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1 // Copyright 2014 The Chromium Authors. All rights reserved. | 1 // Copyright 2014 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 // ELF shared object file updates handler. | 5 // ELF shared object file updates handler. |
6 // | 6 // |
7 // Provides functions to remove R_ARM_RELATIVE relocations from the .rel.dyn | 7 // Provides functions to remove ARM relative relocations from the .rel.dyn |
8 // section and pack them in .android.rel.dyn, and unpack to return the file | 8 // section and pack them in .android.rel.dyn, and unpack to return the file |
9 // to its pre-packed state. | 9 // to its pre-packed state. |
10 // | 10 // |
11 // Files to be packed or unpacked must include an existing .android.rel.dyn | 11 // Files to be packed or unpacked must include an existing .android.rel.dyn |
12 // section. A standard libchrome.<version>.so will not contain this section, | 12 // section. A standard libchrome.<version>.so will not contain this section, |
13 // so the following can be used to add one: | 13 // so the following can be used to add one: |
14 // | 14 // |
15 // echo -n 'NULL' >/tmp/small | 15 // echo -n 'NULL' >/tmp/small |
16 // arm-linux-gnueabi-objcopy | 16 // arm-linux-gnueabi-objcopy |
17 // --add-section .android.rel.dyn=/tmp/small | 17 // --add-section .android.rel.dyn=/tmp/small |
18 // libchrome.<version>.so libchrome.<version>.so.packed | 18 // libchrome.<version>.so libchrome.<version>.so.packed |
19 // rm /tmp/small | 19 // rm /tmp/small |
20 // | 20 // |
21 // To use, open the file and pass the file descriptor to the constructor, | 21 // To use, open the file and pass the file descriptor to the constructor, |
22 // then pack or unpack as desired. Packing or unpacking will flush the file | 22 // then pack or unpack as desired. Packing or unpacking will flush the file |
23 // descriptor on success. Example: | 23 // descriptor on success. Example: |
24 // | 24 // |
25 // int fd = open(..., O_RDWR); | 25 // int fd = open(..., O_RDWR); |
26 // ElfFile elf_file(fd); | 26 // ElfFile elf_file(fd); |
27 // bool status; | 27 // bool status; |
28 // if (is_packing) | 28 // if (is_packing) |
29 // status = elf_file.PackRelocations(); | 29 // status = elf_file.PackRelocations(); |
30 // else | 30 // else |
31 // status = elf_file.UnpackRelocations(); | 31 // status = elf_file.UnpackRelocations(); |
32 // close(fd); | 32 // close(fd); |
33 // | 33 // |
34 // SetPadding() causes PackRelocations() to pad .rel.dyn with R_ARM_NONE | 34 // SetPadding() causes PackRelocations() to pad .rel.dyn with NONE-type |
35 // entries rather than cutting a hole out of the shared object file. This | 35 // entries rather than cutting a hole out of the shared object file. This |
36 // keeps all load addresses and offsets constant, and enables easier | 36 // keeps all load addresses and offsets constant, and enables easier |
37 // debugging and testing. | 37 // debugging and testing. |
38 // | 38 // |
39 // A packed shared object file has all of its R_ARM_RELATIVE relocations | 39 // A packed shared object file has all of its ARM relative relocations |
40 // removed from .rel.dyn, and replaced as packed data in .android.rel.dyn. | 40 // removed from .rel.dyn, and replaced as packed data in .android.rel.dyn. |
41 // The resulting file is shorter than its non-packed original. | 41 // The resulting file is shorter than its non-packed original. |
42 // | 42 // |
43 // Unpacking a packed file restores the file to its non-packed state, by | 43 // Unpacking a packed file restores the file to its non-packed state, by |
44 // expanding the packed data in android.rel.dyn, combining the R_ARM_RELATIVE | 44 // expanding the packed data in android.rel.dyn, combining the ARM relative |
45 // relocations with the data already in .rel.dyn, and then writing back the | 45 // relocations with the data already in .rel.dyn, and then writing back the |
