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     ~ARMELFObjectWriter() override;
36 
37     unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
38                           const MCFixup &Fixup, bool IsPCRel) const override;
39 
40     bool needsRelocateWithSymbol(const MCSymbol &Sym,
41                                  unsigned Type) const override;
42   };
43 }
44 
45 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
46   : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
47                             ELF::EM_ARM,
48                             /*HasRelocationAddend*/ false) {}
49 
50 ARMELFObjectWriter::~ARMELFObjectWriter() {}
51 
52 bool ARMELFObjectWriter::needsRelocateWithSymbol(const MCSymbol &Sym,
53                                                  unsigned Type) const {
54   // FIXME: This is extremely conservative. This really needs to use a
55   // whitelist with a clear explanation for why each realocation needs to
56   // point to the symbol, not to the section.
57   switch (Type) {
58   default:
59     return true;
60 
61   case ELF::R_ARM_PREL31:
62   case ELF::R_ARM_ABS32:
63     return false;
64   }
65 }
66 
67 // Need to examine the Fixup when determining whether to
68 // emit the relocation as an explicit symbol or as a section relative
69 // offset
70 unsigned ARMELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
71                                           const MCFixup &Fixup,
72                                           bool IsPCRel) const {
73   return GetRelocTypeInner(Target, Fixup, IsPCRel);
74 }
75 
76 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
77                                                const MCFixup &Fixup,
78                                                bool IsPCRel) const  {
79   MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
80 
81   unsigned Type = 0;
82   if (IsPCRel) {
83     switch ((unsigned)Fixup.getKind()) {
84     default:
85       report_fatal_error("unsupported relocation on symbol");
86       return ELF::R_ARM_NONE;
87     case FK_Data_4:
88       switch (Modifier) {
89       default: llvm_unreachable("Unsupported Modifier");
90       case MCSymbolRefExpr::VK_None:
91         Type = ELF::R_ARM_REL32;
92         break;
93       case MCSymbolRefExpr::VK_TLSGD:
94         llvm_unreachable("unimplemented");
95       case MCSymbolRefExpr::VK_GOTTPOFF:
96         Type = ELF::R_ARM_TLS_IE32;
97         break;
98       case MCSymbolRefExpr::VK_ARM_GOT_PREL:
99         Type = ELF::R_ARM_GOT_PREL;
100         break;
101       case MCSymbolRefExpr::VK_ARM_PREL31:
102         Type = ELF::R_ARM_PREL31;
103         break;
104       }
105       break;
106     case ARM::fixup_arm_blx:
107     case ARM::fixup_arm_uncondbl:
108       switch (Modifier) {
109       case MCSymbolRefExpr::VK_PLT:
110         Type = ELF::R_ARM_CALL;
111         break;
112       case MCSymbolRefExpr::VK_TLSCALL:
113         Type = ELF::R_ARM_TLS_CALL;
114         break;
115       default:
116         Type = ELF::R_ARM_CALL;
117         break;
118       }
119       break;
120     case ARM::fixup_arm_condbl:
121     case ARM::fixup_arm_condbranch:
122     case ARM::fixup_arm_uncondbranch:
123       Type = ELF::R_ARM_JUMP24;
124       break;
125     case ARM::fixup_t2_condbranch:
126       Type = ELF::R_ARM_THM_JUMP19;
127       break;
128     case ARM::fixup_t2_uncondbranch:
129       Type = ELF::R_ARM_THM_JUMP24;
130       break;
131     case ARM::fixup_arm_movt_hi16:
132       Type = ELF::R_ARM_MOVT_PREL;
133       break;
134     case ARM::fixup_arm_movw_lo16:
135       Type = ELF::R_ARM_MOVW_PREL_NC;
136       break;
137     case ARM::fixup_t2_movt_hi16:
138       Type = ELF::R_ARM_THM_MOVT_PREL;
139       break;
140     case ARM::fixup_t2_movw_lo16:
141       Type = ELF::R_ARM_THM_MOVW_PREL_NC;
142       break;
143     case ARM::fixup_arm_thumb_br:
144       Type = ELF::R_ARM_THM_JUMP11;
145       break;
146     case ARM::fixup_arm_thumb_bcc:
147       Type = ELF::R_ARM_THM_JUMP8;
148       break;
149     case ARM::fixup_arm_thumb_bl:
150     case ARM::fixup_arm_thumb_blx:
151       switch (Modifier) {
152       case MCSymbolRefExpr::VK_TLSCALL:
153         Type = ELF::R_ARM_THM_TLS_CALL;
154         break;
155       default:
156         Type = ELF::R_ARM_THM_CALL;
157         break;
158       }
159       break;
160     }
