Fortran: Avoid accessing gfc_charlen when not looking at BT_CHARACTER (PR 110677)

This patch addresses an issue uncovered by the undefined behavior
sanitizer.  In function resolve_structure_cons in resolve.cc there is
a test starting with:

      if (cons->expr->ts.type == BT_CHARACTER && comp->ts.u.cl
	  && comp->ts.u.cl->length
	  && comp->ts.u.cl->length->expr_type == EXPR_CONSTANT

and UBSAN complained of loads from comp->ts.u.cl->length->expr_type of
integer value 1818451807 which is outside of the value range expr_t
enum.  If I understand the code correctly it the entire load was
unwanted because comp->ts.type in those cases is BT_CLASS and not
BT_CHARACTER.  This patch simply adds a check to make sure it is only
accessed in those cases.

During review, Harald Anlauf noticed that length types also need to be
checked and so I added also checks that he suggested to the condition.

Co-authored-by: Harald Anlauf <anlauf@gmx.de>
gcc/fortran/ChangeLog:

2023-08-14  Martin Jambor  <mjambor@suse.cz>

	PR fortran/110677
	* resolve.cc (resolve_structure_cons): Check comp->ts is character
	type before accessing stuff through comp->ts.u.cl.

diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
index e7c8d919bef0bad7610a694dd410055383c7d5f1..f51674f7faa5ad04dd3a42ac003c3ac705924733 100644 (file)
--- a/gcc/fortran/resolve.cc
+++ b/gcc/fortran/resolve.cc
@@ -1396,11 +1396,14 @@ resolve_structure_cons (gfc_expr *expr, int init)
         the one of the structure, ensure this if the lengths are known at
         compile time and when we are dealing with PARAMETER or structure
         constructors.  */
-      if (cons->expr->ts.type == BT_CHARACTER && comp->ts.u.cl
-         && comp->ts.u.cl->length
+      if (cons->expr->ts.type == BT_CHARACTER
+         && comp->ts.type == BT_CHARACTER
+         && comp->ts.u.cl && comp->ts.u.cl->length
          && comp->ts.u.cl->length->expr_type == EXPR_CONSTANT
          && cons->expr->ts.u.cl && cons->expr->ts.u.cl->length
          && cons->expr->ts.u.cl->length->expr_type == EXPR_CONSTANT
+         && cons->expr->ts.u.cl->length->ts.type == BT_INTEGER
+         && comp->ts.u.cl->length->ts.type == BT_INTEGER
          && mpz_cmp (cons->expr->ts.u.cl->length->value.integer,
                      comp->ts.u.cl->length->value.integer) != 0)
        {