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/MCValue.h"
23 #include "llvm/Support/ErrorHandling.h"
24 #include "llvm/Support/MachO.h"
25 using namespace llvm;
26 
27 namespace {
28 class 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,
48                                 unsigned RelocType, const MCSymbolData *SD,
49                                 uint64_t FixedValue);
50 
51 public:
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 
64 static 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     return false;
92 
93     // Handle 24-bit branch kinds.
94   case ARM::fixup_arm_condbranch:
95   case ARM::fixup_arm_uncondbranch:
96   case ARM::fixup_arm_uncondbl:
97   case ARM::fixup_arm_condbl:
98   case ARM::fixup_arm_blx:
99     RelocType = unsigned(MachO::ARM_RELOC_BR24);
100     // Report as 'long', even though that is not quite accurate.
101     Log2Size = llvm::Log2_32(4);
102     return true;
103 
104     // Handle Thumb branches.
105   case ARM::fixup_arm_thumb_br:
106     RelocType = unsigned(MachO::ARM_THUMB_RELOC_BR22);
107     Log2Size = llvm::Log2_32(2);
108     return true;
109 
110   case ARM::fixup_t2_uncondbranch:
111   case ARM::fixup_arm_thumb_bl:
112   case ARM::fixup_arm_thumb_blx:
113     RelocType = unsigned(MachO::ARM_THUMB_RELOC_BR22);
114     Log2Size = llvm::Log2_32(4);
115     return true;
116 
117   // For movw/movt r_type relocations they always have a pair following them and
118   // the r_length bits are used differently.  The encoding of the r_length is as
119   // follows:
120   //   low bit of r_length:
121   //      0 - :lower16: for movw instructions
122   //      1 - :upper16: for movt instructions
123   //   high bit of r_length:
124   //      0 - arm instructions
125   //      1 - thumb instructions
126   case ARM::fixup_arm_movt_hi16:
127     RelocType = unsigned(MachO::ARM_RELOC_HALF);
128     Log2Size = 1;
129     return true;
130   case ARM::fixup_t2_movt_hi16:
131     RelocType = unsigned(MachO::ARM_RELOC_HALF);
132     Log2Size = 3;
133     return true;
134 
135   case ARM::fixup_arm_movw_lo16:
136     RelocType = unsigned(MachO::ARM_RELOC_HALF);
137     Log2Size = 0;
138     return true;
139   case ARM::fixup_t2_movw_lo16:
140     RelocType = unsigned(MachO::ARM_RELOC_HALF);
141     Log2Size = 2;
142     return true;
143   }
144 }
145 
146 void ARMMachObjectWriter::
147 RecordARMScatteredHalfRelocation(MachObjectWriter *Writer,
148                                  const MCAssembler &Asm,
149                                  const MCAsmLayout &Layout,
150                                  const MCFragment *Fragment,
151                                  const MCFixup &Fixup,
152                                  MCValue Target,
153                                  uint64_t &FixedValue) {
154   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
155   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
156   unsigned Type = MachO::ARM_RELOC_HALF;
157 
158   // See <reloc.h>.
159   const MCSymbol *A = &Target.getSymA()->getSymbol();
160   const MCSymbolData *A_SD = &Asm.getSymbolData(*A);
161 
162   if (!A_SD->getFragment())
163     Asm.getContext().FatalError(Fixup.getLoc(),
164                        "symbol '" + A->getName() +
165                        "' can not be undefined in a subtraction expression");
166 
167   uint32_t Value = Writer->getSymbolAddress(A_SD, Layout);
168   uint32_t Value2 = 0;
169   uint64_t SecAddr =
170     Writer->getSectionAddress(A_SD->getFragment()->getParent());
171   FixedValue += SecAddr;
172 
173   if (const MCSymbolRefExpr *B = Target.getSymB()) {
174     const MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
175 
176     if (!B_SD->getFragment())
177       Asm.getContext().FatalError(Fixup.getLoc(),
178                          "symbol '" + B->getSymbol().getName() +
179                          "' can not be undefined in a subtraction expression");
180 
181     // Select the appropriate difference relocation type.
