1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef CRAZY_LINKER_ELF_LOADER_H
6 #define CRAZY_LINKER_ELF_LOADER_H
7 
8 #include "crazy_linker_error.h"
9 #include "crazy_linker_system.h"  // For ScopedFileDescriptor
10 #include "elf_traits.h"
11 
12 namespace crazy {
13 
14 // Helper class used to load an ELF binary in memory.
15 //
16 // Note that this doesn't not perform any relocation, the purpose
17 // of this class is strictly to map all loadable segments from the
18 // file to their correct location.
19 //
20 class ElfLoader {
21  public:
22   ElfLoader();
23   ~ElfLoader();
24 
25   // Try to load a library at a given address. On failure, this will
26   // update the linker error message and returns false.
27   //
28   // |lib_path| is the full library path, and |wanted_address| should
29   // be the desired load address, or 0 to enable randomization.
30   //
31   // |file_offset| is an offset in the file where the ELF header will
32   // be looked for.
33   //
34   // |wanted_address| is the wanted load address (of the first loadable
35   // segment), or 0 to enable randomization.
36   //
37   // On success, the library's loadable segments will be mapped in
38   // memory with their original protection. However, no further processing
39   // will be performed.
40   //
41   // On failure, returns false and assign an error message to |error|.
42   bool LoadAt(const char* lib_path,
43               off_t file_offset,
44               uintptr_t wanted_address,
45               Error* error);
46 
47   // Only call the following functions after a succesfull LoadAt() call.
48 
phdr_count()49   size_t phdr_count() { return phdr_num_; }
load_start()50   ELF::Addr load_start() { return reinterpret_cast<ELF::Addr>(load_start_); }
load_size()51   ELF::Addr load_size() { return load_size_; }
load_bias()52   ELF::Addr load_bias() { return load_bias_; }
loaded_phdr()53   const ELF::Phdr* loaded_phdr() { return loaded_phdr_; }
54 
55  private:
56   FileDescriptor fd_;
57   const char* path_;
58 
59   ELF::Ehdr header_;
60   size_t phdr_num_;
61 
62   void* phdr_mmap_;  // temporary copy of the program header.
63   ELF::Phdr* phdr_table_;
64   ELF::Addr phdr_size_;  // and its size.
65 
66   off_t file_offset_;
67   void* wanted_load_address_;
68   void* load_start_;     // First page of reserved address space.
69   ELF::Addr load_size_;  // Size in bytes of reserved address space.
70   ELF::Addr load_bias_;  // load_bias, add this value to all "vaddr"
71                          // values in the library to get the corresponding
72                          // memory address.
73 
74   const ELF::Phdr* loaded_phdr_;  // points to the loaded program header.
75 
76   // Individual steps used by ::LoadAt()
77   bool ReadElfHeader(Error* error);
78   bool ReadProgramHeader(Error* error);
79   bool ReserveAddressSpace(Error* error);
80   bool LoadSegments(Error* error);
81   bool FindPhdr(Error* error);
82   bool CheckPhdr(ELF::Addr, Error* error);
83 };
84 
85 }  // namespace crazy
86 
87 #endif  // CRAZY_LINKER_ELF_LOADER_H
88