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

[James Jones]

On 2/4/11 3:26 PM, "Benoit Jacob" <bjacob at mozilla.com> 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. But I
> don't mind having it exposed elsewhere than in GLX if that makes more sense :)
> 
> 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. Zhenyao Mo, in CC, is working on
> similar features in Chromium.
> 
> Cheers,
> Benoit

Chiming in because it's in my interest to not get dragged into supporting
unnecessary extensions.

Suppose an extension were added that allowed
glXQueryServerString()/glXQueryClientString() to return the information you
request some how.  You'll still need to check for the extension string for
that new GLX extension before requesting those new strings.  And then what
will you do if it isn't present?  If you try to press on and create a
context anyway, you'll still get crashes with whatever buggy driver release
the user reported this crash with, because it won't have this new extension.
If you treat the absence of the extension as a failure and don't create a
context, you've excluded all currently shipping OpenGL implementations from
your list of supported configs.

The only nearly robust way to solve this issue is Brian Paul's suggestion.
If spawning a separate process to run the test is too expensive, install a
signal/exception handler around your GLX initialization and tests.  That way
you can detect crashes AND actually use the resulting context if it passes
your tests.

Thanks,
-James

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