Created attachment 57139 [details]
xorg.log

There's something fishy going on here as if everything goes to plan we shouldn't hit this path.

The bug in question will be fixed by:

commit 52b11f63d7922032caef0f0a5979b080dbddcbfc
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Thu Feb 16 11:22:23 2012 +0000

    sna: Upconvert fallback trapezoids to a8
    
    Since the hardware only handles a8 without tricky emulation and pixman
    insists on using a1 for sharp trapezoids we need to ensure that we
    convert the a1 to a8 for our trapezoidal mask.
    
    More worryingly, this path should never be hit...
    
    References: https://bugs.freedesktop.org/show_bug.cgi?id=46156
    Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

But do you mind compiling with ./configure --enable-debug=full and attaching the complete Xorg.log that leads to this crash?

Hi Chris,

ok, recompiled without(!) your fix using --enable-sna and --enable-debug=full.
xorg.log grew pretty large so I've packed it. see attachment.

gdb yields:
Program received signal SIGABRT, Aborted.
0x00007f2541fe8115 in raise () from /lib64/libc.so.6
(gdb) backtrace full
#0  0x00007f2541fe8115 in raise () from /lib64/libc.so.6
No symbol table info available.
#1  0x00007f2541fe9352 in abort () from /lib64/libc.so.6
No symbol table info available.
#2  0x00007f2541fe156a in __assert_fail_base () from /lib64/libc.so.6
No symbol table info available.
#3  0x00007f2541fe1608 in __assert_fail () from /lib64/libc.so.6
No symbol table info available.
#4  0x00007f25400faf1e in kgem_create_buffer (kgem=0x10b4290, size=0, flags=1, ret=0x7fffa158b468)
    at kgem.c:3140
        bo = 0x3000000030
        offset = 32767
        alloc = 2706945072
        old = 0x5558f4
        __FUNCTION__ = "kgem_create_buffer"
        __PRETTY_FUNCTION__ = "kgem_create_buffer"
#5  0x00007f25400fc14b in kgem_create_buffer_2d (kgem=0x10b4290, width=2, height=41, bpp=1, flags=1, 
    ret=0x7fffa158b468) at kgem.c:3468
        bo = 0x7f25400fdd7e
        stride = 0
        __PRETTY_FUNCTION__ = "kgem_create_buffer_2d"
        __FUNCTION__ = "kgem_create_buffer_2d"
#6  0x00007f2540103365 in sna_pixmap_create_upload (screen=0x10cb180, width=2, height=41, depth=1, 
    flags=1) at sna_accel.c:1970
        sna = 0x10b40a0
        pixmap = 0x12e4110
        priv = 0x12e4180
        bpp = 1
        ptr = 0x0
        __FUNCTION__ = "sna_pixmap_create_upload"
        __PRETTY_FUNCTION__ = "sna_pixmap_create_upload"
#7  0x00007f2540150d36 in trapezoids_fallback (op=12 '\f', src=0x149efb0, dst=0x12f1a00, 
    maskFormat=0x10cb780, xSrc=257, ySrc=0, ntrap=2, traps=0x12723a4) at sna_trapezoids.c:2011
        scratch = 0x149ede0
        dst_x = 1
        width = 2
        height = 41
        mask = 0x7f254014d432
        dst_y = 0
        bounds = {x1 = 0, y1 = 0, x2 = 2, y2 = 41}
        depth = 1
        image = 0x7f254014d2ba
        format = PIXMAN_a1
        error = 0
        screen = 0x10cb180
        __FUNCTION__ = "trapezoids_fallback"
#8  0x00007f25401568d7 in sna_composite_trapezoids (op=12 '\f', src=0x149efb0, dst=0x12f1a00, 
    maskFormat=0x10cb780, xSrc=257, ySrc=0, ntrap=2, traps=0x12723a4) at sna_trapezoids.c:3753
        sna = 0x10b40a0
        rectilinear = false
        pixel_aligned = false
        n = 8112888
        __FUNCTION__ = "sna_composite_trapezoids"
#9  0x00000000004dddf0 in ProcRenderTrapezoids ()
No symbol table info available.
#10 0x00000000004351cd in Dispatch ()
No symbol table info available.
#11 0x0000000000425f3a in main ()
No symbol table info available.

Regards
Nic

Created attachment 57151 [details]
xorg.log with --enable-debug=full

Thanks for the debug log. According to the tail we hit the fallback path for precise rendering of a mono trapezoid. Now my span rasterisation should adhere to the render specification in this regard (and if not there already exist paths that do...) so I think the fallback in that particular case is superfluous.

With the fix, and the attempt to close the optimisation loophole, I think I have this bug covered. I'll read through your debug log for any other gems, ta.