ARMELFObjectWriter.cpp revision 7609785d2b9b79b9aafc3b3afabcb691cfc8afa5 
1//===-- ARMELFObjectWriter.cpp - ARM ELF 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/ARMFixupKinds.h"
11#include "MCTargetDesc/ARMMCTargetDesc.h"
12#include "llvm/Support/Debug.h"
13#include "llvm/Support/ErrorHandling.h"
14#include "llvm/ADT/Statistic.h"
15#include "llvm/ADT/StringSwitch.h"
16#include "llvm/MC/MCELFObjectWriter.h"
17#include "llvm/MC/MCExpr.h"
18#include "llvm/MC/MCSectionELF.h"
19#include "llvm/MC/MCValue.h"
20
21using namespace llvm;
22
23namespace {
24  class ARMELFObjectWriter : public MCELFObjectTargetWriter {
25    enum { DefaultEABIVersion = 0x05000000U };
26
27    const MCSymbol *ExplicitRelSym(const MCAssembler &Asm,
28                                   const MCValue &Target,
29                                   const MCFragment &F,
30                                   const MCFixup &Fixup,
31                                   bool IsPCRel) const;
32    unsigned GetRelocTypeInner(const MCValue &Target,
33                               const MCFixup &Fixup,
34                               bool IsPCRel) const;
35
36
37  public:
38    ARMELFObjectWriter(uint8_t OSABI);
39
40    virtual ~ARMELFObjectWriter();
41  protected:
42    virtual unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
43                                  bool IsPCRel, bool IsRelocWithSymbol,
44                                  int64_t Addend) const;
45    virtual unsigned getEFlags() const;
46  };
47}
48
49ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
50  : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
51                            ELF::EM_ARM,
52                            /*HasRelocationAddend*/ false) {}
53
54ARMELFObjectWriter::~ARMELFObjectWriter() {}
55
56// FIXME: get the real EABI Version from the Triple.
57unsigned ARMELFObjectWriter::getEFlags() const {
58  return ELF::EF_ARM_EABIMASK & DefaultEABIVersion;
59}
60
61// In ARM, _MergedGlobals and other most symbols get emitted directly.
62// I.e. not as an offset to a section symbol.
63// This code is an approximation of what ARM/gcc does.
64
65STATISTIC(PCRelCount, "Total number of PIC Relocations");
66STATISTIC(NonPCRelCount, "Total number of non-PIC relocations");
67
68const MCSymbol *ARMELFObjectWriter::ExplicitRelSym(const MCAssembler &Asm,
69                                                   const MCValue &Target,
70                                                   const MCFragment &F,
71                                                   const MCFixup &Fixup,
72                                                   bool IsPCRel) const {
73  const MCSymbol &Symbol = Target.getSymA()->getSymbol();
74  bool EmitThisSym = false;
75
76  const MCSectionELF &Section =
77    static_cast<const MCSectionELF&>(Symbol.getSection());
78  bool InNormalSection = true;
79  unsigned RelocType = 0;
80  RelocType = GetRelocTypeInner(Target, Fixup, IsPCRel);
81
82  DEBUG(
83      const MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
84      MCSymbolRefExpr::VariantKind Kind2;
85      Kind2 = Target.getSymB() ?  Target.getSymB()->getKind() :
86        MCSymbolRefExpr::VK_None;
87      dbgs() << "considering symbol "
88        << Section.getSectionName() << "/"
89        << Symbol.getName() << "/"
90        << " Rel:" << (unsigned)RelocType
91        << " Kind: " << (int)Kind << "/" << (int)Kind2
92        << " Tmp:"
93        << Symbol.isAbsolute() << "/" << Symbol.isDefined() << "/"
94        << Symbol.isVariable() << "/" << Symbol.isTemporary()
95        << " Counts:" << PCRelCount << "/" << NonPCRelCount << "\n");
96
97  if (IsPCRel) { ++PCRelCount;
98    switch (RelocType) {
99    default:
100      // Most relocation types are emitted as explicit symbols
101      InNormalSection =
102        StringSwitch<bool>(Section.getSectionName())
103        .Case(".data.rel.ro.local", false)
104        .Case(".data.rel", false)
105        .Case(".bss", false)
106        .Default(true);
107      EmitThisSym = true;
108      break;
109    case ELF::R_ARM_ABS32:
110      // But things get strange with R_ARM_ABS32
111      // In this case, most things that go in .rodata show up
112      // as section relative relocations
113      InNormalSection =
114        StringSwitch<bool>(Section.getSectionName())
115        .Case(".data.rel.ro.local", false)
116        .Case(".data.rel", false)
117        .Case(".rodata", false)
118        .Case(".bss", false)
119        .Default(true);
120      EmitThisSym = false;
121      break;
122    }
123  } else {
124    NonPCRelCount++;
125    InNormalSection =
126      StringSwitch<bool>(Section.getSectionName())
127      .Case(".data.rel.ro.local", false)
128      .Case(".rodata", false)
129      .Case(".data.rel", false)
130      .Case(".bss", false)
131      .Default(true);
132
133    switch (RelocType) {
134    default: EmitThisSym = true; break;
135    case ELF::R_ARM_ABS32: EmitThisSym = false; break;
136    }
137  }
138
139  if (EmitThisSym)
140    return &Symbol;
141  if (! Symbol.isTemporary() && InNormalSection) {
142    return &Symbol;
143  }
144  return NULL;
145}
146
147// Need to examine the Fixup when determining whether to
148// emit the relocation as an explicit symbol or as a section relative
149// offset
150unsigned ARMELFObjectWriter::GetRelocType(const MCValue &Target,
151                                          const MCFixup &Fixup,
152                                          bool IsPCRel,
153                                          bool IsRelocWithSymbol,
154                                          int64_t Addend) const {
155  return GetRelocTypeInner(Target, Fixup, IsPCRel);
