[Mesa-dev] glXMakeCurrent crashes (was: Re: How to obtain OpenGL implementation/driver information?)

[Michel Dänzer]

On Fre, 2011-02-04 at 15:26 -0800, Benoit Jacob wrote: 
> 
> ----- Original Message -----
> > On Fre, 2011-02-04 at 14:21 -0800, Benoit Jacob wrote:
> > >
> > > ----- Original Message -----
> > > > Benoit Jacob wrote:
> > > > > ----- Original Message -----
> > > > >> On Thu, Feb 3, 2011 at 4:37 PM, Benoit Jacob
> > > > >> <bjacob at mozilla.com>
> > > > >> wrote:
> > > > >>> I'm trying to see how to implement selective
> > > > >>> whitelisting/blacklisting of driver versions on X11 (my use
> > > > >>> case
> > > > >>> is
> > > > >>> to whitelist drivers for Firefox). The naive approach consists
> > > > >>> in
> > > > >>> creating an OpenGL context and calling glGetString(), however
> > > > >>> that
> > > > >>> is not optimal for me, for these reasons:
> > > > >>>  * This has been enough to trigger crashes in the past.
> > > > >>>
> > > > >>> Ideally I want to be able to know the driver name, driver
> > > > >>> version,
> > > > >>> Mesa version, and any other thing that you think may be
> > > > >>> relevant.
> > > > >>> I
> > > > >>> need to get that information in a fast and safe way.
> > > > >>>
> > > > >> There is no other way than glGetString if you ever experienced
> > > > >> crash
> > > > >> with it, it would be because you are doing something terribly
> > > > >> wrong
> > > > >> like using it without current context.
> > > > >
> > > > > It's not glGetString that's crashing, it's glXMakeCurrent.
> > > > >
> > > > > I forwarded a bug report from a user, though he's not been able
> > > > > to
> > > > > reproduce since:
> > > > >
> > > > >   https://bugs.freedesktop.org/show_bug.cgi?id=32238
> > > > >
> > > > > A search in Mesa's bugzilla confirms that I'm not alone:
> > > > >
> > > > >   https://bugs.freedesktop.org/show_bug.cgi?id=30557
> > > >
> > > > This latter bug looks like an i915 driver bug, as opposed to a
> > > > MakeCurrent bug.
> > > >
> > > > > Since the glGetString way will at best be slow, especially if we
> > > > > have
> > > > > to XSync and check for errors, could you consider exposing this
> > > > > information as new glXGetServerString / glXGetClientString
> > > > > strings?
> > > >
> > > > ? I don't understand the logic here.
> > > >
> > > > You're hitting a bug in glXCreateContext or MakeCurrent or
> > > > something
> > > > like that. So you'd like to add an entire new way to query the
> > > > same
> > > > information a driver already provides, just to provide an
> > > > alternate
> > > > path
> > > > that hopefully doesn't exhibit the bug?
> > > >
> > > > Just fix the bug! There's no reason for glX extensions to add new
> > > > functions here.
> > >
> > > My point is just that bugs exist.
> > >
> > > Since bugs exist, I am trying to implement a driver blacklist.
> > >
> > > My problem is that with GLX it's tricky because I can't get answer
> > > to
> > > the question "should I avoid creating GL contexts on this driver"
> > > without creating a GL context.
> > >
> > > I proposed to allow handling this in glXQuery(Server|Client)String
> > > because these functions are known to be non-crashy.
> > 
> > What you're asking for is not possible, because the information you
> > need
> > depends on the context which is current. No shortcuts here I'm
> > afraid. :)
> 
> We're doing driver blacklists on all platforms, and it tends to be
> quite easy on other platforms. For example, on Windows, we just read
> all the driver information from the registry. Couldn't X drivers
> likewise have some metadata stored on disk, that could be queried via
> some new API? I proposed GLX because glXQueryServerString already
> knows about at least the driver vendor.

Actually no, glXQueryServerString merely tells you context-independent
information about the server portion of the GLX implementation being
used (and correspondingly glXGetClientString for the client side). Which
renderer is actually used is not known before the context is current.


> Please take this request seriously: driver blacklists are useful, not
> limited to Firefox, and certainly not limited to X11. As I say, we
> blacklist drivers on all platforms, and we'd never have been able to
> make Firefox 4 releasable without blacklisting many Windows drivers. 

I can see the value of blacklists or whitelists for proprietary drivers,
but with free drivers it seems more useful to spend effort on getting
any bugs fixed rather than on guessing whether the drivers you happen to
be running on are affected by any of them (which due to things like
backports of bug fixes is probably not reliably possible in general even
based on context-specific information).


-- 
Earthling Michel Dänzer           |                http://www.vmware.com
Libre software enthusiast         |          Debian, X and DRI developer