1 //===-- ARMELFObjectWriter.cpp - ARM 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/ARMFixupKinds.h"
10 #include "MCTargetDesc/ARMMCTargetDesc.h"
11 #include "llvm/BinaryFormat/ELF.h"
12 #include "llvm/MC/MCContext.h"
13 #include "llvm/MC/MCELFObjectWriter.h"
14 #include "llvm/MC/MCExpr.h"
15 #include "llvm/MC/MCFixup.h"
16 #include "llvm/MC/MCObjectFileInfo.h"
17 #include "llvm/MC/MCObjectWriter.h"
18 #include "llvm/MC/MCValue.h"
19 #include "llvm/Support/ErrorHandling.h"
20 #include "llvm/Support/raw_ostream.h"
21 #include <cstdint>
22
23 using namespace llvm;
24
25 namespace {
26
27 class ARMELFObjectWriter : public MCELFObjectTargetWriter {
28 enum { DefaultEABIVersion = 0x05000000U };
29
30 unsigned GetRelocTypeInner(const MCValue &Target, const MCFixup &Fixup,
31 bool IsPCRel, MCContext &Ctx) const;
32
33 public:
34 ARMELFObjectWriter(uint8_t OSABI);
35
36 ~ARMELFObjectWriter() override = default;
37
38 unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
39 const MCFixup &Fixup, bool IsPCRel) const override;
40
41 bool needsRelocateWithSymbol(const MCSymbol &Sym,
42 unsigned Type) const override;
43
44 void addTargetSectionFlags(MCContext &Ctx, MCSectionELF &Sec) override;
45 };
46
47 } // end anonymous namespace
48
ARMELFObjectWriter(uint8_t OSABI)49 ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
50 : MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
51 ELF::EM_ARM,
52 /*HasRelocationAddend*/ false) {}
53
needsRelocateWithSymbol(const MCSymbol & Sym,unsigned Type) const54 bool ARMELFObjectWriter::needsRelocateWithSymbol(const MCSymbol &Sym,
55 unsigned Type) const {
56 // FIXME: This is extremely conservative. This really needs to use a
57 // whitelist with a clear explanation for why each realocation needs to
58 // point to the symbol, not to the section.
59 switch (Type) {
60 default:
61 return true;
62
63 case ELF::R_ARM_PREL31:
64 case ELF::R_ARM_ABS32:
65 return false;
66 }
67 }
68
69 // Need to examine the Fixup when determining whether to
70 // emit the relocation as an explicit symbol or as a section relative
71 // offset
getRelocType(MCContext & Ctx,const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const72 unsigned ARMELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
73 const MCFixup &Fixup,
74 bool IsPCRel) const {
75 return GetRelocTypeInner(Target, Fixup, IsPCRel, Ctx);
76 }
77
GetRelocTypeInner(const MCValue & Target,const MCFixup & Fixup,bool IsPCRel,MCContext & Ctx) const78 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
79 const MCFixup &Fixup,
80 bool IsPCRel,
81 MCContext &Ctx) const {
82 MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
83
84 if (IsPCRel) {
85 switch (Fixup.getTargetKind()) {
86 default:
87 Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol");
88 return ELF::R_ARM_NONE;
89 case FK_Data_4:
90 switch (Modifier) {
91 default:
92 llvm_unreachable("Unsupported Modifier");
