[Mesa-dev] [PATCH] egl_dri2: check if driver_name is NULL before releasing it

[Erik Faye-Lund]

On Tue, 2018-10-30 at 18:28 +0800, Zhaowei YUan wrote:
> I don't think it's fine, usually, freeing an NULL pointer will cause 
> unexpected errors. It's better to check this for the robustness.
> 

>From http://pubs.opengroup.org/onlinepubs/009695399/functions/free.html
:

"If ptr is a null pointer, no action shall occur."

So, it should be fine. If your system free does something when passed a
null-pointer, it sounds like there's a problem with your system. This
assumption is made all over the place, not just in Mesa.

> On 10/30/18 3:17 PM, Tapani Pälli wrote:
> > On 10/30/18 8:26 AM, Zhaowei Yuan wrote:
> > > Pointer dri2_dpy->driver_name is probably NULL when calling
> > > dri2_display_destory, check this before releasing it.
> > 
> > It's fine for it to be NULL though and it looks like all the
> > drivers set 
> > it correctly, there is no need for such check. Does this change
> > fix 
> > something for you, what was the motivation for this change?
> > 
> > (same applies for the device_name patch)
> > 
> > > Signed-off-by: Zhaowei Yuan <zhaowei.yuan at samsung.com>
> > > ---
> > >   src/egl/drivers/dri2/egl_dri2.c | 3 ++-
> > >   1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/src/egl/drivers/dri2/egl_dri2.c 
> > > b/src/egl/drivers/dri2/egl_dri2.c
> > > index c5fa935..54cc334 100644
> > > --- a/src/egl/drivers/dri2/egl_dri2.c
> > > +++ b/src/egl/drivers/dri2/egl_dri2.c
> > > @@ -967,7 +967,8 @@ dri2_display_destroy(_EGLDisplay *disp)
> > >         close(dri2_dpy->fd);
> > >      if (dri2_dpy->driver)
> > >         dlclose(dri2_dpy->driver);
> > > -   free(dri2_dpy->driver_name);
> > > +   if (dri2_dpy->driver_name)
> > > +      free(dri2_dpy->driver_name);
> > >   #ifdef HAVE_WAYLAND_PLATFORM
> > >      free(dri2_dpy->device_name);
> > > 
> > 
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> 
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