182     Type = MachO::ARM_RELOC_HALF_SECTDIFF;
183     Value2 = Writer->getSymbolAddress(B_SD, Layout);
184     FixedValue -= Writer->getSectionAddress(B_SD->getFragment()->getParent());
185   }
186 
187   // Relocations are written out in reverse order, so the PAIR comes first.
188   // ARM_RELOC_HALF and ARM_RELOC_HALF_SECTDIFF abuse the r_length field:
189   //
190   // For these two r_type relocations they always have a pair following them and
191   // the r_length bits are used differently.  The encoding of the r_length is as
192   // follows:
193   //   low bit of r_length:
194   //      0 - :lower16: for movw instructions
195   //      1 - :upper16: for movt instructions
196   //   high bit of r_length:
197   //      0 - arm instructions
198   //      1 - thumb instructions
199   // the other half of the relocated expression is in the following pair
200   // relocation entry in the low 16 bits of r_address field.
201   unsigned ThumbBit = 0;
202   unsigned MovtBit = 0;
203   switch ((unsigned)Fixup.getKind()) {
204   default: break;
205   case ARM::fixup_arm_movt_hi16:
206     MovtBit = 1;
207     // The thumb bit shouldn't be set in the 'other-half' bit of the
208     // relocation, but it will be set in FixedValue if the base symbol
209     // is a thumb function. Clear it out here.
210     if (Asm.isThumbFunc(A))
211       FixedValue &= 0xfffffffe;
212     break;
213   case ARM::fixup_t2_movt_hi16:
214     if (Asm.isThumbFunc(A))
215       FixedValue &= 0xfffffffe;
216     MovtBit = 1;
217     // Fallthrough
218   case ARM::fixup_t2_movw_lo16:
219     ThumbBit = 1;
220     break;
221   }
222 
223   if (Type == MachO::ARM_RELOC_HALF_SECTDIFF) {
224     uint32_t OtherHalf = MovtBit
225       ? (FixedValue & 0xffff) : ((FixedValue & 0xffff0000) >> 16);
226 
227     MachO::any_relocation_info MRE;
228     MRE.r_word0 = ((OtherHalf             <<  0) |
229                    (MachO::ARM_RELOC_PAIR << 24) |
230                    (MovtBit               << 28) |
231                    (ThumbBit              << 29) |
232                    (IsPCRel               << 30) |
233                    MachO::R_SCATTERED);
234     MRE.r_word1 = Value2;
235     Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
236   }
237 
238   MachO::any_relocation_info MRE;
239   MRE.r_word0 = ((FixupOffset <<  0) |
240                  (Type        << 24) |
241                  (MovtBit     << 28) |
242                  (ThumbBit    << 29) |
243                  (IsPCRel     << 30) |
244                  MachO::R_SCATTERED);
245   MRE.r_word1 = Value;
246   Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
247 }
248 
249 void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
250                                                     const MCAssembler &Asm,
251                                                     const MCAsmLayout &Layout,
252                                                     const MCFragment *Fragment,
253                                                     const MCFixup &Fixup,
254                                                     MCValue Target,
255                                                     unsigned Type,
256                                                     unsigned Log2Size,
257                                                     uint64_t &FixedValue) {
258   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
259   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
260 
261   // See <reloc.h>.
262   const MCSymbol *A = &Target.getSymA()->getSymbol();
263   const MCSymbolData *A_SD = &Asm.getSymbolData(*A);
264 
265   if (!A_SD->getFragment())
266     Asm.getContext().FatalError(Fixup.getLoc(),
267                        "symbol '" + A->getName() +
268                        "' can not be undefined in a subtraction expression");
269 
270   uint32_t Value = Writer->getSymbolAddress(A_SD, Layout);
271   uint64_t SecAddr = Writer->getSectionAddress(A_SD->getFragment()->getParent());
272   FixedValue += SecAddr;
273   uint32_t Value2 = 0;
274 
275   if (const MCSymbolRefExpr *B = Target.getSymB()) {
276     assert(Type == MachO::ARM_RELOC_VANILLA && "invalid reloc for 2 symbols");
277     const MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
278 
279     if (!B_SD->getFragment())
280       Asm.getContext().FatalError(Fixup.getLoc(),
281                          "symbol '" + B->getSymbol().getName() +
282                          "' can not be undefined in a subtraction expression");
283 
284     // Select the appropriate difference relocation type.
