Probem with some drawing ops falling back to software
Aaron Plattner
aplattner at nvidia.com
Tue Sep 15 16:35:52 PDT 2009
On Tue, Sep 15, 2009 at 04:18:22PM -0700, Michael wrote:
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> Hello,
>
> I have a driver for a graphics device which doesn't let me map the
> framebuffer ( at least not in a form usable by the Xserver as it is ),
> so the driver attempts to do all drawing operations by hardware. This
> used to work fine in 1.4.2 but in 1.6 some operations started falling
> back to software. The reason for this appears to be, that at some point
> a Drawable is created from what X thinks is the visible screen but its
> type is set to DRAWABLE_PIXMAP so fallback drawing ops are used and
> fail. For some reason this happens when xterm tries to draw its border
> as a series of narrow rectangles. The other operations seem to use the
> right drawing ops.
>
> Any idea where to start digging? This doesn't seem to be XAA's fault
> since as far as XAA can tell the drawable is in memory so falling back
> to software is what it's supposed to do. The question is why do we end
> up with a drawable with the wrong type here?
The server creates a "pixmap" for the pixels on the screen in
miCreateScreenResources. You get this pixmap if you call the
GetScreenPixmap hook on the screen, or GetWindowPixmap for a non-redirected
window.
Until fairly recently, drivers and acceleration architectures like XAA
would never see rendering to the screen pixmap, so they could essentially
ignore it and just fall back to software for all pixmaps. miPaintWindow
used to call through a screen hook into a driver-specific PaintWindow
screen hook that allowed the driver to handle screen painting specially.
At some point, miPaintWindow was modified to render to the screen pixmap
instead. To the best of my knowledge, this is the first use of the screen
pixmap for rendering requests in the server. It wouldn't surprise me at
all if this broke XAA.
> The resulting stack trace looks like this:
> Program received signal SIGBUS, Bus error.
> fast_path_fill (imp=<value optimized out>, bits=0x7c3d0000,
> stride=<value optimized out>, bpp=<value optimized out>, x=0, y=0,
> width=486, height=1, xor=0)
> at /usr/xsrc/external/mit/pixman/dist/pixman/pixman-fast-path.c:
> 1320
> 1320 bits[i] = xor;
> (gdb) bt
> #0 fast_path_fill (imp=<value optimized out>, bits=0x7c3d0000,
> stride=<value optimized out>, bpp=<value optimized out>, x=0, y=0,
> width=486, height=1, xor=0)
> at /usr/xsrc/external/mit/pixman/dist/pixman/pixman-fast-path.c:
> 1320
> #1 0x7dea3980 in pixman_fill (bits=0x7c3d0000, stride=1280, bpp=32,
> x=0, y=0,
> width=486, height=1, xor=0)
> at /usr/xsrc/external/mit/pixman/dist/pixman/pixman.c:185
> #2 0x00638710 in fbFill (pDrawable=0x7d20d790, pGC=<value optimized
> out>,
> x=0, y=0, width=486, height=1)
> at /usr/xsrc/external/mit/xorg-server/dist/fb/fbfill.c:48
> #3 0x0062d474 in fbPolyFillRect (pDrawable=0x7d20d790, pGC=0x7d266260,
> nrect=3, prect=0x7bbacda0)
> at /usr/xsrc/external/mit/xorg-server/dist/fb/fbfillrect.c:77
> #4 0x7ce57bb8 in XAAPolyFillRectPixmap (pDraw=0x7d20d790,
> pGC=0x7d266260,
> nrectFill=4, prectInit=0x7bbacda0)
> at /usr/xsrc/external/mit/xorg-server/dist/hw/xfree86/xaa/xaaGC.c:
> 523
> #5 0x00573530 in cwPolyFillRect (pDst=<value optimized out>,
> pGC=0x7d266260,
> nrects=4, pRects=0x7bbacda0)
> at /usr/xsrc/external/mit/xorg-server/dist/miext/cw/cw_ops.c:345
This pDrawable is probably pScreen->GetScreenPixmap(pScreen)
vvvvvvvvv
> #6 0x00568bc4 in damagePolyFillRect (pDrawable=0x7d20d790,
> pGC=0x7d266260,
> nRects=4, pRects=0x7bbacda0)
> at /usr/xsrc/external/mit/xorg-server/dist/miext/damage/damage.c:
> 1404
> #7 0x0051b688 in miPaintWindow (pWin=<value optimized out>,
> prgn=0x7bbacd6c,
> what=<value optimized out>)
> at /usr/xsrc/external/mit/xorg-server/dist/mi/miexpose.c:629
> #8 0x00515ab4 in miHandleValidateExposures (pWin=0x7d2511a0)
> at /usr/xsrc/external/mit/xorg-server/dist/mi/miwindow.c:243
> #9 0x004378a0 in MapWindow (pWin=0x7d251470, client=0x7d210600)
> at /usr/xsrc/external/mit/xorg-server/dist/dix/window.c:2706
> #10 0x004617c8 in ProcMapWindow (client=0x7d266260)
> at /usr/xsrc/external/mit/xorg-server/dist/dix/dispatch.c:675
> #11 0x0046244c in Dispatch ()
> at /usr/xsrc/external/mit/xorg-server/dist/dix/dispatch.c:439
> #12 0x004441e4 in main (argc=1, argv=0x7fffd814, envp=<value optimized
> out>)
> at /usr/xsrc/external/mit/xorg-server/dist/dix/main.c:397
>
> The SIGBUS is not the bug - I intntionally hand the Xserver a write-
> protected buffer to catch attempts to scribble into framebuffer memory.
> Also, the DAMAGE extension is disabled, why is it still being called?
>
> In fast_path_fill() the bits parameter points at my fake framebuffer,
> the pDrawable and pGC in fbPolyFillRect() look like this:
> (gdb) print *pDrawable
> $17 = {type = 1 '\001', class = 0 '\0', depth = 24 '\030',
> bitsPerPixel = 32 ' ', id = 0, x = 0, y = 0, width = 1280, height =
> 1024,
> pScreen = 0x7d23c180, serialNumber = 2}
> (gdb) print *pGC
> $18 = {pScreen = 0x7d23c180, depth = 24 '\030', alu = 3 '\003',
> lineWidth = 0,
> dashOffset = 0, numInDashList = 2, dash = 0x6b3990 "\004\004",
> lineStyle = 0, capStyle = 1, joinStyle = 0, fillStyle = 0, fillRule
> = 0,
> arcMode = 0, subWindowMode = 0, graphicsExposures = 0,
> clientClipType = 0,
> miTranslate = 1, tileIsPixel = 1, fExpose = 1, freeCompClip = 1,
> unused = 189, planemask = 4294967295, fgPixel = 0, bgPixel = 1,
> tile = {
> pixmap = 0x0, pixel = 0}, stipple = 0x0, patOrg = {x = 0, y = 0},
> font = 0x0, clipOrg = {x = 0, y = 0}, lastWinOrg = {x = 0, y = 0},
> clientClip = 0x0, stateChanges = 0, serialNumber = 2, funcs =
> 0x6b2a4c,
> ops = 0x6b2a6c, devPrivates = 0x7d224480, pRotatedPixmap = 0x0,
> pCompositeClip = 0x7bb41be0}
>
> Any ideas?
>
> have fun
> Michael
>
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