gdb/frame: Add reinflation method for frame_info_ptr

Currently, despite having a smart pointer for frame_infos, GDB may
attempt to use an invalidated frame_info_ptr, which would cause internal
errors to happen.  One such example has been documented as PR
python/28856, that happened when printing frame arguments calls an
inferior function.

To avoid failures, the smart wrapper was changed to also cache the frame
id, so the pointer can be reinflated later.  For this to work, the
frame-id stuff had to be moved to their own .h file, which is included
by frame-info.h.

Frame_id caching is done explicitly using the prepare_reinflate method.
Caching is done manually so that only the pointers that need to be saved
will be, and reinflating has to be done manually using the reinflate
method because the get method and the -> operator must not change
the internals of the class.  Finally, attempting to reinflate when the
pointer is being invalidated causes the following assertion errors:

check_ptrace_stopped_lwp_gone: assertion `lp->stopped` failed.
get_frame_pc: Assertion `frame->next != NULL` failed.

As for performance concerns, my personal testing with `time make
chec-perf GDB_PERFTEST_MODE=run` showed an actual reduction of around
10% of time running.

This commit also adds a testcase that exercises the python/28856 bug with
7 different triggers, run, continue, step, backtrace, finish, up and down.
Some of them can seem to be testing the same thing twice, but since this
test relies on stale pointers, there is always a chance that GDB got lucky
when testing, so better to test extra.

Regression tested on x86_64, using both gcc and clang.

