AArch64MachObjectWriter.cpp revision cd81d94322a39503e4a3e87b6ee03d4fcb3465fb 
1//===-- AArch64MachObjectWriter.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/AArch64FixupKinds.h"
11#include "MCTargetDesc/AArch64MCTargetDesc.h"
12#include "llvm/MC/MCAssembler.h"
13#include "llvm/MC/MCAsmLayout.h"
14#include "llvm/MC/MCContext.h"
15#include "llvm/MC/MCExpr.h"
16#include "llvm/MC/MCFixup.h"
17#include "llvm/MC/MCMachObjectWriter.h"
18#include "llvm/MC/MCSectionMachO.h"
19#include "llvm/MC/MCValue.h"
20#include "llvm/ADT/Twine.h"
21#include "llvm/Support/ErrorHandling.h"
22#include "llvm/Support/MachO.h"
23using namespace llvm;
24
25namespace {
26class AArch64MachObjectWriter : public MCMachObjectTargetWriter {
27  bool getAArch64FixupKindMachOInfo(const MCFixup &Fixup, unsigned &RelocType,
28                                  const MCSymbolRefExpr *Sym,
29                                  unsigned &Log2Size, const MCAssembler &Asm);
30
31public:
32  AArch64MachObjectWriter(uint32_t CPUType, uint32_t CPUSubtype)
33      : MCMachObjectTargetWriter(true /* is64Bit */, CPUType, CPUSubtype,
34                                 /*UseAggressiveSymbolFolding=*/true) {}
35
36  void RecordRelocation(MachObjectWriter *Writer, const MCAssembler &Asm,
37                        const MCAsmLayout &Layout, const MCFragment *Fragment,
38                        const MCFixup &Fixup, MCValue Target,
39                        uint64_t &FixedValue) override;
40};
41}
42
43bool AArch64MachObjectWriter::getAArch64FixupKindMachOInfo(
44    const MCFixup &Fixup, unsigned &RelocType, const MCSymbolRefExpr *Sym,
45    unsigned &Log2Size, const MCAssembler &Asm) {
46  RelocType = unsigned(MachO::ARM64_RELOC_UNSIGNED);
47  Log2Size = ~0U;
48
49  switch ((unsigned)Fixup.getKind()) {
50  default:
51    return false;
52
53  case FK_Data_1:
54    Log2Size = llvm::Log2_32(1);
55    return true;
56  case FK_Data_2:
57    Log2Size = llvm::Log2_32(2);
58    return true;
59  case FK_Data_4:
60    Log2Size = llvm::Log2_32(4);
61    if (Sym->getKind() == MCSymbolRefExpr::VK_GOT)
62      RelocType = unsigned(MachO::ARM64_RELOC_POINTER_TO_GOT);
63    return true;
64  case FK_Data_8:
65    Log2Size = llvm::Log2_32(8);
66    if (Sym->getKind() == MCSymbolRefExpr::VK_GOT)
67      RelocType = unsigned(MachO::ARM64_RELOC_POINTER_TO_GOT);
68    return true;
69  case AArch64::fixup_aarch64_add_imm12:
70  case AArch64::fixup_aarch64_ldst_imm12_scale1:
71  case AArch64::fixup_aarch64_ldst_imm12_scale2:
72  case AArch64::fixup_aarch64_ldst_imm12_scale4:
73  case AArch64::fixup_aarch64_ldst_imm12_scale8:
74  case AArch64::fixup_aarch64_ldst_imm12_scale16:
75    Log2Size = llvm::Log2_32(4);
76    switch (Sym->getKind()) {
77    default:
78      llvm_unreachable("Unexpected symbol reference variant kind!");
79    case MCSymbolRefExpr::VK_PAGEOFF:
80      RelocType = unsigned(MachO::ARM64_RELOC_PAGEOFF12);
81      return true;
82    case MCSymbolRefExpr::VK_GOTPAGEOFF:
83      RelocType = unsigned(MachO::ARM64_RELOC_GOT_LOAD_PAGEOFF12);
84      return true;
85    case MCSymbolRefExpr::VK_TLVPPAGEOFF:
86      RelocType = unsigned(MachO::ARM64_RELOC_TLVP_LOAD_PAGEOFF12);
87      return true;
88    }
89  case AArch64::fixup_aarch64_pcrel_adrp_imm21:
90    Log2Size = llvm::Log2_32(4);
91    // This encompasses the relocation for the whole 21-bit value.
