Bug Summary

File:tools/lld/ELF/OutputSections.cpp
Warning:line 277, column 24
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-eagerly-assume -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-7/lib/clang/7.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/tools/lld/ELF -I /build/llvm-toolchain-snapshot-7~svn338205/tools/lld/ELF -I /build/llvm-toolchain-snapshot-7~svn338205/tools/lld/include -I /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/tools/lld/include -I /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/include -I /build/llvm-toolchain-snapshot-7~svn338205/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/backward -internal-isystem /usr/include/clang/7.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-7/lib/clang/7.0.0/include -internal-externc-isystem /usr/lib/gcc/x86_64-linux-gnu/8/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-class-memaccess -Wno-comment -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-7~svn338205/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-2018-07-29-043837-17923-1 -x c++ /build/llvm-toolchain-snapshot-7~svn338205/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::DebugInfo;
36OutputSection *Out::ElfHeader;
37OutputSection *Out::ProgramHeaders;
38OutputSection *Out::PreinitArray;
39OutputSection *Out::InitArray;
40OutputSection *Out::FiniArray;
41
42std::vector<OutputSection *> elf::OutputSections;
43
44uint32_t OutputSection::getPhdrFlags() const {
45 uint32_t Ret = 0;
46 if (Config->EMachine != EM_ARM || !(Flags & SHF_ARM_PURECODE))
47 Ret |= PF_R;
48 if (Flags & SHF_WRITE)
49 Ret |= PF_W;
50 if (Flags & SHF_EXECINSTR)
51 Ret |= PF_X;
52 return Ret;
53}
54
55template <class ELFT>
56void OutputSection::writeHeaderTo(typename ELFT::Shdr *Shdr) {
57 Shdr->sh_entsize = Entsize;
58 Shdr->sh_addralign = Alignment;
59 Shdr->sh_type = Type;
60 Shdr->sh_offset = Offset;
61 Shdr->sh_flags = Flags;
62 Shdr->sh_info = Info;
63 Shdr->sh_link = Link;
64 Shdr->sh_addr = Addr;
65 Shdr->sh_size = Size;
66 Shdr->sh_name = ShName;
67}
68
69OutputSection::OutputSection(StringRef Name, uint32_t Type, uint64_t Flags)
70 : BaseCommand(OutputSectionKind),
71 SectionBase(Output, Name, Flags, /*Entsize*/ 0, /*Alignment*/ 1, Type,
72 /*Info*/ 0, /*Link*/ 0) {
73 Live = false;
74}
75
76// We allow sections of types listed below to merged into a
77// single progbits section. This is typically done by linker
78// scripts. Merging nobits and progbits will force disk space
79// to be allocated for nobits sections. Other ones don't require
80// any special treatment on top of progbits, so there doesn't
81// seem to be a harm in merging them.
82static bool canMergeToProgbits(unsigned Type) {
83 return Type == SHT_NOBITS || Type == SHT_PROGBITS || Type == SHT_INIT_ARRAY ||
84 Type == SHT_PREINIT_ARRAY || Type == SHT_FINI_ARRAY ||
85 Type == SHT_NOTE;
86}
87
88void OutputSection::addSection(InputSection *IS) {
89 if (!Live) {
90 // If IS is the first section to be added to this section,
91 // initialize Type, Entsize and flags from IS.
92 Live = true;
93 Type = IS->Type;
94 Entsize = IS->Entsize;
95 Flags = IS->Flags;
96 } else {
97 // Otherwise, check if new type or flags are compatible with existing ones.
