Re: [PATCH bpf-next 04/15] bpf: Support bpf program calling kernel function

[Alexei Starovoitov <ast@xxxxxx>]

On 3/18/21 6:03 PM, Andrii Nakryiko wrote:
> > +       desc->imm = BPF_CAST_CALL(addr) - __bpf_call_base;
> Is this difference guaranteed to always fit within s32?

we have this restriction in many places: JIT, dispatcher, trampoline,
and bpf interpreter.
Modules and kernel .text are in the same 4G for the same reason: 
performance.