Left shift button crashing SDL Code Events in Android

SDL Development
1

I think I’m using SDL 2.0.10 for Android

if (event.type == SDL_KEYDOWN)
{
bKeysHeld[event.key.keysym.sym] = true;
}

It works fine with letters and numbers, but the shift key crashs it, also few other buttons, like enter.

anyone have any idea why it’s crashing?

2

event.key.keysym.sym is of the type SDL_Keycode which is essentially a signed 32-bit integer. I’m assuming that bKeysHeld is a fixed size array that doesn’t have the space to hold a billion+ entries (that would be very silly). The left shift key has the value SDLK_LSHIFT, which is done with a macro on the SDL_Scancode going by the name SDL_SCANCODE_LSHIFT (with a value of 225). The macro SDL_SCANCODE_TO_KEYCODE sets the second highest bit (highest non-sign bit) to 1 and ORs this with the scancode, producing the expression (1 << 30) | 225 which has the value 1073742049 or just over a billion. This means you’re trying to write to a location that is around 4GiB past the start of your array, resulting in a buffer overflow.

If you want similar semantics to what you’re currently doing, you could for instance use a hash map of booleans instead of an array, or a hash set of keysyms where you either add or remove entries as you come across key events.

Hope this helps.

3

Or you could just use the event.key.keysym.scancode field instead and make bKeysHeld have its size be SDL_NUM_SCANCODES. That would require the fewest changes to your code.

4

I don’t get it works fine for the smaller buttons, I found this.

" The value of event.key.keysym.sym is wrong for sdl.SDL_KEYDOWN/sdl.SDL_KEYUP events on ARM64/postmarketOS/sdl2-2.0.12-r1. For example, this is what I get for a t key: 1073742095, when it should be 116 according to SDL_keycode.h.

This is on an ARM64 device running postmarketOS (based on Alpine Linux) with sdl2-2.0.12-r1. It works fine on my Fedora 32 x64 machine with its SDL2 2.0.12-1.fc32, so I do wonder if this is a bug with PySDL2’s assumption of how the event struct is laid out on ARM64 platforms? At least that is my best guess as to what the issue could be.

Edit: also yes, that means all key input other than SDL_TEXTINPUT is currently unusable on that platform which is a bit of a shame"

5

I did this and it worked

 if (event.type == SDL_KEYDOWN)
    {
        //KeysHeld[event.key.keysym.sym] = true;
        if(event.key.keysym.sym == SDLK_LSHIFT)
            bLeftShift = true;
    }