ARMMachObjectWriter.cpp revision 577b09155f9a6fa38e5a7918da9701e120b3642f 
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/ARMBaseInfo.h"
11#include "MCTargetDesc/ARMFixupKinds.h"
12#include "llvm/ADT/Twine.h"
13#include "llvm/MC/MCAssembler.h"
14#include "llvm/MC/MCAsmLayout.h"
15#include "llvm/MC/MCMachObjectWriter.h"
16#include "llvm/MC/MCExpr.h"
17#include "llvm/MC/MCFixup.h"
18#include "llvm/MC/MCFixupKindInfo.h"
19#include "llvm/MC/MCMachOSymbolFlags.h"
20#include "llvm/MC/MCValue.h"
21#include "llvm/Object/MachOFormat.h"
22#include "llvm/Support/ErrorHandling.h"
23using namespace llvm;
24using namespace llvm::object;
25
26namespace {
27class ARMMachObjectWriter : public MCMachObjectTargetWriter {
28  void RecordARMScatteredRelocation(MachObjectWriter *Writer,
29                                    const MCAssembler &Asm,
30                                    const MCAsmLayout &Layout,
31                                    const MCFragment *Fragment,
32                                    const MCFixup &Fixup,
33                                    MCValue Target,
34                                    unsigned Log2Size,
35                                    uint64_t &FixedValue);
36  void RecordARMMovwMovtRelocation(MachObjectWriter *Writer,
37                                   const MCAssembler &Asm,
38                                   const MCAsmLayout &Layout,
39                                   const MCFragment *Fragment,
40                                   const MCFixup &Fixup, MCValue Target,
41                                   uint64_t &FixedValue);
42
43public:
44  ARMMachObjectWriter(bool Is64Bit, uint32_t CPUType,
45                      uint32_t CPUSubtype)
46    : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
47                               /*UseAggressiveSymbolFolding=*/true) {}
48
49  void RecordRelocation(MachObjectWriter *Writer,
50                        const MCAssembler &Asm, const MCAsmLayout &Layout,
51                        const MCFragment *Fragment, const MCFixup &Fixup,
52                        MCValue Target, uint64_t &FixedValue);
53};
54}
55
56static bool getARMFixupKindMachOInfo(unsigned Kind, unsigned &RelocType,
57                              unsigned &Log2Size) {
58  RelocType = unsigned(macho::RIT_Vanilla);
59  Log2Size = ~0U;
60
61  switch (Kind) {
62  default:
63    return false;
64
65  case ARM::fixup_t2_condbranch:
66    assert(0);
67    return false;
68  case FK_Data_1:
69    Log2Size = llvm::Log2_32(1);
70    return true;
71  case FK_Data_2:
72    Log2Size = llvm::Log2_32(2);
73    return true;
74  case FK_Data_4:
75    Log2Size = llvm::Log2_32(4);
76    return true;
77  case FK_Data_8:
78    Log2Size = llvm::Log2_32(8);
79    return true;
80
81    // Handle 24-bit branch kinds.
82  case ARM::fixup_arm_ldst_pcrel_12:
83  case ARM::fixup_arm_pcrel_10:
84  case ARM::fixup_arm_adr_pcrel_12:
85  case ARM::fixup_arm_condbranch:
86  case ARM::fixup_arm_uncondbranch:
87    RelocType = unsigned(macho::RIT_ARM_Branch24Bit);
88    // Report as 'long', even though that is not quite accurate.
89    Log2Size = llvm::Log2_32(4);
90    return true;
91
92    // Handle Thumb branches.
93  case ARM::fixup_arm_thumb_br:
94    RelocType = unsigned(macho::RIT_ARM_ThumbBranch22Bit);
95    Log2Size = llvm::Log2_32(2);
96    return true;
97
98  case ARM::fixup_t2_uncondbranch:
99  case ARM::fixup_arm_thumb_bl:
100  case ARM::fixup_arm_thumb_blx:
101    RelocType = unsigned(macho::RIT_ARM_ThumbBranch22Bit);
102    Log2Size = llvm::Log2_32(4);
103    return true;
104
105  case ARM::fixup_arm_movt_hi16:
106  case ARM::fixup_arm_movt_hi16_pcrel:
107  case ARM::fixup_t2_movt_hi16:
108  case ARM::fixup_t2_movt_hi16_pcrel:
109    RelocType = unsigned(macho::RIT_ARM_HalfDifference);
110    // Report as 'long', even though that is not quite accurate.
