[Mesa-dev] glxinfo proposed change

Jorge Ramirez Ortiz, HCL Europe Jorge.Ramirez-Ortiz at hcl.com
Mon Jan 7 22:39:01 PST 2013

>>> -----Original Message-----
>>> From: Ian Romanick [mailto:idr at freedesktop.org]
>>> Sent: Monday, January 07, 2013 7:48 PM
>>> To: Jorge Ramirez Ortiz, HCL Europe
>>> Cc: Dan Nicholson; mesa-dev at lists.freedesktop.org
>>> Subject: Re: [Mesa-dev] glxinfo proposed change
>>> On 01/07/2013 06:35 AM, Jorge Ramirez Ortiz, HCL Europe wrote:
>>>>> -----Original Message-----
>>>>> From: Dan Nicholson [mailto:dbn.lists at gmail.com]
>>>>> Sent: Monday, January 07, 2013 2:31 PM
>>>>> To: Jorge Ramirez Ortiz, HCL Europe
>>>>> Cc: mesa-dev at lists.freedesktop.org
>>>>> Subject: Re: [Mesa-dev] glxinfo proposed change
>>>>> On Mon, Jan 7, 2013 at 5:06 AM, Jorge Ramirez Ortiz,  HCL Europe
>>>>> <Jorge.Ramirez-Ortiz at hcl.com> wrote:
>>>>>> Hi all,
>>>>>> Does this patch make sense? glVersion can be NULL and not having the
>>>>> changes below could cause a SIGSEGV
>>>>>> [jramirez at calypso-2 mesa-demos.git (tmp *)]$ git diff
>>>>>> diff --git a/src/xdemos/glxinfo.c b/src/xdemos/glxinfo.c
>>>>>> index aa6430d..97b6539 100644
>>>>>> --- a/src/xdemos/glxinfo.c
>>>>>> +++ b/src/xdemos/glxinfo.c
>>>>>> @@ -639,7 +639,7 @@ print_screen_info(Display *dpy, int scrnum, Bool
>>>>> allowDirect, Bool limits, Bool
>>>>>>          printf("OpenGL renderer string: %s\n", glRenderer);
>>>>>>          printf("OpenGL version string: %s\n", glVersion);
>>>>>>    #ifdef GL_VERSION_2_0
>>>>>> -      if (glVersion[0] >= '2' && glVersion[1] == '.') {
>>>>>> +      if (glVersion && glVersion[0] >= '2' && glVersion[1] == '.') {
>>>>>>             char *v = (char *)
>>>>>>             printf("OpenGL shading language version string: %s\n", v);
>>>>>>          }
>>>>> Normally, this is a good idea. However, glVersion is already
>>>>> dereferenced in the printf on the previous line. So, any actual
>>>>> checking for NULL glVersion should at least come earlier in the
>>>>> function. On the other hand, returning NULL from
>>>>> glGetString(GL_VERSION) might be so rare that bothering to guard for
>>>>> it would be more effort than it's worth.
>>>> Bear in mind that printf of a null string wont SIGSEGV.
>>>> Only trying to access glVersion[] elements presents -and indeed is - a risk
>>> therefore a critical bug (for my usual standards that is).
>>> The critical bug is that glGetString is not allowed to return NULL.
>>> Your GL is horrifically broken in that case, and no application will
>>> work either.
>> You are absolutely wrong. NULL is a valid return value. Please read the code.
>I've been working on this project for almost twelve years, and I've been
>a voting member of the OpenGL Architecture Review Board for almost as
>long.  I'm quite familiar with the code.
>glGetString returns 0 only when an error is generated, and it is not
>allowed to generate an error for a valid enum, such as GL_VERSION, when
>there is a context.  Previous code in glxinfo has already made the
>context current and checked that it was successful.
>I wasn't interested in seeing this patch ever land, and after your rude,
>disrespectful attitude, I'm even less interested.

It wasn't my intention to came across rude and disrespectful and I apologize if it seemed that way to you.


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