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/BinaryFormat/ELF.h"
13 #include "llvm/MC/MCContext.h"
14 #include "llvm/MC/MCELFObjectWriter.h"
15 #include "llvm/MC/MCExpr.h"
16 #include "llvm/MC/MCFixup.h"
17 #include "llvm/MC/MCObjectFileInfo.h"
18 #include "llvm/MC/MCObjectWriter.h"
19 #include "llvm/MC/MCValue.h"
20 #include "llvm/Support/ErrorHandling.h"
21 #include "llvm/Support/raw_ostream.h"
22 #include <cstdint>
23 
24 using namespace llvm;
25 
26 namespace {
27 
28   class ARMELFObjectWriter : public MCELFObjectTargetWriter {
29     enum { DefaultEABIVersion = 0x05000000U };
30 
31     unsigned GetRelocTypeInner(const MCValue &Target, const MCFixup &Fixup,
32                                bool IsPCRel, MCContext &Ctx) const;
33 
34   public:
35     ARMELFObjectWriter(uint8_t OSABI);
36 
37     ~ARMELFObjectWriter() override = default;
38 
39     unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
40                           const MCFixup &Fixup, bool IsPCRel) const override;
41 
42     bool needsRelocateWithSymbol(const MCSymbol &Sym,
43                                  unsigned Type) const override;
44 
45     void addTargetSectionFlags(MCContext &Ctx, MCSectionELF &Sec) override;
46   };
47 
48 } // end anonymous namespace
49 
ARMELFObjectWriter(uint8_t OSABI)50 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
51   : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
52                             ELF::EM_ARM,
53                             /*HasRelocationAddend*/ false) {}
54 
needsRelocateWithSymbol(const MCSymbol & Sym,unsigned Type) const55 bool ARMELFObjectWriter::needsRelocateWithSymbol(const MCSymbol &Sym,
56                                                  unsigned Type) const {
57   // FIXME: This is extremely conservative. This really needs to use a
58   // whitelist with a clear explanation for why each realocation needs to
59   // point to the symbol, not to the section.
60   switch (Type) {
61   default:
62     return true;
63 
64   case ELF::R_ARM_PREL31:
65   case ELF::R_ARM_ABS32:
66     return false;
67   }
68 }
69 
70 // Need to examine the Fixup when determining whether to
71 // emit the relocation as an explicit symbol or as a section relative
72 // offset
getRelocType(MCContext & Ctx,const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const73 unsigned ARMELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
74                                           const MCFixup &Fixup,
75                                           bool IsPCRel) const {
76   return GetRelocTypeInner(Target, Fixup, IsPCRel, Ctx);
77 }
78 
GetRelocTypeInner(const MCValue & Target,const MCFixup & Fixup,bool IsPCRel,MCContext & Ctx) const79 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
80                                                const MCFixup &Fixup,
81                                                bool IsPCRel,
82                                                MCContext &Ctx) const {
83   MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
84 
85   if (IsPCRel) {
86     switch ((unsigned)Fixup.getKind()) {
87     default:
88       Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol");
89       return ELF::R_ARM_NONE;
90     case FK_Data_4:
91       switch (Modifier) {
92       default:
93         llvm_unreachable("Unsupported Modifier");
94       case MCSymbolRefExpr::VK_None:
95         return ELF::R_ARM_REL32;
96       case MCSymbolRefExpr::VK_GOTTPOFF:
97         return ELF::R_ARM_TLS_IE32;
98       case MCSymbolRefExpr::VK_ARM_GOT_PREL:
99         return ELF::R_ARM_GOT_PREL;
100       case MCSymbolRefExpr::VK_ARM_PREL31:
101         return ELF::R_ARM_PREL31;
102       }
103     case ARM::fixup_arm_blx:
104     case ARM::fixup_arm_uncondbl:
105       switch (Modifier) {
106       case MCSymbolRefExpr::VK_PLT:
107         return ELF::R_ARM_CALL;
108       case MCSymbolRefExpr::VK_TLSCALL:
109         return ELF::R_ARM_TLS_CALL;
110       default:
111         return ELF::R_ARM_CALL;
112       }
113     case ARM::fixup_arm_condbl:
114     case ARM::fixup_arm_condbranch:
115     case ARM::fixup_arm_uncondbranch:
116       return ELF::R_ARM_JUMP24;
117     case ARM::fixup_t2_condbranch:
118       return ELF::R_ARM_THM_JUMP19;
119     case ARM::fixup_t2_uncondbranch:
120       return ELF::R_ARM_THM_JUMP24;
121     case ARM::fixup_arm_movt_hi16:
122       return ELF::R_ARM_MOVT_PREL;
123     case ARM::fixup_arm_movw_lo16:
124       return ELF::R_ARM_MOVW_PREL_NC;
125     case ARM::fixup_t2_movt_hi16:
126       return ELF::R_ARM_THM_MOVT_PREL;
127     case ARM::fixup_t2_movw_lo16:
128       return ELF::R_ARM_THM_MOVW_PREL_NC;
129     case ARM::fixup_arm_thumb_br:
130       return ELF::R_ARM_THM_JUMP11;
131     case ARM::fixup_arm_thumb_bcc:
132       return ELF::R_ARM_THM_JUMP8;
133     case ARM::fixup_arm_thumb_bl:
134     case ARM::fixup_arm_thumb_blx:
135       switch (Modifier) {
136       case MCSymbolRefExpr::VK_TLSCALL:
137         return ELF::R_ARM_THM_TLS_CALL;
138       default:
139         return ELF::R_ARM_THM_CALL;
140       }
141     }
142   }
143   switch ((unsigned)Fixup.getKind()) {
144   default:
145     Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol");
146     return ELF::R_ARM_NONE;
147   case FK_Data_1:
148     switch (Modifier) {
149     default:
150       llvm_unreachable("unsupported Modifier");
151     case MCSymbolRefExpr::VK_None:
152       return ELF::R_ARM_ABS8;
153     }
154   case FK_Data_2:
155     switch (Modifier) {
156     default:
157       llvm_unreachable("unsupported modifier");
158     case MCSymbolRefExpr::VK_None:
159       return ELF::R_ARM_ABS16;
160     }
161   case FK_Data_4:
162     switch (Modifier) {
163     default:
164       llvm_unreachable("Unsupported Modifier");
165     case MCSymbolRefExpr::VK_ARM_NONE:
166       return ELF::R_ARM_NONE;
167     case MCSymbolRefExpr::VK_GOT:
168       return ELF::R_ARM_GOT_BREL;
169     case MCSymbolRefExpr::VK_TLSGD:
170       return ELF::R_ARM_TLS_GD32;
171     case MCSymbolRefExpr::VK_TPOFF:
172       return ELF::R_ARM_TLS_LE32;
173     case MCSymbolRefExpr::VK_GOTTPOFF:
174       return ELF::R_ARM_TLS_IE32;
175     case MCSymbolRefExpr::VK_None:
176       return ELF::R_ARM_ABS32;
177     case MCSymbolRefExpr::VK_GOTOFF:
178       return ELF::R_ARM_GOTOFF32;
179     case MCSymbolRefExpr::VK_ARM_GOT_PREL:
180       return ELF::R_ARM_GOT_PREL;
181     case MCSymbolRefExpr::VK_ARM_TARGET1:
182       return ELF::R_ARM_TARGET1;
183     case MCSymbolRefExpr::VK_ARM_TARGET2:
184       return ELF::R_ARM_TARGET2;
185     case MCSymbolRefExpr::VK_ARM_PREL31:
186       return ELF::R_ARM_PREL31;
187     case MCSymbolRefExpr::VK_ARM_SBREL:
188       return ELF::R_ARM_SBREL32;
189     case MCSymbolRefExpr::VK_ARM_TLSLDO:
190       return ELF::R_ARM_TLS_LDO32;
191     case MCSymbolRefExpr::VK_TLSCALL:
192       return ELF::R_ARM_TLS_CALL;
193     case MCSymbolRefExpr::VK_TLSDESC:
194       return ELF::R_ARM_TLS_GOTDESC;
195     case MCSymbolRefExpr::VK_TLSLDM:
196       return ELF::R_ARM_TLS_LDM32;
197     case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
198       return ELF::R_ARM_TLS_DESCSEQ;
199     }
200   case ARM::fixup_arm_condbranch:
201   case ARM::fixup_arm_uncondbranch:
202     return ELF::R_ARM_JUMP24;
203   case ARM::fixup_arm_movt_hi16:
204     switch (Modifier) {
205     default:
206       llvm_unreachable("Unsupported Modifier");
207     case MCSymbolRefExpr::VK_None:
208       return ELF::R_ARM_MOVT_ABS;
209     case MCSymbolRefExpr::VK_ARM_SBREL:
210       return ELF::R_ARM_MOVT_BREL;
211     }
212   case ARM::fixup_arm_movw_lo16:
213     switch (Modifier) {
214     default:
215       llvm_unreachable("Unsupported Modifier");
216     case MCSymbolRefExpr::VK_None:
217       return ELF::R_ARM_MOVW_ABS_NC;
218     case MCSymbolRefExpr::VK_ARM_SBREL:
219       return ELF::R_ARM_MOVW_BREL_NC;
220     }
221   case ARM::fixup_t2_movt_hi16:
222     switch (Modifier) {
223     default:
224       llvm_unreachable("Unsupported Modifier");
225     case MCSymbolRefExpr::VK_None:
226       return ELF::R_ARM_THM_MOVT_ABS;
227     case MCSymbolRefExpr::VK_ARM_SBREL:
228       return ELF::R_ARM_THM_MOVT_BREL;
229     }
230   case ARM::fixup_t2_movw_lo16:
231     switch (Modifier) {
232     default:
233       llvm_unreachable("Unsupported Modifier");
234     case MCSymbolRefExpr::VK_None:
235       return ELF::R_ARM_THM_MOVW_ABS_NC;
236     case MCSymbolRefExpr::VK_ARM_SBREL:
237       return ELF::R_ARM_THM_MOVW_BREL_NC;
238     }
239   }
240 }
241 
addTargetSectionFlags(MCContext & Ctx,MCSectionELF & Sec)242 void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx,
243                                                MCSectionELF &Sec) {
244   // The mix of execute-only and non-execute-only at link time is
245   // non-execute-only. To avoid the empty implicitly created .text
246   // section from making the whole .text section non-execute-only, we
247   // mark it execute-only if it is empty and there is at least one
248   // execute-only section in the object.
249   MCSectionELF *TextSection =
250       static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection());
251   if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions() &&
252       !TextSection->hasData()) {
253     TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE);
254   }
255 }
256 
257 std::unique_ptr<MCObjectTargetWriter>
createARMELFObjectWriter(uint8_t OSABI)258 llvm::createARMELFObjectWriter(uint8_t OSABI) {
259   return llvm::make_unique<ARMELFObjectWriter>(OSABI);
260 }
261