Approved-by: Tom Tomey <tom@tromey.com>

3 files changed, 230 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.python/pretty-print-call-by-hand.c b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.c
new file mode 100644
index 0000000..3be5675
--- /dev/null
+++ b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.c
@@ -0,0 +1,53 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2022 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/>.  */
+
+struct mytype
+{
+  char *x;
+};
+
+void
+rec (int i)
+{
+  if (i <= 0)
+    return;
+  rec (i-1);
+}
+
+int
+f ()
+{
+  rec (100);
+  return 2;
+}
+
+void
+g (struct mytype mt, int depth)
+{
+  if (depth <= 0)
+    return; /* TAG: final frame */
+  g (mt, depth - 1); /* TAG: first frame */
+}
+
+int
+main ()
+{
+  struct mytype mt;
+  mt.x = "hello world";
+  g (mt, 10); /* TAG: outside the frame */
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.python/pretty-print-call-by-hand.exp b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.exp
new file mode 100644
index 0000000..0aeb221
--- /dev/null
+++ b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.exp
@@ -0,0 +1,136 @@
+# Copyright (C) 2022 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/>.
+
+# This file is part of the GDB testsuite.  It tests a pretty printer that
+# calls an inferior function by hand, triggering a Use-after-Free bug
+# (PR gdb/28856).
+
+load_lib gdb-python.exp
+
+standard_testfile
+
+# gdb needs to be started here for skip_python_tests to work.
+# prepare_for_testing could be used instead, but it could compile the program
+# unnecessarily, so starting GDB like this is preferable.
+gdb_start
+
+# Skip all tests if Python scripting is not enabled.
+if { [skip_python_tests] } { continue }
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile debug] } {
+    untested "failed to compile"
+    return -1
+}
+
+# This proc restarts GDB, makes the inferior reach the desired spot - marked
+# by a comment in the .c file - and turns on the pretty printer for testing.
+# Starting with a new GDB is important because the test may crash GDB.  The
+# return values are here to avoid us trying to test the pretty printer if
+# there was a problem getting to main.
+proc start_test { breakpoint_comment } {
+    global srcdir subdir testfile binfile
+
+    # Start with a fresh gdb.
+    # This is important because the test can crash GDB.
+
+    clean_restart ${binfile}
+
+    if { ![runto_main] } then {
+	untested "couldn't run to breakpoint"
+	return -1
+    }
+
+    # Let GDB get to the return line.
+    gdb_breakpoint [gdb_get_line_number ${breakpoint_comment} ${testfile}.c ]
+    gdb_continue_to_breakpoint ${breakpoint_comment} ".*"
+
+    gdb_test_no_output "set print pretty on" "starting to pretty print"
+
+    set remote_python_file [gdb_remote_download host ${srcdir}/${subdir}/${testfile}.py]
+    gdb_test_no_output "source ${remote_python_file}" "load python file"
+
+    return 0
+}
+
+# Start by testing the "run" command, it can't leverage start_test
+with_test_prefix "run to frame" {
+    if { ![runto_main] } then {
+	untested "couldn't run to main"
+    }
+
+    gdb_test_no_output "set print pretty on" "starting to pretty print"
+
+    set remote_python_file [gdb_remote_download host ${srcdir}/${subdir}/${testfile}.py]
+    gdb_test_no_output "source ${remote_python_file}" "load python file"
+
+    gdb_breakpoint [gdb_get_line_number "TAG: final frame" ${testfile}.c]
+    gdb_continue_to_breakpoint "TAG: final frame" ".*"
+}
+
+# Testing the backtrace command.
+with_test_prefix "frame print" {
+    if { [start_test "TAG: final frame"] == 0 } {
+	gdb_test "backtrace -frame-arguments all" [multi_line \
+	"#0 .*g \\(mt=mytype is .*\\, depth=0\\).*"\
+	"#1 .*g \\(mt=mytype is .*\\, depth=1\\).*"\
+	"#2 .*g \\(mt=mytype is .*\\, depth=2\\).*"\
+	"#3 .*g \\(mt=mytype is .*\\, depth=3\\).*"\
+	"#4 .*g \\(mt=mytype is .*\\, depth=4\\).*"\
+	"#5 .*g \\(mt=mytype is .*\\, depth=5\\).*"\
+	"#6 .*g \\(mt=mytype is .*\\, depth=6\\).*"\
+	"#7 .*g \\(mt=mytype is .*\\, depth=7\\).*"\
+	"#8 .*g \\(mt=mytype is .*\\, depth=8\\).*"\
+	"#9 .*g \\(mt=mytype is .*\\, depth=9\\).*"\
+	"#10 .*g \\(mt=mytype is .*\\, depth=10\\).*"\
+	"#11 .*main \\(\\).*"] \
+	"backtrace test"
+    }
+}
+# Testing the down command.
+with_test_prefix "frame movement down" {
+    if { [start_test "TAG: first frame"] == 0 } {
+	gdb_test "up" [multi_line "#1 .*in main \\(\\) at .*" ".*outside the frame.*"]
+	gdb_test "down" [multi_line "#0\\s+g \\(mt=mytype is .*\\, depth=10\\).*" ".*first frame.*"]
+    }
+}
+
+# Testing the up command.
+with_test_prefix "frame movement up" {
+    if { [start_test "TAG: final frame"] == 0 } {
+	gdb_test "up" [multi_line "#1 .*in g \\(mt=mytype is .*\\, depth=1\\).*" ".*first frame.*"]
+    }
+}
+
+# Testing the finish command.
+with_test_prefix "frame exit through finish" {
+    if { [start_test "TAG: final frame"] == 0 } {
+	gdb_test "finish" [multi_line ".*.*g \\(mt=mytype is .*\\, depth=0\\).*" ".*g \\(mt=mytype is .*\\, depth=1\\).*" ".*"]
+    }
+}
+
+# Testing the step command.
+with_test_prefix "frame enter through step" {
+    if { [start_test "TAG: outside the frame"] == 0 } {
+	gdb_test "step" [multi_line "g \\(mt=mytype is .*\\, depth=10\\).*" "41.*if \\(depth \\<= 0\\)"]
+    }
+}
+
+# Testing the continue command.
+with_test_prefix "frame enter through continue" {
+    if { [start_test "TAG: outside the frame"] == 0 } {
+	gdb_breakpoint [gdb_get_line_number "TAG: first frame" ${testfile}.c ]
+	gdb_continue_to_breakpoint "TAG: first frame" ".*TAG: first frame.*"
+    }
+}
diff --git a/gdb/testsuite/gdb.python/pretty-print-call-by-hand.py b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.py
new file mode 100644
index 0000000..f8f5df6
--- /dev/null
+++ b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.py
@@ -0,0 +1,41 @@
+# Copyright (C) 2022 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/>.
+
+
+class MytypePrinter:
+    """pretty print my type"""
+
+    def __init__(self, val):
+        self.val = val
+
+    def to_string(self):
+        calls = gdb.parse_and_eval('f()')
+        return "mytype is %s" % self.val['x']
+
+def ec_lookup_function(val):
+    typ = val.type
+    if typ.code == gdb.TYPE_CODE_REF:
+        typ = typ.target()
+    if str(typ) == 'struct mytype':
+        return MytypePrinter(val)
+    return None
+
+def disable_lookup_function():
+    ec_lookup_function.enabled = False
+
+def enable_lookup_function():
+    ec_lookup_function.enabled = True
+
+gdb.pretty_printers.append(ec_lookup_function)