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#!/usr/bin/python3 -I
# SPDX-FileCopyrightText: 2026 Tomasz Kramkowski <tomasz@kramkow.ski>
# SPDX-License-Identifier: CC0-1.0
"""A minimally intrusive Frame SteamOS patcher"""
import argparse
import hashlib
import json
import os
import subprocess
import sys
from dataclasses import dataclass
from pathlib import Path
MARKER = "x-valve-please-fix"
RUNTIME = Path(os.environ.get("RUNTIME_DIRECTORY", "/run/patcher"))
@dataclass(frozen=True)
class Edit:
offset: int
replacement: bytes
@dataclass(frozen=True)
class Patch:
original_hash: bytes
edits: tuple[Edit, ...]
def apply_to(self, data: bytes) -> bytearray:
result = bytearray(data)
for edit in self.edits:
end = edit.offset + len(edit.replacement)
if edit.offset < 0 or end > len(result):
raise ValueError(f"Patch outside file at {edit.offset:#x}")
result[edit.offset : end] = edit.replacement
return result
def patch(original_hash: str, edits: tuple[tuple[int, str], ...]) -> Patch:
return Patch(
bytes.fromhex(original_hash),
tuple(
Edit(offset, bytes.fromhex(replacement)) for offset, replacement in edits
),
)
PATCHES = {
"/opt/steamvr/tools/vrlink/bin/linuxarm64/vrlink": patch(
original_hash="31addef0c9553d3770b5570487699e96d70271d4073cd6c03b080fdee6ae2153",
edits=(
# Clear the lists of ready and submitted frame IDs after a reset.
# If not done, this can cause empty frames to be submitted to the
# decoder, or skip submitting a received frame that hasn't been
# submitted since the reset.
(0x53EB4, "75d40214"),
(
0x109088,
"6072049161720c9102008092020881a81f0001ebc1ffff54616202916082249103048052020881a863040071c1ffff54802bfd17",
),
# Let the decoder worker continue running when either DQBUF returns
# EAGAIN. This can happen after a reset, and will trigger more
# resets, and can only recover after the decoder stalls for at
# least an absurd 0.8s.
(0x32D50, "db580314"),
(0x1090BC, "090040b93f2d0071e0d29454130040b922a7fc17"),
(0x32D90, "d0580314"),
(0x1090D0, "090040b93f2d007140d89454130040b92da7fc17"),
# Fix a possible bug where a missing frame wouldn't trigger a
# request when a newer frame arrived and the gap straddled the 16
# bit wrapping boundary.
(0x53F84, "a102024b213c00133f080071ab0100547316931a06000014"),
(0x53FB0, "613e0053"),
# Ignore packets which are for an older frame when re-assembling.
# There are 16 slots and this could otherwise cause an old packet
# to override a newer one.
(0x53F34, "6cd40214"),
(0x1090E4, "c00a40b96000f837a002004b60007837c0324039902bfd17b22bfd17"),
# Avoid two corner cases:
# - After reset, wait for a complete recovery frame instead of
# simply waiting for _a_ frame to avoid trying to start decoding
# from a frame which depends on prior ones.
# - Ignore frames which complete reassembly but which are older
# than the last submitted frame.
(0x541E0, "c8d30214"),
(
0x109100,
"092061f92a1941b9ca00f8370b0840b96b010a4b0b017837fd7bbea9322cfd170a3040398a0000340a1040914a754d394aff0f37c0035fd6",
