Hacker News Reader

Comment by smcameron | Hacker News Reader

SDL should probably use inotify() on linux so the kernel can let it know when /dev/input has changed rather than polling it.

View on HN

SDL has three methods for detecting input devices [1]: udev, inotify, and, as a fallback, enumerating /dev/input.

It seems like Papers, Please uses a statically linked version of SDL, without udev or inotify support compiled in.

1: https://github.com/libsdl-org/SDL/blob/d0de4c625ad26ef540166...

I've been wondering.. is it possible to write something to override the statically linked functions? In this case, most (if not all) functions have an SDL_ prefix. Would it be possible to LD_PRELOAD a library that loads a shared version of SDL and goes over all the function pointers to move them point them to a new location? Is there a tool for this?

Well if you know where to fork, you could use Intel Pin and divert the CFG, favorite tool for binary 'patching'.

Edit: though here if it's a problem of file enumeration and access, I'd probably just LD_PRELOAD something to bypass libc file access functions and return the same result than the first time, with no delay.

> I've been wondering.. is it possible to write something to override the statically linked functions?

SDL does have a built-in way to do that trick. A quick web search tells me it's called SDL_DYNAMIC_API.

cool, I never knew! Somehow the game I thought it would add a feature is still lacking it. For some reason rumble on my xbox joystick with Enter the Gungeon never worked. I thought it was because of an old SDL version, because experimentation showed that. But by using the SDL_DYNAMIC_API env and loading my system SDL the game still not added rumble to my joystick. Ohwell.

SDL_DYNAMIC_API is a relatively recent addition (IIRC 2014), so static SDL2 builds from before that won't work this way.

It looks like SDL's public symbols are all global in lime.ndll so LD_PRELOADing SDL should do what you want. Of course it is possible that lime.ndll was built with -fno-semantic-interposition or equivalent in which case the functions might be called directly without going through the dynamic linker or even (partially) inlined.

Static linking means the features of the Linux dynamic loader, like using the environment variable LD_PRELOAD to pre-load a dynamic library, are not going to have any effect.

Actually, I think the truly preferred path is to just monitor for udev events, which SDL supports but is presumably not enabled for Papers, Please for one reason or another.

Reply on news.ycombinator.com