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Fix Android startup crash: move TMPDIR off FUSE so Realm can mkfifo() #233

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Merged
winnerspiros merged 1 commit into from
Apr 22, 2026
Merged

Fix Android startup crash: move TMPDIR off FUSE so Realm can mkfifo() #233

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86 changes: 0 additions & 86 deletions build_test/CMakeCache.txt
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1 change: 0 additions & 1 deletion build_test/CMakeFiles/cmake.check_cache
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8,959 changes: 0 additions & 8,959 deletions build_test/native_crash.log
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21 changes: 15 additions & 6 deletions osu.Android/Native/crash_handler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -180,10 +180,17 @@ static void logcatWrite(const char* msg) {
// To enable the perfmap output (step 1) for a build:
// - Add an `AndroidEnvironment` text file to the project containing:
// MONO_ENV_OPTIONS=--jitmap
// TMPDIR=/storage/emulated/0/Android/data/<pkg>/files
// so Mono writes the perfmap into the same dir as `native_crash.log`.
// `crash_handler.cpp` searches that dir, plus `/tmp` and `/data/local/tmp`,
// plus the directory containing `g_logPath`.
// TMPDIR=/data/user/0/<pkg>/cache
// TMPDIR MUST point at the app's internal storage (not the external
// /storage/emulated/... path): Realm calls mkfifo() under TMPDIR for its
// cross-process notifier, and FUSE-backed external storage rejects
// mkfifo() with EACCES, which crashes Realm.GetInstance() at startup.
// Internal storage (ext4/f2fs) supports FIFOs. The crash handler then
// reads `getenv("TMPDIR")` at signal time to locate the perfmap and
// emits the symbolicated frames into native_crash.log (which lives in
// the external files dir and IS user-retrievable).
// `crash_handler.cpp` also searches `/tmp`, `/data/local/tmp`, and the
// directory containing `g_logPath` as fallbacks.
//
// Async-signal safety:
// - All file I/O uses open/read/close (signal-safe).
Expand Down Expand Up @@ -255,8 +262,10 @@ static bool ensurePerfmapLoaded() {
nameBuf[np] = '\0';

// Candidate directories, in priority order. The dir containing g_logPath
// is checked first so a build that sets `TMPDIR=<external-files-dir>`
// (the recommended config) finds its perfmap immediately.
// (external files dir) is checked first as a historical fallback, but
// current builds set TMPDIR to the app's internal cache dir (FUSE-backed
// external storage cannot host the FIFOs Realm needs — see mono.env), so
// the perfmap normally lives at $TMPDIR/perf-<pid>.map.
Comment on lines 264 to +268

Copilot AI Apr 22, 2026

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With TMPDIR now recommended to point to internal cache, ensurePerfmapLoaded() will usually fail the first lookup attempt in the external-files log directory before trying $TMPDIR. Since this runs in the crash handler, consider reordering the candidate directories to check getenv("TMPDIR") first (and only fall back to the log dir), to reduce crash-time syscalls and simplify the “priority order” comment.

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const char* tmpEnv = getenv("TMPDIR");
char logDir[kMaxLogPathLen] = {};
if (g_logPath[0] != '\0') {
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29 changes: 22 additions & 7 deletions osu.Android/mono.env
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Expand Up @@ -14,11 +14,26 @@
# crash backtraces. Has negligible runtime overhead (a single fprintf per
# JIT compile, which already happens infrequently after warm-up).
#
# TMPDIR=/storage/emulated/0/Android/data/sh.ppy.osulazer/files
# Redirects Mono's perfmap output into the same external-files directory
# that we already write native_crash.log to. This is the *only* path that
# is (a) writable by the app, (b) readable post-mortem by the user via
# the Files app on an unrooted device, and (c) survives app uninstall on
# most devices' "external files" semantics.
# TMPDIR=/data/user/0/sh.ppy.osulazer/cache
# Redirects Mono's temp-file output (and, transitively, anything that goes
# through .NET's Path.GetTempPath()) into the app's *internal* cache dir.
#
# IMPORTANT: this MUST point at internal storage, not at the external
# /storage/emulated/... path. External storage on modern Android is a
# FUSE/sdcardfs mount, and the Linux kernel disallows mkfifo() on FUSE
# mounts (returns EACCES/13). RealmAccess.getConfiguration() sets
# FallbackPipePath = Path.GetTempPath() + "/lazer", and Realm calls
# mkfifo() there to create its cross-process notifier (.cv / .note files);
# pointing TMPDIR at external storage causes Realm.GetInstance() to throw
# "Failed to create fifo … Permission denied" on every startup, before the
# managed file logger is up. An internal path (ext4/f2fs-backed) supports
# FIFOs and is also writable by the app without runtime permissions.
#
# Side-effect: perf-<pid>.map is now in internal cache and is not directly
# retrievable by the user on an unrooted device. That's fine — it is only
# consumed by our in-process native crash handler at crash time (which
# reads getenv("TMPDIR") to find it), and the symbolicated output it
# produces is written into native_crash.log in the external files dir,
# which IS user-retrievable.
MONO_ENV_OPTIONS=--jitmap
TMPDIR=/storage/emulated/0/Android/data/sh.ppy.osulazer/files
TMPDIR=/data/user/0/sh.ppy.osulazer/cache
7 changes: 4 additions & 3 deletions osu.Android/osu.Android.csproj
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Expand Up @@ -22,9 +22,10 @@
</ItemGroup>
<!-- Mono runtime environment variables baked into the APK. Enables Mono's
jitmap output (read by Native/crash_handler.cpp's resolveViaPerfmap()
to symbolicate JIT frames in native_crash.log) and redirects TMPDIR so
the perfmap lands in the app's external-files dir (same place as the
crash log). See mono.env for details. -->
to symbolicate JIT frames in native_crash.log) and redirects TMPDIR
to the app's internal cache dir. TMPDIR must NOT point at external
(FUSE-backed) storage — that breaks Realm's mkfifo() notifier.
See mono.env for the full rationale. -->
<ItemGroup>
<AndroidEnvironment Include="mono.env" />
</ItemGroup>
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