),
# To compensate for the first of the above two fixes, any frames
# which completed out of order before a recovery frame must be
# revisited after that frame.
(0x53A90, "41b55a54"),
(
0x109138,
"800e4092000f008b004c40f9010840b93f00146be150a554242cfd97852afd17",
),
# If decoder submission fails, request reset without advancing the
# last-submitted frame number as though submission succeeded.
(0x53B08, "94d50214"),
(0x109158, "4050a534001b46f96b2afd17"),
# With FEC, audio gets sent as two blocks (A, B) followed by their
# parity (A^B) block. If the next block arrives (C) while the
# headset has received B but not A and is still waiting for A^B
# then B gets discarded without playing it. This loses two blocks
# worth of audio (10.67ms) rather than just skipping one missed
# block (5.33ms) and flushing the second one (B). This fixes that
# issue by just flushing B in that case.
(0x3ADA8, "ef380314"),
(
0x109164,
"2000004b6000f836e2ff9f520000020b1f080071ece19854cbe49854620080522308c21a6384021b43e1983421c7fc17",
),
# Patch incorrect sequence gap calculation when sequence numbers
# wrap modulo 65535 (recurring theme...)
(0x3AFB0, "79380314"),
(0x109194, "6000f836e1ff9f520000010b0dc7fc17"),
# Don't request retransmission of frames that the headset has
# already moved ahead of (i.e. the last-submitted frame or older).
# Assume that a frame with a size of 4 MiB with missing metadata is
# not actually 4 MiB to avoid requesting way too many potentially
# missing fragments automatically. This can cause too many requests
# which triggers an unnecessary stream reset. Requests for the
# frame's metadata fragment continue which will contain and
# populate the size field allowing the retransmit request code to
# work normally from that point.
(0x52BF8, "6bd90214"),
(
0x1091A4,
"832261f9641841b99f04003180000054e400044bc4e3a434e40078378032403960e2a435951240b9bf025071f503951a8d26fd171627fd17",
),
# Don't trigger a reset if more than 512 missing fragments need to
# be requested as a result of a time based repair. Instead stop
# early once 20 entries are accumulated, reserving an extra 21st
# entry so that a request for a fresh metadata fragment can always
# be sent. This avoids an unnecessary reset and can speed up
# recovery.
(0x52E8C, "d4d80214"),
(
0x1091DC,
"130080523f04003161e5a45484364079a0fe0f11007c0a539f00006bc2e4a45402008012e2c30079330080522227fd17",
),
(0x52EC8, "d1d80214"),
(0x10920C, "8a3240394a01130a4a4d0011852640b92c27fd17"),
(0x52F38, "7f020a6b6c040054"),
(0x52F98, "7f020a6b6c010054"),
(0x52FC0, "7f020a6bedeaff5453050011647a1f53"),
),
),
}
def start():
for name, patch in PATCHES.items():
target = Path(name).resolve(strict=True)
data = target.read_bytes()
checksum = hashlib.sha256(data).digest()
if checksum != patch.original_hash:
print(
f"Skipping {target}: unrecognised checksum {checksum.hex()}",
file=sys.stderr,
)
continue
patched = patch.apply_to(data)
source = RUNTIME / hashlib.sha256(os.fsencode(target)).hexdigest()
source.parent.mkdir(parents=True, exist_ok=True)
source.write_bytes(patched)
attributes = target.stat()
os.chown(source, attributes.st_uid, attributes.st_gid)
source.chmod(attributes.st_mode)
subprocess.run(
["mount", "-o", f"bind,ro,{MARKER}", str(source), str(target)],
check=True,
)
print(f"Patched {target}", file=sys.stderr)
def stop():
result = subprocess.run(
[
"findmnt",
"--mtab",
"--options",
MARKER,
"--json",
"--output",
"TARGET",
],
check=True,
capture_output=True,
text=True,
)
for target in reversed(
[
Path(row["target"])
for row in json.loads(result.stdout).get("filesystems", [])
]
):
subprocess.run(["umount", str(target)], check=True)
print(f"Unmounted {target}", file=sys.stderr)
def main():
parser = argparse.ArgumentParser(description=__doc__)
parser.add_argument("action", choices=("start", "stop"))
args = parser.parse_args()
if args.action == "start":
start()
else:
stop()
if __name__ == "__main__":
main()
|
