ARMELFObjectWriter.cpp revision 360784 
1//===-- ARMELFObjectWriter.cpp - ARM ELF Writer ---------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "MCTargetDesc/ARMFixupKinds.h"
10#include "MCTargetDesc/ARMMCTargetDesc.h"
11#include "llvm/BinaryFormat/ELF.h"
12#include "llvm/MC/MCContext.h"
13#include "llvm/MC/MCELFObjectWriter.h"
14#include "llvm/MC/MCExpr.h"
15#include "llvm/MC/MCFixup.h"
16#include "llvm/MC/MCObjectFileInfo.h"
17#include "llvm/MC/MCObjectWriter.h"
18#include "llvm/MC/MCValue.h"
19#include "llvm/Support/ErrorHandling.h"
20#include "llvm/Support/raw_ostream.h"
21#include <cstdint>
22
23using namespace llvm;
24
25namespace {
26
27  class ARMELFObjectWriter : public MCELFObjectTargetWriter {
28    enum { DefaultEABIVersion = 0x05000000U };
29
30    unsigned GetRelocTypeInner(const MCValue &Target, const MCFixup &Fixup,
31                               bool IsPCRel, MCContext &Ctx) const;
32
33  public:
34    ARMELFObjectWriter(uint8_t OSABI);
35
36    ~ARMELFObjectWriter() override = default;
37
38    unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
39                          const MCFixup &Fixup, bool IsPCRel) const override;
40
41    bool needsRelocateWithSymbol(const MCSymbol &Sym,
42                                 unsigned Type) const override;
43
44    void addTargetSectionFlags(MCContext &Ctx, MCSectionELF &Sec) override;
45  };
46
47} // end anonymous namespace
48
49ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
50  : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
51                            ELF::EM_ARM,
52                            /*HasRelocationAddend*/ false) {}
53
54bool ARMELFObjectWriter::needsRelocateWithSymbol(const MCSymbol &Sym,
55                                                 unsigned Type) const {
56  // FIXME: This is extremely conservative. This really needs to use a
57  // whitelist with a clear explanation for why each realocation needs to
58  // point to the symbol, not to the section.
59  switch (Type) {
60  default:
61    return true;
62
63  case ELF::R_ARM_PREL31:
64  case ELF::R_ARM_ABS32:
65    return false;
66  }
67}
68
69// Need to examine the Fixup when determining whether to
70// emit the relocation as an explicit symbol or as a section relative
71// offset
72unsigned ARMELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
73                                          const MCFixup &Fixup,
74                                          bool IsPCRel) const {
75  return GetRelocTypeInner(Target, Fixup, IsPCRel, Ctx);
76}
77
78unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
79                                               const MCFixup &Fixup,
80                                               bool IsPCRel,
81                                               MCContext &Ctx) const {
82  MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
83
84  if (IsPCRel) {
85    switch (Fixup.getTargetKind()) {
86    default:
87      Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol");
88      return ELF::R_ARM_NONE;
89    case FK_Data_4:
90      switch (Modifier) {
91      default:
92        llvm_unreachable("Unsupported Modifier");
93      case MCSymbolRefExpr::VK_None:
94        return ELF::R_ARM_REL32;
95      case MCSymbolRefExpr::VK_GOTTPOFF:
96        return ELF::R_ARM_TLS_IE32;
97      case MCSymbolRefExpr::VK_ARM_GOT_PREL:
98        return ELF::R_ARM_GOT_PREL;
99      case MCSymbolRefExpr::VK_ARM_PREL31:
100        return ELF::R_ARM_PREL31;
101      }
102    case ARM::fixup_arm_blx:
103    case ARM::fixup_arm_uncondbl:
104      switch (Modifier) {
105      case MCSymbolRefExpr::VK_PLT:
106        return ELF::R_ARM_CALL;
107      case MCSymbolRefExpr::VK_TLSCALL:
108        return ELF::R_ARM_TLS_CALL;
109      default:
110        return ELF::R_ARM_CALL;
111      }
112    case ARM::fixup_arm_condbl:
113    case ARM::fixup_arm_condbranch:
114    case ARM::fixup_arm_uncondbranch:
115      return ELF::R_ARM_JUMP24;
116    case ARM::fixup_t2_condbranch:
117      return ELF::R_ARM_THM_JUMP19;
118    case ARM::fixup_t2_uncondbranch:
119      return ELF::R_ARM_THM_JUMP24;
120    case ARM::fixup_arm_movt_hi16:
121      return ELF::R_ARM_MOVT_PREL;
122    case ARM::fixup_arm_movw_lo16:
123      return ELF::R_ARM_MOVW_PREL_NC;
124    case ARM::fixup_t2_movt_hi16:
125      return ELF::R_ARM_THM_MOVT_PREL;
126    case ARM::fixup_t2_movw_lo16:
127      return ELF::R_ARM_THM_MOVW_PREL_NC;
128    case ARM::fixup_arm_thumb_br:
129      return ELF::R_ARM_THM_JUMP11;
130    case ARM::fixup_arm_thumb_bcc:
131      return ELF::R_ARM_THM_JUMP8;
132    case ARM::fixup_arm_thumb_bl:
133    case ARM::fixup_arm_thumb_blx:
134      switch (Modifier) {
135      case MCSymbolRefExpr::VK_TLSCALL:
136        return ELF::R_ARM_THM_TLS_CALL;
