo<ELFT>(Buf.data());
199 if (Error E = zlib::compress(toStringRef(Buf), CompressedData))
200 fatal("compress failed: " + llvm::toString(std::move(E)));
201
202 // Update section headers.
203 Size = sizeof(Elf_Chdr) + CompressedData.size();
204 Flags |= SHF_COMPRESSED;
205}
206
207static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
208 if (Size == 1)
209 *Buf = Data;
210 else if (Size == 2)
211 write16(Buf, Data);
212 else if (Size == 4)
213 write32(Buf, Data);
214 else if (Size == 8)
215 write64(Buf, Data);
216 else
217 llvm_unreachable("unsupported Size argument")::llvm::llvm_unreachable_internal("unsupported Size argument"
, "/build/llvm-toolchain-snapshot-8~svn345461/tools/lld/ELF/OutputSections.cpp"
, 217)
;
218}
219
220template <class ELFT> void OutputSection::writeTo(uint8_t *Buf) {
221 if (Type == SHT_NOBITS)
222 return;
223
224 Loc = Buf;
225
226 // If -compress-debug-section is specified and if this is a debug seciton,
227 // we've already compressed section contents. If that's the case,
228 // just write it down.
229 if (!CompressedData.empty()) {
230 memcpy(Buf, ZDebugHeader.data(), ZDebugHeader.size());
231 memcpy(Buf + ZDebugHeader.size(), CompressedData.data(),
232 CompressedData.size());
233 return;
234 }
235
236 // Write leading padding.
237 std::vector<InputSection *> Sections = getInputSections(this);
238 uint32_t Filler = getFiller();
239 if (Filler)
240 fill(Buf, Sections.empty() ? Size : Sections[0]->OutSecOff, Filler);
241
242 parallelForEachN(0, Sections.size(), [&](size_t I) {
243 InputSection *IS = Sections[I];
244 IS->writeTo<ELFT>(Buf);
245
246 // Fill gaps between sections.
247 if (Filler) {
248 uint8_t *Start = Buf + IS->OutSecOff + IS->getSize();
249 uint8_t *End;
250 if (I + 1 == Sections.size())
251 End = Buf + Size;
252 else
253 End = Buf + Sections[I + 1]->OutSecOff;
254 fill(Start, End - Start, Filler);
255 }
256 });
257
258 // Linker scripts may have BYTE()-family commands with which you
259 // can write arbitrary bytes to the output. Process them if any.
260 for (BaseCommand *Base : SectionCommands)
261 if (auto *Data = dyn_cast<ByteCommand>(Base))
262 writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size);
263}
264
265template <class ELFT>
266static void finalizeShtGroup(OutputSection *OS,
267 InputSection *Section) {
268 assert(Config->Relocatable)((Config->Relocatable) ? static_cast<void> (0) : __assert_fail
("Config->Relocatable", "/build/llvm-toolchain-snapshot-8~svn345461/tools/lld/ELF/OutputSections.cpp"
, 268, __PRETTY_FUNCTION__))
;
269
270 // sh_link field for SHT_GROUP sections should contain the section index of
271 // the symbol table.
272 OS->Link = In.SymTab->getParent()->SectionIndex;
273
274 // sh_info then contain index of an entry in symbol table section which
275 // provides signature of the section group.
276 ObjFile<ELFT> *Obj = Section->getFile<ELFT>();
277 ArrayRef<Symbol *> Symbols = Obj->getSymbols();
278 OS->Info = In.SymTab->getSymbolIndex(Symbols[Section->Info]);
279}
280
281template <class ELFT> void OutputSection::finalize() {
282 if (Type == SHT_NOBITS)
1
Assuming the condition is false
2
Taking false branch
283 for (BaseCommand *Base : SectionCommands)
284 if (isa<ByteCommand>(Base))
285 Type = SHT_PROGBITS;
286
287 std::vector<InputSection *> V = getInputSections(this);
288 InputSection *First = V.empty() ? nullptr : V[0];
3
Assuming the condition is true
4
'?' condition is true
5
'First' initialized to a null pointer value
289
290 if (Flags & SHF_LINK_ORDER) {
6
Assuming the condition is true
7
Taking true branch
291 // We must preserve the link order dependency of sections with the
292 // SHF_LINK_ORDER flag. The dependency is indicated by the sh_link field. We
293 // need to translate the InputSection sh_link to the OutputSection sh_link,
294 // all InputSections in the OutputSection have the same dependency.
