1 //===-- X86ELFObjectWriter.cpp - X86 ELF Writer ---------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "MCTargetDesc/X86FixupKinds.h"
10 #include "MCTargetDesc/X86MCTargetDesc.h"
11 #include "llvm/BinaryFormat/ELF.h"
12 #include "llvm/MC/MCAsmInfo.h"
13 #include "llvm/MC/MCContext.h"
14 #include "llvm/MC/MCELFObjectWriter.h"
15 #include "llvm/MC/MCExpr.h"
16 #include "llvm/MC/MCFixup.h"
17 #include "llvm/MC/MCObjectWriter.h"
18 #include "llvm/MC/MCValue.h"
19 #include "llvm/Support/ErrorHandling.h"
20 #include <cassert>
21 #include <cstdint>
22 
23 using namespace llvm;
24 
25 namespace {
26 
27 class X86ELFObjectWriter : public MCELFObjectTargetWriter {
28 public:
29   X86ELFObjectWriter(bool IsELF64, uint8_t OSABI, uint16_t EMachine);
30   ~X86ELFObjectWriter() override = default;
31 
32 protected:
33   unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
34                         const MCFixup &Fixup, bool IsPCRel) const override;
35 };
36 
37 } // end anonymous namespace
38 
X86ELFObjectWriter(bool IsELF64,uint8_t OSABI,uint16_t EMachine)39 X86ELFObjectWriter::X86ELFObjectWriter(bool IsELF64, uint8_t OSABI,
40                                        uint16_t EMachine)
41     : MCELFObjectTargetWriter(IsELF64, OSABI, EMachine,
42                               // Only i386 and IAMCU use Rel instead of RelA.
43                               /*HasRelocationAddend*/
44                               (EMachine != ELF::EM_386) &&
45                                   (EMachine != ELF::EM_IAMCU)) {}
46 
47 enum X86_64RelType { RT64_NONE, RT64_64, RT64_32, RT64_32S, RT64_16, RT64_8 };
48 
getType64(MCFixupKind Kind,MCSymbolRefExpr::VariantKind & Modifier,bool & IsPCRel)49 static X86_64RelType getType64(MCFixupKind Kind,
50                                MCSymbolRefExpr::VariantKind &Modifier,
51                                bool &IsPCRel) {
52   switch (unsigned(Kind)) {
53   default:
54     llvm_unreachable("Unimplemented");
55   case FK_NONE:
56     return RT64_NONE;
57   case X86::reloc_global_offset_table8:
58     Modifier = MCSymbolRefExpr::VK_GOT;
59     IsPCRel = true;
60     return RT64_64;
61   case FK_Data_8:
62     return RT64_64;
63   case X86::reloc_signed_4byte:
64   case X86::reloc_signed_4byte_relax:
65     if (Modifier == MCSymbolRefExpr::VK_None && !IsPCRel)
66       return RT64_32S;
67     return RT64_32;
68   case X86::reloc_global_offset_table:
69     Modifier = MCSymbolRefExpr::VK_GOT;
70     IsPCRel = true;
71     return RT64_32;
72   case FK_Data_4:
73   case FK_PCRel_4:
74   case X86::reloc_riprel_4byte:
75   case X86::reloc_riprel_4byte_relax:
76   case X86::reloc_riprel_4byte_relax_rex:
77   case X86::reloc_riprel_4byte_movq_load:
78     return RT64_32;
79   case X86::reloc_branch_4byte_pcrel:
80     Modifier = MCSymbolRefExpr::VK_PLT;
81     return RT64_32;
82   case FK_PCRel_2:
83   case FK_Data_2:
84     return RT64_16;
85   case FK_PCRel_1:
86   case FK_Data_1:
87     return RT64_8;
88   }
89 }
90 
checkIs32(MCContext & Ctx,SMLoc Loc,X86_64RelType Type)91 static void checkIs32(MCContext &Ctx, SMLoc Loc, X86_64RelType Type) {
92   if (Type != RT64_32)
93     Ctx.reportError(Loc,
94                     "32 bit reloc applied to a field with a different size");
95 }
96 
