Merge branch 'Fix accessing syscall arguments'

Ilya Leoshkevich says:

====================

libbpf now has macros to access syscall arguments in an
architecture-agnostic manner, but unfortunately they have a number of
issues on non-Intel arches, which this series aims to fix.

v1: https://lore.kernel.org/bpf/20220201234200.1836443-1-iii@linux.ibm.com/
v1 -> v2:
* Put orig_gpr2 in place of args[1] on s390 (Vasily).
* Fix arm64, powerpc and riscv (Heiko).

v2: https://lore.kernel.org/bpf/20220204041955.1958263-1-iii@linux.ibm.com/
v2 -> v3:
* Undo args[1] change (Andrii).
* Rename PT_REGS_SYSCALL to PT_REGS_SYSCALL_REGS (Andrii).
* Split the riscv patch (Andrii).

v3: https://lore.kernel.org/bpf/20220204145018.1983773-1-iii@linux.ibm.com/
v3 -> v4:
* Undo arm64's and s390's user_pt_regs changes.
* Use struct pt_regs when vmlinux.h is available (Andrii).
* Use offsetofend for accessing orig_gpr2 and orig_x0 (Andrii).
* Move libbpf's copy of offsetofend to a new header.
* Fix riscv's __PT_FP_REG.
* Use PT_REGS_SYSCALL_REGS in test_probe_user.c.
* Test bpf_syscall_macro with userspace headers.
* Use Naveen's suggestions and code in patches 5 and 6.
* Add warnings to arm64's and s390's ptrace.h (Andrii).

v4: https://lore.kernel.org/bpf/20220208051635.2160304-1-iii@linux.ibm.com/
v4 -> v5:
* Go back to v3.
* Do not touch arch headers.
* Use CO-RE struct flavors to access orig_x0 and orig_gpr2.
* Fail compilation if non-CO-RE macros are used to access the first
  syscall parameter on arm64 and s390.
* Fix accessing frame pointer on riscv.
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>