98 unsigned Mask = SHF_ALLOC | SHF_TLS | SHF_LINK_ORDER;
99 if ((Flags & Mask) != (IS->Flags & Mask))
100 error("incompatible section flags for " + Name + "\n>>> " + toString(IS) +
101 ": 0x" + utohexstr(IS->Flags) + "\n>>> output section " + Name +
102 ": 0x" + utohexstr(Flags));
103
104 if (Type != IS->Type) {
105 if (!canMergeToProgbits(Type) || !canMergeToProgbits(IS->Type))
106 error("section type mismatch for " + IS->Name + "\n>>> " +
107 toString(IS) + ": " +
108 getELFSectionTypeName(Config->EMachine, IS->Type) +
109 "\n>>> output section " + Name + ": " +
110 getELFSectionTypeName(Config->EMachine, Type));
111 Type = SHT_PROGBITS;
112 }
113 }
114
115 IS->Parent = this;
116 uint64_t AndMask =
117 Config->EMachine == EM_ARM ? (uint64_t)SHF_ARM_PURECODE : 0;
118 uint64_t OrMask = ~AndMask;
119 uint64_t AndFlags = (Flags & IS->Flags) & AndMask;
120 uint64_t OrFlags = (Flags | IS->Flags) & OrMask;
121 Flags = AndFlags | OrFlags;
122
123 Alignment = std::max(Alignment, IS->Alignment);
124
125 // If this section contains a table of fixed-size entries, sh_entsize
126 // holds the element size. If it contains elements of different size we
127 // set sh_entsize to 0.
128 if (Entsize != IS->Entsize)
129 Entsize = 0;
130
131 if (!IS->Assigned) {
132 IS->Assigned = true;
133 if (SectionCommands.empty() ||
134 !isa<InputSectionDescription>(SectionCommands.back()))
135 SectionCommands.push_back(make<InputSectionDescription>(""));
136 auto *ISD = cast<InputSectionDescription>(SectionCommands.back());
137 ISD->Sections.push_back(IS);
138 }
139}
140
141static void sortByOrder(MutableArrayRef<InputSection *> In,
142 llvm::function_ref<int(InputSectionBase *S)> Order) {
143 typedef std::pair<int, InputSection *> Pair;
144 auto Comp = [](const Pair &A, const Pair &B) { return A.first < B.first; };
145
146 std::vector<Pair> V;
147 for (InputSection *S : In)
148 V.push_back({Order(S), S});
149 std::stable_sort(V.begin(), V.end(), Comp);
150
151 for (size_t I = 0; I < V.size(); ++I)
152 In[I] = V[I].second;
153}
154
155uint64_t elf::getHeaderSize() {
156 if (Config->OFormatBinary)
157 return 0;
158 return Out::ElfHeader->Size + Out::ProgramHeaders->Size;
159}
160
161bool OutputSection::classof(const BaseCommand *C) {
162 return C->Kind == OutputSectionKind;
163}
164
165void OutputSection::sort(llvm::function_ref<int(InputSectionBase *S)> Order) {
166 assert(Live)(static_cast <bool> (Live) ? void (0) : __assert_fail (
"Live", "/build/llvm-toolchain-snapshot-7~svn338205/tools/lld/ELF/OutputSections.cpp"
, 166, __extension__ __PRETTY_FUNCTION__))
;
167 for (BaseCommand *B : SectionCommands)
168 if (auto *ISD = dyn_cast<InputSectionDescription>(B))
169 sortByOrder(ISD->Sections, Order);
170}
171
172// Fill [Buf, Buf + Size) with Filler.
173// This is used for linker script "=fillexp" command.
174static void fill(uint8_t *Buf, size_t Size, uint32_t Filler) {
175 size_t I = 0;
176 for (; I + 4 < Size; I += 4)
177 memcpy(Buf + I, &Filler, 4);
178 memcpy(Buf + I, &Filler, Size - I);
179}
180
181// Compress section contents if this section contains debug info.
182template <class ELFT> void OutputSection::maybeCompress() {
183 typedef typename ELFT::Chdr Elf_Chdr;
184
185 // Compress only DWARF debug sections.
186 if (!Config->CompressDebugSections || (Flags & SHF_ALLOC) ||
187 !Name.startswith(".debug_"))
188 return;
189
190 // Create a section header.
191 ZDebugHeader.resize(sizeof(Elf_Chdr));
192 auto *Hdr = reinterpret_cast<Elf_Chdr *>(ZDebugHeader.data());
193 Hdr->ch_type = ELFCOMPRESS_ZLIB;
194 Hdr->ch_size = Size;
195 Hdr->ch_addralign = Alignment;
196
197 // Write section contents to a temporary buffer and compress it.
