It now seems to me that the issue is with MIT-SHM, that the code to detect whether MIT-SHM is working (so whether to enable) is "broken". Using the workaround below, fudging MIT-SHM to report as not present:
cc -shared -o XlibNoSHM.so XlibNoSHM.c LD_PRELOAD='libdl.so ./XlibNoSHM.so' chromium solves the issue for me. (That code is "ancient", with comments about some old Firefox; the Firefox issue was fixed some time ago.) Cheers, Paul -- Paul Szabo p...@maths.usyd.edu.au http://www.maths.usyd.edu.au/u/psz/ School of Mathematics and Statistics University of Sydney Australia I support NTEU members taking a stand for workplace rights in the face of poorly-run change management. Visit www.nteu.org.au/sydney to learn more.
/* * Firefox47 and above has a "bug": * https://bugzilla.mozilla.org/show_bug.cgi?id=1271100 * Firefox attempts to use the X (X11, X-windows) extension MIT-SHM. * It is "known" that MIT-SHM can only work on "local" displays. However: * - some X servers report supporting MIT-SHM even on remote (e.g. * TCP-connected) displays. (Maybe "right" so not a bug: the client * might have access to the X server machine.) * - the ssh "port forwarding" feature makes both the X server and client * appear to be "local" (somewhat: using TCP localhost, not Unix domain * sockets); and ssh makes no attempt to intercept or disable MIT-SHM. * To work around this confusion, when we know MIT-SHM should not be used, * (in the client application) we fudge the returns of the * XQueryExtension * XListExtensions * XShmQueryExtension * XShmQueryVersion * to "hide" the MIT-SHM extension. * (Firefox48 only uses XQueryExtension, others for future robustness.) * * Firefox already has code to detect when MIT-SHM is not working, but that * does not seem reliable enough. Maybe in future (from FF50 or 51) it will * use XCB instead of Xlib and then its detection will work better; if not, * a similar workaround will be needed. * * May need to explicitly mention /usr/lib/libdl.so in LD_PRELOAD * (or could or should it be /lib/libdl-2.11.3.so ?), otherwise ...? * * Compile and build library: cc -shared -o XlibNoSHM.so XlibNoSHM.c * to be used with * LD_PRELOAD='libdl.so ./XlibNoSHM.so' firefox */ #include <stdio.h> #include <string.h> #include <X11/Xlib.h> #include <dlfcn.h> #define LIBXLIB "libXext.so" Bool XQueryExtension(Display* dpl, _Xconst char* name, int* major, int* event, int* error) { static Bool (*original_XQueryExtension)(Display*, _Xconst char*, int*, int*, int*) = NULL; /* printf("Got XQueryExtension %s\n",name); */ if (!strcmp(name,"MIT-SHM")) { /* printf("Returning False for XQueryExtension %s\n",name); */ *major = 0; return False; } if (!original_XQueryExtension) { void *handle = dlopen(LIBXLIB, RTLD_LAZY); if (!handle) return False; original_XQueryExtension = dlsym(handle, "XQueryExtension"); if (!original_XQueryExtension) return False; } /* printf("Doing original_XQueryExtension ...\n"); */ return original_XQueryExtension(dpl, name, major, event, error); } char** XListExtensions(Display* dpl, int* nexts) { static char** (*original_XListExtensions)(Display*, int*) = NULL; char** extNames; int i; /* printf("Got XListExtensions\n"); */ if (!original_XListExtensions) { *nexts = 0; void *handle = dlopen(LIBXLIB, RTLD_LAZY); if (!handle) return NULL; original_XListExtensions = dlsym(handle, "XListExtensions"); if (!original_XListExtensions) return NULL; } /* printf("Doing original_XListExtensions ...\n"); */ extNames = original_XListExtensions(dpl, nexts); if (extNames && *nexts > 0) { for (i = 0; i < *nexts; ++i) { if (extNames[i] && !strcmp(extNames[i],"MIT-SHM")) { /* printf("Replacing MIT-SHM by No-... in XListExtensions output\n"); */ (void)strncpy(extNames[i],"No-",3); } } } return extNames; } Bool XShmQueryExtension(Display* display) { /* printf("Returning False for XShmQueryExtension\n",); */ return False; } Bool XShmQueryVersion(Display *display, int *major, int *minor, Bool *pixmaps) { /* printf("Returning False for XShmQueryVersion\n",); */ return False; }
