Bug#1041211: libsdl-perl: FTBFS and autopkgtest failure with sdl12-compat, especially on 32-bit

[Simon McVittie]

Control: reassign -1 src:sdl12-compat 1.2.64-5
Control: affects -1 src:libsdl-perl
Control: forwarded -1 https://github.com/libsdl-org/sdl12-compat/issues/305

On Mon, 17 Jul 2023 at 10:35:14 +0100, Simon McVittie wrote:
> I can reproduce a use-after-free on amd64. The test doesn't crash on amd64
> for whatever reason, but it's visible when using valgrind, or when
> recompiling sdl12-compat and libsdl2 with -fsanitize=address.
> 
> I think this is probably the same root cause as the crash on 32-bit
> architectures, it's just less fatal on 64-bit for whatever reason.
> An easy reproducer is to run `perl ./t/core_video.t` from the libsdl-perl
> source tree: it is not necessary to recompile it.

I was able to reduce the Perl test to a small C reproducer, which I've
sent upstream to sdl12-compat (see URL above). As far as I can tell,
it's most likely to be a sdl12-compat bug, but I don't understand the
memory management for these surfaces well enough to fix it.

A brute-force workaround would be to intentionally leak every surface
object that was previously the video surface, by adding a flag that
would make SDL_FreeSurface ignore it, but I hope upstream will be able
to suggest something less bad than that.

    smcv