Bug Summary

File:lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
Location:line 399, column 9
Description:Called C++ object pointer is null

Annotated Source Code

1//===-- ARMMachObjectWriter.cpp - ARM Mach Object Writer ------------------===//
2//
3// The LLVM Compiler Infrastructure
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 "MCTargetDesc/ARMMCTargetDesc.h"
11#include "MCTargetDesc/ARMBaseInfo.h"
12#include "MCTargetDesc/ARMFixupKinds.h"
13#include "llvm/ADT/Twine.h"
14#include "llvm/MC/MCAsmLayout.h"
15#include "llvm/MC/MCAssembler.h"
16#include "llvm/MC/MCContext.h"
17#include "llvm/MC/MCExpr.h"
18#include "llvm/MC/MCFixup.h"
19#include "llvm/MC/MCFixupKindInfo.h"
20#include "llvm/MC/MCMachObjectWriter.h"
21#include "llvm/MC/MCSection.h"
22#include "llvm/MC/MCValue.h"
23#include "llvm/Support/ErrorHandling.h"
24#include "llvm/Support/MachO.h"
25using namespace llvm;
26
27namespace {
28class ARMMachObjectWriter : public MCMachObjectTargetWriter {
29 void RecordARMScatteredRelocation(MachObjectWriter *Writer,
30 const MCAssembler &Asm,
31 const MCAsmLayout &Layout,
32 const MCFragment *Fragment,
33 const MCFixup &Fixup,
34 MCValue Target,
35 unsigned Type,
36 unsigned Log2Size,
37 uint64_t &FixedValue);
38 void RecordARMScatteredHalfRelocation(MachObjectWriter *Writer,
39 const MCAssembler &Asm,
40 const MCAsmLayout &Layout,
41 const MCFragment *Fragment,
42 const MCFixup &Fixup, MCValue Target,
43 uint64_t &FixedValue);
44
45 bool requiresExternRelocation(MachObjectWriter *Writer,
46 const MCAssembler &Asm,
47 const MCFragment &Fragment, unsigned RelocType,
48 const MCSymbol &S, uint64_t FixedValue);
49
50public:
51 ARMMachObjectWriter(bool Is64Bit, uint32_t CPUType, uint32_t CPUSubtype)
52 : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype) {}
53
54 void recordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
55 const MCAsmLayout &Layout, const MCFragment *Fragment,
56 const MCFixup &Fixup, MCValue Target,
57 uint64_t &FixedValue) override;
58};
59}
60
61static bool getARMFixupKindMachOInfo(unsigned Kind, unsigned &RelocType,
62 unsigned &Log2Size) {
63 RelocType = unsigned(MachO::ARM_RELOC_VANILLA);
64 Log2Size = ~0U;
65
66 switch (Kind) {
67 default:
68 return false;
69
70 case FK_Data_1:
71 Log2Size = llvm::Log2_32(1);
72 return true;
73 case FK_Data_2:
74 Log2Size = llvm::Log2_32(2);
75 return true;
76 case FK_Data_4:
77 Log2Size = llvm::Log2_32(4);
78 return true;
79 case FK_Data_8:
80 Log2Size = llvm::Log2_32(8);
81 return true;
82
83 // These fixups are expected to always be resolvable at assembly time and
84 // have no relocations supported.
85 case ARM::fixup_arm_ldst_pcrel_12:
86 case ARM::fixup_arm_pcrel_10:
87 case ARM::fixup_arm_adr_pcrel_12:
88 case ARM::fixup_arm_thumb_br:
89 return false;
90
91 // Handle 24-bit branch kinds.
92 case ARM::fixup_arm_condbranch:
93 case ARM::fixup_arm_uncondbranch:
94 case ARM::fixup_arm_uncondbl:
95 case ARM::fixup_arm_condbl:
96 case ARM::fixup_arm_blx:
97 RelocType = unsigned(MachO::ARM_RELOC_BR24);
98 // Report as 'long', even though that is not quite accurate.
