1 //===-- X86MachObjectWriter.cpp - X86 Mach-O Writer -----------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #include "MCTargetDesc/X86FixupKinds.h"
10 #include "MCTargetDesc/X86MCTargetDesc.h"
11 #include "llvm/ADT/Twine.h"
12 #include "llvm/BinaryFormat/MachO.h"
13 #include "llvm/MC/MCAsmInfo.h"
14 #include "llvm/MC/MCAsmInfoDarwin.h"
15 #include "llvm/MC/MCAssembler.h"
16 #include "llvm/MC/MCContext.h"
17 #include "llvm/MC/MCMachObjectWriter.h"
18 #include "llvm/MC/MCSectionMachO.h"
19 #include "llvm/MC/MCValue.h"
20 #include "llvm/Support/ErrorHandling.h"
21 #include "llvm/Support/Format.h"
22
23 using namespace llvm;
24
25 namespace {
26 class X86MachObjectWriter : public MCMachObjectTargetWriter {
27 bool recordScatteredRelocation(MachObjectWriter *Writer,
28 const MCAssembler &Asm,
29 const MCFragment *Fragment,
30 const MCFixup &Fixup,
31 MCValue Target,
32 unsigned Log2Size,
33 uint64_t &FixedValue);
34 void recordTLVPRelocation(MachObjectWriter *Writer,
35 const MCAssembler &Asm,
36 const MCFragment *Fragment,
37 const MCFixup &Fixup,
38 MCValue Target,
39 uint64_t &FixedValue);
40
41 void RecordX86Relocation(MachObjectWriter *Writer,
42 const MCAssembler &Asm,
43 const MCFragment *Fragment,
44 const MCFixup &Fixup,
45 MCValue Target,
46 uint64_t &FixedValue);
47 void RecordX86_64Relocation(MachObjectWriter *Writer, MCAssembler &Asm,
48 const MCFragment *Fragment, const MCFixup &Fixup,
49 MCValue Target, uint64_t &FixedValue);
50
51 public:
X86MachObjectWriter(bool Is64Bit,uint32_t CPUType,uint32_t CPUSubtype)52 X86MachObjectWriter(bool Is64Bit, uint32_t CPUType, uint32_t CPUSubtype)
53 : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype) {}
54
recordRelocation(MachObjectWriter * Writer,MCAssembler & Asm,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,uint64_t & FixedValue)55 void recordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
56 const MCFragment *Fragment, const MCFixup &Fixup,
57 MCValue Target, uint64_t &FixedValue) override {
58 if (Writer->is64Bit())
59 RecordX86_64Relocation(Writer, Asm, Fragment, Fixup, Target, FixedValue);
60 else
61 RecordX86Relocation(Writer, Asm, Fragment, Fixup, Target, FixedValue);
62 }
63 };
64 } // namespace
65
isFixupKindRIPRel(unsigned Kind)66 static bool isFixupKindRIPRel(unsigned Kind) {
67 return Kind == X86::reloc_riprel_4byte ||
68 Kind == X86::reloc_riprel_4byte_movq_load ||
69 Kind == X86::reloc_riprel_4byte_relax ||
70 Kind == X86::reloc_riprel_4byte_relax_rex;
71 }
72
getFixupKindLog2Size(unsigned Kind)73 static unsigned getFixupKindLog2Size(unsigned Kind) {
74 switch (Kind) {
75 default:
76 llvm_unreachable("invalid fixup kind!");
77 case FK_PCRel_1:
78 case FK_Data_1: return 0;
79 case FK_PCRel_2:
80 case FK_Data_2: return 1;
81 case FK_PCRel_4:
82 // FIXME: Remove these!!!
83 case X86::reloc_riprel_4byte:
84 case X86::reloc_riprel_4byte_relax:
85 case X86::reloc_riprel_4byte_relax_rex:
86 case X86::reloc_riprel_4byte_movq_load:
87 case X86::reloc_signed_4byte:
88 case X86::reloc_signed_4byte_relax:
89 case X86::reloc_branch_4byte_pcrel:
90 case FK_Data_4: return 2;
91 case FK_Data_8: return 3;
92 }
93 }
94
RecordX86_64Relocation(MachObjectWriter * Writer,MCAssembler & Asm,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,uint64_t & FixedValue)95 void X86MachObjectWriter::RecordX86_64Relocation(
96 MachObjectWriter *Writer, MCAssembler &Asm, const MCFragment *Fragment,
97 const MCFixup &Fixup, MCValue Target, uint64_t &FixedValue) {
98 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
99 unsigned IsRIPRel = isFixupKindRIPRel(Fixup.getKind());
100 unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
101
102 // See <reloc.h>.