111    Log2Size = llvm::Log2_32(4);
112    return true;
113
114  case ARM::fixup_arm_movw_lo16:
115  case ARM::fixup_arm_movw_lo16_pcrel:
116  case ARM::fixup_t2_movw_lo16:
117  case ARM::fixup_t2_movw_lo16_pcrel:
118    RelocType = unsigned(macho::RIT_ARM_Half);
119    // Report as 'long', even though that is not quite accurate.
120    Log2Size = llvm::Log2_32(4);
121    return true;
122  }
123}
124
125void ARMMachObjectWriter::
126RecordARMMovwMovtRelocation(MachObjectWriter *Writer,
127                            const MCAssembler &Asm,
128                            const MCAsmLayout &Layout,
129                            const MCFragment *Fragment,
130                            const MCFixup &Fixup,
131                            MCValue Target,
132                            uint64_t &FixedValue) {
133  uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
134  unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
135  unsigned Type = macho::RIT_ARM_Half;
136
137  // See <reloc.h>.
138  const MCSymbol *A = &Target.getSymA()->getSymbol();
139  MCSymbolData *A_SD = &Asm.getSymbolData(*A);
140
141  if (!A_SD->getFragment())
142    report_fatal_error("symbol '" + A->getName() +
143                       "' can not be undefined in a subtraction expression");
144
145  uint32_t Value = Writer->getSymbolAddress(A_SD, Layout);
146  uint32_t Value2 = 0;
147  uint64_t SecAddr =
148    Writer->getSectionAddress(A_SD->getFragment()->getParent());
149  FixedValue += SecAddr;
150
151  if (const MCSymbolRefExpr *B = Target.getSymB()) {
152    MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
153
154    if (!B_SD->getFragment())
155      report_fatal_error("symbol '" + B->getSymbol().getName() +
156                         "' can not be undefined in a subtraction expression");
157
158    // Select the appropriate difference relocation type.
159    Type = macho::RIT_ARM_HalfDifference;
160    Value2 = Writer->getSymbolAddress(B_SD, Layout);
161    FixedValue -= Writer->getSectionAddress(B_SD->getFragment()->getParent());
162  }
163
164  // Relocations are written out in reverse order, so the PAIR comes first.
165  // ARM_RELOC_HALF and ARM_RELOC_HALF_SECTDIFF abuse the r_length field:
166  //
167  // For these two r_type relocations they always have a pair following them and
168  // the r_length bits are used differently.  The encoding of the r_length is as
169  // follows:
170  //   low bit of r_length:
171  //      0 - :lower16: for movw instructions
172  //      1 - :upper16: for movt instructions
173  //   high bit of r_length:
174  //      0 - arm instructions
175  //      1 - thumb instructions
176  // the other half of the relocated expression is in the following pair
177  // relocation entry in the the low 16 bits of r_address field.
178  unsigned ThumbBit = 0;
179  unsigned MovtBit = 0;
180  switch ((unsigned)Fixup.getKind()) {
181  default: break;
182  case ARM::fixup_arm_movt_hi16:
183  case ARM::fixup_arm_movt_hi16_pcrel:
184    MovtBit = 1;
185    // The thumb bit shouldn't be set in the 'other-half' bit of the
186    // relocation, but it will be set in FixedValue if the base symbol
187    // is a thumb function. Clear it out here.
