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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 
22 using namespace llvm;
23 
24 namespace {
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     ~ARMELFObjectWriter() override;
36 
37     unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
38                           const MCFixup &Fixup, bool IsPCRel) const override;
39 
40     bool needsRelocateWithSymbol(const MCSymbol &Sym,
41                                  unsigned Type) const override;
42   };
43 }
44 
ARMELFObjectWriter(uint8_t OSABI)45 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
46   : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
47                             ELF::EM_ARM,
48                             /*HasRelocationAddend*/ false) {}
49 
~ARMELFObjectWriter()50 ARMELFObjectWriter::~ARMELFObjectWriter() {}
51 
needsRelocateWithSymbol(const MCSymbol & Sym,unsigned Type) const52 bool ARMELFObjectWriter::needsRelocateWithSymbol(const MCSymbol &Sym,
53                                                  unsigned Type) const {
54   // FIXME: This is extremely conservative. This really needs to use a
55   // whitelist with a clear explanation for why each realocation needs to
56   // point to the symbol, not to the section.
57   switch (Type) {
58   default:
59     return true;
60 
61   case ELF::R_ARM_PREL31:
62   case ELF::R_ARM_ABS32:
63     return false;
64   }
65 }
66 
67 // Need to examine the Fixup when determining whether to
68 // emit the relocation as an explicit symbol or as a section relative
69 // offset
getRelocType(MCContext & Ctx,const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const70 unsigned ARMELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
71                                           const MCFixup &Fixup,
72                                           bool IsPCRel) const {
73   return GetRelocTypeInner(Target, Fixup, IsPCRel);
74 }
75 
GetRelocTypeInner(const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const76 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
77                                                const MCFixup &Fixup,
78                                                bool IsPCRel) const  {
79   MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
80 
81   unsigned Type = 0;
82   if (IsPCRel) {
83     switch ((unsigned)Fixup.getKind()) {
84     default:
85       report_fatal_error("unsupported relocation on symbol");
86       return ELF::R_ARM_NONE;
87     case FK_Data_4:
88       switch (Modifier) {
89       default: llvm_unreachable("Unsupported Modifier");
90       case MCSymbolRefExpr::VK_None:
91         Type = ELF::R_ARM_REL32;
92         break;
93       case MCSymbolRefExpr::VK_TLSGD:
94         llvm_unreachable("unimplemented");
95       case MCSymbolRefExpr::VK_GOTTPOFF:
96         Type = ELF::R_ARM_TLS_IE32;
97         break;
98       case MCSymbolRefExpr::VK_ARM_GOT_PREL:
99         Type = ELF::R_ARM_GOT_PREL;
100         break;
101       case MCSymbolRefExpr::VK_ARM_PREL31:
102         Type = ELF::R_ARM_PREL31;
103         break;
104       }
105       break;
106     case ARM::fixup_arm_blx:
107     case ARM::fixup_arm_uncondbl:
108       switch (Modifier) {
109       case MCSymbolRefExpr::VK_PLT:
110         Type = ELF::R_ARM_CALL;
111         break;
112       case MCSymbolRefExpr::VK_TLSCALL:
113         Type = ELF::R_ARM_TLS_CALL;
114         break;
115       default:
116         Type = ELF::R_ARM_CALL;
117         break;
118       }
119       break;
120     case ARM::fixup_arm_condbl:
121     case ARM::fixup_arm_condbranch:
122     case ARM::fixup_arm_uncondbranch:
123       Type = ELF::R_ARM_JUMP24;
124       break;
125     case ARM::fixup_t2_condbranch:
126       Type = ELF::R_ARM_THM_JUMP19;
127       break;
128     case ARM::fixup_t2_uncondbranch:
129       Type = ELF::R_ARM_THM_JUMP24;
130       break;
131     case ARM::fixup_arm_movt_hi16:
132       Type = ELF::R_ARM_MOVT_PREL;
133       break;
134     case ARM::fixup_arm_movw_lo16:
135       Type = ELF::R_ARM_MOVW_PREL_NC;
136       break;
137     case ARM::fixup_t2_movt_hi16:
138       Type = ELF::R_ARM_THM_MOVT_PREL;
139       break;
140     case ARM::fixup_t2_movw_lo16:
