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     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 
48 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
49   : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
50                             ELF::EM_ARM,
51                             /*HasRelocationAddend*/ false) {}
52 
53 ARMELFObjectWriter::~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 
59 STATISTIC(PCRelCount, "Total number of PIC Relocations");
60 STATISTIC(NonPCRelCount, "Total number of non-PIC relocations");
61 
62 const 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
145 unsigned 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 
153 unsigned 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_TLSGD:
170         llvm_unreachable("unimplemented");
171       case MCSymbolRefExpr::VK_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_PLT:
180         Type = ELF::R_ARM_PLT32;
181         break;
182       case MCSymbolRefExpr::VK_ARM_TLSCALL:
183         Type = ELF::R_ARM_TLS_CALL;
184         break;
185       default:
186         Type = ELF::R_ARM_CALL;
187         break;
188       }
189       break;
190     case ARM::fixup_arm_condbl:
191     case ARM::fixup_arm_condbranch:
192     case ARM::fixup_arm_uncondbranch:
193       Type = ELF::R_ARM_JUMP24;
194       break;
195     case ARM::fixup_t2_condbranch:
196     case ARM::fixup_t2_uncondbranch:
197       Type = ELF::R_ARM_THM_JUMP24;
198       break;
199     case ARM::fixup_arm_movt_hi16:
200     case ARM::fixup_arm_movt_hi16_pcrel:
201       Type = ELF::R_ARM_MOVT_PREL;
202       break;
203     case ARM::fixup_arm_movw_lo16:
204     case ARM::fixup_arm_movw_lo16_pcrel:
205       Type = ELF::R_ARM_MOVW_PREL_NC;
206       break;
207     case ARM::fixup_t2_movt_hi16:
208     case ARM::fixup_t2_movt_hi16_pcrel:
209       Type = ELF::R_ARM_THM_MOVT_PREL;
210       break;
211     case ARM::fixup_t2_movw_lo16:
212     case ARM::fixup_t2_movw_lo16_pcrel:
213       Type = ELF::R_ARM_THM_MOVW_PREL_NC;
214       break;
215     case ARM::fixup_arm_thumb_bl:
216     case ARM::fixup_arm_thumb_blx:
217       switch (Modifier) {
218       case MCSymbolRefExpr::VK_ARM_TLSCALL:
219         Type = ELF::R_ARM_THM_TLS_CALL;
220         break;
221       default:
222         Type = ELF::R_ARM_THM_CALL;
223         break;
224       }
225       break;
226     }
227   } else {
228     switch ((unsigned)Fixup.getKind()) {
229     default: llvm_unreachable("invalid fixup kind!");
230     case FK_Data_4:
231       switch (Modifier) {
232       default: llvm_unreachable("Unsupported Modifier");
233       case MCSymbolRefExpr::VK_ARM_NONE:
234         Type = ELF::R_ARM_NONE;
235         break;
236       case MCSymbolRefExpr::VK_GOT:
237         Type = ELF::R_ARM_GOT_BREL;
238         break;
239       case MCSymbolRefExpr::VK_TLSGD:
240         Type = ELF::R_ARM_TLS_GD32;
241         break;
242       case MCSymbolRefExpr::VK_TPOFF:
243         Type = ELF::R_ARM_TLS_LE32;
244         break;
245       case MCSymbolRefExpr::VK_GOTTPOFF:
246         Type = ELF::R_ARM_TLS_IE32;
247         break;
248       case MCSymbolRefExpr::VK_None:
249         Type = ELF::R_ARM_ABS32;
250         break;
251       case MCSymbolRefExpr::VK_GOTOFF:
252         Type = ELF::R_ARM_GOTOFF32;
253         break;
254       case MCSymbolRefExpr::VK_ARM_TARGET1:
255         Type = ELF::R_ARM_TARGET1;
256         break;
257       case MCSymbolRefExpr::VK_ARM_TARGET2:
258         Type = ELF::R_ARM_TARGET2;
259         break;
260       case MCSymbolRefExpr::VK_ARM_PREL31:
261         Type = ELF::R_ARM_PREL31;
262         break;
263       case MCSymbolRefExpr::VK_ARM_TLSLDO:
264         Type = ELF::R_ARM_TLS_LDO32;
265         break;
266       case MCSymbolRefExpr::VK_ARM_TLSCALL:
267         Type = ELF::R_ARM_TLS_CALL;
268         break;
269       case MCSymbolRefExpr::VK_ARM_TLSDESC:
270         Type = ELF::R_ARM_TLS_GOTDESC;
271         break;
272       case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
273         Type = ELF::R_ARM_TLS_DESCSEQ;
274         break;
275       }
276       break;
277     case ARM::fixup_arm_ldst_pcrel_12:
278     case ARM::fixup_arm_pcrel_10:
279     case ARM::fixup_arm_adr_pcrel_12:
280     case ARM::fixup_arm_thumb_bl:
281     case ARM::fixup_arm_thumb_cb:
282     case ARM::fixup_arm_thumb_cp:
283     case ARM::fixup_arm_thumb_br:
284       llvm_unreachable("Unimplemented");
285     case ARM::fixup_arm_condbranch:
286     case ARM::fixup_arm_uncondbranch:
287       Type = ELF::R_ARM_JUMP24;
288       break;
289     case ARM::fixup_arm_movt_hi16:
290       Type = ELF::R_ARM_MOVT_ABS;
291       break;
292     case ARM::fixup_arm_movw_lo16:
293       Type = ELF::R_ARM_MOVW_ABS_NC;
294       break;
295     case ARM::fixup_t2_movt_hi16:
296       Type = ELF::R_ARM_THM_MOVT_ABS;
297       break;
298     case ARM::fixup_t2_movw_lo16:
299       Type = ELF::R_ARM_THM_MOVW_ABS_NC;
300       break;
301     }
302   }
303 
304   return Type;
305 }
306 
307 MCObjectWriter *llvm::createARMELFObjectWriter(raw_ostream &OS,
308                                                uint8_t OSABI) {
309   MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
310   return createELFObjectWriter(MOTW, OS,  /*IsLittleEndian=*/true);
311 }
312