Merge branch 'libbpf-extend-arguments-tracing'

Andrii Nakryiko says:

====================
This patch set fixes and extends libbpf's bpf_tracing.h support for tracing
arguments of kprobes/uprobes, and syscall as a special case.

Depending on the architecture, anywhere between 3 and 8 arguments can be
passed to a function in registers (so relevant to kprobes and uprobes), but
before this patch set libbpf's macros in bpf_tracing.h only supported up to
5 arguments, which is limiting in practice. This patch set extends
bpf_tracing.h to support up to 8 arguments, if architecture allows. This
includes explicit PT_REGS_PARMx() macro family, as well as BPF_KPROBE() macro.

Now, with tracing syscall arguments situation is sometimes quite different.
For a lot of architectures syscall argument passing through registers differs
from function call sequence at least a little. For i386 it differs *a lot*.
This patch set addresses this issue across all currently supported
architectures and hopefully fixes existing issues. syscall(2) manpage defines
that either 6 or 7 arguments can be supported, depending on architecture, so
libbpf defines 6 or 7 registers per architecture to be used to fetch syscall
arguments.

Also, BPF_UPROBE and BPF_URETPROBE are introduced as part of this patch set.
They are aliases for BPF_KPROBE and BPF_KRETPROBE (as mechanics of argument
fetching of kernel functions and user-space functions are identical), but it
allows BPF users to have less confusing BPF-side code when working with
uprobes.

For both sets of changes selftests are extended to test these new register
definitions to architecture-defined limits. Unfortunately I don't have ability
to test it on all architectures, and BPF CI only tests 3 architecture (x86-64,
arm64, and s390x), so it would be greatly appreciated if people with access to
architectures other than above 3 helped review and test changes.
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

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