1 //===-- RuntimeDyldCOFFX86_64.h --- COFF/X86_64 specific code ---*- C++ -*-===//
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 // COFF x86_x64 support for MC-JIT runtime dynamic linker.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_LIB_EXECUTIONENGINE_RUNTIMEDYLD_TARGETS_RUNTIMEDYLDCOFF86_64_H
14 #define LLVM_LIB_EXECUTIONENGINE_RUNTIMEDYLD_TARGETS_RUNTIMEDYLDCOFF86_64_H
15 
16 #include "../RuntimeDyldCOFF.h"
17 #include "llvm/BinaryFormat/COFF.h"
18 #include "llvm/Object/COFF.h"
19 
20 #define DEBUG_TYPE "dyld"
21 
22 namespace llvm {
23 
24 class RuntimeDyldCOFFX86_64 : public RuntimeDyldCOFF {
25 
26 private:
27   // When a module is loaded we save the SectionID of the unwind
28   // sections in a table until we receive a request to register all
29   // unregisteredEH frame sections with the memory manager.
30   SmallVector<SID, 2> UnregisteredEHFrameSections;
31   SmallVector<SID, 2> RegisteredEHFrameSections;
32   uint64_t ImageBase;
33 
34   // Fake an __ImageBase pointer by returning the section with the lowest adress
35   uint64_t getImageBase() {
36     if (!ImageBase) {
37       ImageBase = std::numeric_limits<uint64_t>::max();
38       for (const SectionEntry &Section : Sections)
39         // The Sections list may contain sections that weren't loaded for
40         // whatever reason: they may be debug sections, and ProcessAllSections
41         // is false, or they may be sections that contain 0 bytes. If the
42         // section isn't loaded, the load address will be 0, and it should not
43         // be included in the ImageBase calculation.
44         if (Section.getLoadAddress() != 0)
45           ImageBase = std::min(ImageBase, Section.getLoadAddress());
46     }
47     return ImageBase;
48   }
49 
50   void write32BitOffset(uint8_t *Target, int64_t Addend, uint64_t Delta) {
51     uint64_t Result = Addend + Delta;
52     assert(Result <= UINT32_MAX && "Relocation overflow");
53     writeBytesUnaligned(Result, Target, 4);
54   }
55 
56 public:
57   RuntimeDyldCOFFX86_64(RuntimeDyld::MemoryManager &MM,
58                         JITSymbolResolver &Resolver)
59     : RuntimeDyldCOFF(MM, Resolver), ImageBase(0) {}
60 
61   unsigned getStubAlignment() override { return 1; }
62 
63   // 2-byte jmp instruction + 32-bit relative address + 64-bit absolute jump
64   unsigned getMaxStubSize() const override { return 14; }
65 
66   // The target location for the relocation is described by RE.SectionID and
67   // RE.Offset.  RE.SectionID can be used to find the SectionEntry.  Each
68   // SectionEntry has three members describing its location.
69   // SectionEntry::Address is the address at which the section has been loaded
70   // into memory in the current (host) process.  SectionEntry::LoadAddress is
71   // the address that the section will have in the target process.
72   // SectionEntry::ObjAddress is the address of the bits for this section in the
73   // original emitted object image (also in the current address space).
74   //
75   // Relocations will be applied as if the section were loaded at
76   // SectionEntry::LoadAddress, but they will be applied at an address based
77   // on SectionEntry::Address.  SectionEntry::ObjAddress will be used to refer
78   // to Target memory contents if they are required for value calculations.
79   //
80   // The Value parameter here is the load address of the symbol for the
81   // relocation to be applied.  For relocations which refer to symbols in the
82   // current object Value will be the LoadAddress of the section in which
83   // the symbol resides (RE.Addend provides additional information about the
84   // symbol location).  For external symbols, Value will be the address of the
85   // symbol in the target address space.
86   void resolveRelocation(const RelocationEntry &RE, uint64_t Value) override {
87     const SectionEntry &Section = Sections[RE.SectionID];
88     uint8_t *Target = Section.getAddressWithOffset(RE.Offset);
89 
90     switch (RE.RelType) {
91 
92     case COFF::IMAGE_REL_AMD64_REL32:
93     case COFF::IMAGE_REL_AMD64_REL32_1:
94     case COFF::IMAGE_REL_AMD64_REL32_2:
95     case COFF::IMAGE_REL_AMD64_REL32_3:
96     case COFF::IMAGE_REL_AMD64_REL32_4:
97     case COFF::IMAGE_REL_AMD64_REL32_5: {
98       uint64_t FinalAddress = Section.getLoadAddressWithOffset(RE.Offset);
99       // Delta is the distance from the start of the reloc to the end of the
100       // instruction with the reloc.
