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      1 /*
      2  * Copyright (C) 2017 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef ELF_HANDLING_H_
     18 #define ELF_HANDLING_H_
     19 
     20 #include <map>
     21 #include <memory>
     22 #include <string>
     23 #include <system_error>
     24 #include <vector>
     25 
     26 #include <llvm/Object/ELFObjectFile.h>
     27 #include <llvm/Object/ELFTypes.h>
     28 #include <llvm/Object/SymbolSize.h>
     29 #include <llvm/Support/Endian.h>
     30 #include <llvm/Support/raw_ostream.h>
     31 
     32 using llvm::object::ObjectFile;
     33 using llvm::object::ELFObjectFile;
     34 using llvm::object::SectionRef;
     35 using llvm::object::RelocationRef;
     36 using llvm::object::ELFFile;
     37 using llvm::object::ELFType;
     38 using llvm::object::ELFDataTypeTypedefHelper;
     39 using llvm::object::SymbolRef;
     40 using llvm::outs;
     41 
     42 class SharedObject {
     43 public:
     44     static std::unique_ptr<SharedObject> create(const ObjectFile *);
     45     virtual void printVTables() const = 0;
     46     virtual ~SharedObject() = 0;
     47 private:
     48     virtual bool getVTables() = 0;
     49 };
     50 
     51 class VFunction {
     52 public:
     53     VFunction(
     54             const std::string &,
     55             const std::string &,
     56             uint64_t);
     57 
     58     uint64_t getOffset() const;
     59     bool operator<(const VFunction &) const;
     60     const std::string &getMangledName() const;
     61     const std::string &getDemangledName() const;
     62 private:
     63     std::string mMangledName;
     64     std::string mDemangledName;
     65     uint64_t mOffset;
     66 };
     67 
     68 class VTable {
     69 public:
     70     using func_iterator = std::vector<VFunction>::const_iterator;
     71     VTable(
     72             const std::string &,
     73             const std::string &,
     74             uint64_t,
     75             uint64_t);
     76 
     77     uint64_t getStartAddr() const;
     78     uint64_t getEndAddr() const;
     79     uint64_t getBaseOffset() const;
     80     uint64_t getVTableSize() const;
     81     func_iterator begin() const;
     82     func_iterator end() const;
     83     const std::string &getMangledName() const;
     84     const std::string &getDemangledName() const;
     85     void sortVFunctions();
     86     void addVFunction(
     87             const std::string &,
     88             const std::string &,
     89             uint64_t);
     90 
     91     bool operator<(const VTable &) const;
     92     bool operator<(const uint64_t) const;
     93 private:
     94     std::vector<VFunction> mFunctions;
     95     std::string mMangledName;
     96     std::string mDemangledName;
     97     /* This holds the range(st_value, st_value) through which the
     98      * VTable spans.
     99      */
    100     uint64_t mStartAddr;
    101     uint64_t mEndAddr;
    102     uint64_t mBaseOffset;
    103 };
    104 
    105 template<typename ELFT>
    106 class ELFSharedObject : public SharedObject {
    107 public:
    108     void printVTables() const override;
    109     bool getVTables() override;
    110     ~ELFSharedObject();
    111     ELFSharedObject(const ELFObjectFile<ELFT> *);
    112 
    113 private:
    114     /* We need a sym value to SymbolRef map in case the relocation provides
    115      * us with an addr instead of a sym index into dynsym / symtab.
    116      */
    117     LLVM_ELF_IMPORT_TYPES_ELFT(ELFT)
    118     typedef ELFFile<ELFT> ELFO;
    119     typedef typename ELFO::Elf_Shdr Elf_Shdr;
    120     typedef typename ELFO::Elf_Ehdr Elf_Ehdr;
    121     typedef typename ELFO::Elf_Sym Elf_Sym;
    122     typedef typename ELFO::Elf_Rela Elf_Rela;
    123     typedef typename ELFO::uintX_t uintX_t;
    124     std::map<uint64_t, std::vector<SymbolRef>> mAddrToSymbolRef;
    125     const ELFObjectFile<ELFT> *mObj;
    126     /* We cache the relocation sections, to look through their relocations for
    127      * vfunctions. Sections with type SHT_PROGBITS are cached since they contain
    128      * vtables. We might need to peek at the contents of a vtable in cases of
    129      * relative relocations.
    130      */
    131     std::vector<SectionRef> mRelSectionRefs;
    132     std::vector<SectionRef> mProgBitSectionRefs;
    133     std::vector<VTable> mVTables;
    134 
    135 private:
    136     bool cacheELFSections();
    137     bool initVTableRanges();
    138     void getVFunctions();
    139     VTable *identifyVTable(uint64_t);
    140     void relocateSym(
    141             const RelocationRef &,
    142             const SectionRef &,
    143             VTable *);
    144 
    145     bool absoluteRelocation(const RelocationRef &, VTable *);
    146     bool relativeRelocation(
    147             const RelocationRef &,
    148             const SectionRef &,
    149             VTable *);
    150 
    151     uint64_t identifyAddend(uint64_t);
    152     uint64_t getAddendFromSection(const SectionRef &, uint64_t);
    153     SymbolRef matchValueToSymbol(std::vector<SymbolRef> &, VTable *);
    154 };
    155 
    156 template <typename T>
    157 static inline T UnWrap(llvm::Expected<T> ValueOrError) {
    158     if (!ValueOrError) {
    159         outs() << "\nError: "
    160                << llvm::toString(ValueOrError.takeError())
    161                << ".\n";
    162         outs().flush();
    163         exit(1);
    164     }
    165     return std::move(ValueOrError.get());
    166 }
    167 
    168 
    169 #endif  // ELF_HANDLING_H_
    170