1 //===-- MipsELFObjectWriter.cpp - Mips ELF Writer -------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #include "MCTargetDesc/MipsBaseInfo.h"
11 #include "MCTargetDesc/MipsFixupKinds.h"
12 #include "MCTargetDesc/MipsMCTargetDesc.h"
13 #include "llvm/ADT/STLExtras.h"
14 #include "llvm/MC/MCAssembler.h"
15 #include "llvm/MC/MCELFObjectWriter.h"
16 #include "llvm/MC/MCExpr.h"
17 #include "llvm/MC/MCSection.h"
18 #include "llvm/MC/MCSymbolELF.h"
19 #include "llvm/MC/MCValue.h"
20 #include "llvm/Support/ErrorHandling.h"
26 // A helper structure based on ELFRelocationEntry, used for sorting entries in
27 // the relocation table.
28 struct MipsRelocationEntry {
29 MipsRelocationEntry(const ELFRelocationEntry &R)
30 : R(R), SortOffset(R.Offset), HasMatchingHi(false) {}
31 const ELFRelocationEntry R;
32 // SortOffset equals R.Offset except for the *HI16 relocations, for which it
33 // will be set based on the R.Offset of the matching *LO16 relocation.
35 // True when this is a *LO16 relocation chosen as a match for a *HI16
40 class MipsELFObjectWriter : public MCELFObjectTargetWriter {
42 MipsELFObjectWriter(bool _is64Bit, uint8_t OSABI,
43 bool _isN64, bool IsLittleEndian);
45 ~MipsELFObjectWriter() override;
47 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
48 bool IsPCRel) const override;
49 bool needsRelocateWithSymbol(const MCSymbol &Sym,
50 unsigned Type) const override;
51 virtual void sortRelocs(const MCAssembler &Asm,
52 std::vector<ELFRelocationEntry> &Relocs) override;
56 MipsELFObjectWriter::MipsELFObjectWriter(bool _is64Bit, uint8_t OSABI,
57 bool _isN64, bool IsLittleEndian)
58 : MCELFObjectTargetWriter(_is64Bit, OSABI, ELF::EM_MIPS,
59 /*HasRelocationAddend*/ _isN64,
62 MipsELFObjectWriter::~MipsELFObjectWriter() {}
64 unsigned MipsELFObjectWriter::GetRelocType(const MCValue &Target,
67 // Determine the type of the relocation.
68 unsigned Kind = (unsigned)Fixup.getKind();
71 case Mips::fixup_Mips_NONE:
72 return ELF::R_MIPS_NONE;
73 case Mips::fixup_Mips_16:
75 return IsPCRel ? ELF::R_MIPS_PC16 : ELF::R_MIPS_16;
76 case Mips::fixup_Mips_32:
78 return IsPCRel ? ELF::R_MIPS_PC32 : ELF::R_MIPS_32;
83 case Mips::fixup_Mips_Branch_PCRel:
84 case Mips::fixup_Mips_PC16:
85 return ELF::R_MIPS_PC16;
86 case Mips::fixup_MICROMIPS_PC7_S1:
87 return ELF::R_MICROMIPS_PC7_S1;
88 case Mips::fixup_MICROMIPS_PC10_S1:
89 return ELF::R_MICROMIPS_PC10_S1;
90 case Mips::fixup_MICROMIPS_PC16_S1:
91 return ELF::R_MICROMIPS_PC16_S1;
92 case Mips::fixup_MIPS_PC19_S2:
93 return ELF::R_MIPS_PC19_S2;
94 case Mips::fixup_MIPS_PC18_S3:
95 return ELF::R_MIPS_PC18_S3;
96 case Mips::fixup_MIPS_PC21_S2:
97 return ELF::R_MIPS_PC21_S2;
98 case Mips::fixup_MIPS_PC26_S2:
99 return ELF::R_MIPS_PC26_S2;
100 case Mips::fixup_MIPS_PCHI16:
101 return ELF::R_MIPS_PCHI16;
102 case Mips::fixup_MIPS_PCLO16:
103 return ELF::R_MIPS_PCLO16;
106 llvm_unreachable("invalid PC-relative fixup kind!");
110 case Mips::fixup_Mips_64:
112 return ELF::R_MIPS_64;
115 unsigned Type = (unsigned)ELF::R_MIPS_NONE;
116 Type = setRType((unsigned)ELF::R_MIPS_GPREL32, Type);
117 Type = setRType2((unsigned)ELF::R_MIPS_64, Type);
118 Type = setRType3((unsigned)ELF::R_MIPS_NONE, Type);
121 return ELF::R_MIPS_GPREL32;
122 case Mips::fixup_Mips_GPREL16:
123 return ELF::R_MIPS_GPREL16;
124 case Mips::fixup_Mips_26:
125 return ELF::R_MIPS_26;
126 case Mips::fixup_Mips_CALL16:
127 return ELF::R_MIPS_CALL16;
128 case Mips::fixup_Mips_GOT_Global:
129 case Mips::fixup_Mips_GOT_Local:
130 return ELF::R_MIPS_GOT16;
131 case Mips::fixup_Mips_HI16:
132 return ELF::R_MIPS_HI16;
133 case Mips::fixup_Mips_LO16:
134 return ELF::R_MIPS_LO16;
135 case Mips::fixup_Mips_TLSGD:
136 return ELF::R_MIPS_TLS_GD;
137 case Mips::fixup_Mips_GOTTPREL:
138 return ELF::R_MIPS_TLS_GOTTPREL;
139 case Mips::fixup_Mips_TPREL_HI:
140 return ELF::R_MIPS_TLS_TPREL_HI16;
141 case Mips::fixup_Mips_TPREL_LO:
142 return ELF::R_MIPS_TLS_TPREL_LO16;
143 case Mips::fixup_Mips_TLSLDM:
144 return ELF::R_MIPS_TLS_LDM;
145 case Mips::fixup_Mips_DTPREL_HI:
146 return ELF::R_MIPS_TLS_DTPREL_HI16;
147 case Mips::fixup_Mips_DTPREL_LO:
148 return ELF::R_MIPS_TLS_DTPREL_LO16;
149 case Mips::fixup_Mips_GOT_PAGE:
150 return ELF::R_MIPS_GOT_PAGE;
151 case Mips::fixup_Mips_GOT_OFST:
152 return ELF::R_MIPS_GOT_OFST;
153 case Mips::fixup_Mips_GOT_DISP:
154 return ELF::R_MIPS_GOT_DISP;
155 case Mips::fixup_Mips_GPOFF_HI: {
156 unsigned Type = (unsigned)ELF::R_MIPS_NONE;
157 Type = setRType((unsigned)ELF::R_MIPS_GPREL16, Type);
158 Type = setRType2((unsigned)ELF::R_MIPS_SUB, Type);
159 Type = setRType3((unsigned)ELF::R_MIPS_HI16, Type);
162 case Mips::fixup_Mips_GPOFF_LO: {
163 unsigned Type = (unsigned)ELF::R_MIPS_NONE;
164 Type = setRType((unsigned)ELF::R_MIPS_GPREL16, Type);
165 Type = setRType2((unsigned)ELF::R_MIPS_SUB, Type);
166 Type = setRType3((unsigned)ELF::R_MIPS_LO16, Type);
169 case Mips::fixup_Mips_HIGHER:
170 return ELF::R_MIPS_HIGHER;
171 case Mips::fixup_Mips_HIGHEST:
172 return ELF::R_MIPS_HIGHEST;
173 case Mips::fixup_Mips_GOT_HI16:
174 return ELF::R_MIPS_GOT_HI16;
175 case Mips::fixup_Mips_GOT_LO16:
176 return ELF::R_MIPS_GOT_LO16;
177 case Mips::fixup_Mips_CALL_HI16:
178 return ELF::R_MIPS_CALL_HI16;
179 case Mips::fixup_Mips_CALL_LO16:
180 return ELF::R_MIPS_CALL_LO16;
181 case Mips::fixup_MICROMIPS_26_S1:
182 return ELF::R_MICROMIPS_26_S1;
183 case Mips::fixup_MICROMIPS_HI16:
184 return ELF::R_MICROMIPS_HI16;
185 case Mips::fixup_MICROMIPS_LO16:
186 return ELF::R_MICROMIPS_LO16;
187 case Mips::fixup_MICROMIPS_GOT16:
188 return ELF::R_MICROMIPS_GOT16;
189 case Mips::fixup_MICROMIPS_CALL16:
190 return ELF::R_MICROMIPS_CALL16;
191 case Mips::fixup_MICROMIPS_GOT_DISP:
192 return ELF::R_MICROMIPS_GOT_DISP;
193 case Mips::fixup_MICROMIPS_GOT_PAGE:
194 return ELF::R_MICROMIPS_GOT_PAGE;
195 case Mips::fixup_MICROMIPS_GOT_OFST:
196 return ELF::R_MICROMIPS_GOT_OFST;
197 case Mips::fixup_MICROMIPS_TLS_GD:
198 return ELF::R_MICROMIPS_TLS_GD;
199 case Mips::fixup_MICROMIPS_TLS_LDM:
200 return ELF::R_MICROMIPS_TLS_LDM;
201 case Mips::fixup_MICROMIPS_TLS_DTPREL_HI16:
202 return ELF::R_MICROMIPS_TLS_DTPREL_HI16;
203 case Mips::fixup_MICROMIPS_TLS_DTPREL_LO16:
204 return ELF::R_MICROMIPS_TLS_DTPREL_LO16;
205 case Mips::fixup_MICROMIPS_TLS_TPREL_HI16:
206 return ELF::R_MICROMIPS_TLS_TPREL_HI16;
207 case Mips::fixup_MICROMIPS_TLS_TPREL_LO16:
208 return ELF::R_MICROMIPS_TLS_TPREL_LO16;
211 llvm_unreachable("invalid fixup kind!");
214 // Sort entries by SortOffset in descending order.
215 // When there are more *HI16 relocs paired with one *LO16 reloc, the 2nd rule
216 // sorts them in ascending order of R.Offset.
217 static int cmpRelMips(const MipsRelocationEntry *AP,
218 const MipsRelocationEntry *BP) {
219 const MipsRelocationEntry &A = *AP;
220 const MipsRelocationEntry &B = *BP;
221 if (A.SortOffset != B.SortOffset)
222 return B.SortOffset - A.SortOffset;
223 if (A.R.Offset != B.R.Offset)
224 return A.R.Offset - B.R.Offset;
225 if (B.R.Type != A.R.Type)
226 return B.R.Type - A.R.Type;
227 //llvm_unreachable("ELFRelocs might be unstable!");
231 // For the given Reloc.Type, return the matching relocation type, as in the
233 static unsigned getMatchingLoType(const MCAssembler &Asm,
234 const ELFRelocationEntry &Reloc) {
235 unsigned Type = Reloc.Type;
236 if (Type == ELF::R_MIPS_HI16)
237 return ELF::R_MIPS_LO16;
238 if (Type == ELF::R_MICROMIPS_HI16)
239 return ELF::R_MICROMIPS_LO16;
240 if (Type == ELF::R_MIPS16_HI16)
241 return ELF::R_MIPS16_LO16;
243 if (Reloc.Symbol->getBinding() != ELF::STB_LOCAL)
244 return ELF::R_MIPS_NONE;
246 if (Type == ELF::R_MIPS_GOT16)
247 return ELF::R_MIPS_LO16;
248 if (Type == ELF::R_MICROMIPS_GOT16)
249 return ELF::R_MICROMIPS_LO16;
250 if (Type == ELF::R_MIPS16_GOT16)
251 return ELF::R_MIPS16_LO16;
253 return ELF::R_MIPS_NONE;
256 // Return true if First needs a matching *LO16, its matching *LO16 type equals
257 // Second's type and both relocations are against the same symbol.
