[DTrace-devel] [PATCH] Allow dt_cg_arglist() to handle the NULL case

[Kris Van Hees]

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, &noargs, 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 at oracle.com>
---
 libdtrace/dt_bpf.c  | 18 +++++++++++-------
 libdtrace/dt_cg.c   | 10 +++++++---
 libdtrace/dt_impl.h |  1 +
 libdtrace/dt_open.c |  4 +++-
 4 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
index 4cb0eec6..f3f8c79d 100644
--- a/libdtrace/dt_bpf.c
+++ b/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);
diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
index 175c4b95..0963f202 100644
--- a/libdtrace/dt_cg.c
+++ b/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);
diff --git a/libdtrace/dt_impl.h b/libdtrace/dt_impl.h
index c1ff6256..85a1e7c9 100644
--- a/libdtrace/dt_impl.h
+++ b/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 */
diff --git a/libdtrace/dt_open.c b/libdtrace/dt_open.c
index f5cbd499..581172e2 100644
--- a/libdtrace/dt_open.c
+++ b/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);
--
2.34.1

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