Merge "Remove unused/unusable relocation packer files."
This commit is contained in:
Simon Baldwin
@@ -1,135 +0,0 @@
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Introduction:
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-------------
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Relative relocations are the bulk of dynamic relocations (the .rel.dyn
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or .rela.dyn sections) in libchrome.<version>.so. The ELF standard
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representation of them is wasteful.
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Packing uses a combination of run length encoding, delta encoding, and LEB128
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encoding to store them more efficiently. Packed relocations are placed in
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a new .android.rel.dyn or .android.rela.dyn section. Packing reduces
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the footprint of libchrome.<version>.so in the filesystem, in APK downloads,
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and in memory when loaded on the device.
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A packed libchrome.<version>.so is designed so that it can be loaded directly
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on Android, but requires the explicit support of a crazy linker that has been
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extended to understand packed relocations. Packed relocations are currently
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only supported on ARM.
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A packed libchrome.<version>.so cannot currently be used with the standard
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Android runtime linker.
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See src/*.h for design and implementation notes.
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Notes:
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------
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Packing does not adjust debug data. An unstripped libchrome.<version>.so
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can be packed and will run, but may no longer be useful for debugging.
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Unpacking on the device requires the explicit support of an extended crazy
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linker. Adds the following new .dynamic tags, used by the crazy linker to
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find the packed .android.rel.dyn or .android.rela.dyn section data:
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DT_ANDROID_REL_OFFSET = DT_LOOS (Operating System specific: 0x6000000d)
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- The offset of packed relocation data in libchrome.<version>.so
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DT_ANDROID_REL_SIZE = DT_LOOS + 1 (Operating System Specific: 0x6000000e)
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- The size of packed relocation data in bytes
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32 bit ARM libraries use relocations without addends. 64 bit ARM libraries
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use relocations with addends. The packing strategy necessarily differs for
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the two relocation types.
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Where libchrome.<version>.so contains relocations without addends, the format
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of .android.rel.dyn data is:
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"APR1" identifier
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N: the number of count-delta pairs in the encoding
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A: the initial offset
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N * C,D: N count-delta pairs
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Where libchrome.<version>.so contains relocations with addends, the format
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of .android.rela.dyn data is:
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"APA1" identifier
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N: the number of addr-addend delta pairs in the encoding
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N * A,V: N addr-addend delta pairs
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All numbers in the encoding stream are stored as LEB128 values. For details
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see http://en.wikipedia.org/wiki/LEB128.
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The streaming unpacking algorithm for 32 bit ARM is:
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skip over "APR1"
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pairs, addr = next leb128 value, next leb128 value
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emit R_ARM_RELATIVE relocation with r_offset = addr
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while pairs:
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count, delta = next leb128 value, next leb128 value
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while count:
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addr += delta
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emit R_ARM_RELATIVE relocation with r_offset = addr
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count--
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pairs--
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The streaming unpacking algorithm for 64 bit ARM is:
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skip over "APA1"
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pairs = next signed leb128 value
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addr, addend = 0, 0
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while pairs:
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addr += next signed leb128 value
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addend += next signed leb128 value
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emit R_AARCH64_RELATIVE relocation with r_offset = addr, r_addend = addend
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pairs--
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Usage instructions:
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-------------------
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To pack relocations, add an empty .android.rel.dyn or .android.rela.dyn and
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then run the tool:
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echo -n 'NULL' >/tmp/small
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if file libchrome.<version>.so | grep -q 'ELF 32'; then
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arm-linux-androideabi-objcopy
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--add-section .android.rel.dyn=/tmp/small
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libchrome.<version>.so libchrome.<version>.so.packed
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else
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aarch64-linux-android-objcopy
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--add-section .android.rela.dyn=/tmp/small
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libchrome.<version>.so libchrome.<version>.so.packed
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fi
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rm /tmp/small
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relocation_packer libchrome.<version>.so.packed
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To unpack and restore the shared library to its original state:
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cp libchrome.<version>.so.packed unpackable
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relocation_packer -u unpackable
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if file libchrome.<version>.so | grep -q 'ELF 32'; then
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arm-linux-androideabi-objcopy \
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--remove-section=.android.rel.dyn unpackable libchrome.<version>.so
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else
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aarch64-linux-android-objcopy \
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--remove-section=.android.rela.dyn unpackable libchrome.<version>.so
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endif
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rm unpackable
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Bugs & TODOs:
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-------------
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Requires two free slots in the .dynamic section. Uses these to add data that
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tells the crazy linker where to find the packed relocation data. Fails
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if insufficient free slots exist (use gold --spare-dynamic-slots to increase
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the allocation).
