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From: "anlauf at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/85130] Substrings out of range are not rejected
Date: Sat, 11 Sep 2021 18:42:13 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D85130

anlauf at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |anlauf at gcc dot g=
nu.org
             Status|NEW                         |ASSIGNED

--- Comment #5 from anlauf at gcc dot gnu.org ---
We should handle the substring bounds as signed instead of unsigned.
This is obviously fixed by:

diff --git a/gcc/fortran/expr.c b/gcc/fortran/expr.c
index dfecc3012e1..604e63e6164 100644
--- a/gcc/fortran/expr.c
+++ b/gcc/fortran/expr.c
@@ -1724,8 +1724,8 @@ find_substring_ref (gfc_expr *p, gfc_expr **newp)
   *newp =3D gfc_copy_expr (p);
   free ((*newp)->value.character.string);

-  end =3D (gfc_charlen_t) mpz_get_ui (p->ref->u.ss.end->value.integer);
-  start =3D (gfc_charlen_t) mpz_get_ui (p->ref->u.ss.start->value.integer);
+  end =3D (gfc_charlen_t) mpz_get_si (p->ref->u.ss.end->value.integer);
+  start =3D (gfc_charlen_t) mpz_get_si (p->ref->u.ss.start->value.integer);
   if (end >=3D start)
     length =3D end - start + 1;
   else


and regtests cleanly.  :-)

@Thomas: although the wording is slightly different between F2003 and F2018=
, it
always results in length zero if the starting point exceeds the ending poin=
t.
Would you agree in reverting your commit r258976 after applying the above?=