99 Log2Size = llvm::Log2_32(4);
100 return true;
101
102 case ARM::fixup_t2_uncondbranch:
103 case ARM::fixup_arm_thumb_bl:
104 case ARM::fixup_arm_thumb_blx:
105 RelocType = unsigned(MachO::ARM_THUMB_RELOC_BR22);
106 Log2Size = llvm::Log2_32(4);
107 return true;
108
109 // For movw/movt r_type relocations they always have a pair following them and
110 // the r_length bits are used differently. The encoding of the r_length is as
111 // follows:
112 // low bit of r_length:
113 // 0 - :lower16: for movw instructions
114 // 1 - :upper16: for movt instructions
115 // high bit of r_length:
116 // 0 - arm instructions
117 // 1 - thumb instructions
118 case ARM::fixup_arm_movt_hi16:
119 RelocType = unsigned(MachO::ARM_RELOC_HALF);
120 Log2Size = 1;
121 return true;
122 case ARM::fixup_t2_movt_hi16:
123 RelocType = unsigned(MachO::ARM_RELOC_HALF);
124 Log2Size = 3;
125 return true;
126
127 case ARM::fixup_arm_movw_lo16:
128 RelocType = unsigned(MachO::ARM_RELOC_HALF);
129 Log2Size = 0;
130 return true;
131 case ARM::fixup_t2_movw_lo16:
132 RelocType = unsigned(MachO::ARM_RELOC_HALF);
133 Log2Size = 2;
134 return true;
135 }
136}
137
138void ARMMachObjectWriter::
139RecordARMScatteredHalfRelocation(MachObjectWriter *Writer,
140 const MCAssembler &Asm,
141 const MCAsmLayout &Layout,
142 const MCFragment *Fragment,
143 const MCFixup &Fixup,
144 MCValue Target,
145 uint64_t &FixedValue) {
146 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
147 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
148 unsigned Type = MachO::ARM_RELOC_HALF;
149
150 // See <reloc.h>.
151 const MCSymbol *A = &Target.getSymA()->getSymbol();
152
153 if (!A->getFragment())
154 Asm.getContext().reportFatalError(Fixup.getLoc(),
155 "symbol '" + A->getName() +
156 "' can not be undefined in a subtraction expression");
157
158 uint32_t Value = Writer->getSymbolAddress(*A, Layout);
159 uint32_t Value2 = 0;
160 uint64_t SecAddr = Writer->getSectionAddress(A->getFragment()->getParent());
161 FixedValue += SecAddr;
162
163 if (const MCSymbolRefExpr *B = Target.getSymB()) {
164 const MCSymbol *SB = &B->getSymbol();
165
166 if (!SB->getFragment())
167 Asm.getContext().reportFatalError(Fixup.getLoc(),
168 "symbol '" + B->getSymbol().getName() +
169 "' can not be undefined in a subtraction expression");
170
171 // Select the appropriate difference relocation type.
172 Type = MachO::ARM_RELOC_HALF_SECTDIFF;
173 Value2 = Writer->getSymbolAddress(B->getSymbol(), Layout);
174 FixedValue -= Writer->getSectionAddress(SB->getFragment()->getParent());
175 }
176
177 // Relocations are written out in reverse order, so the PAIR comes first.
178 // ARM_RELOC_HALF and ARM_RELOC_HALF_SECTDIFF abuse the r_length field:
179 //
180 // For these two r_type relocations they always have a pair following them and
181 // the r_length bits are used differently. The encoding of the r_length is as
182 // follows:
183 // low bit of r_length:
184 // 0 - :lower16: for movw instructions
185 // 1 - :upper16: for movt instructions
186 // high bit of r_length:
187 // 0 - arm instructions
188 // 1 - thumb instructions
189 // the other half of the relocated expression is in the following pair
190 // relocation entry in the low 16 bits of r_address field.
