Bug Summary

File:tools/lld/ELF/OutputSections.cpp
Warning:line 279, column 24
Called C++ object pointer is null

Annotated Source Code

Press '?' to see keyboard shortcuts

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~svn329677/build-llvm/tools/lld/ELF -I /build/llvm-toolchain-snapshot-7~svn329677/tools/lld/ELF -I /build/llvm-toolchain-snapshot-7~svn329677/tools/lld/include -I /build/llvm-toolchain-snapshot-7~svn329677/build-llvm/tools/lld/include -I /build/llvm-toolchain-snapshot-7~svn329677/build-llvm/include -I /build/llvm-toolchain-snapshot-7~svn329677/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.3.0/../../../../include/c++/7.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.3.0/../../../../include/x86_64-linux-gnu/c++/7.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.3.0/../../../../include/x86_64-linux-gnu/c++/7.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.3.0/../../../../include/c++/7.3.0/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/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-7~svn329677/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-checker optin.performance.Padding -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2018-04-11-031539-24776-1 -x c++ /build/llvm-toolchain-snapshot-7~svn329677/tools/lld/ELF/OutputSections.cpp
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;
34OutputSection *Out::Opd;
35uint8_t *Out::OpdBuf;
36PhdrEntry *Out::TlsPhdr;
37OutputSection *Out::DebugInfo;
38OutputSection *Out::ElfHeader;
39OutputSection *Out::ProgramHeaders;
40OutputSection *Out::PreinitArray;
41OutputSection *Out::InitArray;
42OutputSection *Out::FiniArray;
43
44std::vector<OutputSection *> elf::OutputSections;
45
46uint32_t OutputSection::getPhdrFlags() const {
47 uint32_t Ret = 0;
48 if (Config->EMachine != EM_ARM || !(Flags & SHF_ARM_PURECODE))
49 Ret |= PF_R;
50 if (Flags & SHF_WRITE)
51 Ret |= PF_W;
52 if (Flags & SHF_EXECINSTR)
53 Ret |= PF_X;
54 return Ret;
55}
56
57template <class ELFT>
58void OutputSection::writeHeaderTo(typename ELFT::Shdr *Shdr) {
59 Shdr->sh_entsize = Entsize;
60 Shdr->sh_addralign = Alignment;
61 Shdr->sh_type = Type;
62 Shdr->sh_offset = Offset;
63 Shdr->sh_flags = Flags;
64 Shdr->sh_info = Info;
65 Shdr->sh_link = Link;
66 Shdr->sh_addr = Addr;
67 Shdr->sh_size = Size;
68 Shdr->sh_name = ShName;
69}
70
71OutputSection::OutputSection(StringRef Name, uint32_t Type, uint64_t Flags)
72 : BaseCommand(OutputSectionKind),
73 SectionBase(Output, Name, Flags, /*Entsize*/ 0, /*Alignment*/ 1, Type,
74 /*Info*/ 0, /*Link*/ 0) {
75 Live = false;
76}
77
78// We allow sections of types listed below to merged into a
79// single progbits section. This is typically done by linker
80// scripts. Merging nobits and progbits will force disk space
81// to be allocated for nobits sections. Other ones don't require
82// any special treatment on top of progbits, so there doesn't
83// seem to be a harm in merging them.
84static bool canMergeToProgbits(unsigned Type) {
85 return Type == SHT_NOBITS || Type == SHT_PROGBITS || Type == SHT_INIT_ARRAY ||
86 Type == SHT_PREINIT_ARRAY || Type == SHT_FINI_ARRAY ||
87 Type == SHT_NOTE;
88}
89
90void OutputSection::addSection(InputSection *IS) {
91 if (!Live) {
92 // If IS is the first section to be added to this section,
93 // initialize Type, Entsize and flags from IS.
94 Live = true;
95 Type = IS->Type;
96 Entsize = IS->Entsize;
97 Flags = IS->Flags;
98 } else {
99 // Otherwise, check if new type or flags are compatible with existing ones.
