Limit the number of frames in backtrace collection

[adambratschikaye]

Add Config::wasm_backtrace_max_frames option to limit the number of frames collected in backtraces and set the default at 20. This helps prevent expensive work from very deep call stacks.

Setting the value to 0 is the same as disabling backtraces and so this change deprecates Config::wasm_backtrace.

Addresses #5052

[fitzgen]

Thanks! A couple nitpicks inline below before we merge this.

[fitzgen]

Can we represent this as an Option<NonZeroUsize>? That will make use sites clearer, rather than checking for zero.

[fitzgen]

Minor nitpick, but I think the logic is a little more clear when collapsing the nested conditionals into a single match:

Suggested change

	if enable {
	if self.wasm_backtrace_max_frames == 0 {
	self.wasm_backtrace_max_frames = DEFAULT_WASM_BACKTRACE_MAX_FRAMES;
	}
	} else {
	self.wasm_backtrace_max_frames = 0;
	}
	match (enable, self.wasm_backtrace_max_frames) {
	(false, _) => self.wasm_backtrace_max_frames = None,
	// Wasm backtraces were disabled; enable them with the
	// default maximum number of frames to capture.
	(true, None) => self.wasm_backtrace_max_frames = {
	Some(NonZeroUsize::new(DEFAULT_WASM_BACKTRACE_MAX_FRAMES).unwrap());
	}
	// Wasm backtraces are already enabled; keep the existing
	// max-frames configuration.
	(true, Some(_)) => {}
	}

[fitzgen]

(Also, we could avoid the NonZeroUsize::new(...).unwrap() noise here by making the DEFAULT_WASM_BACKTRACE_MAX_FRAMES constant be a NonZeroUsize already.)

[github-actions]

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[venkkatesh-sekar]

Suggested change

	let mut wasm_trace = Vec::<FrameInfo>::with_capacity(runtime_trace.frames().len());
	let mut wasm_trace = Vec::<FrameInfo>::with_capacity(max_frames);

[adambratschikaye]

Regarding the note on fuzzing - I guess we don't need to do anything because fuzzing always used the default of enabling backtraces and that isn't changing.

[fitzgen]

Thanks!