103 uint32_t FixupOffset = Asm.getFragmentOffset(*Fragment) + Fixup.getOffset();
104 uint32_t FixupAddress =
105 Writer->getFragmentAddress(Asm, Fragment) + Fixup.getOffset();
106 int64_t Value = 0;
107 unsigned Index = 0;
108 unsigned IsExtern = 0;
109 unsigned Type = 0;
110 const MCSymbol *RelSymbol = nullptr;
111
112 Value = Target.getConstant();
113
114 if (IsPCRel) {
115 // Compensate for the relocation offset, Darwin x86_64 relocations only have
116 // the addend and appear to have attempted to define it to be the actual
117 // expression addend without the PCrel bias. However, instructions with data
118 // following the relocation are not accommodated for (see comment below
119 // regarding SIGNED{1,2,4}), so it isn't exactly that either.
120 Value += 1LL << Log2Size;
121 }
122
123 if (Target.isAbsolute()) { // constant
124 // SymbolNum of 0 indicates the absolute section.
125 Type = MachO::X86_64_RELOC_UNSIGNED;
126
127 // FIXME: I believe this is broken, I don't think the linker can understand
128 // it. I think it would require a local relocation, but I'm not sure if that
129 // would work either. The official way to get an absolute PCrel relocation
130 // is to use an absolute symbol (which we don't support yet).
131 if (IsPCRel) {
132 IsExtern = 1;
133 Type = MachO::X86_64_RELOC_BRANCH;
134 }
135 } else if (Target.getSymB()) { // A - B + constant
136 const MCSymbol *A = &Target.getSymA()->getSymbol();
137 if (A->isTemporary())
138 A = &Writer->findAliasedSymbol(*A);
139 const MCSymbol *A_Base = Writer->getAtom(*A);
140
141 const MCSymbol *B = &Target.getSymB()->getSymbol();
142 if (B->isTemporary())
143 B = &Writer->findAliasedSymbol(*B);
144 const MCSymbol *B_Base = Writer->getAtom(*B);
145
146 // Neither symbol can be modified.
147 if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None) {
148 Asm.getContext().reportError(Fixup.getLoc(),
149 "unsupported relocation of modified symbol");
150 return;
151 }
152
153 // We don't support PCrel relocations of differences. Darwin 'as' doesn't
154 // implement most of these correctly.
155 if (IsPCRel) {
156 Asm.getContext().reportError(
157 Fixup.getLoc(), "unsupported pc-relative relocation of difference");
158 return;
159 }
160
161 // The support for the situation where one or both of the symbols would
162 // require a local relocation is handled just like if the symbols were
163 // external. This is certainly used in the case of debug sections where the
164 // section has only temporary symbols and thus the symbols don't have base
165 // symbols. This is encoded using the section ordinal and non-extern
166 // relocation entries.
167
168 // Darwin 'as' doesn't emit correct relocations for this (it ends up with a
169 // single SIGNED relocation); reject it for now. Except the case where both
170 // symbols don't have a base, equal but both NULL.
171 if (A_Base == B_Base && A_Base) {
172 Asm.getContext().reportError(
173 Fixup.getLoc(), "unsupported relocation with identical base");
174 return;
175 }
176
177 // A subtraction expression where either symbol is undefined is a
178 // non-relocatable expression.
