1 //===-- X86ELFObjectWriter.cpp - X86 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/X86FixupKinds.h"
11 #include "MCTargetDesc/X86MCTargetDesc.h"
12 #include "llvm/BinaryFormat/ELF.h"
13 #include "llvm/MC/MCAsmInfo.h"
14 #include "llvm/MC/MCContext.h"
15 #include "llvm/MC/MCELFObjectWriter.h"
16 #include "llvm/MC/MCExpr.h"
17 #include "llvm/MC/MCFixup.h"
18 #include "llvm/MC/MCObjectWriter.h"
19 #include "llvm/MC/MCValue.h"
20 #include "llvm/Support/ErrorHandling.h"
21 #include <cassert>
22 #include <cstdint>
23 
24 using namespace llvm;
25 
26 namespace {
27 
28 class X86ELFObjectWriter : public MCELFObjectTargetWriter {
29 public:
30   X86ELFObjectWriter(bool IsELF64, uint8_t OSABI, uint16_t EMachine);
31   ~X86ELFObjectWriter() override = default;
32 
33 protected:
34   unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
35                         const MCFixup &Fixup, bool IsPCRel) const override;
36 };
37 
38 } // end anonymous namespace
39 
X86ELFObjectWriter(bool IsELF64,uint8_t OSABI,uint16_t EMachine)40 X86ELFObjectWriter::X86ELFObjectWriter(bool IsELF64, uint8_t OSABI,
41                                        uint16_t EMachine)
42     : MCELFObjectTargetWriter(IsELF64, OSABI, EMachine,
43                               // Only i386 and IAMCU use Rel instead of RelA.
44                               /*HasRelocationAddend*/
45                               (EMachine != ELF::EM_386) &&
46                                   (EMachine != ELF::EM_IAMCU)) {}
47 
48 enum X86_64RelType { RT64_64, RT64_32, RT64_32S, RT64_16, RT64_8 };
49 
getType64(unsigned Kind,MCSymbolRefExpr::VariantKind & Modifier,bool & IsPCRel)50 static X86_64RelType getType64(unsigned Kind,
51                                MCSymbolRefExpr::VariantKind &Modifier,
52                                bool &IsPCRel) {
53   switch (Kind) {
54   default:
55     llvm_unreachable("Unimplemented");
56   case X86::reloc_global_offset_table8:
57     Modifier = MCSymbolRefExpr::VK_GOT;
58     IsPCRel = true;
59     return RT64_64;
60   case FK_Data_8:
61     return RT64_64;
62   case X86::reloc_signed_4byte:
63   case X86::reloc_signed_4byte_relax:
64     if (Modifier == MCSymbolRefExpr::VK_None && !IsPCRel)
65       return RT64_32S;
66     return RT64_32;
67   case X86::reloc_global_offset_table:
68     Modifier = MCSymbolRefExpr::VK_GOT;
69     IsPCRel = true;
70     return RT64_32;
71   case FK_Data_4:
72   case FK_PCRel_4:
73   case X86::reloc_riprel_4byte:
74   case X86::reloc_riprel_4byte_relax:
75   case X86::reloc_riprel_4byte_relax_rex:
76   case X86::reloc_riprel_4byte_movq_load:
77     return RT64_32;
78   case X86::reloc_branch_4byte_pcrel:
79     Modifier = MCSymbolRefExpr::VK_PLT;
80     return RT64_32;
81   case FK_PCRel_2:
82   case FK_Data_2:
83     return RT64_16;
84   case FK_PCRel_1:
85   case FK_Data_1:
86     return RT64_8;
87   }
88 }
89 
checkIs32(MCContext & Ctx,SMLoc Loc,X86_64RelType Type)90 static void checkIs32(MCContext &Ctx, SMLoc Loc, X86_64RelType Type) {
91   if (Type != RT64_32)
92     Ctx.reportError(Loc,
93                     "32 bit reloc applied to a field with a different size");
94 }
95 