93 case MCSymbolRefExpr::VK_None:
94 return ELF::R_ARM_REL32;
95 case MCSymbolRefExpr::VK_GOTTPOFF:
96 return ELF::R_ARM_TLS_IE32;
97 case MCSymbolRefExpr::VK_ARM_GOT_PREL:
98 return ELF::R_ARM_GOT_PREL;
99 case MCSymbolRefExpr::VK_ARM_PREL31:
100 return ELF::R_ARM_PREL31;
101 }
102 case ARM::fixup_arm_blx:
103 case ARM::fixup_arm_uncondbl:
104 switch (Modifier) {
105 case MCSymbolRefExpr::VK_PLT:
106 return ELF::R_ARM_CALL;
107 case MCSymbolRefExpr::VK_TLSCALL:
108 return ELF::R_ARM_TLS_CALL;
109 default:
110 return ELF::R_ARM_CALL;
111 }
112 case ARM::fixup_arm_condbl:
113 case ARM::fixup_arm_condbranch:
114 case ARM::fixup_arm_uncondbranch:
115 return ELF::R_ARM_JUMP24;
116 case ARM::fixup_t2_condbranch:
117 return ELF::R_ARM_THM_JUMP19;
118 case ARM::fixup_t2_uncondbranch:
119 return ELF::R_ARM_THM_JUMP24;
120 case ARM::fixup_arm_movt_hi16:
121 return ELF::R_ARM_MOVT_PREL;
122 case ARM::fixup_arm_movw_lo16:
123 return ELF::R_ARM_MOVW_PREL_NC;
124 case ARM::fixup_t2_movt_hi16:
125 return ELF::R_ARM_THM_MOVT_PREL;
126 case ARM::fixup_t2_movw_lo16:
127 return ELF::R_ARM_THM_MOVW_PREL_NC;
128 case ARM::fixup_arm_thumb_br:
129 return ELF::R_ARM_THM_JUMP11;
130 case ARM::fixup_arm_thumb_bcc:
131 return ELF::R_ARM_THM_JUMP8;
132 case ARM::fixup_arm_thumb_bl:
133 case ARM::fixup_arm_thumb_blx:
134 switch (Modifier) {
135 case MCSymbolRefExpr::VK_TLSCALL:
136 return ELF::R_ARM_THM_TLS_CALL;
137 default:
138 return ELF::R_ARM_THM_CALL;
139 }
140 case ARM::fixup_bf_target:
141 return ELF::R_ARM_THM_BF16;
142 case ARM::fixup_bfc_target:
143 return ELF::R_ARM_THM_BF12;
144 case ARM::fixup_bfl_target:
145 return ELF::R_ARM_THM_BF18;
146 }
147 }
148 switch (Fixup.getTargetKind()) {
149 default:
150 Ctx.reportFatalError(Fixup.getLoc(), "unsupported relocation on symbol");
151 return ELF::R_ARM_NONE;
152 case FK_NONE:
153 return ELF::R_ARM_NONE;
154 case FK_Data_1:
155 switch (Modifier) {
156 default:
157 llvm_unreachable("unsupported Modifier");
158 case MCSymbolRefExpr::VK_None:
159 return ELF::R_ARM_ABS8;
160 }
161 case FK_Data_2:
162 switch (Modifier) {
163 default:
164 llvm_unreachable("unsupported modifier");
165 case MCSymbolRefExpr::VK_None:
166 return ELF::R_ARM_ABS16;
167 }
168 case FK_Data_4:
169 switch (Modifier) {
170 default:
171 llvm_unreachable("Unsupported Modifier");
172 case MCSymbolRefExpr::VK_ARM_NONE:
173 return ELF::R_ARM_NONE;
174 case MCSymbolRefExpr::VK_GOT:
175 return ELF::R_ARM_GOT_BREL;
176 case MCSymbolRefExpr::VK_TLSGD:
177 return ELF::R_ARM_TLS_GD32;
178 case MCSymbolRefExpr::VK_TPOFF:
179 return ELF::R_ARM_TLS_LE32;
180 case MCSymbolRefExpr::VK_GOTTPOFF:
181 return ELF::R_ARM_TLS_IE32;
182 case MCSymbolRefExpr::VK_None:
183 return ELF::R_ARM_ABS32;
184 case MCSymbolRefExpr::VK_GOTOFF:
185 return ELF::R_ARM_GOTOFF32;
186 case MCSymbolRefExpr::VK_ARM_GOT_PREL:
187 return ELF::R_ARM_GOT_PREL;
188 case MCSymbolRefExpr::VK_ARM_TARGET1:
189 return ELF::R_ARM_TARGET1;
190 case MCSymbolRefExpr::VK_ARM_TARGET2:
191 return ELF::R_ARM_TARGET2;
192 case MCSymbolRefExpr::VK_ARM_PREL31:
193 return ELF::R_ARM_PREL31;
194 case MCSymbolRefExpr::VK_ARM_SBREL:
195 return ELF::R_ARM_SBREL32;
196 case MCSymbolRefExpr::VK_ARM_TLSLDO:
197 return ELF::R_ARM_TLS_LDO32;
198 case MCSymbolRefExpr::VK_TLSCALL:
199 return ELF::R_ARM_TLS_CALL;
200 case MCSymbolRefExpr::VK_TLSDESC:
201 return ELF::R_ARM_TLS_GOTDESC;
202 case MCSymbolRefExpr::VK_TLSLDM:
203 return ELF::R_ARM_TLS_LDM32;
204 case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
205 return ELF::R_ARM_TLS_DESCSEQ;
206 }
207 case ARM::fixup_arm_condbranch:
208 case ARM::fixup_arm_uncondbranch:
209 return ELF::R_ARM_JUMP24;
210 case ARM::fixup_arm_movt_hi16:
211 switch (Modifier) {
212 default:
213 llvm_unreachable("Unsupported Modifier");
214 case MCSymbolRefExpr::VK_None:
215 return ELF::R_ARM_MOVT_ABS;
216 case MCSymbolRefExpr::VK_ARM_SBREL:
217 return ELF::R_ARM_MOVT_BREL;
218 }
219 case ARM::fixup_arm_movw_lo16:
220 switch (Modifier) {
221 default:
222 llvm_unreachable("Unsupported Modifier");
223 case MCSymbolRefExpr::VK_None:
224 return ELF::R_ARM_MOVW_ABS_NC;
225 case MCSymbolRefExpr::VK_ARM_SBREL:
226 return ELF::R_ARM_MOVW_BREL_NC;
227 }
228 case ARM::fixup_t2_movt_hi16:
229 switch (Modifier) {
230 default:
231 llvm_unreachable("Unsupported Modifier");
232 case MCSymbolRefExpr::VK_None:
233 return ELF::R_ARM_THM_MOVT_ABS;
234 case MCSymbolRefExpr::VK_ARM_SBREL:
235 return ELF::R_ARM_THM_MOVT_BREL;
236 }
237 case ARM::fixup_t2_movw_lo16:
238 switch (Modifier) {
239 default:
240 llvm_unreachable("Unsupported Modifier");
241 case MCSymbolRefExpr::VK_None:
242 return ELF::R_ARM_THM_MOVW_ABS_NC;
243 case MCSymbolRefExpr::VK_ARM_SBREL:
244 return ELF::R_ARM_THM_MOVW_BREL_NC;
245 }
246 }
247 }
248
addTargetSectionFlags(MCContext & Ctx,MCSectionELF & Sec)249 void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx,
250 MCSectionELF &Sec) {
251 // The mix of execute-only and non-execute-only at link time is
252 // non-execute-only. To avoid the empty implicitly created .text
253 // section from making the whole .text section non-execute-only, we
254 // mark it execute-only if it is empty and there is at least one
255 // execute-only section in the object.
256 MCSectionELF *TextSection =
257 static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection());
258 if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions()) {
259 for (auto &F : TextSection->getFragmentList())
260 if (auto *DF = dyn_cast<MCDataFragment>(&F))
261 if (!DF->getContents().empty())
262 return;
263 TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE);
264 }
265 }
266
267 std::unique_ptr<MCObjectTargetWriter>
createARMELFObjectWriter(uint8_t OSABI)268 llvm::createARMELFObjectWriter(uint8_t OSABI) {
269 return std::make_unique<ARMELFObjectWriter>(OSABI);
270 }
271