Bug Summary

File:lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
Location:line 402, 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/MCMachOSymbolFlags.h"
21#include "llvm/MC/MCMachObjectWriter.h"
22#include "llvm/MC/MCSection.h"
23#include "llvm/MC/MCValue.h"
24#include "llvm/Support/ErrorHandling.h"
25#include "llvm/Support/MachO.h"
26using namespace llvm;
27
28namespace {
29class ARMMachObjectWriter : public MCMachObjectTargetWriter {
30 void RecordARMScatteredRelocation(MachObjectWriter *Writer,
31 const MCAssembler &Asm,
32 const MCAsmLayout &Layout,
33 const MCFragment *Fragment,
34 const MCFixup &Fixup,
35 MCValue Target,
36 unsigned Type,
37 unsigned Log2Size,
38 uint64_t &FixedValue);
39 void RecordARMScatteredHalfRelocation(MachObjectWriter *Writer,
40 const MCAssembler &Asm,
41 const MCAsmLayout &Layout,
42 const MCFragment *Fragment,
43 const MCFixup &Fixup, MCValue Target,
44 uint64_t &FixedValue);
45
46 bool requiresExternRelocation(MachObjectWriter *Writer,
47 const MCAssembler &Asm,
48 const MCFragment &Fragment, unsigned RelocType,
49 const MCSymbol &S, uint64_t FixedValue);
50
51public:
52 ARMMachObjectWriter(bool Is64Bit, uint32_t CPUType,
53 uint32_t CPUSubtype)
54 : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
55 /*UseAggressiveSymbolFolding=*/true) {}
56
57 void RecordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
58 const MCAsmLayout &Layout, const MCFragment *Fragment,
59 const MCFixup &Fixup, MCValue Target,
60 uint64_t &FixedValue) override;
61};
62}
63
64static bool getARMFixupKindMachOInfo(unsigned Kind, unsigned &RelocType,
65 unsigned &Log2Size) {
66 RelocType = unsigned(MachO::ARM_RELOC_VANILLA);
67 Log2Size = ~0U;
68
69 switch (Kind) {
70 default:
71 return false;
72
73 case FK_Data_1:
74 Log2Size = llvm::Log2_32(1);
75 return true;
76 case FK_Data_2:
77 Log2Size = llvm::Log2_32(2);
78 return true;
79 case FK_Data_4:
80 Log2Size = llvm::Log2_32(4);
81 return true;
82 case FK_Data_8:
83 Log2Size = llvm::Log2_32(8);
84 return true;
85
86 // These fixups are expected to always be resolvable at assembly time and
87 // have no relocations supported.
88 case ARM::fixup_arm_ldst_pcrel_12:
89 case ARM::fixup_arm_pcrel_10:
90 case ARM::fixup_arm_adr_pcrel_12:
91 case ARM::fixup_arm_thumb_br:
92 return false;
93
94 // Handle 24-bit branch kinds.
95 case ARM::fixup_arm_condbranch:
96 case ARM::fixup_arm_uncondbranch:
97 case ARM::fixup_arm_uncondbl:
98 case ARM::fixup_arm_condbl:
99 case ARM::fixup_arm_blx:
100 RelocType = unsigned(MachO::ARM_RELOC_BR24);
101 // Report as 'long', even though that is not quite accurate.
102 Log2Size = llvm::Log2_32(4);
103 return true;
104
105 case ARM::fixup_t2_uncondbranch:
106 case ARM::fixup_arm_thumb_bl:
107 case ARM::fixup_arm_thumb_blx:
108 RelocType = unsigned(MachO::ARM_THUMB_RELOC_BR22);
109 Log2Size = llvm::Log2_32(4);
110 return true;
111
112 // For movw/movt r_type relocations they always have a pair following them and
113 // the r_length bits are used differently. The encoding of the r_length is as
114 // follows:
115 // low bit of r_length:
116 // 0 - :lower16: for movw instructions
117 // 1 - :upper16: for movt instructions
118 // high bit of r_length:
119 // 0 - arm instructions
120 // 1 - thumb instructions
121 case ARM::fixup_arm_movt_hi16:
122 RelocType = unsigned(MachO::ARM_RELOC_HALF);
123 Log2Size = 1;
124 return true;
125 case ARM::fixup_t2_movt_hi16:
126 RelocType = unsigned(MachO::ARM_RELOC_HALF);
127 Log2Size = 3;
128 return true;
129
130 case ARM::fixup_arm_movw_lo16:
131 RelocType = unsigned(MachO::ARM_RELOC_HALF);
132 Log2Size = 0;
133 return true;
134 case ARM::fixup_t2_movw_lo16:
135 RelocType = unsigned(MachO::ARM_RELOC_HALF);
136 Log2Size = 2;
137 return true;
138 }
139}
140
141void ARMMachObjectWriter::
142RecordARMScatteredHalfRelocation(MachObjectWriter *Writer,
143 const MCAssembler &Asm,
144 const MCAsmLayout &Layout,
145 const MCFragment *Fragment,
146 const MCFixup &Fixup,
147 MCValue Target,
148 uint64_t &FixedValue) {
149 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
150 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
151 unsigned Type = MachO::ARM_RELOC_HALF;
152
153 // See <reloc.h>.