198 std::vector<uint8_t> Buf(Size);
199 writeTo<ELFT>(Buf.data());
200 if (Error E = zlib::compress(toStringRef(Buf), CompressedData))
201 fatal("compress failed: " + llvm::toString(std::move(E)));
202
203 // Update section headers.
204 Size = sizeof(Elf_Chdr) + CompressedData.size();
205 Flags |= SHF_COMPRESSED;
206}
207
208static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
209 if (Size == 1)
210 *Buf = Data;
211 else if (Size == 2)
212 write16(Buf, Data);
213 else if (Size == 4)
214 write32(Buf, Data);
215 else if (Size == 8)
216 write64(Buf, Data);
217 else
218 llvm_unreachable("unsupported Size argument")::llvm::llvm_unreachable_internal("unsupported Size argument"
, "/build/llvm-toolchain-snapshot-7~svn338205/tools/lld/ELF/OutputSections.cpp"
, 218)
;
219}
220
221template <class ELFT> void OutputSection::writeTo(uint8_t *Buf) {
222 if (Type == SHT_NOBITS)
223 return;
224
225 Loc = Buf;
226
227 // If -compress-debug-section is specified and if this is a debug seciton,
228 // we've already compressed section contents. If that's the case,
229 // just write it down.
230 if (!CompressedData.empty()) {
231 memcpy(Buf, ZDebugHeader.data(), ZDebugHeader.size());
232 memcpy(Buf + ZDebugHeader.size(), CompressedData.data(),
233 CompressedData.size());
234 return;
235 }
236
237 // Write leading padding.
238 std::vector<InputSection *> Sections = getInputSections(this);
239 uint32_t Filler = getFiller();
240 if (Filler)
241 fill(Buf, Sections.empty() ? Size : Sections[0]->OutSecOff, Filler);
242
243 parallelForEachN(0, Sections.size(), [&](size_t I) {
244 InputSection *IS = Sections[I];
245 IS->writeTo<ELFT>(Buf);
246
247 // Fill gaps between sections.
248 if (Filler) {
249 uint8_t *Start = Buf + IS->OutSecOff + IS->getSize();
250 uint8_t *End;
251 if (I + 1 == Sections.size())
252 End = Buf + Size;
253 else
254 End = Buf + Sections[I + 1]->OutSecOff;
255 fill(Start, End - Start, Filler);
256 }
257 });
258
259 // Linker scripts may have BYTE()-family commands with which you
260 // can write arbitrary bytes to the output. Process them if any.
261 for (BaseCommand *Base : SectionCommands)
262 if (auto *Data = dyn_cast<ByteCommand>(Base))
263 writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size);
264}
265
266template <class ELFT>
267static void finalizeShtGroup(OutputSection *OS,
268 InputSection *Section) {
269 assert(Config->Relocatable)(static_cast <bool> (Config->Relocatable) ? void (0)
: __assert_fail ("Config->Relocatable", "/build/llvm-toolchain-snapshot-7~svn338205/tools/lld/ELF/OutputSections.cpp"
, 269, __extension__ __PRETTY_FUNCTION__))
;
270
271 // sh_link field for SHT_GROUP sections should contain the section index of
272 // the symbol table.
273 OS->Link = InX::SymTab->getParent()->SectionIndex;
274
275 // sh_info then contain index of an entry in symbol table section which
276 // provides signature of the section group.
