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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     /* Print mangled names if the argument is true; demangled if false.
     46      */
     47     virtual void printVTables(bool) const = 0;
     48     virtual ~SharedObject() = 0;
     49 private:
     50     virtual bool getVTables() = 0;
     51 };
     52 
     53 class VFunction {
     54 public:
     55     VFunction(
     56             const std::string &,
     57             const std::string &,
     58             uint64_t);
     59 
     60     uint64_t getOffset() const;
     61     bool operator<(const VFunction &) const;
     62     const std::string &getMangledName() const;
     63     const std::string &getDemangledName() const;
     64 private:
     65     std::string mMangledName;
     66     std::string mDemangledName;
     67     uint64_t mOffset;
     68 };
     69 
     70 class VTable {
     71 public:
     72     using func_iterator = std::vector<VFunction>::const_iterator;
     73     VTable(
     74             const std::string &,
     75             const std::string &,
     76             uint64_t,
     77             uint64_t);
     78 
     79     uint64_t getStartAddr() const;
     80     uint64_t getEndAddr() const;
     81     uint64_t getBaseOffset() const;
     82     uint64_t getVTableSize() const;
     83     func_iterator begin() const;
     84     func_iterator end() const;
     85     const std::string &getMangledName() const;
     86     const std::string &getDemangledName() const;
     87     void sortVFunctions();
     88     void addVFunction(
     89             const std::string &,
     90             const std::string &,
     91             uint64_t);
     92 
     93     bool operator<(const VTable &) const;
     94     bool operator<(const uint64_t) const;
     95 private:
     96     std::vector<VFunction> mFunctions;
     97     std::string mMangledName;
     98     std::string mDemangledName;
     99     /* This holds the range(st_value, st_value) through which the
    100      * VTable spans.
    101      */
    102     uint64_t mStartAddr;
    103     uint64_t mEndAddr;
    104     uint64_t mBaseOffset;
    105 };
    106 
    107 template<typename ELFT>
    108 class ELFSharedObject : public SharedObject {
    109 public:
    110     void printVTables(bool) const override;
    111     bool getVTables() override;
    112     ~ELFSharedObject();
    113     ELFSharedObject(const ELFObjectFile<ELFT> *);
    114 
    115 private:
    116     /* We need a sym value to SymbolRef map in case the relocation provides
    117      * us with an addr instead of a sym index into dynsym / symtab.
    118      */
    119     LLVM_ELF_IMPORT_TYPES_ELFT(ELFT)
    120     typedef ELFFile<ELFT> ELFO;
    121     typedef typename ELFO::Elf_Shdr Elf_Shdr;
    122     typedef typename ELFO::Elf_Ehdr Elf_Ehdr;
    123     typedef typename ELFO::Elf_Sym Elf_Sym;
    124     typedef typename ELFO::Elf_Rela Elf_Rela;
    125     typedef typename ELFO::uintX_t uintX_t;
    126     std::map<uint64_t, std::vector<SymbolRef>> mAddrToSymbolRef;
    127     const ELFObjectFile<ELFT> *mObj;
    128     /* We cache the relocation sections, to look through their relocations for
    129      * vfunctions. Sections with type SHT_PROGBITS are cached since they contain
    130      * vtables. We might need to peek at the contents of a vtable in cases of
    131      * relative relocations.
    132      */
    133     std::vector<SectionRef> mRelSectionRefs;
    134     std::vector<SectionRef> mProgBitSectionRefs;
    135     std::vector<VTable> mVTables;
    136 
    137 private:
    138     bool cacheELFSections();
    139     bool initVTableRanges();
    140     void getVFunctions();
    141     VTable *identifyVTable(uint64_t);
    142     void relocateSym(
    143             const RelocationRef &,
    144             const SectionRef &,
    145             VTable *);
    146 
    147     bool absoluteRelocation(const RelocationRef &, VTable *);
    148     bool relativeRelocation(
    149             const RelocationRef &,
    150             const SectionRef &,
    151             VTable *);
    152 
    153     uint64_t identifyAddend(uint64_t);
    154     uint64_t getAddendFromSection(const SectionRef &, uint64_t);
    155     SymbolRef matchValueToSymbol(std::vector<SymbolRef> &, VTable *);
    156 };
    157 
    158 template <typename T>
    159 static inline T UnWrap(llvm::Expected<T> ValueOrError) {
    160     if (!ValueOrError) {
    161         outs() << "\nError: "
    162                << llvm::toString(ValueOrError.takeError())
    163                << ".\n";
    164         outs().flush();
    165         exit(1);
    166     }
    167     return std::move(ValueOrError.get());
    168 }
    169 
    170 
    171 #endif  // ELF_HANDLING_H_
    172