46 // now expanded .rel.dyn section. | 46 // now expanded .rel.dyn section. |
47 | 47 |
48 #ifndef TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_ | 48 #ifndef TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_ |
49 #define TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_ | 49 #define TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_ |
50 | 50 |
51 #include <string.h> | 51 #include <string.h> |
52 | 52 |
53 #include "elf.h" | 53 #include "elf.h" |
54 #include "libelf.h" | 54 #include "libelf.h" |
55 #include "packer.h" | 55 #include "packer.h" |
56 | 56 |
57 namespace relocation_packer { | 57 namespace relocation_packer { |
58 | 58 |
59 // An ElfFile reads shared objects, and shuttles R_ARM_RELATIVE relocations | 59 // An ElfFile reads shared objects, and shuttles ARM relative relocations |
60 // between .rel.dyn and .android.rel.dyn sections. | 60 // between .rel.dyn and .android.rel.dyn sections. |
61 class ElfFile { | 61 class ElfFile { |
62 public: | 62 public: |
63 explicit ElfFile(int fd) { memset(this, 0, sizeof(*this)); fd_ = fd; } | 63 explicit ElfFile(int fd) { memset(this, 0, sizeof(*this)); fd_ = fd; } |
64 ~ElfFile() {} | 64 ~ElfFile() {} |
65 | 65 |
66 // Set padding mode. When padding, PackRelocations() will not shrink | 66 // Set padding mode. When padding, PackRelocations() will not shrink |
67 // the .rel.dyn section, but instead replace R_ARM_RELATIVE with | 67 // the .rel.dyn section, but instead replace ARM relative with |
68 // R_ARM_NONE entries. | 68 // NONE-type entries. |
69 // |flag| is true to pad .rel.dyn, false to shrink it. | 69 // |flag| is true to pad .rel.dyn, false to shrink it. |
70 inline void SetPadding(bool flag) { is_padding_rel_dyn_ = flag; } | 70 inline void SetPadding(bool flag) { is_padding_rel_dyn_ = flag; } |
71 | 71 |
72 // Transfer R_ARM_RELATIVE relocations from .rel.dyn to a packed | 72 // Transfer ARM relative relocations from .rel.dyn to a packed |
73 // representation in .android.rel.dyn. Returns true on success. | 73 // representation in .android.rel.dyn. Returns true on success. |
74 bool PackRelocations(); | 74 bool PackRelocations(); |
75 | 75 |
76 // Transfer R_ARM_RELATIVE relocations from a packed representation in | 76 // Transfer ARM relative relocations from a packed representation in |
77 // .android.rel.dyn to .rel.dyn. Returns true on success. | 77 // .android.rel.dyn to .rel.dyn. Returns true on success. |
78 bool UnpackRelocations(); | 78 bool UnpackRelocations(); |
79 | 79 |
80 private: | 80 private: |
81 // Load a new ElfFile from a filedescriptor. If flushing, the file must | 81 // Load a new ElfFile from a filedescriptor. If flushing, the file must |
82 // be open for read/write. Returns true on successful ELF file load. | 82 // be open for read/write. Returns true on successful ELF file load. |
83 // |fd| is an open file descriptor for the shared object. | 83 // |fd| is an open file descriptor for the shared object. |
84 bool Load(); | 84 bool Load(); |
85 | 85 |
86 // Write ELF file changes. | 86 // Write ELF file changes. |
(...skipping 11 matching lines...) Expand all Loading... |
98 | 98 |
99 // Sections that we manipulate, assigned by Load(). | 99 // Sections that we manipulate, assigned by Load(). |
100 Elf_Scn* rel_dyn_section_; | 100 Elf_Scn* rel_dyn_section_; |
101 Elf_Scn* dynamic_section_; | 101 Elf_Scn* dynamic_section_; |
102 Elf_Scn* android_rel_dyn_section_; | 102 Elf_Scn* android_rel_dyn_section_; |
103 }; | 103 }; |
104 | 104 |
105 } // namespace relocation_packer | 105 } // namespace relocation_packer |
106 | 106 |
107 #endif // TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_ | 107 #endif // TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_ |
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