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Side by Side Diff: tools/relocation_packer/src/elf_file.h

Issue 404553003: Create builds configured for ARM and AARCH64. (Closed) Base URL: https://chromium.googlesource.com/chromium/src.git@master
Patch Set: Rename DT tags to DT_ANDROID_REL_XXX Created 6 years, 5 months ago
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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
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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