There were a lot of bug fixed (improvements?) if you believe Oracle change.log
Version 5.1.2 (2016-07-21)
Version 5.1.0 (2016-07-12)
Version 5.0.24 (2016-06-28)
Version 5.0.22 (2016-06-16)
Version 5.0.20 (2016-04-28)
Version 5.0.18 (2016-04-18)
I tried and I can not re-compile the kernel modules myself. But we have them on tinycore site...
So I cheated and extracted from VBoxGuestAdditions_5.1.2.iso the VBoxGuestAdditions-x86.tar and from there I replaced the main programs and exit/enter Xorg.
VboxClient, VboxControl, VboxService. (no need for VboxGreeter -> Ubuntu lightLM, or pax_vbox.so for Fedora SElinux)
And of course all the /lib/VboxOGL*.so & vboxvideo_drv.so (Xorg 1.18.0)
Bottom line: In a running VirtualBox 5.1.2 machine for Tinycore 7.2 I installed the (actual) Guest additions 5.018. Then replaced all files with the new versions.
All are OK. Except just the same SOFTWARE acceleration in 5.1.2 like in 5.018.
I tried also to do like in Archlinux (virtualbox-guest-utils-5.1.2-2-i686.pkg.tar), to simlink the VboxOGL.so -> vboxvideo_dri.so
in both /lib/dri and /lib/Xorg/module/dri. but no improvement.
Latest Virualbox 5.1.2 runs on Windows 10 ver 1511, with AMD A6-310 APU & AMD Radeon R4 1.8 GHz
Any idea why is no hardware acceleration even in Xorg 1.18.4?
Edit: /dev/dri/card0 -> no such directory, hm.. a missing/not loaded dependency maybe some OGL