258 static bool areMatchingHiAndLo(const MCAssembler &Asm,
259 const ELFRelocationEntry &First,
260 const ELFRelocationEntry &Second) {
261 return getMatchingLoType(Asm, First) != ELF::R_MIPS_NONE &&
262 getMatchingLoType(Asm, First) == Second.Type &&
263 First.Symbol && First.Symbol == Second.Symbol;
266 // Return true if MipsRelocs[Index] is a *LO16 preceded by a matching *HI16.
268 isPrecededByMatchingHi(const MCAssembler &Asm, uint32_t Index,
269 std::vector<MipsRelocationEntry> &MipsRelocs) {
270 return Index < MipsRelocs.size() - 1 &&
271 areMatchingHiAndLo(Asm, MipsRelocs[Index + 1].R, MipsRelocs[Index].R);
274 // Return true if MipsRelocs[Index] is a *LO16 not preceded by a matching *HI16
275 // and not chosen by a *HI16 as a match.
276 static bool isFreeLo(const MCAssembler &Asm, uint32_t Index,
277 std::vector<MipsRelocationEntry> &MipsRelocs) {
278 return Index < MipsRelocs.size() && !MipsRelocs[Index].HasMatchingHi &&
279 !isPrecededByMatchingHi(Asm, Index, MipsRelocs);
282 // Lo is chosen as a match for Hi, set their fields accordingly.
283 // Mips instructions have fixed length of at least two bytes (two for
284 // micromips/mips16, four for mips32/64), so we can set HI's SortOffset to
285 // matching LO's Offset minus one to simplify the sorting function.
286 static void setMatch(MipsRelocationEntry &Hi, MipsRelocationEntry &Lo) {
287 Lo.HasMatchingHi = true;
288 Hi.SortOffset = Lo.R.Offset - 1;
291 // We sort relocation table entries by offset, except for one additional rule
292 // required by MIPS ABI: every *HI16 relocation must be immediately followed by
293 // the corresponding *LO16 relocation. We also support a GNU extension that
294 // allows more *HI16s paired with one *LO16.
296 // *HI16 relocations and their matching *LO16 are:
298 // +---------------------------------------------+-------------------+
299 // | *HI16 | matching *LO16 |
300 // |---------------------------------------------+-------------------|
301 // | R_MIPS_HI16, local R_MIPS_GOT16 | R_MIPS_LO16 |
302 // | R_MICROMIPS_HI16, local R_MICROMIPS_GOT16 | R_MICROMIPS_LO16 |
303 // | R_MIPS16_HI16, local R_MIPS16_GOT16 | R_MIPS16_LO16 |
304 // +---------------------------------------------+-------------------+
306 // (local R_*_GOT16 meaning R_*_GOT16 against the local symbol.)
308 // To handle *HI16 and *LO16 relocations, the linker needs a combined addend
309 // ("AHL") calculated from both *HI16 ("AHI") and *LO16 ("ALO") relocations:
310 // AHL = (AHI << 16) + (short)ALO;
312 // We are reusing gnu as sorting algorithm so we are emitting the relocation
313 // table sorted the same way as gnu as would sort it, for easier comparison of
314 // the generated .o files.
317 // search the table (starting from the highest offset and going back to zero)
318 // for all *HI16 relocations that don't have a matching *LO16.
319 // For every such HI, find a matching LO with highest offset that isn't already
320 // matched with another HI. If there are no free LOs, match it with the first
321 // found (starting from lowest offset).
