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 MCValue &Val, 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 MCValue &,const MCSymbol &,unsigned Type) const54 bool ARMELFObjectWriter::needsRelocateWithSymbol(const MCValue &,
55                                                  const MCSymbol &,
56                                                  unsigned Type) const {
57   // FIXME: This is extremely conservative. This really needs to use an
58   // explicit list with a clear explanation for why each realocation needs to
59   // point to the symbol, not to the section.
60   switch (Type) {
61   default:
62     return true;
63 
64   case ELF::R_ARM_PREL31:
65   case ELF::R_ARM_ABS32:
66     return false;
67   }
68 }
69 
70 // Need to examine the Fixup when determining whether to
71 // emit the relocation as an explicit symbol or as a section relative
72 // offset
getRelocType(MCContext & Ctx,const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const73 unsigned ARMELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
74                                           const MCFixup &Fixup,
75                                           bool IsPCRel) const {
76   return GetRelocTypeInner(Target, Fixup, IsPCRel, Ctx);
77 }
78 
GetRelocTypeInner(const MCValue & Target,const MCFixup & Fixup,bool IsPCRel,MCContext & Ctx) const79 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
80                                                const MCFixup &Fixup,
81                                                bool IsPCRel,
82                                                MCContext &Ctx) const {
83   unsigned Kind = Fixup.getTargetKind();
84   if (Kind >= FirstLiteralRelocationKind)
85     return Kind - FirstLiteralRelocationKind;
86   MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
87 
88   if (IsPCRel) {
89     switch (Fixup.getTargetKind()) {
90     default:
91       Ctx.reportError(Fixup.getLoc(), "unsupported relocation type");
92       return ELF::R_ARM_NONE;
93     case FK_Data_4:
94       switch (Modifier) {
95       default:
96         Ctx.reportError(Fixup.getLoc(),
97                         "invalid fixup for 4-byte pc-relative data relocation");
98         return ELF::R_ARM_NONE;
99       case MCSymbolRefExpr::VK_None: {
100         if (const MCSymbolRefExpr *SymRef = Target.getSymA()) {
101           // For GNU AS compatibility expressions such as
102           // _GLOBAL_OFFSET_TABLE_ - label emit a R_ARM_BASE_PREL relocation.
103           if (SymRef->getSymbol().getName() == "_GLOBAL_OFFSET_TABLE_")
104             return ELF::R_ARM_BASE_PREL;
105         }
106         return ELF::R_ARM_REL32;
107       }
108       case MCSymbolRefExpr::VK_GOTTPOFF:
109         return ELF::R_ARM_TLS_IE32;
110       case MCSymbolRefExpr::VK_ARM_GOT_PREL:
111         return ELF::R_ARM_GOT_PREL;
112       case MCSymbolRefExpr::VK_ARM_PREL31:
113         return ELF::R_ARM_PREL31;
114       }
115     case ARM::fixup_arm_blx:
116     case ARM::fixup_arm_uncondbl:
117       switch (Modifier) {
118       case MCSymbolRefExpr::VK_PLT:
119         return ELF::R_ARM_CALL;
120       case MCSymbolRefExpr::VK_TLSCALL:
121         return ELF::R_ARM_TLS_CALL;
122       default:
123         return ELF::R_ARM_CALL;
124       }
125     case ARM::fixup_arm_condbl:
126     case ARM::fixup_arm_condbranch:
127     case ARM::fixup_arm_uncondbranch:
128       return ELF::R_ARM_JUMP24;
129     case ARM::fixup_t2_condbranch:
130       return ELF::R_ARM_THM_JUMP19;
131     case ARM::fixup_t2_uncondbranch:
132       return ELF::R_ARM_THM_JUMP24;
133     case ARM::fixup_arm_movt_hi16:
134       return ELF::R_ARM_MOVT_PREL;