191 unsigned ThumbBit = 0;
192 unsigned MovtBit = 0;
193 switch ((unsigned)Fixup.getKind()) {
194 default: break;
195 case ARM::fixup_arm_movt_hi16:
196 MovtBit = 1;
197 // The thumb bit shouldn't be set in the 'other-half' bit of the
198 // relocation, but it will be set in FixedValue if the base symbol
199 // is a thumb function. Clear it out here.
200 if (Asm.isThumbFunc(A))
201 FixedValue &= 0xfffffffe;
202 break;
203 case ARM::fixup_t2_movt_hi16:
204 if (Asm.isThumbFunc(A))
205 FixedValue &= 0xfffffffe;
206 MovtBit = 1;
207 // Fallthrough
208 case ARM::fixup_t2_movw_lo16:
209 ThumbBit = 1;
210 break;
211 }
212
213 if (Type == MachO::ARM_RELOC_HALF_SECTDIFF) {
214 uint32_t OtherHalf = MovtBit
215 ? (FixedValue & 0xffff) : ((FixedValue & 0xffff0000) >> 16);
216
217 MachO::any_relocation_info MRE;
218 MRE.r_word0 = ((OtherHalf << 0) |
219 (MachO::ARM_RELOC_PAIR << 24) |
220 (MovtBit << 28) |
221 (ThumbBit << 29) |
222 (IsPCRel << 30) |
223 MachO::R_SCATTERED);
224 MRE.r_word1 = Value2;
225 Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
226 }
227
228 MachO::any_relocation_info MRE;
229 MRE.r_word0 = ((FixupOffset << 0) |
230 (Type << 24) |
231 (MovtBit << 28) |
232 (ThumbBit << 29) |
233 (IsPCRel << 30) |
234 MachO::R_SCATTERED);
235 MRE.r_word1 = Value;
236 Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
237}
238
239void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
240 const MCAssembler &Asm,
241 const MCAsmLayout &Layout,
242 const MCFragment *Fragment,
243 const MCFixup &Fixup,
244 MCValue Target,
245 unsigned Type,
246 unsigned Log2Size,
247 uint64_t &FixedValue) {
248 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
249 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
250
251 // See <reloc.h>.
252 const MCSymbol *A = &Target.getSymA()->getSymbol();
253
254 if (!A->getFragment())
255 Asm.getContext().reportFatalError(Fixup.getLoc(),
256 "symbol '" + A->getName() +
257 "' can not be undefined in a subtraction expression");
258
259 uint32_t Value = Writer->getSymbolAddress(*A, Layout);
260 uint64_t SecAddr = Writer->getSectionAddress(A->getFragment()->getParent());
261 FixedValue += SecAddr;
262 uint32_t Value2 = 0;
263
264 if (const MCSymbolRefExpr *B = Target.getSymB()) {
265 assert(Type == MachO::ARM_RELOC_VANILLA && "invalid reloc for 2 symbols")((Type == MachO::ARM_RELOC_VANILLA && "invalid reloc for 2 symbols"
) ? static_cast<void> (0) : __assert_fail ("Type == MachO::ARM_RELOC_VANILLA && \"invalid reloc for 2 symbols\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn253036/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp"
, 265, __PRETTY_FUNCTION__))
;
266 const MCSymbol *SB = &B->getSymbol();
267
268 if (!SB->getFragment())
269 Asm.getContext().reportFatalError(Fixup.getLoc(),
270 "symbol '" + B->getSymbol().getName() +
271 "' can not be undefined in a subtraction expression");
272
273 // Select the appropriate difference relocation type.
274 Type = MachO::ARM_RELOC_SECTDIFF;
275 Value2 = Writer->getSymbolAddress(B->getSymbol(), Layout);
276 FixedValue -= Writer->getSectionAddress(SB->getFragment()->getParent());
277 }
278
279 // Relocations are written out in reverse order, so the PAIR comes first.