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Requires libelf 0.158 or later. Earlier libelf releases may be buggy in
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ways that prevent the packer from working correctly.
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Testing:
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--------
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Unittests run under gtest, on the host system.
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@@ -1,81 +0,0 @@
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// Copyright 2014 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// Run-length encode and decode relative relocations.
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//
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// Relative relocations are the bulk of dynamic relocations (the
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// .rel.dyn or .rela.dyn sections) in libchrome.<version>.so, and the ELF
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// standard representation of them is wasteful. .rel.dyn contains
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// relocations without addends, .rela.dyn relocations with addends.
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//
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// A relocation with no addend is 8 bytes on 32 bit platforms and 16 bytes
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// on 64 bit plaforms, split into offset and info fields. Offsets strictly
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// increase, and each is commonly a few bytes different from its predecessor.
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// There are long runs where the difference does not change. The info field
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// is constant. Example, from 'readelf -x4 libchrome.<version>.so' 32 bit:
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//
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// offset info offset info
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// 808fef01 17000000 848fef01 17000000 ................
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// 888fef01 17000000 8c8fef01 17000000 ................
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// 908fef01 17000000 948fef01 17000000 ................
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//
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// Run length encoding packs this data more efficiently, by representing it
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// as a delta and a count of entries each differing from its predecessor
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// by this delta. The above can be represented as a start address followed
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// by an encoded count of 6 and offset difference of 4:
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//
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// start count diff
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// 01ef8f80 00000006 00000004
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//
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// Because relative relocation offsets strictly increase, the complete
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// set of relative relocations in libchrome.<version>.so can be
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// represented by a single start address followed by one or more difference
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// and count encoded word pairs:
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//
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// start run1 count run1 diff run2 count run2 diff
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// 01ef8f80 00000006 00000004 00000010 00000008 ...
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//
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// Decoding regenerates relative relocations beginning at address
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// 'start' and for each encoded run, incrementing the address by 'difference'
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// for 'count' iterations and emitting a new relative relocation.
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//
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// Once encoded, data is prefixed by a single word count of packed delta and
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// count pairs. A final run-length encoded relative relocations vector
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// might therefore look something like:
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//
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// pairs start run 1 run 2 ... run 15
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// 0000000f 01ef8f80 00000006 00000004 00000010 00000008 ...
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// Interpreted as:
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// pairs=15 start=.. count=6,delta=4 count=16,delta=8
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#ifndef TOOLS_RELOCATION_PACKER_SRC_RUN_LENGTH_ENCODER_H_
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#define TOOLS_RELOCATION_PACKER_SRC_RUN_LENGTH_ENCODER_H_
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#include <vector>
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#include "elf.h"
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#include "elf_traits.h"
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namespace relocation_packer {
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// A RelocationRunLengthCodec packs vectors of relative relocations
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// into more compact forms, and unpacks them to reproduce the pre-packed data.
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class RelocationRunLengthCodec {
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public:
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// Encode relative relocations into a more compact form.
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// |relocations| is a vector of relative relocation structs.
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// |packed| is the vector of packed words into which relocations are packed.
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static void Encode(const std::vector<ELF::Rel>& relocations,
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std::vector<ELF::Xword>* packed);
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// Decode relative relocations from their more compact form.
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// |packed| is the vector of packed relocations.
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// |relocations| is a vector of unpacked relative relocation structs.
