Internal error from multi-heap allocation

[peterbarker]

Bug report

Issue details

An ArduPilot partner running a custom frame configured via scripting is getting internal errors and failure-to-allocate errors.

2025-03-18 12:29:53 PM : PreArm: Internal errors 0x100000 l:58 flow_of_ctrl

That's from this:

    if (heapp->current_heap_usage != 0) {
        // lua should guarantee that there is no memory still
        // allocated when we destroy the heap. Throw an error in SITL
        // if this proves not to be true
        INTERNAL_ERROR(AP_InternalError::error_t::flow_of_control);
    }

Version
stable, "latest" and 4.6.0-beta4

Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[x] Plane
[ ] Rover
[ ] Submarine

Airframe type
scripted

Hardware type
SITL

Logs
Ask partner

[tpwrules]

We weren't sure if there was a perhaps-error-case where the "guarantee" won't hold. I don't think it matters on a real vehicle but it will cause a memory leak in SITL. It might also cause a problem with reallocation which would indeed be bad.

Can the script be shared so I can reproduce locally? Why is scripting restarting before they arm?

[tpwrules]

I am able to replicate this using mission planner SITL on real Windows by restarting scripting enough times (sometimes zero times). In my case the internal error is always paired with this error:

ardupilot/libraries/AP_Scripting/lua_scripts.cpp

Lines 493 to 497 in d5098c6

	lua_State *L = lua_state;
	if (L == nullptr) {
	GCS_SEND_TEXT(MAV_SEVERITY_CRITICAL, "Lua: Couldn't allocate a lua state");
	return;
	}

which AFAICT only happens if Lua can't allocate memory to start.

This suggests the heap is not being initialized properly (current_heap_usage doesn't start at zero) which also explains why it's failing to be consistent on shutdown. We sort of assume it's initialized based on our various hacks to make malloc/new zero memory blocks on allocation, but that keeps breaking on various platforms and in various ways and I think it has again here. I do not personally plan to fix it again.

[tpwrules]

This needs attention from @tridge , users are hitting it.