280 if (Type == MachO::ARM_RELOC_SECTDIFF ||
281 Type == MachO::ARM_RELOC_LOCAL_SECTDIFF) {
282 MachO::any_relocation_info MRE;
283 MRE.r_word0 = ((0 << 0) |
284 (MachO::ARM_RELOC_PAIR << 24) |
285 (Log2Size << 28) |
286 (IsPCRel << 30) |
287 MachO::R_SCATTERED);
288 MRE.r_word1 = Value2;
289 Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
290 }
291
292 MachO::any_relocation_info MRE;
293 MRE.r_word0 = ((FixupOffset << 0) |
294 (Type << 24) |
295 (Log2Size << 28) |
296 (IsPCRel << 30) |
297 MachO::R_SCATTERED);
298 MRE.r_word1 = Value;
299 Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
300}
301
302bool ARMMachObjectWriter::requiresExternRelocation(MachObjectWriter *Writer,
303 const MCAssembler &Asm,
304 const MCFragment &Fragment,
305 unsigned RelocType,
306 const MCSymbol &S,
307 uint64_t FixedValue) {
308 // Most cases can be identified purely from the symbol.
309 if (Writer->doesSymbolRequireExternRelocation(S))
310 return true;
311 int64_t Value = (int64_t)FixedValue; // The displacement is signed.
312 int64_t Range;
313 switch (RelocType) {
314 default:
315 return false;
316 case MachO::ARM_RELOC_BR24:
317 // PC pre-adjustment of 8 for these instructions.
318 Value -= 8;
319 // ARM BL/BLX has a 25-bit offset.
320 Range = 0x1ffffff;
321 break;
322 case MachO::ARM_THUMB_RELOC_BR22:
323 // PC pre-adjustment of 4 for these instructions.
324 Value -= 4;
325 // Thumb BL/BLX has a 24-bit offset.
326 Range = 0xffffff;
327 }
328 // BL/BLX also use external relocations when an internal relocation
329 // would result in the target being out of range. This gives the linker
330 // enough information to generate a branch island.
331 Value += Writer->getSectionAddress(&S.getSection());
332 Value -= Writer->getSectionAddress(Fragment.getParent());
333 // If the resultant value would be out of range for an internal relocation,
334 // use an external instead.
335 if (Value > Range || Value < -(Range + 1))
336 return true;
337 return false;
338}
339
340void ARMMachObjectWriter::recordRelocation(MachObjectWriter *Writer,
341 MCAssembler &Asm,
342 const MCAsmLayout &Layout,
343 const MCFragment *Fragment,
344 const MCFixup &Fixup, MCValue Target,
345 uint64_t &FixedValue) {
346 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
347 unsigned Log2Size;
348 unsigned RelocType = MachO::ARM_RELOC_VANILLA;
349 if (!getARMFixupKindMachOInfo(Fixup.getKind(), RelocType, Log2Size))
1
Taking false branch
350 // If we failed to get fixup kind info, it's because there's no legal
351 // relocation type for the fixup kind. This happens when it's a fixup that's
352 // expected to always be resolvable at assembly time and not have any
353 // relocations needed.
354 Asm.getContext().reportFatalError(Fixup.getLoc(),
355 "unsupported relocation on symbol");
356
357 // If this is a difference or a defined symbol plus an offset, then we need a
358 // scattered relocation entry. Differences always require scattered
359 // relocations.
360 if (Target.getSymB()) {
2
Taking false branch
361 if (RelocType == MachO::ARM_RELOC_HALF)
362 return RecordARMScatteredHalfRelocation(Writer, Asm, Layout, Fragment,
363 Fixup, Target, FixedValue);
364 return RecordARMScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
365 Target, RelocType, Log2Size,
366 FixedValue);
367 }
368
369 // Get the symbol data, if any.
