PlayoutCallback::onAudioReady crashed with SIGSEGV(SEGV_ACCERR) on the
first AAudio callback because g_rings was a `const WzpOboeRings*` pointing
at the caller's stack frame. wzp_native_audio_start() constructs the
rings struct as a stack local in Rust, passes &rings to wzp_oboe_start
(which stored the raw pointer), and returns — at which point the stack
frame unwinds and g_rings becomes a dangling reference. The first audio
callback then read from freed memory and died.
- g_rings is now a static WzpOboeRings value (was `const WzpOboeRings*`).
The raw int16 buffer + atomic index pointers inside the struct still
point into the Rust-owned AudioBackend singleton, which is leaked for
the lifetime of the process, so deep-copying the struct by value is
safe and keeps the inner pointers valid forever.
- g_rings_valid atomic bool gates the audio-callback reads: set to true
after the value copy in wzp_oboe_start, cleared in wzp_oboe_stop BEFORE
the streams are torn down so any in-flight callback sees "no backend"
and returns Stop instead of racing on g_rings.
- All g_rings->x accesses in the capture + playout callbacks switched to
g_rings.x (member-of-value).
Reproduced on Pixel 6 / Android 15 with build 0105b0f:
F libc: Fatal signal 11 (SIGSEGV), code 2 (SEGV_ACCERR),
fault addr 0x71aa717eb0 in tid 11822 (AudioTrack)
#00 PlayoutCallback::onAudioReady(oboe::AudioStream*, void*, int)+120
#01 oboe::AudioStream::fireDataCallback(void*, int)+136
...
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