154 const MCSymbol *A = &Target.getSymA()->getSymbol();
155
156 if (!A->getFragment())
157 Asm.getContext().reportFatalError(Fixup.getLoc(),
158 "symbol '" + A->getName() +
159 "' can not be undefined in a subtraction expression");
160
161 uint32_t Value = Writer->getSymbolAddress(*A, Layout);
162 uint32_t Value2 = 0;
163 uint64_t SecAddr = Writer->getSectionAddress(A->getFragment()->getParent());
164 FixedValue += SecAddr;
165
166 if (const MCSymbolRefExpr *B = Target.getSymB()) {
167 const MCSymbol *SB = &B->getSymbol();
168
169 if (!SB->getFragment())
170 Asm.getContext().reportFatalError(Fixup.getLoc(),
171 "symbol '" + B->getSymbol().getName() +
172 "' can not be undefined in a subtraction expression");
173
174 // Select the appropriate difference relocation type.
175 Type = MachO::ARM_RELOC_HALF_SECTDIFF;
176 Value2 = Writer->getSymbolAddress(B->getSymbol(), Layout);
177 FixedValue -= Writer->getSectionAddress(SB->getFragment()->getParent());
178 }
179
180 // Relocations are written out in reverse order, so the PAIR comes first.
181 // ARM_RELOC_HALF and ARM_RELOC_HALF_SECTDIFF abuse the r_length field:
182 //
183 // For these two r_type relocations they always have a pair following them and
184 // the r_length bits are used differently. The encoding of the r_length is as
185 // follows:
186 // low bit of r_length:
187 // 0 - :lower16: for movw instructions
188 // 1 - :upper16: for movt instructions
189 // high bit of r_length:
190 // 0 - arm instructions
191 // 1 - thumb instructions
192 // the other half of the relocated expression is in the following pair
193 // relocation entry in the low 16 bits of r_address field.
194 unsigned ThumbBit = 0;
195 unsigned MovtBit = 0;
196 switch ((unsigned)Fixup.getKind()) {
197 default: break;
198 case ARM::fixup_arm_movt_hi16:
199 MovtBit = 1;
200 // The thumb bit shouldn't be set in the 'other-half' bit of the
201 // relocation, but it will be set in FixedValue if the base symbol
202 // is a thumb function. Clear it out here.
203 if (Asm.isThumbFunc(A))
204 FixedValue &= 0xfffffffe;
205 break;
206 case ARM::fixup_t2_movt_hi16:
207 if (Asm.isThumbFunc(A))
208 FixedValue &= 0xfffffffe;
209 MovtBit = 1;
210 // Fallthrough
211 case ARM::fixup_t2_movw_lo16:
212 ThumbBit = 1;
213 break;
214 }
215
216 if (Type == MachO::ARM_RELOC_HALF_SECTDIFF) {
217 uint32_t OtherHalf = MovtBit
218 ? (FixedValue & 0xffff) : ((FixedValue & 0xffff0000) >> 16);
219
220 MachO::any_relocation_info MRE;
221 MRE.r_word0 = ((OtherHalf << 0) |
222 (MachO::ARM_RELOC_PAIR << 24) |
223 (MovtBit << 28) |
224 (ThumbBit << 29) |
225 (IsPCRel << 30) |
226 MachO::R_SCATTERED);
227 MRE.r_word1 = Value2;
228 Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
229 }
230
231 MachO::any_relocation_info MRE;
232 MRE.r_word0 = ((FixupOffset << 0) |
233 (Type << 24) |
234 (MovtBit << 28) |
235 (ThumbBit << 29) |
236 (IsPCRel << 30) |
237 MachO::R_SCATTERED);
238 MRE.r_word1 = Value;
239 Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
240}
241
242void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
243 const MCAssembler &Asm,
244 const MCAsmLayout &Layout,
245 const MCFragment *Fragment,
246 const MCFixup &Fixup,
247 MCValue Target,
248 unsigned Type,
249 unsigned Log2Size,
250 uint64_t &FixedValue) {
251 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
252 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
253
254 // See <reloc.h>.