getRelocType64(MCContext & Ctx,SMLoc Loc,MCSymbolRefExpr::VariantKind Modifier,X86_64RelType Type,bool IsPCRel,unsigned Kind)96 static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
97                                MCSymbolRefExpr::VariantKind Modifier,
98                                X86_64RelType Type, bool IsPCRel,
99                                unsigned Kind) {
100   switch (Modifier) {
101   default:
102     llvm_unreachable("Unimplemented");
103   case MCSymbolRefExpr::VK_None:
104   case MCSymbolRefExpr::VK_X86_ABS8:
105     switch (Type) {
106     case RT64_64:
107       return IsPCRel ? ELF::R_X86_64_PC64 : ELF::R_X86_64_64;
108     case RT64_32:
109       return IsPCRel ? ELF::R_X86_64_PC32 : ELF::R_X86_64_32;
110     case RT64_32S:
111       return ELF::R_X86_64_32S;
112     case RT64_16:
113       return IsPCRel ? ELF::R_X86_64_PC16 : ELF::R_X86_64_16;
114     case RT64_8:
115       return IsPCRel ? ELF::R_X86_64_PC8 : ELF::R_X86_64_8;
116     }
117   case MCSymbolRefExpr::VK_GOT:
118     switch (Type) {
119     case RT64_64:
120       return IsPCRel ? ELF::R_X86_64_GOTPC64 : ELF::R_X86_64_GOT64;
121     case RT64_32:
122       return IsPCRel ? ELF::R_X86_64_GOTPC32 : ELF::R_X86_64_GOT32;
123     case RT64_32S:
124     case RT64_16:
125     case RT64_8:
126       llvm_unreachable("Unimplemented");
127     }
128   case MCSymbolRefExpr::VK_GOTOFF:
129     assert(Type == RT64_64);
130     assert(!IsPCRel);
131     return ELF::R_X86_64_GOTOFF64;
132   case MCSymbolRefExpr::VK_TPOFF:
133     assert(!IsPCRel);
134     switch (Type) {
135     case RT64_64:
136       return ELF::R_X86_64_TPOFF64;
137     case RT64_32:
138       return ELF::R_X86_64_TPOFF32;
139     case RT64_32S:
140     case RT64_16:
141     case RT64_8:
142       llvm_unreachable("Unimplemented");
143     }
144   case MCSymbolRefExpr::VK_DTPOFF:
145     assert(!IsPCRel);
146     switch (Type) {
147     case RT64_64:
148       return ELF::R_X86_64_DTPOFF64;
149     case RT64_32:
150       return ELF::R_X86_64_DTPOFF32;
151     case RT64_32S:
152     case RT64_16:
153     case RT64_8:
154       llvm_unreachable("Unimplemented");
155     }
156   case MCSymbolRefExpr::VK_SIZE:
157     assert(!IsPCRel);
158     switch (Type) {
159     case RT64_64:
160       return ELF::R_X86_64_SIZE64;
161     case RT64_32:
162       return ELF::R_X86_64_SIZE32;
163     case RT64_32S:
164     case RT64_16:
165     case RT64_8:
166       llvm_unreachable("Unimplemented");
167     }
168   case MCSymbolRefExpr::VK_TLSCALL:
169     return ELF::R_X86_64_TLSDESC_CALL;
170   case MCSymbolRefExpr::VK_TLSDESC:
171     return ELF::R_X86_64_GOTPC32_TLSDESC;
172   case MCSymbolRefExpr::VK_TLSGD:
173     checkIs32(Ctx, Loc, Type);
174     return ELF::R_X86_64_TLSGD;
175   case MCSymbolRefExpr::VK_GOTTPOFF:
176     checkIs32(Ctx, Loc, Type);
177     return ELF::R_X86_64_GOTTPOFF;
178   case MCSymbolRefExpr::VK_TLSLD:
179     checkIs32(Ctx, Loc, Type);
180     return ELF::R_X86_64_TLSLD;
181   case MCSymbolRefExpr::VK_PLT:
182     checkIs32(Ctx, Loc, Type);
183     return ELF::R_X86_64_PLT32;
184   case MCSymbolRefExpr::VK_GOTPCREL:
185     checkIs32(Ctx, Loc, Type);
186     // Older versions of ld.bfd/ld.gold/lld
187     // do not support GOTPCRELX/REX_GOTPCRELX,
188     // and we want to keep back-compatibility.
