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().reportError(Fixup.getLoc(),
155                       "symbol '" + A->getName() +
156                       "' can not be undefined in a subtraction expression");
157    return;
158  }
159
160  uint32_t Value = Writer->getSymbolAddress(*A, Layout);
161  uint32_t Value2 = 0;
162  uint64_t SecAddr = Writer->getSectionAddress(A->getFragment()->getParent());
163  FixedValue += SecAddr;
164
165  if (const MCSymbolRefExpr *B = Target.getSymB()) {
166    const MCSymbol *SB = &B->getSymbol();
167
168    if (!SB->getFragment()) {
169      Asm.getContext().reportError(Fixup.getLoc(),
170                         "symbol '" + B->getSymbol().getName() +
171                         "' can not be undefined in a subtraction expression");
172      return;
173    }
174
175    // Select the appropriate difference relocation type.
176    Type = MachO::ARM_RELOC_HALF_SECTDIFF;
177    Value2 = Writer->getSymbolAddress(B->getSymbol(), Layout);
178    FixedValue -= Writer->getSectionAddress(SB->getFragment()->getParent());
179  }
180
181  // Relocations are written out in reverse order, so the PAIR comes first.
182  // ARM_RELOC_HALF and ARM_RELOC_HALF_SECTDIFF abuse the r_length field:
183  //
184  // For these two r_type relocations they always have a pair following them and
185  // the r_length bits are used differently.  The encoding of the r_length is as
186  // follows:
187  //   low bit of r_length:
188  //      0 - :lower16: for movw instructions
189  //      1 - :upper16: for movt instructions
190  //   high bit of r_length:
191  //      0 - arm instructions
192  //      1 - thumb instructions
193  // the other half of the relocated expression is in the following pair
194  // relocation entry in the low 16 bits of r_address field.
195  unsigned ThumbBit = 0;
196  unsigned MovtBit = 0;
197  switch ((unsigned)Fixup.getKind()) {
198  default: break;
199  case ARM::fixup_arm_movt_hi16:
200    MovtBit = 1;
201    // The thumb bit shouldn't be set in the 'other-half' bit of the
202    // relocation, but it will be set in FixedValue if the base symbol
203    // is a thumb function. Clear it out here.
204    if (Asm.isThumbFunc(A))
205      FixedValue &= 0xfffffffe;
206    break;
207  case ARM::fixup_t2_movt_hi16:
208    if (Asm.isThumbFunc(A))
209      FixedValue &= 0xfffffffe;
210    MovtBit = 1;
211    // Fallthrough
212  case ARM::fixup_t2_movw_lo16:
213    ThumbBit = 1;
214    break;
215  }
216
217  if (Type == MachO::ARM_RELOC_HALF_SECTDIFF) {
218    uint32_t OtherHalf = MovtBit
219      ? (FixedValue & 0xffff) : ((FixedValue & 0xffff0000) >> 16);
220
221    MachO::any_relocation_info MRE;
222    MRE.r_word0 = ((OtherHalf             <<  0) |
223                   (MachO::ARM_RELOC_PAIR << 24) |
224                   (MovtBit               << 28) |
225                   (ThumbBit              << 29) |
226                   (IsPCRel               << 30) |
227                   MachO::R_SCATTERED);
228    MRE.r_word1 = Value2;
229    Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
230  }
231
232  MachO::any_relocation_info MRE;
233  MRE.r_word0 = ((FixupOffset <<  0) |
234                 (Type        << 24) |
235                 (MovtBit     << 28) |
236                 (ThumbBit    << 29) |
237                 (IsPCRel     << 30) |
238                 MachO::R_SCATTERED);
239  MRE.r_word1 = Value;
240  Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
241}
242
243void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
244                                                    const MCAssembler &Asm,
245                                                    const MCAsmLayout &Layout,
246                                                    const MCFragment *Fragment,
247                                                    const MCFixup &Fixup,
248                                                    MCValue Target,
249                                                    unsigned Type,
250                                                    unsigned Log2Size,
251                                                    uint64_t &FixedValue) {
252  uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
253  unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
254
255  // See <reloc.h>.
