selftests/bpf: fix lots of silly mistakes pointed out by compiler

Once we enable -Wall for BPF sources, compiler will complain about lots
of unused variables, variables that are set but never read, etc.

Fix all these issues first before enabling -Wall in Makefile.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230309054015.4068562-4-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: BPF test_prog selftests for bpf_loop inlining

Two new test BPF programs for test_prog selftests checking bpf_loop
behavior. Both are corner cases for bpf_loop inlinig transformation:
- check that bpf_loop behaves correctly when callback function is not
a compile time constant
- check that local function variables are not affected by allocating
additional stack storage for registers spilled by loop inlining

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/r/20220620235344.569325-6-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: Fix tests to use arch-dependent syscall entry points

Some of the tests are using x86_64 ABI-specific syscall entry points
(such as __x64_sys_nanosleep and __x64_sys_getpgid). Update them to use
architecture-dependent syscall entry names.

Also update fexit_sleep test to not use BPF_PROG() so that it is clear
that the syscall parameters aren't being accessed in the bpf prog.

Note that none of the bpf progs in these tests are actually accessing
any of the syscall parameters. The only exception is perfbuf_bench, which
passes on the bpf prog context into bpf_perf_event_output() as a pointer
to pt_regs, but that looks to be mostly ignored.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/e35f7051f03e269b623a68b139d8ed131325f7b7.1643973917.git.naveen.n.rao@linux.vnet.ibm.com

selftests/bpf: Add bpf_loop test

Add test for bpf_loop testing a variety of cases:
various nr_loops, null callback ctx, invalid flags, nested callbacks.

Signed-off-by: Joanne Koong <joannekoong@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211130030622.4131246-3-joannekoong@fb.com