1 //===------- ELF_riscv.cpp -JIT linker implementation for ELF/riscv -------===//
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 // ELF/riscv jit-link implementation.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/ExecutionEngine/JITLink/ELF_riscv.h"
14 #include "ELFLinkGraphBuilder.h"
15 #include "JITLinkGeneric.h"
16 #include "PerGraphGOTAndPLTStubsBuilder.h"
17 #include "llvm/BinaryFormat/ELF.h"
18 #include "llvm/ExecutionEngine/JITLink/JITLink.h"
19 #include "llvm/ExecutionEngine/JITLink/riscv.h"
20 #include "llvm/Object/ELF.h"
21 #include "llvm/Object/ELFObjectFile.h"
22 
23 #define DEBUG_TYPE "jitlink"
24 using namespace llvm;
25 using namespace llvm::jitlink;
26 using namespace llvm::jitlink::riscv;
27 
28 namespace {
29 
30 class PerGraphGOTAndPLTStubsBuilder_ELF_riscv
31     : public PerGraphGOTAndPLTStubsBuilder<
32           PerGraphGOTAndPLTStubsBuilder_ELF_riscv> {
33 public:
34   static constexpr size_t StubEntrySize = 16;
35   static const uint8_t NullGOTEntryContent[8];
36   static const uint8_t RV64StubContent[StubEntrySize];
37   static const uint8_t RV32StubContent[StubEntrySize];
38 
39   using PerGraphGOTAndPLTStubsBuilder<
40       PerGraphGOTAndPLTStubsBuilder_ELF_riscv>::PerGraphGOTAndPLTStubsBuilder;
41 
42   bool isRV64() const { return G.getPointerSize() == 8; }
43 
44   bool isGOTEdgeToFix(Edge &E) const { return E.getKind() == R_RISCV_GOT_HI20; }
45 
46   Symbol &createGOTEntry(Symbol &Target) {
47     Block &GOTBlock = G.createContentBlock(
48         getGOTSection(), getGOTEntryBlockContent(), 0, G.getPointerSize(), 0);
49     GOTBlock.addEdge(isRV64() ? R_RISCV_64 : R_RISCV_32, 0, Target, 0);
50     return G.addAnonymousSymbol(GOTBlock, 0, G.getPointerSize(), false, false);
51   }
52 
53   Symbol &createPLTStub(Symbol &Target) {
54     Block &StubContentBlock =
55         G.createContentBlock(getStubsSection(), getStubBlockContent(), 0, 4, 0);
56     auto &GOTEntrySymbol = getGOTEntry(Target);
57     StubContentBlock.addEdge(R_RISCV_CALL, 0, GOTEntrySymbol, 0);
58     return G.addAnonymousSymbol(StubContentBlock, 0, StubEntrySize, true,
59                                 false);
60   }
61 
62   void fixGOTEdge(Edge &E, Symbol &GOTEntry) {
63     // Replace the relocation pair (R_RISCV_GOT_HI20, R_RISCV_PCREL_LO12)
64     // with (R_RISCV_PCREL_HI20, R_RISCV_PCREL_LO12)
65     // Therefore, here just change the R_RISCV_GOT_HI20 to R_RISCV_PCREL_HI20
66     E.setKind(R_RISCV_PCREL_HI20);
67     E.setTarget(GOTEntry);
68   }
69 
70   void fixPLTEdge(Edge &E, Symbol &PLTStubs) {
71     assert(E.getKind() == R_RISCV_CALL_PLT && "Not a R_RISCV_CALL_PLT edge?");
72     E.setKind(R_RISCV_CALL);
73     E.setTarget(PLTStubs);
74   }
75 
76   bool isExternalBranchEdge(Edge &E) const {
77     return E.getKind() == R_RISCV_CALL_PLT;
78   }
79 
80 private:
81   Section &getGOTSection() const {
82     if (!GOTSection)
83       GOTSection = &G.createSection("$__GOT", sys::Memory::MF_READ);
84     return *GOTSection;
85   }
86 
87   Section &getStubsSection() const {
88     if (!StubsSection) {
89       auto StubsProt = static_cast<sys::Memory::ProtectionFlags>(
90           sys::Memory::MF_READ | sys::Memory::MF_EXEC);
91       StubsSection = &G.createSection("$__STUBS", StubsProt);
92     }
93     return *StubsSection;
94   }
95 
96   ArrayRef<char> getGOTEntryBlockContent() {
97     return {reinterpret_cast<const char *>(NullGOTEntryContent),
98             G.getPointerSize()};
99   }
100 
101   ArrayRef<char> getStubBlockContent() {
102     auto StubContent = isRV64() ? RV64StubContent : RV32StubContent;
103     return {reinterpret_cast<const char *>(StubContent), StubEntrySize};
104   }
105 
106   mutable Section *GOTSection = nullptr;
107   mutable Section *StubsSection = nullptr;
108 };
109 
110 const uint8_t PerGraphGOTAndPLTStubsBuilder_ELF_riscv::NullGOTEntryContent[8] =