295 if (auto *D = First->getLinkOrderDep())
8
Called C++ object pointer is null
296 Link = D->getParent()->SectionIndex;
297 }
298
299 if (Type == SHT_GROUP) {
300 finalizeShtGroup<ELFT>(this, First);
301 return;
302 }
303
304 if (!Config->CopyRelocs || (Type != SHT_RELA && Type != SHT_REL))
305 return;
306
307 if (isa<SyntheticSection>(First))
308 return;
309
310 Link = In.SymTab->getParent()->SectionIndex;
311 // sh_info for SHT_REL[A] sections should contain the section header index of
312 // the section to which the relocation applies.
313 InputSectionBase *S = First->getRelocatedSection();
314 Info = S->getOutputSection()->SectionIndex;
315 Flags |= SHF_INFO_LINK;
316}
317
318// Returns true if S matches /Filename.?\.o$/.
319static bool isCrtBeginEnd(StringRef S, StringRef Filename) {
320 if (!S.endswith(".o"))
321 return false;
322 S = S.drop_back(2);
323 if (S.endswith(Filename))
324 return true;
325 return !S.empty() && S.drop_back().endswith(Filename);
326}
327
328static bool isCrtbegin(StringRef S) { return isCrtBeginEnd(S, "crtbegin"); }
329static bool isCrtend(StringRef S) { return isCrtBeginEnd(S, "crtend"); }
330
331// .ctors and .dtors are sorted by this priority from highest to lowest.
332//
333// 1. The section was contained in crtbegin (crtbegin contains
334// some sentinel value in its .ctors and .dtors so that the runtime
335// can find the beginning of the sections.)
336//
337// 2. The section has an optional priority value in the form of ".ctors.N"
338// or ".dtors.N" where N is a number. Unlike .{init,fini}_array,
339// they are compared as string rather than number.
340//
341// 3. The section is just ".ctors" or ".dtors".
342//
343// 4. The section was contained in crtend, which contains an end marker.
344//
345// In an ideal world, we don't need this function because .init_array and
346// .ctors are duplicate features (and .init_array is newer.) However, there
347// are too many real-world use cases of .ctors, so we had no choice to
348// support that with this rather ad-hoc semantics.
349static bool compCtors(const InputSection *A, const InputSection *B) {
350 bool BeginA = isCrtbegin(A->File->getName());
351 bool BeginB = isCrtbegin(B->File->getName());
352 if (BeginA != BeginB)
353 return BeginA;
354 bool EndA = isCrtend(A->File->getName());
355 bool EndB = isCrtend(B->File->getName());
356 if (EndA != EndB)
357 return EndB;
358 StringRef X = A->Name;
359 StringRef Y = B->Name;
360 assert(X.startswith(".ctors") || X.startswith(".dtors"))((X.startswith(".ctors") || X.startswith(".dtors")) ? static_cast
<void> (0) : __assert_fail ("X.startswith(\".ctors\") || X.startswith(\".dtors\")"
, "/build/llvm-toolchain-snapshot-8~svn345461/tools/lld/ELF/OutputSections.cpp"
, 360, __PRETTY_FUNCTION__))
;
361 assert(Y.startswith(".ctors") || Y.startswith(".dtors"))((Y.startswith(".ctors") || Y.startswith(".dtors")) ? static_cast
<void> (0) : __assert_fail ("Y.startswith(\".ctors\") || Y.startswith(\".dtors\")"
, "/build/llvm-toolchain-snapshot-8~svn345461/tools/lld/ELF/OutputSections.cpp"
, 361, __PRETTY_FUNCTION__))
;
362 X = X.substr(6);
363 Y = Y.substr(6);
364 return X < Y;
365}
366
367// Sorts input sections by the special rules for .ctors and .dtors.
