Allow dt_cg_arglist() to handle the NULL case

Even if an argument is empty, we might want to call dt_cg_arglist() to
construct a pointer to a tuple.

Callers can use the following pseudo-code to accomplish this:

	dt_node_t	noargs = {
				dnp->dn_ctfp,
				dtp->dt_type_void,
			};

	...

	if (dnp->dn_aggtup == NULL)
		dnp->dn_aggtup = &noargs;

	dt_cg_arglist(aid, dnp->dn_aggtup, dlp, drp);

	... <use dnp->dn_aggtup->dn_reg> ...

	if (dnp->aggtup == &noargs)
		dnp->aggtup = NULL;

	... <dnp->dn_aggtup->dn_reg is not used anympre> ...

Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>
Reviewed-by: Eugene Loh <eugene.loh@oracle.com>

libdtrace/dt_bpf.c

@@ -510,15 +510,19 @@ dt_bpf_gmap_create(dtrace_hdl_t *dtp)
 		dvarc = dtp->dt_options[DTRACEOPT_DYNVARSIZE] /
 			dtp->dt_maxdvarsize;
 
-	if (dvarc > 0 &&
-	    create_gmap(dtp, "dvars", BPF_MAP_TYPE_HASH,
-			sizeof(uint64_t), dtp->dt_maxdvarsize, dvarc) == -1)
+	if (dvarc > 0) {
+		if (create_gmap(dtp, "dvars", BPF_MAP_TYPE_HASH,
+				sizeof(uint64_t), dtp->dt_maxdvarsize,
+				dvarc) == -1)
 			return -1;	/* dt_errno is set for us */
 
-	if (dtp->dt_maxtuplesize > 0 &&
-	    create_gmap(dtp, "tuples", BPF_MAP_TYPE_HASH,
-			dtp->dt_maxtuplesize, sizeof(uint64_t), dvarc) == -1)
-		return -1;		/* dt_errno is set for us */
+		assert(dtp->dt_maxtuplesize > 0);
+
+		if (create_gmap(dtp, "tuples", BPF_MAP_TYPE_HASH,
+			    dtp->dt_maxtuplesize, sizeof(uint64_t),
+			    dvarc) == -1)
+			return -1;	/* dt_errno is set for us */
+	}
 
 	/* Populate the 'cpuinfo' map. */
 	dt_bpf_map_update(ci_mapfd, &key, dtp->dt_conf.cpus);

libdtrace/dt_cg.c

@@ -2600,13 +2600,17 @@ dt_cg_arglist(dt_ident_t *idp, dt_node_t *args, dt_irlist_t *dlp,
 	const dt_idsig_t	*isp = idp->di_data;
 	dt_node_t		*dnp;
 	dt_ident_t		*maxtupsz = dt_dlib_get_var(dtp, "TUPSZ");
-	int			i;
+	int			i = 0;
 	int			treg, areg;
 	uint_t			tuplesize;
 
 	TRACE_REGSET("      arglist: Begin");
 
-	for (dnp = args, i = 0; dnp != NULL; dnp = dnp->dn_list, i++) {
+	/* A 'void' args node indicates an empty argument list. */
+	if (dt_node_is_void(args))
+		goto empty_args;
+
+	for (dnp = args; dnp != NULL; dnp = dnp->dn_list, i++) {
 		/* Bail early if we run out of tuple slots. */
 		if (i > dtp->dt_conf.dtc_diftupregs)
 			longjmp(yypcb->pcb_jmpbuf, EDT_NOTUPREG);
@@ -2623,6 +2627,7 @@ dt_cg_arglist(dt_ident_t *idp, dt_node_t *args, dt_irlist_t *dlp,
 		dt_regset_free(drp, BPF_REG_0);
 	}
 
+empty_args:
 	TRACE_REGSET("      arglist: Stack");
 
 	/*
@@ -6669,7 +6674,6 @@ dt_cg_agg(dt_pcb_t *pcb, dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
 		dnerror(dnp->dn_aggtup, D_ARR_BADREF, "indexing is not "
 			"supported yet: @%s\n", dnp->dn_ident->di_name);
 
-
 	assert(fid->di_id >= DT_AGG_BASE && fid->di_id < DT_AGG_HIGHEST);
 
 	dt_cg_clsflags(pcb, DTRACEACT_AGGREGATION, dnp);

libdtrace/dt_impl.h

@@ -329,6 +329,7 @@ struct dtrace_hdl {
 	ctf_id_t dt_type_stack;	/* cached CTF identifier for stack type */
 	ctf_id_t dt_type_symaddr; /* cached CTF identifier for _symaddr type */
 	ctf_id_t dt_type_usymaddr; /* cached CTF ident. for _usymaddr type */
+	ctf_id_t dt_type_void;	/* cached CTF identifier for void type */
 	dtrace_epid_t dt_nextepid; /* next enabled probe ID to assign */
 	size_t dt_maxprobe;	/* max enabled probe ID */
 	dtrace_datadesc_t **dt_ddesc; /* probe data descriptions */

libdtrace/dt_open.c

@@ -1055,10 +1055,12 @@ dt_vopen(int version, int flags, int *errp,
 	dtp->dt_type_usymaddr = ctf_add_typedef(dmp->dm_ctfp, CTF_ADD_ROOT,
 	    "_usymaddr", ctf_lookup_by_name(dmp->dm_ctfp, "void"));
 
+	dtp->dt_type_void = ctf_lookup_by_name(dmp->dm_ctfp, "void");
+
 	if (dtp->dt_type_func == CTF_ERR || dtp->dt_type_fptr == CTF_ERR ||
 	    dtp->dt_type_str == CTF_ERR || dtp->dt_type_dyn == CTF_ERR ||
 	    dtp->dt_type_stack == CTF_ERR || dtp->dt_type_symaddr == CTF_ERR ||
-	    dtp->dt_type_usymaddr == CTF_ERR) {
+	    dtp->dt_type_usymaddr == CTF_ERR || dtp->dt_type_void == CTF_ERR) {
 		dt_dprintf("failed to add intrinsic to D container: %s\n",
 		    ctf_errmsg(ctf_errno(dmp->dm_ctfp)));
 		return set_open_errno(dtp, errp, EDT_CTF);