188    if (A_SD->getFlags() & SF_ThumbFunc)
189      FixedValue &= 0xfffffffe;
190    break;
191  case ARM::fixup_t2_movt_hi16:
192  case ARM::fixup_t2_movt_hi16_pcrel:
193    if (A_SD->getFlags() & SF_ThumbFunc)
194      FixedValue &= 0xfffffffe;
195    MovtBit = 1;
196    // Fallthrough
197  case ARM::fixup_t2_movw_lo16:
198  case ARM::fixup_t2_movw_lo16_pcrel:
199    ThumbBit = 1;
200    break;
201  }
202
203  if (Type == macho::RIT_ARM_HalfDifference) {
204    uint32_t OtherHalf = MovtBit
205      ? (FixedValue & 0xffff) : ((FixedValue & 0xffff0000) >> 16);
206
207    macho::RelocationEntry MRE;
208    MRE.Word0 = ((OtherHalf       <<  0) |
209                 (macho::RIT_Pair << 24) |
210                 (MovtBit         << 28) |
211                 (ThumbBit        << 29) |
212                 (IsPCRel         << 30) |
213                 macho::RF_Scattered);
214    MRE.Word1 = Value2;
215    Writer->addRelocation(Fragment->getParent(), MRE);
216  }
217
218  macho::RelocationEntry MRE;
219  MRE.Word0 = ((FixupOffset <<  0) |
220               (Type        << 24) |
221               (MovtBit     << 28) |
222               (ThumbBit    << 29) |
223               (IsPCRel     << 30) |
224               macho::RF_Scattered);
225  MRE.Word1 = Value;
226  Writer->addRelocation(Fragment->getParent(), MRE);
227}
228
229void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
230                                                    const MCAssembler &Asm,
231                                                    const MCAsmLayout &Layout,
232                                                    const MCFragment *Fragment,
233                                                    const MCFixup &Fixup,
234                                                    MCValue Target,
235                                                    unsigned Log2Size,
236                                                    uint64_t &FixedValue) {
237  uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
238  unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
239  unsigned Type = macho::RIT_Vanilla;
240
241  // See <reloc.h>.
242  const MCSymbol *A = &Target.getSymA()->getSymbol();
243  MCSymbolData *A_SD = &Asm.getSymbolData(*A);
244
245  if (!A_SD->getFragment())
246    report_fatal_error("symbol '" + A->getName() +
247                       "' can not be undefined in a subtraction expression");
248
249  uint32_t Value = Writer->getSymbolAddress(A_SD, Layout);
250  uint64_t SecAddr = Writer->getSectionAddress(A_SD->getFragment()->getParent());
251  FixedValue += SecAddr;
252  uint32_t Value2 = 0;
253
254  if (const MCSymbolRefExpr *B = Target.getSymB()) {
255    MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
256
257    if (!B_SD->getFragment())
258      report_fatal_error("symbol '" + B->getSymbol().getName() +
259                         "' can not be undefined in a subtraction expression");
260
261    // Select the appropriate difference relocation type.
262    Type = macho::RIT_Difference;
263    Value2 = Writer->getSymbolAddress(B_SD, Layout);
264    FixedValue -= Writer->getSectionAddress(B_SD->getFragment()->getParent());
265  }
266
267  // Relocations are written out in reverse order, so the PAIR comes first.
268  if (Type == macho::RIT_Difference ||
269      Type == macho::RIT_Generic_LocalDifference) {
270    macho::RelocationEntry MRE;
271    MRE.Word0 = ((0         <<  0) |
272                 (macho::RIT_Pair  << 24) |
273                 (Log2Size  << 28) |
274                 (IsPCRel   << 30) |
275                 macho::RF_Scattered);
276    MRE.Word1 = Value2;
277    Writer->addRelocation(Fragment->getParent(), MRE);
278  }
279
280  macho::RelocationEntry MRE;
281  MRE.Word0 = ((FixupOffset <<  0) |
282               (Type        << 24) |
283               (Log2Size    << 28) |
284               (IsPCRel     << 30) |
285               macho::RF_Scattered);
286  MRE.Word1 = Value;
287  Writer->addRelocation(Fragment->getParent(), MRE);
288}
289
290void ARMMachObjectWriter::RecordRelocation(MachObjectWriter *Writer,
291                                           const MCAssembler &Asm,
292                                           const MCAsmLayout &Layout,
293                                           const MCFragment *Fragment,
294                                           const MCFixup &Fixup,
295                                           MCValue Target,
296                                           uint64_t &FixedValue) {
297  unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
298  unsigned Log2Size;
299  unsigned RelocType = macho::RIT_Vanilla;
300  if (!getARMFixupKindMachOInfo(Fixup.getKind(), RelocType, Log2Size)) {
301    report_fatal_error("unknown ARM fixup kind!");
302    return;
303  }
304
305  // If this is a difference or a defined symbol plus an offset, then we need a
306  // scattered relocation entry.  Differences always require scattered
307  // relocations.