255 const MCSymbol *A = &Target.getSymA()->getSymbol();
256
257 if (!A->getFragment())
258 Asm.getContext().reportFatalError(Fixup.getLoc(),
259 "symbol '" + A->getName() +
260 "' can not be undefined in a subtraction expression");
261
262 uint32_t Value = Writer->getSymbolAddress(*A, Layout);
263 uint64_t SecAddr = Writer->getSectionAddress(A->getFragment()->getParent());
264 FixedValue += SecAddr;
265 uint32_t Value2 = 0;
266
267 if (const MCSymbolRefExpr *B = Target.getSymB()) {
268 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-3.7~svn239079/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp"
, 268, __PRETTY_FUNCTION__))
;
269 const MCSymbol *SB = &B->getSymbol();
270
271 if (!SB->getFragment())
272 Asm.getContext().reportFatalError(Fixup.getLoc(),
273 "symbol '" + B->getSymbol().getName() +
274 "' can not be undefined in a subtraction expression");
275
276 // Select the appropriate difference relocation type.
277 Type = MachO::ARM_RELOC_SECTDIFF;
278 Value2 = Writer->getSymbolAddress(B->getSymbol(), Layout);
279 FixedValue -= Writer->getSectionAddress(SB->getFragment()->getParent());
280 }
281
282 // Relocations are written out in reverse order, so the PAIR comes first.
283 if (Type == MachO::ARM_RELOC_SECTDIFF ||
284 Type == MachO::ARM_RELOC_LOCAL_SECTDIFF) {
285 MachO::any_relocation_info MRE;
286 MRE.r_word0 = ((0 << 0) |
287 (MachO::ARM_RELOC_PAIR << 24) |
288 (Log2Size << 28) |
289 (IsPCRel << 30) |
290 MachO::R_SCATTERED);
291 MRE.r_word1 = Value2;
292 Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
293 }
294
295 MachO::any_relocation_info MRE;
296 MRE.r_word0 = ((FixupOffset << 0) |
297 (Type << 24) |
298 (Log2Size << 28) |
299 (IsPCRel << 30) |
300 MachO::R_SCATTERED);
301 MRE.r_word1 = Value;
302 Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
303}
304
305bool ARMMachObjectWriter::requiresExternRelocation(MachObjectWriter *Writer,
306 const MCAssembler &Asm,
307 const MCFragment &Fragment,
308 unsigned RelocType,
309 const MCSymbol &S,
310 uint64_t FixedValue) {
311 // Most cases can be identified purely from the symbol.
312 if (Writer->doesSymbolRequireExternRelocation(S))
313 return true;
314 int64_t Value = (int64_t)FixedValue; // The displacement is signed.
315 int64_t Range;
316 switch (RelocType) {
317 default:
318 return false;
319 case MachO::ARM_RELOC_BR24:
320 // PC pre-adjustment of 8 for these instructions.
321 Value -= 8;
322 // ARM BL/BLX has a 25-bit offset.
323 Range = 0x1ffffff;
324 break;
325 case MachO::ARM_THUMB_RELOC_BR22:
326 // PC pre-adjustment of 4 for these instructions.
327 Value -= 4;
328 // Thumb BL/BLX has a 24-bit offset.
329 Range = 0xffffff;
330 }
331 // BL/BLX also use external relocations when an internal relocation
332 // would result in the target being out of range. This gives the linker
333 // enough information to generate a branch island.
334 Value += Writer->getSectionAddress(&S.getSection());
335 Value -= Writer->getSectionAddress(Fragment.getParent());
336 // If the resultant value would be out of range for an internal relocation,
337 // use an external instead.
338 if (Value > Range || Value < -(Range + 1))
339 return true;
340 return false;
341}
342
343void ARMMachObjectWriter::RecordRelocation(MachObjectWriter *Writer,
344 MCAssembler &Asm,
345 const MCAsmLayout &Layout,
346 const MCFragment *Fragment,
347 const MCFixup &Fixup, MCValue Target,
348 uint64_t &FixedValue) {
349 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
350 unsigned Log2Size;
351 unsigned RelocType = MachO::ARM_RELOC_VANILLA;
352 if (!getARMFixupKindMachOInfo(Fixup.getKind(), RelocType, Log2Size))
1
Taking false branch
353 // If we failed to get fixup kind info, it's because there's no legal
354 // relocation type for the fixup kind. This happens when it's a fixup that's
355 // expected to always be resolvable at assembly time and not have any
356 // relocations needed.