137      default:
138        return ELF::R_ARM_THM_CALL;
139      }
140    case ARM::fixup_bf_target:
141      return ELF::R_ARM_THM_BF16;
142    case ARM::fixup_bfc_target:
143      return ELF::R_ARM_THM_BF12;
144    case ARM::fixup_bfl_target:
145      return ELF::R_ARM_THM_BF18;
146    }
147  }
148  switch (Fixup.getTargetKind()) {
149  default:
150    Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol");
151    return ELF::R_ARM_NONE;
152  case FK_NONE:
153    return ELF::R_ARM_NONE;
154  case FK_Data_1:
155    switch (Modifier) {
156    default:
157      llvm_unreachable("unsupported Modifier");
158    case MCSymbolRefExpr::VK_None:
159      return ELF::R_ARM_ABS8;
160    }
161  case FK_Data_2:
162    switch (Modifier) {
163    default:
164      llvm_unreachable("unsupported modifier");
165    case MCSymbolRefExpr::VK_None:
166      return ELF::R_ARM_ABS16;
167    }
168  case FK_Data_4:
169    switch (Modifier) {
170    default:
171      llvm_unreachable("Unsupported Modifier");
172    case MCSymbolRefExpr::VK_ARM_NONE:
173      return ELF::R_ARM_NONE;
174    case MCSymbolRefExpr::VK_GOT:
175      return ELF::R_ARM_GOT_BREL;
176    case MCSymbolRefExpr::VK_TLSGD:
177      return ELF::R_ARM_TLS_GD32;
178    case MCSymbolRefExpr::VK_TPOFF:
179      return ELF::R_ARM_TLS_LE32;
180    case MCSymbolRefExpr::VK_GOTTPOFF:
181      return ELF::R_ARM_TLS_IE32;
182    case MCSymbolRefExpr::VK_None:
183      return ELF::R_ARM_ABS32;
184    case MCSymbolRefExpr::VK_GOTOFF:
185      return ELF::R_ARM_GOTOFF32;
186    case MCSymbolRefExpr::VK_ARM_GOT_PREL:
187      return ELF::R_ARM_GOT_PREL;
188    case MCSymbolRefExpr::VK_ARM_TARGET1:
189      return ELF::R_ARM_TARGET1;
190    case MCSymbolRefExpr::VK_ARM_TARGET2:
191      return ELF::R_ARM_TARGET2;
192    case MCSymbolRefExpr::VK_ARM_PREL31:
193      return ELF::R_ARM_PREL31;
194    case MCSymbolRefExpr::VK_ARM_SBREL:
195      return ELF::R_ARM_SBREL32;
196    case MCSymbolRefExpr::VK_ARM_TLSLDO:
197      return ELF::R_ARM_TLS_LDO32;
198    case MCSymbolRefExpr::VK_TLSCALL:
199      return ELF::R_ARM_TLS_CALL;
200    case MCSymbolRefExpr::VK_TLSDESC:
201      return ELF::R_ARM_TLS_GOTDESC;
202    case MCSymbolRefExpr::VK_TLSLDM:
203      return ELF::R_ARM_TLS_LDM32;
204    case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
205      return ELF::R_ARM_TLS_DESCSEQ;
206    }
207  case ARM::fixup_arm_condbranch:
208  case ARM::fixup_arm_uncondbranch:
209    return ELF::R_ARM_JUMP24;
210  case ARM::fixup_arm_movt_hi16:
211    switch (Modifier) {
212    default:
213      llvm_unreachable("Unsupported Modifier");
214    case MCSymbolRefExpr::VK_None:
215      return ELF::R_ARM_MOVT_ABS;
216    case MCSymbolRefExpr::VK_ARM_SBREL:
217      return ELF::R_ARM_MOVT_BREL;
218    }
219  case ARM::fixup_arm_movw_lo16:
220    switch (Modifier) {
221    default:
222      llvm_unreachable("Unsupported Modifier");
223    case MCSymbolRefExpr::VK_None:
224      return ELF::R_ARM_MOVW_ABS_NC;
225    case MCSymbolRefExpr::VK_ARM_SBREL:
226      return ELF::R_ARM_MOVW_BREL_NC;
227    }
228  case ARM::fixup_t2_movt_hi16:
229    switch (Modifier) {
230    default:
231      llvm_unreachable("Unsupported Modifier");
232    case MCSymbolRefExpr::VK_None:
233      return ELF::R_ARM_THM_MOVT_ABS;
234    case MCSymbolRefExpr::VK_ARM_SBREL:
235      return ELF::R_ARM_THM_MOVT_BREL;
236    }
237  case ARM::fixup_t2_movw_lo16:
238    switch (Modifier) {
239    default:
240      llvm_unreachable("Unsupported Modifier");
241    case MCSymbolRefExpr::VK_None:
242      return ELF::R_ARM_THM_MOVW_ABS_NC;
243    case MCSymbolRefExpr::VK_ARM_SBREL:
244      return ELF::R_ARM_THM_MOVW_BREL_NC;
245    }
246  }
247}
248
249void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx,
250                                               MCSectionELF &Sec) {
251  // The mix of execute-only and non-execute-only at link time is
252  // non-execute-only. To avoid the empty implicitly created .text
253  // section from making the whole .text section non-execute-only, we
254  // mark it execute-only if it is empty and there is at least one
255  // execute-only section in the object.
256  MCSectionELF *TextSection =
257      static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection());
258  if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions()) {
259    for (auto &F : TextSection->getFragmentList())
260      if (auto *DF = dyn_cast<MCDataFragment>(&F))
261        if (!DF->getContents().empty())
262          return;
263    TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE);
264  }
265}
266
267std::unique_ptr<MCObjectTargetWriter>
268llvm::createARMELFObjectWriter(uint8_t OSABI) {
269  return std::make_unique<ARMELFObjectWriter>(OSABI);
270}
271