179 if (A->isUndefined() || B->isUndefined()) {
180 StringRef Name = A->isUndefined() ? A->getName() : B->getName();
181 Asm.getContext().reportError(Fixup.getLoc(),
182 "unsupported relocation with subtraction expression, symbol '" +
183 Name + "' can not be undefined in a subtraction expression");
184 return;
185 }
186
187 Value += Writer->getSymbolAddress(*A, Asm) -
188 (!A_Base ? 0 : Writer->getSymbolAddress(*A_Base, Asm));
189 Value -= Writer->getSymbolAddress(*B, Asm) -
190 (!B_Base ? 0 : Writer->getSymbolAddress(*B_Base, Asm));
191
192 if (!A_Base)
193 Index = A->getFragment()->getParent()->getOrdinal() + 1;
194 Type = MachO::X86_64_RELOC_UNSIGNED;
195
196 MachO::any_relocation_info MRE;
197 MRE.r_word0 = FixupOffset;
198 MRE.r_word1 =
199 (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
200 Writer->addRelocation(A_Base, Fragment->getParent(), MRE);
201
202 if (B_Base)
203 RelSymbol = B_Base;
204 else
205 Index = B->getFragment()->getParent()->getOrdinal() + 1;
206 Type = MachO::X86_64_RELOC_SUBTRACTOR;
207 } else {
208 const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
209 if (Symbol->isTemporary() && Value) {
210 const MCSection &Sec = Symbol->getSection();
211 if (!MCAsmInfoDarwin::isSectionAtomizableBySymbols(Sec))
212 Symbol->setUsedInReloc();
213 }
214 RelSymbol = Writer->getAtom(*Symbol);
215
216 // Relocations inside debug sections always use local relocations when
217 // possible. This seems to be done because the debugger doesn't fully
218 // understand x86_64 relocation entries, and expects to find values that
219 // have already been fixed up.
220 if (Symbol->isInSection()) {
221 const MCSectionMachO &Section =
222 static_cast<const MCSectionMachO &>(*Fragment->getParent());
223 if (Section.hasAttribute(MachO::S_ATTR_DEBUG))
224 RelSymbol = nullptr;
225 }
226
227 // x86_64 almost always uses external relocations, except when there is no
228 // symbol to use as a base address (a local symbol with no preceding
229 // non-local symbol).
230 if (RelSymbol) {
231 // Add the local offset, if needed.
232 if (RelSymbol != Symbol)
233 Value += Asm.getSymbolOffset(*Symbol) - Asm.getSymbolOffset(*RelSymbol);
234 } else if (Symbol->isInSection() && !Symbol->isVariable()) {
235 // The index is the section ordinal (1-based).
236 Index = Symbol->getFragment()->getParent()->getOrdinal() + 1;
237 Value += Writer->getSymbolAddress(*Symbol, Asm);
238
239 if (IsPCRel)
240 Value -= FixupAddress + (1 << Log2Size);
241 } else if (Symbol->isVariable()) {
242 const MCExpr *Value = Symbol->getVariableValue();
243 int64_t Res;
244 bool isAbs =
245 Value->evaluateAsAbsolute(Res, Asm, Writer->getSectionAddressMap());
246 if (isAbs) {
247 FixedValue = Res;
248 return;
249 } else {
250 Asm.getContext().reportError(Fixup.getLoc(),
251 "unsupported relocation of variable '" +
252 Symbol->getName() + "'");
253 return;
254 }
255 } else {
256 Asm.getContext().reportError(
257 Fixup.getLoc(), "unsupported relocation of undefined symbol '" +
258 Symbol->getName() + "'");
259 return;
260 }
261
262 MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
263 if (IsPCRel) {
264 if (IsRIPRel) {
265 if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
266 // x86_64 distinguishes movq foo@GOTPCREL so that the linker can
267 // rewrite the movq to an leaq at link time if the symbol ends up in
268 // the same linkage unit.
269 if (Fixup.getTargetKind() == X86::reloc_riprel_4byte_movq_load)
270 Type = MachO::X86_64_RELOC_GOT_LOAD;
271 else
272 Type = MachO::X86_64_RELOC_GOT;
273 } else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
274 Type = MachO::X86_64_RELOC_TLV;
275 } else if (Modifier != MCSymbolRefExpr::VK_None) {
276 Asm.getContext().reportError(
277 Fixup.getLoc(), "unsupported symbol modifier in relocation");
278 return;
279 } else {
280 Type = MachO::X86_64_RELOC_SIGNED;
281
282 // The Darwin x86_64 relocation format has a problem where it cannot
283 // encode an address (L<foo> + <constant>) which is outside the atom
284 // containing L<foo>. Generally, this shouldn't occur but it does
285 // happen when we have a RIPrel instruction with data following the
286 // relocation entry (e.g., movb $012, L0(%rip)). Even with the PCrel
287 // adjustment Darwin x86_64 uses, the offset is still negative and the
288 // linker has no way to recognize this.