256  const MCSymbol *A = &Target.getSymA()->getSymbol();
257
258  if (!A->getFragment()) {
259    Asm.getContext().reportError(Fixup.getLoc(),
260                       "symbol '" + A->getName() +
261                       "' can not be undefined in a subtraction expression");
262    return;
263  }
264
265  uint32_t Value = Writer->getSymbolAddress(*A, Layout);
266  uint64_t SecAddr = Writer->getSectionAddress(A->getFragment()->getParent());
267  FixedValue += SecAddr;
268  uint32_t Value2 = 0;
269
270  if (const MCSymbolRefExpr *B = Target.getSymB()) {
271    assert(Type == MachO::ARM_RELOC_VANILLA && "invalid reloc for 2 symbols");
272    const MCSymbol *SB = &B->getSymbol();
273
274    if (!SB->getFragment()) {
275      Asm.getContext().reportError(Fixup.getLoc(),
276                         "symbol '" + B->getSymbol().getName() +
277                         "' can not be undefined in a subtraction expression");
278      return;
279    }
280
281    // Select the appropriate difference relocation type.
282    Type = MachO::ARM_RELOC_SECTDIFF;
283    Value2 = Writer->getSymbolAddress(B->getSymbol(), Layout);
284    FixedValue -= Writer->getSectionAddress(SB->getFragment()->getParent());
285  }
286
287  // Relocations are written out in reverse order, so the PAIR comes first.
288  if (Type == MachO::ARM_RELOC_SECTDIFF ||
289      Type == MachO::ARM_RELOC_LOCAL_SECTDIFF) {
290    MachO::any_relocation_info MRE;
291    MRE.r_word0 = ((0                     <<  0) |
292                   (MachO::ARM_RELOC_PAIR << 24) |
293                   (Log2Size              << 28) |
294                   (IsPCRel               << 30) |
295                   MachO::R_SCATTERED);
296    MRE.r_word1 = Value2;
297    Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
298  }
299
300  MachO::any_relocation_info MRE;
301  MRE.r_word0 = ((FixupOffset <<  0) |
302                 (Type        << 24) |
303                 (Log2Size    << 28) |
304                 (IsPCRel     << 30) |
305                 MachO::R_SCATTERED);
306  MRE.r_word1 = Value;
307  Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
308}
309
310bool ARMMachObjectWriter::requiresExternRelocation(MachObjectWriter *Writer,
311                                                   const MCAssembler &Asm,
312                                                   const MCFragment &Fragment,
313                                                   unsigned RelocType,
314                                                   const MCSymbol &S,
315                                                   uint64_t FixedValue) {
316  // Most cases can be identified purely from the symbol.
317  if (Writer->doesSymbolRequireExternRelocation(S))
318    return true;
319  int64_t Value = (int64_t)FixedValue;  // The displacement is signed.
320  int64_t Range;
321  switch (RelocType) {
322  default:
323    return false;
324  case MachO::ARM_RELOC_BR24:
325    // PC pre-adjustment of 8 for these instructions.
326    Value -= 8;
327    // ARM BL/BLX has a 25-bit offset.
328    Range = 0x1ffffff;
329    break;
330  case MachO::ARM_THUMB_RELOC_BR22:
331    // PC pre-adjustment of 4 for these instructions.
332    Value -= 4;
333    // Thumb BL/BLX has a 24-bit offset.
334    Range = 0xffffff;
335  }
336  // BL/BLX also use external relocations when an internal relocation
337  // would result in the target being out of range. This gives the linker
338  // enough information to generate a branch island.
339  Value += Writer->getSectionAddress(&S.getSection());
340  Value -= Writer->getSectionAddress(Fragment.getParent());
341  // If the resultant value would be out of range for an internal relocation,
342  // use an external instead.
343  if (Value > Range || Value < -(Range + 1))
344    return true;
345  return false;
346}
347
348void ARMMachObjectWriter::recordRelocation(MachObjectWriter *Writer,
349                                           MCAssembler &Asm,
350                                           const MCAsmLayout &Layout,
351                                           const MCFragment *Fragment,
352                                           const MCFixup &Fixup, MCValue Target,
353                                           uint64_t &FixedValue) {
354  unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
355  unsigned Log2Size;
356  unsigned RelocType = MachO::ARM_RELOC_VANILLA;
357  if (!getARMFixupKindMachOInfo(Fixup.getKind(), RelocType, Log2Size)) {
358    // If we failed to get fixup kind info, it's because there's no legal
359    // relocation type for the fixup kind. This happens when it's a fixup that's
360    // expected to always be resolvable at assembly time and not have any
361    // relocations needed.
362    Asm.getContext().reportError(Fixup.getLoc(),
363                                 "unsupported relocation on symbol");
364    return;
365  }
366
367  // If this is a difference or a defined symbol plus an offset, then we need a
368  // scattered relocation entry.  Differences always require scattered
369  // relocations.