285     Type = MachO::ARM_RELOC_SECTDIFF;
286     Value2 = Writer->getSymbolAddress(B_SD, Layout);
287     FixedValue -= Writer->getSectionAddress(B_SD->getFragment()->getParent());
288   }
289 
290   // Relocations are written out in reverse order, so the PAIR comes first.
291   if (Type == MachO::ARM_RELOC_SECTDIFF ||
292       Type == MachO::ARM_RELOC_LOCAL_SECTDIFF) {
293     MachO::any_relocation_info MRE;
294     MRE.r_word0 = ((0                     <<  0) |
295                    (MachO::ARM_RELOC_PAIR << 24) |
296                    (Log2Size              << 28) |
297                    (IsPCRel               << 30) |
298                    MachO::R_SCATTERED);
299     MRE.r_word1 = Value2;
300     Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
301   }
302 
303   MachO::any_relocation_info MRE;
304   MRE.r_word0 = ((FixupOffset <<  0) |
305                  (Type        << 24) |
306                  (Log2Size    << 28) |
307                  (IsPCRel     << 30) |
308                  MachO::R_SCATTERED);
309   MRE.r_word1 = Value;
310   Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
311 }
312 
313 bool ARMMachObjectWriter::requiresExternRelocation(MachObjectWriter *Writer,
314                                                    const MCAssembler &Asm,
315                                                    const MCFragment &Fragment,
316                                                    unsigned RelocType,
317                                                    const MCSymbolData *SD,
318                                                    uint64_t FixedValue) {
319   // Most cases can be identified purely from the symbol.
320   if (Writer->doesSymbolRequireExternRelocation(SD))
321     return true;
322   int64_t Value = (int64_t)FixedValue;  // The displacement is signed.
323   int64_t Range;
324   switch (RelocType) {
325   default:
326     return false;
327   case MachO::ARM_RELOC_BR24:
328     // PC pre-adjustment of 8 for these instructions.
329     Value -= 8;
330     // ARM BL/BLX has a 25-bit offset.
331     Range = 0x1ffffff;
332     break;
333   case MachO::ARM_THUMB_RELOC_BR22:
334     // PC pre-adjustment of 4 for these instructions.
335     Value -= 4;
336     // Thumb BL/BLX has a 24-bit offset.
337     Range = 0xffffff;
338   }
339   // BL/BLX also use external relocations when an internal relocation
340   // would result in the target being out of range. This gives the linker
341   // enough information to generate a branch island.
342   const MCSectionData &SymSD = Asm.getSectionData(
343     SD->getSymbol().getSection());
344   Value += Writer->getSectionAddress(&SymSD);
345   Value -= Writer->getSectionAddress(Fragment.getParent());
346   // If the resultant value would be out of range for an internal relocation,
347   // use an external instead.
348   if (Value > Range || Value < -(Range + 1))
349     return true;
350   return false;
351 }
352 
353 void ARMMachObjectWriter::RecordRelocation(MachObjectWriter *Writer,
354                                            MCAssembler &Asm,
355                                            const MCAsmLayout &Layout,
356                                            const MCFragment *Fragment,
357                                            const MCFixup &Fixup, MCValue Target,
358                                            uint64_t &FixedValue) {
359   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
360   unsigned Log2Size;
361   unsigned RelocType = MachO::ARM_RELOC_VANILLA;
362   if (!getARMFixupKindMachOInfo(Fixup.getKind(), RelocType, Log2Size))
363     // If we failed to get fixup kind info, it's because there's no legal
364     // relocation type for the fixup kind. This happens when it's a fixup that's
365     // expected to always be resolvable at assembly time and not have any
366     // relocations needed.
367     Asm.getContext().FatalError(Fixup.getLoc(),
368                                 "unsupported relocation on symbol");
369 
370   // If this is a difference or a defined symbol plus an offset, then we need a
371   // scattered relocation entry.  Differences always require scattered
372   // relocations.
373   if (Target.getSymB()) {
374     if (RelocType == MachO::ARM_RELOC_HALF)
375       return RecordARMScatteredHalfRelocation(Writer, Asm, Layout, Fragment,
376                                               Fixup, Target, FixedValue);
377     return RecordARMScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
378                                         Target, RelocType, Log2Size,
379                                         FixedValue);
380   }
381 
382   // Get the symbol data, if any.
