Update Obtaining the Oodle library
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The Unreal Engine (currently v5.0.3) includes a version of the Oodle data compression library compiled for Linux (at `Engine/Source/Runtime/OodleDataCompression/Sdks/2.9.5/lib/Linux`). However, this archive was compiled for static linking, and all symbols were marked as hidden.
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To be able to create a shared library from that, follow the steps described in [StackOverflow - Keep all exported symbols when creating a shared library from a static library](https://stackoverflow.com/questions/54664759/keep-all-exported-symbols-when-creating-a-shared-library-from-a-static-library):
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**elf_unhide.py**:
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```python
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#!/usr/bin/python
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# unhide.py - Replace hidden with default visibility on global symbols defined
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# in an ELF object file
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import argparse, sys, lief
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from lief.ELF import SYMBOL_BINDINGS, SYMBOL_VISIBILITY, SYMBOL_TYPES
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def warn(msg):
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sys.stderr.write("WARNING: " + msg + "\n")
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def unhide(objfile_in, objfile_out = None, namedsyms=None):
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if not objfile_out:
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objfile_out = objfile_in
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binary = lief.parse(objfile_in)
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allsyms = { sym.name for sym in binary.symbols }
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selectedsyms = set([])
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nasyms = { sym.name for sym in binary.symbols if \
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sym.type == SYMBOL_TYPES.NOTYPE or \
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sym.binding != SYMBOL_BINDINGS.GLOBAL or \
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sym.visibility != SYMBOL_VISIBILITY.HIDDEN }
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if namedsyms:
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namedsyms = set(namedsyms)
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nosyms = namedsyms - allsyms
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for nosym in nosyms:
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warn("No symbol " + nosym + " in " + objfile_in + ": ignored")
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for sym in namedsyms & nasyms:
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warn("Input symbol " + sym + \
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" is not a hidden global symbol defined in " + objfile_in + \
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": ignored")
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selectedsyms = namedsyms - nosyms
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else:
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selectedsyms = allsyms
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selectedsyms -= nasyms
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unhidden = 0;
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for sym in binary.symbols:
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if sym.name in selectedsyms:
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sym.visibility = SYMBOL_VISIBILITY.DEFAULT
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unhidden += 1
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print("Unhidden: " + sym.name)
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print("{} symbols were unhidden".format(unhidden))
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binary.write(objfile_out)
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def get_args():
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parser = argparse.ArgumentParser(
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description="Replace hidden with default visibility on " + \
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"global symbols defined in an ELF object file.")
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parser.add_argument("ELFIN",help="ELF object file to read")
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parser.add_argument("-s","--symbol",metavar="SYMBOL",action="append",
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help="Unhide SYMBOL. " + \
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"If unspecified, unhide all hidden global symbols defined in ELFIN")
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parser.add_argument("--symfile",
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help="File of whitespace-delimited symbols to unhide")
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parser.add_argument("-o","--out",metavar="ELFOUT",
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help="ELF object file to write. If unspecified, rewrite ELFIN")
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return parser.parse_args()
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def main():
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args = get_args()
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objfile_in = args.ELFIN
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objfile_out = args.out
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symlist = args.symbol
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if not symlist:
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symlist = []
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symfile = args.symfile
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if symfile:
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with open(symfile,"r") as fh:
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symlist += [word for line in fh for word in line.split()]
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unhide(objfile_in,objfile_out,symlist)
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main()
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```
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**elf_unhide.sh**:
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```bash
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#!/bin/bash
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TEMP=$(mktemp -d)
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OLD_ARCHIVE="$(realpath "$1")"
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NEW_ARCHIVE="$(realpath "$2")"
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ar --output $TEMP xv $OLD_ARCHIVE
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find $TEMP -type f -exec ./elf_unhide.py --symfile symbols.txt "{}" \;
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ar rcs $NEW_ARCHIVE $TEMP/*.o
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rm -r $TEMP
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echo "$(basename $NEW_ARCHIVE) made"
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```
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**Create the shared library**:
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Create the files above, as well as a file `symbols.txt`, where each line lists one symbol you want to make available for linking.
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Then run:
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```shell
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./elf_unhide.sh liboo2corelinux64.a liboo2corelinux64_out.a
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g++ -shared -o liboo2corelinux64.so -Wl,--whole-archive ./liboo2corelinux64_out.a -Wl,--no-whole-archive
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```
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20
Obtaining-the-Oodle-library.md
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20
Obtaining-the-Oodle-library.md
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Darktide ships with a `.dll` for Oodle 2.8, and that could be linked to for DTMT. However, that creates two problems:
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* It's only available on Windows. Linux users would have to run everything through Wine.
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* DTMT needs to know the path to the library file. It's hard to make automatic detection reliable, and it's confusing for people to specify it manually.
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Therefore, linking the libraries statically is the better option, but requires additional files on both systems.
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To compile for Windows (native or cross), a `oo2core_win_release.lib` file is needed. Compiling for Linux requires an `liboo2corelinux64.a` archive file instead.
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## Generating a `.lib` file
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A `.lib` file can be generated from a `.dll` file. The MSVC command line tools (from the Visual Studio installer) are required.
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1. `dumpbin /EXPORTS oo2core_win_release.dll > oo2core_win_release.def`
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2. Add a line `EXPORTS` at the top of the `.def` file
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2.1. (Optional) Remove unused function definitions
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3. `lib /def:oo2core_win_release.def /machine:x64 /out:oo2core_win_release.lib`
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## Acquiring a `.lib` or `.a` file from Unreal Engine
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The Unreal Engine source code (currently v5.0.3) includes a version of the Oodle data compression library (at `Engine/Source/Runtime/OodleDataCompression/Sdks/2.9.5`). While this is a never version than the one Darktide uses, they are ABI compatible.
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