135     case ARM::fixup_arm_movw_lo16:
136       return ELF::R_ARM_MOVW_PREL_NC;
137     case ARM::fixup_t2_movt_hi16:
138       return ELF::R_ARM_THM_MOVT_PREL;
139     case ARM::fixup_t2_movw_lo16:
140       return ELF::R_ARM_THM_MOVW_PREL_NC;
141     case ARM::fixup_arm_thumb_upper_8_15:
142       return ELF::R_ARM_THM_ALU_ABS_G3;
143     case ARM::fixup_arm_thumb_upper_0_7:
144       return ELF::R_ARM_THM_ALU_ABS_G2_NC;
145     case ARM::fixup_arm_thumb_lower_8_15:
146       return ELF::R_ARM_THM_ALU_ABS_G1_NC;
147     case ARM::fixup_arm_thumb_lower_0_7:
148       return ELF::R_ARM_THM_ALU_ABS_G0_NC;
149     case ARM::fixup_arm_thumb_br:
150       return ELF::R_ARM_THM_JUMP11;
151     case ARM::fixup_arm_thumb_bcc:
152       return ELF::R_ARM_THM_JUMP8;
153     case ARM::fixup_arm_thumb_bl:
154     case ARM::fixup_arm_thumb_blx:
155       switch (Modifier) {
156       case MCSymbolRefExpr::VK_TLSCALL:
157         return ELF::R_ARM_THM_TLS_CALL;
158       default:
159         return ELF::R_ARM_THM_CALL;
160       }
161     case ARM::fixup_arm_ldst_pcrel_12:
162       return ELF::R_ARM_LDR_PC_G0;
163     case ARM::fixup_arm_pcrel_10_unscaled:
164       return ELF::R_ARM_LDRS_PC_G0;
165     case ARM::fixup_t2_ldst_pcrel_12:
166       return ELF::R_ARM_THM_PC12;
167     case ARM::fixup_arm_adr_pcrel_12:
168       return ELF::R_ARM_ALU_PC_G0;
169     case ARM::fixup_thumb_adr_pcrel_10:
170       return ELF::R_ARM_THM_PC8;
171     case ARM::fixup_t2_adr_pcrel_12:
172       return ELF::R_ARM_THM_ALU_PREL_11_0;
173     case ARM::fixup_bf_target:
174       return ELF::R_ARM_THM_BF16;
175     case ARM::fixup_bfc_target:
176       return ELF::R_ARM_THM_BF12;
177     case ARM::fixup_bfl_target:
178       return ELF::R_ARM_THM_BF18;
179     }
180   }
181   switch (Kind) {
182   default:
183     Ctx.reportError(Fixup.getLoc(), "unsupported relocation type");
184     return ELF::R_ARM_NONE;
185   case FK_Data_1:
186     switch (Modifier) {
187     default:
188       Ctx.reportError(Fixup.getLoc(),
189                       "invalid fixup for 1-byte data relocation");
190       return ELF::R_ARM_NONE;
191     case MCSymbolRefExpr::VK_None:
192       return ELF::R_ARM_ABS8;
193     }
194   case FK_Data_2:
195     switch (Modifier) {
196     default:
197       Ctx.reportError(Fixup.getLoc(),
198                       "invalid fixup for 2-byte data relocation");
199       return ELF::R_ARM_NONE;
200     case MCSymbolRefExpr::VK_None:
201       return ELF::R_ARM_ABS16;
202     }
203   case FK_Data_4:
204     switch (Modifier) {
205     default:
206       Ctx.reportError(Fixup.getLoc(),
207                       "invalid fixup for 4-byte data relocation");
208       return ELF::R_ARM_NONE;
209     case MCSymbolRefExpr::VK_ARM_NONE:
210       return ELF::R_ARM_NONE;
211     case MCSymbolRefExpr::VK_GOT:
212       return ELF::R_ARM_GOT_BREL;
213     case MCSymbolRefExpr::VK_TLSGD:
214       return ELF::R_ARM_TLS_GD32;
215     case MCSymbolRefExpr::VK_TPOFF:
216       return ELF::R_ARM_TLS_LE32;
217     case MCSymbolRefExpr::VK_GOTTPOFF:
218       return ELF::R_ARM_TLS_IE32;
219     case MCSymbolRefExpr::VK_None:
220       return ELF::R_ARM_ABS32;
221     case MCSymbolRefExpr::VK_GOTOFF:
222       return ELF::R_ARM_GOTOFF32;
223     case MCSymbolRefExpr::VK_ARM_GOT_PREL:
224       return ELF::R_ARM_GOT_PREL;
225     case MCSymbolRefExpr::VK_ARM_TARGET1:
226       return ELF::R_ARM_TARGET1;
227     case MCSymbolRefExpr::VK_ARM_TARGET2:
228       return ELF::R_ARM_TARGET2;
229     case MCSymbolRefExpr::VK_ARM_PREL31:
230       return ELF::R_ARM_PREL31;
231     case MCSymbolRefExpr::VK_ARM_SBREL:
232       return ELF::R_ARM_SBREL32;
