a18e34417b
The previous implementation of the wl_container_of macro was dereferencing the sample pointer in order to get an address of the member to calculate the offset. Ideally this shouldn't cause any problems because the dereference doesn't actually cause the address to be read from so it shouldn't matter if the pointer is uninitialised. However this is probably technically invalid and could cause undefined behavior. Clang appears to take advantage of this undefined behavior and doesn't bother doing the subtraction. It also gives a warning when it does this. The documentation for wl_container_of implies that it should only be given an initialised pointer and if that is done then there is no problem with clang. However this is quite easy to forget and doesn't cause any problems or warnings with gcc so it's quite easy to accidentally break clang. To fix the problem this changes the macro to use pointer - offsetof(__typeof__(sample), member) so that it doesn't need to deref the sample pointer. This does however require that the __typeof__ operator is supported by the compiler. In practice we probably only care about gcc and clang and both of these happily support the operator. The previous implementation was also using __typeof__ but it had a fallback path avoiding it when the operator isn't available. The fallback effectively has undefined behaviour and it is targetting unknown compilers so it is probably not a good idea to leave it in. Instead, this patch just removes it. If someone finds a compiler that doesn't have __typeof__ but does work with the old implementation then maybe they could add it back in as a special case. This patch removes the initialisation anywhere where the sample pointer was being unitialised before using wl_container_of. The documentation for the macro has also been updated to specify that this is OK. |
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| cursor | ||
| doc | ||
| m4 | ||
| protocol | ||
| spec | ||
| src | ||
| tests | ||
| .gitignore | ||
| autogen.sh | ||
| configure.ac | ||
| COPYING | ||
| Makefile.am | ||
| README | ||
| TODO | ||
| wayland-scanner.m4 | ||
| wayland-scanner.mk | ||
What is Wayland
Wayland is a project to define a protocol for a compositor to talk to
its clients as well as a library implementation of the protocol. The
compositor can be a standalone display server running on Linux kernel
modesetting and evdev input devices, an X application, or a wayland
client itself. The clients can be traditional applications, X servers
(rootless or fullscreen) or other display servers.
The wayland protocol is essentially only about input handling and
buffer management. The compositor receives input events and forwards
them to the relevant client. The clients creates buffers and renders
into them and notifies the compositor when it needs to redraw. The
protocol also handles drag and drop, selections, window management and
other interactions that must go through the compositor. However, the
protocol does not handle rendering, which is one of the features that
makes wayland so simple. All clients are expected to handle rendering
themselves, typically through cairo or OpenGL.
The weston compositor is a reference implementation of a wayland
compositor and the weston repository also includes a few example
clients.
Building the wayland libraries is fairly simple, aside from libffi,
they don't have many dependencies:
$ git clone git://anongit.freedesktop.org/wayland/wayland
$ cd wayland
$ ./autogen.sh --prefix=PREFIX
$ make
$ make install
where PREFIX is where you want to install the libraries. See
http://wayland.freedesktop.org for more complete build instructions
for wayland, weston, xwayland and various toolkits.