PR fortran/95088 - Buffer overflows with PDTs, submodules and long symbols

With PDTs (parameterized derived types) and submodules, name mangling
results in variably long internal symbols.  Instead of using a fixed-size
intermediate buffer, which is actually not really needed, just use a
pointer to strings.

2020-06-14  Harald Anlauf  <anlauf@gmx.de>

gcc/fortran/
	PR fortran/95088
	* class.c (get_unique_type_string): Replace use of fixed size
	buffer by internally passing a pointer to strings.

(cherry picked from commit 3ee9d82484bdc0ae5b1b21f4a3d8ff46d40e36fd)

gcc/fortran/class.c

@@ -479,19 +479,11 @@ gfc_class_initializer (gfc_typespec *ts, gfc_expr *init_expr)
 static void
 get_unique_type_string (char *string, gfc_symbol *derived)
 {
-  /* Provide sufficient space to hold "Pdtsymbol".  */
-  char dt_name[GFC_MAX_SYMBOL_LEN+4];
+  const char *dt_name;
   if (derived->attr.unlimited_polymorphic)
-    strcpy (dt_name, "STAR");
+    dt_name = "STAR";
   else
-    {
-      const char *upper = gfc_dt_upper_string (derived->name);
-      size_t len = strnlen (upper, sizeof (dt_name));
-      if (len >= sizeof (dt_name))
-	gfc_internal_error ("get_unique_type_string: identifier overflow");
-      memcpy (dt_name, upper, len);
-      dt_name[len] = '\0';
-    }
+    dt_name = gfc_dt_upper_string (derived->name);
   if (derived->attr.unlimited_polymorphic)
     sprintf (string, "_%s", dt_name);
   else if (derived->module)

gcc/testsuite/gfortran.dg/pr95088.f90

+! { dg-do compile }
+! { dg-options "-fsecond-underscore" }
+! PR fortran/95088 - ICE in gfc_build_class_symbol, at fortran/class.c:653
+
+module m2345678901234567890123456789012345678901234567890123456789_123
+  type t2345678901234567890123456789012345678901234567890123456789_123 &
+      (n2345678901234567890123456789012345678901234567890123456789_123,&
+       r2345678901234567890123456789012345678901234567890123456789_123,&
+       k2345678901234567890123456789012345678901234567890123456789_123,&
+       l2345678901234567890123456789012345678901234567890123456789_123 )
+     integer, kind :: n2345678901234567890123456789012345678901234567890123456789_123
+     integer, kind :: r2345678901234567890123456789012345678901234567890123456789_123
+     integer, kind :: k2345678901234567890123456789012345678901234567890123456789_123
+     integer, len  :: l2345678901234567890123456789012345678901234567890123456789_123
+     complex (kind  = r2345678901234567890123456789012345678901234567890123456789_123) &
+                   :: z2345678901234567890123456789012345678901234567890123456789_123
+     character(kind = k2345678901234567890123456789012345678901234567890123456789_123, &
+                len = l2345678901234567890123456789012345678901234567890123456789_123) &
+                   :: c2345678901234567890123456789012345678901234567890123456789_123
+  end type
+  type, extends (t2345678901234567890123456789012345678901234567890123456789_123) :: &
+      a2345678901234567890123456789012345678901234567890123456789_123
+  end type
+  interface
+     module subroutine s2345678901234567890123456789012345678901234567890123456789_123 &
+                      (x2345678901234567890123456789012345678901234567890123456789_123)
+       class(a2345678901234567890123456789012345678901234567890123456789_123(16,8,4,1234567890)) :: &
+             x2345678901234567890123456789012345678901234567890123456789_123
+     end
+  end interface
+end