100 unsigned Mask = SHF_ALLOC | SHF_TLS | SHF_LINK_ORDER;
101 if ((Flags & Mask) != (IS->Flags & Mask))
102 error("incompatible section flags for " + Name + "\n>>> " + toString(IS) +
103 ": 0x" + utohexstr(IS->Flags) + "\n>>> output section " + Name +
104 ": 0x" + utohexstr(Flags));
105
106 if (Type != IS->Type) {
107 if (!canMergeToProgbits(Type) || !canMergeToProgbits(IS->Type))
108 error("section type mismatch for " + IS->Name + "\n>>> " +
109 toString(IS) + ": " +
110 getELFSectionTypeName(Config->EMachine, IS->Type) +
111 "\n>>> output section " + Name + ": " +
112 getELFSectionTypeName(Config->EMachine, Type));
113 Type = SHT_PROGBITS;
114 }
115 }
116
117 IS->Parent = this;
118 uint64_t AndMask =
119 Config->EMachine == EM_ARM ? (uint64_t)SHF_ARM_PURECODE : 0;
120 uint64_t OrMask = ~AndMask;
121 uint64_t AndFlags = (Flags & IS->Flags) & AndMask;
122 uint64_t OrFlags = (Flags | IS->Flags) & OrMask;
123 Flags = AndFlags | OrFlags;
124
125 Alignment = std::max(Alignment, IS->Alignment);
126
127 // If this section contains a table of fixed-size entries, sh_entsize
128 // holds the element size. If it contains elements of different size we
129 // set sh_entsize to 0.
130 if (Entsize != IS->Entsize)
131 Entsize = 0;
132
133 if (!IS->Assigned) {
134 IS->Assigned = true;
135 if (SectionCommands.empty() ||
136 !isa<InputSectionDescription>(SectionCommands.back()))
137 SectionCommands.push_back(make<InputSectionDescription>(""));
138 auto *ISD = cast<InputSectionDescription>(SectionCommands.back());
139 ISD->Sections.push_back(IS);
140 }
141}
142
143static void sortByOrder(MutableArrayRef<InputSection *> In,
144 std::function<int(InputSectionBase *S)> Order) {
145 typedef std::pair<int, InputSection *> Pair;
146 auto Comp = [](const Pair &A, const Pair &B) { return A.first < B.first; };
147
148 std::vector<Pair> V;
149 for (InputSection *S : In)
150 V.push_back({Order(S), S});
151 std::stable_sort(V.begin(), V.end(), Comp);
152
153 for (size_t I = 0; I < V.size(); ++I)
154 In[I] = V[I].second;
155}
156
157uint64_t elf::getHeaderSize() {
158 if (Config->OFormatBinary)
159 return 0;
160 return Out::ElfHeader->Size + Out::ProgramHeaders->Size;
161}
162
163bool OutputSection::classof(const BaseCommand *C) {
164 return C->Kind == OutputSectionKind;
165}
166
167void OutputSection::sort(std::function<int(InputSectionBase *S)> Order) {
168 assert(Live)(static_cast <bool> (Live) ? void (0) : __assert_fail (
"Live", "/build/llvm-toolchain-snapshot-7~svn329677/tools/lld/ELF/OutputSections.cpp"
, 168, __extension__ __PRETTY_FUNCTION__))
;
169 for (BaseCommand *B : SectionCommands)
170 if (auto *ISD = dyn_cast<InputSectionDescription>(B))
171 sortByOrder(ISD->Sections, Order);
172}
173
174// Fill [Buf, Buf + Size) with Filler.
175// This is used for linker script "=fillexp" command.
176static void fill(uint8_t *Buf, size_t Size, uint32_t Filler) {
177 size_t I = 0;
178 for (; I + 4 < Size; I += 4)
179 memcpy(Buf + I, &Filler, 4);
180 memcpy(Buf + I, &Filler, Size - I);
181}
182
183// Compress section contents if this section contains debug info.
