Restore the wasm stack pointer after exec() and ffprobe() - #943
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Restore the wasm stack pointer after exec() and ffprobe()#943Mrmaxmeier wants to merge 1 commit into
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ffmpeg and ffprobe finish by calling exit(), which Emscripten implements
by throwing. exec() and ffprobe() swallow that exception, but nothing
unwinds the WebAssembly stack, so the stack pointer stays wherever the C
code left it. Every call therefore leaks part of the stack.
With the 64 KB default stack of the current release, exec("-h") leaks
768 B a call and the module traps with "memory access out of bounds" in
<100 calls.
This saves the stack pointer before entering wasm and restore it in a
finally block, which is what Emscripten does in its own invoke_* helpers
for exactly this situation.
stackSave is exported so the tests can assert the stack pointer is where
it started after a successful command, a failing command, and ffprobe.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Hi,
I ran into memory corruption / WASM stack overflows in a setting where
ffmpeg.wasmis called repeatedly in one session (Ente Photos web import).ffmpeg and ffprobe finish by calling exit(), which Emscripten implements by throwing. exec() and ffprobe() swallow that exception, but nothing unwinds the WebAssembly stack, so the stack pointer stays wherever the C code left it.
With the 64 KB default stack of the current release (since bumped to 5 MB in b409e36), exec("-h") leaks 768 B a call and the module traps with "memory access out of bounds" in <100 calls.
This saves the stack pointer before entering wasm and restore it in a finally block, which is what Emscripten does in its own invoke_* helpers for exactly this situation.
This might fix #563.