9.7.2.2 Register Names

The eBPF processor provides ten general-purpose 64-bit registers, which are read-write, and a read-only frame pointer register:

%r0 .. %r9
General-purpose registers.
%r10
Frame pointer register.

Some registers have additional names, to reflect their role in the eBPF ABI:

%a
This is ‘ %r0 ’.
%ctx
This is ‘ %r6 ’.
%fp
This is ‘ %r10 ’.