GDB backtrace:

#0  __strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:76
<a href="/~alcinnz/fontconfig-pure/1" title="~alcinnz/fontconfig-pure#1: Heisenbug in fontset decoding needs fixing.">#1</a>  0x00007ffff52b4353 in __GI___strdup (s=0x0) at ./string/strdup.c:41
<a href="/~alcinnz/fontconfig-pure/2" title="~alcinnz/fontconfig-pure#2: Some Values are not getting decoded">#2</a>  0x00007ffff7c9aff8 in FcValueSave () from /lib/x86_64-linux-gnu/libfontconfig.so.1
<a href="/~alcinnz/fontconfig-pure/3" title="~alcinnz/fontconfig-pure#3: Segfault upon calling FcCharSetFirstPage">#3</a>  0x00007ffff7c9fe87 in ?? () from /lib/x86_64-linux-gnu/libfontconfig.so.1
<a href="/~alcinnz/fontconfig-pure/4" title="~alcinnz/fontconfig-pure#4: fontconfig-pure error">#4</a>  0x000000000157c039 in decodePattern ()
<a href="/~alcinnz/fontconfig-pure/5" title="~alcinnz/fontconfig-pure#5: fontconfig-pure hackage package">#5</a>  0x0000000001566a6f in fcFontRenderPrepare ()
<a href="/~alcinnz/fontconfig-pure/6" title="~alcinnz/fontconfig-pure#6: Occasionally segfaults upon saving values">#6</a>  0x000000000156477a in ghczuwrapperZC5ZCfontconfigzmpurezm0zi5zi1zi0zm3171f8bee6b9ef76754f3b647eb2798fabe8ead713bfb5f87120575aee3bfc0cZCGraphicsziTextziFontziChooseziConfigziAccessorsZCfcFontRenderPrepare ()
#7  0x000000000155fe8b in ?? ()
#8  0x0000000000000000 in ?? ()