92    switch (Sym->getKind()) {
93    default:
94      Asm.getContext().FatalError(Fixup.getLoc(),
95                                  "ADR/ADRP relocations must be GOT relative");
96    case MCSymbolRefExpr::VK_PAGE:
97      RelocType = unsigned(MachO::ARM64_RELOC_PAGE21);
98      return true;
99    case MCSymbolRefExpr::VK_GOTPAGE:
100      RelocType = unsigned(MachO::ARM64_RELOC_GOT_LOAD_PAGE21);
101      return true;
102    case MCSymbolRefExpr::VK_TLVPPAGE:
103      RelocType = unsigned(MachO::ARM64_RELOC_TLVP_LOAD_PAGE21);
104      return true;
105    }
106    return true;
107  case AArch64::fixup_aarch64_pcrel_branch26:
108  case AArch64::fixup_aarch64_pcrel_call26:
109    Log2Size = llvm::Log2_32(4);
110    RelocType = unsigned(MachO::ARM64_RELOC_BRANCH26);
111    return true;
112  }
113}
114
115void AArch64MachObjectWriter::RecordRelocation(
116    MachObjectWriter *Writer, const MCAssembler &Asm, const MCAsmLayout &Layout,
117    const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target,
118    uint64_t &FixedValue) {
119  unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
120
121  // See <reloc.h>.
122  uint32_t FixupOffset = Layout.getFragmentOffset(Fragment);
123  unsigned Log2Size = 0;
124  int64_t Value = 0;
125  unsigned Index = 0;
126  unsigned IsExtern = 0;
127  unsigned Type = 0;
128  unsigned Kind = Fixup.getKind();
129
130  FixupOffset += Fixup.getOffset();
131
132  // AArch64 pcrel relocation addends do not include the section offset.
133  if (IsPCRel)
134    FixedValue += FixupOffset;
135
136  // ADRP fixups use relocations for the whole symbol value and only
137  // put the addend in the instruction itself. Clear out any value the
138  // generic code figured out from the sybmol definition.
139  if (Kind == AArch64::fixup_aarch64_pcrel_adrp_imm21)
140    FixedValue = 0;
141
142  // imm19 relocations are for conditional branches, which require
143  // assembler local symbols. If we got here, that's not what we have,
144  // so complain loudly.
145  if (Kind == AArch64::fixup_aarch64_pcrel_branch19) {
146    Asm.getContext().FatalError(Fixup.getLoc(),
147                                "conditional branch requires assembler-local"
148                                " label. '" +
149                                    Target.getSymA()->getSymbol().getName() +
150                                    "' is external.");
151    return;
152  }
153
154  // 14-bit branch relocations should only target internal labels, and so
155  // should never get here.
156  if (Kind == AArch64::fixup_aarch64_pcrel_branch14) {
157    Asm.getContext().FatalError(Fixup.getLoc(),
158                                "Invalid relocation on conditional branch!");
159    return;
160  }
161
162  if (!getAArch64FixupKindMachOInfo(Fixup, Type, Target.getSymA(), Log2Size,
163                                  Asm)) {
164    Asm.getContext().FatalError(Fixup.getLoc(), "unknown AArch64 fixup kind!");
165    return;
166  }
167
168  Value = Target.getConstant();
169
170  if (Target.isAbsolute()) { // constant
171    // FIXME: Should this always be extern?
172    // SymbolNum of 0 indicates the absolute section.
173    Type = MachO::ARM64_RELOC_UNSIGNED;
174    Index = 0;
175
176    if (IsPCRel) {
177      IsExtern = 1;
178      Asm.getContext().FatalError(Fixup.getLoc(),
179                                  "PC relative absolute relocation!");
180
181      // FIXME: x86_64 sets the type to a branch reloc here. Should we do
182      // something similar?
183    }
184  } else if (Target.getSymB()) { // A - B + constant
185    const MCSymbol *A = &Target.getSymA()->getSymbol();
186    const MCSymbolData &A_SD = Asm.getSymbolData(*A);
187    const MCSymbolData *A_Base = Asm.getAtom(&A_SD);
188
189    const MCSymbol *B = &Target.getSymB()->getSymbol();
190    const MCSymbolData &B_SD = Asm.getSymbolData(*B);
191    const MCSymbolData *B_Base = Asm.getAtom(&B_SD);
192
193    // Check for "_foo@got - .", which comes through here as:
194    // Ltmp0:
195    //    ... _foo@got - Ltmp0
196    if (Target.getSymA()->getKind() == MCSymbolRefExpr::VK_GOT &&
197        Target.getSymB()->getKind() == MCSymbolRefExpr::VK_None &&
198        Layout.getSymbolOffset(&B_SD) ==
199            Layout.getFragmentOffset(Fragment) + Fixup.getOffset()) {
200      // SymB is the PC, so use a PC-rel pointer-to-GOT relocation.
