exa, kdrive, and segfault

[Michel Dänzer]

On Thu, 2009-12-03 at 09:48 +0100, Arnaud Mouiche wrote:
> Hi,
> 
> I start to play with EXA and tried to implement it under kdrive, for a
> Davinci implementation
> (http://focus.ti.com/docs/prod/folders/print/tms320dm6446.html)
> 
> - staring with version 1.7.1 of xserver (getting from xorg 7.5)
> - as davinci can be consider as a slow platform, so target kdrive for
> that job
> - copy/paste  hw/kdrive/fbdev as a starting point (working fine) and
> looks at what hw/kdrive/ephyr is doing for EXA init, and with a EXA
> implementation that does nothing first.
> 
> there is a segfault when using "ExaMigrationSmart" and/or when
> "checkDirtyCorrectness" is true.
> not happened with "ExaMigrationGreedy", 

Note that the default in Xorg is ExaMigrationAlways, and the other
heuristics haven't been actively maintained since that's been the case.


> and the segfault  is due to a use of 
>     REGION_NOTEMPTY (pScreen, DamageRegion(pExaPixmap->pDamage)
> with pExaPixmap->pDamage == NULL
> (see background informations for the whole details)

Does the patch below fix the crash?


diff --git a/exa/exa_migration_classic.c b/exa/exa_migration_classic.c
index 95189be..871679f 100644
--- a/exa/exa_migration_classic.c
+++ b/exa/exa_migration_classic.c
@@ -75,6 +75,9 @@ exaPixmapIsDirty (PixmapPtr pPix)
     if (pExaPixmap == NULL)
 	EXA_FatalErrorDebugWithRet(("EXA bug: exaPixmapIsDirty was called on a non-exa pixmap.\n"), TRUE);
 
+    if (!pExaPixmap->pDamage)
+	return FALSE;
+
     return REGION_NOTEMPTY (pScreen, DamageRegion(pExaPixmap->pDamage)) ||
 	!REGION_EQUAL(pScreen, &pExaPixmap->validSys, &pExaPixmap->validFB);
 }


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