184template <class ELFT> void OutputSection::maybeCompress() {
185 typedef typename ELFT::Chdr Elf_Chdr;
186
187 // Compress only DWARF debug sections.
188 if (!Config->CompressDebugSections || (Flags & SHF_ALLOC) ||
189 !Name.startswith(".debug_"))
190 return;
191
192 // Create a section header.
193 ZDebugHeader.resize(sizeof(Elf_Chdr));
194 auto *Hdr = reinterpret_cast<Elf_Chdr *>(ZDebugHeader.data());
195 Hdr->ch_type = ELFCOMPRESS_ZLIB;
196 Hdr->ch_size = Size;
197 Hdr->ch_addralign = Alignment;
198
199 // Write section contents to a temporary buffer and compress it.
200 std::vector<uint8_t> Buf(Size);
201 writeTo<ELFT>(Buf.data());
202 if (Error E = zlib::compress(toStringRef(Buf), CompressedData))
203 fatal("compress failed: " + llvm::toString(std::move(E)));
204
205 // Update section headers.
206 Size = sizeof(Elf_Chdr) + CompressedData.size();
207 Flags |= SHF_COMPRESSED;
208}
209
210static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
211 if (Size == 1)
212 *Buf = Data;
213 else if (Size == 2)
214 write16(Buf, Data);
215 else if (Size == 4)
216 write32(Buf, Data);
217 else if (Size == 8)
218 write64(Buf, Data);
219 else
220 llvm_unreachable("unsupported Size argument")::llvm::llvm_unreachable_internal("unsupported Size argument"
, "/build/llvm-toolchain-snapshot-7~svn329677/tools/lld/ELF/OutputSections.cpp"
, 220)
;
221}
222
223template <class ELFT> void OutputSection::writeTo(uint8_t *Buf) {
224 if (Type == SHT_NOBITS)
225 return;
226
227 Loc = Buf;
228
229 // If -compress-debug-section is specified and if this is a debug seciton,
230 // we've already compressed section contents. If that's the case,
231 // just write it down.
232 if (!CompressedData.empty()) {
233 memcpy(Buf, ZDebugHeader.data(), ZDebugHeader.size());
234 memcpy(Buf + ZDebugHeader.size(), CompressedData.data(),
235 CompressedData.size());
236 return;
237 }
238
239 // Write leading padding.
240 std::vector<InputSection *> Sections = getInputSections(this);
241 uint32_t Filler = getFiller();
242 if (Filler)
243 fill(Buf, Sections.empty() ? Size : Sections[0]->OutSecOff, Filler);
244
245 parallelForEachN(0, Sections.size(), [&](size_t I) {
246 InputSection *IS = Sections[I];
247 IS->writeTo<ELFT>(Buf);
248
249 // Fill gaps between sections.
250 if (Filler) {
251 uint8_t *Start = Buf + IS->OutSecOff + IS->getSize();
252 uint8_t *End;
253 if (I + 1 == Sections.size())
254 End = Buf + Size;
255 else
256 End = Buf + Sections[I + 1]->OutSecOff;
257 fill(Start, End - Start, Filler);
258 }
259 });
260
261 // Linker scripts may have BYTE()-family commands with which you
262 // can write arbitrary bytes to the output. Process them if any.
263 for (BaseCommand *Base : SectionCommands)
264 if (auto *Data = dyn_cast<ByteCommand>(Base))
265 writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size);
266}
267
268template <class ELFT>
269static void finalizeShtGroup(OutputSection *OS,
270 InputSection *Section) {
271 assert(Config->Relocatable)(static_cast <bool> (Config->Relocatable) ? void (0)
: __assert_fail ("Config->Relocatable", "/build/llvm-toolchain-snapshot-7~svn329677/tools/lld/ELF/OutputSections.cpp"
, 271, __extension__ __PRETTY_FUNCTION__))
;
272
273 // sh_link field for SHT_GROUP sections should contain the section index of
274 // the symbol table.
