Package: libsdl2-2.0-0
Version: 2.24.2+dfsg-1
Severity: normal
X-Debbugs-Cc: msl0000023...@gmail.com
Hello.
When trying to run some simple SDL2-based programs over a remote X11 display
(for example SSH X11 forwarding), this version of SDL2 incorrectly enables
MIT-SHM extension, which isn't possible on a remote X11 display.
Running the following test program over a remote display would producing the
error:
$ cat hello-sdl.c
#include <SDL.h>
#include <stdio.h>
int main() {
if(SDL_Init(SDL_INIT_VIDEO) < 0) {
fprintf(stderr, "SDL_Init: %s\n", SDL_GetError());
return 1;
}
SDL_Window *window = SDL_CreateWindow("Hello world",
SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 240, 240, 0);
if(!window) {
fprintf(stderr, "SDL_CreateWindow: %s\n", SDL_GetError());
return 1;
}
SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, 0);
if(!renderer) {
fprintf(stderr, "SDL_CreateRenderer: %s\n", SDL_GetError());
return 1;
}
SDL_RenderPresent(renderer);
SDL_Event event;
while(SDL_WaitEvent(&event)) {
if(event.type == SDL_QUIT) {
SDL_Quit();
return 0;
}
}
fprintf(stderr, "SDL_WaitEvent: %s\n", SDL_GetError());
return 1;
}
$ gcc -Wall -O1 -I /usr/include/SDL2 hello-sdl.c -o hello-sdl -l SDL2
$ echo $DISPLAY
localhost:11.0
$ ./hello-sdl
X Error of failed request: BadShmSeg (invalid shared segment parameter)
Major opcode of failed request: 130 (MIT-SHM)
Minor opcode of failed request: 3 (X_ShmPutImage)
Segment id in failed request: 0x460000b
Serial number of failed request: 232
Current serial number in output stream: 233
This issue didn't exist in previous versions of SDL2; I have tested
libsdl2-2.0-0 versions 2.0.5+dfsg1-2+deb9u2 and 2.0.9+dfsg1-1 with SSH X11
forwarding, and they are all working fine.
The root cause I think was code in src/video/x11/SDL_x11framebuffer.c uses
XShmQueryExtension(3) to detect whether this extension is available, however
the remote X11 server would simply report that it is available without aware
that it couldn't be used remotely. I think it would be very helpful if SDL
can also check an environment variable for an explicit disablement of this
extension, such as SDL_VIDEO_X11_NO_SHM=1, in case it failed to detect such
automatically. I will submit a patch for this feature later.\
-- System Information:
Debian Release: bookworm/sid
APT prefers unstable
APT policy: (500, 'unstable')
merged-usr: no
Architecture: ppc64
Foreign Architectures: powerpc
Kernel: Linux 4.1.42-rivoreo-powerpc64-largepage (SMP w/4 CPU threads)
Kernel taint flags: TAINT_DIE
Locale: LANG=zh_TW.UTF-8, LC_CTYPE=zh_TW.UTF-8 (charmap=UTF-8),
LANGUAGE=zh_TW:zh_CN:zh:en_GB:en
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages libsdl2-2.0-0 depends on:
ii libasound2 1.2.7.2-1
ii libc6 2.36-4
ii libdecor-0-0 0.1.1-1
ii libdrm2 2.4.114-1
ii libgbm1 22.2.3-1
ii libpulse0 16.1+dfsg1-2+b1
ii libsamplerate0 0.2.2-2
ii libwayland-client0 1.21.0-1
ii libwayland-cursor0 1.21.0-1
ii libwayland-egl1 1.21.0-1
ii libx11-6 2:1.8.1-2
ii libxcursor1 1:1.2.1-1
ii libxext6 2:1.3.4-1+b1
ii libxfixes3 1:6.0.0-2
ii libxi6 2:1.8-1+b1
ii libxkbcommon0 1.4.1-1
ii libxrandr2 2:1.5.2-2+b1
ii libxss1 1:1.2.3-1
libsdl2-2.0-0 recommends no packages.
Versions of packages libsdl2-2.0-0 suggests:
pn xdg-utils <none>
-- no debconf information
