tracing/probes: Support BTF argument on module functions

Since the btf returned from bpf_get_btf_vmlinux() only covers functions in
the vmlinux, BTF argument is not available on the functions in the modules.
Use bpf_find_btf_id() instead of bpf_get_btf_vmlinux()+btf_find_name_kind()
so that BTF argument can find the correct struct btf and btf_type in it.
With this fix, fprobe events can use `$arg*` on module functions as below

 # grep nf_log_ip_packet /proc/kallsyms
ffffffffa0005c00 t nf_log_ip_packet	[nf_log_syslog]
ffffffffa0005bf0 t __pfx_nf_log_ip_packet	[nf_log_syslog]
 # echo 'f nf_log_ip_packet $arg*' > dynamic_events
 # cat dynamic_events
f:fprobes/nf_log_ip_packet__entry nf_log_ip_packet net=net pf=pf hooknum=hooknum skb=skb in=in out=out loginfo=loginfo prefix=prefix

To support the module's btf which is removable, the struct btf needs to be
ref-counted. So this also records the btf in the traceprobe_parse_context
and returns the refcount when the parse has done.

Link: https://lore.kernel.org/all/169272154223.160970.3507930084247934031.stgit@devnote2/

Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 11 insertions, 3 deletions

diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 01ea148723de..4dc91460a75d 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -383,9 +383,11 @@ static inline bool tparg_is_function_entry(unsigned int flags)
 
 struct traceprobe_parse_context {
 	struct trace_event_call *event;
-	const struct btf_param *params;
-	s32 nr_params;
-	const char *funcname;
+	/* BTF related parameters */
+	const char *funcname;		/* Function name in BTF */
+	const struct btf_param *params;	/* Parameter of the function */
+	s32 nr_params;			/* The number of the parameters */
+	struct btf *btf;		/* The BTF to be used */
 	unsigned int flags;
 	int offset;
 };
@@ -400,6 +402,12 @@ const char **traceprobe_expand_meta_args(int argc, const char *argv[],
 extern int traceprobe_update_arg(struct probe_arg *arg);
 extern void traceprobe_free_probe_arg(struct probe_arg *arg);
 
+/*
+ * If either traceprobe_parse_probe_arg() or traceprobe_expand_meta_args() is called,
+ * this MUST be called for clean up the context and return a resource.
+ */
+void traceprobe_finish_parse(struct traceprobe_parse_context *ctx);
+
 extern int traceprobe_split_symbol_offset(char *symbol, long *offset);
 int traceprobe_parse_event_name(const char **pevent, const char **pgroup,
 				char *buf, int offset);