tools/relocation_packer/README.TXT - Issue 407093003: Switch from ELF CPU-specific to OS-specific DT_ tags.

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Issue 407093003: Switch from ELF CPU-specific to OS-specific DT_ tags. (Closed) Base URL: https://chromium.googlesource.com/chromium/src.git@master

Patch Set: Rebase to master Created 6 years, 5 months ago

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1 Introduction:	1 Introduction:

2 -------------	2 -------------

3	3

4 R_ARM_RELATIVE relocations are the bulk of dynamic relocations (the .rel.dyn	4 R_ARM_RELATIVE relocations are the bulk of dynamic relocations (the .rel.dyn

5 section) in libchrome.<version>.so. The ELF standard representation of them	5 section) in libchrome.<version>.so. The ELF standard representation of them

6 is wasteful.	6 is wasteful.

7	7

8 Packing uses run length encoding to store them more efficiently. Packed	8 Packing uses run length encoding to store them more efficiently. Packed

9 relocations are placed in a new .android.rel.dyn section. Packing reduces	9 relocations are placed in a new .android.rel.dyn section. Packing reduces

10 the footprint of libchrome.<version>.so in the filesystem, in APK downloads,	10 the footprint of libchrome.<version>.so in the filesystem, in APK downloads,

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24 Notes:	24 Notes:

25 ------	25 ------

26	26

27 Packing does not adjust debug data. An unstripped libchrome.<version>.so	27 Packing does not adjust debug data. An unstripped libchrome.<version>.so

28 can be packed and will run, but may no longer be useful for debugging.	28 can be packed and will run, but may no longer be useful for debugging.

29	29

30 Unpacking on the device requires the explicit support of an extended crazy	30 Unpacking on the device requires the explicit support of an extended crazy

31 linker. Adds the following new .dynamic tags, used by the crazy linker to	31 linker. Adds the following new .dynamic tags, used by the crazy linker to

32 find the packed .android.rel.dyn section data:	32 find the packed .android.rel.dyn section data:

33	33

34 DT_ANDROID_ARM_REL_OFFSET = DT_LOPROC (Processor specific: 0x70000000)	34 DT_ANDROID_REL_OFFSET = DT_LOOS (Operating System specific: 0x6000000d)

35 - The offset of .android.rel.dyn data in libchrome.<version>.so	35 - The offset of .android.rel.dyn data in libchrome.<version>.so

36 DT_ANDROID_ARM_REL_SIZE = DT_LOPROC + 1 (Processor Specific: 0x70000001)	36 DT_ANDROID_REL_SIZE = DT_LOOS + 1 (Operating System Specific: 0x6000000e)

37 - The size of .android.rel.dyn data in bytes	37 - The size of .android.rel.dyn data in bytes

38	38

39 The format of .android.rel.dyn data is:	39 The format of .android.rel.dyn data is:

40	40

41 "APR1" identifier	41 "APR1" identifier

42 N: the number of count-delta pairs in the encoding	42 N: the number of count-delta pairs in the encoding

43 A: the initial offset	43 A: the initial offset

44 N * C,D: N count-delta pairs	44 N * C,D: N count-delta pairs

45	45

46 All numbers in the encoding stream are stored as LEB128 values. For details	46 All numbers in the encoding stream are stored as LEB128 values. For details

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93 the allocation).	93 the allocation).

94	94

95 Requires libelf 0.158 or later. Earlier libelf releases may be buggy in	95 Requires libelf 0.158 or later. Earlier libelf releases may be buggy in

96 ways that prevent the packer from working correctly.	96 ways that prevent the packer from working correctly.

97	97

98	98

99 Testing:	99 Testing:

100 --------	100 --------

101	101

102 Unittests run under gtest, on the host system.	102 Unittests run under gtest, on the host system.

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