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Merge "Fix comment drift in assorted relocation packer modules."

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Simon Baldwin 2015-03-26 18:01:13 +00:00 committed by Gerrit Code Review
commit 7c01e3a9ba
5 changed files with 8 additions and 87 deletions
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45
tools/relocation_packer/src/elf_file.h
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@ -4,53 +4,16 @@
// ELF shared object file updates handler.
//
// Provides functions to remove relative relocations from the .rel.dyn
// or .rela.dyn sections and pack into .android.rel.dyn or .android.rela.dyn,
// and unpack to return the file to its pre-packed state.
//
// Files to be packed or unpacked must include an existing .android.rel.dyn
// or android.rela.dyn section. A standard libchrome.<version>.so will not
// contain this section, so the following can be used to add one:
//
// echo -n 'NULL' >/tmp/small
// if file libchrome.<version>.so | grep -q 'ELF 32'; then
// arm-linux-androideabi-objcopy
// --add-section .android.rel.dyn=/tmp/small
// libchrome.<version>.so libchrome.<version>.so.packed
// else
// aarch64-linux-android-objcopy
// --add-section .android.rela.dyn=/tmp/small
// libchrome.<version>.so libchrome.<version>.so.packed
// fi
// rm /tmp/small
//
// To use, open the file and pass the file descriptor to the constructor,
// then pack or unpack as desired. Packing or unpacking will flush the file
// descriptor on success. Example:
//
// int fd = open(..., O_RDWR);
// ElfFile elf_file(fd);
// bool status;
// if (is_packing)
// status = elf_file.PackRelocations();
// else
// status = elf_file.UnpackRelocations();
// close(fd);
// Provides functions to pack relocations in the .rel.dyn or .rela.dyn
// sections, and unpack to return the file to its pre-packed state.
//
// SetPadding() causes PackRelocations() to pad .rel.dyn or .rela.dyn with
// NONE-type entries rather than cutting a hole out of the shared object
// file. This keeps all load addresses and offsets constant, and enables
// easier debugging and testing.
//
// A packed shared object file has all of its relative relocations
// removed from .rel.dyn or .rela.dyn, and replaced as packed data in
// .android.rel.dyn or .android.rela.dyn respectively. The resulting file
// is shorter than its non-packed original.
//
// Unpacking a packed file restores the file to its non-packed state, by
// expanding the packed data in .android.rel.dyn or .android.rela.dyn,
// combining the relative relocations with the data already in .rel.dyn
// or .rela.dyn, and then writing back the now expanded section.
// A packed shared object file is shorter than its non-packed original.
// Unpacking a packed file restores the file to its non-packed state.
#ifndef TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_
#define TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_

5
tools/relocation_packer/src/leb128.h
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@ -4,9 +4,8 @@
// LEB128 encoder and decoder for packed relative relocations.
//
// Run-length encoded relative relocations consist of a large number
// of pairs of relatively small positive integer values. Encoding these as
// LEB128 saves space.
// Packed relocations consist of a large number of relatively small
// integer values. Encoding these as LEB128 saves space.
//
// For more on LEB128 see http://en.wikipedia.org/wiki/LEB128.

3
tools/relocation_packer/src/main.cc
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@ -4,9 +4,6 @@
// Tool to pack and unpack relative relocations in a shared library.
//
// Packing removes relative relocations from .rel.dyn and writes them
// in a more compact form to .android.rel.dyn. Unpacking does the reverse.
//
// Invoke with -v to trace actions taken when packing or unpacking.
// Invoke with -p to pad removed relocations with R_*_NONE. Suppresses
// shrinking of .rel.dyn.

37
tools/relocation_packer/src/packer.h
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@ -3,43 +3,6 @@
// found in the LICENSE file.
// Pack relative relocations into a more compact form.
//
//
// For relative relocations without addends (32 bit platforms)
// -----------------------------------------------------------
//
// Applies two packing strategies. The first is run-length encoding, which
// turns a large set of relative relocations into a much smaller set
// of delta-count pairs, prefixed with a two-word header comprising the
// count of pairs and the initial relocation offset. The second is LEB128
// encoding, which compresses the result of run-length encoding.
//
// Once packed, data is prefixed by an identifier that allows for any later
// versioning of packing strategies.
//
// A complete packed stream of relocations without addends might look
// something like:
//
// "APR1" pairs init_offset count1 delta1 count2 delta2 ...
// 41505231 f2b003 b08ac716 e001 04 01 10 ...
//
//
// For relative relocations with addends (64 bit platforms)
// --------------------------------------------------------
//
// Applies two packing strategies. The first is delta encoding, which
// turns a large set of relative relocations into a smaller set
// of offset and addend delta pairs, prefixed with a header indicating the
// count of pairs. The second is signed LEB128 encoding, which compacts
// the result of delta encoding.
//
// Once packed, data is prefixed by an identifier that allows for any later
// versioning of packing strategies.
//
// A complete packed stream might look something like:
//
// "APA1" pairs offset_d1 addend_d1 offset_d2 addend_d2 ...
// 41505232 f2b018 04 28 08 9f01 ...
#ifndef TOOLS_RELOCATION_PACKER_SRC_PACKER_H_
#define TOOLS_RELOCATION_PACKER_SRC_PACKER_H_

5
tools/relocation_packer/src/sleb128.h
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@ -4,9 +4,8 @@
// SLEB128 encoder and decoder for packed relative relocations.
//
// Delta encoded relative relocations consist of a large number
// of pairs signed integer values, many with small values. Encoding these
// as signed LEB128 saves space.
// Packed relocations consist of a large number of relatively small
// integer values. Encoding these as LEB128 saves space.
//
// For more on LEB128 see http://en.wikipedia.org/wiki/LEB128.