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
ARMELFObjectWriter(uint8_t OSABI)48 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
49 : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
50 ELF::EM_ARM,
51 /*HasRelocationAddend*/ false) {}
52
~ARMELFObjectWriter()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
ExplicitRelSym(const MCAssembler & Asm,const MCValue & Target,const MCFragment & F,const MCFixup & Fixup,bool IsPCRel) const62 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
GetRelocType(const MCValue & Target,const MCFixup & Fixup,bool IsPCRel,bool IsRelocWithSymbol,int64_t Addend) const145 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
GetRelocTypeInner(const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const153 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_ARM_TLSGD:
170 llvm_unreachable("unimplemented");
171 case MCSymbolRefExpr::VK_ARM_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_ARM_PLT:
180 Type = ELF::R_ARM_PLT32;
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 Type = ELF::R_ARM_THM_CALL;
215 break;
216 }
217 } else {
218 switch ((unsigned)Fixup.getKind()) {
219 default: llvm_unreachable("invalid fixup kind!");
220 case FK_Data_4:
221 switch (Modifier) {
222 default: llvm_unreachable("Unsupported Modifier");
223 case MCSymbolRefExpr::VK_ARM_NONE:
224 Type = ELF::R_ARM_NONE;
225 break;
226 case MCSymbolRefExpr::VK_ARM_GOT:
227 Type = ELF::R_ARM_GOT_BREL;
228 break;
229 case MCSymbolRefExpr::VK_ARM_TLSGD:
230 Type = ELF::R_ARM_TLS_GD32;
231 break;
232 case MCSymbolRefExpr::VK_ARM_TPOFF:
233 Type = ELF::R_ARM_TLS_LE32;
234 break;
235 case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
236 Type = ELF::R_ARM_TLS_IE32;
237 break;
238 case MCSymbolRefExpr::VK_None:
239 Type = ELF::R_ARM_ABS32;
240 break;
241 case MCSymbolRefExpr::VK_ARM_GOTOFF:
242 Type = ELF::R_ARM_GOTOFF32;
243 break;
244 case MCSymbolRefExpr::VK_ARM_TARGET1:
245 Type = ELF::R_ARM_TARGET1;
246 break;
247 case MCSymbolRefExpr::VK_ARM_TARGET2:
248 Type = ELF::R_ARM_TARGET2;
249 break;
250 case MCSymbolRefExpr::VK_ARM_PREL31:
251 Type = ELF::R_ARM_PREL31;
252 break;
253 }
254 break;
255 case ARM::fixup_arm_ldst_pcrel_12:
256 case ARM::fixup_arm_pcrel_10:
257 case ARM::fixup_arm_adr_pcrel_12:
258 case ARM::fixup_arm_thumb_bl:
259 case ARM::fixup_arm_thumb_cb:
260 case ARM::fixup_arm_thumb_cp:
261 case ARM::fixup_arm_thumb_br:
262 llvm_unreachable("Unimplemented");
263 case ARM::fixup_arm_condbranch:
264 case ARM::fixup_arm_uncondbranch:
265 Type = ELF::R_ARM_JUMP24;
266 break;
267 case ARM::fixup_arm_movt_hi16:
268 Type = ELF::R_ARM_MOVT_ABS;
269 break;
270 case ARM::fixup_arm_movw_lo16:
271 Type = ELF::R_ARM_MOVW_ABS_NC;
272 break;
273 case ARM::fixup_t2_movt_hi16:
274 Type = ELF::R_ARM_THM_MOVT_ABS;
275 break;
276 case ARM::fixup_t2_movw_lo16:
277 Type = ELF::R_ARM_THM_MOVW_ABS_NC;
278 break;
279 }
280 }
281
282 return Type;
283 }
284
createARMELFObjectWriter(raw_ostream & OS,uint8_t OSABI)285 MCObjectWriter *llvm::createARMELFObjectWriter(raw_ostream &OS,
286 uint8_t OSABI) {
287 MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
288 return createELFObjectWriter(MOTW, OS, /*IsLittleEndian=*/true);
289 }
290