289 //
290 // To work around this, Darwin uses several special relocation types
291 // to indicate the offsets. However, the specification or
292 // implementation of these seems to also be incomplete; they should
293 // adjust the addend as well based on the actual encoded instruction
294 // (the additional bias), but instead appear to just look at the final
295 // offset.
296 switch (-(Target.getConstant() + (1LL << Log2Size))) {
297 case 1: Type = MachO::X86_64_RELOC_SIGNED_1; break;
298 case 2: Type = MachO::X86_64_RELOC_SIGNED_2; break;
299 case 4: Type = MachO::X86_64_RELOC_SIGNED_4; break;
300 }
301 }
302 } else {
303 if (Modifier != MCSymbolRefExpr::VK_None) {
304 Asm.getContext().reportError(
305 Fixup.getLoc(),
306 "unsupported symbol modifier in branch relocation");
307 return;
308 }
309
310 Type = MachO::X86_64_RELOC_BRANCH;
311 }
312 } else {
313 if (Modifier == MCSymbolRefExpr::VK_GOT) {
314 Type = MachO::X86_64_RELOC_GOT;
315 } else if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
316 // GOTPCREL is allowed as a modifier on non-PCrel instructions, in which
317 // case all we do is set the PCrel bit in the relocation entry; this is
318 // used with exception handling, for example. The source is required to
319 // include any necessary offset directly.
320 Type = MachO::X86_64_RELOC_GOT;
321 IsPCRel = 1;
322 } else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
323 Asm.getContext().reportError(
324 Fixup.getLoc(), "TLVP symbol modifier should have been rip-rel");
325 return;
326 } else if (Modifier != MCSymbolRefExpr::VK_None) {
327 Asm.getContext().reportError(
328 Fixup.getLoc(), "unsupported symbol modifier in relocation");
329 return;
330 } else {
331 Type = MachO::X86_64_RELOC_UNSIGNED;
332 if (Fixup.getTargetKind() == X86::reloc_signed_4byte) {
333 Asm.getContext().reportError(
334 Fixup.getLoc(),
335 "32-bit absolute addressing is not supported in 64-bit mode");
336 return;
337 }
338 }
339 }
340 }
341
342 // x86_64 always writes custom values into the fixups.
343 FixedValue = Value;
344
345 // struct relocation_info (8 bytes)
346 MachO::any_relocation_info MRE;
347 MRE.r_word0 = FixupOffset;
348 MRE.r_word1 = (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
349 (IsExtern << 27) | (Type << 28);
350 Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
351 }
352
recordScatteredRelocation(MachObjectWriter * Writer,const MCAssembler & Asm,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,unsigned Log2Size,uint64_t & FixedValue)353 bool X86MachObjectWriter::recordScatteredRelocation(MachObjectWriter *Writer,
354 const MCAssembler &Asm,
355 const MCFragment *Fragment,
356 const MCFixup &Fixup,
357 MCValue Target,
358 unsigned Log2Size,
359 uint64_t &FixedValue) {
360 uint64_t OriginalFixedValue = FixedValue;
361 uint32_t FixupOffset = Asm.getFragmentOffset(*Fragment) + Fixup.getOffset();
362 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
363 unsigned Type = MachO::GENERIC_RELOC_VANILLA;
364
365 // See <reloc.h>.
366 const MCSymbol *A = &Target.getSymA()->getSymbol();
367
368 if (!A->getFragment()) {
369 Asm.getContext().reportError(
370 Fixup.getLoc(),
371 "symbol '" + A->getName() +
372 "' can not be undefined in a subtraction expression");
373 return false;
374 }
375
376 uint32_t Value = Writer->getSymbolAddress(*A, Asm);
377 uint64_t SecAddr = Writer->getSectionAddress(A->getFragment()->getParent());
378 FixedValue += SecAddr;
379 uint32_t Value2 = 0;
380
381 if (const MCSymbolRefExpr *B = Target.getSymB()) {
382 const MCSymbol *SB = &B->getSymbol();
383
384 if (!SB->getFragment()) {
385 Asm.getContext().reportError(
386 Fixup.getLoc(),
387 "symbol '" + SB->getName() +
388 "' can not be undefined in a subtraction expression");
389 return false;
390 }
391
392 // Select the appropriate difference relocation type.
