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     unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
38                           bool IsPCRel) const override;
39 
40     bool needsRelocateWithSymbol(const MCSymbolData &SD,
41                                  unsigned Type) const override;
42   };
43 }
44 
ARMELFObjectWriter(uint8_t OSABI)45 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
46   : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
47                             ELF::EM_ARM,
48                             /*HasRelocationAddend*/ false) {}
49 
~ARMELFObjectWriter()50 ARMELFObjectWriter::~ARMELFObjectWriter() {}
51 
needsRelocateWithSymbol(const MCSymbolData & SD,unsigned Type) const52 bool ARMELFObjectWriter::needsRelocateWithSymbol(const MCSymbolData &SD,
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
GetRelocType(const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const70 unsigned ARMELFObjectWriter::GetRelocType(const MCValue &Target,
71                                           const MCFixup &Fixup,
72                                           bool IsPCRel) const {
73   return GetRelocTypeInner(Target, Fixup, IsPCRel);
74 }
75 
GetRelocTypeInner(const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const76 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: llvm_unreachable("Unimplemented");
85     case FK_Data_4:
86       switch (Modifier) {
87       default: llvm_unreachable("Unsupported Modifier");
88       case MCSymbolRefExpr::VK_None:
89         Type = ELF::R_ARM_REL32;
90         break;
91       case MCSymbolRefExpr::VK_TLSGD:
92         llvm_unreachable("unimplemented");
93       case MCSymbolRefExpr::VK_GOTTPOFF:
94         Type = ELF::R_ARM_TLS_IE32;
95         break;
96       case MCSymbolRefExpr::VK_GOTPCREL:
97         Type = ELF::R_ARM_GOT_PREL;
98         break;
99       }
100       break;
101     case ARM::fixup_arm_blx:
102     case ARM::fixup_arm_uncondbl:
103       switch (Modifier) {
104       case MCSymbolRefExpr::VK_PLT:
105         Type = ELF::R_ARM_CALL;
106         break;
107       case MCSymbolRefExpr::VK_ARM_TLSCALL:
108         Type = ELF::R_ARM_TLS_CALL;
109         break;
110       default:
111         Type = ELF::R_ARM_CALL;
112         break;
113       }
114       break;
115     case ARM::fixup_arm_condbl:
116     case ARM::fixup_arm_condbranch:
117     case ARM::fixup_arm_uncondbranch:
118       Type = ELF::R_ARM_JUMP24;
119       break;
120     case ARM::fixup_t2_condbranch:
121     case ARM::fixup_t2_uncondbranch:
122       Type = ELF::R_ARM_THM_JUMP24;
123       break;
124     case ARM::fixup_arm_movt_hi16:
125       Type = ELF::R_ARM_MOVT_PREL;
126       break;
127     case ARM::fixup_arm_movw_lo16:
128       Type = ELF::R_ARM_MOVW_PREL_NC;
129       break;
130     case ARM::fixup_t2_movt_hi16:
131       Type = ELF::R_ARM_THM_MOVT_PREL;
132       break;
133     case ARM::fixup_t2_movw_lo16:
134       Type = ELF::R_ARM_THM_MOVW_PREL_NC;
135       break;
136     case ARM::fixup_arm_thumb_bl:
137     case ARM::fixup_arm_thumb_blx:
138       switch (Modifier) {
139       case MCSymbolRefExpr::VK_ARM_TLSCALL:
140         Type = ELF::R_ARM_THM_TLS_CALL;
141         break;
142       default:
143         Type = ELF::R_ARM_THM_CALL;
144         break;
145       }
146       break;
147     }
148   } else {
149     switch ((unsigned)Fixup.getKind()) {
150     default: llvm_unreachable("invalid fixup kind!");
151     case FK_Data_1:
152       switch (Modifier) {