368// Unfortunately, the rules are different from the one for .{init,fini}_array.
369// Read the comment above.
370void OutputSection::sortCtorsDtors() {
371 assert(SectionCommands.size() == 1)((SectionCommands.size() == 1) ? static_cast<void> (0) :
__assert_fail ("SectionCommands.size() == 1", "/build/llvm-toolchain-snapshot-8~svn345461/tools/lld/ELF/OutputSections.cpp"
, 371, __PRETTY_FUNCTION__))
;
372 auto *ISD = cast<InputSectionDescription>(SectionCommands[0]);
373 std::stable_sort(ISD->Sections.begin(), ISD->Sections.end(), compCtors);
374}
375
376// If an input string is in the form of "foo.N" where N is a number,
377// return N. Otherwise, returns 65536, which is one greater than the
378// lowest priority.
379int elf::getPriority(StringRef S) {
380 size_t Pos = S.rfind('.');
381 if (Pos == StringRef::npos)
382 return 65536;
383 int V;
384 if (!to_integer(S.substr(Pos + 1), V, 10))
385 return 65536;
386 return V;
387}
388
389std::vector<InputSection *> elf::getInputSections(OutputSection *OS) {
390 std::vector<InputSection *> Ret;
391 for (BaseCommand *Base : OS->SectionCommands)
392 if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
393 Ret.insert(Ret.end(), ISD->Sections.begin(), ISD->Sections.end());
394 return Ret;
395}
396
397// Sorts input sections by section name suffixes, so that .foo.N comes
398// before .foo.M if N < M. Used to sort .{init,fini}_array.N sections.
399// We want to keep the original order if the priorities are the same
400// because the compiler keeps the original initialization order in a
401// translation unit and we need to respect that.
402// For more detail, read the section of the GCC's manual about init_priority.
403void OutputSection::sortInitFini() {
404 // Sort sections by priority.
405 sort([](InputSectionBase *S) { return getPriority(S->Name); });
406}
407
408uint32_t OutputSection::getFiller() {
409 if (Filler)
410 return *Filler;
411 if (Flags & SHF_EXECINSTR)
412 return Target->TrapInstr;
413 return 0;
414}
415
416template void OutputSection::writeHeaderTo<ELF32LE>(ELF32LE::Shdr *Shdr);
417template void OutputSection::writeHeaderTo<ELF32BE>(ELF32BE::Shdr *Shdr);
418template void OutputSection::writeHeaderTo<ELF64LE>(ELF64LE::Shdr *Shdr);
419template void OutputSection::writeHeaderTo<ELF64BE>(ELF64BE::Shdr *Shdr);
420
421template void OutputSection::writeTo<ELF32LE>(uint8_t *Buf);
422template void OutputSection::writeTo<ELF32BE>(uint8_t *Buf);
423template void OutputSection::writeTo<ELF64LE>(uint8_t *Buf);
424template void OutputSection::writeTo<ELF64BE>(uint8_t *Buf);
425
426template void OutputSection::maybeCompress<ELF32LE>();
427template void OutputSection::maybeCompress<ELF32BE>();
428template void OutputSection::maybeCompress<ELF64LE>();
429template void OutputSection::maybeCompress<ELF64BE>();
430
431template void OutputSection::finalize<ELF32LE>();
432template void OutputSection::finalize<ELF32BE>();
433template void OutputSection::finalize<ELF64LE>();
434template void OutputSection::finalize<ELF64BE>();