189     if (!Ctx.getAsmInfo()->canRelaxRelocations())
190       return ELF::R_X86_64_GOTPCREL;
191     switch (Kind) {
192     default:
193       return ELF::R_X86_64_GOTPCREL;
194     case X86::reloc_riprel_4byte_relax:
195       return ELF::R_X86_64_GOTPCRELX;
196     case X86::reloc_riprel_4byte_relax_rex:
197     case X86::reloc_riprel_4byte_movq_load:
198       return ELF::R_X86_64_REX_GOTPCRELX;
199     }
200   }
201 }
202 
203 enum X86_32RelType { RT32_32, RT32_16, RT32_8 };
204 
getType32(X86_64RelType T)205 static X86_32RelType getType32(X86_64RelType T) {
206   switch (T) {
207   case RT64_64:
208     llvm_unreachable("Unimplemented");
209   case RT64_32:
210   case RT64_32S:
211     return RT32_32;
212   case RT64_16:
213     return RT32_16;
214   case RT64_8:
215     return RT32_8;
216   }
217   llvm_unreachable("unexpected relocation type!");
218 }
219 
getRelocType32(MCContext & Ctx,MCSymbolRefExpr::VariantKind Modifier,X86_32RelType Type,bool IsPCRel,unsigned Kind)220 static unsigned getRelocType32(MCContext &Ctx,
221                                MCSymbolRefExpr::VariantKind Modifier,
222                                X86_32RelType Type, bool IsPCRel,
223                                unsigned Kind) {
224   switch (Modifier) {
225   default:
226     llvm_unreachable("Unimplemented");
227   case MCSymbolRefExpr::VK_None:
228   case MCSymbolRefExpr::VK_X86_ABS8:
229     switch (Type) {
230     case RT32_32:
231       return IsPCRel ? ELF::R_386_PC32 : ELF::R_386_32;
232     case RT32_16:
233       return IsPCRel ? ELF::R_386_PC16 : ELF::R_386_16;
234     case RT32_8:
235       return IsPCRel ? ELF::R_386_PC8 : ELF::R_386_8;
236     }
237   case MCSymbolRefExpr::VK_GOT:
238     assert(Type == RT32_32);
239     if (IsPCRel)
240       return ELF::R_386_GOTPC;
241     // Older versions of ld.bfd/ld.gold/lld do not support R_386_GOT32X and we
242     // want to maintain compatibility.
243     if (!Ctx.getAsmInfo()->canRelaxRelocations())
244       return ELF::R_386_GOT32;
245 
246     return Kind == X86::reloc_signed_4byte_relax ? ELF::R_386_GOT32X
247                                                  : ELF::R_386_GOT32;
248   case MCSymbolRefExpr::VK_GOTOFF:
249     assert(Type == RT32_32);
250     assert(!IsPCRel);
251     return ELF::R_386_GOTOFF;
252   case MCSymbolRefExpr::VK_TPOFF:
253     assert(Type == RT32_32);
254     assert(!IsPCRel);
255     return ELF::R_386_TLS_LE_32;
256   case MCSymbolRefExpr::VK_DTPOFF:
257     assert(Type == RT32_32);
258     assert(!IsPCRel);
259     return ELF::R_386_TLS_LDO_32;
260   case MCSymbolRefExpr::VK_TLSGD:
261     assert(Type == RT32_32);
262     assert(!IsPCRel);
263     return ELF::R_386_TLS_GD;
264   case MCSymbolRefExpr::VK_GOTTPOFF:
265     assert(Type == RT32_32);
266     assert(!IsPCRel);
267     return ELF::R_386_TLS_IE_32;
268   case MCSymbolRefExpr::VK_PLT:
269     assert(Type == RT32_32);
270     return ELF::R_386_PLT32;
271   case MCSymbolRefExpr::VK_INDNTPOFF:
272     assert(Type == RT32_32);
273     assert(!IsPCRel);
274     return ELF::R_386_TLS_IE;
275   case MCSymbolRefExpr::VK_NTPOFF:
276     assert(Type == RT32_32);
277     assert(!IsPCRel);
278     return ELF::R_386_TLS_LE;
279   case MCSymbolRefExpr::VK_GOTNTPOFF:
280     assert(Type == RT32_32);
281     assert(!IsPCRel);
282     return ELF::R_386_TLS_GOTIE;
283   case MCSymbolRefExpr::VK_TLSLDM:
284     assert(Type == RT32_32);
285     assert(!IsPCRel);
286     return ELF::R_386_TLS_LDM;
287   }
288 }
289 
getRelocType(MCContext & Ctx,const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const290 unsigned X86ELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
291                                           const MCFixup &Fixup,
292                                           bool IsPCRel) const {
293   MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
294   unsigned Kind = Fixup.getKind();
295   X86_64RelType Type = getType64(Kind, Modifier, IsPCRel);
296   if (getEMachine() == ELF::EM_X86_64)
297     return getRelocType64(Ctx, Fixup.getLoc(), Modifier, Type, IsPCRel, Kind);
298 
299   assert((getEMachine() == ELF::EM_386 || getEMachine() == ELF::EM_IAMCU) &&
300          "Unsupported ELF machine type.");
301   return getRelocType32(Ctx, Modifier, getType32(Type), IsPCRel, Kind);
302 }
303 
304 std::unique_ptr<MCObjectTargetWriter>
createX86ELFObjectWriter(bool IsELF64,uint8_t OSABI,uint16_t EMachine)305 llvm::createX86ELFObjectWriter(bool IsELF64, uint8_t OSABI, uint16_t EMachine) {
306   return llvm::make_unique<X86ELFObjectWriter>(IsELF64, OSABI, EMachine);
307 }
308