370  if (Target.getSymB()) {
371    if (RelocType == MachO::ARM_RELOC_HALF)
372      return RecordARMScatteredHalfRelocation(Writer, Asm, Layout, Fragment,
373                                              Fixup, Target, FixedValue);
374    return RecordARMScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
375                                        Target, RelocType, Log2Size,
376                                        FixedValue);
377  }
378
379  // Get the symbol data, if any.
380  const MCSymbol *A = nullptr;
381  if (Target.getSymA())
382    A = &Target.getSymA()->getSymbol();
383
384  // FIXME: For other platforms, we need to use scattered relocations for
385  // internal relocations with offsets.  If this is an internal relocation with
386  // an offset, it also needs a scattered relocation entry.
387  //
388  // Is this right for ARM?
389  uint32_t Offset = Target.getConstant();
390  if (IsPCRel && RelocType == MachO::ARM_RELOC_VANILLA)
391    Offset += 1 << Log2Size;
392  if (Offset && A && !Writer->doesSymbolRequireExternRelocation(*A))
393    return RecordARMScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
394                                        Target, RelocType, Log2Size,
395                                        FixedValue);
396
397  // See <reloc.h>.
398  uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
399  unsigned Index = 0;
400  unsigned Type = 0;
401  const MCSymbol *RelSymbol = nullptr;
402
403  if (Target.isAbsolute()) { // constant
404    // FIXME!
405    report_fatal_error("FIXME: relocations to absolute targets "
406                       "not yet implemented");
407  } else {
408    // Resolve constant variables.
409    if (A->isVariable()) {
410      int64_t Res;
411      if (A->getVariableValue()->evaluateAsAbsolute(
412              Res, Layout, Writer->getSectionAddressMap())) {
413        FixedValue = Res;
414        return;
415      }
416    }
417
418    // Check whether we need an external or internal relocation.
419    if (requiresExternRelocation(Writer, Asm, *Fragment, RelocType, *A,
420                                 FixedValue)) {
421      RelSymbol = A;
422
423      // For external relocations, make sure to offset the fixup value to
424      // compensate for the addend of the symbol address, if it was
425      // undefined. This occurs with weak definitions, for example.
426      if (!A->isUndefined())
427        FixedValue -= Layout.getSymbolOffset(*A);
428    } else {
429      // The index is the section ordinal (1-based).
430      const MCSection &Sec = A->getSection();
431      Index = Sec.getOrdinal() + 1;
432      FixedValue += Writer->getSectionAddress(&Sec);
433    }
434    if (IsPCRel)
435      FixedValue -= Writer->getSectionAddress(Fragment->getParent());
436
437    // The type is determined by the fixup kind.
438    Type = RelocType;
439  }
440
441  // struct relocation_info (8 bytes)
442  MachO::any_relocation_info MRE;
443  MRE.r_word0 = FixupOffset;
444  MRE.r_word1 =
445      (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
446
447  // Even when it's not a scattered relocation, movw/movt always uses
448  // a PAIR relocation.
449  if (Type == MachO::ARM_RELOC_HALF) {
450    // The other-half value only gets populated for the movt and movw
451    // relocation entries.
452    uint32_t Value = 0;
453    switch ((unsigned)Fixup.getKind()) {
454    default: break;
455    case ARM::fixup_arm_movw_lo16:
456    case ARM::fixup_t2_movw_lo16:
457      Value = (FixedValue >> 16) & 0xffff;
458      break;
459    case ARM::fixup_arm_movt_hi16:
460    case ARM::fixup_t2_movt_hi16:
461      Value = FixedValue & 0xffff;
462      break;
463    }
464    MachO::any_relocation_info MREPair;
465    MREPair.r_word0 = Value;
466    MREPair.r_word1 = ((0xffffff              <<  0) |
467                       (Log2Size              << 25) |
468                       (MachO::ARM_RELOC_PAIR << 28));
469
470    Writer->addRelocation(nullptr, Fragment->getParent(), MREPair);
471  }
472
473  Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
474}
475
476MCObjectWriter *llvm::createARMMachObjectWriter(raw_pwrite_stream &OS,
477                                                bool Is64Bit, uint32_t CPUType,
478                                                uint32_t CPUSubtype) {
479  return createMachObjectWriter(new ARMMachObjectWriter(Is64Bit,
480                                                        CPUType,
481                                                        CPUSubtype),
482                                OS, /*IsLittleEndian=*/true);
483}
484