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/ARMMCTargetDesc.h"
11#include "MCTargetDesc/ARMFixupKinds.h"
12#include "llvm/ADT/Statistic.h"
13#include "llvm/ADT/StringSwitch.h"
14#include "llvm/MC/MCELFObjectWriter.h"
15#include "llvm/MC/MCExpr.h"
16#include "llvm/MC/MCSectionELF.h"
17#include "llvm/MC/MCValue.h"
18#include "llvm/Support/Debug.h"
19#include "llvm/Support/ErrorHandling.h"
20#include "llvm/Support/raw_ostream.h"
21
22using namespace llvm;
23
24namespace {
25  class ARMELFObjectWriter : public MCELFObjectTargetWriter {
26    enum { DefaultEABIVersion = 0x05000000U };
27    unsigned GetRelocTypeInner(const MCValue &Target,
28                               const MCFixup &Fixup,
29                               bool IsPCRel) const;
30
31
32  public:
33    ARMELFObjectWriter(uint8_t OSABI);
34
35    virtual ~ARMELFObjectWriter();
36
37    virtual unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
38                                  bool IsPCRel, bool IsRelocWithSymbol,
39                                  int64_t Addend) const;
40    virtual const MCSymbol *ExplicitRelSym(const MCAssembler &Asm,
41                                   const MCValue &Target,
42                                   const MCFragment &F,
43                                   const MCFixup &Fixup,
44                                   bool IsPCRel) const;
45  };
46}
47
48ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
49  : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
50                            ELF::EM_ARM,
51                            /*HasRelocationAddend*/ false) {}
52
53ARMELFObjectWriter::~ARMELFObjectWriter() {}
54
55// In ARM, _MergedGlobals and other most symbols get emitted directly.
56// I.e. not as an offset to a section symbol.
57// This code is an approximation of what ARM/gcc does.
58
59STATISTIC(PCRelCount, "Total number of PIC Relocations");
60STATISTIC(NonPCRelCount, "Total number of non-PIC relocations");
61
62const MCSymbol *ARMELFObjectWriter::ExplicitRelSym(const MCAssembler &Asm,
63                                                   const MCValue &Target,
64                                                   const MCFragment &F,
65                                                   const MCFixup &Fixup,
66                                                   bool IsPCRel) const {
67  const MCSymbol &Symbol = Target.getSymA()->getSymbol().AliasedSymbol();
68  bool EmitThisSym = false;
69
70  const MCSectionELF &Section =
71    static_cast<const MCSectionELF&>(Symbol.getSection());
72  bool InNormalSection = true;
73  unsigned RelocType = 0;
74  RelocType = GetRelocTypeInner(Target, Fixup, IsPCRel);
75
76  DEBUG(
77      const MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
78      MCSymbolRefExpr::VariantKind Kind2;
79      Kind2 = Target.getSymB() ?  Target.getSymB()->getKind() :
80        MCSymbolRefExpr::VK_None;
81      dbgs() << "considering symbol "
82        << Section.getSectionName() << "/"
83        << Symbol.getName() << "/"
84        << " Rel:" << (unsigned)RelocType
85        << " Kind: " << (int)Kind << "/" << (int)Kind2
86        << " Tmp:"
87        << Symbol.isAbsolute() << "/" << Symbol.isDefined() << "/"
88        << Symbol.isVariable() << "/" << Symbol.isTemporary()
89        << " Counts:" << PCRelCount << "/" << NonPCRelCount << "\n");
90
91  if (IsPCRel) { ++PCRelCount;
92    switch (RelocType) {
93    default:
94      // Most relocation types are emitted as explicit symbols
95      InNormalSection =
96        StringSwitch<bool>(Section.getSectionName())
97        .Case(".data.rel.ro.local", false)
98        .Case(".data.rel", false)
99        .Case(".bss", false)
100        .Default(true);
101      EmitThisSym = true;
102      break;
103    case ELF::R_ARM_ABS32:
104      // But things get strange with R_ARM_ABS32
105      // In this case, most things that go in .rodata show up
106      // as section relative relocations
107      InNormalSection =
108        StringSwitch<bool>(Section.getSectionName())
109        .Case(".data.rel.ro.local", false)
110        .Case(".data.rel", false)
111        .Case(".rodata", false)
112        .Case(".bss", false)
113        .Default(true);
114      EmitThisSym = false;
115      break;
116    }
117  } else {
118    NonPCRelCount++;
119    InNormalSection =
120      StringSwitch<bool>(Section.getSectionName())
121      .Case(".data.rel.ro.local", false)
122      .Case(".rodata", false)
123      .Case(".data.rel", false)
124      .Case(".bss", false)
125      .Default(true);
126
127    switch (RelocType) {
128    default: EmitThisSym = true; break;
129    case ELF::R_ARM_ABS32: EmitThisSym = false; break;
130    case ELF::R_ARM_PREL31: EmitThisSym = false; break;
131    }
132  }
133
134  if (EmitThisSym)
135    return &Symbol;
136  if (! Symbol.isTemporary() && InNormalSection) {
137    return &Symbol;
138  }
139  return NULL;
140}
141
142// Need to examine the Fixup when determining whether to
143// emit the relocation as an explicit symbol or as a section relative
144// offset
145unsigned ARMELFObjectWriter::GetRelocType(const MCValue &Target,
146                                          const MCFixup &Fixup,
147                                          bool IsPCRel,
148                                          bool IsRelocWithSymbol,
149                                          int64_t Addend) const {
150  return GetRelocTypeInner(Target, Fixup, IsPCRel);
