[gdb] Fix segv in "maint print symbols" for ada exec

When using the executable from test-case gdb.ada/access_to_packed_array.exp
(read-in using -readnow) and printing the symbols using "maint print symbols",
we run into a segv:
...
$ gdb -readnow -batch access_to_packed_array/foo -ex "maint print symbols"
   ...
     info: array (<>) of character; computed at runtime
     ptr: range 0 .. 2147483647; computed at runtime
Aborted (core dumped)
...

What happens is that dwarf2_evaluate_property gets called and sets the local
frame variable to the current frame, which happens to be NULL.  Subsequently
the PROP_LOCLIST handling code is executed, where get_frame_address_in_block
gets called with argument NULL, and the segv is triggered.

Fix this by handling a NULL frame in the PROP_LOCLIST handling code in
dwarf2_evaluate_property.

Build and reg-tested on x86_64-linux.

gdb/ChangeLog:

2020-03-11  Tom de Vries  <tdevries@suse.de>

	* dwarf2/loc.c (dwarf2_evaluate_property): Handle NULL frame in
	PROP_LOCLIST handling code.

gdb/testsuite/ChangeLog:

2020-03-11  Tom de Vries  <tdevries@suse.de>

	* gdb.ada/access_to_packed_array.exp: Test printing of expanded
	symtabs.

4 files changed, 25 insertions, 1 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1013e91..5c3d740 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-11  Tom de Vries  <tdevries@suse.de>
+
+	* dwarf2/loc.c (dwarf2_evaluate_property): Handle NULL frame in
+	PROP_LOCLIST handling code.
+
 2020-03-10  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* buildsym-legacy.c (record_line): Pass extra parameter to
diff --git a/gdb/dwarf2/loc.c b/gdb/dwarf2/loc.c
index a5074da..5155cff 100644
--- a/gdb/dwarf2/loc.c
+++ b/gdb/dwarf2/loc.c
@@ -2511,11 +2511,15 @@ dwarf2_evaluate_property (const struct dynamic_prop *prop,
       {
 	struct dwarf2_property_baton *baton
 	  = (struct dwarf2_property_baton *) prop->data.baton;
-	CORE_ADDR pc = get_frame_address_in_block (frame);
+	CORE_ADDR pc;
 	const gdb_byte *data;
 	struct value *val;
 	size_t size;
 
+	if (frame == NULL
+	    || !get_frame_address_in_block_if_available (frame, &pc))
+	  return false;
+
 	data = dwarf2_find_location_expression (&baton->loclist, &size, pc);
 	if (data != NULL)
 	  {
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index dca2d30..c5aa0e6 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-11  Tom de Vries  <tdevries@suse.de>
+
+	* gdb.ada/access_to_packed_array.exp: Test printing of expanded
+	symtabs.
+
 2020-03-10  Andrew Burgess  <andrew.burgess@embecosm.com>
 	    Bernd Edlinger  <bernd.edlinger@hotmail.de>
 
diff --git a/gdb/testsuite/gdb.ada/access_to_packed_array.exp b/gdb/testsuite/gdb.ada/access_to_packed_array.exp
index 61ad230..0e1532b 100644
--- a/gdb/testsuite/gdb.ada/access_to_packed_array.exp
+++ b/gdb/testsuite/gdb.ada/access_to_packed_array.exp
@@ -23,6 +23,16 @@ if {[gdb_compile_ada "${srcfile}" "${binfile}" executable [list debug]] != "" }
 
 clean_restart ${testfile}
 
+# Test that printing symbols does not cause segv.
+gdb_test_no_output "maint expand-symtabs"
+set file [standard_output_file gdb.txt]
+gdb_test_no_output "set logging file $file" "set logging file"
+gdb_test_no_output "set logging redirect on"
+gdb_test "set logging on"
+gdb_test_no_output "maint print symbols"
+gdb_test "set logging off"
+file delete $file
+
 set bp_location [gdb_get_line_number "BREAK" ${testdir}/foo.adb]
 runto "foo.adb:$bp_location"