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(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:
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_GOTPCREL:
99         Type = ELF::R_ARM_GOT_PREL;
100         break;
101       }
102       break;
103     case ARM::fixup_arm_blx:
104     case ARM::fixup_arm_uncondbl:
105       switch (Modifier) {
106       case MCSymbolRefExpr::VK_PLT:
107         Type = ELF::R_ARM_CALL;
108         break;
109       case MCSymbolRefExpr::VK_ARM_TLSCALL:
110         Type = ELF::R_ARM_TLS_CALL;
111         break;
112       default:
113         Type = ELF::R_ARM_CALL;
114         break;
115       }
116       break;
117     case ARM::fixup_arm_condbl:
118     case ARM::fixup_arm_condbranch:
119     case ARM::fixup_arm_uncondbranch:
120       Type = ELF::R_ARM_JUMP24;
121       break;
122     case ARM::fixup_t2_condbranch:
123     case ARM::fixup_t2_uncondbranch:
124       Type = ELF::R_ARM_THM_JUMP24;
125       break;
126     case ARM::fixup_arm_movt_hi16:
127       Type = ELF::R_ARM_MOVT_PREL;
128       break;
129     case ARM::fixup_arm_movw_lo16:
130       Type = ELF::R_ARM_MOVW_PREL_NC;
131       break;
132     case ARM::fixup_t2_movt_hi16:
133       Type = ELF::R_ARM_THM_MOVT_PREL;
134       break;
135     case ARM::fixup_t2_movw_lo16:
136       Type = ELF::R_ARM_THM_MOVW_PREL_NC;
137       break;
138     case ARM::fixup_arm_thumb_bl:
139     case ARM::fixup_arm_thumb_blx:
140       switch (Modifier) {
141       case MCSymbolRefExpr::VK_ARM_TLSCALL:
142         Type = ELF::R_ARM_THM_TLS_CALL;
143         break;
144       default:
145         Type = ELF::R_ARM_THM_CALL;
146         break;
147       }
148       break;
149     }
150   } else {
151     switch ((unsigned)Fixup.getKind()) {
152     default:
153       report_fatal_error("unsupported relocation on symbol");
154       return ELF::R_ARM_NONE;
155     case FK_Data_1:
156       switch (Modifier) {
157       default: llvm_unreachable("unsupported Modifier");
158       case MCSymbolRefExpr::VK_None:
159         Type = ELF::R_ARM_ABS8;
160         break;
161       }
162       break;
163     case FK_Data_2:
164       switch (Modifier) {
165       default: llvm_unreachable("unsupported modifier");
166       case MCSymbolRefExpr::VK_None:
167         Type = ELF::R_ARM_ABS16;
168         break;
169       }
170       break;
171     case FK_Data_4:
172       switch (Modifier) {
173       default: llvm_unreachable("Unsupported Modifier");
174       case MCSymbolRefExpr::VK_ARM_NONE:
175         Type = ELF::R_ARM_NONE;
176         break;
177       case MCSymbolRefExpr::VK_GOT:
178         Type = ELF::R_ARM_GOT_BREL;
179         break;
180       case MCSymbolRefExpr::VK_TLSGD:
181         Type = ELF::R_ARM_TLS_GD32;
182         break;
183       case MCSymbolRefExpr::VK_TPOFF:
184         Type = ELF::R_ARM_TLS_LE32;
185         break;
186       case MCSymbolRefExpr::VK_GOTTPOFF:
187         Type = ELF::R_ARM_TLS_IE32;
188         break;
189       case MCSymbolRefExpr::VK_None:
190         Type = ELF::R_ARM_ABS32;
191         break;
192       case MCSymbolRefExpr::VK_GOTOFF:
193         Type = ELF::R_ARM_GOTOFF32;
194         break;
195       case MCSymbolRefExpr::VK_GOTPCREL:
196         Type = ELF::R_ARM_GOT_PREL;
197         break;
198       case MCSymbolRefExpr::VK_ARM_TARGET1:
199         Type = ELF::R_ARM_TARGET1;
200         break;
201       case MCSymbolRefExpr::VK_ARM_TARGET2:
202         Type = ELF::R_ARM_TARGET2;
203         break;
204       case MCSymbolRefExpr::VK_ARM_PREL31:
205         Type = ELF::R_ARM_PREL31;
206         break;
207       case MCSymbolRefExpr::VK_ARM_SBREL:
208         Type = ELF::R_ARM_SBREL32;
209         break;
210       case MCSymbolRefExpr::VK_ARM_TLSLDO:
211         Type = ELF::R_ARM_TLS_LDO32;
212         break;
213       case MCSymbolRefExpr::VK_ARM_TLSCALL:
214         Type = ELF::R_ARM_TLS_CALL;
215         break;
216       case MCSymbolRefExpr::VK_ARM_TLSDESC:
217         Type = ELF::R_ARM_TLS_GOTDESC;
218         break;
219       case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
220         Type = ELF::R_ARM_TLS_DESCSEQ;
221         break;
222       }
223       break;
224     case ARM::fixup_arm_ldst_pcrel_12:
225     case ARM::fixup_arm_pcrel_10:
226     case ARM::fixup_arm_adr_pcrel_12:
227     case ARM::fixup_arm_thumb_bl:
228     case ARM::fixup_arm_thumb_cb:
229     case ARM::fixup_arm_thumb_cp:
230     case ARM::fixup_arm_thumb_br:
231       llvm_unreachable("Unimplemented");
232     case ARM::fixup_arm_condbranch:
233     case ARM::fixup_arm_uncondbranch:
234       Type = ELF::R_ARM_JUMP24;
235       break;
236     case ARM::fixup_arm_movt_hi16:
237       Type = ELF::R_ARM_MOVT_ABS;
238       break;
239     case ARM::fixup_arm_movw_lo16:
240       Type = ELF::R_ARM_MOVW_ABS_NC;
241       break;
242     case ARM::fixup_t2_movt_hi16:
243       Type = ELF::R_ARM_THM_MOVT_ABS;
244       break;
245     case ARM::fixup_t2_movw_lo16:
246       Type = ELF::R_ARM_THM_MOVW_ABS_NC;
247       break;
248     }
249   }
250 
251   return Type;
252 }
253 
createARMELFObjectWriter(raw_pwrite_stream & OS,uint8_t OSABI,bool IsLittleEndian)254 MCObjectWriter *llvm::createARMELFObjectWriter(raw_pwrite_stream &OS,
255                                                uint8_t OSABI,
256                                                bool IsLittleEndian) {
257   MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
258   return createELFObjectWriter(MOTW, OS, IsLittleEndian);
259 }
260