275 OS->Link = InX::SymTab->getParent()->SectionIndex;
276
277 // sh_info then contain index of an entry in symbol table section which
278 // provides signature of the section group.
279 ObjFile<ELFT> *Obj = Section->getFile<ELFT>();
12
Called C++ object pointer is null
280 ArrayRef<Symbol *> Symbols = Obj->getSymbols();
281 OS->Info = InX::SymTab->getSymbolIndex(Symbols[Section->Info]);
282}
283
284template <class ELFT> void OutputSection::finalize() {
285 if (Type == SHT_NOBITS)
1
Assuming the condition is false
2
Taking false branch
286 for (BaseCommand *Base : SectionCommands)
287 if (isa<ByteCommand>(Base))
288 Type = SHT_PROGBITS;
289
290 std::vector<InputSection *> V = getInputSections(this);
291 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
292
293 if (Flags & SHF_LINK_ORDER) {
6
Assuming the condition is false
7
Taking false branch
294 // We must preserve the link order dependency of sections with the
295 // SHF_LINK_ORDER flag. The dependency is indicated by the sh_link field. We
296 // need to translate the InputSection sh_link to the OutputSection sh_link,
297 // all InputSections in the OutputSection have the same dependency.
298 if (auto *D = First->getLinkOrderDep())
299 Link = D->getParent()->SectionIndex;
300 }
301
302 if (Type == SHT_GROUP) {
8
Assuming the condition is true
9
Taking true branch
303 finalizeShtGroup<ELFT>(this, First);
10
Passing null pointer value via 2nd parameter 'Section'
11
Calling 'finalizeShtGroup'
304 return;
305 }
306
307 if (!Config->CopyRelocs || (Type != SHT_RELA && Type != SHT_REL))
308 return;
309
310 if (isa<SyntheticSection>(First))
311 return;
312
313 Link = InX::SymTab->getParent()->SectionIndex;
314 // sh_info for SHT_REL[A] sections should contain the section header index of
315 // the section to which the relocation applies.
316 InputSectionBase *S = First->getRelocatedSection();
317 Info = S->getOutputSection()->SectionIndex;
318 Flags |= SHF_INFO_LINK;
319}
320
321// Returns true if S matches /Filename.?\.o$/.
322static bool isCrtBeginEnd(StringRef S, StringRef Filename) {
323 if (!S.endswith(".o"))
324 return false;
325 S = S.drop_back(2);
326 if (S.endswith(Filename))
327 return true;
328 return !S.empty() && S.drop_back().endswith(Filename);
329}
330
331static bool isCrtbegin(StringRef S) { return isCrtBeginEnd(S, "crtbegin"); }
332static bool isCrtend(StringRef S) { return isCrtBeginEnd(S, "crtend"); }
333
334// .ctors and .dtors are sorted by this priority from highest to lowest.
335//
336// 1. The section was contained in crtbegin (crtbegin contains
337// some sentinel value in its .ctors and .dtors so that the runtime
338// can find the beginning of the sections.)
339//
340// 2. The section has an optional priority value in the form of ".ctors.N"
341// or ".dtors.N" where N is a number. Unlike .{init,fini}_array,
342// they are compared as string rather than number.
343//
344// 3. The section is just ".ctors" or ".dtors".
345//
346// 4. The section was contained in crtend, which contains an end marker.
347//
348// In an ideal world, we don't need this function because .init_array and
349// .ctors are duplicate features (and .init_array is newer.) However, there
350// are too many real-world use cases of .ctors, so we had no choice to
351// support that with this rather ad-hoc semantics.