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static void Decode(const std::vector<ELF::Xword>& packed,
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std::vector<ELF::Rel>* relocations);
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};
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} // namespace relocation_packer
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#endif // TOOLS_RELOCATION_PACKER_SRC_RUN_LENGTH_ENCODER_H_
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@@ -1,88 +0,0 @@
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#!/usr/bin/env python
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#
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# Copyright 2014 The Chromium Authors. All rights reserved.
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# Use of this source code is governed by a BSD-style license that can be
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# found in the LICENSE file.
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"""Build relocation packer unit test data.
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Uses a built relocation packer to generate 'golden' reference test data
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files for elf_file_unittests.cc.
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"""
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import optparse
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import os
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import shutil
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import subprocess
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import sys
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import tempfile
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def PackArmLibraryRelocations(android_pack_relocations,
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android_objcopy,
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added_section,
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input_path,
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output_path):
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# Copy and add a 'NULL' .android.rel.dyn section for the packing tool.
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with tempfile.NamedTemporaryFile() as stream:
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stream.write('NULL')
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stream.flush()
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objcopy_command = [android_objcopy,
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'--add-section', '%s=%s' % (added_section, stream.name),
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input_path, output_path]
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subprocess.check_call(objcopy_command)
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# Pack relocations.
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pack_command = [android_pack_relocations, output_path]
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subprocess.check_call(pack_command)
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def UnpackArmLibraryRelocations(android_pack_relocations,
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input_path,
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output_path):
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shutil.copy(input_path, output_path)
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# Unpack relocations. We leave the .android.rel.dyn or .android.rela.dyn
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# in place.
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unpack_command = [android_pack_relocations, '-u', output_path]
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subprocess.check_call(unpack_command)
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def main():
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parser = optparse.OptionParser()
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parser.add_option('--android-pack-relocations',
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help='Path to the ARM relocations packer binary')
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parser.add_option('--android-objcopy',
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help='Path to the toolchain\'s objcopy binary')
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parser.add_option('--added-section',
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choices=['.android.rel.dyn', '.android.rela.dyn'],
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help='Section to add, one of ".android.rel.dyn" or ".android.rela.dyn"')
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parser.add_option('--test-file',
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help='Path to the input test file, an unpacked ARM .so')
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parser.add_option('--unpacked-output',
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help='Path to the output file for reference unpacked data')
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parser.add_option('--packed-output',
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help='Path to the output file for reference packed data')
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options, _ = parser.parse_args()
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for output in [options.unpacked_output, options.packed_output]:
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directory = os.path.dirname(output)
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if not os.path.exists(directory):
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os.makedirs(directory)
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PackArmLibraryRelocations(options.android_pack_relocations,
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options.android_objcopy,
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options.added_section,
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options.test_file,
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options.packed_output)
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UnpackArmLibraryRelocations(options.android_pack_relocations,
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options.packed_output,
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options.unpacked_output)
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return 0
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if __name__ == '__main__':
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sys.exit(main())
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@@ -1,35 +0,0 @@
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#!/bin/bash
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#
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# Copyright 2014 The Chromium Authors. All rights reserved.
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# Use of this source code is governed by a BSD-style license that can be
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# found in the LICENSE file.
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# Generates elf_file_unittest_relocs_arm{32,64}{,_packed}.so test data files
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# from elf_file_unittest_relocs.cc. Run once to create these test data
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# files; the files are checked into the source tree.
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#
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# To use:
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# ./generate_elf_file_unittest_relocs.sh
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# git add elf_file_unittest_relocs_arm{32,64}{,_packed}.so
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function main() {
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local '-r' test_data_directory="$(pwd)"
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cd '../../..'
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source tools/cr/cr-bash-helpers.sh
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local arch
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for arch in 'arm32' 'arm64'; do
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cr 'init' '--platform=android' '--type=Debug' '--architecture='"${arch}"
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cr 'build' 'relocation_packer_unittests_test_data'
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done
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local '-r' packer='out_android/Debug/obj/tools/relocation_packer'
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local '-r' gen="${packer}/relocation_packer_unittests_test_data.gen"
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cp "${gen}/elf_file_unittest_relocs_arm"{32,64}{,_packed}'.so' \
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"${test_data_directory}"
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return 0
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}
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main
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Reference in New Issue
Block a user