156}
157
158unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
159                                               const MCFixup &Fixup,
160                                               bool IsPCRel) const  {
161  MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ?
162    MCSymbolRefExpr::VK_None : Target.getSymA()->getKind();
163
164  unsigned Type = 0;
165  if (IsPCRel) {
166    switch ((unsigned)Fixup.getKind()) {
167    default: assert(0 && "Unimplemented");
168    case FK_Data_4:
169      switch (Modifier) {
170      default: llvm_unreachable("Unsupported Modifier");
171      case MCSymbolRefExpr::VK_None:
172        Type = ELF::R_ARM_REL32;
173        break;
174      case MCSymbolRefExpr::VK_ARM_TLSGD:
175        assert(0 && "unimplemented");
176        break;
177      case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
178        Type = ELF::R_ARM_TLS_IE32;
179        break;
180      }
181      break;
182    case ARM::fixup_arm_uncondbranch:
183      switch (Modifier) {
184      case MCSymbolRefExpr::VK_ARM_PLT:
185        Type = ELF::R_ARM_PLT32;
186        break;
187      default:
188        Type = ELF::R_ARM_CALL;
189        break;
190      }
191      break;
192    case ARM::fixup_arm_condbranch:
193      Type = ELF::R_ARM_JUMP24;
194      break;
195    case ARM::fixup_arm_movt_hi16:
196    case ARM::fixup_arm_movt_hi16_pcrel:
197      Type = ELF::R_ARM_MOVT_PREL;
198      break;
199    case ARM::fixup_arm_movw_lo16:
200    case ARM::fixup_arm_movw_lo16_pcrel:
201      Type = ELF::R_ARM_MOVW_PREL_NC;
202      break;
203    case ARM::fixup_t2_movt_hi16:
204    case ARM::fixup_t2_movt_hi16_pcrel:
205      Type = ELF::R_ARM_THM_MOVT_PREL;
206      break;
207    case ARM::fixup_t2_movw_lo16:
208    case ARM::fixup_t2_movw_lo16_pcrel:
209      Type = ELF::R_ARM_THM_MOVW_PREL_NC;
210      break;
211    case ARM::fixup_arm_thumb_bl:
212    case ARM::fixup_arm_thumb_blx:
213      switch (Modifier) {
214      case MCSymbolRefExpr::VK_ARM_PLT:
215        Type = ELF::R_ARM_THM_CALL;
216        break;
217      default:
218        Type = ELF::R_ARM_NONE;
219        break;
220      }
221      break;
222    }
223  } else {
224    switch ((unsigned)Fixup.getKind()) {
225    default: llvm_unreachable("invalid fixup kind!");
226    case FK_Data_4:
227      switch (Modifier) {
228      default: llvm_unreachable("Unsupported Modifier"); break;
229      case MCSymbolRefExpr::VK_ARM_GOT:
230        Type = ELF::R_ARM_GOT_BREL;
231        break;
232      case MCSymbolRefExpr::VK_ARM_TLSGD:
233        Type = ELF::R_ARM_TLS_GD32;
234        break;
235      case MCSymbolRefExpr::VK_ARM_TPOFF:
236        Type = ELF::R_ARM_TLS_LE32;
237        break;
238      case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
239        Type = ELF::R_ARM_TLS_IE32;
240        break;
241      case MCSymbolRefExpr::VK_None:
242        Type = ELF::R_ARM_ABS32;
243        break;
244      case MCSymbolRefExpr::VK_ARM_GOTOFF:
245        Type = ELF::R_ARM_GOTOFF32;
246        break;
247      }
248      break;
249    case ARM::fixup_arm_ldst_pcrel_12:
250    case ARM::fixup_arm_pcrel_10:
251    case ARM::fixup_arm_adr_pcrel_12:
252    case ARM::fixup_arm_thumb_bl:
253    case ARM::fixup_arm_thumb_cb:
254    case ARM::fixup_arm_thumb_cp:
255    case ARM::fixup_arm_thumb_br:
256      assert(0 && "Unimplemented");
257      break;
258    case ARM::fixup_arm_uncondbranch:
259      Type = ELF::R_ARM_CALL;
260      break;
261    case ARM::fixup_arm_condbranch:
262      Type = ELF::R_ARM_JUMP24;
263      break;
264    case ARM::fixup_arm_movt_hi16:
265      Type = ELF::R_ARM_MOVT_ABS;
266      break;
267    case ARM::fixup_arm_movw_lo16:
268      Type = ELF::R_ARM_MOVW_ABS_NC;
269      break;
270    case ARM::fixup_t2_movt_hi16:
271      Type = ELF::R_ARM_THM_MOVT_ABS;
272      break;
273    case ARM::fixup_t2_movw_lo16:
274      Type = ELF::R_ARM_THM_MOVW_ABS_NC;
275      break;
276    }
277  }
278
279  return Type;
280}
281
282MCObjectWriter *llvm::createARMELFObjectWriter(raw_ostream &OS,
283                                               uint8_t OSABI) {
284  MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
285  return createELFObjectWriter(MOTW, OS,  /*IsLittleEndian=*/true);
286}
287