3 files changed, 63 insertions, 25 deletions
diff --git a/src/3rdparty/xcb/README b/src/3rdparty/xcb/README
index 362fa54bf8..a97d883867 100644
--- a/src/3rdparty/xcb/README
+++ b/src/3rdparty/xcb/README
@@ -20,3 +20,27 @@ The xcb-xinput files where modified to use system includes, see:
 src/3rdparty/xcb/include/xcb/fixup-xinput-h.patch
 src/3rdparty/xcb/libxcb/fixup-xinput-c.patch
 
+*****************************************************************
+
+Additionally, a forwards compatibility bug in libxcb xinput has been addressed
+by the following patch:
+
+src/3rdparty/xcb/libxcb/xinput-device-class-sizeof.patch
+
+The crux of the issue is that libxcb thinks that it knows about all device
+class types sent by the X server XInput extension. With the addition of
+touchpad gestures in XInput 2.4 and X server 21.1 this is no longer the case
+and libxcb fails horribly by thinking that the protocol was malformed.
+
+The X server currently has a workaround, but it would not address the following
+situation:
+
+ - there are multiple modules within the same X client (e.g. part of the application
+   uses Qt, another part talks to X server via another library)
+ - both of the modules talk to XI
+ - at least one module requests for XI 2.4 protocol support.
+
+The request for XI 2.4 disables the workaround on the X server and Qt side would
+crash horribly.
+
+For more details, see https://gitlab.freedesktop.org/xorg/lib/libxcb/-/merge_requests/20
diff --git a/src/3rdparty/xcb/libxcb/xinput-device-class-sizeof.patch b/src/3rdparty/xcb/libxcb/xinput-device-class-sizeof.patch
new file mode 100644
index 0000000000..2eacd7f3d2
--- /dev/null
+++ b/src/3rdparty/xcb/libxcb/xinput-device-class-sizeof.patch
@@ -0,0 +1,38 @@
+diff --git a/src/3rdparty/xcb/libxcb/xinput.c b/src/3rdparty/xcb/libxcb/xinput.c
+index d4e3c250bc..5113213a61 100644
+--- a/src/3rdparty/xcb/libxcb/xinput.c
++++ b/src/3rdparty/xcb/libxcb/xinput.c
+@@ -10535,32 +10535,8 @@ xcb_input_device_class_data_sizeof (const void  *_buffer,
+ int
+ xcb_input_device_class_sizeof (const void  *_buffer)
+ {
+-    char *xcb_tmp = (char *)_buffer;
+     const xcb_input_device_class_t *_aux = (xcb_input_device_class_t *)_buffer;
+-    unsigned int xcb_buffer_len = 0;
+-    unsigned int xcb_block_len = 0;
+-    unsigned int xcb_pad = 0;
+-    unsigned int xcb_align_to = 0;
+-
+-
+-    xcb_block_len += sizeof(xcb_input_device_class_t);
+-    xcb_tmp += xcb_block_len;
+-    xcb_buffer_len += xcb_block_len;
+-    xcb_block_len = 0;
+-    /* data */
+-    xcb_block_len += xcb_input_device_class_data_sizeof(xcb_tmp, _aux->type);
+-    xcb_tmp += xcb_block_len;
+-    xcb_align_to = ALIGNOF(char);
+-    /* insert padding */
+-    xcb_pad = -xcb_block_len & (xcb_align_to - 1);
+-    xcb_buffer_len += xcb_block_len + xcb_pad;
+-    if (0 != xcb_pad) {
+-        xcb_tmp += xcb_pad;
+-        xcb_pad = 0;
+-    }
+-    xcb_block_len = 0;
+-
+-    return xcb_buffer_len;
++    return (_aux->len * 4);
+ }
+ 
+ void *
diff --git a/src/3rdparty/xcb/libxcb/xinput.c b/src/3rdparty/xcb/libxcb/xinput.c
index d4e3c250bc..5113213a61 100644
--- a/src/3rdparty/xcb/libxcb/xinput.c
+++ b/src/3rdparty/xcb/libxcb/xinput.c
@@ -10535,32 +10535,8 @@ xcb_input_device_class_data_sizeof (const void  *_buffer,
 int
 xcb_input_device_class_sizeof (const void  *_buffer)
 {
-    char *xcb_tmp = (char *)_buffer;
     const xcb_input_device_class_t *_aux = (xcb_input_device_class_t *)_buffer;
-    unsigned int xcb_buffer_len = 0;
-    unsigned int xcb_block_len = 0;
-    unsigned int xcb_pad = 0;
-    unsigned int xcb_align_to = 0;
-
-
-    xcb_block_len += sizeof(xcb_input_device_class_t);
-    xcb_tmp += xcb_block_len;
-    xcb_buffer_len += xcb_block_len;
-    xcb_block_len = 0;
-    /* data */
-    xcb_block_len += xcb_input_device_class_data_sizeof(xcb_tmp, _aux->type);
-    xcb_tmp += xcb_block_len;
-    xcb_align_to = ALIGNOF(char);
-    /* insert padding */
-    xcb_pad = -xcb_block_len & (xcb_align_to - 1);
-    xcb_buffer_len += xcb_block_len + xcb_pad;
-    if (0 != xcb_pad) {
-        xcb_tmp += xcb_pad;
-        xcb_pad = 0;
-    }
-    xcb_block_len = 0;
-
-    return xcb_buffer_len;
+    return (_aux->len * 4);
 }
 
 void *