The recovery system TWRP 2.8.x on an Android device requires an adb version >=1.0.32 Please upgrade dev-util/android-tools. Thanks, Helmut
Helmut, You could also use /opt/android-sdk-update-manager/platform-tools/adb But I agree, it would be nice to see an update of android-tools.
I also had a need for the newer adb and fastboot so I hacked together (hacked being the operative word here) some ebuilds based on existing ones if anyone is interested. I put them in my overlay: https://github.com/MathyV/gentoo-overlay-mathy The version numbering is off as I took them from the actual tags (which are called android-5.1.1_r13 and the likes) in the git repositories without knowing they had separate versions. Maybe I'll fix that in a future update :-)
Just to be clear, I used the adb and fastboot ebuilds I created to root a phone, flash TWRP 2.8.6.0 and afterwards CM12 so everything seems to be working as expected. No warranty if your phone explodes though ;-)
*** Bug 557926 has been marked as a duplicate of this bug. ***
This is fixed in git: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=a93daa3e70d77f43db98d5daa8337405a749dca2