322 // When there are more HIs matched with one LO, sort them in descending order by
325 // In other words, when searching for a matching LO:
326 // - don't look for a 'better' match for the HIs that are already followed by a
328 // - prefer LOs without a pair;
329 // - prefer LOs with higher offset;
330 void MipsELFObjectWriter::sortRelocs(const MCAssembler &Asm,
331 std::vector<ELFRelocationEntry> &Relocs) {
332 if (Relocs.size() < 2)
335 // The default function sorts entries by Offset in descending order.
336 MCELFObjectTargetWriter::sortRelocs(Asm, Relocs);
338 // Init MipsRelocs from Relocs.
339 std::vector<MipsRelocationEntry> MipsRelocs;
340 for (unsigned I = 0, E = Relocs.size(); I != E; ++I)
341 MipsRelocs.push_back(MipsRelocationEntry(Relocs[I]));
343 // Find a matching LO for all HIs that need it.
344 for (int32_t I = 0, E = MipsRelocs.size(); I != E; ++I) {
345 if (getMatchingLoType(Asm, MipsRelocs[I].R) == ELF::R_MIPS_NONE ||
346 (I > 0 && isPrecededByMatchingHi(Asm, I - 1, MipsRelocs)))
349 int32_t MatchedLoIndex = -1;
351 // Search the list in the ascending order of Offset.
352 for (int32_t J = MipsRelocs.size() - 1, N = -1; J != N; --J) {
354 if (areMatchingHiAndLo(Asm, MipsRelocs[I].R, MipsRelocs[J].R) &&
355 (MatchedLoIndex == -1 || // first match
356 // or we already have a match,
357 // but this one is with higher offset and it's free
358 (MatchedLoIndex > J && isFreeLo(Asm, J, MipsRelocs))))
362 if (MatchedLoIndex != -1)
364 setMatch(MipsRelocs[I], MipsRelocs[MatchedLoIndex]);
367 // SortOffsets are calculated, call the sorting function.
368 array_pod_sort(MipsRelocs.begin(), MipsRelocs.end(), cmpRelMips);
370 // Copy sorted MipsRelocs back to Relocs.
371 for (unsigned I = 0, E = MipsRelocs.size(); I != E; ++I)
372 Relocs[I] = MipsRelocs[I].R;
375 bool MipsELFObjectWriter::needsRelocateWithSymbol(const MCSymbol &Sym,
376 unsigned Type) const {
377 // FIXME: This is extremely conservative. This really needs to use a
378 // whitelist with a clear explanation for why each realocation needs to
379 // point to the symbol, not to the section.
384 case ELF::R_MIPS_GOT16:
385 case ELF::R_MIPS16_GOT16:
386 case ELF::R_MICROMIPS_GOT16:
387 llvm_unreachable("Should have been handled already");
389 // These relocations might be paired with another relocation. The pairing is
390 // done by the static linker by matching the symbol. Since we only see one
391 // relocation at a time, we have to force them to relocate with a symbol to
392 // avoid ending up with a pair where one points to a section and another
393 // points to a symbol.
394 case ELF::R_MIPS_HI16:
395 case ELF::R_MIPS16_HI16:
396 case ELF::R_MICROMIPS_HI16:
397 case ELF::R_MIPS_LO16:
398 case ELF::R_MIPS16_LO16:
399 case ELF::R_MICROMIPS_LO16:
403 if (cast<MCSymbolELF>(Sym).getOther() & ELF::STO_MIPS_MICROMIPS)
408 case ELF::R_MIPS_GPREL16:
413 MCObjectWriter *llvm::createMipsELFObjectWriter(raw_pwrite_stream &OS,
417 MCELFObjectTargetWriter *MOTW =
418 new MipsELFObjectWriter(Is64Bit, OSABI, Is64Bit, IsLittleEndian);
419 return createELFObjectWriter(MOTW, OS, IsLittleEndian);