111     {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
112 
113 const uint8_t
114     PerGraphGOTAndPLTStubsBuilder_ELF_riscv::RV64StubContent[StubEntrySize] = {
115         0x17, 0x0e, 0x00, 0x00,  // auipc t3, literal
116         0x03, 0x3e, 0x0e, 0x00,  // ld    t3, literal(t3)
117         0x67, 0x00, 0x0e, 0x00,  // jr    t3
118         0x13, 0x00, 0x00, 0x00}; // nop
119 
120 const uint8_t
121     PerGraphGOTAndPLTStubsBuilder_ELF_riscv::RV32StubContent[StubEntrySize] = {
122         0x17, 0x0e, 0x00, 0x00,  // auipc t3, literal
123         0x03, 0x2e, 0x0e, 0x00,  // lw    t3, literal(t3)
124         0x67, 0x00, 0x0e, 0x00,  // jr    t3
125         0x13, 0x00, 0x00, 0x00}; // nop
126 } // namespace
127 namespace llvm {
128 namespace jitlink {
129 
130 static Expected<const Edge &> getRISCVPCRelHi20(const Edge &E) {
131   using namespace riscv;
132   assert((E.getKind() == R_RISCV_PCREL_LO12_I ||
133           E.getKind() == R_RISCV_PCREL_LO12_S) &&
134          "Can only have high relocation for R_RISCV_PCREL_LO12_I or "
135          "R_RISCV_PCREL_LO12_S");
136 
137   const Symbol &Sym = E.getTarget();
138   const Block &B = Sym.getBlock();
139   JITTargetAddress Offset = Sym.getOffset();
140 
141   struct Comp {
142     bool operator()(const Edge &Lhs, JITTargetAddress Offset) {
143       return Lhs.getOffset() < Offset;
144     }
145     bool operator()(JITTargetAddress Offset, const Edge &Rhs) {
146       return Offset < Rhs.getOffset();
147     }
148   };
149 
150   auto Bound =
151       std::equal_range(B.edges().begin(), B.edges().end(), Offset, Comp{});
152 
153   for (auto It = Bound.first; It != Bound.second; ++It) {
154     if (It->getKind() == R_RISCV_PCREL_HI20)
155       return *It;
156   }
157 
158   return make_error<JITLinkError>(
159       "No HI20 PCREL relocation type be found for LO12 PCREL relocation type");
160 }
161 
162 static uint32_t extractBits(uint64_t Num, unsigned High, unsigned Low) {
163   return (Num & ((1ULL << (High + 1)) - 1)) >> Low;
164 }
165 
166 class ELFJITLinker_riscv : public JITLinker<ELFJITLinker_riscv> {
167   friend class JITLinker<ELFJITLinker_riscv>;
168 
169 public:
170   ELFJITLinker_riscv(std::unique_ptr<JITLinkContext> Ctx,
171                      std::unique_ptr<LinkGraph> G, PassConfiguration PassConfig)
172       : JITLinker(std::move(Ctx), std::move(G), std::move(PassConfig)) {}
173 
174 private:
175   Error applyFixup(LinkGraph &G, Block &B, const Edge &E) const {
176     using namespace riscv;
177     using namespace llvm::support;
178 
179     char *BlockWorkingMem = B.getAlreadyMutableContent().data();
180     char *FixupPtr = BlockWorkingMem + E.getOffset();
181     JITTargetAddress FixupAddress = B.getAddress() + E.getOffset();
182     switch (E.getKind()) {
183     case R_RISCV_32: {
184       int64_t Value = E.getTarget().getAddress() + E.getAddend();
185       *(little32_t *)FixupPtr = static_cast<uint32_t>(Value);
186       break;
187     }
188     case R_RISCV_64: {
189       int64_t Value = E.getTarget().getAddress() + E.getAddend();
190       *(little64_t *)FixupPtr = static_cast<uint64_t>(Value);
191       break;
192     }
193     case R_RISCV_HI20: {
194       int64_t Value = E.getTarget().getAddress() + E.getAddend();
195       int32_t Hi = (Value + 0x800) & 0xFFFFF000;
196       uint32_t RawInstr = *(little32_t *)FixupPtr;
197       *(little32_t *)FixupPtr = (RawInstr & 0xFFF) | static_cast<uint32_t>(Hi);
198       break;
199     }
200     case R_RISCV_LO12_I: {
201       int64_t Value = E.getTarget().getAddress() + E.getAddend();
202       int32_t Lo = Value & 0xFFF;
203       uint32_t RawInstr = *(little32_t *)FixupPtr;
204       *(little32_t *)FixupPtr =
205           (RawInstr & 0xFFFFF) | (static_cast<uint32_t>(Lo & 0xFFF) << 20);
206       break;