393 //
394 // Note that there is no longer any semantic difference between these two
395 // relocation types from the linkers point of view, this is done solely for
396 // pedantic compatibility with 'as'.
397 Type = A->isExternal() ? (unsigned)MachO::GENERIC_RELOC_SECTDIFF
398 : (unsigned)MachO::GENERIC_RELOC_LOCAL_SECTDIFF;
399 Value2 = Writer->getSymbolAddress(*SB, Asm);
400 FixedValue -= Writer->getSectionAddress(SB->getFragment()->getParent());
401 }
402
403 // Relocations are written out in reverse order, so the PAIR comes first.
404 if (Type == MachO::GENERIC_RELOC_SECTDIFF ||
405 Type == MachO::GENERIC_RELOC_LOCAL_SECTDIFF) {
406 // If the offset is too large to fit in a scattered relocation,
407 // we're hosed. It's an unfortunate limitation of the MachO format.
408 if (FixupOffset > 0xffffff) {
409 char Buffer[32];
410 format("0x%x", FixupOffset).print(Buffer, sizeof(Buffer));
411 Asm.getContext().reportError(Fixup.getLoc(),
412 Twine("Section too large, can't encode "
413 "r_address (") + Buffer +
414 ") into 24 bits of scattered "
415 "relocation entry.");
416 return false;
417 }
418
419 MachO::any_relocation_info MRE;
420 MRE.r_word0 = ((0 << 0) | // r_address
421 (MachO::GENERIC_RELOC_PAIR << 24) | // r_type
422 (Log2Size << 28) |
423 (IsPCRel << 30) |
424 MachO::R_SCATTERED);
425 MRE.r_word1 = Value2;
426 Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
427 } else {
428 // If the offset is more than 24-bits, it won't fit in a scattered
429 // relocation offset field, so we fall back to using a non-scattered
430 // relocation. This is a bit risky, as if the offset reaches out of
431 // the block and the linker is doing scattered loading on this
432 // symbol, things can go badly.
433 //
434 // Required for 'as' compatibility.
435 if (FixupOffset > 0xffffff) {
436 FixedValue = OriginalFixedValue;
437 return false;
438 }
439 }
440
441 MachO::any_relocation_info MRE;
442 MRE.r_word0 = ((FixupOffset << 0) |
443 (Type << 24) |
444 (Log2Size << 28) |
445 (IsPCRel << 30) |
446 MachO::R_SCATTERED);
447 MRE.r_word1 = Value;
448 Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
449 return true;
450 }
451
recordTLVPRelocation(MachObjectWriter * Writer,const MCAssembler & Asm,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,uint64_t & FixedValue)452 void X86MachObjectWriter::recordTLVPRelocation(MachObjectWriter *Writer,
453 const MCAssembler &Asm,
454 const MCFragment *Fragment,
455 const MCFixup &Fixup,
456 MCValue Target,
457 uint64_t &FixedValue) {
458 const MCSymbolRefExpr *SymA = Target.getSymA();
459 assert(SymA->getKind() == MCSymbolRefExpr::VK_TLVP && !is64Bit() &&
460 "Should only be called with a 32-bit TLVP relocation!");
461
462 unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
463 uint32_t Value = Asm.getFragmentOffset(*Fragment) + Fixup.getOffset();
464 unsigned IsPCRel = 0;
465
466 // We're only going to have a second symbol in pic mode and it'll be a
467 // subtraction from the picbase. For 32-bit pic the addend is the difference
468 // between the picbase and the next address. For 32-bit static the addend is
469 // zero.
470 if (auto *SymB = Target.getSymB()) {
471 // If this is a subtraction then we're pcrel.
472 uint32_t FixupAddress =
473 Writer->getFragmentAddress(Asm, Fragment) + Fixup.getOffset();
474 IsPCRel = 1;
475 FixedValue = FixupAddress -
476 Writer->getSymbolAddress(SymB->getSymbol(), Asm) +
477 Target.getConstant();
478 FixedValue += 1ULL << Log2Size;
479 } else {
480 FixedValue = 0;
481 }
482
483 // struct relocation_info (8 bytes)
484 MachO::any_relocation_info MRE;
485 MRE.r_word0 = Value;
486 MRE.r_word1 =
487 (IsPCRel << 24) | (Log2Size << 25) | (MachO::GENERIC_RELOC_TLV << 28);
488 Writer->addRelocation(&SymA->getSymbol(), Fragment->getParent(), MRE);
489 }
490
RecordX86Relocation(MachObjectWriter * Writer,const MCAssembler & Asm,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,uint64_t & FixedValue)491 void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
492 const MCAssembler &Asm,
493 const MCFragment *Fragment,
494 const MCFixup &Fixup,
495 MCValue Target,
496 uint64_t &FixedValue) {
497 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
498 unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
499
500 // If this is a 32-bit TLVP reloc it's handled a bit differently.