153       default: llvm_unreachable("unsupported Modifier");
154       case MCSymbolRefExpr::VK_None:
155         Type = ELF::R_ARM_ABS8;
156         break;
157       }
158       break;
159     case FK_Data_2:
160       switch (Modifier) {
161       default: llvm_unreachable("unsupported modifier");
162       case MCSymbolRefExpr::VK_None:
163         Type = ELF::R_ARM_ABS16;
164         break;
165       }
166       break;
167     case FK_Data_4:
168       switch (Modifier) {
169       default: llvm_unreachable("Unsupported Modifier");
170       case MCSymbolRefExpr::VK_ARM_NONE:
171         Type = ELF::R_ARM_NONE;
172         break;
173       case MCSymbolRefExpr::VK_GOT:
174         Type = ELF::R_ARM_GOT_BREL;
175         break;
176       case MCSymbolRefExpr::VK_TLSGD:
177         Type = ELF::R_ARM_TLS_GD32;
178         break;
179       case MCSymbolRefExpr::VK_TPOFF:
180         Type = ELF::R_ARM_TLS_LE32;
181         break;
182       case MCSymbolRefExpr::VK_GOTTPOFF:
183         Type = ELF::R_ARM_TLS_IE32;
184         break;
185       case MCSymbolRefExpr::VK_None:
186         Type = ELF::R_ARM_ABS32;
187         break;
188       case MCSymbolRefExpr::VK_GOTOFF:
189         Type = ELF::R_ARM_GOTOFF32;
190         break;
191       case MCSymbolRefExpr::VK_GOTPCREL:
192         Type = ELF::R_ARM_GOT_PREL;
193         break;
194       case MCSymbolRefExpr::VK_ARM_TARGET1:
195         Type = ELF::R_ARM_TARGET1;
196         break;
197       case MCSymbolRefExpr::VK_ARM_TARGET2:
198         Type = ELF::R_ARM_TARGET2;
199         break;
200       case MCSymbolRefExpr::VK_ARM_PREL31:
201         Type = ELF::R_ARM_PREL31;
202         break;
203       case MCSymbolRefExpr::VK_ARM_SBREL:
204         Type = ELF::R_ARM_SBREL32;
205         break;
206       case MCSymbolRefExpr::VK_ARM_TLSLDO:
207         Type = ELF::R_ARM_TLS_LDO32;
208         break;
209       case MCSymbolRefExpr::VK_ARM_TLSCALL:
210         Type = ELF::R_ARM_TLS_CALL;
211         break;
212       case MCSymbolRefExpr::VK_ARM_TLSDESC:
213         Type = ELF::R_ARM_TLS_GOTDESC;
214         break;
215       case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
216         Type = ELF::R_ARM_TLS_DESCSEQ;
217         break;
218       }
219       break;
220     case ARM::fixup_arm_ldst_pcrel_12:
221     case ARM::fixup_arm_pcrel_10:
222     case ARM::fixup_arm_adr_pcrel_12:
223     case ARM::fixup_arm_thumb_bl:
224     case ARM::fixup_arm_thumb_cb:
225     case ARM::fixup_arm_thumb_cp:
226     case ARM::fixup_arm_thumb_br:
227       llvm_unreachable("Unimplemented");
228     case ARM::fixup_arm_condbranch:
229     case ARM::fixup_arm_uncondbranch:
230       Type = ELF::R_ARM_JUMP24;
231       break;
232     case ARM::fixup_arm_movt_hi16:
233       Type = ELF::R_ARM_MOVT_ABS;
234       break;
235     case ARM::fixup_arm_movw_lo16:
236       Type = ELF::R_ARM_MOVW_ABS_NC;
237       break;
238     case ARM::fixup_t2_movt_hi16:
239       Type = ELF::R_ARM_THM_MOVT_ABS;
240       break;
241     case ARM::fixup_t2_movw_lo16:
242       Type = ELF::R_ARM_THM_MOVW_ABS_NC;
243       break;
244     }
245   }
246 
247   return Type;
248 }
249 
createARMELFObjectWriter(raw_ostream & OS,uint8_t OSABI,bool IsLittleEndian)250 MCObjectWriter *llvm::createARMELFObjectWriter(raw_ostream &OS,
251                                                uint8_t OSABI,
252                                                bool IsLittleEndian) {
253   MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
254   return createELFObjectWriter(MOTW, OS, IsLittleEndian);
255 }
256