207     }
208     case R_RISCV_CALL: {
209       int64_t Value = E.getTarget().getAddress() + E.getAddend() - FixupAddress;
210       int32_t Hi = (Value + 0x800) & 0xFFFFF000;
211       int32_t Lo = Value & 0xFFF;
212       uint32_t RawInstrAuipc = *(little32_t *)FixupPtr;
213       uint32_t RawInstrJalr = *(little32_t *)(FixupPtr + 4);
214       *(little32_t *)FixupPtr = RawInstrAuipc | static_cast<uint32_t>(Hi);
215       *(little32_t *)(FixupPtr + 4) =
216           RawInstrJalr | (static_cast<uint32_t>(Lo) << 20);
217       break;
218     }
219     case R_RISCV_PCREL_HI20: {
220       int64_t Value = E.getTarget().getAddress() + E.getAddend() - FixupAddress;
221       int32_t Hi = (Value + 0x800) & 0xFFFFF000;
222       uint32_t RawInstr = *(little32_t *)FixupPtr;
223       *(little32_t *)FixupPtr = (RawInstr & 0xFFF) | static_cast<uint32_t>(Hi);
224       break;
225     }
226     case R_RISCV_PCREL_LO12_I: {
227       auto RelHI20 = getRISCVPCRelHi20(E);
228       if (!RelHI20)
229         return RelHI20.takeError();
230       int64_t Value = RelHI20->getTarget().getAddress() +
231                       RelHI20->getAddend() - E.getTarget().getAddress();
232       int64_t Lo = Value & 0xFFF;
233       uint32_t RawInstr = *(little32_t *)FixupPtr;
234       *(little32_t *)FixupPtr =
235           (RawInstr & 0xFFFFF) | (static_cast<uint32_t>(Lo & 0xFFF) << 20);
236       break;
237     }
238     case R_RISCV_PCREL_LO12_S: {
239       auto RelHI20 = getRISCVPCRelHi20(E);
240       int64_t Value = RelHI20->getTarget().getAddress() +
241                       RelHI20->getAddend() - E.getTarget().getAddress();
242       int64_t Lo = Value & 0xFFF;
243       uint32_t Imm31_25 = extractBits(Lo, 11, 5) << 25;
244       uint32_t Imm11_7 = extractBits(Lo, 4, 0) << 7;
245       uint32_t RawInstr = *(little32_t *)FixupPtr;
246 
247       *(little32_t *)FixupPtr = (RawInstr & 0x1FFF07F) | Imm31_25 | Imm11_7;
248       break;
249     }
250     }
251     return Error::success();
252   }
253 };
254 
255 template <typename ELFT>
256 class ELFLinkGraphBuilder_riscv : public ELFLinkGraphBuilder<ELFT> {
257 private:
258   static Expected<riscv::EdgeKind_riscv>
259   getRelocationKind(const uint32_t Type) {
260     using namespace riscv;
261     switch (Type) {
262     case ELF::R_RISCV_32:
263       return EdgeKind_riscv::R_RISCV_32;
264     case ELF::R_RISCV_64:
265       return EdgeKind_riscv::R_RISCV_64;
266     case ELF::R_RISCV_HI20:
267       return EdgeKind_riscv::R_RISCV_HI20;
268     case ELF::R_RISCV_LO12_I:
269       return EdgeKind_riscv::R_RISCV_LO12_I;
270     case ELF::R_RISCV_CALL:
271       return EdgeKind_riscv::R_RISCV_CALL;
272     case ELF::R_RISCV_PCREL_HI20:
273       return EdgeKind_riscv::R_RISCV_PCREL_HI20;
274     case ELF::R_RISCV_PCREL_LO12_I:
275       return EdgeKind_riscv::R_RISCV_PCREL_LO12_I;
276     case ELF::R_RISCV_PCREL_LO12_S:
277       return EdgeKind_riscv::R_RISCV_PCREL_LO12_S;
278     case ELF::R_RISCV_GOT_HI20:
279       return EdgeKind_riscv::R_RISCV_GOT_HI20;
280     case ELF::R_RISCV_CALL_PLT:
281       return EdgeKind_riscv::R_RISCV_CALL_PLT;
282     }
283 
284     return make_error<JITLinkError>("Unsupported riscv relocation:" +
285                                     formatv("{0:d}", Type));
286   }
287 
288   Error addRelocations() override {
289     LLVM_DEBUG(dbgs() << "Processing relocations:\n");
290 
291     using Base = ELFLinkGraphBuilder<ELFT>;
292     using Self = ELFLinkGraphBuilder_riscv<ELFT>;
293     for (const auto &RelSect : Base::Sections)
294       if (Error Err = Base::forEachRelocation(RelSect, this,
295                                               &Self::addSingleRelocation))
296         return Err;
297 
298     return Error::success();
299   }
300 
301   Error addSingleRelocation(const typename ELFT::Rela &Rel,