161   } else {
162     switch ((unsigned)Fixup.getKind()) {
163     default:
164       report_fatal_error("unsupported relocation on symbol");
165       return ELF::R_ARM_NONE;
166     case FK_Data_1:
167       switch (Modifier) {
168       default: llvm_unreachable("unsupported Modifier");
169       case MCSymbolRefExpr::VK_None:
170         Type = ELF::R_ARM_ABS8;
171         break;
172       }
173       break;
174     case FK_Data_2:
175       switch (Modifier) {
176       default: llvm_unreachable("unsupported modifier");
177       case MCSymbolRefExpr::VK_None:
178         Type = ELF::R_ARM_ABS16;
179         break;
180       }
181       break;
182     case FK_Data_4:
183       switch (Modifier) {
184       default: llvm_unreachable("Unsupported Modifier");
185       case MCSymbolRefExpr::VK_ARM_NONE:
186         Type = ELF::R_ARM_NONE;
187         break;
188       case MCSymbolRefExpr::VK_GOT:
189         Type = ELF::R_ARM_GOT_BREL;
190         break;
191       case MCSymbolRefExpr::VK_TLSGD:
192         Type = ELF::R_ARM_TLS_GD32;
193         break;
194       case MCSymbolRefExpr::VK_TPOFF:
195         Type = ELF::R_ARM_TLS_LE32;
196         break;
197       case MCSymbolRefExpr::VK_GOTTPOFF:
198         Type = ELF::R_ARM_TLS_IE32;
199         break;
200       case MCSymbolRefExpr::VK_None:
201         Type = ELF::R_ARM_ABS32;
202         break;
203       case MCSymbolRefExpr::VK_GOTOFF:
204         Type = ELF::R_ARM_GOTOFF32;
205         break;
206       case MCSymbolRefExpr::VK_ARM_GOT_PREL:
207         Type = ELF::R_ARM_GOT_PREL;
208         break;
209       case MCSymbolRefExpr::VK_ARM_TARGET1:
210         Type = ELF::R_ARM_TARGET1;
211         break;
212       case MCSymbolRefExpr::VK_ARM_TARGET2:
213         Type = ELF::R_ARM_TARGET2;
214         break;
215       case MCSymbolRefExpr::VK_ARM_PREL31:
216         Type = ELF::R_ARM_PREL31;
217         break;
218       case MCSymbolRefExpr::VK_ARM_SBREL:
219         Type = ELF::R_ARM_SBREL32;
220         break;
221       case MCSymbolRefExpr::VK_ARM_TLSLDO:
222         Type = ELF::R_ARM_TLS_LDO32;
223         break;
224       case MCSymbolRefExpr::VK_TLSCALL:
225         Type = ELF::R_ARM_TLS_CALL;
226         break;
227       case MCSymbolRefExpr::VK_TLSDESC:
228         Type = ELF::R_ARM_TLS_GOTDESC;
229         break;
230       case MCSymbolRefExpr::VK_TLSLDM:
231         Type = ELF::R_ARM_TLS_LDM32;
232         break;
233       case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
234         Type = ELF::R_ARM_TLS_DESCSEQ;
235         break;
236       }
237       break;
238     case ARM::fixup_arm_ldst_pcrel_12:
239     case ARM::fixup_arm_pcrel_10:
240     case ARM::fixup_arm_adr_pcrel_12:
241     case ARM::fixup_arm_thumb_bl:
242     case ARM::fixup_arm_thumb_cb:
243     case ARM::fixup_arm_thumb_cp:
244     case ARM::fixup_arm_thumb_br:
245       llvm_unreachable("Unimplemented");
246     case ARM::fixup_arm_condbranch:
247     case ARM::fixup_arm_uncondbranch:
248       Type = ELF::R_ARM_JUMP24;
249       break;
250     case ARM::fixup_arm_movt_hi16:
251       switch (Modifier) {
252       default: llvm_unreachable("Unsupported Modifier");
253       case MCSymbolRefExpr::VK_None:
254         Type = ELF::R_ARM_MOVT_ABS;
255         break;
256       case MCSymbolRefExpr::VK_ARM_SBREL:
257         Type = ELF:: R_ARM_MOVT_BREL;
258         break;
259       }
260       break;
261     case ARM::fixup_arm_movw_lo16:
262       switch (Modifier) {
263       default: llvm_unreachable("Unsupported Modifier");
264       case MCSymbolRefExpr::VK_None:
265         Type = ELF::R_ARM_MOVW_ABS_NC;
266         break;
267       case MCSymbolRefExpr::VK_ARM_SBREL:
268         Type = ELF:: R_ARM_MOVW_BREL_NC;
269         break;
270       }
271       break;
272     case ARM::fixup_t2_movt_hi16:
273       Type = ELF::R_ARM_THM_MOVT_ABS;
274       break;
275     case ARM::fixup_t2_movw_lo16:
276       Type = ELF::R_ARM_THM_MOVW_ABS_NC;
277       break;
278     }
279   }
280 
281   return Type;
282 }
283 
284 MCObjectWriter *llvm::createARMELFObjectWriter(raw_pwrite_stream &OS,
285                                                uint8_t OSABI,
286                                                bool IsLittleEndian) {
287   MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
288   return createELFObjectWriter(MOTW, OS, IsLittleEndian);
289 }
290