This patch fixes a tailcall issue caused by abusing the tailcall in
bpf2bpf feature on arm64 like the way of "bpf, x64: Fix tailcall
hierarchy".

On arm64, when a tail call happens, it uses tail_call_cnt_ptr to
increment tail_call_cnt, too.

At the prologue of main prog, it has to initialize tail_call_cnt and
prepare tail_call_cnt_ptr.

At the prologue of subprog, it pushes x26 register twice, and does not
initialize tail_call_cnt.

At the epilogue, it pops x26 twice, no matter whether it is main prog or
subprog.

Fixes: d4609a5d ("bpf, arm64: Keep tail call count across bpf2bpf calls")
Acked-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>
Link: https://lore.kernel.org/r/20240714123902.32305-3-hffilwlqm@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>