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From: "kargl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/95104] Segfault on a legal WAIT statement
Date: Wed, 13 May 2020 16:24:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95104

--- Comment #4 from kargl at gcc dot gnu.org ---
(In reply to Bill Long from comment #3)
> A comment from the original user:  gfortran 8.3.0 appears to do the right
> thing. So perhaps a regression somewhere in the 9.x line?

A note of the gfortran  wiki says full asynchronous support became
available in 9.1.  SO, likely a bug introduced in 9.  This fixes=20
the segfault as it is never correct to dereference a NULL pointer.

Index: libgfortran/io/transfer.c
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
--- libgfortran/io/transfer.c   (revision 280157)
+++ libgfortran/io/transfer.c   (working copy)
@@ -4492,7 +4492,7 @@ void
 st_wait_async (st_parameter_wait *wtp)
 {
   gfc_unit *u =3D find_unit (wtp->common.unit);
-  if (ASYNC_IO && u->au)
+  if (ASYNC_IO && u && u->au)
     {
       if (wtp->common.flags & IOPARM_WAIT_HAS_ID)
        async_wait_id (&(wtp->common), u->au, *wtp->id);


With this patch, your program prints '0'.  Don't know if this
is the only thing that needs fixing.  Thanks for the bug report.=