[DTrace-devel] [PATCH 5/8] sdt: retrieve probe arguments from CTF data (if possible)

[Kris Van Hees]

We were determining the probe argument types based on data from the
TRCAEFS/events/<group>/<probe>/format file.  If the CTF type for the
trace event data struct can be found, we can use that instead.

If no such CTF data is available, we fall back to the EVENTFS based
approach.

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 libdtrace/dt_prov_sdt.c | 97 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 82 insertions(+), 15 deletions(-)

diff --git a/libdtrace/dt_prov_sdt.c b/libdtrace/dt_prov_sdt.c
index 7742ffac..25e3c2d8 100644
--- a/libdtrace/dt_prov_sdt.c
+++ b/libdtrace/dt_prov_sdt.c
@@ -186,13 +186,45 @@ static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 	return 0;
 }
 
+/*
+ * If thre is no trace_event_raw_* struct available in CTF, we can still get
+ * argument count and type information from the tracefs data.
+ */
+static int probe_info_tracefs(dtrace_hdl_t *dtp, const dt_probe_t *prp,
+			      int *argcp, dt_argdesc_t **argvp)
+{
+	FILE				*f;
+	char				*fn;
+	int				rc;
+	tp_probe_t			*tpp = prp->prv_data;
+	const dtrace_probedesc_t	*pdp = prp->desc;
+
+	if (asprintf(&fn, EVENTSFS "%s/%s/format", pdp->mod, pdp->prb) == -1)
+		return dt_set_errno(dtp, EDT_NOMEM);
+
+	f = fopen(fn, "r");
+	free(fn);
+	if (!f)
+		return -ENOENT;
+
+	rc = dt_tp_event_info(dtp, f, 0, tpp, argcp, argvp);
+	fclose(f);
+
+	return rc;
+}
+
 static int probe_info(dtrace_hdl_t *dtp, const dt_probe_t *prp,
 		      int *argcp, dt_argdesc_t **argvp)
 {
-	FILE		*f;
-	char		fn[256];
-	int		rc;
-	tp_probe_t	*tpp = prp->prv_data;
+	tp_probe_t		*tpp = prp->prv_data;
+	int			rc, i;
+	char			*str;
+	ctf_dict_t		*ctfp;
+	ctf_id_t		type;
+	ctf_next_t		*it = NULL;
+	int			argc = 0;
+	dt_argdesc_t		*argv = NULL;
+	dtrace_typeinfo_t	sym;
 
 	/*
 	 * If the tracepoint has already been created and we have its info,
@@ -201,20 +233,55 @@ static int probe_info(dtrace_hdl_t *dtp, const dt_probe_t *prp,
 	if (dt_tp_is_created(tpp))
 		return -1;
 
-	strcpy(fn, EVENTSFS);
-	strcat(fn, prp->desc->mod);
-	strcat(fn, "/");
-	strcat(fn, prp->desc->prb);
-	strcat(fn, "/format");
+#ifdef HAVE_LIBCTF
+	if (asprintf(&str, "struct trace_event_raw_%s", prp->desc->prb) == -1)
+		return dt_set_errno(dtp, EDT_NOMEM);
+	rc = dtrace_lookup_by_type(dtp, DTRACE_OBJ_EVERY, str, &sym);
+	free(str);
+	if (rc ||
+	    ctf_type_kind(sym.dtt_ctfp, sym.dtt_type) != CTF_K_STRUCT)
+		goto use_alt;
 
-	f = fopen(fn, "r");
-	if (!f)
-		return -ENOENT;
+	/*
+	 * Tracepoints have an extra member at the beginning and end of the
+	 * struct.  We need to skip those.  (We also handle the case where one
+	 * or both of those members are missing even though that is not
+	 * supposed to happen.)
+	 */
+	ctfp = sym.dtt_ctfp;
+	type = sym.dtt_type;
+	rc = ctf_member_count(ctfp, type);
+	if (rc <= 2)
+		goto done;
+
+	rc--;
+	argc = rc - 1;
+	argv = dt_zalloc(dtp, argc * sizeof(dt_argdesc_t));
+	if (argv == NULL)
+		return dt_set_errno(dtp, EDT_NOMEM);
+	/* Skip first member. */
+	ctf_member_next(ctfp, type, &it, NULL, NULL, 0);
+	for (i = 0; i < argc; i++) {
+		ctf_id_t	mtyp;
+		char		n[DT_TYPE_NAMELEN];
+
+		if (ctf_member_next(ctfp, type, &it, NULL, &mtyp, 0) == CTF_ERR)
+			return dt_set_errno(dtp, EDT_CTF);
+		ctf_type_name(ctfp, mtyp, n, sizeof(n));
+		argv[i].mapping = i;
+		argv[i].native = strdup(n);
+		argv[i].xlate = NULL;
+	}
+	ctf_next_destroy(it);
+done:
+	*argcp = argc;
+	*argvp = argv;
 
-	rc = dt_tp_event_info(dtp, f, 0, tpp, argcp, argvp);
-	fclose(f);
+	return 0;
 
-	return rc;
+use_alt:
+#endif
+	return probe_info_tracefs(dtp, prp, argcp, argvp);
 }
 
 dt_provimpl_t	dt_sdt = {
-- 
2.42.0