Fix crash on Python frame filters with unreadable arg

https://bugzilla.redhat.com/show_bug.cgi?id=1126177

ERROR: AddressSanitizer: SEGV on unknown address 0x000000000050 (pc 0x000000992bef sp 0x7ffff9039530 bp 0x7ffff9039540
T0)
    #0 0x992bee in value_type .../gdb/value.c:925
    #1 0x87c951 in py_print_single_arg python/py-framefilter.c:445
    #2 0x87cfae in enumerate_args python/py-framefilter.c:596
    #3 0x87e0b0 in py_print_args python/py-framefilter.c:968

It crashes because frame_arg::val is documented it may contain NULL
(frame_arg::error is then non-NULL) but the code does not handle it.

Another bug is that py_print_single_arg() calls goto out of its TRY_CATCH
which messes up GDB cleanup chain crashing GDB later.

It is probably 7.7 regression (I have not verified it) due to the introduction
of Python frame filters.

gdb/ChangeLog

	PR python/17355
	* python/py-framefilter.c (py_print_single_arg): Handle NULL FA->VAL.
	Fix goto out of TRY_CATCH.

gdb/testsuite/ChangeLog

	PR python/17355
	* gdb.python/amd64-py-framefilter-invalidarg.S: New file.
	* gdb.python/py-framefilter-invalidarg-gdb.py.in: New file.
	* gdb.python/py-framefilter-invalidarg.exp: New file.
	* gdb.python/py-framefilter-invalidarg.py: New file.

1 files changed, 67 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.python/py-framefilter-invalidarg.exp b/gdb/testsuite/gdb.python/py-framefilter-invalidarg.exp
new file mode 100644
index 0000000..f70d16e
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-framefilter-invalidarg.exp
@@ -0,0 +1,67 @@
+# Copyright (C) 2014 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 gdb-python.exp
+
+standard_testfile amd64-py-framefilter-invalidarg.S
+
+if { ![istarget x86_64-*-* ] || ![is_lp64_target] } {
+    verbose "Skipping py-framefilter-invalidarg."
+    return
+}
+
+# We cannot use prepare_for_testing as we have to set the safe-patch
+# to check objfile and progspace printers.
+if {[build_executable $testfile.exp $testfile $srcfile {}] == -1} {
+    return -1
+}
+
+# Start with a fresh gdb.
+gdb_exit
+gdb_start
+
+# Skip all tests if Python scripting is not enabled.
+if { [skip_python_tests] } { continue }
+
+# Make the -gdb.py script available to gdb, it is automagically loaded by gdb.
+# Care is taken to put it in the same directory as the binary so that
+# gdb will find it.
+set remote_obj_python_file \
+    [remote_download \
+	 host ${srcdir}/${subdir}/${testfile}-gdb.py.in \
+	 [standard_output_file ${testfile}-gdb.py]]
+
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_test_no_output "set auto-load safe-path ${remote_obj_python_file}" \
+    "set auto-load safe-path"
+gdb_load ${binfile}
+# Verify gdb loaded the script.
+gdb_test "info auto-load python-scripts" "Yes.*/${testfile}-gdb.py.*" \
+    "Test auto-load had loaded python scripts"
+
+if ![runto_main] then {
+    perror "couldn't run to breakpoint"
+    return
+}
+gdb_test_no_output "set python print-stack full" \
+    "Set python print-stack to full"
+
+# Load global frame-filters
+set remote_python_file [gdb_remote_download host \
+			    ${srcdir}/${subdir}/${testfile}.py]
+gdb_test_no_output "python exec (open ('${remote_python_file}').read ())" \
+    "Load python file"
+
+gdb_test "bt" " in niam \\(argc=<error reading variable: dwarf expression stack underflow>, argv=0x\[0-9a-f\]+\\) at py-framefilter-invalidarg.c:\[0-9\]+" "bt full with filters"