101       uint64_t Delta = 4 + (RE.RelType - COFF::IMAGE_REL_AMD64_REL32);
102       Value -= FinalAddress + Delta;
103       uint64_t Result = Value + RE.Addend;
104       assert(((int64_t)Result <= INT32_MAX) && "Relocation overflow");
105       assert(((int64_t)Result >= INT32_MIN) && "Relocation underflow");
106       writeBytesUnaligned(Result, Target, 4);
107       break;
108     }
109 
110     case COFF::IMAGE_REL_AMD64_ADDR32NB: {
111       // ADDR32NB requires an offset less than 2GB from 'ImageBase'.
112       // The MemoryManager can make sure this is always true by forcing the
113       // memory layout to be: CodeSection < ReadOnlySection < ReadWriteSection.
114       const uint64_t ImageBase = getImageBase();
115       if (Value < ImageBase || ((Value - ImageBase) > UINT32_MAX)) {
116         llvm::errs() << "IMAGE_REL_AMD64_ADDR32NB relocation requires an"
117                      << "ordered section layout.\n";
118         write32BitOffset(Target, 0, 0);
119       } else {
120         write32BitOffset(Target, RE.Addend, Value - ImageBase);
121       }
122       break;
123     }
124 
125     case COFF::IMAGE_REL_AMD64_ADDR64: {
126       writeBytesUnaligned(Value + RE.Addend, Target, 8);
127       break;
128     }
129 
130     case COFF::IMAGE_REL_AMD64_SECREL: {
131       assert(static_cast<int64_t>(RE.Addend) <= INT32_MAX && "Relocation overflow");
132       assert(static_cast<int64_t>(RE.Addend) >= INT32_MIN && "Relocation underflow");
133       writeBytesUnaligned(RE.Addend, Target, 4);
134       break;
135     }
136 
137     default:
138       llvm_unreachable("Relocation type not implemented yet!");
139       break;
140     }
141   }
142 
143   std::tuple<uint64_t, uint64_t, uint64_t>
144   generateRelocationStub(unsigned SectionID, StringRef TargetName,
145                          uint64_t Offset, uint64_t RelType, uint64_t Addend,
146                          StubMap &Stubs) {
147     uintptr_t StubOffset;
148     SectionEntry &Section = Sections[SectionID];
149 
150     RelocationValueRef OriginalRelValueRef;
151     OriginalRelValueRef.SectionID = SectionID;
152     OriginalRelValueRef.Offset = Offset;
153     OriginalRelValueRef.Addend = Addend;
154     OriginalRelValueRef.SymbolName = TargetName.data();
155 
156     auto Stub = Stubs.find(OriginalRelValueRef);
157     if (Stub == Stubs.end()) {
158       LLVM_DEBUG(dbgs() << " Create a new stub function for "
159                         << TargetName.data() << "\n");
160 
161       StubOffset = Section.getStubOffset();
162       Stubs[OriginalRelValueRef] = StubOffset;
163       createStubFunction(Section.getAddressWithOffset(StubOffset));
164       Section.advanceStubOffset(getMaxStubSize());
165     } else {
166       LLVM_DEBUG(dbgs() << " Stub function found for " << TargetName.data()
167                         << "\n");
168       StubOffset = Stub->second;
169     }
170 
171     // FIXME: If RelType == COFF::IMAGE_REL_AMD64_ADDR32NB we should be able
172     // to ignore the __ImageBase requirement and just forward to the stub
173     // directly as an offset of this section:
174     // write32BitOffset(Section.getAddressWithOffset(Offset), 0, StubOffset);
175     // .xdata exception handler's aren't having this though.
176 
177     // Resolve original relocation to stub function.
178     const RelocationEntry RE(SectionID, Offset, RelType, Addend);
179     resolveRelocation(RE, Section.getLoadAddressWithOffset(StubOffset));
180 
181     // adjust relocation info so resolution writes to the stub function
182     Addend = 0;
183     Offset = StubOffset + 6;
184     RelType = COFF::IMAGE_REL_AMD64_ADDR64;
185 
186     return std::make_tuple(Offset, RelType, Addend);
187   }
188 
189   Expected<object::relocation_iterator>
190   processRelocationRef(unsigned SectionID,
191                        object::relocation_iterator RelI,
192                        const object::ObjectFile &Obj,
193                        ObjSectionToIDMap &ObjSectionToID,
194                        StubMap &Stubs) override {
195     // If possible, find the symbol referred to in the relocation,
196     // and the section that contains it.
