When verifier sees a timed may_goto instruction, it emits a call to
arch_bpf_timed_may_goto() with a stack offset in BPF_REG_AX (arm64 r9)
and expects a count value to be returned in the same register. The
verifier doesn't save or restore any registers before emitting this
call.

arch_bpf_timed_may_goto() should act as a trampoline to call
bpf_check_timed_may_goto() with AAPCS64 calling convention.

To support this custom calling convention, implement
arch_bpf_timed_may_goto() in assembly and make sure BPF caller saved
registers are saved and restored, call bpf_check_timed_may_goto with
arm64 calling convention where first argument and return value both are
in x0, then put the result back into BPF_REG_AX before returning.

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Xu Kuohai <xukuohai@huawei.com>
Link: https://lore.kernel.org/r/20250827113245.52629-2-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Add SPDX license identifiers to all Make/Kconfig files which:

 - Have no license information of any form

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

  GPL-2.0-only

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The JIT compiler emits A64 instructions. It supports eBPF only.
Legacy BPF is supported thanks to conversion by BPF core.

JIT is enabled in the same way as for other architectures:

	echo 1 > /proc/sys/net/core/bpf_jit_enable

Or for additional compiler output:

	echo 2 > /proc/sys/net/core/bpf_jit_enable

See Documentation/networking/filter.txt for more information.

The implementation passes all 57 tests in lib/test_bpf.c
on ARMv8 Foundation Model :) Also tested by Will on Juno platform.

Signed-off-by: Zi Shen Lim <zlim.lnx@gmail.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>