Squirrel Level.edit bug

[brmbrmcar]

Running Level.edit(true); then Level.edit(false); closes the game.

[Karkus476]

The Scripting Reference is here, but it's not clear what this does. What are you trying to do?

[brmbrmcar]

Allow the player to look around.

[Hypernoot]

I can't reproduce it.

[tobbi]

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000004
SQVM::Execute (this=0x10235c660, closure=@0x104082600, nargs=1, stackbase=1, outres=@0x7fff5fbfbb68, raiseerror=1, et=ET_CALL) at supertux/external/squirrel/squirrel/sqvm.cpp:710
710 switch(i.op)
(gdb) bt
0 SQVM::Execute (this=0x10235c660, closure=@0x104082600, nargs=1, stackbase=1, outres=@0x7fff5fbfbb68, raiseerror=1, et=ET_CALL) at supertux/external/squirrel/squirrel/sqvm.cpp:710
1 0x0000000100576f77 in SQVM::Call (this=0x10235c660, closure=@0x104082600, nparams=1, stackbase=1, outres=@0x7fff5fbfbb68, raiseerror=1) at supertux/external/squirrel/squirrel/sqvm.cpp:1545
2 0x0000000100544419 in sq_call (v=0x10235c660, params=1, retval=0, raiseerror=1) at supertux/external/squirrel/squirrel/sqapi.cpp:1155
3 0x000000010022e896 in scripting::compile_and_run (vm=0x10235c660, in=@0x7fff5fbfc910, sourcename=@0x7fff5fbfbdb0) at supertux/src/scripting/squirrel_util.cpp:237
4 0x0000000100451517 in Sector::run_script ()
5 0x00000001004b9c6f in Switch::update (this=0x1020b0538) at supertux/src/trigger/switch.cpp:87
6 0x0000000100454d0d in Sector::update ()
7 0x00000001002c3593 in GameSession::update (this=0x102710d70, elapsed_time=0.015625) at supertux/src/supertux/game_session.cpp:524
8 0x0000000100446a36 in ScreenManager::update_gamelogic (this=0x7fff5fbfd998, elapsed_time=0.015625) at supertux/src/supertux/screen_manager.cpp:219
9 0x00000001004486fe in ScreenManager::run (this=0x7fff5fbfd998, context=@0x7fff5fbfdcb8) at supertux/src/supertux/screen_manager.cpp:416
10 0x00000001002f3047 in Main::launch_game (this=0x7fff5fbffae8) at supertux/src/supertux/main.cpp:448
11 0x00000001002f3b37 in Main::run (this=0x7fff5fbffae8, argc=2, argv=0x7fff5fbffb28) at supertux/src/supertux/main.cpp:504
12 0x0000000100005059 in main (argc=2, argv=0x7fff5fbffb28) at supertux/src/main.cpp:23

[tobbi]

bug.stl.txt
(Only press one switch now).

[christ2go]

Can reproduce this from the switch, but not when running the same commands through the command line.

[brmbrmcar]

No, that doesn't result in anything unusual.

[christ2go]

My initial assesement was wrong, ... if you seperate the two commands into two switches, the execution of the command Level.edit(false) from the script block causes the game to crash. Level.edit(false) in the standard configuration only causes harm if they level is in editing mode, else nothing is done, nevertheless even if you remove this constraint calling the method anytime causes the same error.

[christ2go]

I just fixed this bug, the error was, that when edit mode is left, a new level instance is created, and when the squirrel vm calls the closure the level is restarted, and the old level object is destroyed, thus the reference the vm has to the closure function is invalid, possibly when squirrel tries to clean up or something, it tries to access a destroyed object. The easy fix is/would be to have a reference to the level created before the now played level in the GameSession class, then everything works as exspected.
But this does show a fundamental rule about squirrel functions (which mybe should be included in the scripting guide): The closure function which is called must exist until the script is finished / native methods called by squirrel mustn't destroy the object which holds the closure.

Should I open a pr with this fix?

[tobbi]

Yes, please do open a PR, and we can take a look at it.