Bug #880869: Some bug with tolua-5.2 garbage collecting Direction objects - Freeciv - HostedRedmine by Planio

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Bug #880869

closed

Some bug with tolua-5.2 garbage collecting Direction objects

Added by Alexandro Ignatiev over 2 years ago. Updated over 2 years ago.

Status:

Closed

Priority:

Normal

Assignee:

Marko Lindqvist

Category:

Scripting API

Sprint/Milestone:

2.6.2.1

Start date:

Due date:

% Done:

Estimated time:

Description

To reproduce, just type consequently in client Lua console, replace 154 on any visible unit id:

c = find.unit(nil,154)
d= c:facing()
c=nil
d=nil
collectgarbage()

If you collect only the unit, there is no failure, but the queer Direction object fails the client.
Backtrace shows calling NULL in such a stack:

(gdb) backtrace
#0  0x0000000000000000 in  ()
#1  0x0000555555696f57 in luaD_precall
    (L=L@entry=0x555555b310a8, func=0x555556d0c1b0, nresults=0) at ldo.c:434
...
#5  0x00005555556aa401 in class_gc_event (L=0x555555b310a8) at tolua_event.c:392
...
(gdb) print func
$1 = (StkId) 0x555556d0c1b0
(gdb) print *func
$2 = {value_ = {gc = 0x0, p = 0x0, b = 0, f = 0x0, i = 0, n = 0}, tt_ = 22}

Files

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no-segfault-Direction-gc.patch (10.1 KB) no-segfault-Direction-gc.patch		Alexandro Ignatiev, 2020-07-12 08:22 PM
no-segfault-Direction-gc2.patch (9.87 KB) no-segfault-Direction-gc2.patch		Alexandro Ignatiev, 2020-07-13 08:46 PM
no-segfault-Direction-gc3.patch (9.84 KB) no-segfault-Direction-gc3.patch		Alexandro Ignatiev, 2020-07-14 06:08 PM
no-segfault-Direction-gc4.patch (9.6 KB) no-segfault-Direction-gc4.patch	the working patch preventing segfaults from tolua gc	Alexandro Ignatiev, 2020-07-14 09:16 PM
0016-Scripting-Fix-segfaults-with-Direction-objects.patch (9.7 KB) 0016-Scripting-Fix-segfaults-with-Direction-objects.patch	master	Marko Lindqvist, 2020-08-02 02:09 PM

Related issues

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Updated by Marko Lindqvist over 2 years ago

Related to Bug #688119: Intermittent segfault invoking Lua direction functions added

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Updated by Alexandro Ignatiev over 2 years ago

File no-segfault-Direction-gc.patch no-segfault-Direction-gc.patch added

It's a tolua problem with returning user types in C projects: it does not supply any garbagecollector but tries to call it. I've made a patch that uses my own collector. It's still a question if we really need to put 4-bit enum into a dynamically allocated object but this patch ~~keeps current behaviour~~ produces objects as it's done now for valid directions and returns nil for invalid ones, but currently direction.next_ccw(direction.str2dir("somewhere")) just hangs the application and it's a bad idea to turn units into invalid directions, so I think nothing meaningful is harmed.

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Updated by Alexandro Ignatiev over 2 years ago

File no-segfault-Direction-gc2.patch no-segfault-Direction-gc2.patch added

Well, this is shooting a cannon at sparrows, also, still eats up memory. Let's remember this way for some better task like creating virtual units (or just fix a couple of lines in tolua code) and now put a more adequate solution with returning all directions from a static array.
EDIT: testing found abnormal jumping between "const Direction" and "Direction" classes, something wrong...

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Updated by Alexandro Ignatiev over 2 years ago

File no-segfault-Direction-gc3.patch no-segfault-Direction-gc3.patch added

All what was needed is just removing const's from tolua functions. This tolua version does not interest const function modifiers except giving different methods (needs clarification but you understand how const objects can be violated...) Now it does not segfault on gc.

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