201      Index = A_Base->getIndex();
202      IsExtern = 1;
203      Type = MachO::ARM64_RELOC_POINTER_TO_GOT;
204      IsPCRel = 1;
205      MachO::any_relocation_info MRE;
206      MRE.r_word0 = FixupOffset;
207      MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
208                     (IsExtern << 27) | (Type << 28));
209      Writer->addRelocation(Fragment->getParent(), MRE);
210      return;
211    } else if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None ||
212               Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None)
213      // Otherwise, neither symbol can be modified.
214      Asm.getContext().FatalError(Fixup.getLoc(),
215                                  "unsupported relocation of modified symbol");
216
217    // We don't support PCrel relocations of differences.
218    if (IsPCRel)
219      Asm.getContext().FatalError(Fixup.getLoc(),
220                                  "unsupported pc-relative relocation of "
221                                  "difference");
222
223    // AArch64 always uses external relocations. If there is no symbol to use as
224    // a base address (a local symbol with no preceding non-local symbol),
225    // error out.
226    //
227    // FIXME: We should probably just synthesize an external symbol and use
228    // that.
229    if (!A_Base)
230      Asm.getContext().FatalError(
231          Fixup.getLoc(),
232          "unsupported relocation of local symbol '" + A->getName() +
233              "'. Must have non-local symbol earlier in section.");
234    if (!B_Base)
235      Asm.getContext().FatalError(
236          Fixup.getLoc(),
237          "unsupported relocation of local symbol '" + B->getName() +
238              "'. Must have non-local symbol earlier in section.");
239
240    if (A_Base == B_Base && A_Base)
241      Asm.getContext().FatalError(Fixup.getLoc(),
242                                  "unsupported relocation with identical base");
243
244    Value += (!A_SD.getFragment() ? 0
245                                  : Writer->getSymbolAddress(&A_SD, Layout)) -
246             (!A_Base || !A_Base->getFragment()
247                  ? 0
248                  : Writer->getSymbolAddress(A_Base, Layout));
249    Value -= (!B_SD.getFragment() ? 0
250                                  : Writer->getSymbolAddress(&B_SD, Layout)) -
251             (!B_Base || !B_Base->getFragment()
252                  ? 0
253                  : Writer->getSymbolAddress(B_Base, Layout));
254
255    Index = A_Base->getIndex();
256    IsExtern = 1;
257    Type = MachO::ARM64_RELOC_UNSIGNED;
258
259    MachO::any_relocation_info MRE;
260    MRE.r_word0 = FixupOffset;
261    MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
262                   (IsExtern << 27) | (Type << 28));
263    Writer->addRelocation(Fragment->getParent(), MRE);
264
265    Index = B_Base->getIndex();
266    IsExtern = 1;
267    Type = MachO::ARM64_RELOC_SUBTRACTOR;
268  } else { // A + constant
269    const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
270    const MCSymbolData &SD = Asm.getSymbolData(*Symbol);
271    const MCSymbolData *Base = Asm.getAtom(&SD);
272    const MCSectionMachO &Section = static_cast<const MCSectionMachO &>(
273        Fragment->getParent()->getSection());
274
275    // If the symbol is a variable and we weren't able to get a Base for it
276    // (i.e., it's not in the symbol table associated with a section) resolve
277    // the relocation based its expansion instead.
278    if (Symbol->isVariable() && !Base) {
279      // If the evaluation is an absolute value, just use that directly
280      // to keep things easy.
281      int64_t Res;
282      if (SD.getSymbol().getVariableValue()->EvaluateAsAbsolute(
283              Res, Layout, Writer->getSectionAddressMap())) {
284        FixedValue = Res;
285        return;
286      }
287
288      // FIXME: Will the Target we already have ever have any data in it
289      // we need to preserve and merge with the new Target? How about
290      // the FixedValue?