357 Asm.getContext().reportFatalError(Fixup.getLoc(),
358 "unsupported relocation on symbol");
359
360 // If this is a difference or a defined symbol plus an offset, then we need a
361 // scattered relocation entry. Differences always require scattered
362 // relocations.
363 if (Target.getSymB()) {
2
Taking false branch
364 if (RelocType == MachO::ARM_RELOC_HALF)
365 return RecordARMScatteredHalfRelocation(Writer, Asm, Layout, Fragment,
366 Fixup, Target, FixedValue);
367 return RecordARMScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
368 Target, RelocType, Log2Size,
369 FixedValue);
370 }
371
372 // Get the symbol data, if any.
373 const MCSymbol *A = nullptr;
3
'A' initialized to a null pointer value
374 if (Target.getSymA())
4
Taking false branch
375 A = &Target.getSymA()->getSymbol();
376
377 // FIXME: For other platforms, we need to use scattered relocations for
378 // internal relocations with offsets. If this is an internal relocation with
379 // an offset, it also needs a scattered relocation entry.
380 //
381 // Is this right for ARM?
382 uint32_t Offset = Target.getConstant();
383 if (IsPCRel && RelocType == MachO::ARM_RELOC_VANILLA)
384 Offset += 1 << Log2Size;
385 if (Offset && A && !Writer->doesSymbolRequireExternRelocation(*A))
386 return RecordARMScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
387 Target, RelocType, Log2Size,
388 FixedValue);
389
390 // See <reloc.h>.
391 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
392 unsigned Index = 0;
393 unsigned Type = 0;
394 const MCSymbol *RelSymbol = nullptr;
395
396 if (Target.isAbsolute()) { // constant
5
Taking false branch
397 // FIXME!
398 report_fatal_error("FIXME: relocations to absolute targets "
399 "not yet implemented");
400 } else {
401 // Resolve constant variables.
402 if (A->isVariable()) {
6
Called C++ object pointer is null
403 int64_t Res;
404 if (A->getVariableValue()->evaluateAsAbsolute(
405 Res, Layout, Writer->getSectionAddressMap())) {
406 FixedValue = Res;
407 return;
408 }
409 }
410
411 // Check whether we need an external or internal relocation.
412 if (requiresExternRelocation(Writer, Asm, *Fragment, RelocType, *A,
413 FixedValue)) {
414 RelSymbol = A;
415
416 // For external relocations, make sure to offset the fixup value to
417 // compensate for the addend of the symbol address, if it was
418 // undefined. This occurs with weak definitions, for example.
419 if (!A->isUndefined())
420 FixedValue -= Layout.getSymbolOffset(*A);
421 } else {
422 // The index is the section ordinal (1-based).
423 const MCSection &Sec = A->getSection();
424 Index = Sec.getOrdinal() + 1;
425 FixedValue += Writer->getSectionAddress(&Sec);
426 }
427 if (IsPCRel)
428 FixedValue -= Writer->getSectionAddress(Fragment->getParent());
429
430 // The type is determined by the fixup kind.
431 Type = RelocType;
432 }
433
434 // struct relocation_info (8 bytes)
435 MachO::any_relocation_info MRE;
436 MRE.r_word0 = FixupOffset;
437 MRE.r_word1 =
438 (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
439
440 // Even when it's not a scattered relocation, movw/movt always uses
441 // a PAIR relocation.
442 if (Type == MachO::ARM_RELOC_HALF) {
443 // The other-half value only gets populated for the movt and movw
444 // relocation entries.
445 uint32_t Value = 0;
446 switch ((unsigned)Fixup.getKind()) {
447 default: break;
448 case ARM::fixup_arm_movw_lo16:
449 case ARM::fixup_t2_movw_lo16:
450 Value = (FixedValue >> 16) & 0xffff;
451 break;
452 case ARM::fixup_arm_movt_hi16:
453 case ARM::fixup_t2_movt_hi16:
454 Value = FixedValue & 0xffff;
455 break;
456 }
457 MachO::any_relocation_info MREPair;
458 MREPair.r_word0 = Value;
459 MREPair.r_word1 = ((0xffffff << 0) |
460 (Log2Size << 25) |
461 (MachO::ARM_RELOC_PAIR << 28));
462
463 Writer->addRelocation(nullptr, Fragment->getParent(), MREPair);
464 }
465
466 Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
467}
468
469MCObjectWriter *llvm::createARMMachObjectWriter(raw_pwrite_stream &OS,
470 bool Is64Bit, uint32_t CPUType,
471 uint32_t CPUSubtype) {
472 return createMachObjectWriter(new ARMMachObjectWriter(Is64Bit,
473 CPUType,
474 CPUSubtype),
475 OS, /*IsLittleEndian=*/true);
476}