checkIs64(MCContext & Ctx,SMLoc Loc,X86_64RelType Type)97 static void checkIs64(MCContext &Ctx, SMLoc Loc, X86_64RelType Type) {
98   if (Type != RT64_64)
99     Ctx.reportError(Loc,
100                     "64 bit reloc applied to a field with a different size");
101 }
102 
getRelocType64(MCContext & Ctx,SMLoc Loc,MCSymbolRefExpr::VariantKind Modifier,X86_64RelType Type,bool IsPCRel,MCFixupKind Kind)103 static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
104                                MCSymbolRefExpr::VariantKind Modifier,
105                                X86_64RelType Type, bool IsPCRel,
106                                MCFixupKind Kind) {
107   switch (Modifier) {
108   default:
109     llvm_unreachable("Unimplemented");
110   case MCSymbolRefExpr::VK_None:
111   case MCSymbolRefExpr::VK_X86_ABS8:
112     switch (Type) {
113     case RT64_NONE:
114       if (Modifier == MCSymbolRefExpr::VK_None)
115         return ELF::R_X86_64_NONE;
116       llvm_unreachable("Unimplemented");
117     case RT64_64:
118       return IsPCRel ? ELF::R_X86_64_PC64 : ELF::R_X86_64_64;
119     case RT64_32:
120       return IsPCRel ? ELF::R_X86_64_PC32 : ELF::R_X86_64_32;
121     case RT64_32S:
122       return ELF::R_X86_64_32S;
123     case RT64_16:
124       return IsPCRel ? ELF::R_X86_64_PC16 : ELF::R_X86_64_16;
125     case RT64_8:
126       return IsPCRel ? ELF::R_X86_64_PC8 : ELF::R_X86_64_8;
127     }
128     llvm_unreachable("unexpected relocation type!");
129   case MCSymbolRefExpr::VK_GOT:
130     switch (Type) {
131     case RT64_64:
132       return IsPCRel ? ELF::R_X86_64_GOTPC64 : ELF::R_X86_64_GOT64;
133     case RT64_32:
134       return IsPCRel ? ELF::R_X86_64_GOTPC32 : ELF::R_X86_64_GOT32;
135     case RT64_32S:
136     case RT64_16:
137     case RT64_8:
138     case RT64_NONE:
139       llvm_unreachable("Unimplemented");
140     }
141     llvm_unreachable("unexpected relocation type!");
142   case MCSymbolRefExpr::VK_GOTOFF:
143     assert(Type == RT64_64);
144     assert(!IsPCRel);
145     return ELF::R_X86_64_GOTOFF64;
146   case MCSymbolRefExpr::VK_TPOFF:
147     assert(!IsPCRel);
148     switch (Type) {
149     case RT64_64:
150       return ELF::R_X86_64_TPOFF64;
151     case RT64_32:
152       return ELF::R_X86_64_TPOFF32;
153     case RT64_32S:
154     case RT64_16:
155     case RT64_8:
156     case RT64_NONE:
157       llvm_unreachable("Unimplemented");
158     }
159     llvm_unreachable("unexpected relocation type!");
160   case MCSymbolRefExpr::VK_DTPOFF:
161     assert(!IsPCRel);
162     switch (Type) {
163     case RT64_64:
164       return ELF::R_X86_64_DTPOFF64;
165     case RT64_32:
166       return ELF::R_X86_64_DTPOFF32;
167     case RT64_32S:
168     case RT64_16:
169     case RT64_8:
170     case RT64_NONE:
171       llvm_unreachable("Unimplemented");
172     }
173     llvm_unreachable("unexpected relocation type!");
174   case MCSymbolRefExpr::VK_SIZE:
175     assert(!IsPCRel);
176     switch (Type) {
177     case RT64_64:
178       return ELF::R_X86_64_SIZE64;
179     case RT64_32:
180       return ELF::R_X86_64_SIZE32;
181     case RT64_32S:
182     case RT64_16:
183     case RT64_8:
184     case RT64_NONE:
185       llvm_unreachable("Unimplemented");
186     }
187     llvm_unreachable("unexpected relocation type!");
188   case MCSymbolRefExpr::VK_TLSCALL:
189     return ELF::R_X86_64_TLSDESC_CALL;
190   case MCSymbolRefExpr::VK_TLSDESC:
191     return ELF::R_X86_64_GOTPC32_TLSDESC;
192   case MCSymbolRefExpr::VK_TLSGD:
193     checkIs32(Ctx, Loc, Type);
194     return ELF::R_X86_64_TLSGD;
195   case MCSymbolRefExpr::VK_GOTTPOFF:
196     checkIs32(Ctx, Loc, Type);
197     return ELF::R_X86_64_GOTTPOFF;
198   case MCSymbolRefExpr::VK_TLSLD:
199     checkIs32(Ctx, Loc, Type);
200     return ELF::R_X86_64_TLSLD;
201   case MCSymbolRefExpr::VK_PLT:
202     checkIs32(Ctx, Loc, Type);
203     return ELF::R_X86_64_PLT32;
204   case MCSymbolRefExpr::VK_GOTPCREL:
205     checkIs32(Ctx, Loc, Type);
206     // Older versions of ld.bfd/ld.gold/lld
207     // do not support GOTPCRELX/REX_GOTPCRELX,
208     // and we want to keep back-compatibility.
209     if (!Ctx.getAsmInfo()->canRelaxRelocations())
210       return ELF::R_X86_64_GOTPCREL;
211     switch (unsigned(Kind)) {
212     default:
213       return ELF::R_X86_64_GOTPCREL;
214     case X86::reloc_riprel_4byte_relax:
215       return ELF::R_X86_64_GOTPCRELX;
216     case X86::reloc_riprel_4byte_relax_rex:
217     case X86::reloc_riprel_4byte_movq_load:
218       return ELF::R_X86_64_REX_GOTPCRELX;
219     }
220     llvm_unreachable("unexpected relocation type!");
221   case MCSymbolRefExpr::VK_GOTPCREL_NORELAX:
222     checkIs32(Ctx, Loc, Type);
223     return ELF::R_X86_64_GOTPCREL;
224   case MCSymbolRefExpr::VK_X86_PLTOFF:
225     checkIs64(Ctx, Loc, Type);
226     return ELF::R_X86_64_PLTOFF64;
227   }
228 }
229 
230 enum X86_32RelType { RT32_NONE, RT32_32, RT32_16, RT32_8 };
231 
getType32(X86_64RelType T)232 static X86_32RelType getType32(X86_64RelType T) {
233   switch (T) {
234   case RT64_NONE:
235     return RT32_NONE;
236   case RT64_64:
237     llvm_unreachable("Unimplemented");
238   case RT64_32:
239   case RT64_32S:
240     return RT32_32;
241   case RT64_16:
242     return RT32_16;
243   case RT64_8:
244     return RT32_8;
245   }
246   llvm_unreachable("unexpected relocation type!");
247 }
248 
getRelocType32(MCContext & Ctx,MCSymbolRefExpr::VariantKind Modifier,X86_32RelType Type,bool IsPCRel,MCFixupKind Kind)249 static unsigned getRelocType32(MCContext &Ctx,
250                                MCSymbolRefExpr::VariantKind Modifier,
251                                X86_32RelType Type, bool IsPCRel,
252                                MCFixupKind Kind) {
253   switch (Modifier) {
254   default:
255     llvm_unreachable("Unimplemented");
256   case MCSymbolRefExpr::VK_None:
257   case MCSymbolRefExpr::VK_X86_ABS8:
258     switch (Type) {
259     case RT32_NONE:
260       if (Modifier == MCSymbolRefExpr::VK_None)
261         return ELF::R_386_NONE;
262       llvm_unreachable("Unimplemented");
263     case RT32_32:
264       return IsPCRel ? ELF::R_386_PC32 : ELF::R_386_32;
265     case RT32_16:
266       return IsPCRel ? ELF::R_386_PC16 : ELF::R_386_16;
267     case RT32_8:
268       return IsPCRel ? ELF::R_386_PC8 : ELF::R_386_8;
269     }
270     llvm_unreachable("unexpected relocation type!");
271   case MCSymbolRefExpr::VK_GOT:
272     assert(Type == RT32_32);
273     if (IsPCRel)
274       return ELF::R_386_GOTPC;
275     // Older versions of ld.bfd/ld.gold/lld do not support R_386_GOT32X and we
276     // want to maintain compatibility.