370 const MCSymbol *A = nullptr;
3
'A' initialized to a null pointer value
371 if (Target.getSymA())
4
Taking false branch
372 A = &Target.getSymA()->getSymbol();
373
374 // FIXME: For other platforms, we need to use scattered relocations for
375 // internal relocations with offsets. If this is an internal relocation with
376 // an offset, it also needs a scattered relocation entry.
377 //
378 // Is this right for ARM?
379 uint32_t Offset = Target.getConstant();
380 if (IsPCRel && RelocType == MachO::ARM_RELOC_VANILLA)
381 Offset += 1 << Log2Size;
382 if (Offset && A && !Writer->doesSymbolRequireExternRelocation(*A))
383 return RecordARMScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
384 Target, RelocType, Log2Size,
385 FixedValue);
386
387 // See <reloc.h>.
388 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
389 unsigned Index = 0;
390 unsigned Type = 0;
391 const MCSymbol *RelSymbol = nullptr;
392
393 if (Target.isAbsolute()) { // constant
5
Taking false branch
394 // FIXME!
395 report_fatal_error("FIXME: relocations to absolute targets "
396 "not yet implemented");
397 } else {
398 // Resolve constant variables.
399 if (A->isVariable()) {
6
Called C++ object pointer is null
400 int64_t Res;
401 if (A->getVariableValue()->evaluateAsAbsolute(
402 Res, Layout, Writer->getSectionAddressMap())) {
403 FixedValue = Res;
404 return;
405 }
406 }
407
408 // Check whether we need an external or internal relocation.
409 if (requiresExternRelocation(Writer, Asm, *Fragment, RelocType, *A,
410 FixedValue)) {
411 RelSymbol = A;
412
413 // For external relocations, make sure to offset the fixup value to
414 // compensate for the addend of the symbol address, if it was
415 // undefined. This occurs with weak definitions, for example.
416 if (!A->isUndefined())
417 FixedValue -= Layout.getSymbolOffset(*A);
418 } else {
419 // The index is the section ordinal (1-based).
420 const MCSection &Sec = A->getSection();
421 Index = Sec.getOrdinal() + 1;
422 FixedValue += Writer->getSectionAddress(&Sec);
423 }
424 if (IsPCRel)
425 FixedValue -= Writer->getSectionAddress(Fragment->getParent());
426
427 // The type is determined by the fixup kind.
428 Type = RelocType;
429 }
430
431 // struct relocation_info (8 bytes)
432 MachO::any_relocation_info MRE;
433 MRE.r_word0 = FixupOffset;
434 MRE.r_word1 =
435 (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
436
437 // Even when it's not a scattered relocation, movw/movt always uses
438 // a PAIR relocation.
439 if (Type == MachO::ARM_RELOC_HALF) {
440 // The other-half value only gets populated for the movt and movw
441 // relocation entries.
442 uint32_t Value = 0;
443 switch ((unsigned)Fixup.getKind()) {
444 default: break;
445 case ARM::fixup_arm_movw_lo16:
446 case ARM::fixup_t2_movw_lo16:
447 Value = (FixedValue >> 16) & 0xffff;
448 break;
449 case ARM::fixup_arm_movt_hi16:
450 case ARM::fixup_t2_movt_hi16:
451 Value = FixedValue & 0xffff;
452 break;
453 }
454 MachO::any_relocation_info MREPair;
455 MREPair.r_word0 = Value;
456 MREPair.r_word1 = ((0xffffff << 0) |
457 (Log2Size << 25) |
458 (MachO::ARM_RELOC_PAIR << 28));
459
460 Writer->addRelocation(nullptr, Fragment->getParent(), MREPair);
461 }
462
463 Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
464}
465
466MCObjectWriter *llvm::createARMMachObjectWriter(raw_pwrite_stream &OS,
467 bool Is64Bit, uint32_t CPUType,
468 uint32_t CPUSubtype) {
469 return createMachObjectWriter(new ARMMachObjectWriter(Is64Bit,
470 CPUType,
471 CPUSubtype),
472 OS, /*IsLittleEndian=*/true);
473}