277 ObjFile<ELFT> *Obj = Section->getFile<ELFT>();
12
Called C++ object pointer is null
278 ArrayRef<Symbol *> Symbols = Obj->getSymbols();
279 OS->Info = InX::SymTab->getSymbolIndex(Symbols[Section->Info]);
280}
281
282template <class ELFT> void OutputSection::finalize() {
283 if (Type == SHT_NOBITS)
1
Assuming the condition is false
2
Taking false branch
284 for (BaseCommand *Base : SectionCommands)
285 if (isa<ByteCommand>(Base))
286 Type = SHT_PROGBITS;
287
288 std::vector<InputSection *> V = getInputSections(this);
289 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
290
291 if (Flags & SHF_LINK_ORDER) {
6
Assuming the condition is false
7
Taking false branch
292 // We must preserve the link order dependency of sections with the
293 // SHF_LINK_ORDER flag. The dependency is indicated by the sh_link field. We
294 // need to translate the InputSection sh_link to the OutputSection sh_link,
295 // all InputSections in the OutputSection have the same dependency.
296 if (auto *D = First->getLinkOrderDep())
297 Link = D->getParent()->SectionIndex;
298 }
299
300 if (Type == SHT_GROUP) {
8
Assuming the condition is true
9
Taking true branch
301 finalizeShtGroup<ELFT>(this, First);
10
Passing null pointer value via 2nd parameter 'Section'
11
Calling 'finalizeShtGroup<llvm::object::ELFType<llvm::support::big, true>>'
302 return;
303 }
304
305 if (!Config->CopyRelocs || (Type != SHT_RELA && Type != SHT_REL))
306 return;
307
308 if (isa<SyntheticSection>(First))
309 return;
310
311 Link = InX::SymTab->getParent()->SectionIndex;
312 // sh_info for SHT_REL[A] sections should contain the section header index of
313 // the section to which the relocation applies.
314 InputSectionBase *S = First->getRelocatedSection();
315 Info = S->getOutputSection()->SectionIndex;
316 Flags |= SHF_INFO_LINK;
317}
318
319// Returns true if S matches /Filename.?\.o$/.
320static bool isCrtBeginEnd(StringRef S, StringRef Filename) {
321 if (!S.endswith(".o"))
322 return false;
323 S = S.drop_back(2);
324 if (S.endswith(Filename))
325 return true;
326 return !S.empty() && S.drop_back().endswith(Filename);
327}
328
329static bool isCrtbegin(StringRef S) { return isCrtBeginEnd(S, "crtbegin"); }
330static bool isCrtend(StringRef S) { return isCrtBeginEnd(S, "crtend"); }
331
332// .ctors and .dtors are sorted by this priority from highest to lowest.
333//
334// 1. The section was contained in crtbegin (crtbegin contains
335// some sentinel value in its .ctors and .dtors so that the runtime
336// can find the beginning of the sections.)
337//
338// 2. The section has an optional priority value in the form of ".ctors.N"
339// or ".dtors.N" where N is a number. Unlike .{init,fini}_array,
340// they are compared as string rather than number.
341//
342// 3. The section is just ".ctors" or ".dtors".
343//
344// 4. The section was contained in crtend, which contains an end marker.
345//
346// In an ideal world, we don't need this function because .init_array and
347// .ctors are duplicate features (and .init_array is newer.) However, there
348// are too many real-world use cases of .ctors, so we had no choice to
349// support that with this rather ad-hoc semantics.
350static bool compCtors(const InputSection *A, const InputSection *B) {
351 bool BeginA = isCrtbegin(A->File->getName());
352 bool BeginB = isCrtbegin(B->File->getName());
353 if (BeginA != BeginB)
354 return BeginA;
355 bool EndA = isCrtend(A->File->getName());
356 bool EndB = isCrtend(B->File->getName());
357 if (EndA != EndB)
358 return EndB;
359 StringRef X = A->Name;
360 StringRef Y = B->Name;
361 assert(X.startswith(".ctors") || X.startswith(".dtors"))(static_cast <bool> (X.startswith(".ctors") || X.startswith
(".dtors")) ? void (0) : __assert_fail ("X.startswith(\".ctors\") || X.startswith(\".dtors\")"
, "/build/llvm-toolchain-snapshot-7~svn338205/tools/lld/ELF/OutputSections.cpp"
, 361, __extension__ __PRETTY_FUNCTION__))
;
362 assert(Y.startswith(".ctors") || Y.startswith(".dtors"))(static_cast <bool> (Y.startswith(".ctors") || Y.startswith
(".dtors")) ? void (0) : __assert_fail ("Y.startswith(\".ctors\") || Y.startswith(\".dtors\")"
, "/build/llvm-toolchain-snapshot-7~svn338205/tools/lld/ELF/OutputSections.cpp"
, 362, __extension__ __PRETTY_FUNCTION__))
;
363 X = X.substr(6);
364 Y = Y.substr(6);
365 return X < Y;
366}
367
368// Sorts input sections by the special rules for .ctors and .dtors.
