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     virtual ~ARMELFObjectWriter();
36 
37     unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
38                           bool IsPCRel, bool IsRelocWithSymbol,
39                           int64_t Addend) const override;
40     const MCSymbol *ExplicitRelSym(const MCAssembler &Asm,
41                                    const MCValue &Target, const MCFragment &F,
42                                    const MCFixup &Fixup,
43                                    bool IsPCRel) const override;
44   };
45 }
46 
47 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
48   : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
49                             ELF::EM_ARM,
50                             /*HasRelocationAddend*/ false) {}
51 
52 ARMELFObjectWriter::~ARMELFObjectWriter() {}
53 
54 // In ARM, _MergedGlobals and other most symbols get emitted directly.
55 // I.e. not as an offset to a section symbol.
56 // This code is an approximation of what ARM/gcc does.
57 
58 STATISTIC(PCRelCount, "Total number of PIC Relocations");
59 STATISTIC(NonPCRelCount, "Total number of non-PIC relocations");
60 
61 const MCSymbol *ARMELFObjectWriter::ExplicitRelSym(const MCAssembler &Asm,
62                                                    const MCValue &Target,
63                                                    const MCFragment &F,
64                                                    const MCFixup &Fixup,
65                                                    bool IsPCRel) const {
66   const MCSymbol &Symbol = Target.getSymA()->getSymbol().AliasedSymbol();
67   bool EmitThisSym = false;
68 
69   const MCSectionELF &Section =
70     static_cast<const MCSectionELF&>(Symbol.getSection());
71   bool InNormalSection = true;
72   unsigned RelocType = 0;
73   RelocType = GetRelocTypeInner(Target, Fixup, IsPCRel);
74   assert(!Target.getSymB() ||
75          Target.getSymB()->getKind() == MCSymbolRefExpr::VK_None);
76 
77   DEBUG(
78       MCSymbolRefExpr::VariantKind Kind = Fixup.getAccessVariant();
79       dbgs() << "considering symbol "
80         << Section.getSectionName() << "/"
81         << Symbol.getName() << "/"
82         << " Rel:" << (unsigned)RelocType
83         << " Kind: " << (int)Kind
84         << " Tmp:"
85         << Symbol.isAbsolute() << "/" << Symbol.isDefined() << "/"
86         << Symbol.isVariable() << "/" << Symbol.isTemporary()
87         << " Counts:" << PCRelCount << "/" << NonPCRelCount << "\n");
88 
89   if (IsPCRel) { ++PCRelCount;
90     switch (RelocType) {
91     default:
92       // Most relocation types are emitted as explicit symbols
93       InNormalSection =
94         StringSwitch<bool>(Section.getSectionName())
95         .Case(".data.rel.ro.local", false)
96         .Case(".data.rel", false)
97         .Case(".bss", false)
98         .Default(true);
99       EmitThisSym = true;
100       break;
101     case ELF::R_ARM_ABS32:
102       // But things get strange with R_ARM_ABS32
103       // In this case, most things that go in .rodata show up
104       // as section relative relocations
105       InNormalSection =
106         StringSwitch<bool>(Section.getSectionName())
107         .Case(".data.rel.ro.local", false)
108         .Case(".data.rel", false)
109         .Case(".rodata", false)
110         .Case(".bss", false)
111         .Default(true);
112       EmitThisSym = false;
113       break;
114     }
115   } else {
116     NonPCRelCount++;
117     InNormalSection =
118       StringSwitch<bool>(Section.getSectionName())
119       .Case(".data.rel.ro.local", false)
120       .Case(".rodata", false)
121       .Case(".data.rel", false)
122       .Case(".bss", false)
123       .Default(true);
124 
125     switch (RelocType) {
126     default: EmitThisSym = true; break;
127     case ELF::R_ARM_ABS32: EmitThisSym = false; break;
128     case ELF::R_ARM_PREL31: EmitThisSym = false; break;
129     }
130   }
131 
132   if (EmitThisSym)
133     return &Symbol;
134   if (! Symbol.isTemporary() && InNormalSection) {
135     return &Symbol;
136   }
137   return NULL;
138 }
139 
140 // Need to examine the Fixup when determining whether to
141 // emit the relocation as an explicit symbol or as a section relative
142 // offset
143 unsigned ARMELFObjectWriter::GetRelocType(const MCValue &Target,
144                                           const MCFixup &Fixup,
145                                           bool IsPCRel,
146                                           bool IsRelocWithSymbol,