383   const MCSymbolData *SD = nullptr;
384   if (Target.getSymA())
385     SD = &Asm.getSymbolData(Target.getSymA()->getSymbol());
386 
387   // FIXME: For other platforms, we need to use scattered relocations for
388   // internal relocations with offsets.  If this is an internal relocation with
389   // an offset, it also needs a scattered relocation entry.
390   //
391   // Is this right for ARM?
392   uint32_t Offset = Target.getConstant();
393   if (IsPCRel && RelocType == MachO::ARM_RELOC_VANILLA)
394     Offset += 1 << Log2Size;
395   if (Offset && SD && !Writer->doesSymbolRequireExternRelocation(SD))
396     return RecordARMScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
397                                         Target, RelocType, Log2Size,
398                                         FixedValue);
399 
400   // See <reloc.h>.
401   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
402   unsigned Index = 0;
403   unsigned Type = 0;
404   const MCSymbolData *RelSymbol = nullptr;
405 
406   if (Target.isAbsolute()) { // constant
407     // FIXME!
408     report_fatal_error("FIXME: relocations to absolute targets "
409                        "not yet implemented");
410   } else {
411     // Resolve constant variables.
412     if (SD->getSymbol().isVariable()) {
413       int64_t Res;
414       if (SD->getSymbol().getVariableValue()->EvaluateAsAbsolute(
415             Res, Layout, Writer->getSectionAddressMap())) {
416         FixedValue = Res;
417         return;
418       }
419     }
420 
421     // Check whether we need an external or internal relocation.
422     if (requiresExternRelocation(Writer, Asm, *Fragment, RelocType, SD,
423                                  FixedValue)) {
424       RelSymbol = SD;
425 
426       // For external relocations, make sure to offset the fixup value to
427       // compensate for the addend of the symbol address, if it was
428       // undefined. This occurs with weak definitions, for example.
429       if (!SD->getSymbol().isUndefined())
430         FixedValue -= Layout.getSymbolOffset(SD);
431     } else {
432       // The index is the section ordinal (1-based).
433       const MCSectionData &SymSD = Asm.getSectionData(
434         SD->getSymbol().getSection());
435       Index = SymSD.getOrdinal() + 1;
436       FixedValue += Writer->getSectionAddress(&SymSD);
437     }
438     if (IsPCRel)
439       FixedValue -= Writer->getSectionAddress(Fragment->getParent());
440 
441     // The type is determined by the fixup kind.
442     Type = RelocType;
443   }
444 
445   // struct relocation_info (8 bytes)
446   MachO::any_relocation_info MRE;
447   MRE.r_word0 = FixupOffset;
448   MRE.r_word1 =
449       (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
450 
451   // Even when it's not a scattered relocation, movw/movt always uses
452   // a PAIR relocation.
453   if (Type == MachO::ARM_RELOC_HALF) {
454     // The other-half value only gets populated for the movt and movw
455     // relocation entries.
456     uint32_t Value = 0;
457     switch ((unsigned)Fixup.getKind()) {
458     default: break;
459     case ARM::fixup_arm_movw_lo16:
460     case ARM::fixup_t2_movw_lo16:
461       Value = (FixedValue >> 16) & 0xffff;
462       break;
463     case ARM::fixup_arm_movt_hi16:
464     case ARM::fixup_t2_movt_hi16:
465       Value = FixedValue & 0xffff;
466       break;
467     }
468     MachO::any_relocation_info MREPair;
469     MREPair.r_word0 = Value;
470     MREPair.r_word1 = ((0xffffff              <<  0) |
471                        (Log2Size              << 25) |
472                        (MachO::ARM_RELOC_PAIR << 28));
473 
474     Writer->addRelocation(nullptr, Fragment->getParent(), MREPair);
475   }
476 
477   Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
478 }
479 
480 MCObjectWriter *llvm::createARMMachObjectWriter(raw_ostream &OS,
481                                                 bool Is64Bit,
482                                                 uint32_t CPUType,
483                                                 uint32_t CPUSubtype) {
484   return createMachObjectWriter(new ARMMachObjectWriter(Is64Bit,
485                                                         CPUType,
486                                                         CPUSubtype),
487                                 OS, /*IsLittleEndian=*/true);
488 }
489