[PATCH] Fortran: error handling of global entity appearing in COMMON block [PR103259]

[Harald Anlauf <anlauf@gmx.de>]

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Dear all,

the attached trivial patch by Steve fixes a NULL pointer dereference
that occurs when an error shall be emitted for a global entity that
conflicts with a symbol appearing in a COMMON block, but the symbol's
location is not set.  This may happen e.g. in the testcase in the PR,
where the COMMON variables are imported from a module.

Regtested on x86_64-pc-linux-gnu with no failures.

I intend to commit as obvious within 24h unless there are comments.

Thanks,
Harald


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From 1c225608e0cabbe909cc4d6e69fb0281bb99418f Mon Sep 17 00:00:00 2001
From: Steve Kargl <kargl@gcc.gnu.org>
Date: Tue, 7 Feb 2023 20:18:42 +0100
Subject: [PATCH] Fortran: error handling of global entity appearing in COMMON
 block [PR103259]

gcc/fortran/ChangeLog:

	PR fortran/103259
	* resolve.cc (resolve_common_vars): Avoid NULL pointer dereference
	when a symbol's location is not set.

gcc/testsuite/ChangeLog:

	PR fortran/103259
	* gfortran.dg/pr103259.f90: New test.
---
 gcc/fortran/resolve.cc                 | 12 +++++++++---
 gcc/testsuite/gfortran.dg/pr103259.f90 | 11 +++++++++++
 2 files changed, 20 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gfortran.dg/pr103259.f90

diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
index 100b2382e22..549916c2b53 100644
--- a/gcc/fortran/resolve.cc
+++ b/gcc/fortran/resolve.cc
@@ -953,9 +953,15 @@ resolve_common_vars (gfc_common_head *common_block, bool named_common)
     {
       gsym = gfc_find_gsymbol (gfc_gsym_root, csym->name);
       if (gsym && (gsym->type == GSYM_MODULE || gsym->type == GSYM_PROGRAM))
-	gfc_error_now ("Global entity %qs at %L cannot appear in a "
-			"COMMON block at %L", gsym->name,
-			&gsym->where, &csym->common_block->where);
+	{
+	  if (csym->common_block)
+	    gfc_error_now ("Global entity %qs at %L cannot appear in a "
+			   "COMMON block at %L", gsym->name,
+			   &gsym->where, &csym->common_block->where);
+	  else
+	    gfc_error_now ("Global entity %qs at %L cannot appear in a "
+			   "COMMON block", gsym->name, &gsym->where);
+	}

       /* gfc_add_in_common may have been called before, but the reported errors
 	 have been ignored to continue parsing.
diff --git a/gcc/testsuite/gfortran.dg/pr103259.f90 b/gcc/testsuite/gfortran.dg/pr103259.f90
new file mode 100644
index 00000000000..f78ff26180e
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr103259.f90
@@ -0,0 +1,11 @@
+! { dg-do compile }
+! PR fortran/103259 - ICE in resolve_common_vars
+! Contributed by G.Steinmetz
+
+module m
+  integer :: p
+  common /c/ p
+end
+program p ! { dg-error "cannot appear in a COMMON block" }
+  use m   ! { dg-error "is also the name of the current program unit" }
+end
--
2.35.3