233     case MCSymbolRefExpr::VK_ARM_TLSLDO:
234       return ELF::R_ARM_TLS_LDO32;
235     case MCSymbolRefExpr::VK_TLSCALL:
236       return ELF::R_ARM_TLS_CALL;
237     case MCSymbolRefExpr::VK_TLSDESC:
238       return ELF::R_ARM_TLS_GOTDESC;
239     case MCSymbolRefExpr::VK_TLSLDM:
240       return ELF::R_ARM_TLS_LDM32;
241     case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
242       return ELF::R_ARM_TLS_DESCSEQ;
243     }
244   case ARM::fixup_arm_condbranch:
245   case ARM::fixup_arm_uncondbranch:
246     return ELF::R_ARM_JUMP24;
247   case ARM::fixup_arm_movt_hi16:
248     switch (Modifier) {
249     default:
250       Ctx.reportError(Fixup.getLoc(), "invalid fixup for ARM MOVT instruction");
251       return ELF::R_ARM_NONE;
252     case MCSymbolRefExpr::VK_None:
253       return ELF::R_ARM_MOVT_ABS;
254     case MCSymbolRefExpr::VK_ARM_SBREL:
255       return ELF::R_ARM_MOVT_BREL;
256     }
257   case ARM::fixup_arm_movw_lo16:
258     switch (Modifier) {
259     default:
260       Ctx.reportError(Fixup.getLoc(), "invalid fixup for ARM MOVW instruction");
261       return ELF::R_ARM_NONE;
262     case MCSymbolRefExpr::VK_None:
263       return ELF::R_ARM_MOVW_ABS_NC;
264     case MCSymbolRefExpr::VK_ARM_SBREL:
265       return ELF::R_ARM_MOVW_BREL_NC;
266     }
267   case ARM::fixup_t2_movt_hi16:
268     switch (Modifier) {
269     default:
270       Ctx.reportError(Fixup.getLoc(),
271                       "invalid fixup for Thumb MOVT instruction");
272       return ELF::R_ARM_NONE;
273     case MCSymbolRefExpr::VK_None:
274       return ELF::R_ARM_THM_MOVT_ABS;
275     case MCSymbolRefExpr::VK_ARM_SBREL:
276       return ELF::R_ARM_THM_MOVT_BREL;
277     }
278   case ARM::fixup_t2_movw_lo16:
279     switch (Modifier) {
280     default:
281       Ctx.reportError(Fixup.getLoc(),
282                       "invalid fixup for Thumb MOVW instruction");
283       return ELF::R_ARM_NONE;
284     case MCSymbolRefExpr::VK_None:
285       return ELF::R_ARM_THM_MOVW_ABS_NC;
286     case MCSymbolRefExpr::VK_ARM_SBREL:
287       return ELF::R_ARM_THM_MOVW_BREL_NC;
288     }
289 
290   case ARM::fixup_arm_thumb_upper_8_15:
291     return ELF::R_ARM_THM_ALU_ABS_G3;
292   case ARM::fixup_arm_thumb_upper_0_7:
293     return ELF::R_ARM_THM_ALU_ABS_G2_NC;
294   case ARM::fixup_arm_thumb_lower_8_15:
295     return ELF::R_ARM_THM_ALU_ABS_G1_NC;
296   case ARM::fixup_arm_thumb_lower_0_7:
297     return ELF::R_ARM_THM_ALU_ABS_G0_NC;
298   }
299 }
300 
addTargetSectionFlags(MCContext & Ctx,MCSectionELF & Sec)301 void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx,
302                                                MCSectionELF &Sec) {
303   // The mix of execute-only and non-execute-only at link time is
304   // non-execute-only. To avoid the empty implicitly created .text
305   // section from making the whole .text section non-execute-only, we
306   // mark it execute-only if it is empty and there is at least one
307   // execute-only section in the object.
308   MCSectionELF *TextSection =
309       static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection());
310   if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions()) {
311     for (auto &F : TextSection->getFragmentList())
312       if (auto *DF = dyn_cast<MCDataFragment>(&F))
313         if (!DF->getContents().empty())
314           return;
315     TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE);
316   }
317 }
318 
319 std::unique_ptr<MCObjectTargetWriter>
createARMELFObjectWriter(uint8_t OSABI)320 llvm::createARMELFObjectWriter(uint8_t OSABI) {
321   return std::make_unique<ARMELFObjectWriter>(OSABI);
322 }
323