291      if (!Symbol->getVariableValue()->EvaluateAsRelocatable(Target, &Layout))
292        Asm.getContext().FatalError(Fixup.getLoc(),
293                                    "unable to resolve variable '" +
294                                        Symbol->getName() + "'");
295      return RecordRelocation(Writer, Asm, Layout, Fragment, Fixup, Target,
296                              FixedValue);
297    }
298
299    // Relocations inside debug sections always use local relocations when
300    // possible. This seems to be done because the debugger doesn't fully
301    // understand relocation entries and expects to find values that
302    // have already been fixed up.
303    if (Symbol->isInSection()) {
304      if (Section.hasAttribute(MachO::S_ATTR_DEBUG))
305        Base = nullptr;
306    }
307
308    // AArch64 uses external relocations as much as possible. For debug
309    // sections, and for pointer-sized relocations (.quad), we allow section
310    // relocations.  It's code sections that run into trouble.
311    if (Base) {
312      Index = Base->getIndex();
313      IsExtern = 1;
314
315      // Add the local offset, if needed.
316      if (Base != &SD)
317        Value += Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(Base);
318    } else if (Symbol->isInSection()) {
319      // Pointer-sized relocations can use a local relocation. Otherwise,
320      // we have to be in a debug info section.
321      if (!Section.hasAttribute(MachO::S_ATTR_DEBUG) && Log2Size != 3)
322        Asm.getContext().FatalError(
323            Fixup.getLoc(),
324            "unsupported relocation of local symbol '" + Symbol->getName() +
325                "'. Must have non-local symbol earlier in section.");
326      // Adjust the relocation to be section-relative.
327      // The index is the section ordinal (1-based).
328      const MCSectionData &SymSD =
329          Asm.getSectionData(SD.getSymbol().getSection());
330      Index = SymSD.getOrdinal() + 1;
331      IsExtern = 0;
332      Value += Writer->getSymbolAddress(&SD, Layout);
333
334      if (IsPCRel)
335        Value -= Writer->getFragmentAddress(Fragment, Layout) +
336                 Fixup.getOffset() + (1ULL << Log2Size);
337    } else {
338      // Resolve constant variables.
339      if (SD.getSymbol().isVariable()) {
340        int64_t Res;
341        if (SD.getSymbol().getVariableValue()->EvaluateAsAbsolute(
342                Res, Layout, Writer->getSectionAddressMap())) {
343          FixedValue = Res;
344          return;
345        }
346      }
347      Asm.getContext().FatalError(Fixup.getLoc(),
348                                  "unsupported relocation of variable '" +
349                                      Symbol->getName() + "'");
350    }
351  }
352
353  // If the relocation kind is Branch26, Page21, or Pageoff12, any addend
354  // is represented via an Addend relocation, not encoded directly into
355  // the instruction.
356  if ((Type == MachO::ARM64_RELOC_BRANCH26 ||
357       Type == MachO::ARM64_RELOC_PAGE21 ||
358       Type == MachO::ARM64_RELOC_PAGEOFF12) &&
359      Value) {
360    assert((Value & 0xff000000) == 0 && "Added relocation out of range!");
361
362    MachO::any_relocation_info MRE;
363    MRE.r_word0 = FixupOffset;
364    MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
365                   (IsExtern << 27) | (Type << 28));
366    Writer->addRelocation(Fragment->getParent(), MRE);
367
368    // Now set up the Addend relocation.
369    Type = MachO::ARM64_RELOC_ADDEND;
370    Index = Value;
371    IsPCRel = 0;
372    Log2Size = 2;
373    IsExtern = 0;
374
375    // Put zero into the instruction itself. The addend is in the relocation.
376    Value = 0;
377  }
378
379  // If there's any addend left to handle, encode it in the instruction.
380  FixedValue = Value;
381
382  // struct relocation_info (8 bytes)
383  MachO::any_relocation_info MRE;
384  MRE.r_word0 = FixupOffset;
385  MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
386                 (IsExtern << 27) | (Type << 28));
387  Writer->addRelocation(Fragment->getParent(), MRE);
388}
389
390MCObjectWriter *llvm::createAArch64MachObjectWriter(raw_ostream &OS,
391                                                  uint32_t CPUType,
392                                                  uint32_t CPUSubtype) {
393  return createMachObjectWriter(
394      new AArch64MachObjectWriter(CPUType, CPUSubtype), OS,
395      /*IsLittleEndian=*/true);
396}
397