(In reply to comment #14)
> Please recompile the ddx with --enable-debug.

add --enable-debug
(gdb) bt
#0  0x00007f3d325b2f77 in __GI_raise (sig=sig@entry=6)
    at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007f3d325b65e8 in __GI_abort () at abort.c:90
#2  0x00007f3d325f04fb in __libc_message (do_abort=do_abort@entry=2,
    fmt=fmt@entry=0x7f3d32704240 "*** Error in `%s': %s: 0x%s ***\n")
    at ../sysdeps/unix/sysv/linux/libc_fatal.c:199
#3  0x00007f3d325fc996 in malloc_printerr (ptr=0xf31570,
    str=0x7f3d32704370 "double free or corruption (out)", action=3)
    at malloc.c:4923
#4  _int_free (av=<optimized out>, p=0xf31560, have_lock=0) at malloc.c:3779
#5  0x0000000000434632 in DoGetImage (planemask=<optimized out>, height=5,
    width=5, y=0, x=0, drawable=<optimized out>, format=<optimized out>,
    client=<optimized out>) at dispatch.c:2170
#6  ProcGetImage (client=<optimized out>) at dispatch.c:2181
#7  0x0000000000437427 in Dispatch () at dispatch.c:432
#8  0x000000000043b20a in dix_main (argc=2, argv=0x7fffeaabfb88,
    envp=<optimized out>) at main.c:296
#9  0x00007f3d3259dde5 in __libc_start_main (main=0x4268f0 <main>, argc=2,
    ubp_av=0x7fffeaabfb88, init=<optimized out>, fini=<optimized out>,
    rtld_fini=<optimized out>, stack_end=0x7fffeaabfb78) at libc-start.c:260
#10 0x0000000000426921 in _start ()

output:
rendercheck 1.4
Render extension version 0.11
Window format: r8g8b8
Found server-supported format: a8
Found server-supported format: a8r8g8b8
Found server-supported format: x8r8g8b8
Found server-supported format: b8g8r8a8
Found server-supported format: b8g8r8x8
Found server-supported format: r8g8b8
Found server-supported format: b8g8r8
Found server-supported format: r5g5b5
Found server-supported format: b5g5r5
Found server-supported format: x1r5g5b5
Found server-supported format: x1b5g5r5
Found server-supported format: r5g6b5
Found server-supported format: b5g6r5
Found server-supported format: x8b8g8r8
Found server-supported format: x2r10g10b10
Found server-supported format: x2b10g10r10
Beginning dest coords test
dst coords test error of 255.0000 at (0, 0) --
           R     G     B     A
got:       1.000 0.000 0.000 1.000
expected:  1.000 1.000 1.000 1.000
dst coords test error of 255.0000 at (0, 1) --
           R     G     B     A
got:       0.000 0.000 0.000 1.000
expected:  1.000 1.000 1.000 1.000
dst coords test error of 255.0000 at (0, 2) --
           R     G     B     A
got:       1.000 0.000 0.000 1.000
expected:  1.000 1.000 1.000 1.000
dst coords test error of 255.0000 at (0, 4) --
           R     G     B     A
got:       0.000 0.000 0.000 1.000
expected:  1.000 1.000 1.000 1.000
dst coords test error of 255.0000 at (1, 1) --
           R     G     B     A
got:       0.000 0.000 0.000 1.000
expected:  1.000 0.000 0.000 1.000
dst coords test error of 255.0000 at (1, 2) --
           R     G     B     A
got:       1.000 1.000 1.000 1.000
expected:  1.000 0.000 0.000 1.000
dst coords test error of 255.0000 at (1, 3) --
           R     G     B     A
got:       1.000 1.000 1.000 1.000
expected:  1.000 0.000 0.000 1.000
dst coords test error of 255.0000 at (1, 4) --
           R     G     B     A
got:       0.000 0.000 0.000 1.000
expected:  1.000 1.000 1.000 1.000
dst coords test error of 255.0000 at (2, 1) --
           R     G     B     A
got:       1.000 1.000 1.000 1.000
expected:  1.000 0.000 0.000 1.000
dst coords test error of 255.0000 at (2, 2) --
           R     G     B     A
got:       1.000 1.000 1.000 1.000
expected:  1.000 0.000 0.000 1.000
dst coords test error of 255.0000 at (2, 3) --
           R     G     B     A
got:       0.000 0.000 0.000 1.000
expected:  1.000 0.000 0.000 1.000
dst coords test error of 255.0000 at (2, 4) --
           R     G     B     A
got:       0.000 0.000 0.000 1.000
expected:  1.000 1.000 1.000 1.000
dst coords test error of 255.0000 at (3, 2) --
           R     G     B     A
got:       1.000 1.000 1.000 1.000
expected:  1.000 0.000 0.000 1.000
dst coords test error of 255.0000 at (3, 3) --
           R     G     B     A
got:       0.000 0.000 0.000 1.000
expected:  1.000 0.000 0.000 1.000
dst coords test error of 255.0000 at (3, 4) --
           R     G     B     A
got:       0.000 0.000 0.000 1.000
expected:  1.000 1.000 1.000 1.000
dst coords test error of 255.0000 at (4, 1) --
           R     G     B     A
got:       1.000 0.000 0.000 1.000
expected:  1.000 1.000 1.000 1.000
dst coords test error of 255.0000 at (4, 3) --
           R     G     B     A
got:       0.000 0.000 0.000 1.000
expected:  1.000 1.000 1.000 1.000
dst coords test error of 255.0000 at (4, 4) --
           R     G     B     A
got:       0.000 0.000 0.000 1.000
expected:  1.000 1.000 1.000 1.000