197     object::symbol_iterator Symbol = RelI->getSymbol();
198     if (Symbol == Obj.symbol_end())
199       report_fatal_error("Unknown symbol in relocation");
200     auto SectionOrError = Symbol->getSection();
201     if (!SectionOrError)
202       return SectionOrError.takeError();
203     object::section_iterator SecI = *SectionOrError;
204     // If there is no section, this must be an external reference.
205     const bool IsExtern = SecI == Obj.section_end();
206 
207     // Determine the Addend used to adjust the relocation value.
208     uint64_t RelType = RelI->getType();
209     uint64_t Offset = RelI->getOffset();
210     uint64_t Addend = 0;
211     SectionEntry &Section = Sections[SectionID];
212     uintptr_t ObjTarget = Section.getObjAddress() + Offset;
213 
214     Expected<StringRef> TargetNameOrErr = Symbol->getName();
215     if (!TargetNameOrErr)
216       return TargetNameOrErr.takeError();
217     StringRef TargetName = *TargetNameOrErr;
218 
219     switch (RelType) {
220 
221     case COFF::IMAGE_REL_AMD64_REL32:
222     case COFF::IMAGE_REL_AMD64_REL32_1:
223     case COFF::IMAGE_REL_AMD64_REL32_2:
224     case COFF::IMAGE_REL_AMD64_REL32_3:
225     case COFF::IMAGE_REL_AMD64_REL32_4:
226     case COFF::IMAGE_REL_AMD64_REL32_5:
227     case COFF::IMAGE_REL_AMD64_ADDR32NB: {
228       uint8_t *Displacement = (uint8_t *)ObjTarget;
229       Addend = readBytesUnaligned(Displacement, 4);
230 
231       if (IsExtern)
232         std::tie(Offset, RelType, Addend) = generateRelocationStub(
233           SectionID, TargetName, Offset, RelType, Addend, Stubs);
234 
235       break;
236     }
237 
238     case COFF::IMAGE_REL_AMD64_ADDR64: {
239       uint8_t *Displacement = (uint8_t *)ObjTarget;
240       Addend = readBytesUnaligned(Displacement, 8);
241       break;
242     }
243 
244     default:
245       break;
246     }
247 
248     LLVM_DEBUG(dbgs() << "\t\tIn Section " << SectionID << " Offset " << Offset
249                       << " RelType: " << RelType << " TargetName: "
250                       << TargetName << " Addend " << Addend << "\n");
251 
252     if (IsExtern) {
253       RelocationEntry RE(SectionID, Offset, RelType, Addend);
254       addRelocationForSymbol(RE, TargetName);
255     } else {
256       bool IsCode = SecI->isText();
257       unsigned TargetSectionID;
258       if (auto TargetSectionIDOrErr =
259           findOrEmitSection(Obj, *SecI, IsCode, ObjSectionToID))
260         TargetSectionID = *TargetSectionIDOrErr;
261       else
262         return TargetSectionIDOrErr.takeError();
263       uint64_t TargetOffset = getSymbolOffset(*Symbol);
264       RelocationEntry RE(SectionID, Offset, RelType, TargetOffset + Addend);
265       addRelocationForSection(RE, TargetSectionID);
266     }
267 
268     return ++RelI;
269   }
270 
271   void registerEHFrames() override {
272     for (auto const &EHFrameSID : UnregisteredEHFrameSections) {
273       uint8_t *EHFrameAddr = Sections[EHFrameSID].getAddress();
274       uint64_t EHFrameLoadAddr = Sections[EHFrameSID].getLoadAddress();
275       size_t EHFrameSize = Sections[EHFrameSID].getSize();
276       MemMgr.registerEHFrames(EHFrameAddr, EHFrameLoadAddr, EHFrameSize);
277       RegisteredEHFrameSections.push_back(EHFrameSID);
278     }
279     UnregisteredEHFrameSections.clear();
280   }
281 
282   Error finalizeLoad(const object::ObjectFile &Obj,
283                      ObjSectionToIDMap &SectionMap) override {
284     // Look for and record the EH frame section IDs.
285     for (const auto &SectionPair : SectionMap) {
286       const object::SectionRef &Section = SectionPair.first;
287       Expected<StringRef> NameOrErr = Section.getName();
288       if (!NameOrErr)
289         return NameOrErr.takeError();
290 
291       // Note unwind info is stored in .pdata but often points to .xdata
292       // with an IMAGE_REL_AMD64_ADDR32NB relocation. Using a memory manager
293       // that keeps sections ordered in relation to __ImageBase is necessary.
294       if ((*NameOrErr) == ".pdata")
295         UnregisteredEHFrameSections.push_back(SectionPair.second);
296     }
297     return Error::success();
298   }
299 };
300 
301 } // end namespace llvm
302 
303 #undef DEBUG_TYPE
304 
305 #endif
306