277     if (!Ctx.getAsmInfo()->canRelaxRelocations())
278       return ELF::R_386_GOT32;
279 
280     return Kind == MCFixupKind(X86::reloc_signed_4byte_relax)
281                ? ELF::R_386_GOT32X
282                : ELF::R_386_GOT32;
283   case MCSymbolRefExpr::VK_GOTOFF:
284     assert(Type == RT32_32);
285     assert(!IsPCRel);
286     return ELF::R_386_GOTOFF;
287   case MCSymbolRefExpr::VK_TLSCALL:
288     return ELF::R_386_TLS_DESC_CALL;
289   case MCSymbolRefExpr::VK_TLSDESC:
290     return ELF::R_386_TLS_GOTDESC;
291   case MCSymbolRefExpr::VK_TPOFF:
292     assert(Type == RT32_32);
293     assert(!IsPCRel);
294     return ELF::R_386_TLS_LE_32;
295   case MCSymbolRefExpr::VK_DTPOFF:
296     assert(Type == RT32_32);
297     assert(!IsPCRel);
298     return ELF::R_386_TLS_LDO_32;
299   case MCSymbolRefExpr::VK_TLSGD:
300     assert(Type == RT32_32);
301     assert(!IsPCRel);
302     return ELF::R_386_TLS_GD;
303   case MCSymbolRefExpr::VK_GOTTPOFF:
304     assert(Type == RT32_32);
305     assert(!IsPCRel);
306     return ELF::R_386_TLS_IE_32;
307   case MCSymbolRefExpr::VK_PLT:
308     assert(Type == RT32_32);
309     return ELF::R_386_PLT32;
310   case MCSymbolRefExpr::VK_INDNTPOFF:
311     assert(Type == RT32_32);
312     assert(!IsPCRel);
313     return ELF::R_386_TLS_IE;
314   case MCSymbolRefExpr::VK_NTPOFF:
315     assert(Type == RT32_32);
316     assert(!IsPCRel);
317     return ELF::R_386_TLS_LE;
318   case MCSymbolRefExpr::VK_GOTNTPOFF:
319     assert(Type == RT32_32);
320     assert(!IsPCRel);
321     return ELF::R_386_TLS_GOTIE;
322   case MCSymbolRefExpr::VK_TLSLDM:
323     assert(Type == RT32_32);
324     assert(!IsPCRel);
325     return ELF::R_386_TLS_LDM;
326   }
327 }
328 
getRelocType(MCContext & Ctx,const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const329 unsigned X86ELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
330                                           const MCFixup &Fixup,
331                                           bool IsPCRel) const {
332   MCFixupKind Kind = Fixup.getKind();
333   if (Kind >= FirstLiteralRelocationKind)
334     return Kind - FirstLiteralRelocationKind;
335   MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
336   X86_64RelType Type = getType64(Kind, Modifier, IsPCRel);
337   if (getEMachine() == ELF::EM_X86_64)
338     return getRelocType64(Ctx, Fixup.getLoc(), Modifier, Type, IsPCRel, Kind);
339 
340   assert((getEMachine() == ELF::EM_386 || getEMachine() == ELF::EM_IAMCU) &&
341          "Unsupported ELF machine type.");
342   return getRelocType32(Ctx, Modifier, getType32(Type), IsPCRel, Kind);
343 }
344 
345 std::unique_ptr<MCObjectTargetWriter>
createX86ELFObjectWriter(bool IsELF64,uint8_t OSABI,uint16_t EMachine)346 llvm::createX86ELFObjectWriter(bool IsELF64, uint8_t OSABI, uint16_t EMachine) {
347   return std::make_unique<X86ELFObjectWriter>(IsELF64, OSABI, EMachine);
348 }
349