352static bool compCtors(const InputSection *A, const InputSection *B) {
353 bool BeginA = isCrtbegin(A->File->getName());
354 bool BeginB = isCrtbegin(B->File->getName());
355 if (BeginA != BeginB)
356 return BeginA;
357 bool EndA = isCrtend(A->File->getName());
358 bool EndB = isCrtend(B->File->getName());
359 if (EndA != EndB)
360 return EndB;
361 StringRef X = A->Name;
362 StringRef Y = B->Name;
363 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~svn329677/tools/lld/ELF/OutputSections.cpp"
, 363, __extension__ __PRETTY_FUNCTION__))
;
364 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~svn329677/tools/lld/ELF/OutputSections.cpp"
, 364, __extension__ __PRETTY_FUNCTION__))
;
365 X = X.substr(6);
366 Y = Y.substr(6);
367 return X < Y;
368}
369
370// Sorts input sections by the special rules for .ctors and .dtors.
371// Unfortunately, the rules are different from the one for .{init,fini}_array.
372// Read the comment above.
373void OutputSection::sortCtorsDtors() {
374 assert(SectionCommands.size() == 1)(static_cast <bool> (SectionCommands.size() == 1) ? void
(0) : __assert_fail ("SectionCommands.size() == 1", "/build/llvm-toolchain-snapshot-7~svn329677/tools/lld/ELF/OutputSections.cpp"
, 374, __extension__ __PRETTY_FUNCTION__))
;
375 auto *ISD = cast<InputSectionDescription>(SectionCommands[0]);
376 std::stable_sort(ISD->Sections.begin(), ISD->Sections.end(), compCtors);
377}
378
379// If an input string is in the form of "foo.N" where N is a number,
380// return N. Otherwise, returns 65536, which is one greater than the
381// lowest priority.
382int elf::getPriority(StringRef S) {
383 size_t Pos = S.rfind('.');
384 if (Pos == StringRef::npos)
385 return 65536;
386 int V;
387 if (!to_integer(S.substr(Pos + 1), V, 10))
388 return 65536;
389 return V;
390}
391
392std::vector<InputSection *> elf::getInputSections(OutputSection *OS) {
393 std::vector<InputSection *> Ret;
394 for (BaseCommand *Base : OS->SectionCommands)
395 if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
396 Ret.insert(Ret.end(), ISD->Sections.begin(), ISD->Sections.end());
397 return Ret;
398}
399
400// Sorts input sections by section name suffixes, so that .foo.N comes
401// before .foo.M if N < M. Used to sort .{init,fini}_array.N sections.
402// We want to keep the original order if the priorities are the same
403// because the compiler keeps the original initialization order in a
404// translation unit and we need to respect that.
405// For more detail, read the section of the GCC's manual about init_priority.
406void OutputSection::sortInitFini() {
407 // Sort sections by priority.
408 sort([](InputSectionBase *S) { return getPriority(S->Name); });
409}
410
411uint32_t OutputSection::getFiller() {
412 if (Filler)
413 return *Filler;
414 if (Flags & SHF_EXECINSTR)
415 return Target->TrapInstr;
416 return 0;
417}
418
419template void OutputSection::writeHeaderTo<ELF32LE>(ELF32LE::Shdr *Shdr);
420template void OutputSection::writeHeaderTo<ELF32BE>(ELF32BE::Shdr *Shdr);
421template void OutputSection::writeHeaderTo<ELF64LE>(ELF64LE::Shdr *Shdr);
422template void OutputSection::writeHeaderTo<ELF64BE>(ELF64BE::Shdr *Shdr);
423
424template void OutputSection::writeTo<ELF32LE>(uint8_t *Buf);
425template void OutputSection::writeTo<ELF32BE>(uint8_t *Buf);
426template void OutputSection::writeTo<ELF64LE>(uint8_t *Buf);
427template void OutputSection::writeTo<ELF64BE>(uint8_t *Buf);
428
429template void OutputSection::maybeCompress<ELF32LE>();
430template void OutputSection::maybeCompress<ELF32BE>();
431template void OutputSection::maybeCompress<ELF64LE>();
432template void OutputSection::maybeCompress<ELF64BE>();
433
434template void OutputSection::finalize<ELF32LE>();
435template void OutputSection::finalize<ELF32BE>();
436template void OutputSection::finalize<ELF64LE>();
437template void OutputSection::finalize<ELF64BE>();