Avoid crash with Ada and -fdata-sections

A user noticed that gdb would crash when showing a backtrace.
Investigation showed this to be a crash in the DWARF reader when
handling a "pragma export" symbol.  The bug here is that earlier code
decides to eliminate the symbol, but the export code tries to add it
anyway -- but to a NULL list.

3 files changed, 55 insertions, 1 deletions

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index a538cb5..ef7f570 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -19203,7 +19203,8 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu,
 	      else
 		list_to_add = cu->list_in_scope;
 
-	      if (is_ada_import_or_export (cu, name, linkagename))
+	      if (list_to_add != nullptr
+		  && is_ada_import_or_export (cu, name, linkagename))
 		{
 		  /* This is a Pragma Export.  A Pragma Import won't
 		     be seen here, because it will not have a location
diff --git a/gdb/testsuite/gdb.ada/data-sections.exp b/gdb/testsuite/gdb.ada/data-sections.exp
new file mode 100644
index 0000000..9cc6023
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/data-sections.exp
@@ -0,0 +1,34 @@
+# Copyright 2023 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+load_lib "ada.exp"
+
+require allow_ada_tests
+
+standard_ada_testfile main
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable \
+	 {debug additional_flags=-fdata-sections ldflags=-Wl,--gc-sections}] \
+	!= ""} {
+    return -1
+}
+
+# The bug was that the DWARF reader would crash when processing a
+# certain symbol.
+save_vars {GDBFLAGS} {
+    append GDBFLAGS " --readnow"
+
+    clean_restart ${testfile}
+}
diff --git a/gdb/testsuite/gdb.ada/data-sections/main.adb b/gdb/testsuite/gdb.ada/data-sections/main.adb
new file mode 100644
index 0000000..a4ca8b6
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/data-sections/main.adb
@@ -0,0 +1,19 @@
+--  Copyright 2023 Free Software Foundation, Inc.
+--
+--  This program is free software; you can redistribute it and/or modify
+--  it under the terms of the GNU General Public License as published by
+--  the Free Software Foundation; either version 3 of the License, or
+--  (at your option) any later version.
+--
+--  This program is distributed in the hope that it will be useful,
+--  but WITHOUT ANY WARRANTY; without even the implied warranty of
+--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+--  GNU General Public License for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+procedure Main is
+begin
+   null;
+end Main;