369// Unfortunately, the rules are different from the one for .{init,fini}_array.
370// Read the comment above.
371void OutputSection::sortCtorsDtors() {
372 assert(SectionCommands.size() == 1)(static_cast <bool> (SectionCommands.size() == 1) ? void
(0) : __assert_fail ("SectionCommands.size() == 1", "/build/llvm-toolchain-snapshot-7~svn338205/tools/lld/ELF/OutputSections.cpp"
, 372, __extension__ __PRETTY_FUNCTION__))
;
373 auto *ISD = cast<InputSectionDescription>(SectionCommands[0]);
374 std::stable_sort(ISD->Sections.begin(), ISD->Sections.end(), compCtors);
375}
376
377// If an input string is in the form of "foo.N" where N is a number,
378// return N. Otherwise, returns 65536, which is one greater than the
379// lowest priority.
380int elf::getPriority(StringRef S) {
381 size_t Pos = S.rfind('.');
382 if (Pos == StringRef::npos)
383 return 65536;
384 int V;
385 if (!to_integer(S.substr(Pos + 1), V, 10))
386 return 65536;
387 return V;
388}
389
390std::vector<InputSection *> elf::getInputSections(OutputSection *OS) {
391 std::vector<InputSection *> Ret;
392 for (BaseCommand *Base : OS->SectionCommands)
393 if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
394 Ret.insert(Ret.end(), ISD->Sections.begin(), ISD->Sections.end());
395 return Ret;
396}
397
398// Sorts input sections by section name suffixes, so that .foo.N comes
399// before .foo.M if N < M. Used to sort .{init,fini}_array.N sections.
400// We want to keep the original order if the priorities are the same
401// because the compiler keeps the original initialization order in a
402// translation unit and we need to respect that.
403// For more detail, read the section of the GCC's manual about init_priority.
404void OutputSection::sortInitFini() {
405 // Sort sections by priority.
406 sort([](InputSectionBase *S) { return getPriority(S->Name); });
407}
408
409uint32_t OutputSection::getFiller() {
410 if (Filler)
411 return *Filler;
412 if (Flags & SHF_EXECINSTR)
413 return Target->TrapInstr;
414 return 0;
415}
416
417template void OutputSection::writeHeaderTo<ELF32LE>(ELF32LE::Shdr *Shdr);
418template void OutputSection::writeHeaderTo<ELF32BE>(ELF32BE::Shdr *Shdr);
419template void OutputSection::writeHeaderTo<ELF64LE>(ELF64LE::Shdr *Shdr);
420template void OutputSection::writeHeaderTo<ELF64BE>(ELF64BE::Shdr *Shdr);
421
422template void OutputSection::writeTo<ELF32LE>(uint8_t *Buf);
423template void OutputSection::writeTo<ELF32BE>(uint8_t *Buf);
424template void OutputSection::writeTo<ELF64LE>(uint8_t *Buf);
425template void OutputSection::writeTo<ELF64BE>(uint8_t *Buf);
426
427template void OutputSection::maybeCompress<ELF32LE>();
428template void OutputSection::maybeCompress<ELF32BE>();
429template void OutputSection::maybeCompress<ELF64LE>();
430template void OutputSection::maybeCompress<ELF64BE>();
431
432template void OutputSection::finalize<ELF32LE>();
433template void OutputSection::finalize<ELF32BE>();
434template void OutputSection::finalize<ELF64LE>();
435template void OutputSection::finalize<ELF64BE>();