151}
152
153unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
154                                               const MCFixup &Fixup,
155                                               bool IsPCRel) const  {
156  MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ?
157    MCSymbolRefExpr::VK_None : Target.getSymA()->getKind();
158
159  unsigned Type = 0;
160  if (IsPCRel) {
161    switch ((unsigned)Fixup.getKind()) {
162    default: llvm_unreachable("Unimplemented");
163    case FK_Data_4:
164      switch (Modifier) {
165      default: llvm_unreachable("Unsupported Modifier");
166      case MCSymbolRefExpr::VK_None:
167        Type = ELF::R_ARM_REL32;
168        break;
169      case MCSymbolRefExpr::VK_ARM_TLSGD:
170        llvm_unreachable("unimplemented");
171      case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
172        Type = ELF::R_ARM_TLS_IE32;
173        break;
174      }
175      break;
176    case ARM::fixup_arm_blx:
177    case ARM::fixup_arm_uncondbl:
178      switch (Modifier) {
179      case MCSymbolRefExpr::VK_ARM_PLT:
180        Type = ELF::R_ARM_PLT32;
181        break;
182      default:
183        Type = ELF::R_ARM_CALL;
184        break;
185      }
186      break;
187    case ARM::fixup_arm_condbl:
188    case ARM::fixup_arm_condbranch:
189    case ARM::fixup_arm_uncondbranch:
190      Type = ELF::R_ARM_JUMP24;
191      break;
192    case ARM::fixup_t2_condbranch:
193    case ARM::fixup_t2_uncondbranch:
194      Type = ELF::R_ARM_THM_JUMP24;
195      break;
196    case ARM::fixup_arm_movt_hi16:
197    case ARM::fixup_arm_movt_hi16_pcrel:
198      Type = ELF::R_ARM_MOVT_PREL;
199      break;
200    case ARM::fixup_arm_movw_lo16:
201    case ARM::fixup_arm_movw_lo16_pcrel:
202      Type = ELF::R_ARM_MOVW_PREL_NC;
203      break;
204    case ARM::fixup_t2_movt_hi16:
205    case ARM::fixup_t2_movt_hi16_pcrel:
206      Type = ELF::R_ARM_THM_MOVT_PREL;
207      break;
208    case ARM::fixup_t2_movw_lo16:
209    case ARM::fixup_t2_movw_lo16_pcrel:
210      Type = ELF::R_ARM_THM_MOVW_PREL_NC;
211      break;
212    case ARM::fixup_arm_thumb_bl:
213    case ARM::fixup_arm_thumb_blx:
214      Type = ELF::R_ARM_THM_CALL;
215      break;
216    }
217  } else {
218    switch ((unsigned)Fixup.getKind()) {
219    default: llvm_unreachable("invalid fixup kind!");
220    case FK_Data_4:
221      switch (Modifier) {
222      default: llvm_unreachable("Unsupported Modifier");
223      case MCSymbolRefExpr::VK_ARM_NONE:
224        Type = ELF::R_ARM_NONE;
225        break;
226      case MCSymbolRefExpr::VK_ARM_GOT:
227        Type = ELF::R_ARM_GOT_BREL;
228        break;
229      case MCSymbolRefExpr::VK_ARM_TLSGD:
230        Type = ELF::R_ARM_TLS_GD32;
231        break;
232      case MCSymbolRefExpr::VK_ARM_TPOFF:
233        Type = ELF::R_ARM_TLS_LE32;
234        break;
235      case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
236        Type = ELF::R_ARM_TLS_IE32;
237        break;
238      case MCSymbolRefExpr::VK_None:
239        Type = ELF::R_ARM_ABS32;
240        break;
241      case MCSymbolRefExpr::VK_ARM_GOTOFF:
242        Type = ELF::R_ARM_GOTOFF32;
243        break;
244      case MCSymbolRefExpr::VK_ARM_TARGET1:
245        Type = ELF::R_ARM_TARGET1;
246        break;
247      case MCSymbolRefExpr::VK_ARM_TARGET2:
248        Type = ELF::R_ARM_TARGET2;
249        break;
250      case MCSymbolRefExpr::VK_ARM_PREL31:
251        Type = ELF::R_ARM_PREL31;
252        break;
253      }
254      break;
255    case ARM::fixup_arm_ldst_pcrel_12:
256    case ARM::fixup_arm_pcrel_10:
257    case ARM::fixup_arm_adr_pcrel_12:
258    case ARM::fixup_arm_thumb_bl:
259    case ARM::fixup_arm_thumb_cb:
260    case ARM::fixup_arm_thumb_cp:
261    case ARM::fixup_arm_thumb_br:
262      llvm_unreachable("Unimplemented");
263    case ARM::fixup_arm_condbranch:
264    case ARM::fixup_arm_uncondbranch:
265      Type = ELF::R_ARM_JUMP24;
266      break;
267    case ARM::fixup_arm_movt_hi16:
268      Type = ELF::R_ARM_MOVT_ABS;
269      break;
270    case ARM::fixup_arm_movw_lo16:
271      Type = ELF::R_ARM_MOVW_ABS_NC;
272      break;
273    case ARM::fixup_t2_movt_hi16:
274      Type = ELF::R_ARM_THM_MOVT_ABS;
275      break;
276    case ARM::fixup_t2_movw_lo16:
277      Type = ELF::R_ARM_THM_MOVW_ABS_NC;
278      break;
279    }
280  }
281
282  return Type;
283}
284
285MCObjectWriter *llvm::createARMELFObjectWriter(raw_ostream &OS,
286                                               uint8_t OSABI) {
287  MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
288  return createELFObjectWriter(MOTW, OS,  /*IsLittleEndian=*/true);
289}
290