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 unsigned getEFlags() const;
41     virtual const MCSymbol *ExplicitRelSym(const MCAssembler &Asm,
42                                    const MCValue &Target,
43                                    const MCFragment &F,
44                                    const MCFixup &Fixup,
45                                    bool IsPCRel) const;
46   };
47 }
48 
49 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
50   : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
51                             ELF::EM_ARM,
52                             /*HasRelocationAddend*/ false) {}
53 
54 ARMELFObjectWriter::~ARMELFObjectWriter() {}
55 
56 // FIXME: get the real EABI Version from the Triple.
57 unsigned ARMELFObjectWriter::getEFlags() const {
58   return ELF::EF_ARM_EABIMASK & DefaultEABIVersion;
59 }
60 
61 // In ARM, _MergedGlobals and other most symbols get emitted directly.
62 // I.e. not as an offset to a section symbol.
63 // This code is an approximation of what ARM/gcc does.
64 
65 STATISTIC(PCRelCount, "Total number of PIC Relocations");
66 STATISTIC(NonPCRelCount, "Total number of non-PIC relocations");
67 
68 const MCSymbol *ARMELFObjectWriter::ExplicitRelSym(const MCAssembler &Asm,
69                                                    const MCValue &Target,
70                                                    const MCFragment &F,
71                                                    const MCFixup &Fixup,
72                                                    bool IsPCRel) const {
73   const MCSymbol &Symbol = Target.getSymA()->getSymbol().AliasedSymbol();
74   bool EmitThisSym = false;
75 
76   const MCSectionELF &Section =
77     static_cast<const MCSectionELF&>(Symbol.getSection());
78   bool InNormalSection = true;
79   unsigned RelocType = 0;
80   RelocType = GetRelocTypeInner(Target, Fixup, IsPCRel);
81 
82   DEBUG(
83       const MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
84       MCSymbolRefExpr::VariantKind Kind2;
85       Kind2 = Target.getSymB() ?  Target.getSymB()->getKind() :
86         MCSymbolRefExpr::VK_None;
87       dbgs() << "considering symbol "
88         << Section.getSectionName() << "/"
89         << Symbol.getName() << "/"
90         << " Rel:" << (unsigned)RelocType
91         << " Kind: " << (int)Kind << "/" << (int)Kind2
92         << " Tmp:"
93         << Symbol.isAbsolute() << "/" << Symbol.isDefined() << "/"
94         << Symbol.isVariable() << "/" << Symbol.isTemporary()
95         << " Counts:" << PCRelCount << "/" << NonPCRelCount << "\n");
96 
97   if (IsPCRel) { ++PCRelCount;
98     switch (RelocType) {
99     default:
100       // Most relocation types are emitted as explicit symbols
101       InNormalSection =
102         StringSwitch<bool>(Section.getSectionName())
103         .Case(".data.rel.ro.local", false)
104         .Case(".data.rel", false)
105         .Case(".bss", false)
106         .Default(true);
107       EmitThisSym = true;
108       break;
109     case ELF::R_ARM_ABS32:
110       // But things get strange with R_ARM_ABS32
111       // In this case, most things that go in .rodata show up
112       // as section relative relocations
113       InNormalSection =
114         StringSwitch<bool>(Section.getSectionName())
115         .Case(".data.rel.ro.local", false)
116         .Case(".data.rel", false)
117         .Case(".rodata", false)
118         .Case(".bss", false)
119         .Default(true);
120       EmitThisSym = false;
121       break;
122     }
123   } else {
124     NonPCRelCount++;
125     InNormalSection =
126       StringSwitch<bool>(Section.getSectionName())
127       .Case(".data.rel.ro.local", false)
128       .Case(".rodata", false)
129       .Case(".data.rel", false)
130       .Case(".bss", false)
131       .Default(true);
132 
133     switch (RelocType) {
134     default: EmitThisSym = true; break;
135     case ELF::R_ARM_ABS32: EmitThisSym = false; break;
136     case ELF::R_ARM_PREL31: EmitThisSym = false; break;
137     }
138   }
139 
140   if (EmitThisSym)
141     return &Symbol;
142   if (! Symbol.isTemporary() && InNormalSection) {
143     return &Symbol;
144   }
145   return NULL;
146 }
147 
148 // Need to examine the Fixup when determining whether to
149 // emit the relocation as an explicit symbol or as a section relative
150 // offset
151 unsigned ARMELFObjectWriter::GetRelocType(const MCValue &Target,
152                                           const MCFixup &Fixup,
153                                           bool IsPCRel,
154                                           bool IsRelocWithSymbol,
155                                           int64_t Addend) const {
156   return GetRelocTypeInner(Target, Fixup, IsPCRel);
