[PATCH] Fortran: fix NULL pointer dereference on overlapping initialization [PR50410]

[Harald Anlauf <anlauf@gmx.de>]

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Dear all,

the attached simple, obvious and ancient patch from the PR fixes a
NULL pointer dereference that occurs on overlapping initializations
of derived types/DT components in DATA statements.

Gfortran currently does not detect or report overlapping initializations
in such cases, and some other compilers also do not (Intel) or give only
a warning (e.g. Nvidia).  For this reason I decided to add -std=legacy
to the options in the testcase.  Detecting the overlapping initializations
appears to require deeper changes in the way we look up DT components when
handling DATA statements, which is beyond the current stage.

Regtested on x86_64-pc-linux-gnu.

I intend to commit soon unless there are objections.

Thanks,
Harald


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From b3970a30679959eed159dffa816899e4430e9da5 Mon Sep 17 00:00:00 2001
From: Harald Anlauf <anlauf@gmx.de>
Date: Thu, 28 Mar 2024 22:34:40 +0100
Subject: [PATCH] Fortran: fix NULL pointer dereference on overlapping
 initialization [PR50410]

gcc/fortran/ChangeLog:

	PR fortran/50410
	* trans-expr.cc (gfc_conv_structure): Check for NULL pointer.

gcc/testsuite/ChangeLog:

	PR fortran/50410
	* gfortran.dg/data_initialized_4.f90: New test.
---
 gcc/fortran/trans-expr.cc                        |  2 +-
 gcc/testsuite/gfortran.dg/data_initialized_4.f90 | 16 ++++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gfortran.dg/data_initialized_4.f90

diff --git a/gcc/fortran/trans-expr.cc b/gcc/fortran/trans-expr.cc
index 76bed9830c4..7ce798ab8a5 100644
--- a/gcc/fortran/trans-expr.cc
+++ b/gcc/fortran/trans-expr.cc
@@ -9650,7 +9650,7 @@ gfc_conv_structure (gfc_se * se, gfc_expr * expr, int init)
   cm = expr->ts.u.derived->components;

   for (c = gfc_constructor_first (expr->value.constructor);
-       c; c = gfc_constructor_next (c), cm = cm->next)
+       c && cm; c = gfc_constructor_next (c), cm = cm->next)
     {
       /* Skip absent members in default initializers and allocatable
 	 components.  Although the latter have a default initializer
diff --git a/gcc/testsuite/gfortran.dg/data_initialized_4.f90 b/gcc/testsuite/gfortran.dg/data_initialized_4.f90
new file mode 100644
index 00000000000..156b6607edf
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/data_initialized_4.f90
@@ -0,0 +1,16 @@
+! { dg-do compile }
+! { dg-additional-options "-std=legacy" }
+!
+! PR fortran/50410
+!
+! Silently allow overlapping initialization in legacy mode (used to ICE)
+
+program p
+  implicit none
+  type t
+     integer :: g = 1
+  end type t
+  type(t) :: u = t(2)
+  data u%g /3/
+  print *, u    ! this might print "2"
+end
--
2.35.3