147                                           int64_t Addend) const {
148   return GetRelocTypeInner(Target, Fixup, IsPCRel);
149 }
150 
151 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
152                                                const MCFixup &Fixup,
153                                                bool IsPCRel) const  {
154   MCSymbolRefExpr::VariantKind Modifier = Fixup.getAccessVariant();
155 
156   unsigned Type = 0;
157   if (IsPCRel) {
158     switch ((unsigned)Fixup.getKind()) {
159     default: llvm_unreachable("Unimplemented");
160     case FK_Data_4:
161       switch (Modifier) {
162       default: llvm_unreachable("Unsupported Modifier");
163       case MCSymbolRefExpr::VK_None:
164         Type = ELF::R_ARM_REL32;
165         break;
166       case MCSymbolRefExpr::VK_TLSGD:
167         llvm_unreachable("unimplemented");
168       case MCSymbolRefExpr::VK_GOTTPOFF:
169         Type = ELF::R_ARM_TLS_IE32;
170         break;
171       }
172       break;
173     case ARM::fixup_arm_blx:
174     case ARM::fixup_arm_uncondbl:
175       switch (Modifier) {
176       case MCSymbolRefExpr::VK_PLT:
177         Type = ELF::R_ARM_PLT32;
178         break;
179       case MCSymbolRefExpr::VK_ARM_TLSCALL:
180         Type = ELF::R_ARM_TLS_CALL;
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       switch (Modifier) {
215       case MCSymbolRefExpr::VK_ARM_TLSCALL:
216         Type = ELF::R_ARM_THM_TLS_CALL;
217         break;
218       default:
219         Type = ELF::R_ARM_THM_CALL;
220         break;
221       }
222       break;
223     }
224   } else {
225     switch ((unsigned)Fixup.getKind()) {
226     default: llvm_unreachable("invalid fixup kind!");
227     case FK_Data_4:
228       switch (Modifier) {
229       default: llvm_unreachable("Unsupported Modifier");
230       case MCSymbolRefExpr::VK_ARM_NONE:
231         Type = ELF::R_ARM_NONE;
232         break;
233       case MCSymbolRefExpr::VK_GOT:
234         Type = ELF::R_ARM_GOT_BREL;
235         break;
236       case MCSymbolRefExpr::VK_TLSGD:
237         Type = ELF::R_ARM_TLS_GD32;
238         break;
239       case MCSymbolRefExpr::VK_TPOFF:
240         Type = ELF::R_ARM_TLS_LE32;
241         break;
242       case MCSymbolRefExpr::VK_GOTTPOFF:
243         Type = ELF::R_ARM_TLS_IE32;
244         break;
245       case MCSymbolRefExpr::VK_None:
246         Type = ELF::R_ARM_ABS32;
247         break;
248       case MCSymbolRefExpr::VK_GOTOFF:
249         Type = ELF::R_ARM_GOTOFF32;
250         break;
251       case MCSymbolRefExpr::VK_ARM_TARGET1:
252         Type = ELF::R_ARM_TARGET1;
253         break;
254       case MCSymbolRefExpr::VK_ARM_TARGET2:
255         Type = ELF::R_ARM_TARGET2;
256         break;
257       case MCSymbolRefExpr::VK_ARM_PREL31:
258         Type = ELF::R_ARM_PREL31;
259         break;
260       case MCSymbolRefExpr::VK_ARM_TLSLDO:
261         Type = ELF::R_ARM_TLS_LDO32;
262         break;
263       case MCSymbolRefExpr::VK_ARM_TLSCALL:
264         Type = ELF::R_ARM_TLS_CALL;
265         break;
266       case MCSymbolRefExpr::VK_ARM_TLSDESC:
267         Type = ELF::R_ARM_TLS_GOTDESC;
268         break;
269       case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
270         Type = ELF::R_ARM_TLS_DESCSEQ;
271         break;
272       }
273       break;
274     case ARM::fixup_arm_ldst_pcrel_12:
275     case ARM::fixup_arm_pcrel_10:
276     case ARM::fixup_arm_adr_pcrel_12:
277     case ARM::fixup_arm_thumb_bl:
278     case ARM::fixup_arm_thumb_cb:
279     case ARM::fixup_arm_thumb_cp:
280     case ARM::fixup_arm_thumb_br:
281       llvm_unreachable("Unimplemented");
282     case ARM::fixup_arm_condbranch:
283     case ARM::fixup_arm_uncondbranch:
284       Type = ELF::R_ARM_JUMP24;
285       break;
286     case ARM::fixup_arm_movt_hi16:
287       Type = ELF::R_ARM_MOVT_ABS;
288       break;
289     case ARM::fixup_arm_movw_lo16:
290       Type = ELF::R_ARM_MOVW_ABS_NC;
291       break;
292     case ARM::fixup_t2_movt_hi16:
293       Type = ELF::R_ARM_THM_MOVT_ABS;
294       break;
295     case ARM::fixup_t2_movw_lo16:
296       Type = ELF::R_ARM_THM_MOVW_ABS_NC;
297       break;
298     }
299   }
300 
301   return Type;
302 }
303 
304 MCObjectWriter *llvm::createARMELFObjectWriter(raw_ostream &OS,
305                                                uint8_t OSABI) {
306   MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
307   return createELFObjectWriter(MOTW, OS,  /*IsLittleEndian=*/true);
308 }
309