This commit adds a test prog for vprintk which confirms that:
* bpf_trace_vprintk is writing to /sys/kernel/debug/tracing/trace_pipe
* __bpf_vprintk macro works as expected
* >3 args are printed
* bpf_printk w/ 0 format args compiles
* bpf_trace_vprintk call w/ a fmt specifier but NULL fmt data fails
Approach and code are borrowed from trace_printk test.
Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210917182911.2426606-9-davemarchevsky@fb.com