157 }
158 
159 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
160                                                const MCFixup &Fixup,
161                                                bool IsPCRel) const  {
162   MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ?
163     MCSymbolRefExpr::VK_None : Target.getSymA()->getKind();
164 
165   unsigned Type = 0;
166   if (IsPCRel) {
167     switch ((unsigned)Fixup.getKind()) {
168     default: llvm_unreachable("Unimplemented");
169     case FK_Data_4:
170       switch (Modifier) {
171       default: llvm_unreachable("Unsupported Modifier");
172       case MCSymbolRefExpr::VK_None:
173         Type = ELF::R_ARM_REL32;
174         break;
175       case MCSymbolRefExpr::VK_ARM_TLSGD:
176         llvm_unreachable("unimplemented");
177       case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
178         Type = ELF::R_ARM_TLS_IE32;
179         break;
180       }
181       break;
182     case ARM::fixup_arm_blx:
183     case ARM::fixup_arm_uncondbl:
184       switch (Modifier) {
185       case MCSymbolRefExpr::VK_ARM_PLT:
186         Type = ELF::R_ARM_PLT32;
187         break;
188       default:
189         Type = ELF::R_ARM_CALL;
190         break;
191       }
192       break;
193     case ARM::fixup_arm_condbl:
194     case ARM::fixup_arm_condbranch:
195     case ARM::fixup_arm_uncondbranch:
196       Type = ELF::R_ARM_JUMP24;
197       break;
198     case ARM::fixup_t2_condbranch:
199     case ARM::fixup_t2_uncondbranch:
200       Type = ELF::R_ARM_THM_JUMP24;
201       break;
202     case ARM::fixup_arm_movt_hi16:
203     case ARM::fixup_arm_movt_hi16_pcrel:
204       Type = ELF::R_ARM_MOVT_PREL;
205       break;
206     case ARM::fixup_arm_movw_lo16:
207     case ARM::fixup_arm_movw_lo16_pcrel:
208       Type = ELF::R_ARM_MOVW_PREL_NC;
209       break;
210     case ARM::fixup_t2_movt_hi16:
211     case ARM::fixup_t2_movt_hi16_pcrel:
212       Type = ELF::R_ARM_THM_MOVT_PREL;
213       break;
214     case ARM::fixup_t2_movw_lo16:
215     case ARM::fixup_t2_movw_lo16_pcrel:
216       Type = ELF::R_ARM_THM_MOVW_PREL_NC;
217       break;
218     case ARM::fixup_arm_thumb_bl:
219     case ARM::fixup_arm_thumb_blx:
220       Type = ELF::R_ARM_THM_CALL;
221       break;
222     }
223   } else {
224     switch ((unsigned)Fixup.getKind()) {
225     default: llvm_unreachable("invalid fixup kind!");
226     case FK_Data_4:
227       switch (Modifier) {
228       default: llvm_unreachable("Unsupported Modifier");
229       case MCSymbolRefExpr::VK_ARM_NONE:
230         Type = ELF::R_ARM_NONE;
231         break;
232       case MCSymbolRefExpr::VK_ARM_GOT:
233         Type = ELF::R_ARM_GOT_BREL;
234         break;
235       case MCSymbolRefExpr::VK_ARM_TLSGD:
236         Type = ELF::R_ARM_TLS_GD32;
237         break;
238       case MCSymbolRefExpr::VK_ARM_TPOFF:
239         Type = ELF::R_ARM_TLS_LE32;
240         break;
241       case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
242         Type = ELF::R_ARM_TLS_IE32;
243         break;
244       case MCSymbolRefExpr::VK_None:
245         Type = ELF::R_ARM_ABS32;
246         break;
247       case MCSymbolRefExpr::VK_ARM_GOTOFF:
248         Type = ELF::R_ARM_GOTOFF32;
249         break;
250       case MCSymbolRefExpr::VK_ARM_TARGET1:
251         Type = ELF::R_ARM_TARGET1;
252         break;
253       case MCSymbolRefExpr::VK_ARM_TARGET2:
254         Type = ELF::R_ARM_TARGET2;
255         break;
256       case MCSymbolRefExpr::VK_ARM_PREL31:
257         Type = ELF::R_ARM_PREL31;
258         break;
259       }
260       break;
261     case ARM::fixup_arm_ldst_pcrel_12:
262     case ARM::fixup_arm_pcrel_10:
263     case ARM::fixup_arm_adr_pcrel_12:
264     case ARM::fixup_arm_thumb_bl:
265     case ARM::fixup_arm_thumb_cb:
266     case ARM::fixup_arm_thumb_cp:
267     case ARM::fixup_arm_thumb_br:
268       llvm_unreachable("Unimplemented");
269     case ARM::fixup_arm_condbranch:
270     case ARM::fixup_arm_uncondbranch:
271       Type = ELF::R_ARM_JUMP24;
272       break;
273     case ARM::fixup_arm_movt_hi16:
274       Type = ELF::R_ARM_MOVT_ABS;
275       break;
276     case ARM::fixup_arm_movw_lo16:
277       Type = ELF::R_ARM_MOVW_ABS_NC;
278       break;
279     case ARM::fixup_t2_movt_hi16:
280       Type = ELF::R_ARM_THM_MOVT_ABS;
281       break;
282     case ARM::fixup_t2_movw_lo16:
283       Type = ELF::R_ARM_THM_MOVW_ABS_NC;
284       break;
285     }
286   }
287 
288   return Type;
289 }
290 
291 MCObjectWriter *llvm::createARMELFObjectWriter(raw_ostream &OS,
292                                                uint8_t OSABI) {
293   MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
294   return createELFObjectWriter(MOTW, OS,  /*IsLittleEndian=*/true);
295 }
296