501 if (Target.getSymA() &&
502 Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP) {
503 recordTLVPRelocation(Writer, Asm, Fragment, Fixup, Target, FixedValue);
504 return;
505 }
506
507 // If this is a difference or a defined symbol plus an offset, then we need a
508 // scattered relocation entry. Differences always require scattered
509 // relocations.
510 if (Target.getSymB()) {
511 recordScatteredRelocation(Writer, Asm, Fragment, Fixup, Target, Log2Size,
512 FixedValue);
513 return;
514 }
515
516 // Get the symbol data, if any.
517 const MCSymbol *A = nullptr;
518 if (Target.getSymA())
519 A = &Target.getSymA()->getSymbol();
520
521 // If this is an internal relocation with an offset, it also needs a scattered
522 // relocation entry.
523 uint32_t Offset = Target.getConstant();
524 if (IsPCRel)
525 Offset += 1 << Log2Size;
526
527 // Try to record the scattered relocation if needed. Fall back to non
528 // scattered if necessary (see comments in recordScatteredRelocation()
529 // for details).
530 if (Offset && A && !Writer->doesSymbolRequireExternRelocation(*A) &&
531 recordScatteredRelocation(Writer, Asm, Fragment, Fixup, Target, Log2Size,
532 FixedValue))
533 return;
534
535 // See <reloc.h>.
536 uint32_t FixupOffset = Asm.getFragmentOffset(*Fragment) + Fixup.getOffset();
537 unsigned Index = 0;
538 unsigned Type = 0;
539 const MCSymbol *RelSymbol = nullptr;
540
541 if (Target.isAbsolute()) { // constant
542 // SymbolNum of 0 indicates the absolute section.
543 //
544 // FIXME: Currently, these are never generated (see code below). I cannot
545 // find a case where they are actually emitted.
546 Type = MachO::GENERIC_RELOC_VANILLA;
547 } else {
548 assert(A && "Unknown symbol data");
549
550 // Resolve constant variables.
551 if (A->isVariable()) {
552 int64_t Res;
553 if (A->getVariableValue()->evaluateAsAbsolute(
554 Res, Asm, Writer->getSectionAddressMap())) {
555 FixedValue = Res;
556 return;
557 }
558 }
559
560 // Check whether we need an external or internal relocation.
561 if (Writer->doesSymbolRequireExternRelocation(*A)) {
562 RelSymbol = A;
563 // For external relocations, make sure to offset the fixup value to
564 // compensate for the addend of the symbol address, if it was
565 // undefined. This occurs with weak definitions, for example.
566 if (!A->isUndefined())
567 FixedValue -= Asm.getSymbolOffset(*A);
568 } else {
569 // The index is the section ordinal (1-based).
570 const MCSection &Sec = A->getSection();
571 Index = Sec.getOrdinal() + 1;
572 FixedValue += Writer->getSectionAddress(&Sec);
573 }
574 if (IsPCRel)
575 FixedValue -= Writer->getSectionAddress(Fragment->getParent());
576
577 Type = MachO::GENERIC_RELOC_VANILLA;
578 }
579
580 // struct relocation_info (8 bytes)
581 MachO::any_relocation_info MRE;
582 MRE.r_word0 = FixupOffset;
583 MRE.r_word1 =
584 (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
585 Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
586 }
587
588 std::unique_ptr<MCObjectTargetWriter>
createX86MachObjectWriter(bool Is64Bit,uint32_t CPUType,uint32_t CPUSubtype)589 llvm::createX86MachObjectWriter(bool Is64Bit, uint32_t CPUType,
590 uint32_t CPUSubtype) {
591 return std::make_unique<X86MachObjectWriter>(Is64Bit, CPUType, CPUSubtype);
592 }
593