141       Type = ELF::R_ARM_THM_MOVW_PREL_NC;
142       break;
143     case ARM::fixup_arm_thumb_bl:
144     case ARM::fixup_arm_thumb_blx:
145       switch (Modifier) {
146       case MCSymbolRefExpr::VK_TLSCALL:
147         Type = ELF::R_ARM_THM_TLS_CALL;
148         break;
149       default:
150         Type = ELF::R_ARM_THM_CALL;
151         break;
152       }
153       break;
154     }
155   } else {
156     switch ((unsigned)Fixup.getKind()) {
157     default:
158       report_fatal_error("unsupported relocation on symbol");
159       return ELF::R_ARM_NONE;
160     case FK_Data_1:
161       switch (Modifier) {
162       default: llvm_unreachable("unsupported Modifier");
163       case MCSymbolRefExpr::VK_None:
164         Type = ELF::R_ARM_ABS8;
165         break;
166       }
167       break;
168     case FK_Data_2:
169       switch (Modifier) {
170       default: llvm_unreachable("unsupported modifier");
171       case MCSymbolRefExpr::VK_None:
172         Type = ELF::R_ARM_ABS16;
173         break;
174       }
175       break;
176     case FK_Data_4:
177       switch (Modifier) {
178       default: llvm_unreachable("Unsupported Modifier");
179       case MCSymbolRefExpr::VK_ARM_NONE:
180         Type = ELF::R_ARM_NONE;
181         break;
182       case MCSymbolRefExpr::VK_GOT:
183         Type = ELF::R_ARM_GOT_BREL;
184         break;
185       case MCSymbolRefExpr::VK_TLSGD:
186         Type = ELF::R_ARM_TLS_GD32;
187         break;
188       case MCSymbolRefExpr::VK_TPOFF:
189         Type = ELF::R_ARM_TLS_LE32;
190         break;
191       case MCSymbolRefExpr::VK_GOTTPOFF:
192         Type = ELF::R_ARM_TLS_IE32;
193         break;
194       case MCSymbolRefExpr::VK_None:
195         Type = ELF::R_ARM_ABS32;
196         break;
197       case MCSymbolRefExpr::VK_GOTOFF:
198         Type = ELF::R_ARM_GOTOFF32;
199         break;
200       case MCSymbolRefExpr::VK_ARM_GOT_PREL:
201         Type = ELF::R_ARM_GOT_PREL;
202         break;
203       case MCSymbolRefExpr::VK_ARM_TARGET1:
204         Type = ELF::R_ARM_TARGET1;
205         break;
206       case MCSymbolRefExpr::VK_ARM_TARGET2:
207         Type = ELF::R_ARM_TARGET2;
208         break;
209       case MCSymbolRefExpr::VK_ARM_PREL31:
210         Type = ELF::R_ARM_PREL31;
211         break;
212       case MCSymbolRefExpr::VK_ARM_SBREL:
213         Type = ELF::R_ARM_SBREL32;
214         break;
215       case MCSymbolRefExpr::VK_ARM_TLSLDO:
216         Type = ELF::R_ARM_TLS_LDO32;
217         break;
218       case MCSymbolRefExpr::VK_TLSCALL:
219         Type = ELF::R_ARM_TLS_CALL;
220         break;
221       case MCSymbolRefExpr::VK_TLSDESC:
222         Type = ELF::R_ARM_TLS_GOTDESC;
223         break;
224       case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
225         Type = ELF::R_ARM_TLS_DESCSEQ;
226         break;
227       }
228       break;
229     case ARM::fixup_arm_ldst_pcrel_12:
230     case ARM::fixup_arm_pcrel_10:
231     case ARM::fixup_arm_adr_pcrel_12:
232     case ARM::fixup_arm_thumb_bl:
233     case ARM::fixup_arm_thumb_cb:
234     case ARM::fixup_arm_thumb_cp:
235     case ARM::fixup_arm_thumb_br:
236       llvm_unreachable("Unimplemented");
237     case ARM::fixup_arm_condbranch:
238     case ARM::fixup_arm_uncondbranch:
239       Type = ELF::R_ARM_JUMP24;
240       break;
241     case ARM::fixup_arm_movt_hi16:
242       Type = ELF::R_ARM_MOVT_ABS;
243       break;
244     case ARM::fixup_arm_movw_lo16:
245       Type = ELF::R_ARM_MOVW_ABS_NC;
246       break;
247     case ARM::fixup_t2_movt_hi16:
248       Type = ELF::R_ARM_THM_MOVT_ABS;
249       break;
250     case ARM::fixup_t2_movw_lo16:
251       Type = ELF::R_ARM_THM_MOVW_ABS_NC;
252       break;
253     }
254   }
255 
256   return Type;
257 }
258 
createARMELFObjectWriter(raw_pwrite_stream & OS,uint8_t OSABI,bool IsLittleEndian)259 MCObjectWriter *llvm::createARMELFObjectWriter(raw_pwrite_stream &OS,
260                                                uint8_t OSABI,
261                                                bool IsLittleEndian) {
262   MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
263   return createELFObjectWriter(MOTW, OS, IsLittleEndian);
264 }
265