libctf, create: fix ctf_type_add of structs with unnamed members

Our recent commit to support unnamed structure members better ditched
the old ctf_member_iter iterator body in favour of ctf_member_next.
However, these functions treat unnamed structure members differently:
ctf_member_iter just returned whatever the internal representation
contained, while ctf_member_next took care to always return "" rather
than sometimes returning "" and sometimes NULL depending on whether the
dict was dynamic (a product of ctf_create) or not (a product of
ctf_open).  After this commit, ctf_member_iter did the same.

It was always a bug for external callers not to treat a "" return from
these functions as if it were NULL, so only buggy callers could be
affected -- but one of those buggy callers was ctf_add_type, which
assumed that it could just take whatever name was returned from
ctf_member_iter and slam it directly into the internal representation of
a dynamic dict -- which expects NULL for unnamed members, not "".  The
net effect of all of this is that taking a struct containing unnamed
members and ctf_add_type'ing it into a dynamic dict produced a dict
whose unnamed members were inaccessible to ctf_member_info (though if
you wrote that dict out and then ctf_open'ed it, they would magically
reappear again).

Compensate for this by suitably transforming a "" name into NULL in the
internal representation, as should have been done all along.

libctf/ChangeLog
2021-01-19  Nick Alcock  <nick.alcock@oracle.com>

	* ctf-create.c (membadd): Transform ""-named members into
	NULL-named ones.
	* testsuite/libctf-regression/type-add-unnamed-struct*: New test.

libctf/ChangeLog

@@ -1,3 +1,9 @@
+2021-01-19  Nick Alcock  <nick.alcock@oracle.com>
+
+	* ctf-create.c (membadd): Transform ""-named members into
+	NULL-named ones.
+	* testsuite/libctf-regression/type-add-unnamed-struct*: New test.
+
 2021-01-19  Nick Alcock  <nick.alcock@oracle.com>
 
 	* ctf-lookup.c (ctf_lookup_by_name_internal): Do not return the

libctf/ctf-create.c

@@ -2403,6 +2403,12 @@ membadd (const char *name, ctf_id_t type, unsigned long offset, void *arg)
   if ((dmd = malloc (sizeof (ctf_dmdef_t))) == NULL)
     return (ctf_set_errno (ctb->ctb_dict, EAGAIN));
 
+  /* Unnamed members in non-dynamic dicts have a name of "", while dynamic dicts
+     use NULL.  Adapt.  */
+
+  if (name[0] == 0)
+    name = NULL;
+
   if (name != NULL && (s = strdup (name)) == NULL)
     {
       free (dmd);

libctf/testsuite/libctf-regression/type-add-unnamed-struct-ctf.c

@@ -0,0 +1,19 @@
+struct foo
+{
+  union
+  {
+    struct
+    {
+      int bar;
+    };
+  };
+  union
+  {
+    struct
+    {
+      int baz;
+    };
+  };
+};
+
+struct foo *bar;

libctf/testsuite/libctf-regression/type-add-unnamed-struct.c

@@ -0,0 +1,72 @@
+#include <ctf-api.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int
+main (int argc, char *argv[])
+{
+  ctf_dict_t *fp;
+  ctf_archive_t *ctf;
+  ctf_dict_t *dyn;
+  ctf_next_t *i = NULL;
+  ctf_id_t type;
+  ctf_id_t newtype;
+  const char *memb;
+  ctf_membinfo_t mi;
+  const char *membs[] = { "bar", "baz", NULL };
+  const char **walk;
+  int err;
+
+  if (argc != 2)
+    {
+      fprintf (stderr, "Syntax: %s PROGRAM\n", argv[0]);
+      exit(1);
+    }
+
+  if ((ctf = ctf_open (argv[1], NULL, &err)) == NULL)
+    goto open_err;
+
+  if ((fp = ctf_dict_open (ctf, NULL, &err)) == NULL)
+    goto open_err;
+
+  if ((dyn = ctf_create (&err)) == NULL)
+    goto create_err;
+
+  /* Copy 'struct foo' into the dynamic dict, then make sure we can look up a
+     member situated inside an unnamed struct.  */
+
+  if ((type = ctf_lookup_by_name (fp, "struct foo")) == CTF_ERR)
+    {
+      fprintf (stderr, "Cannot look up struct foo: %s\n", ctf_errmsg (ctf_errno (dyn)));
+      return 1;
+    }
+
+  if ((newtype = ctf_add_type (dyn, fp, type)) == CTF_ERR)
+    goto copy_err;
+
+  for (walk = membs; *walk != NULL; walk++)
+    {
+      if (ctf_member_info (dyn, newtype, *walk, &mi) < 0)
+        goto lookup_err;
+      printf ("Looked up %s, type %lx, offset %lx\n", *walk, (long) mi.ctm_type, mi.ctm_offset);
+    }
+
+  ctf_dict_close (dyn);
+  ctf_dict_close (fp);
+  ctf_close (ctf);
+
+  return 0;
+
+ open_err:
+  fprintf (stderr, "%s: cannot open: %s\n", argv[0], ctf_errmsg (err));
+  return 1;
+ create_err:
+  fprintf (stderr, "%s: cannot create: %s\n", argv[0], ctf_errmsg (err));
+  return 1;
+ copy_err:
+  fprintf (stderr, "Type addition failed: %s\n", ctf_errmsg (ctf_errno (dyn)));
+  return 1;
+ lookup_err:
+  fprintf (stderr, "Cannot look up %s: %s\n", *walk, ctf_errmsg (ctf_errno (dyn)));
+  return 1;
+}

libctf/testsuite/libctf-regression/type-add-unnamed-struct.lk

@@ -0,0 +1,3 @@
+# source: type-add-unnamed-struct-ctf.c
+Looked up bar, type [0-9a-f]*, offset [0-9a-f]*
+Looked up baz, type [0-9a-f]*, offset [0-9a-f]*