308  if (Target.getSymB()) {
309    if (RelocType == macho::RIT_ARM_Half ||
310        RelocType == macho::RIT_ARM_HalfDifference)
311      return RecordARMMovwMovtRelocation(Writer, Asm, Layout, Fragment, Fixup,
312                                         Target, FixedValue);
313    return RecordARMScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
314                                        Target, Log2Size, FixedValue);
315  }
316
317  // Get the symbol data, if any.
318  MCSymbolData *SD = 0;
319  if (Target.getSymA())
320    SD = &Asm.getSymbolData(Target.getSymA()->getSymbol());
321
322  // FIXME: For other platforms, we need to use scattered relocations for
323  // internal relocations with offsets.  If this is an internal relocation with
324  // an offset, it also needs a scattered relocation entry.
325  //
326  // Is this right for ARM?
327  uint32_t Offset = Target.getConstant();
328  if (IsPCRel && RelocType == macho::RIT_Vanilla)
329    Offset += 1 << Log2Size;
330  if (Offset && SD && !Writer->doesSymbolRequireExternRelocation(SD))
331    return RecordARMScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
332                                        Target, Log2Size, FixedValue);
333
334  // See <reloc.h>.
335  uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
336  unsigned Index = 0;
337  unsigned IsExtern = 0;
338  unsigned Type = 0;
339
340  if (Target.isAbsolute()) { // constant
341    // FIXME!
342    report_fatal_error("FIXME: relocations to absolute targets "
343                       "not yet implemented");
344  } else {
345    // Resolve constant variables.
346    if (SD->getSymbol().isVariable()) {
347      int64_t Res;
348      if (SD->getSymbol().getVariableValue()->EvaluateAsAbsolute(
349            Res, Layout, Writer->getSectionAddressMap())) {
350        FixedValue = Res;
351        return;
352      }
353    }
354
355    // Check whether we need an external or internal relocation.
356    if (Writer->doesSymbolRequireExternRelocation(SD)) {
357      IsExtern = 1;
358      Index = SD->getIndex();
359
360      // For external relocations, make sure to offset the fixup value to
361      // compensate for the addend of the symbol address, if it was
362      // undefined. This occurs with weak definitions, for example.
363      if (!SD->Symbol->isUndefined())
364        FixedValue -= Layout.getSymbolOffset(SD);
365    } else {
366      // The index is the section ordinal (1-based).
367      const MCSectionData &SymSD = Asm.getSectionData(
368        SD->getSymbol().getSection());
369      Index = SymSD.getOrdinal() + 1;
370      FixedValue += Writer->getSectionAddress(&SymSD);
371    }
372    if (IsPCRel)
373      FixedValue -= Writer->getSectionAddress(Fragment->getParent());
374
375    // The type is determined by the fixup kind.
376    Type = RelocType;
377  }
378
379  // struct relocation_info (8 bytes)
380  macho::RelocationEntry MRE;
381  MRE.Word0 = FixupOffset;
382  MRE.Word1 = ((Index     <<  0) |
383               (IsPCRel   << 24) |
384               (Log2Size  << 25) |
385               (IsExtern  << 27) |
386               (Type      << 28));
387  Writer->addRelocation(Fragment->getParent(), MRE);
388}
389
390MCObjectWriter *llvm::createARMMachObjectWriter(raw_ostream &OS,
391                                                bool Is64Bit,
392                                                uint32_t CPUType,
393                                                uint32_t CPUSubtype) {
394  return createMachObjectWriter(new ARMMachObjectWriter(Is64Bit,
395                                                        CPUType,
396                                                        CPUSubtype),
397                                OS, /*IsLittleEndian=*/true);
398}
399