302                             const typename ELFT::Shdr &FixupSect,
303                             Section &GraphSection) {
304     using Base = ELFLinkGraphBuilder<ELFT>;
305 
306     uint32_t SymbolIndex = Rel.getSymbol(false);
307     auto ObjSymbol = Base::Obj.getRelocationSymbol(Rel, Base::SymTabSec);
308     if (!ObjSymbol)
309       return ObjSymbol.takeError();
310 
311     Symbol *GraphSymbol = Base::getGraphSymbol(SymbolIndex);
312     if (!GraphSymbol)
313       return make_error<StringError>(
314           formatv("Could not find symbol at given index, did you add it to "
315                   "JITSymbolTable? index: {0}, shndx: {1} Size of table: {2}",
316                   SymbolIndex, (*ObjSymbol)->st_shndx,
317                   Base::GraphSymbols.size()),
318           inconvertibleErrorCode());
319 
320     uint32_t Type = Rel.getType(false);
321     Expected<riscv::EdgeKind_riscv> Kind = getRelocationKind(Type);
322     if (!Kind)
323       return Kind.takeError();
324 
325     int64_t Addend = Rel.r_addend;
326     Block *BlockToFix = *(GraphSection.blocks().begin());
327     JITTargetAddress FixupAddress = FixupSect.sh_addr + Rel.r_offset;
328     Edge::OffsetT Offset = FixupAddress - BlockToFix->getAddress();
329     Edge GE(*Kind, Offset, *GraphSymbol, Addend);
330     LLVM_DEBUG({
331       dbgs() << "    ";
332       printEdge(dbgs(), *BlockToFix, GE, riscv::getEdgeKindName(*Kind));
333       dbgs() << "\n";
334     });
335 
336     BlockToFix->addEdge(std::move(GE));
337     return Error::success();
338   }
339 
340 public:
341   ELFLinkGraphBuilder_riscv(StringRef FileName,
342                             const object::ELFFile<ELFT> &Obj, const Triple T)
343       : ELFLinkGraphBuilder<ELFT>(Obj, std::move(T), FileName,
344                                   riscv::getEdgeKindName) {}
345 };
346 
347 Expected<std::unique_ptr<LinkGraph>>
348 createLinkGraphFromELFObject_riscv(MemoryBufferRef ObjectBuffer) {
349   LLVM_DEBUG({
350     dbgs() << "Building jitlink graph for new input "
351            << ObjectBuffer.getBufferIdentifier() << "...\n";
352   });
353 
354   auto ELFObj = object::ObjectFile::createELFObjectFile(ObjectBuffer);
355   if (!ELFObj)
356     return ELFObj.takeError();
357 
358   if ((*ELFObj)->getArch() == Triple::riscv64) {
359     auto &ELFObjFile = cast<object::ELFObjectFile<object::ELF64LE>>(**ELFObj);
360     return ELFLinkGraphBuilder_riscv<object::ELF64LE>(
361                (*ELFObj)->getFileName(), ELFObjFile.getELFFile(),
362                (*ELFObj)->makeTriple())
363         .buildGraph();
364   } else {
365     assert((*ELFObj)->getArch() == Triple::riscv32 &&
366            "Invalid triple for RISCV ELF object file");
367     auto &ELFObjFile = cast<object::ELFObjectFile<object::ELF32LE>>(**ELFObj);
368     return ELFLinkGraphBuilder_riscv<object::ELF32LE>(
369                (*ELFObj)->getFileName(), ELFObjFile.getELFFile(),
370                (*ELFObj)->makeTriple())
371         .buildGraph();
372   }
373 }
374 
375 void link_ELF_riscv(std::unique_ptr<LinkGraph> G,
376                     std::unique_ptr<JITLinkContext> Ctx) {
377   PassConfiguration Config;
378   const Triple &TT = G->getTargetTriple();
379   if (Ctx->shouldAddDefaultTargetPasses(TT)) {
380     if (auto MarkLive = Ctx->getMarkLivePass(TT))
381       Config.PrePrunePasses.push_back(std::move(MarkLive));
382     else
383       Config.PrePrunePasses.push_back(markAllSymbolsLive);
384     Config.PostPrunePasses.push_back(
385         PerGraphGOTAndPLTStubsBuilder_ELF_riscv::asPass);
386   }
387   if (auto Err = Ctx->modifyPassConfig(*G, Config))
388     return Ctx->notifyFailed(std::move(Err));
389 
390   ELFJITLinker_riscv::link(std::move(Ctx), std::move(G), std::move(Config));
391 }
392 
393 } // namespace jitlink
394 } // namespace llvm
395